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w wm8737l stereo adc with microphone preamplifier wolfson microelectronics plc to receive regular email updates, sign up at http://www.wolfsonmicro.com/enews production data, january 2012, rev 4.4 copyright ? 2012 wolfson microelectronics plc description the wm8737l is a low power stereo audio adc designed specifically for portable applications such as minidisc and memory audio / voice recorders. the device offers three sets of stereo inputs, which can be configured for line-level signals, for internal or table-top microphones, or for dc measurement (battery monitor). a programmable gain amplifier can be used for automatic level control (alc) with user programmable hold, attack and decay times. the device also has a selectable high pass filter to remove residual dc offsets. if the signal source is mono, the wm8737l can run in mono mode, saving power. it can also mix two channels to mono, either in the analogue or the digital domain. master or slave mode clocking schemes are offered. stereo 24-bit multi-bit sigma-delta adcs are used with digital audio output word lengths from 16-32 bits, and sampling rates from 16khz to 96khz supported. the device is controlled via a 2 or 3 wire serial interface. the interface provides access to all features including gain controls, analogue or digital mono mixing, and power management facilities. the device is supplied in a leadless 5x5mm qfn package. features ? snr 97db (?a? weighted @ 3.3v, 48khz, normal power mode) ? thd ?84db (at ?1db, 3.3v, normal power mode) ? complete stereo / mono microphone interface - programmable microphone preamp - automatic level control - low-noise microphone bias voltage ? configurable power / performance ? low power mode - 8.5mw at avdd = 1.8v (stereo, mic preamps off) - 20mw at avdd = 3.3v (stereo, mic preamps off) ? low supply voltages - analogue 1.8v to 3.6v - digital core: 1.42v to 3.6v - digital i/o: 1.8v to 3.6v ? 256fs / 384fs or usb master clock rates: 12mhz, 24mhz ? audio sample rates: 16, 22.05, 24, 32, 44.1, 48, 88.2, 96khz generated internally from master clock ? 32-pin qfn package, 5 x 5 x 0.9mm applications ? memory audio / voice recorders ? minidisc recorders ? portable digital music systems block diagram linsel rinsel csb sdi n sclk mode vref av dd ag nd vmid vrefp vrefn audio interface vrefp vre fn 50k
wm8737l production data w pd, rev 4.4, january 2012 2 table of contents description ....................................................................................................... 1 ? features ............................................................................................................ 1 ? applications ..................................................................................................... 1 ? block diagram ................................................................................................ 1 ? table of contents ......................................................................................... 2 ? pin configuration .......................................................................................... 3 ? ordering information .................................................................................. 3 ? pin description ................................................................................................ 4 ? absolute maximum ratings ........................................................................ 5 ? recommended operating conditions ..................................................... 5 ? electrical characteristics ..................................................................... 6 ? terminology ............................................................................................................... 8 ? power consumption ...................................................................................... 9 ? signal timing requirements .................................................................... 11 ? device description ...................................................................................... 14 ? introduction ............................................................................................................ 14 ? input signal path .................................................................................................... 14 ? analogue to digital converter (adc) ............................................................ 19 ? 3d stereo enhancement ...................................................................................... 20 ? automatic level control (alc) ......................................................................... 21 ? digital audio interface ........................................................................................ 24 ? master clock and audio sample rates .......................................................... 28 ? control interface................................................................................................. 30 ? power supplies ....................................................................................................... 31 ? power management ............................................................................................... 31 ? register map .................................................................................................. 32 ? digital filter characteristics .............................................................. 33 ? terminology ............................................................................................................. 33 ? digital filter responses ..................................................................................... 34 ? applications information ........................................................................ 36 ? line input configuration ..................................................................................... 36 ? microphone input configuration .................................................................... 36 ? recommended external components .................................................. 37 ? package dimensions .................................................................................... 38 ? important notice ......................................................................................... 39 ? address: ..................................................................................................................... 39 ? revision history ........................................................................................... 40 ?
production data wm8737l w pd, rev 4.4, january 2012 3 pin configuration ordering information order code temperature range package moisture sensitivity level peak soldering temperature WM8737CLGEFL -25 ? c to +85 ? c 32-pin qfn (5x5x0.9mm) lead free msl1 260c WM8737CLGEFL/r -25 ? c to +85 ? c 32-pin qfn (5x5x0.9mm) lead free, tape and reel msl1 260c note: reel quantity = 3,500
wm8737l production data w pd, rev 4.4, january 2012 4 pin description pin no name type description 1 nc no connect no internal connection 2 sclk digital input control interface clock input 3 dbvdd supply digital buffer (i/o) supply 4 dcvdd supply digital core supply 5 dgnd supply digital ground (return path for both dcvdd and dbvdd) 6 nc no connect no internal connection 7 mclk digital input master clock 8 bclk digital input / output audio interface bit clock 9 adcdat digital output adc digital audio data 10 adclrc digital input / output audio interface left / right clock 11 mode digital input control interface selection 12 agnd supply analogue ground (return path for both avdd and mvdd) 13 micbias analogue output microphone bias 14 mvdd supply microphone bias and microphone pre-amplifier positive supply 15 avdd supply analogue positive supply 16 racin analogue input right channel dc blocking capacitor 17 racout analogue output right channel dc blocking capacitor 18 rinput3 analogue input right channel input 3 19 rinput2 analogue input right channel input 2 20 rinput1 analogue input right channel input 1 21 linput1 analogue input left channel input 1 22 linput2 analogue input left channel input 2 23 linput3 analogue input left channel input 3 24 lacout analogue output left channel dc blocking capacitor 25 lacin analogue input left channel dc blocking capacitor 26 vmid analogue output midrail voltage decoupling capacitor 27 vref analogue output reference voltage decoupling capacitor 28 vrefp analogue output positive reference decoupling connection 29 vrefn analogue output negative reference decoupling connection 30 agnd supply analogue ground (return path for both avdd and mvdd) 31 csb digital input chip select / device address selection 32 sdin digital input / output control interface data port
production data wm8737l w pd, rev 4.4, january 2012 5 absolute maximum ratings absolute maximum ratings are stress ratings only. permanent damage to the device may be caused by continuously operating at or beyond these limits. device functional operating limits and guaranteed performance specifications are given under electrical characteristics at the test conditions specified. esd sensitive device. this device is manufactured on a cmos process. it is therefore generically susceptible to damage from excessive static voltages. proper esd precautions must be taken during handling and storage of this device. wolfson tests its package types according to ipc/jedec j- std-020b for moisture sensitivity to determine acceptable storage conditions prior to surface mount assembly. these levels are: msl1 = unlimited floor life at <30 ? c / 85% relative humidity. not normally stored in moisture barrier bag. msl2 = out of bag storage for 1 year at <30 ? c / 60% relative humidity. supplied in moisture barrier bag. msl3 = out of bag storage for 168 hours at <30 ? c / 60% relative humidity. supplied in moisture barrier bag. condition min max supply voltages -0.3v +3.63v voltage range digital inputs dgnd -0.3v dbvdd +0.3v voltage range analogue inputs agnd -0.3v avdd +0.3v voltage range lacin, racin, lacout, racout, micbias agnd -0.3v mvdd +0.3v master clock frequency 40mhz operating temperature range, t a -25 ? c +85 ? c storage temperature after soldering -65 ? c +150 ? c notes: 1. analogue and digital grounds must always be within 0.3v of each other. 2. all digital and analogue supplies are completely independent from each other. recommended operating conditions parameter symbol test conditions min typ max unit digital supply range (core) dcvdd 1.42 3.6 v digital supply range (i/o buffers) dbvdd 1.8 3.6 v analogue supplies range avdd, mvdd 1.8 3.6 v ground dgnd, agnd 0 v notes: 1. dbvdd must be greater than or equal to dcvdd.
wm8737l production data w pd, rev 4.4, january 2012 6 electrical characteristics test conditions dcvdd = 1.5v, avdd = mvdd = 3.3v, t a = +25 o c, 1khz -1dbfs signal, normal power mode, fs = 48khz, pga gain = 0db, 24- bit audio data, unless otherwise stated. microphone preamplifier at maximum bias (default) and gain 13db, unless otherwise stated. parameter symbol test conditions min typ max unit microphone preamplifier (linput1/2/3, rinput1/2/3) to adc microphone pre-amp (boost) gain micboost = 00 13 db micboost = 01 18 micboost = 10 28 micboost = 11 33 microphone preamplifier noise (referred to input) (a-weighted) voltage at 1khz micboost gain = 28db 6 nv / ? hz at 20hz ? 20khz micboost gain = 28db 0.7 -123 ? v rms dbv input offset voltage 1 mv microphone preamplifier signal to noise ratio (a-weighted) (note 1) snr avdd = 3.3v 600 ? r source 109 db avdd=1.8v 600 ? r source 102 28 db gain, avdd = 3.3v 600 ? r source 94 dynamic range (note 2) dnr a-weighted, -60dbfs gain = 0db 94 db total harmonic distortion (note 3) thd 13db gain, avdd = 3.3v, single channel -74 0.02 db % 13db gain, avdd=1.8v, single channel -70 0.03 channel separation -65 db power supply rejection ratio psrr 1khz, 100mv pk-pk, 60 db input leakage m icrophone preamplifier enabled -10 1 10 ? a input resistance ? 500k ?
production data wm8737l w pd, rev 4.4, january 2012 7 test conditions dcvdd = 1.5v, avdd = mvdd = 3.3v, t a = +25 o c, 1khz -1dbfs signal, normal power mode, fs = 48khz, pga gain = 0db, 24- bit audio data, unless otherwise stated. parameter symbol test conditions min typ max unit line inputs (linput1/2/3, rinput1/2/3) to adc ? mic pre-amp bypassed full scale input signal level (for adc 0db input at 0db gain) avdd = 3.3v 1.0 v rms avdd = 1.8v 0.545 signal to noise ratio (a-weighted) (note 1) snr avdd = 3.3v, normal power mode 90 97 db avdd = 2.7v, normal power mode 95 avdd = 1.8v, normal power mode 92 avdd = 3.3v, low power mode 95 avdd = 2.7v, low power mode 93 avdd = 1.8v, low power mode 90 dynamic range (a-weighted) (note 2) dnr -60dbfs, normal power mode 90 97 db -60dbfs, low power mode 95 total harmonic distortion (note 3) thd -1db input -84 (0.006%) db % -1db input, avdd=1.8v -81 (0.009%) adc channel separation (note 4) 1khz signal 105 db channel matching 1khz signal 0.2 db programmable gain amplifier (pga) programmable gain -97 0 30 db programmable gain step size monotonic 0.5 db gain error (deviation from ideal 0.5db/step gain characteristic) 1khz signal -0.3 0.3 db input resistance 0db gain 30 k ? 30db gain 1.9 input capacitance 16.9pf pf automatic level control (alc) typical record level -18 -3 db gain hold time (note 5) t hld mclk = 12.288mhz (note 3) 0, 2.67, 5.33, 10.67, ? , 43691 (time doubles with each step) ms gain ramp-up (decay) time (notes 6, 7) t dcy 33.6, 67.2, 134.4, ? , 3441 (time doubles with each step) ms gain ramp-down (attack) time (notes 6, 7) t atk 8.4, 16.8, 33.6, ? , 8600 (time doubles with each step) ms
wm8737l production data w pd, rev 4.4, january 2012 8 test conditions dcvdd = 1.5v, avdd = mvdd = 3.3v, t a = +25 o c, 1khz -1dbfs signal, normal power mode, fs = 48khz, pga gain = 0db, 24- bit audio data, unless otherwise stated. parameter symbol test conditions min typ max unit analogue reference levels mid-rail reference voltage vmid ?3% avdd/2 +3% v vmid output resistance r vmid 75 k ? buffered reference voltage vref ?3% avdd/2 +3% v microphone bias bias voltage v micbias micbias = 01 0.75 ? avdd v micbias = 10 0.9 ? avdd ?3% 0.9 ? avdd 0.9 ? avdd +3% v micbias = 11, avdd = 2.5v 1.2 ? avdd v bias current source i micbias 3 ma output noise voltage vn 1k to 20khz 24 nv/ ? hz digital input / output input high level v ih 0.7 ? dbvdd v input low level v il 0.3 ? dbvdd v output high level v oh i oh = 1ma 0.9 ? dbvdd v output low level v ol i ol = -1ma 0.1 ? dbvdd v terminology 1. signal-to-noise ratio (db) ? for the microphone preamplifiers, quoted snr is the ratio of the rms voltages of the full- scale output at the l/racout pins and the noise observed at thes e pins with no input signals. this figure indicates only the microphone preamplifier noise and does not account for additional noise that will be added by the pgas and adcs in obtaining the final digitised result. for the li ne inputs, quoted snr is the ratio of the rms code ranges as measured at the adc output for a full-scale output signal and the noise observed with no input. this figure combines the pga and adc noise contributions. (no auto-zero or auto- mute function is employed in achieving these results). 2. dynamic range (db) - dr measures the ratio in the adc output between the full-scale signal power and all power contributed by noise and spurious tones in the specified bandw idth. normally thd+n is measured at 60db below full scale (to reduce any distortion components to negligible levels) and the measurement is then corrected by adding the 60db to its magnitude. (e.g. thd+n @ - 60db= -32db, dr= 60 + |-32| = 92db). 3. total harmonic distortion and noise (db) - thd+n is a ratio of the rms values of (noise + distortion) and signal. 4. channel separation (db) - also known as cross-talk. this is a measure of the amount one channel is isolated from the other. normally measured by sending a full scale signal down one channel and measuring how much of this signal appears at the output of the other channel. 5. hold time is the length of time between a signal detected by the alc as being too quiet and beginning to ramp up the gain. it does not apply to ramping down the gain when the signal is too loud, which happens without a delay. 6. ramp-up and ramp-down times are defined as the time it takes for the pga to sweep across 90% of its gain range. 7. all hold, ramp-up and ramp-down times scale proportionally with mclk notes: 1. all performance measurements are done with a 20khz low pass filter, and where noted an a-weight filter. failure to use such a filter will result in higher thd+n and lower snr and dynamic range readings than are found in the electrical characteristics. the low pass filter removes out of band noise; although this is not audible, it may affect dynamic specification values. 2. vmid and vref are each to be decoupled to a clean an alogue ground with 10uf and 0.1uf capacitors placed as close to the device package as possible. smaller capaci tors may reduce performance. vrefp should be connected to vref and vrefn should be connected to agnd using s hort pcb traces. it is not recommended to connect other components to vmid or vref in case of noise injection to the internal references of the device.
production data wm8737l w pd, rev 4.4, january 2012 9 power consumption the power consumption of the wm8737l depends on the following factors. ? supply voltages: reducing the supply voltages also reduces supply currents, and therefore results in significant power savings (at the cost of reduced maximum snr and thd performance). ? operating mode: power consumption is lower when microphone pre-amps are not used. it can be also reduced in mono or analogue mix-to-mono modes by switching off unused pgas and adcs via the power management register. mode description power management register setting typ. supply currents (milliamps) total power (mw) i avdd i dbvdd i dcvdd mvdd = 1.8v, avdd = 1.8v, dbvdd = 1.8v, dcvd = 1.5v, low power mode, no micbias or mic preamps off 000000000 0.000 0.000 0.007 0.011 standby 110000000 0.692 0.004 0.009 1.356 mono (l/r) 111101000 / 111010100 1.978 0.011 1.633 6.029 stereo / digital mono mix 111111100 3.205 0.018 1.666 8.299 analogue mono mix (without dc monitoring via right adc) 111111000 2.543 0.017 1.640 6.537 analogue mono mix (with continuous dc monitoring via right adc) 111111100 3.205 0.018 1.670 8.306 using micbias in 0.9 x avdd mode in addition to any of the above set appropriate micbias[1:0] bits in power management register +0.255 - - +0.459 using microphone boost preamplifiers in addition to any of the above set appropriate mbctrl[1:0] bits in register 09h and set lmbe and/or rmbe bits in registers 02h and 03h +0.692 - - +1.688 mvdd = 3.3v, avdd = 3.3v, dbvdd = 3.3v, dcvdd = 1.5v, low power mode, no micbias or mic preamps off 000000000 0.000 0.000 0.007 0.011 standby 110000000 1.288 0.007 0.064 0.117 mono (l/r) 111101000 / 111010100 2.993 0.018 1.624 12.173 stereo / digital mono mix 111111100 4.453 0.031 1.650 17.273 analogue mono mix (without dc monitoring via right adc) 111111000 3.684 0.018 1.620 14.648 analogue mono mix (with continuous dc monitoring via right adc) 111111100 4.453 0.031 1.660 17.288 using micbias in 0.9 x avdd mode in addition to any of the above set appropriate micbias[1:0] bits in power management register +0.47 - - +1.551 using microphone boost preamplifiers in addition to any of the above set appropriate mbctrl[1:0] bits in register 09h and set lmbe and/or rmbe bits in registers 02h and 03h +1.413 - - +4.663
wm8737l production data w pd, rev 4.4, january 2012 10 mvdd = 1.8v, avdd = 1.8v, dbvdd = 1.8v, dcvdd = 1.5v , normal power mode, no micbias or mic preamps off 000000000 0.000 0.000 0.007 0.011 standby 110000000 0.698 0.004 0.069 1.367 mono (l/r) 111101000 / 111010100 3.453 0.010 1.910 9.098 stereo / digital mono mix 111111100 6.109 0.017 1.955 13.959 analogue mono mix (without dc monitoring via right adc) 111111000 4.574 0.010 1.910 11.116 analogue mono mix (with continuous dc monitoring via right adc) 111111100 6.109 0.017 1.940 13.937 using micbias in 0.9 x avdd mode in addition to any of the above set appropriate micbias[1:0] bits in power management register +0.252 - - +0.454 using microphone boost preamplifiers in addition to any of the above set appropriate mbctrl[1:0] bits in register 09h and set lmbe and/or rmbe bits in registers 02h and 03h +0.738 - - +1.328 mvdd = 3.3v, avdd = 3.3v, dbvdd = 3.3v, dcvdd = 1.5v , normal power mode, no micbias or mic preamps off 000000000 0.001 0.000 0.007 0.014 standby 110000000 1.288 0.007 0.064 4.371 mono (l/r) 111101000 / 111010100 4.632 0.020 1.905 18.210 stereo / digital mono mix 111111100 7.750 0.032 1.950 28.606 analogue mono mix (without dc monitoring via right adc) 111111000 5.996 0.020 1.890 22.688 analogue mono mix (with continuous dc monitoring via right adc) 111111100 7.750 0.033 1.960 28.624 using micbias in 0.9 x avdd mode in addition to any of the above set appropriate micbias[1:0] bits in power management register +0.446 - - +1.472 using microphone boost preamplifiers in addition to any of the above set appropriate mbctrl[1:0] bits in register 09h and set lmbe and/or rmbe bits in registers 02h and 03h +1.406 - - +4.640 table 1 supply current consumption (see also ?power management? section) notes: 1. t a = +25 o c, slave mode, fs = 48khz, mclk = 12.288 mhz (256fs), 24-bit data 2. all figures are quiescent, with no signal.
production data wm8737l w pd, rev 4.4, january 2012 11 signal timing requirements system clock timing mclk t mclkl t mclkh t mclky figure 1 system clock timing requirements test conditions dbvdd = 3.3v, dcvdd = 1.42 to 3.6v, dgnd = 0v, t a = +25 o c, slave mode fs = 48khz, mclk = 256fs, 24-bit data, unless otherwise stated. parameter symbol min typ max unit system clock timing information mclk system clock pulse width high t mclkl 13 ns mclk system clock pulse width low t mclkh 13 ns mclk system clock cycle time t mclky 26 ns audio interface timing ? master mode bclk (output) adcdat adclrc (output) t dl t dda figure 2 digital audio data timing ? master mode (see control interface) test conditions dbvdd = 3.3v, dcvdd = 1.42 to 3.6v, dgnd = 0v, t a = +25 o c, slave mode, fs = 48khz, mclk = 256fs, 24-bit data, unless otherwise stated. parameter symbol min typ max unit audio data input timing information adclrc propagation delay from bclk falling edge t dl 0 10 ns adcdat propagation delay from bclk falling edge t dda 0 10 ns audio interface timing ? slave mode bclk adclrc t bch t bcl t bcy adcdat t lrsu t lrh t dd figure 3 digital audio data timing ? slave mode
wm8737l production data w pd, rev 4.4, january 2012 12 test conditions dbvdd = 3.3v, dcvdd = 1.42 to 3.6v, dgnd = 0v, t a = +25 o c, slave mode, fs = 48khz, mclk = 256fs, 24-bit data, unless otherwise stated. parameter symbol min typ max unit audio data input timing information bclk cycle time t bcy 50 ns bclk pulse width high t bch 20 ns bclk pulse width low t bcl 20 ns adclrc set-up time to bclk rising edge t lrsu 10 ns adclrc hold time from bclk rising edge t lrh 10 ns adcdat propagation delay from bclk falling edge t dd 0 10 ns control interface timing ? 3-wire mode csb sclk sdin t csl t dho t dsu t csh t scy t sch t scl t scs lsb t css figure 4 control interface timing ? 3-wire serial control mode test conditions dbvdd = 3.3v, dcvdd = 1.42 to 3.6v, dgnd = 0v, t a = +25 o c, slave mode, fs = 48khz, mclk = 256fs, 24-bit data, unless otherwise stated. parameter symbol min typ max unit program register input information sclk rising edge to csb rising edge t scs 40 ns sclk pulse cycle time t scy 80 ns sclk pulse width low t scl 40 ns sclk pulse width high t sch 40 ns sdin to sclk set-up time t dsu 10 ns sclk to sdin hold time t dho 10 ns csb pulse width low t csl 10 ns csb pulse width high t csh 10 ns csb rising to sclk rising t css 10 ns pulse width of spikes which will be suppressed t sp 0 5 ns control interface timing ? 2-wire mode sdin sclk t 3 t 1 t 6 t 2 t 7 t 5 t 4 t 3 t 8 t 9 figure 5 control interface timing ? 2-wire serial control mode
production data wm8737l w pd, rev 4.4, january 2012 13 test conditions dbvdd = 3.3v, dcvdd = 1.42 to 3.6v, dgnd = 0v, t a = +25 o c, slave mode, fs = 48khz, mclk = 256fs, 24-bit data, unless otherwise stated. parameter symbol min typ max unit program register input information sclk frequency 0 400 khz sclk low pulse-width t 1 1.3 us sclk high pulse-width t 2 600 ns hold time (start condition) t 3 600 ns setup time (start condition) t 4 600 ns data setup time t 5 100 ns sdin, sclk rise time t 6 300 ns sdin, sclk fall time t 7 300 ns setup time (stop condition) t 8 600 ns data hold time t 9 900 ns
wm8737l production data w pd, rev 4.4, january 2012 14 device description introduction the wm8737l is a low power analogue to digital conv erter (adc) designed for audio recording. its features, performance and low power consumption make it ideal for recordable cd players, mp3 players, portable md players and pdas. the device includes three stereo analogue inputs with a multiplexer to select between inputs. each input can be used as either a line level input or as a microphone input with on-chip microphone pre- amplifiers. a programmable gain amplifier provides additional gain or attenuation, and can be used for automatic level control (alc), keeping the recording volume constant. it is also possible to use the wm8737l as a mono device, or to mix the two channels to mono, either in the analogue or in the digital domain. the adc is of a high quality using a multi-bit high-order oversampling architecture delivering high snr at low power consumption. it can operate at oversampling rates of 64fs (low power mode) or 128fs (normal power mode), allowing users to design for low power consumption or high performance. the adc also includes a digital hi gh pass filter to remove unwanted dc components from the audio signal. this filter may be turned off for dc measurements. the output from the adc is available on a configurabl e digital audio interface. it supports a number of audio data formats including i 2 s, dsp mode, left justified and right justified, and can operate in master or slave modes. the wm8737l master clock can be either an industry standard 256/384 f s clock or a 12mhz/24mhz usb clock. sample rates of 16khz, 22.05khz, 24khz, 32khz, 44.1khz, 48khz, 88.2khz and 96khz can be generated directly from the master clock, without an external pll. the digital filters are optimised for each sample rate. the wm8737l can be controlled through a 2 wire or 3 wire mpu control interface. it is fully compatible and an ideal partner for a range of industry standard microprocessors, controllers and dsps. the design of the wm8737l has minimised power consumption without compromising performance. it can operate at very low voltages, can power off parts of the circuitry under software control and includes standby and power off modes. input signal path the signal path consists of a multiplexer switch to select between three sets of analogue inputs, followed by a microphone boost preamplifier with selectable gain settings of 13db, 18db, 28db and 33db. the microphone preamplifier feeds into a pga (programmable gain amplifier) via an external capacitor which removes dc offsets that could otherwise produce zipper noise when the pga gain changes. alternatively, for line input signals, the microphone preamplifier can be bypassed to reduce power consumption and noise. the pga gain can be controlled either by the user or by the on-chip alc function (see automatic level control). the output signal from each pga (left and right) enters an adc where it is digitised. the two channels can also be mixed in the analogue domain and digitised in one adc while the other adc is switched off to reduce power consumption (see ?power management? section). the mono-mix signal appears on both digital output channels. left and right channel signal inputs the wm8737l has two sets of low capacitance ac coupled analogue inputs, linput1, linput2, linput3 and rinput1, rinput2, rinput3. the lin sel and rinsel control bits select between them. these inputs can be configured as microphone or line inputs by enabling or disabling the microphone preamplifier. all inputs have high impedance when the preamplifier is used and their impedance is between 1.8k ? and 50k ? (depending on pga gain) if the preamplifier is bypassed. the microphone preamplifier has very high gain settings. care should be taken to prevent the input signal to the microphone preamplifier from exceeding the supply rails which will saturate the microphone preamplifier and may cause the preamplifier to oscillate. this is more likely to happen at the higher gain settings of +28db and +33db. the input signal should be limited to prevent the input signal from exceeding the supply rails and saturating the microphone preamplifier.
production data wm8737l w pd, rev 4.4, january 2012 15 the signal inputs are internally high-impedance biased to the reference voltage, vref. whenever line inputs are muted or the device is placed into standby mode 2 (see ?power management? section), the inputs stay biased to vref. this reduces any audible clicks that may otherwise be heard when changing inputs or awakening from standby. dc measurement for dc measurements (battery voltage monitoring for example), the linput1 and/or rinput1 pins can be taken directly into the respective adc, bypassing the microphone preamplifier and pga. in dc mode the adc output is mid-scale for l/rin put1 voltage agnd and full-scale for l/rinput voltage 1.7 x avdd. note that l/rinput1 must not exceed avdd and so a voltage divider will be required to bring the battery voltage into range. register address bit label default description r2 (02h) analogue audio path control (left channel) 8:7 linsel 00 left channel input select 00: linput1 01: linput2 10: linput3 11: dc measure on linput1 6:5 lmicboost[1:0] 00 left channel microphone gain boost 00: 13db boost 01: 18db boost 10: 28db boost 11: 33db boost 4 lmbe 0 left channel mic boost enable 0: mic preamp disabled, bypass switch is closed. 1: mic preamp is enabled, bypass switch is open. r3 (03h) analogue audio path control (right channel) 8:7 rinsel 00 right channel input select 00: rinput1 01: rinput2 10: rinput3 11: dc measure on rinput1 6:5 rmicboost[1:0] 00 right channel microphone gain boost same as lmicboost 4 rmbe 0 right channel mic boost enable same as lmbe table 2 input software control the internal vref input bias may cause unwanted loading of any potential divider connected to l/rinput1 for the purpose of dc measurement. in this case, the internal bias sources can be disabled by setting the appropriate bits of register r10 to zero. register address bit label default description r10 (0ah) dc measure control 0 rinput1 dc bias enable 1 0: disable dc bias to rinput1 1: enable dc bias to rinput1 1 linput1 dc bias enable 1 0: disable dc bias to linput1 1: enable dc bias to linput1 table 3 dc measurement bias control
wm8737l production data w pd, rev 4.4, january 2012 16 microphone preamplifer bypass and bias control when the left or right microphone preamplifier is disabled the user has two options for driving the corresponding left or right pga. default operation is to close a preamplifier bypass switch that connects the pga input directly to the l/rinput1/2/3 multiplexer output. if the application has only a single left or right line level signal source and hence does not require the multiplexer or microphone preamplifier, then better pga gain accuracy and thd+n performance are obtained by disabling the multiplexer and bypass switch and driving the pga directly via the l/racin pin. the multiplexer and switch are disabled by setting to zero the appropriate l/rbypen bit in register r9. the l/rinput1/2/3 pads remain bias ed to vref. these bits should be set to 1 if the multiplexer is required (always required when the microphone preamplifier is enabled). the user can also adjust the microphone preamplifie r bias settings to optimise thd+n versus supply current consumption for their application. default is full bias for best thd+n performance, but the user can reduce the bias to 75%, 50% or 25% of default by programming mbctrl[1:0] in register r9. register address bit label default description r9 (09h) microphone preamplifiers control 3 rbypen 1 right channel bypass enable 0: bypass switch is always open. rinput1/2/3 high-impedance biased to avdd/2. rpga input is racin pin. 1: close bypass switch when right mic preamp is disabled. 2 lbypen 1 left channel bypass enable 0: bypass switch is always open. linput1/2/3 high-impedance biased to avdd/2. lpga input is lacin pin. 1: close bypass switch when left mic preamp is disabled. 1:0 mbctrl[1:0] 11 bias control for left and right microphone preamplifiers 00: bias 25% 01: bias 50% 10: bias 75% 11: nominal (100%) bias table 4 microphone preamplifier control mono-mixing the wm8737l can operate as a stereo or mono device, or the two channels can be mixed to mono in either the analogue domain (before the adc) or in the digital domain (after the adc). in all mono and mono-mix modes unused circuitry can be switched off to save power (see ?power management? section). 3d stereo enhancement (see ?3d stereo enhanc ement? section) is automatically disabled in all mono and mono-mix modes. in analogue mono-mix mode, the signals are mixed in the left adc and the right adc automatically switches to dc measurement mode on pin rinp ut1. if dc measurement mode is not required then the right adc can be powered down by setting bit 2 (adcr) in the power management register r6. note that the high pass filter must be dis abled if d.c. measurements are required. in stereo and mono modes the left/right adc data appear at the corresponding left/right channel outputs. in digital mono-mix mode the mixed data appears on both the left and right channel outputs. in analogue mono-mix mode the monout bit controls whether the right channel output presents the data from the right adc (dc measurement) or a copy of the left channel (mixed) output.
production data wm8737l w pd, rev 4.4, january 2012 17 register address bit label default description r5 (05h) adc control 8:7 monomix[1:0] 00 00: stereo 01: analogue mono-mix 10: digital mono-mix 11: reserved r5 (05h) adc control 1 monout 0 analogue mono-mix format control 0: left adc data appears on left channel output and right adc data appears on right channel output. 1: left adc data appears on both left and right channel outputs. table 5 mono mixing control note: in stereo mode (r5) 00, bit 1 must always be set to 0. microphone bias the micbias output provides a low noise reference voltage suitable for biasing electret type microphones and the associated external resistor biasing network. the output voltage is derived from vref and is programmable in three steps from 0.75 ? avdd to 1.2 ? avdd, as shown below. supply voltage mvdd must be at least 170mv higher than the desired micbias voltage to ensure correct micbias operation. register address bit label default description r6 (06h) power management 1:0 micbias[1:0] 00 microphone bias control 00: micbias off (powered down, high-impedance output) 01: v micbias = 0.75 ? avdd 10: v micbias = 0.9 ? avdd 11: v micbias = 1.2 ? avdd table 6 micbias control the internal micbias circuitry is shown below. mv dd is a separate power supply pin used only for micbias and the microphone preamplifiers. when micbias < avdd, then mvdd can be tied to avdd. however, when micbias = 1.2 ? avdd, then mvdd must be large enough to generate this output voltage, i.e. it must be higher than avdd. note: the maximum voltage for mvdd of 3.6v must be observed. agnd micbias vref internal resistor mvdd figure 6 microphone bias schematic note that the maximum source current capability for micbias is 3ma. the external biasing resistors therefore must be large enough to limit the micbias current to 3ma. please refer to the ?applications information? section for recommended external components.
wm8737l production data w pd, rev 4.4, january 2012 18 pga control the left and right pgas match the input signal levels to the adc input ranges. the pga gain is logarithmically adjustable from ?97db to +30db in 0.5db steps. each pga can be controlled either by the user or by the alc function (see ?automatic level control? section). when alc is enabled for one or both channels then writing to the corresponding pga gain control register has no effect. the gain is independently adjustable on both right and left line inputs. by setting the lvu or rvu bits whilst programming the pga gain, both channels can be simultaneously updated. the inputs can also be muted under software control. the pga control register maps are shown in table 7. register address bit label default description r0 (00h) left channel pga 7:0 linvol[7:0] c3h ( 0db ) left channel input volume control 00000000: mute 00000001: -97db 00000010: -96.5db ? 11000011: 0db ? 11111111: +30db 8 lvu 0 left pga volume update 0: store linvol in left intermediate latch but do not update left gain. 1: update both pga gains simultaneously (left gain = linvol, right gain = right intermediate latch). r1 (01h) right channel pga 7:0 rinvol[7:0] c3h ( 0db ) right channel input volume control. same as linvol. 8 rvu 0 right pga volume update 0: store rinvol in right intermediate latch but do not update right gain. 1: update both pga gains simultaneously (right gain = rinvol, left gain = left intermediate latch). table 7 pga software control zero-cross detection to avoid zipper or click noises, it is preferable to change the microphone preamplifier and pga gains only when the input signal is at zero. the wm8737l has built-in zero-cross detectors to achieve this. this function is enabled by setting the lmzc, lpzc, rmzc and rpzc bits. the zero-cross detection feature includes a programmable time-out, selected by writing to lzcto[1:0] and rzcto[1:0]. if no zero crossing occurs within the time-out period then the wm8737l changes the pga or microphone preamplifier gains when the time-out elapses.
production data wm8737l w pd, rev 4.4, january 2012 19 register address bit label default description r2 (02h) audio path left 3 lmzc none (first gain change would overwrite!) left mic preamp zero-cross enable 0: change gain immediately 1: change gain on zero crossing only 2 lpzc 1 left pga zero-cross enable 0: change gain immediately 1: change gain on zero crossing only 1:0 lzcto[1:0] 11 left zero-cross time-out 00: 256/fs 01: 512/fs 10: 1024/fs 11: 2048/fs (42.67ms at 48khz) this timeout applies to both the pga and mic preamp zero-cross watchdog timers. r3 (03h) audio path right 3 rmzc none right mic preamp zero-cross enable same as lmzc but for right channel 2 rpzc 1 right pga zero-cross enable same as lmzc but for right channel 1:0 rzcto[1:0] 11 right zero-cross time-out same as lmzc but for right channel table 8 zero-cross detection control analogue to digita l converter (adc) the wm8737l uses a multi-bit, oversampled sigma-delta adc for each channel. the use of multi-bit feedback and high oversampling rates reduces the effects of jitter and high frequency noise. the adc full-scale input level is proportional to avdd. with a 3.3v supply voltage the full scale level is 1.0 volt rms (+/-1.414 volts peak). any voltage greater than full-scale will overload the adc and cause distortion. adc thd+n versus power control the adcs can be operated in ?normal mode?, which offers best thd+n performance at the cost of highest power dissipation, or in ?low power mode? which offers significant power savings at the cost of slightly reduced thd+n performance. the adcs operating mode is controlled by the lp bit in register r5. usb mode is not compatible with low power mode, so the lp bit must be set to 0 if usb mode is selected. see the ?power consumption? section for power requirements in both modes. register address bit label default description r5 (05h) adc control 2 lp 0 adc power mode control 0: both adcs in normal mode (best thd+n) 1: both adcs in low power mode table 9 adc power control adc digital filter the adc filters perform true 24 bit signal processing to convert the raw multi-bit oversampled data from the adc to the correct sampling frequency to be output on the digital audio interface. the digital filter path is illustrated below.
wm8737l production data w pd, rev 4.4, january 2012 20 figure 7 adc digital filter the adc digital filters contain a digital high pass fi lter, selectable via software control. the high-pass filter response is detailed in the ?digital filter c haracteristics? section. when the high-pass filter is enabled the dc offset is continuously calculated and subtracted from the input signal. by setting hpor, the last calculated d.c. offset value is maintained but still subtracted from the input. the output data format can be programmed by the user to accommodate stereo or monophonic recording on both inputs. the polarity of the output signal can also be changed under software control. the software control is shown below. register address bit label default description r5 (05h) adc control 0 adchpd 0 adc high pass filter enable (digital) 1: disable high pass filter 0: enable high pass filter 4 hpor 0 store dc offset 0: present offset maintained 1: continuously update offset 6:5 polarity 00 00: polarity not inverted 01: l polarity invert 10: r polarity invert 11: l and r polarity invert table 10 adc control adc maximum output codes the adc output codes are limited by the digital gain of the stage following the 3d enhancement filters. this limits the max full scale positive output to 7f7fffh and full scale negative to 808000h. to get the maximum positive output code (7fffffh) and negative code (800000h) from the adc, the 3d enhancement filters should be bypassed. this can be done by first setting register r13 (0dh) to 1_110x_xxxx (1c0h), where x_xxxx represents the r equired values for the alc in the application, and then setting register r28 (1ch) to 0_0000_0100 (004h). note that the above sequence uses test bits that are not documented and the use of these test bits, other than as described above, is not recommended and is not supported. 3d stereo enhancement the wm8737l has a 3d stereo enhancement function for use in applications where the natural separation between stereo channels is low. the function is activated by the 3den bit, and artificially increases the separation between the left and right channels. the 3ddepth setting controls the degree of stereo expansion. additionally, one of four filter characteristics can be selected for the 3d processing, using the 3dfilt control bits. when 3d enhancement is enabled (and/or the tone control for playback) it may be necessary to attenuate the signal by 6db to avoid limiting. this is a user selectable function, enabled by setting div2.
production data wm8737l w pd, rev 4.4, january 2012 21 note: the 3d enhancement function is not supported at sample frequencies of 88.2khz, 88.235khz, and 96khz. when using these sample frequencie s the 3d enhancement function should be bypassed by first setting register r13 (0dh) to 1_110x_xxx x (1c0h), where x_xxxx r epresents the required values for the alc in the application, and then setting register r28 (1ch) to 0_0000_0100 (004h). note that the above sequence uses test bits that are not documented and the use of these test bits, other than as described above, is not recommended and is not supported. register address bit label default description r4 (04h) 3d control 0 3den 0 3d function enable 0: disable 1: enable 4:1 3ddepth[3:0] 0000 stereo depth 0000: 0% (minimum 3d effect) 0001: 6.67% .... 1110: 93.3% 1111: 100% (maximum 3d effect) 5 3duc 0 upper cut-off frequency 0 = high (2.2khz at 48khz sampling) 1 = low (1.5khz at 48khz sampling) 6 3dlc 0 lower cut-off frequency 0 = low (200hz at 48khz sampling) 1 = high (500hz at 48khz sampling) 7 div2 0 adc 6db attenuate enable 0: disabled (0db) 1: -6db enabled table 11 stereo enhancement control automatic level control (alc) the wm8737l has an automatic level control that aims to keep a constant recording volume irrespective of the input signal level. this is achieved by continuously adjusting the pga gain so that the signal level at the adc input remains constant. a digital peak detector monitors the adc output and changes the pga gain if necessary. hold time decay time attack time input signal signal after alc pga gain alc target level figure 8 alc operation
wm8737l production data w pd, rev 4.4, january 2012 22 the alc function is enabled using the alcsel[1:0] c ontrol bits in register r12. when enabled, the recording volume can be programmed between -3db and -18db (relative to adc full scale) using the alcl[3:0] register bits in register r12. r13 and r14 bits hld[3:0], dcy[3:0] and atk[3:0] control the hold, decay and attack times, respectively: hold time is the time delay between the peak level detected being below target and the pga gain beginning to ramp up. it can be programmed in power-of-two (2 n ) steps, e.g. 2.67ms, 5.33ms, 10.67ms etc. up to 43.7ms. alternatively, the hold time can also be set to zero. the hold time only applies to gain ramp-up, there is no delay before ramping the gain down when the signal level is above target. decay time (gain ramp-up) is the time that it takes for the pga gain to ramp up across 90% of its range (e.g. from ?15db up to 25.5 db). the time it takes for the recording level to return to its target value therefore depends on both the decay time and on the gain adjustment required. if the gain adjustment is small, it will be shorter than the decay time. the decay time can be programmed in power-of-two (2 n ) steps, from 33.6ms, 67.2ms, 134.4ms etc. to 34.41s. attack time (gain ramp-down) is the time that it takes for the pga gain to ramp down across 90% of its range (e.g. from 25.5db down to -15db gain). the time it takes for the recording level to return to its target value therefore depends on both the attack time and on the gain adjustment required. if the gain adjustment is small, it will be shorter than the attack time. the attack time can be programmed in power-of-two (2 n ) steps, from 8.4ms, 16.8ms, 33.6ms etc. to 8.6s. when operating in stereo, the peak detector takes the maximum of left and right channel peak values, and any new gain setting is applied to both left and right pgas, so that the stereo image is preserved. however, the alc function can also be enabled on one channel only. in this case, only one pga is controlled by the alc mechanism, while the other channel runs independently with its pga gain set through the control register. when one adc channel is unused or used for dc measurement, the peak detector disregards that channel. the alc function can operate in digital mono mix mode (monomix = 10), but not in analogue mono mix mode (monomix = 01).
production data wm8737l w pd, rev 4.4, january 2012 23 register address bit label default description r12 (0ch) alc control 1 8:7 alcsel[1:0] 00 alc function select 00 = alc off (pga gain set by register) 01 = right channel only 10 = left channel only 11 = stereo (pga registers unused) 6:4 maxgain 111 set maximum gain for the pga 111 : +30db 110 : +24db ?..(-6db steps) 001 : -6db 000 : -12db 3:0 alcl[3:0] 1100 alc target level ? sets signal level after pga at adc input in 1db steps 0000: -18db fs 0001: -17db fs ? 1110: -4db fs 1111: -3db fs r13 (0dh) alc control 2 3:0 hld[3:0] 0000 alc hold time before gain is increased 0000: 0ms 0001: 2.67ms 0010: 5.33ms ? (time doubles with every step) 1111: 43.691s 4 alczce 0 enable zero-cross function for the alc gain updates 0: zero-cross disabled 1: zero-cross enabled r14 (0eh) alc control 3 3:0 atk[3:0] 0010 alc attack (gain ramp-down) time 0000: 8.4ms 0001: 16.8ms 0010: 33.6ms ? (time doubles with every step) 1010 or higher = 8.6s 7:4 dcy[3:0] 0011 alc decay (gain ramp-up) time 0000: 33.6ms 0001: 67.2ms 0010: 134.4ms ? (time doubles with every step) 1010 or higher = 34.41s table 12 alc control peak limiter to prevent clipping when a large signal occurs just after a period of quiet, the alc circuit includes a limiter function. if the adc input signal exceeds 87.5% of full scale (?1.16dbfs), the pga gain is ramped down at the maximum attack rate (as when atk = 0000), until the signal level falls below 87.5% of full scale. this function is automatically enabled whenever the alc is enabled. (note: if atk = 0000, then the limiter makes no difference to the operation of the alc. it is designed to prevent clipping when long attack times are used.)
wm8737l production data w pd, rev 4.4, january 2012 24 noise gate when the signal is very quiet and consists mainly of noise, the alc function may cause ?noise pumping?, i.e. loud hissing noise during silence periods. the wm8737l has a noise gate function that prevents noise pumping by comparing the signal level at the linput1/2/3 and/or rinput1/2/3 pins against a noise gate threshold, ngth. the noise gate cuts in when: ? signal level at adc [db] < ngth [db] + pga gain [db] + mic preamp gain [db] this is equivalent to: ? signal level at input pin [db] < ngth [db] when the noise gate is triggered, the pga gain is held constant (preventing it from ramping up as it would normally when the signal is quiet). the table below summarises the noise gate control register. the ngth control bits set the noise gate threshold with respect to the adc full-scale range. t he threshold is adjusted in 6db steps. levels at the extremes of the range may cause inappropriate operation, so care should be taken with set?up of the function. note that the noise gate only works in conjunction with the alc function, and always operates on the same channel(s) as the alc (left, right, both, or none). register address bit label default description r11 (0bh) noise gate control 0 ngat 0 noise gate function enable 1 = enable 0 = disable 4:2 ngth[2:0] 000 noise gate threshold (with respect to adc output level) 000: -78dbfs 001: -72dbfs ? 6 db steps 110: -42dbfs 111: -30dbfs table 13 noise gate control digital audio interface the digital audio interface uses three pins: ? adcdat: adc data output ? adclrc: adc data alignment clock ? bclk: bit clock, for synchronisation the digital audio interface takes the data from the internal adc digital filters and places it on adcdat and adclrc. adcdat is the formatted digital audio data stream output from the adc digital filters with left and right channels multiplexed together. adclrc is an alignment clock that indicates whether left or right channel data is present on the adcdat line. adcdat and adclrc are synchronous with the bclk signal with each data bit transition signified by a bclk high to low transition. adcdat is always an output. bc lk and adclrc may be inputs or outputs depending whether the device is in master or slave mode (see master and slave mode operation, below). four different audio data formats are supported: ? left justified ? right justified ? i 2 s ? dsp mode all four of these modes are msb first. they are described in audio data formats, below. refer to the electrical characteristic section for timing information.
production data wm8737l w pd, rev 4.4, january 2012 25 master and slave mode operation the wm8737l can be configured as either a master or slave mode device. as a master device the wm8737l generates bclk and adclrc and thus controls sequencing of the data transfer on adcdat. in slave mode, the wm8737l responds with data to clocks it receives over the digital audio interface. the mode can be selected by writing to the ms bit (see table 14). master and slave modes are illustrated below. bclk adcdat adclrc wm8737 adc dsp / encoder bclk adcdat adclrc wm8737 adc dsp / encoder figure 9a master mode figure 9b slave mode audio data formats in left justified mode, the msb is available on the first rising edge of bclk following an adclrc transition. the other bits up to the lsb are then transmitted in order. depending on word length, bclk frequency and sample rate, there may be unused bclk cycles before each adclrc transition. left channel right channel adclrc bclk adcdat 1/fs n 3 2 1 n-2 n-1 lsb msb n 3 2 1 n-2 n-1 lsb msb figure 10 left justified audio interface (assuming n-bit word length) in right justified mode, the lsb is available on the last rising edge of bclk before an adclrc transition. all other bits are transmitted befor e (msb first). depending on word length, bclk frequency and sample rate, there may be unused bclk cycles after each adclrc transition. left channel right channel adclrc bclk adcdat 1/fs n 3 2 1 n-2 n-1 lsb msb n 3 2 1 n-2 n-1 lsb msb figure 11 right justified audio interface (assuming n-bit word length) in i 2 s mode, the msb is available on the second rising edge of bclk following an adclrc transition. the other bits up to the lsb are then transmitted in order. depending on word length, bclk frequency and sample rate, there may be unused bclk cycles between the lsb of one sample and the msb of the next.
wm8737l production data w pd, rev 4.4, january 2012 26 left channel right channel adclrc bclk adcdat 1/fs n 3 2 1 n-2 n-1 lsb msb n 3 2 1 n-2 n-1 lsb msb 1 bclk 1 bclk figure 12 i 2 s justified audio interface (assuming n-bit word length) in dsp mode, the left channel msb is available on either the 1 st or 2 nd rising edge of bclk (selectable by lrp) following a rising edge of adclrc. right channel data immediately follows left channel data. depending on word length, bclk frequency and sample rate, there may be unused bclk cycles between the lsb of the right channel data and the next sample. figure 13 dsp mode a mater mode figure 14 dsp mode b, master mode audio interface
production data wm8737l w pd, rev 4.4, january 2012 27 figure 15 dsp mode a slave mode figure 16 dsp mode b slave mode audio interface control the register bits controlling audio format, word length and master/slave mode are summarised below. note that dynamically changing the software format may cause erroneous operation of the interfaces and is therefore not recommended. all adc data is signed 2?s complement. the length of the digital audio data is programmable at 16/20/24 or 32 bits, as shown below. the adc digital filters process data using 24 bits. if the wm8737l is programmed to output 16 or 20 bit data then it strips the lsbs from the 24 bit data. if the device is programmed to output 32 bits then it packs the lsbs with zeros. register address bit label default description r7 (07h) digital audio interface format 1:0 format 10 audio data format select 11: dsp mode 10: i 2 s format 01: left justified 00: right justified 3:2 wl 10 audio data word length 11: 32 bits (see note) 10: 24 bits 01: 20 bits 00: 16 bits
wm8737l production data w pd, rev 4.4, january 2012 28 register address bit label default description 4 lrp 0 right, left & i2s modes ? adclrc polarity 1 = invert adclrc polarity 0 = normal adclrc polarity dsp mode ? mode a/b select 1 = msb is available on 1st bclk rising edge after adclrc rising edge (mode b) 0 = msb is available on 2nd bclk rising edge after adclrc rising edge (mode a) 6 ms 0 master / slave mode control 1: master mode 0: slave mode 7 sdodis 0 adcdat serial data pin disable 0: adcdat pin enabled 1: adcdat pin off (high impedance) table 14 audio data format control note: right justified mode does not support 32-bit data. if wl=11 in right justified mode, the actual word length is 24 bits. to prevent any communication problems on the a udio interface, the interface is disabled (adcdat tristated and floating) when the wm8737l starts up. once the audio interface and sample rates have been programmed, the audio interface can be activated under software control by setting the ai bit (see ?power management? section). master clock and audio sample rates the master clock (mclk) is used to operate the digital filters and the noise shaping circuits. the wm8737l supports a wide range of master clock frequencies, and can generate many commonly used audio sample rates directly from the master clock. there are two clocking modes: ? ?normal? mode supports master clocks of 128f s , 192f s , 256f s , 384f s , and their multiples ? usb mode supports 12mhz or 24mhz master clocks. this mode is intended for use in systems with a usb interface, and eliminates the need for an external pll to generate another clock frequency for the audio adc. register address bit label default description r8 (08h) clocking and sample rate control 6 clkdiv2 0 master clock divide by 2 1: mclk is divided by 2 0: mclk is not divided 0 usb 0 clocking mode select 1: usb mode 0: ?normal? mode 5:1 sr[4:0] 0000 sample rate control 7 auto detect 0 clock ratio autodetect (slave mode only) 0: autodetect off 1: autodetect on table 15 clocking and sample rate control
production data wm8737l w pd, rev 4.4, january 2012 29 the clocking of the wm8737l is controlled using the clkdiv2, usb, and sr control bits. setting the clkdiv2 bit divides mclk by two internally. the usb bit selects between ?normal? and usb mode. each combination of the sr4 to sr0 control bits selects one sample rate (see next page). the digital filter characteristics are automatically adjusted to suit the mclk and sample rate selected (see digital filter characteristics). since all sample rates are generated by dividing mclk, their accuracy depends on the accuracy of mclk. if mclk changes, the sample rates change proportionately. note that some sample rates (e.g. 44.1khz in usb mode) are approximated, i.e. they differ from their target value by a very small amount. this is not audible, as the maximum deviation is only 0.27% (48.0214khz instead of 48khz in usb mode - for comparison, a half-tone step corresponds to a 5.9% change in pitch). in slave mode, it is possible to autodetect the audio clock rate ratio, instead of programming it. the wm8737l can autodetect the following clock ratios: ? clkdiv2 = 0: mclk = 128f s , 192f s , 256f s , or 384f s subject to mclk < 40mhz ? clkdiv2 = 1: mclk = 256f s , 384f s , 512f s , 768f s , 1024f s , 1536f s , subject to mclk < 40mhz mclk clkdiv2=0 mclk clkdiv2=1 adc sample rate usb sr [4:0] filter type normal clock mode 12.288mhz 24.576mhz 16 khz (mclk/768) 0 01010 a 24 khz (mclk/512) 0 11100 a 32 khz (mclk/384) 0 01100 a 48 khz (mclk/256) 0 00000 a 96 khz (mclk/128) (see note 1) 0 01110 b 11.2896mhz 22.5792mhz 22.05 khz (mclk/512) 0 11010 a 44.1 khz (mclk/256) 0 10000 a 88.2 khz (mclk/128) (see note 1) 0 11110 b 18.432mhz 36.864mhz 16 khz (mclk/1152) 0 01011 a 24 khz (mclk/768) 0 11101 a 32 khz (mclk/576) 0 01101 a 48 khz (mclk/384) 0 00001 a 96 khz (mclk/192) (see note 1) 0 01111 b 16.9344mhz 33.8688mhz 22.05 khz (mclk/768) 0 11011 a 44.1 khz (mclk/384) 0 10001 a 88.2 khz (mclk/192) (see note 1) 0 11111 b usb mode 12.000mhz 24.000mhz 16 khz (mclk/750) 1 01010 c 22.0588 khz (mclk/544) 1 11011 a 24 khz (mclk/500) 1 11100 c 32 khz (mclk/375) 1 01100 c 44.118 khz (mclk/272) 1 10001 a 48 khz (mclk/250) 1 00000 c 88.235 khz (mclk/136) (see note 1) 1 11111 b 96 khz (mclk/125) 1 01110 d table 16 master clock and sample rates note 1: the 3d enhancement is not supported at sample frequencies of 88.2khz, 88.235khz, and 96khz. when using these sample frequencies the 3d enhancement function should be bypassed by first setting regis ter r13 (0dh) to 1_110x_xxxx (1c0h), where x_xxxx represents the required values for the alc in the applicat ion, and then setting register r28 (1ch) to 0_0000_0100 (004h). note that the above sequence uses test bits that are not documented and the use of these test bits, other than as described above, is not recommended and is not supported.
wm8737l production data w pd, rev 4.4, january 2012 30 control interface selection of control mode the wm8737l is controlled by writing to registers through a serial control interface. a control word consists of 16 bits. the first 7 bits (b15 to b9) are address bits that select which control register is accessed. the remaining 9 bits (b8 to b0) are regist er bits, corresponding to the 9 bits in each control register. the control interface can operate as either a 3-wire or 2-wire mpu interface. the mode pin selects the interface format. mode interface format low 2 wire high 3 wire table 17 control interface mode selection 3-wire serial control mode in 3-wire mode, every rising edge of sclk clocks in one data bit from the sdin pin. a rising edge on csb latches in a complete control word consisting of the last 16 bits. b15 b14 b13 b12 b11 b10 b9 b8 b7 b6 b5 b4 b3 b2 b1 b0 sdin sclk csb control register address control register data bits latch figure 17 3-wire serial control interface 2-wire serial control mode the wm8737l supports software control via a 2-wire serial bus. many devices can be controlled by the same bus, and each device can be identified by one of two 7-bit address (this is not the same as the 7-bit address of each register in the wm8737l). the wm8737l interface can be written to only and cannot be read back. the controller indicates the start of data transfer with a high to low transition on sdin while sclk remains high. this indicates that a device address and data will follow. all devices on the 2-wire bus respond to the start condition and shift in the next eight bits on sdin (7-bit address + read/write bit, msb first). if the device address received matches the address of the wm8737l and the r/w bit is ?0?, indicating a write, then the wm8737l responds by pulling sdin low on the next clock pulse (ack). if the address is not recognised or the r/w bit is ?1?, the wm8737l returns to the idle condition and wait for a new start condition and valid address. once the wm8737l has acknowledged a correct address, the controller sends the first byte of control data (b15 to b8, i.e. the wm8737l register address plus the first bit of register data). the wm8737l then acknowledges the first data byte by pulling sd in low for one clock pulse. the controller then sends the second byte of control data (b7 to b0, i.e. the remaining 8 bits of register data), and the wm8737l acknowledges again by pulling sdin low. the transfer of data is complete when there is a low to high transition on sdin while sclk is high. after receiving a complete address and data sequence the wm8737l returns to the idle state and waits for another start condition. if a start or stop condition is detected out of sequence at any point during data transfer (i.e. sdin changes while sclk is high), the device jumps to the idle condition.
production data wm8737l w pd, rev 4.4, january 2012 31 figure 18 2-wire serial control interface the wm8737l has two possible device addresses, which can be selected using the csb pin. csb state device address low or unconnected 0011010 high 0011011 table 18 2-wire mpu interface address selection power supplies the wm8737l can use up to four separate power supplies: ? avdd/agnd: analogue supply, powers all analogue functions except the microphone pre-amp and micbias. avdd can range from 1.8v to 3.6v and has the most significant impact on overall power consumption. a large avdd improves audio quality by increasing the maximum input signal range and thus snr. ? mvdd: supply pin for microphone pre-amp and micbias only. this separate pin makes it possible to generate micbias voltages larger than avdd up to a maximum of 3.6v. if this is not necessary, mvdd should also be tied to avdd. ? dcvdd: digital core supply, powers all di gital functions except the audio and control interface pins. dcvdd can range from 1.42v to 3.6v, and has no effect on audio quality. the return path for dcvdd is dgnd, which is shared with dbvdd. ? dbvdd: digital buffer supply, powers the audio and control interface pins. this makes it possible to run the digital core at very low voltages, saving power, while interfacing to other digital devices using a higher voltage. dbvdd draws much less power than dcvdd, and has no effect on audio quality. the return path for dbvdd is dgnd, which is shared with dcvdd. it is possible to use the same supply voltage on all three. however, digital and analogue supplies should be routed and decoupled separately to keep digital switching noise out of the analogue signal paths. power management the wm8737l has a power management register that allows users to select which functions are active. for minimum power consumption, unused func tions should be disabled. to avoid any pop or click noise. when the wm8737l is not in use, it can be put into either one of two standby modes or off mode. off mode is achieved by writing zeros to all bits in the power management register and gives lowest power consumption, but wake-up may take several seconds if the vmid decoupling capacitor has discharged, as it must be recharged from the selectable impedance vmid source. the output impedance of vmid can be changed to allow variable voltage stabilization time after vmid is powered on. the 300k ? setting will ensure minimum vmid power consumption but with slow charging time, while the 2.5k ? setting will allow a more rapid charging time but with the penalty of greatly increased vmid power consumption. the default 75k ? setting is recommended for most applications. register address bit label default description r10 (0ah) vmid impedance control 3:2 vmidsel 00 vmid impedance selection control 00: 75k ? output 01: 300k ? output 10: 2.5k ? output table 19 vmid impedance selection
wm8737l production data w pd, rev 4.4, january 2012 32 standby mode 1 is achieved by powering down everything except the vmid source and gives a very low power sleep mode. wake-up may require a few milliseconds to ensure that the vref voltage has stabilized. standby mode 2 is achieved by not powering down vmid and vref. the wm8737l can awaken instantly from standby mode 2 because vref is already stable. register address bit label default description r6 (06h) power manageme nt 8 vmid 0 vmid (necessary for all other functions) 7 vref 0 vref (necessary for all other functions) 6 ai 0 audio interface 5 pgl 0 pga left 4 pgr 0 pga right 3 adl 0 adc left 2 adr 0 adc right 1:0 micbias 00 see ?microphone bias? section r2 (02h) 4 lmbe 0 mic boost left (see ?input signal path?) r3 (03h) 4 rmbe 0 mic boost right (see ?input signal path?) notes: all control bits are 0=off, 1=on table 20 power management register map register address (bit 15 ? 9) remarks bit8 bit7 bit6 bit5 bit4 bit3 bit2 bit1 bit0 r0 (00h) 0000000 left pga lvu linvol [7:0] r1 (01h) 0000001 right pga rvu rinvol [7:0] r2 (02h) 0000010 audio path l linsel lmicboost lmbe lmzc lpzc lzcto[1:0] r3 (03h) 0000011 a udio path r rinsel rmicboost rmbe rmzc rpzc rzcto[1:0] r4 (04h) 0000100 3d enhance 0 div2 3dlc 3duc 3ddepth 3de r5 (05h) 0000101 adc control monomix polarity hpor 0 lp monout adc hpd r6 (06h) 0000110 power mgmt vmid vref ai pgl pgr adl adr micbias r7 (07h) 0000111 a udio format 0 sdodis ms 0 lrp wl format r8 (08h) 0001000 clocking 0 auto detect clk div2 sr (sample rate selection) usb mode r9 (09h) 0001001 mic preamp control 0 0 0 0 0 rbypen lbypen mbctrl[1:0] r10 (0ah) 0001010 misc. biases control 0 0 0 0 0 vmidsel [1:0] linput1 dc bias enable rinput1 dc bias enable r11 (0bh) 0001011 noise gate 0 0 0 0 ngth (threshold) 0 ngat r12 (0ch) 0001100 alc1 alcsel maxgain alcl (target level) r13 (0dh) 0001101 alc2 reserved (must write zeros) 0 alczce hld (hold time) r14 (0eh) 0001110 alc3 0 dcy (decay time) atk (attack time) r15 (0fh) 0001111 reset reset (writing 000000000 to this register resets all registers to their default state) table 21 control register map
production data wm8737l w pd, rev 4.4, january 2012 33 digital filter characteristics the wm8737l has four different types of digital filter characteristics to suit different mclk and sample rates (see master clock and audio sample rates). parameter test conditions min typ max unit adc filter type a passband +/- 0.05db 0 0.4535fs -6db 0.5fs passband ripple +/- 0.05 db stopband 0.5465fs stopband attenuation f > 0.5465fs -60 db high pass filter corner frequency -3db -0.5db -0.1db 3.7 10.4 21.6 hz table 22 digital filter characteristics adc filter type group delay a (256/272) 23/fs b (256/272, 88.2/96k mode) 5/fs c (250 usb) 13/fs d (250 usb, 96k mode) 4/fs table 23 digital filters group delay terminology 1. stop band attenuation (db) - the degree to which the frequency spectrum is attenuated (outside audio band) 2. pass-band ripple ? any variation of the frequency response in the pass-band region 3. the filter responses are shown on the following page.
wm8737l production data w pd, rev 4.4, january 2012 34 digital filter responses -100 -80 -60 -40 -20 0 0 0.5 1 1.5 2 2.5 3 response (db) frequency (fs) -0.06 -0.05 -0.04 -0.03 -0.02 -0.01 0 0.01 0.02 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 response (db) frequency (fs) figure 19 adc digital filter frequency response ? type a figure 20 adc digital filter ripple ? type a -100 -80 -60 -40 -20 0 0 0.5 1 1.5 2 2.5 3 response (db) frequency (fs) -0.25 -0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2 0.25 0 0.05 0.1 0.15 0.2 0.25 response (db) frequency (fs) figure 21 adc digital filter frequency response ? type b figure 22 adc digital filter ripple ? type b -100 -80 -60 -40 -20 0 0 0.5 1 1.5 2 2.5 3 response (db) frequency (fs) -0.04 -0.03 -0.02 -0.01 0 0.01 0.02 0.03 0.04 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 response (db) frequency (fs) figure 23 adc digital filter frequency response ? type c figure 24 adc digital filter ripple ? type c
production data wm8737l w pd, rev 4.4, january 2012 35 -100 -80 -60 -40 -20 0 0 0.5 1 1.5 2 2.5 3 response (db) frequency (fs) -0.25 -0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2 0.25 0 0.05 0.1 0.15 0.2 0.25 response (db) frequency (fs) figure 25 adc digital filter frequency response ? type d figure 26 adc digital filter ripple ? type d
wm8737l production data w pd, rev 4.4, january 2012 36 applications information line input configuration in order to avoid clipping, the user must ens ure that the input signal does not exceed avdd. this may require a potential divider circuit in some applications. it is also recommended to remove rf interference picked up on any cables using a simp le first-order rc filter, as high-frequency components in the input signal may otherwise cause aliasing distortion in the audio band. this filter must not have high output impedance at audio frequencies (e.g. use a lc filter) if pga gain errors are to be minimised when bypassing the microphone preamplifier. when using ac signals with no dc bias they should be coupled to the wm8737l signal inputs through a dc blocking capacitor, e.g. 470nf or 1 ? f when using the microphone preamplifier, and at least 10 ? f if directly driving the pga (bigger capacitance may be required at higher gains due to the low pga input impedance at high gain). microphone input configuration r2 47kohm c1 220pf c2 1uf agnd agnd agnd linput1/2/3 rinput1/2/3 from microphone r1 680 ohm micbias figure 27 recommended circuit for microphone input for interfacing to a microphone, the alc function should be enabled and the microphone boost switched on. microphones held close to a speaker?s mouth would normally use a lower boost setting such as 13db, while tabletop or room microphones would need a higher boost, for example 28db. the recommended application circuit is shown above. r1 and r2 form part of the biasing network (refer to microphone bias section). r1 connected to micbias is necessary only for electret type microphones that require a voltage bias. r2 should always be present to prevent the microphone input from charging to a high voltage which may damage the microphone on connection. r1 and r2 should be large so as not to attenuate the signal from the microphone, which can have source impedance greater than 2k ? . c1 together with the source impedance of the microphone and the wm8737l input impedance forms an rf filter. c2 is a dc blocking capacitor to allow the microphone to be biased at a different dc voltage to the micin signal.
production data wm8737l w pd, rev 4.4, january 2012 37 recommended external components notes: 1. c1-18 should be fitted as close to wm8737 as possible. 2. agnd and dgnd should be connected as close to wm8737 as possible figure 28 external components diagram component reference suggested value description c1 100nf decoupling for avdd c2 10 ? f reservoir capacitor for avdd c3 100nf decoupling for mvdd c4 10 ? f reservoir capacitor for mvdd c5 100nf decoupling for dcvdd c6 10 ? f reservoir capacitor for dcvdd c7 100nf decoupling for dbvdd c8 10 ? f reservoir capacitor for dbvdd c9 100nf decoupling for vmid c10 10 ? f reservoir capacitor for vmid c11 100nf decoupling for micbias c12 10 ? f reservoir capacitor for micbias c9 100nf decoupling for vref c10 10 ? f reservoir capacitor for vref c11 1 ? f racin to racout coupling capacitor c12 1 ? f lacin to lacout coupling capacitor table 24 external components descriptions
wm8737l production data w pd, rev 4.4, january 2012 38 package dimensions dm101.a fl: 32 pin qfn plastic package 5 x 5 x 0.9 mm body, 0.50 mm lead pitch e2 b b 16 15 8 9 e c 0.08 c ccc a a1 c a3 seating plane 1 l index area (d/2 x e/2) top view d c aaa 2 x c aaa 2 x e 1 17 24 25 32 d2 b c bbb m a 5 4 notes: 1. dimension b applies to metallized terminal and is measured between 0.15 mm and 0.30 mm from terminal tip. 2. falls within jedec, mo-220, variation vhhd-5. 3. all dimensions are in millimetres. 4. the terminal #1 identifier and terminal numbering convention shall conform to jedec 95-1 spp-002. 5. coplanarity applies to the exposed heat sink slug as well as the terminals. 6. refer to application note wan_0118 for further information regarding pcb footprints and qfn package soldering. 7. this drawing is subject to change without notice. detail 1 a3 g t h w b exposed lead half etch tie bar dimensions (mm) symbols min nom max note a a1 a3 0.80 0.90 1.00 0.05 0.02 0 0.203 ref b d d2 e e2 e l 0.30 0.18 5.00 bsc 3.60 3.45 3.30 0.50 bsc 0.30 0.40 0.50 1 2 2 5.00 bsc 3.60 3.45 3.30 0.10 aaa bbb ccc ref: 0.15 0.10 jedec, mo-220, variation vhhd-5. tolerances of form and position 0.25 h 0.1 0.20 g t 0.103 w 0.15 detail 1 detail 2 detail 2 exposed ground paddle 6 exposed ground paddle bottom view side view 0.30 45 m m
production data wm8737l w pd, rev 4.4, january 2012 39 important notice wolfson microelectronics plc (?wolfson?) products and services are sold subject to wolfson?s terms and conditions of sale, delivery and payment supplied at the time of order acknowledgement. wolfson warrants performance of its products to the specific ations in effect at the date of shipment. wolfson reserves the right to make changes to its products and specifications or to discontinue any product or service without notice. customers should therefore obtain the latest version of relevant informati on from wolfson to verify that the information is current. testing and other quality control techniques are utilised to the extent wolfson deems necessary to support its warranty. specific testing of all parameters of each device is not nece ssarily performed unless required by law or regulation. in order to minimise risks associated with customer applications, the customer must use adequate design and operating safeguards to minimise inherent or procedural hazards. wolfs on is not liable for applications assistance or customer product design. the customer is solely responsible for its selection and use of wolfson products. wolfson is not liable for such selection or use nor for use of any circuitry other than circuitry entirely embodied in a wolfson product. wolfson?s products are not intended for use in life support sy stems, appliances, nuclear systems or systems where malfunction can reasonably be expected to result in personal injury, death or severe property or environmental damage. any use of products by the customer for such purposes is at the customer?s own risk. wolfson does not grant any licence (express or implied) under any patent right, copyright, mask work right or other intellectual property right of wolfson covering or relating to any combination, machine, or process in which its products or services might be or are used. any provision or publication of any third party?s products or services does not constitute wolfson?s approval, licence, warranty or endorsement thereof. any third party trade marks contained in this document belong to the respective third party owner. reproduction of information from wolfson datasheets is per missible only if reproduction is without alteration and is accompanied by all associated copyright, proprietary and other noti ces (including this notice) and conditions. wolfson is not liable for any unauthorised alteration of such information or for any reliance placed thereon. any representations made, warranties given, and/or liabilities accepted by any person which differ from those contained in this datasheet or in wolfson?s standard terms and conditions of sale, delivery and payment are made, given and/or accepted at that person?s own risk. wolfson is not liable for any such representations, warranties or liabilities or for any reliance placed thereon by any person. address: wolfson microelectronics plc 26 westfield road edinburgh eh11 2qb united kingdom tel :: +44 (0)131 272 7000 fax :: +44 (0)131 272 7001 email :: sales@wolfsonmicro.com
wm8737l production data w pd, rev 4.4, january 2012 40 revision history date rev originator changes 10/05/11 4.3 bt/jmacd 3d stereo enhancement ? note updated. bt removed support for all sample rates below 16khz 16/01/12 4.4 jmacd order codes updated from wm8737lgefl and wm8737lgefl/r to WM8737CLGEFL and WM8737CLGEFL/r to reflect change to copper wire bonding. 16/01/12 4.4 jmacd package diagram changed to dm101.a

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