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rev. 0 information furnished by analog devices is believed to be accurate and reliable. however, no responsibility is assumed by analog devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. no license is granted by implication or otherwise under any patent or patent rights of analog devices. a ssm2005 one technology way, p.o. box 9106, norwood, ma 02062-9106, u.s.a. tel: 781/329-4700 world wide web site: http://www.analog.com fax: 781/326-8703 ? analog devices, inc., 1999 ? decoder 5.1-channel soundfield generator features generates 5.1-channel soundfield from all stereo sources no pre-encoding required excellent decoding of pre-encoded sources 4- or 5-speaker operation subwoofer output full bandwidth on all channels optimized modes for video and music excellent surround image at all positions independent left and right surround steering no surround channel delay required built-in white noise generator applications home theater receivers vcd/dvd players auto sound receivers and amplifiers surround sound decoders karaoke computer audio boards video games steering control generator left right inputs right surround left surround center right left reset serial bus outputs l+r for subwoofer steering matrix and output amplifiers analog signal processing mode control logic and noise generator figure 1. simplified block diagram pin configurations 48-lead ssop (rs suffix) top view (not to scale) 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 ssm2005 center out r filter in r filter out l filter in l filter out l out l out a l in r out r out a r in v ee acom audio gnd gnd v cc (l+r) out (lCr) out (lCr) high in (lCr) low in r high band det. l high band det. high band det. out r low band det. l low band det. low band det. out lf out rf out ls out rs out noise in noise out load reset data in v cc acom audio gnd gnd v ee write clock in front/rear tc filter low band tc filter high band tc filter front/rear det. front/rear (lCr) det. front/rear (l+r) det. autobalance lockout autobalance tc general description the ssm2005 circle surround ? decoder produces true 5.1-channel surround soundfield from any stereo source, including vcd, dvd, vcr, cd and fm stereo broadcasts. the ssm2005 is also compat- ible with encoded sources, such as dolby prologic ? and circle surround encoded movies and music. external delays and noise reduction processors are not required for the surround channels. circle surround encoded stereo signals will produce a full 360o soundfield when played through the ssm2005. recording engi- neers can encode sounds to any of the five speakers surrounding the listener. left front, right front, center, and differentiated left and right surround channels are generated, providing a realis- tic ambiance effect with either 4- or 5-speaker configurations. the ssm2005 is available from analog devices, subject to the license and royalty requirements as described on the following page of the data sheet. and are registered trademarks of srs labs, inc. and valencetechnology ltd. circle surround is a registered trademark of srs labs, inc. and valence technology ltd. dolby prologic is a registered trademark of dolby laboratories licensing corporation, san francisco, california. circle surround technology is protected under one or more of the following u.s. patents and corresponding patents worldwide: 5,319,713; 5,333,201; 5,638,452; 5,771,295.
C2C rev. 0 ssm2005Cspecifications electrical characteristics parameter symbol conditions min typ max units input characteristics level 1 v l , v r z source < 10 w 0 dbd input impedance z in l and r inputs 10 k w output characteristics level left front l t = 0 dbd, r t = off 0 dbd right front r t = 0 dbd, l t = off 0 dbd center l t = r t = 0 dbd, in phase, video mode +6 dbd left rear, right rear l t = r t = 0 dbd, out of phase +3 dbd channel separation left front and right front / center l t = r t , in phase, video mode 30 dbd left rear and right rear / center l t = r t , out of phase 40 dbd left rear, left front l t = r t , out of phase 30 dbd left rear, right rear l t = r t , out of phase 30 dbd output impedance z out 10 w dynamic performance total harmonic distortion + noise thd+n all channels 0.04 % signal-to-noise ratio snr 88 db dynamic range, output dr noise floor to 1% thd 100 db headroom hr all channels 12 db noise generator output level 2 noise mode on, a-weighted C10 dbd matching all channels 0.5 1.5 db autobalance capture range | v h | C | v l | 4db capture time v l = v r > C10 dbd, |v left C v right | < 3 db 5 s control logic logic thresholds logic levels referenced to acom high (1) 2.4 v low (0) 0.8 v input current 1 m a timing characteristics see timing diagrams power supplies operating voltage range 3 v s single supply +10 +12 v +v s , Cv s dual supply 5 6v current i s v l = v r = acom, v s = 12 v 18 30 ma notes 1 0 dbd = 300 mv rms . 2 with filter shown in figure 8. 3 specifications apply for v s = 6 v. specifications subject to change without notice. (v s = 6.0 v, t a = 1 25 8 c, f = 2 khz, modes: video, 5-2-5, center on, sound spread off, autobalance off, noise off) the circle surround ? technology rights incorporated in the ssm2005 are owned by srs labs, inc. and by valence technology ltd., and licensed to analog devices, inc. users of any ssm2005 circle surround decoder must first sign a free use license to purchase oem quantities for consumer electro nics applications which may be granted upon submission of a preproduction sample to, and the satisfactory passing of performance verification tests per formed by srs labs, inc. or valence technology ltd. srs labs, inc. and valence technology ltd. reserve the right to decline a use license for any submis sion that does not pass performance specifications or is not in the consumer electronics classification. all equipment manufactured using any ssm2005 circle surround decoder must carry the circle surround logo on the front panel in a manner approved in writing by srs labs, inc. or valence technology ltd. if the circle surround logo is printed in users manuals, service manual s or advertisements, it must appear in a form approved in writing by srs labs, inc. or valence technology ltd. the rear panel of circle surround produc ts, users manuals, service manuals, and all advertisements must all carry the circle surround legend as specified in the circle surround trademark manual published by srs labs, inc. and valence technology ltd. licensing information
ssm2005 C3C rev. 0 absolute maximum ratings* supply voltage, v s . . . . . . . . . . . . . . . . . . . . . . 8 v or +16 v logic inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v s storage temperature range . . . . . . . . . . . . C65 c to +150 c operating temperature range . . . . . . . . . . . C20 c to +70 c junction temperature range . . . . . . . . . . . . . . . . . . . .+150 c lead temperature range (soldering, 60 sec) . . . . . . . +300 c *stresses above those listed under absolute maximum ratings may cause perma- nent damage to the device. this is a stress rating only; functional operation of the device at these or any other conditions above those listed in the operational sections of this specification is not implied. exposure to absolute maximum rating condi- tions for extended periods may affect device reliability. package type u ja 1 u jc units 48-lead ssop (rs) 100 50 c/w note 1 q ja is specified for worst case conditions. caution esd (electrostatic discharge) sensitive device. electrostatic charges as high as 4000 v readily accumulate on the human body and test equipment and can discharge without detection. although the ssm2005 features proprietary esd protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. therefore, proper esd precautions are recommended to avoid performance degradation or loss of functionality. warning! esd sensitive device ordering guide temperature package package model range description option ssm2005rs-reel C20 c to +70 c 48-lead ssop rs-48
ssm2005 C4C rev. 0 frequency C hz 10 1 0.01 20 20k 100 thd + n C % 1k 0.1 10k center out lf, rf out v sy = 6v v in = 300mv rms r l = 100k v figure 2. thd + n vs. frequency; front channels rs out frequency C hz 10 1 0.01 20 20k 100 thd + n C % 1k 0.1 10k v sy = 6v v in = 300mv rms r l = 100k v ls out figure 3. thd + n vs. frequency; surround channels amplitude C dbr a 10 1 0.01 2 35 15 2 25 thd + n C % 0.1 2 15 2 5 5 v sy = 6v v in = 1khz r l = 100k v 0dbr = 300mv rms lf, rf out center out figure 4. thd + n vs. amplitude; front channels frequency C dbr a 10 1 0.01 2 35 15 2 25 thd + n C % 0.1 2 15 2 5 5 v sy = 6v l t = r t = 1khz; out of phase r l = 100k v 0dbr = 300mv rms ls, rs out figure 5. thd + n vs. frequency; surround channels Ctypical performance characteristics
ssm2005 C5C rev. 0 pin configurations 48-lead ssop (rs suffix) top view (not to scale) 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 ssm2005 center out r filter in r filter out l filter in l filter out l out l out a l in r out r out a r in v ee acom audio gnd gnd v cc (l+r) out (lCr) out (lCr) high in (lCr) low in r high band det. l high band det. high band det. out r low band det. l low band det. low band det. out lf out rf out ls out rs out noise in noise out load reset data in v cc acom audio gnd gnd v ee write clock in front/rear tc filter low band tc filter high band tc filter front/rear det. front/rear (lCr) det. front/rear (l+r) det. autobalance lockout autobalance tc
ssm2005 C6C rev. 0 pin function description pin # name connected to / function: 1 r filter in 3-pole active low-pass filter output; used for center cancelling correction 2 r filter out 3-pole active low-pass filter input 3 l filter in 3-pole active low-pass filter output; used for center cancelling correction 4 l filter out 3-pole active low-pass filter input 5 l out connect to pin 6 6 l out a connect to pin 5 7 l in left stereo source line input; should be 0 dbd (300 mv rms) 8 r out connect to pin 9 9 r out a connect to pin 8 10 r in right stereo source line input; should be 0 dbd (300 mv rms) 11 v ee negative supply 12 acom audio gnd audio ground 13 gnd power ground 14 v cc positive supply 15 (l+r) out rc to front/rear detector input 16 (lCr) out rc to front/rear detector input and input of crossover 17 (lCr) high in output of high-pass crossover 18 (lCr) low in output of low-pass crossover 19 r high band det. rc network fed by right stereo source line input 20 l high band det. rc network fed by left stereo source line input 21 high band det. out capacitor to acom; controls rear high frequency output steering 22 r low band det. right input, used for autobalance and low band steering 23 l low band det. left input, used for autobalance and low band steering 24 low band det. out capacitor to acom; controls left-to-right output steering 25 autobalance tc rc network to acom 26 autobalance lockout rc network to acom 27 front/rear (l+r) det. rc network fed by (l+r) out (pin 15) 28 front/rear (lCr) det. rc network fed by (l-r) out (pin 16) 29 front/rear det. capacitor to acom; controls front-to-back output steering 30 high band tc filter rc network to acom 31 low band tc filter rc network to acom 32 front/rear tc filter rc network to acom 33 clock in clock from serial bus 34 write chip select from serial bus 35 v ee negative supply 36 gnd power ground 37 acom audio gnd audio ground 38 v cc positive supply 39 data in data from serial bus 40 reset reset from serial bus 41 load load from serial bus 42 noise out connect to rc filter; white noise output 43 noise in connect to rc filter output; filtered white noise 44 rs out connect to right surround (rear) amplifier input 45 ls out connect to left surround (rear) amplifier input 46 rf out connect to right front amplifier input 47 lf out connect to left front amplifier input 48 center out connect to center amplifier input
ssm2005 C7C rev. 0 table i. abbreviations and notations used in the text l left r right l t surround encoded left input r t surround encoded right input lf left front output rf right front output ls left surround output rs right surround output c center output dbd 0 dbd = 300 mv rms acom quality audio ground vca voltage controlled amplifier simplified theory of operation general the ssm2005 circle surround decoder processes stereo input signals, and outputs 5 channels of surround sound, plus an l+r output for a subwoofer low-pass filter. the ssm2005 provides signal processing, steering control, input autobalance, and a digital interface for mode control. this device uses analog circuits such as amplifiers, rms detectors, vcas and digital logic to carry out the circle surround algorithm in real time. no artificial reverberation or delay effects are used, preserving the natural sound of the original stereo recording. the ssm2005 can decode any existing media including cd, vcd, dvd, cassette tapes, vhs, fm radio and television stereo broadcasts. for convenience in balancing the system, an on-chip digital noise generator is available. the net result is outstanding 5.1 channel surround sound from all stereo sources, which re- veals the hidden ambiance already contained in existing music and cinematic recordings. the listening experience is greatly enhanced and made more enjoyable when compared to ordinary stereo. in the following description, please refer to figure 6. input signal processing stereo inputs l and r are fed to both the steering control generator, and the autobalance circuitry. the balanced signals are passed through the center channel cancel circuitry to the channel steering vcas. the autobalance output signals also feed the precision sum and difference amplifiers. the sum (l+r) and difference (lCr) signals form the basis for the center and surround channels, respectively. the center channel signal is fed to the center chan- nel cancel circuitry, and to the channel steering vcas. the surround channel signal is separated by an external crossover network into the surround high and surround low bands and fed to the channel steering vcas. steering control generator the purpose of the steering control generator is to analyze the dy- namic characteristics of music, dialog, or special effects, using pro- prietary high speed analog computing circuits. control voltages for all vcas are then computed, and the soundfield expansion per- formed in accordance with the circle surround decoding algorithm. the control signals depend upon the ssm2005 modes selected, and will differ for video mode vs. music mode, 5.2.5 mode vs. 4.2.4 mode, etc. channel steering vcas command signals from the steering control generator are fed to the channel steering vcas, which control the amplitude of the five output channels. high performance, low distortion vcas with typically 12 dbd headroom are used for all channels. output amplifier the output amplifiers receive signals from the vcas and the internal noise generator. each amplifier has a multiplexer switch which will enable it to output a white noise waveform under control of the serial bus. this simplifies balancing of the listening system. the output amplifiers provide load drive capability with typically 12 dbd of headroom. the overall gain from l and r inputs to circle surround outputs is unity; the noise generator gives an output level of C10 dbd (100 mv rms). mode control logic the various ssm2005 modes are shown in figure 7. there are modes for different types of source material, such as video sound tracks or music. other modes include 5.2.5/4.2.4, sound spread, phantom center mode, autobalance, and noise generation. each modes status is stored in the mode control logic, as determined by the data sent via the serial bus. refer to the typical outputs in various modes section for a m ore detailed explanation of the vari- ous modes. applying a logic low to the reset input will override the mode control logic and put the ssm2005 into its default mode. de- fault modes for the device are video/5.2.5/center active/sound spread on/autobalance on/noise off. see figure 9 for logic timing diagrams. autobalance feature the autobalance circuitry is activated when the ssm2005 is placed into autobalance on mode. in this mode, the device will adjust the gains of its input amplifiers to balance the stereo inputs to equal loudness. with a mono input signal, the autobalance circuitry will typically balance l and r to within 0.5 db. a 22 m f external ca- pacitor connected to pin 25 sets a 5 second averaging period for comparing the levels between the stereo inputs. using autobalance will slightly degrade the maximum channel separation from the ssm2005. the autobalance mode can be left off without fear of degrading the soundfield, unless the stereo input signal is expected to be off balance by more than 1.5 db. most cd, vcd and dvd player outputs are specified to within 0.25 db balance. noise generator when the noise mode is selected, the audio inputs are muted. noise will be available from the output of the channel determined by the mode control logic. the noise generator uses a feedback shift register that generates a pseudo-random digital output wave- form with a repeat time of three seconds. this digital noise wave- form is band-pass filtered externally to approximate white noise. power supplies the ssm2005 may be operated from regulated 5 v to 6 v supplies that can supply 45 ma each. the recommended operating voltage is 6 v, which will give a typical headroom of 12 dbd.
ssm2005 C8C rev. 0 power-up the ssm2005 will be in an undefined mode on power-up. reset should be applied to the ssm2005, or the mode control logic should be loaded to put the device into a definite mode state. serial data control inputs the ssm2005 provides a simple 3- or 4-wire serial interface to control the mode settings for the device. data is input on the data in pin, while clock in is the serial clock. data can be shifted into the ssm2005 at clock rates up to 1 mhz. stereo inputs precision sum and difference amplifiers amplifiers circle surround outputs l r l+r = center lCr = surround left reset clock select load serial bus +v gnd 2 vacom input power noise generator l r c l s r s right center surround high band surround low band crossover network 7x steering control generator mode control logic data auto balance and mute to subwoofer filter center channel cancel channel steering vcas output amplifiers figure 6. block diagram the shift register clock at clock in is enabled when the write input is low. the write pin can therefore be used as a chip select input. however, the shift register contents are not transferred into the register banks until the rising edge of load . for a traditional 3-wire serial interface, write and load should be tied together. figure 7 shows the timing diagram and minimum timing requirements for the digital interface. to enable a data transfer, the write and load inputs are driven low. the 8-bit serial data, formatted msb first, should be fed to data in and clocked into the shift register on the rising edge of clock in. the new mode setting will then activate on the rising edge of write and load . table ii. modes list modes effect video center channel cancellation active music center cancel cancellation off; center reduced by C4 db. 5-2-5 5-channel circle surround enabled 4-2-4 4-channel matrix enabled center on center channel output on phantom center center channel output off; divided and added to lf and rf sound spread on hard panned input steered to front and rear side sound spread off hard panned input steered to front side only autobalance on balances l and r to 1 db autobalance off autobalance disabled noise off noise generator disabled noise on noise generator on; inputs muted
ssm2005 C9C rev. 0 table iii. data decoding truth table msb lsb reset d0 d1 d2 d3 d4 d5 d6 d7 mode 1 0 0 1 xxxxx c n oise on 1 1 0 1 xxxxx lf n oise on 1 1 1 0 xxxxx rf n oise on 1 0 1 0 xxxxx ls n oise on 1 1 0 0 xxxxx rs n oise on 1 0 0 0 xxxxx all mute 1 1111 xxxx a utobalance on 1 1110 xxxx a utobalance off 1 111x1xxx c enter active 1 111x0xxx phantom center 1 1 1 1 x x 1 x x sound spread on 1 1 1 1 x x 0 x x sound spread off 1 1 1 1 xxx1 x 5.2.5 mode 1 1 1 1 xxx0 x 4.2.4 mode 1 1 1 1 xxxx1 v ideo mode 1 1 1 1 xxxx0 m usic mode 0 xxxxxxxx n oise off, autobalance on, center active, sound spread on, 5.2.5 mode, video mode
ssm2005 C10C rev. 0 d7 d6 d5 d4 d3 d2 d1 d0 1 0 1 data 0 1 0 1 0 clk data t cl clk 1 0 t ch t ds t dh t wc t cw t w3 write & load write & load 1 0 figure 7. logic timing diagram table iv. timing description timing symbol description min typ max units t cl input clock pulsewidth 50 ns t ch input clock pulsewidth 50 ns t ds data setup time 25 ns t dh data hold time 35 ns t cw positive clk edge to end of write 25 ns t wc write to clock setup time 35 ns t lw end of load pulse to next write (4-wire mode) 20 ns t wl end of write to start of load (4-wire mode) 20 ns t l load pulsewidth (4-wire mode) 250 ns t w3 load pulsewidth (3-wire mode) 250 ns notes: 1. an idle hi (clk-hi) or idle lo (clk-lo) clock may be used. data is latched on the positive edge. 2. for spi tm or microwire tm 3-wire bus operation, tie ld to write and use write pulse to drive both pins. (this generates an automatic internal ld signal.) 3. if an idle hi clock is used, t cw and t wl are measured from the final negative transition to the idle state. 4. the first data byte selects an address (msb hi), and subsequent msb lo states set gain levels. refer to the address/data dec oding truth table. 5. data must be sent msb first. spi is a trademark of motorola, inc. microwire is a trademark of national semiconductor corporation.
ssm2005 C11C rev. 0 typical outputs in various modes the ssm2005 circle surround decoder uses ambiance and directional information already present in a stereo signal, and does not require the audio signal to be encoded. the device requires no delay generators or noise reduction. fully differenti- ated rear channels provide rear stereo separation for enhanced spatial perception, a feature unique to circle surround. video mode provides the highest degree of channel separation between the front and center speakers. video mode cancels com- mon center channel material from the left and right front chan- nels. this restores a wide stereo image to matrix encoded sound tracks, while maintaining a solid center channel for dialogue and mono information. the music mode is optimized for unencoded stereo music repro- duction, with full bandwidth on all channels. the steering for the lf and rf channels is deactivated to prevent any stereo image wandering. the independent two-band rear channel steering provides excellent surround imaging, even in car audio applica- tions. well balanced sound is obtained everywhere within a 4- or 5-speaker setup. the 5.2.5 mode provides the maximum channel separation to the surround channels, and should be used with any encoded stereo input signal. the 4.2.4 mode can be used to reduce the dynamic steering of the surround channels, allowing the ssm2005 to simulate a 4-channel surround sound decoder. sound spread off allows the maximum channel separation between the surround and front speakers. with sound spread off, a hard panned left input signal will produce an output only in the left front output. in sound spread on mode, a hard panned left input signal will produce equal output from the left front and left surround outputs. the following tables demonstrate the differences between the modes of the ssm2005 under various input conditions. the l t and r t inputs are at 2 khz, and are shown in terms of their differences in magnitude (in db) and phase (in degrees). for example, a 0 / 180 input means l t is exactly equal in magni- tude, but opposite in phase to r t . table v. video/5.2.5/sound spread off/center on input output |l t | C |r t | (db) db / f |lf| |rf| |c| |ls| |rs| 0 / 0 C 30 C30 +6 C40 C40 0 / 180 C35 C35 C45 +6 +6 l t only 0 C60 C30 C30 C35 r t only C60 0 C30 C35 C30 C6 / 0 0 C15 C4 C25 C30 C6 / 180 C30 C36 C26 0 C15 table vi. video/5.2.5/sound spread on/center on input output |l t | C |r t | (db) db / f |lf| |rf| |c| |ls| |rs| 0 / 0 C 30 C30 +6 C40 C40 0 / 180 C35 C35 C45 +6 +6 l t only 0 C60 C30 0 C30 r t only C60 0 C30 C30 0 C6 / 0 0 C15 C4 0 C25 C6 / 180 C30 C36 C26 0 C15 table vii. music/5.2.5/sound spread on/center on input output |l t | C |r t | (db) db / f |lf| |rf| |c| |ls| |rs| 0 / 0 0 0 +2 C40 C40 0 / 180 0 0 C45 +6 +6 l t only 0 C60 C30 0 C30 r t only C60 0 C30 C30 0 C6 / 0 0 C6C40 C25 C6 / 180 0 C6 C26 0 C15 table viii. video/5.2.5/sound spread on/phantom center input output |l t | C |r t | (db) db / f |lf| |rf| |c| |ls| |rs| 0 / 0 +3 +3 off C40 C40 0 / 180 C35 C35 off +6 +6 l t only 0 C60 off 0 C30 r t only C60 0 off C30 0 C6 / 0 0 C15 off 0 C25 C6 / 180 C30 C36 off 0 C15 table ix. video/4.2.4/sound spread off/center on input output |l t | C |r t | (db) db / f |lf| |rf| |c| |ls| |rs| 0 / 0 C 30 C30 +6 C40 C40 0 / 180 C35 C35 C45 +6 +6 l t only 0 C60 C30 C32 C32 r t only C60 0 C30 C32 C32 C6 / 0 0 C15 C4 C26 C26 C6 / 180 C30 C36 C26 0 C2
ssm2005 C12C rev. 0 4.7m v 0.01 m f 5.9k v 105k v 48.7k v 4.7nf 0.1 m f 100 v left in 10 m f 10 m f 0.1 m f 100 v right in 10 m f 0.1 m f 2 6v 1 6v ssm2275-a 10 m f 0.1 m f 40.2k v 1nf 1nf 787 v 0.1 m f 1 m f 787k v 909 v 0.1 m f 100pf ssm2275-b 10 m f 0.1 m f 909 v 0.1 m f 453 v 453 v 0.1 m f 0.1 m f 1 m f 453 v 453 v 0.1 m f 1 m f l 1 r out to subwoofer filter (optional) 1 m f 1k v c out lf out rf out ls out rs out 0.47 m f 3.82k v load reset data 1 m f 33.2k v 1 6v 2 6v write clk in 0.1 m f 0.22 m f 274k v 1 m f 100k v 0.1 m f 0.22 m f 274k v 1 m f 1 m f 22 m f 10k v 1 m f denotes control ground denotes signal ground denotes connection 7.87k v + + + + + 162k v + 1 m f 1k v 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 ssm2005 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 787 v 0.01 m f 0.1 m f ssm2275-b 0.01 m f 5.9k v 105k v 48.7k v 4.7nf 0.1 m f ssm2275-a 10 m f + figure 8. typical application schematic
ssm2005 C13C rev. 0 application notes figure 8 shows a typical ssm2005 application schematic. the stereo source signal is connected to the ssm2005 audio signal inputs at pins 7 and 10, as well as the left/right level detectors at pins 19, 20, 22, and 23. the input signal goes through the autobalance circuitry and can be accessed at pins 6 and 9. a sum (l+r) and difference (lCr) signal is available at pins 15 and 16, respectively. these signals are fed into the front/rear level detector at pins 27 and 28. the l+r signal is also fed internally to the center channel vca to produce the center channel output at pin 48. in addition, the lCr signal is fed into two external filters, creating a low-band and high-band signal with a crossover frequency of 2 khz. the cross- over filters are both 3 rd order bessel filters, providing a minimum group delay to the surround channels. the lCr high-band signal is connected to pin 17, and the lCr low-band signal is connected to pin 18. these two pins provide the multiband steering to the two surround outputs. low-pass filters are inserted between pins 1 and 2, and pins 3 and 4. these filters are used for the center-canceling circuitry, which removes center channel information from the left front and right front outputs. this circuitry is only active in video mode, providing maximum channel separation between the center and front outputs. in an application that will only use music mode, these active filters can be removed and replaced with a 1 m f capacitor between pins 1 and 2, and pins 3 and 4. the capacitors and resistors connected to pins 21, 24, 25, 26, 29, 30, 31 and 32 are used to create the time constants for the steer- ing circuitry. the values shown in figure 8 are strongly recom- mended. variation from these values will result in improper operation of the circle surround decoder, and may result in the assembled unit failing srs labs approval. the noise generator output is at pin 42, and the input to the noise steering circuit is at pin 43. the r-c network connected between pins 42 and 43 is used to remove dc voltage and high frequencies, which could damage speakers. other noise-shaping circuitry could be used here to create noise patterns other than white, or to further attenuate the noise output with a resistor divider. adding a subwoofer output the ssm2005 provides an output of the summed left in and right in signals. this l+r signal is used to drive the center chan- nel output, and it can also be used to provide a subwoofer chan- nel by connecting the output from pin 15 to a low-pass filter. the schematic for such a configuration is shown in figure 9. here, pin 15 is connected to a 2nd order bessel low-pass filter. the circuit uses the ssm2275, a low noise audio op amp that can run from the same 6 v that power the ssm2005. using the component values shown in figure 9, the filters cutoff frequency is 100 hz. 48 47 46 45 44 7 10 39 ssm2005* left in right in 10 m f 10 m f center l f r f l s r s outputs *additional pins omitted for clarity ssm2275 2.05k v 4.23k v 1 m f subwoofer 0.47 m f f c = 100hz figure 9. adding a subwoofer output implementing a stereo bypass mode figure 10 shows a schematic for implementing a clickless stereo bypass around the ssm2005. the stereo bypass mode allows the user to defeat the circle surround decoding and listen to two-channel stereo from the left front and right front speakers. the ssm2402 is a clickless dual audio single-pole single-throw (spst) switch. when the control voltage, v byp , is low (below +0.8 v) the switch is open, and the five channel outputs are connected to the outputs of the ssm2005. when v byp goes high (above +2.0 v) the ssm2402 switch closes, connecting the lf and rf outputs to left in and right in respectively. at the same time, a data byte should be loaded into the ssm2005, placing the circle surround decoder into mute mode. the data byte required for mute mode can be found in table iii, and the logic timing diagrams can be found in figure 7. 48 47 46 45 44 7 10 39 14 13 12 11 10 9 8 1 2 3 4 5 6 7 ssm2402 +6v 2 6v v byp v byp high = stereo mode v byp low = circle surround mode ssm2005* data in left in right in 10 m f 10 m f center l f r f l s r s outputs *additional pins omitted for clarity x denotes a don't care bit v byp low = cs mode 0 0 0 x x x xx figure 10. implementing a clickless stereo bypass mode
ssm2005 C14C rev. 0 using the ssm2005 for karaoke in video mode, the ssm2005 removes centered vocal informa- tion from the lf and rf speakers. this allows the device to be used in karaoke applications, where the user can sing along with any music recording. figure 11 shows a circuit diagram for such an application. the op179 is the microphone preamplifier with a gain of +20 db. a 2.2 k w resistor connects the microphone to the +6 v supply rail, providing proper biasing for an electret mic rophone. the ssm2402 is used as a clickless switch, connecting the center output to either the center out from the ssm2005 or the microphone. in circle surround mode, the control voltages to the ssm2402 connect the output from the ssm2005 to the center output. in karaoke mode, this connection is opened, and the micro- phone is directed to the center output. at the same time, the ssm2005 should be loaded with data byte (msb first): 1 1 1 0 1 0 1 1. this activates the center canceling circuitry in the ssm2005, removing centered vocal information from the left front and right front speakers. the overall result is the microphone output comes out of the center speaker, with the vocals-removed music coming from the remaining speakers. 14 13 12 11 10 9 8 1 2 3 4 5 6 7 ssm2402 +6v 2 6v ssm2005* for karaoke, load data byte: 1 1 1 0 1 0 1 1 left in right in 10 m f 10 m f center l f r f l s r s outputs *additional pins omitted for clarity +5v karaoke mode circle surround mode sw-2 7404 2 6v op179 +6v 0.1 m f 1k v mic 2.2k v 10k v +6v 48 47 46 45 44 7 10 39 figure 11. using the ssm2005 for karaoke
ssm2005 C15C rev. 0 outline dimensions dimensions shown in inches and (mm). 48-lead ssop (rs suffix) 0.010 (0.254) 0.005 (0.127) 0.040 (1.02) 0.024 (0.61) 8 8 0 8 48 25 24 1 0.630 (16.00) 0.620 (15.75) 0.410 (10.41) 0.400 (10.16) 0.299 (7.59) 0.292 (7.42) pin 1 seating plane 0.016 (0.41) 0.008 (0.20) 0.025 (0.635) bsc 0.0135 (0.343) 0.008 (0.203) 0.110 (2.79) 0.095 (2.41) 0.092 (2.34) 0.088 (2.24) c3628C8C7/99 printed in u.s.a.

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