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FEATURES 5.0 V Stereo Audio ADC with 3.3 V Tolerant Digital Interface Supports 96 kHz Sample Rates Supports 16-/20-/24-Bit Word Lengths Multibit Sigma-Delta Modulators with "Perfect Differential Linearity Restoration" for Reduced Idle Tones and Noise Floor 105 dB (Typ) Dynamic Range Supports 256/512 and 768 fS Master Clocks Flexible Serial Data Port Allows Right-Justified, Left-Justified, I2S Compatible and DSP Serial Port Modes Cascadable (up to Four Devices) from a Single DSP SPORT Device Control via SPI Compatible Serial Port or Optional Control Pins On-Chip Reference 28-Lead SSOP Package APPLICATIONS Professional Audio Mixing Consoles Musical Instruments Digital Audio Recorders, Including CD-R, MD, DVD-R, DAT, HDD Home Theater Systems Automotive Audio Systems Multimedia
Stereo Audio, 24-Bit, 96 kHz, Multibit - ADC AD1871
PRODUCT OVERVIEW
The AD1871 is a stereo audio ADC intended for digital audio applications requiring high performance analog-to-digital conversion. It features two 24-bit conversion channels each with programmable gain amplifier (PGA), multibit sigma-delta modulator, and decimation filters. Each channel provides 105 db of dynamic range, making the AD1871 suitable for applications such as digital audio recorders and mixing consoles. Each of the AD1871's input channels (left and right) can be configured as either differential or single-ended (two inputs muxed with internal single-ended-to-differential conversion). The input PGA features a gain range of 0 dB to 12 dB in steps of 3 dB. The - modulator features a proprietary multibit architecture that realizes optimum performance over an audio bandwidth with standard audio sampling rates of 32 kHz up to 96 kHz. The decimation filter response features very low passband ripple and excellent stop-band attenuation. The AD1871's audio data interface supports all common interface formats such as I2S, left-justified, right-justified as well as other modes that allow for convenient connection to general-purpose digital signal processors (DSPs). The AD1871 also features an SPI compatible serial control port that allows for convenient control of device parameters and functionality such as sample word-width, PGA settings, interface modes, and so on. The AD1871 operates from a single 5 V power supply--with an optional digital interfacing capability of 3.3 V. It is housed in a 28-lead SSOP package and is characterized for operation over the temperature range -40C to +105C.
FUNCTIONAL BLOCK DIAGRAM
CAPLN CAPLP AVDD DVDD ODVDD
CASC
VINLP
LRCLK
ANALOG INPUT BUFFER
MULTIBIT MODULATOR
DECIMATOR
DATA PORT
BCLK DOUT DIN
VINLN
VREF
AD1871
FILTER ENGINE
RESET
CLOCK DIVIDER
MCLK
VINRP
CLATCH/(M/S)
ANALOG INPUT BUFFER
MULTIBIT MODULATOR
DECIMATOR
SPI PORT
CCLK/(256/512) CIN/(DF1)
COUT/(DF0)
XCTRL
VINRN
CAPRN CAPRP
AGND
DGND
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 that may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781/329-4700 www.analog.com Fax: 781/326-8703 (c) Analog Devices, Inc., 2002
AD1871
TABLE OF CONTENTS FEATURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 FUNCTIONAL BLOCK DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 PRODUCT OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 TEST CONDITIONS UNLESS OTHERWISE SPECIFIED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 ANALOG PERFORMANCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 LOW-PASS DIGITAL FILTER CHARACTERISTICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 HIGH-PASS DIGITAL FILTER CHARACTERISTICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 MASTER CLOCK (MCLK) AND RESET TIMING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 DATA INTERFACE TIMING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 CONTROL INTERFACE TIMING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 DIGITAL I/O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 POWER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 TEMPERATURE RANGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 ABSOLUTE MAXIMUM RATINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 ORDERING GUIDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 PIN CONFIGURATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 PIN FUNCTION DESCRIPTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 TERMINOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 TYPICAL PERFORMANCE CURVES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Filter Responses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Device Performance Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 FUNCTIONAL DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Clocking Scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Modulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Digital Decimating Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 High-Pass Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 ADC Coding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Analog Input Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Serial Data Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 CONTROL/STATUS REGISTERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Control Register I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Control Register II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Control Register III . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Peak Reading Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 EXTERNAL CONTROL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Master/Slave Select . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 MCLK Mode Select . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Serial Data Format Select . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 MODULATOR MODE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 INTERFACING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Analog Interfacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 LAYOUT CONSIDERATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 OUTLINE DIMENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 -2- REV. 0
AD1871-SPECIFICATIONS
TEST CONDITIONS UNLESS OTHERWISE NOTED
Supply Voltages . . . . . . . . . . . . . . . . . . . . . . Ambient Temperature . . . . . . . . . . . . . . . . . Input Clock (fCLKIN) [256 fS] . . . . . . . . . . Input Signal . . . . . . . . . . . . . . . . . . . . . . . . . .................................. Measurement Bandwidth . . . . . . . . . . . . . . . Word Width . . . . . . . . . . . . . . . . . . . . . . . . . Load Capacitance on Digital Outputs . . . . . Input Voltage High (VIH) . . . . . . . . . . . . . . . Input Voltage Low (VIL) . . . . . . . . . . . . . . . Master Mode, Data I2S Justified
ANALOG PERFORMANCE
5.0 V 25C 12.288 MHz 991.768 Hz -0.5 dB Full Scale (dBFS) (Differential, PGA/MUX Enabled) 23.2 Hz to 19.998 kHz 24 Bits 100 pF 2.4 V 0.8 V
Parameter RESOLUTION DIFFERENTIAL INPUT Dynamic Range Unweighted A-Weighted Signal-to-Noise Ratio Total Harmonic Distortion + Noise (THD+N) Multibit Modulator Only Dynamic Range (A-Weighted) SINGLE-ENDED INPUT Dynamic Range Unweighted A-Weighted Signal-to-Noise Ratio Total Harmonic Distortion + Noise (THD+N) DIFFERENTIAL INPUT (BYPASS) Dynamic Range Unweighted A-Weighted Signal-to-Noise Ratio Total Harmonic Distortion + Noise (THD+N) DIFFERENTIAL INPUT (fS = 96 kHz) Dynamic Range Unweighted A-Weighted Signal-to-Noise Ratio Total Harmonic Distortion + Noise (THD+N) Analog Inputs Differential Input Range ( Full Scale) Input Impedance (PGA/MUX) Input Impedance (ByPass) Input Impedance (PGA/MUX) VREF DC Accuracy Gain Error Interchannel Gain Mismatch Gain Drift Crosstalk (EIAJ Method)
Min
Typ 24
Max
Unit Bits
Conditions
PGA/MUX Enabled (20 Hz to 20 kHz, -60 dB Input) 98 100 103 105 106 -85 -103 102 dB dB dB dB dB dB PGA/MUX Enabled (20 Hz to 20 kHz, -60 dB Input) 103 105 106 -85 -103 dB dB dB dB dB
Input = -0.5 dBFS Input = -20 dBFS Modulator Output @ 5.6448 MHz
Input = -0.5 dBFS Input = -20 dBFS PGA/MUX Disabled (20 Hz to 20 kHz, -60 dB Input)
103 106 106 -86 -104
dB dB dB dB dB
Input = -0.5 dBFS Input = -20 dBFS PGA/MUX Enabled; AMC = 1 (20 Hz to 20 kHz, -60 dB Input)
103 106 106 -87 -104 -2.828 8 40 4 2.25 -10 -0.01 100 -100 +2.828
dB dB dB dB dB V kW kW kW V % dB ppm/C dB
Input = -0.5 dBFS Input = -20 dBFS
Differential Differential Single Ended
2.138
2.363
-0.2
+0.2
REV. 0
-3-
AD1871-SPECIFICATIONS
LOW-PASS DIGITAL FILTER CHARACTERISTICS (fS = 48 kHz)
Parameter Decimation Factor Pass-Band Frequency Stop-Band Frequency Pass-Band Ripple Stop-Band Attenuation Group Delay
Min
Typ 128 21.77 26.23 0.01 120 910
Max
Unit kHz kHz dB dB ms
LOW-PASS DIGITAL FILTER CHARACTERISTICS (fS = 96 kHz)
Parameter Decimation Factor Pass-Band Frequency Stop-Band Frequency Pass-Band Ripple Stop-Band Attenuation Group Delay
Min
Typ 64 43.54 52.46 0.01 120 460
Max
Unit kHz kHz dB dB ms
HIGH-PASS DIGITAL FILTER CHARACTERISTICS (fS = 48 kHz)
Parameter Cutoff Frequency
Min
Typ 2
Max
Unit Hz
HIGH-PASS DIGITAL FILTER CHARACTERISTICS (fS = 96 kHz)
Parameter Cutoff Frequency
MASTER CLOCK (MCLK) AND RESET TIMING
Min
Typ 4
Max
Unit Hz
Mnemonic tMCH tMCL tPDR
Description MCLK High Width MCLK Low Width RESET Low Pulsewidth
Min 20 20 20
Typ
Max
Unit ns ns ns
Comment
tMCH
MCLK
tMCL
RESET
tPDR
Figure 1. MCLK/ RESET Timing
-4-
REV. 0
AD1871
DATA INTERFACE TIMING (STANDALONE MODE-MASTER)
Mnemonic tBDLY tBLDLY tBDDLY
Description BCLK Delay LRCLK Delay to Low DOUT Delay
Min 20 10 10
Typ
Max
Unit ns ns ns
Comment From MCLK Rising From BCLK Falling From BCLK Falling
MCLK
tBDLY
BCLK
tBLDLY
LRCLK
tBDDLY
DOUT LEFT-JUSTIFIED MODE MSB MSB-1
DOUT I2S-JUSTIFIED MODE
MSB
DOUT RIGHT-JUSTIFIED MODE 8-BIT CLOCKS (24-BIT DATA) 12-BIT CLOCKS (20-BIT DATA) 16-BIT CLOCKS (16-BIT DATA)
MSB
LSB
Figure 2. Master Data Interface Timing
REV. 0
-5-
AD1871
DATA INTERFACE TIMING (STANDALONE MODE-SLAVE)
Mnemonic tBCH tBCL tBDSD tLRS tLRH
Description BCLK High Width BCLK Low Width DOUT Delay LRCLK Setup LRCLK Hold
tBCH
BCLK
Min
Typ 30 30
Max
Unit ns ns ns ns ns
Comment
20 10 5
tDBP
From BCLK Falling To BCLK Rising From BCLK Rising
tLRS
LRCLK
tBCL
tBDSD
DOUT LEFT-JUSTIFIED MODE MSB MSB-1
DOUT I2S-JUSTIFIED MODE
MSB
DOUT RIGHT-JUSTIFIED MODE 8-BIT CLOCKS (24-BIT DATA) 12-BIT CLOCKS (20-BIT DATA) 16-BIT CLOCKS (16-BIT DATA)
MSB
LSB
Figure 3. Slave Data Interface Timing
-6-
REV. 0
AD1871
DATA INTERFACE TIMING (CASCADE MODE-MASTER)
Mnemonic tBCHDC tBCLDC tBLRDC tBDDC tBDIS tBDIH
Description BCLK High Delay BCLK Low Delay LRCLK Delay DOUT Delay DIN Setup DIN Hold
M CLK
Min 20 20 10 10 10 10
Typ
Max
Unit ns ns ns ns ns ns
Comment From MCLK Rising From MCLK Falling From BCLK Rising From BCLK Rising To BCLK Rising From BCLK Rising
t BCH DC
LRCLK
t BCLDC t BLRDC
BCLK
t BDDC
DOU T
Figure 4. Master Cascade Interface Timing
DATA INTERFACE TIMING (CASCADE MODE-SLAVE)
Mnemonic tBCHC tBCLC tBDSDC tLRSC tLRHC tBDIS tBDIH
Description BCLK High Width BCLK Low Width DOUT Delay LRCLK Setup LRCLK Hold DIN Setup DIN Hold
Min
Typ 30 30
Max
Unit ns ns ns ns ns ns ns
Comment
20 10 5 10 10
From BCLK Rising To BCLK Rising From BCLK Rising To BCLK Rising From BCLK Rising
t LRH C
LRCLK
t LRSC
BCLK
t BCH C
t BDSDC
DOU T
t BCLC
Figure 5. Slave Cascade Interface Timing
DATA INTERFACE TIMING (MODULATOR MODE)
Mnemonic tMOCH tMOCL tMHDD tMLDD tMMDR tMMDF
Description MODCLK High Width MODCLK Low Width MOD DATA High Delay MOD DATA Low Delay MODCLK Delay Rising MODCLK Delay Falling
Min
Typ MCLK MCLK 30 20 30 20
Max
Unit ns ns ns ns ns ns
t M OCH
Comment
From MCLK Rising From MCLK Falling MCLK Falling to MODCLK Rising MCLK Falling to MODCLK Falling
M ODCLK
t M H DD
D[0 - 3 ]
t M OCL
t M LDD
Figure 6. Modulator Mode Timing
REV. 0
-7-
AD1871
CONTROL INTERFACE (SPI) TIMING
Mnemonic tCCH tCCL tCCP tCDS tCDH tCLS tCLH tCOE tCOD tCOTS
Description CCLK High Width CCLK Low Width CCLK Period CDATA Setup Time CDATA Hold Time CLATCH Setup Time CLATCH Hold Time COUT Enable COUT Delay COUT Three-State
tCCH
CCLK
Min 40 40 80 10 10 10 10 15 20 25
Typ
Max
Unit ns ns ns ns ns ns ns ns ns ns
Comment
To CCLK Rising From CCLK Rising To CCLK Rising From CCLK Rising From CLATCH Falling From CCLK Falling From CLATCH Rising
tCCL
CLATCH
tCCL tCSU tCLH
D08 D08 D07 D07 D06 D06 D05 D05 D04 D04 D03 D03 D02 D02 D01 D01 D00 D00 D12 D11 D10 D09 D09
CIN COUT
D15
D14
D13
tCHD
Figure 7. Control Interface Timing
DIGITAL I/O
Parameter Input Voltage High (VIH) Input Voltage Low (VIL) Input Leakage (IIH @ VIH = 5 V) Input Leakage (IIL @ VIL = 0 V) Output Voltage High (VOH @ IOH = -2 mA) Output Voltage Low (VOL @ IOL = +2 mA) Input Capacitance
POWER
Min 2.4
Typ
Max 0.8 10 10
Unit V V mA mA V V pF
ODVDD - 0.4 V 0.4 15
Parameter Supplies Voltage, AVDD, and DVDD Voltage, ODVDD Analog Current Analog Current--Power-Down (MCLK Running) Digital Current, DVDD Digital Current, ODVDD Digital Current--Power-Down (MCLK Running) DVDD* Digital Current--Power-Down (MCLK Running) ODVDD* Power Supply Rejection 1 kHz 300 mV p-p Signal at Analog Supply Pins 20 kHz 300 mV p-p Signal at Analog Supply Pins *RESET held low.
TEMPERATURE RANGE
Min 4.5 2.7
Typ 5 40 4.0 18 0.5 0.8 1.0 -86 -77
Max 5.5 5.5 45 6.0 22 1.0 2.0 15.0
Unit V V mA mA mA mA mA mA dB dB
Parameter Specifications Guaranteed Functionality Guaranteed Storage
Specifications subject to change without notice.
Min -40 -65
Typ 25
Max +105 +150
Unit C C C
-8-
REV. 0
AD1871
ABSOLUTE MAXIMUM RATINGS
Min DVDD to DGND and ODVDD to DGND AVDD to AGND Digital Inputs Analog Inputs AGND to DGND Reference Voltage Soldering (10 sec) 0 0 DGND - 0.3 AGND - 0.3 -0.3
Typ
Max
Unit V V V V V C
6 6 DVDD + 0.3 AVDD + 0.3 +0.3 Indefinite Short Circuit to Ground 300
ORDERING GUIDE
Model AD1871YRS AD1871YRS-REEL EVAL-AD1871EB
Temperature -40C to +105C -40C to +105C
Package Description SSOP SSOP Evaluation Board
Package Option RS-28 RS-28 in 13" Reel (1500 pieces)
PIN CONFIGURATION
MCLK 1 CCLK/(256/512) 2 COUT/(DF0) 3 CIN/(DF1) 4 CLATCH/(M/S) 5 DVDD 6 DGND 7
28 LRCLK 27 BCLK 26 DOUT 25 DIN 24 RESET
AD1871
23 ODVDD
22 DGND TOP VIEW XCTRL 8 (Not to Scale) 21 CASC
AVDD 9 VINLN 10 VINLP 11 CAPLN 12 CAPLP 13 VREF 14
20 AGND 19 VINRN 18 VINRP 17 CAPRN 16 CAPRP 15 AGND
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 AD1871 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
REV. 0
-9-
AD1871
PIN FUNCTION DESCRIPTIONS
Pin No. 1 2 3
Input/ Output I I I/O
Mnemonic MCLK CCLK1 COUT1, 2 CIN1 CLATCH1 DVDD DGND XCTRL
Description Master Clock. The master clock input determines the sample rate of the device. MCLK can be 256, 512, or 768 times the sampling frequency. Control Port Bit Clock--clock signal for control port (SPI) interface. This pin is reconfigured in the External Control Mode (Pin XCTRL is high), see below. Control Port Data Out--serial data output from the control port (SPI) interface (in readback). This pin is reconfigured in the External Control Mode (Pin XCTRL is high), see below; or in Modulator Mode (Bit MME of Control Register II is set), see below. Control Port Data Input--serial data input for control port (SPI) interface. This pin is reconfigured in the External Control Mode (Pin XCTRL is high), see below. Control Port Frame Sync--frame sync (framing signal) for control port (SPI) interface. This pin is reconfigured in the External Control Mode (Pin XCTRL is high), see below. 5 V Digital Core Supply Digital Ground External Control Enable. This pin is used to select the Control Mode for the device. When XCTRL is low, control is via the SPI compatible control port (Pins CCLK, CLATCH, CIN, and COUT). When XCTRL is enabled (high), control of several device functions is possible by hardware pin strapping (Pins 256/512, M/S, DF1, and DF0). In External Control Mode, all other functions are in default state (please refer to the Control Register Descriptions and External Control section). 5 V Analog Supply Left Channel, Negative Input (via MUX/PGA) Left Channel, Positive Input (via MUX/PGA) Left External Filter Capacitor (Negative Input to Modulator) Left External Filter Capacitor (Positive Input to Modulator) Reference Voltage Output. It is recommended to connect a capacitor combination of 10 mF in parallel with 0.1 mF between VREF and AGND (Pin 15). (See Layout Recommendations.) Analog Ground Right External Filter Capacitor (Positive Input to Modulator) Right External Filter Capacitor (Negative Input to Modulator) Right Channel, Positive Input (via MUX/PGA) Right Channel, Negative Input (via MUX/PGA) Analog Ground Cascade Enable. This pin enables cascading of up to four AD1871 devices to a single DSP serial port (see Cascading section). Digital Ground Digital Interface Supply. The digital interface can operate from 3.3 V to 5.0 V (nominal). Reset Serial Data Input. Serial data input pin, only valid when the device is configured in Cascade Mode (Pin CASC is high). This pin is reconfigured in Modulator Mode (Bit MME of Control Register II is set), see below. Audio Serial Data Output. This pin is reconfigured in Modulator Mode (Bit MME of Control Register II is set), see below. Audio Serial Bit Clock. The bit clock is the audio data serial clock and determines the rate of audio data transfer. This pin is reconfigured in Modulator Mode (Bit MME of Control Register II is set), see below. Left/Right Clock. This clock, also known as the word clock, determines the sampling rate. It is an output or input depending on the status of Master/Slave. This pin is reconfigured in Modulator Mode (Bit MME of Control Register II is set), see below.
4 5 6 7 8
I I I I I
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
I I I I/O I/O O I I/O I/O I I I I I I I I/O
AVDD VINLN VINLP CAPLN CAPLP VREF AGND CAPRP CAPRN VINRP VINRN AGND CASC DGND ODVDD RESET DIN2 DOUT2 BCLK2 LRCLK2
26 27
O I/O
28
I/O
NOTES 1 External Control Mode (See pg 11) 2 Modulator Mode (See pg 11)
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AD1871
Pin Function Redefinition in External Control Mode
Pin No. 2 3 4 5
Input/ Output I I I I
Mnemonic 256/512 DF0 DF1 M/S
Description Clock Rate Select. This pin is used to select between an MCLK of 256 fS (pin low) or 512 fS (pin high). Data Format Select 0. This pin is used as the low bit (DF0) of the data format selection (see section on External Control). Data Format Select 1. This pin is used as the high bit (DF1) of the data format selection (see section on External Control). Master/Slave Select. This pin is used to select between the Master (pin low) or Slave (pin high) Modes.
Pin Function Redefinition in Modulator Mode
Pin No. 3
Input/ Output O
Mnemonic MODCLK
Description This pin provides a clock output that allows the user to decode the left and right channel modulator outputs. It is similar to a left/right clock but runs (nominally) at 5.6448 MHz and gates a 4-bit modulator output word in each phase (see section on Modulator Mode). Bit 3 of the Modulator Output Word Bit 2 of the Modulator Output Word Bit 1 of the Modulator Output Word Bit 0 of the Modulator Output Word
25 26 27 28
O O O O
D3 D2 D1 D0
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AD1871
TERMINOLOGY Crosstalk (EIAJ Method)
Dynamic Range The ratio of a full-scale input signal to the integrated input noise in the pass band (20 Hz to 20 kHz), expressed in decibels (dB). Dynamic range is measured with a -60 dB input signal and is equal to (S/[THD+N]) + 60 dB. Note that spurious harmonics are below the noise with a -60 dB input, so the noise level establishes the dynamic range. The dynamic range is specified with and without an A-Weight filter applied. Signal to (Total Harmonic Distortion + Noise)
(S/[THD+N])
Ratio of response on one channel with a grounded input to a full-scale 1 kHz sine-wave input on the other channel, expressed in decibels.
Power Supply Rejection
With no analog input, signal present at the output when a 300 mV p-p signal is applied to power supply pins, expressed in decibels of full scale.
Group Delay
The ratio of the root-mean-square (rms) value of the fundamental input signal to the rms sum of all other spectral components in the pass band, expressed in decibels (dB).
Pass Band
Intuitively, the time interval required for an input pulse to appear at the converter's output, expressed in milliseconds (ms). More precisely, the derivative of radian phase with respect to radian frequency at a given frequency.
GLOSSARY
The region of the frequency spectrum unaffected by the attenuation of the digital decimator's filter.
Pass-Band Ripple
ADC--Analog-to-Digital Converter DSP--Digital Signal Processor IMCLK--Internal master clock signal, used to clock the decimating filter section. (Its frequency must be 256 fS.) MCLK--External master clock signal applied to the AD1871. Its frequency can be 256, 512, or 768 fS. MCLK is divided internally to give an IMCLK frequency that must be 256 fS. MODCLK--This is the - modulator clock that determines the sample rate of the modulator. Ideally, it should not exceed the lower of 6.144 MHz or 128 fS. The MODCLK is derived from the IMCLK by a divider that can be selected as /2 or /4. MUX--Multiplexer PGA--Programmable Gain Amplifier
The peak-to-peak variation in amplitude response from equalamplitude input signal frequencies within the pass band, expressed in decibels.
Stop Band
The region of the frequency spectrum attenuated by the digital decimator's filter to the degree specified by stop-band attenuation.
Gain Error
With a near full-scale input, the ratio of the actual output to the expected output, expressed as a percentage.
Interchannel Gain Mismatch
With identical near full-scale inputs, the ratio of the outputs of the two stereo channels, expressed in decibels.
Gain Drift
Change in response to a near full-scale input with a change in temperature, expressed as parts-per-million (ppm) per C.
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Typical Performance Characteristics-AD1871
FILTER RESPONSES
0 -20 -40
0 -20 -40
MAGNITUDE - dB
0 5 10 15
MAGNITUDE - dB
-60 -80 -100 -120 -140 -160
-60 -80 -100 -120 -140 -160
0
5
10
15
FREQUENCY - NORMALIZED TO fS
FREQUENCY - NORMALIZED TO fS
TPC 1. Sinc Filter Response (AMC = 0)
TPC 4. Second Half-Band Filter Response
0 -20 -40
0
-50 MAGNITUDE - dB
MAGNITUDE - dB
-60 -80 -100 -120
-100
-150 -140 -160
0
5
10
15
0
5
10
15
FREQUENCY - NORMALIZED TO fS
FREQUENCY - NORMALIZED TO fS
TPC 2. First Half-Band Filter Response
TPC 5. Composite Filter Response (AMC = 0)
0 -20 -40
0
MAGNITUDE - dB
MAGNITUDE - dB
-50
-60 -80 -100 -120 -140 -160
-100
-150
0 5 10 15
0
0.5
1.0
1.5
2.0
FREQUENCY - NORMALIZED TO fS
FREQUENCY - NORMALIZED TO fS
TPC 3. Comb Compensation Filter Response
TPC 6. Composite Filter Response (Pass Band Section) (AMC = 0)
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AD1871
DEVICE PERFORMANCE CURVES
5 0 -5 0 -20 -40
MAGNITUDE - dB
-60 -10
dBFS
0 5 10 FREQUENCY - Hz 15 20
-80 -100 -120
-15 -20
-140 -25 -30 -160 -180 2 4 6 8 10 kHz 12 14 16 18 20
TPC 7. High-Pass Filter Response, fS = 48 kHz
TPC 10. 1 kHz Tone at -20 dBFS, (32 k-Point FFT), fS = 48 kHz
5 0 -5
0 -20 -40
MAGNITUDE - dB
-60 -10
dBFS
0 5 10 FREQUENCY - Hz 15 20
-80 -100 -120
-15 -20
-140 -25 -30 -160 -180 2 4 6 8 10 kHz 12 14 16 18 20
TPC 8. High-Pass Filter Response, fS = 96 kHz
TPC 11. 1 kHz Tone at -60 dBFS, (32 k-Point FFT), fS = 48 kHz
-20 -30 -40 -50
0 -20 -40 -60
dBFS
-80
dB
-60 -70
-100 -120 -140 -160 -180 2 4 6 8 10 kHz 12 14 16 18 20 -80 -90 -100 -60 -55 -50 -45 -40 -35 -30 -25 -20 -15 -10 dBr
-5
TPC 9. 1 kHz Tone at -0.5 dBFS, (32 k-Point FFT), fS = 48 kHz
TPC 12. THD+N vs. Input Amplitude at 1 kHz, fS = 48 kHz
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AD1871
-60
0 -10 -20
-70
-30 -40 -50
-80
-60
dB
dBFS
-70 -80 -90 -100 -110
-90
-100
-120 -130 -140
-110 2 4 6 8 10 kHz 12 14 16 18 20
-150 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.1 FREQUENCY-MHz
TPC 13. THD+N vs. Input Frequency at -0.5 dBFS, fS = 48 kHz
TPC 15. FFT of Modulator Output at -0.5 dBFS, fS = 6.144 MHz
-90
-95
-100
dB
-105
-110
-115
-120 2 4 6 8 10 kHz 12 14 16 18 20
TPC 14. Channel Separation vs. Frequency at -0.5 dBFS, fS = 48 kHz
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AD1871
FUNCTIONAL DESCRIPTION Clocking Scheme
The MCLK pin is the input for the master clock frequency to the device. Nominally the MCLK frequency will be 256 fS for correct operation of the device. However, if the user's MCLK is a multiple of 256 fS (perhaps 512 fS or 768 fS), it is possible to divide down the MCLK frequency to a suitable internal master clock frequency (IMCLK) using the MCLK divider block as
AMC BIT (CONT REG I) 0/1
shown in Figure 8. The divide options can be chosen from passthrough (/1), /2, or /3 corresponding with 256 fS, 512 fS, or 768 fS MCLKs, respectively. The MCLK divider can be controlled using the MCD1-MCD0 Bits of Control Register III. (see Table XIII.) The resulting internal MCLK (IMCLK) is used to run the decimating and filtering engine and must be chosen to be at a ratio of 256 fS.
HPE BIT (CONT REG I)
HIGH-PASS FILTERS ANALOG INPUT 6.144MHz MODULATOR SINC FILTER 384kHz/ 768kHz HALF-BAND FILTERS 48kHz/ 96kHz
48kHz/ 96kHz
MODCLK 6.144MHz IMCLK /2 DIVIDER /4
12.288MHz/ 24.576MHz
IMCLK
MCLK DIVIDER /1 /2 /3
MCLK
Figure 8. Clocking Scheme to Modulator and Filter Engine
Modulator
The AD1871's analog - modulator section comprises a second order multibit implementation using Analog Device's proprietary technology for best performance. As shown in Figure 9, the two analog integrator blocks are followed by a Flash ADC section that generates the multibit samples. The output of the Flash ADC, which is thermometer encoded, is decoded to binary for output to the filter sections and is scrambled for feedback to the two integrator stages. The modulator is optimized for operation at a sampling rate of 6.144 MHz (which is 128 fS at 48 kHz sampling and 64 fS at 96 kHz sampling). The modulator clock control (AMC Bit in Control Register I) is used to select the modulator
FROM ANALOG INPUT SECTION
clock (MODCLK) as a ratio from the IMCLK. The modulator clock divider options are /2 (default) for 48 kHz operation and /4 for 96 kHz operation. When operating with an IMCLK of 12.288 MHz, the default divider setting (/2) gives a modulator clock of 6.144 MHz. When operating with an IMCLK of 24.576 MHz, the alternate divider setting (/4) gives a modulator clock of 6.144 MHz (see Figure 8). If it is required to operate the device at a different output sample rate than those detailed above, perhaps 44.1 kHz or 88.2 kHz, the decimation filter cutoff characteristics can then be determined from the normalized frequency response plot shown in TPC 6.
FLASH ADC
THERMOMETER TO BINARY DECODER
DIGITAL OUTPUT (4 BITS/6.144MHz)
SCRAMBLER FEEDBACK DACs
Figure 9. Modulator Block Diagram
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AD1871
Digital Decimating Filters
The filtering and decimation of the AD1871's modulator data stream is implemented in an embedded DSP engine. The first stage of filtering is the sinc filtering, which has selectable decimation (selected by the modulator clock control bit (AMC, see Modulator section). The default decimation in the sinc stage provides a sample rate reduction of 16; this corresponds with a MODCLK rate of 128 fS. The alternate setting of the AMC Bit gives a sinc decimation factor of 8 that corresponds with a MODCLK rate of 64 fS. The output of the sinc decimator stage is at a rate of 8 fS. The filter engine implements two half-band FIR filter sections and a sinc compensation stage that together give a further decimation factor of 8. Please refer to TPCs 1 through 4 for details on the responses of the sinc and FIR filter sections. TPC 5 gives the composite response of the sinc and FIR filters.
High-Pass Filter
CAPxN VINxP CAPxP VINxN VCM VCM
Figure 10. Differential Analog Input
In Single-Ended Mode, either VINxP or VINxN can be selected as the input. The pair of input inverting amplifiers is reconfigured as a single-ended-to-differential conversion stage. Again the outputs of the differential section are connected to Pins CAPxP and CAPxN (see Figure 11).
The AD1871 features an optional high-pass filter section that provides the ability of rejecting dc from the output data stream. The high-pass filter is enabled by setting Bit 8 (HPE) of Control Register I to 1. Please refer to TPC 7 and TPC 8 for details of the high-pass filter characteristics.
ADC Coding
CAPxN VINxP CAPxP VINxN VCM VCM
The ADC's output data stream is in a two's complement encoded format. The word width can be selected from 16 bits, 20 bits, or 24 bits (see Table VI and Table VII). The coding scheme is detailed in Table I.
Table I. ADC Coding
Figure 11. Single-Ended Analog Input
Code 011111.......1111 000000........0000 100000........0001
Analog Input Section
Level +Full Scale 0 (Ref Level) -Full Scale
The analog input section is enabled (powered ON) by default on reset. If it is required to bypass the analog input section by using the modulator input pins (CAPxP and CAPxN) directly, then the analog input section must be powered down by setting Bits MER and MEL in Control Register III.
Serial Data Interface
The analog input section comprises a differential PGA stage. It can also be configured for single-ended inputs, allowing two such inputs to be selected via a multiplex switch. The PGA has five gain settings (see Table V) ranging from 0 dB to 12 dB in 3 dB steps. In Differential Mode, the VINxP and VINxN input pins are connected to a pair of inverting amplifiers whose outputs are connected to the CAPxN and CAPxP pins, respectively. (See Figure 10.)
The AD1871's serial data interface consists of three pins (LRCLK, BCLK, and SDATA). LRCLK is the framing signal for left and right channel samples and its frequency is equal to the sampling frequency (fS). BCLK is the serial clock used to clock the data samples from the AD1871 and its frequency is equal to 64 fS (giving 32 BCLK periods for each of the left and right channels). SDATA outputs the left and right channel sample data coincident with the falling edge of BCLK. The serial data interface supports all the popular audio interface standards, such as I2S, left-justified (LJ), and right-justified (RJ), as well as the serial interfaces of modern DSPs. The Interface Mode is selected by programming the Bits DF1-DF0 of Control Register II (see Tables VI and VIII). The data sample width can be selected from 16, 20, or 24 bits by programming Bits WW1-WW0 of Control Register II (see Tables VI and VII).
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AD1871
I2S Mode
In I2S Mode, the data is left-justified, MSB first, with the MSB placed in the second BCLK period following the transition of the LRCLK. A high-to-low transition of the LRCLK signifies
LRCLK LEFT CHANNEL
the beginning of the left channel data transfer, while a low-tohigh transition on the LRCLK signifies the beginning of the right channel data transfer (see Figure 12).
RIGHT CHANNEL
BCLK
DOUT
MSB MSB-1 MSB-2
LSB+2 LSB+1
LSB
MSB MSB-1 MSB-2
LSB+2 LSB+1
LSB
MSB
Figure 12. I2S Mode
LJ Mode
In LJ Mode, the data is left-justified, MSB first, with the MSB placed in the first BCLK period following the transition of the LRCLK. A high-to-low transition of the LRCLK signifies the
LRCLK LEFT CHANNEL
beginning of the right channel data transfer, while a low-to-high transition on the LRCLK signifies the beginning of the left channel data transfer (see Figure 13).
RIGHT CHANNEL
BCLK
DOUT
MSB
MSB- 1
MSB- 2
LSB+2
LSB+1
LSB
MSB
MSB- 1
MSB- 2
LSB+2
LSB+1
LSB
MSB
MSB- 1
Figure 13. Left-Justified Mode
RJ Mode
In RJ Mode, the data is right-justified, LSB last, with the LSB placed in the last BCLK period preceding the transition of the LRCLK. A high-to-low transition of the LRCLK signifies
LRCLK LEFT CHANNEL
the beginning of the right channel data transfer, while a low-tohigh transition on the LRCLK signifies the beginning of the left channel data transfer (see Figure 14).
RIGHT CHANNEL
BCLK
DOUT
LSB
MSB
MSB-1 MSB-2
LSB+2 LSB+1
LSB
MSB
MSB-1 MSB-2
LSB+2 LSB+1
LSB
Figure 14. Right-Justified Mode
DSP Mode
In DSP Mode, the LRCLK signal becomes a frame sync signal that pulses high for the BCLK period prior to the MSB (or in the BCLK period of the previous LSB-32 bits). The data is leftjustified, MSB first, with the MSB placed in the BCLK period following the LRCLK pulse (see Figure 15).
In I2S and LJ Modes, since the data is left-justified, differences in data word-width between the AD1871 and the controller are not catastrophic since the MSBs are guaranteed to be transferred. There may, however, be a slight reduction in performance depending on the scale of the mismatch. In RJ Mode, however, differences in word-width between the AD1871 and controller have a catastrophic effect on signal performance as the MSBs of each sample may be lost due to the mismatch.
LRCLK
LEFT CHANNEL
RIGHT CHANNEL
BCLK
DOUT
MSB
MSB-1
LSB+2
LSB+1
LSB
MSB
MSB-1
LSB+2
LSB+1
LSB
MSB
MSB-1
Figure 15. DSP Mode
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AD1871
Cascade Mode
The AD1871 supports cascading of up to four devices in a daisy-chain configuration to the serial port of a DSP. In Cascade Mode, each device loads an internal 64-Bit Shift Register with the results of the left and right channel conversions. The 64Bit Register is split into two subframes of 32 bits each; the first for left channel data and the second for right channel data. The results are left-justified, MSB first within the subframes, and the word-width setting in Control Register II applies. Remaining bits within the subframe, beyond the conversion word-width, are set to zero. Please refer to Figure 16. Up to four devices can be connected in a daisy chain as shown in Figure 17. All devices must be set in Cascade Mode by tying the CASC pin of each device to a logic high. The first device in the chain (Device 4) has its DIN pin tied to logic low. Its DOUT pin is connected to the DIN pin of Device 3 whose DOUT is in turn connected to the DIN pin of Device 2. This daisy chaining is continued until the DOUT of Device 1 is connected to the DSP's serial port RX data line (DR0). The DSP's RX serial clock (RXCLK0) is connected to the BCLK pin of all AD1871 devices and the DSP's RX frame sync (RFS0) is connected to the LRCLK pin of all AD1871 devices.
24-BIT RESULT 20-BIT RESULT 16-BIT RESULT 32-BIT LEFT SUBFRAME 24-BIT RESULT 20-BIT RESULT 16-BIT RESULT 32-BIT RIGHT SUBFRAME 64-BIT FRAME
The DSP can be the master and supply the frame sync and serial clock to the AD1871s, or one of the AD1871s can be set as the master with the DSP and all other AD1871s set to slave. Each sampling period begins with a frame sync being generated either by the DSP or one of the AD1871s, depending on the Master/Slave selection. The frame-sync pulse causes each device to load the 64-Bit Data I/O Register with the left and right ADC results. These results are then clocked toward the DSP where they are received in the following order: Device 1, Left; Device 1, Right; Device 2, Left; Device 2, Right; Device 3, Left; Device 3, Right; Device 4, Left; and Device 4, Right. The DSP's serial port must be programmed to accept 32-bit word lengths regardless of the AD1871 word length. The number of sample words to be accepted per sample interval will be determined by the number of AD1871 devices in cascade, up to a maximum of eight words corresponding with the maximum number of four devices. Figure 17 also shows the connection of a separate DSP serial port interface to the control port (SPI) interface of the cascaded AD1871s. Again this cascade is implemented as a daisy chain, where the control words for the four devices are output in sequence (depending on the hookup - 1, 2, 3, and 4 in the example) to be latched simultaneously at each device by the common CLATCH. In this mode, it is necessary to send a control word for each device (16 bits the number of devices) from the SPI port of the control host. The CLATCH signal can be controlled from a separate programmable output line. It is also possible to have individual read/write of the AD1871s using separate CLATCH controls for each device. When using Cascade Mode, the data interface defaults to leftjustified, MSB first data, regardless of the state of the Interface Mode selection (by SPI or external control). The timing relationships of the Cascade Mode are shown in Figure 18.
Figure 16. DSP Mode
DT1 DR1 TXCLK1/RXCLK1 TFS1/RFS1
CIN
CIN
CIN
COUT
COUT
COUT
CLATCH
CLATCH
CLATCH
CLATCH
ADSP-21xxx SHARC DSP
AD1871 No.1
LRCLK DOUT BCLK DIN
AD1871 No.2
LRCLK DOUT BCLK DIN
AD1871 No.3
LRCLK DOUT BCLK DIN
AD1871 No.4
LRCLK DOUT BCLK DIN
RFS0 RXCLK0 DR0
Figure 17. DSP Mode
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COUT
CCLK
CCLK
CCLK
CCLK
CIN
AD1871
LRCLK
BCLK
DOU T
DEV I CE 1
DEV I CE 2
DEV I CE 3
DEV I CE 4
BCLK
DOU T
M SB 1
M SB -1 2
M SB -2 3
LSB +1 23
LSB 24
M SB 1
M SB -1 2
M SB -2 3
LSB +1 23
LSB 24
LEFT CH AN N EL
RI GH T CH AN N EL
Figure 18. Cascade Mode Data Interface Timing
CLAT CH
CCLK
CI N
DEV I CE 1
DEV I CE 2
DEV I CE 3
DEV I CE 4
CCLK
CI N
M SB
M SB -1
LSB +1
LSB
Figure 19. Cascade Mode Control Port Timing
CONTROL/STATUS REGISTERS
The AD1871's Operating Mode is set by programming three, 10-bit Control Registers via an SPI compatible port. Table III details the format of the AD1871 control words, which are 16 bits wide with a 4-bit address field in Positions 15 through 12, a Read/Write Bit in Position 11, a Reserved Bit in Position 10, and 10 bits of register data (corresponding to the control register width) in Positions 9 through 0. The three control words occupy Addresses 0000b through 0010b in the register map (see Table II). The AD1871 also features two readback (status) registers that can be enabled to track the peak reading on each of the channels (left and right). These 6-bit results are read back via the SPI compatible port in a 16-bit frame similar to that of the control words.
The SPI compatible control port features four signals (CCLK, CLATCH, CDATA, and COUT). The CLATCH signal is an enable line that must be low to allow communication to or from the control port. The CCLK is the serial clock that clocks in serial data via the CDATA pin and clocks out serial data via the COUT pin. Figures 20 and 21 show details of the control port timing.
Table II. Register Address Map
Address 0000 0001 0010 0011 0100
Control Register Control Register I Control Register II Control Register III Peak Reading Register I Peak Reading Register II
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AD1871
Table III. Control/Status Word Format
15-12 Address
11 R/W
10 Reserved
CCLK
9
6
5
4
3
2
1
0
Control/Status Data Bits (9-0)
CLATCH CIN COUT
D15 D14 D13 D12 D11 D10 D09 D08 D07 D06 D05 D04 D03 D02 D01 D00
Figure 20. Writing to Register Using Control Port
CCLK
CLATCH CIN COUT
D15 D14 D13 D12 D11 D10 D09 D08 D07 D06 D05 D04 D03 D02 D01 D00
D09
D08
D07
D06
D05
D04
D03
D02
D01
D00
Figure 21. Reading from Register Using Control Port
Table IV. Control Register I (Address 0000b, Write Only)
15-12 0000
11 0
10 0
9 PRE 9 8 7 6 5-3 2-0
8 HPE
7 PD
6 AMC
5 AGL2
4 AGL1
3 AGL0
2 AGR2
1 AGR1
0 AGR0
PRE HPE PD AMC AGL2-AGL0 AGR2-AGL0
Peak Reading Enable (0 = Disabled (Default); 1 = Enabled) High-Pass Filter Enable (0 = Disabled (Default); 1 = Enabled) Power-Down Control (1 = Power-Down; 0 = Normal Operation (Default)) ADC Modulator Clock (1 = 64 fS; 0 = 128 fS (Default)) Input Gain (Left Channel, see Table V) Input Gain (Right Channel, see Table V)
Table V. Analog Gain Settings
Control Register I
Control Register I contains bit settings for control of analog front end gain, modulator clock selection, power-down control, high-pass filtering, and peak hold.
Analog Gain Control
AGx2 0 0 0 0 1 1 1 1
AGx1 0 0 1 1 0 0 1 1
AGx0 0 1 0 1 0 1 0 1
Gain (dB) 0 (Default) 3 6 9 12 0 0 0
The AD1871 features an optional analog front end with selectable gain. Gain is selected using three control bits for each channel, giving five separate and independent gain settings on each channel. Bits 2 through 0 (AGR2-AGR0) set the analog gain for the right channel, while Bits 5 through 3 (AGL2-AGL0) set the analog gain for the left channel. Table V shows the analog gain corresponding to the bit settings in AGx2-ADx0.
REV. 0
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AD1871
The modulator clock can be chosen to be either 128 fS or 64 fS. The AMC Bit (Bit 6) is used to select the modulator's clock rate. When AMC is set to 0 (default), the modulator clock is 128 fS. Otherwise, if set to 1, the modulator clock is 64 fS. This bit is normally set depending on whether the desired sampling frequency is 48 kHz or 96 kHz and is also influenced by the selected MCLK frequency. Please refer to the Functional Description section for more information on MCLK selection and sampling rates.
Power-Down Modulator Clock
Mode, digital activity is suspended and analog sections are powered down, with the exception of the reference.
High-Pass Filter
The AD1871's digital filtering engine allows the insertion of a high-pass filter (HPF) to effectively block dc signals from the output digital waveform. Setting Bit 8 (HPE) enables the high-pass filter. For more details of the HPF, refer to the Functional Description section.
Peak Reading Enable
Power-down of the active clock signals within the AD1871 is effected by writing a Logic 1 to Bit 7 (PD). In Power-Down
The AD1871 has two readback registers that can be enabled to store the peak readings of the left and right channel ADC results. To enable the peak readings to be captured, the Peak Reading Enable Bit (PRE), Bit 9, must be set to Logic 1. When set to Logic 0, the peak reading capture is disabled.
Table VI. Control Register II (Address 0001b)
15-12 0001
11 0
10 0
9
8
7 MME
6 DF1
5 DF0
4 WW1
3 WW0
2 M/S
1 MUR
0 MUL
9-8 7 6-5 4-3 2 1 0
Control Register II
MME DF1-DF0 WW1-WW0 M/S MUR MUL
Reserved Modulator Mode Enable (0 = Normal Mode (Default), 1 = Mod Mode) Data Format (See Table VIII) Word Width (See Table VII) Master/Slave Select (0 = Master Mode (Default); 1 = Slave Mode) Mute Control, Right Channel (0 = Disabled (Default); 1 = Enabled) Mute Control, Left Channel (0 = Disabled (Default); 1 = Enabled)
Table VII. Word-Width Settings
Control Register II contains bit settings for control of left/right channel muting, data sample word width, data interface format, and direct modulator bitstream output.
Mute Control
WW1 0 0 1 1
WW0 0 1 0 1
Word Width (No. of Bits) 24 (Default) 20 16 Reserved
The left and right data channels can be muted to digital zero by setting the MUL and MUR Bits (Bits 0 and 1), respectively. If a channel is muted, its output data stream will remain at digital zero, regardless of the amplitude of the input signal. Setting the bit to 1 mutes the channel while setting the bit to 0 restores normal operation.
Master/Slave Select
Data Format
The AD1871 can operate as either a slave device or a master device. In Slave Mode, the controller must provide the LRCLK and BCLK to determine the sample rate and serial bit rate. In Master Mode, the AD1871 provides the LRCLK and BCLK as outputs that are applied to the controller. The AD1871 defaults to Master Mode (M/S is low) on reset.
Word Width
The AD1871's serial data interface can be configured from a choice of popular interface formats, including I2S, left-justified, right-justified, or DSP Modes. Bits DF1-DF0 are programmed to select the interface format (mode) as shown in Table VIII.
Table VIII. Data Interface Format Settings*
DF1 0 0 1 1
DF0 0 1 0 1
Interface Mode I2S (Default) Right-Justified DSP Left-Justified
The AD1871 allows the output sample word width to be selected from 16, 20, and 24 bits wide. Compact disc (CD) compatibility may require 16 bits, while many modern digital audio formats require 24-bit sample resolution. Bits WW1-WW0 are programmed to select the word width. Table VII details the Control Register Bit settings corresponding to the various word width selections.
*Please refer to the Serial Data Interface section in the Functional Description for more details on the various interface modes.
Modulator Mode Enable
The AD1871 defaults to the conversion of the analog audio to linear, PCM-encoded digital outputs. Modulator Mode allows the user to bypass the digital decimation filter section and access the multibit sigma-delta modulator outputs directly. When in this mode, certain pins are redefined (see Modulator Mode) and the modulator output (at a nominal rate of 128 fS) is available on the modulator data pins (D[0-3]). To enable the Modulator Mode, set the MME Bit to high.
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AD1871
Table IX. Control Register III (Address 0010b)
15-12 0010
11 0
10 0 9-8 7-6 5 4 3 2 1 0
9
8
7
6
5 SEL
4 SER
3 MEL
2 MXL
1 MER
0 MXR
MCD1 MCD0 Reserved MCD1-MCD0 SEL SER MEL MXL MER MXR
(Should Be Programmed to 0) Master Clock Divider (See Table XIII) Single-Ended Enable, Left Channel (0 = Differential (Default); 1 = Single-Ended) Single-Ended Enable, Right Channel (0 = Differential (Default); 1 = Single-Ended) Mux/PGA Disable, Left Channel (0 = Enabled (Default); 1 = Disabled) Mux Select, Left Channel (0 = VINLP Selected (Default); 1 = VINLN Selected) Mux/PGA Disable, Right Channel (0 = Enabled (Default); 1 = Disabled) Mux Select, Right Channel (0 = VINRP Selected (Default); 1 = VINRN Selected)
Single-Ended Mode Enable
Control Register III
Control Register III contains bit settings for configuration of the analog input section (both left and right channels).
Mux Enable
The Mux Enable Left (MEL) and Mux Enable Right (MER) are used to enable the analog buffers. When these bits are set to 1, the analog input buffers are powered down and input signals must be applied directly to the modulator inputs via the CAPxP and CAPxN pins. (see Figure 23). When MEL and MER are set to 0 (default condition after reset), the analog input section is enabled, (see Table X).
Table X. Mux Control Settings
The Single-Ended Mode Enable Bits (SEL and SER for left and right channels, respectively), when set to 1, are used to configure single-ended input on VINxP and VINxN (input is selected by state of MXL and MXR). In this mode, single-ended inputs taken from either VINxP or VINxN (selected using the Mux Select Bits--MXL and MXR) are internally converted to a differential format to be applied to the modulator section (see Table XII).
Table XII. Differential/Single-Ended Select
SEL 0 1 X X
SER X X 0 1
Input Setting Left Channel Input AE Differential Left Channel Input AE Single-Ended Right Channel Input AE Differential Right Channel Input AE Single-Ended
MEL 0 1 X X
Mux Select
MER X X 0 1
Input Setting Left Channel Analog Buffer Enabled Left Channel Analog Buffer Disabled Right Channel Analog Buffer Enabled Right Channel Analog Buffer Disabled
Master Clock Divider
The Mux Select Bits (MXL and MXR for left and right channels, respectively) are used to select the input from VINxP or VINxN when the input is configured as single-ended. When MXx is set to 0, the input is taken from VINxP. When MXx is set to 1, the input is taken from VINxN, (see Table XI).
Table XI. Mux Select Settings*
The master clock divider allows the division of the external MCLK frequency to a more suitable internal master clock frequency (IMCLK). IMCLK must be 256 fS; therefore, if the available MCLK is not at 256 fS but is a multiple of this, the MCD allows conversion of MCLK to a suitable IMCLK at 256 fS (see Table XIII).
Table XIII. Master Clock Divider Settings
MCD1 0 0 1 1
MCD0 0 1 0 1
MCLK Division IMCLK = MCLK (/1) IMCLK = MCLK/2 IMCLK = MCLK/3 IMCLK = MCLK (/1)
MXL 0 1 X X
MXR X X 0 1
Input Setting Left Channel Input from VINLP Left Channel Input from VINLN Right Channel Input from VINRP Right Channel Input from VINRN
*Mux select settings are only valid when single-ended operation is enabled; SEL and SER are set to 1.
REV. 0
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AD1871
Table XIV. Peak Reading Register I (Address 0011b, Read-Only)
15-12 0011
11 1
10 0 9-6 5-0
9
8
7
6
5 A0P5
4 A0P4
3 A0P3
2 A0P2
1 A0P1
0 A0P0
Reserved A0P5-A0P0
(Always Set to Zero) Left Channel Peak Reading (Valid Only When PRE = 1)
Table XV. Peak Reading Register II (Address 0100b, Read-Only)
15-12 0100
11 1
10 0 9-6 5-0
9
8
7
6
5 A1P5
4 A1P4
3 A1P3
2 A1P2
1 A1P1
0 A1P0
Reserved A1P5-A1P0
(Always Set to Zero) Right Channel Peak Reading (Valid Only When PRE = 1)
Master/Slave Select
Peak Reading Registers
The Peak Reading Registers are read-only registers that can be enabled to track-and-hold the peak ADC reading from each channel. The peak reading feature is enabled by setting Bit PRE in Control Register I. The peak reading value is contained in the six LSBs of the 10-bit readback word. The result is binary coded where each LSB is equivalent to -1 dBFS with all zeros corresponding to full scale (0 dBFS) and all ones corresponding to -63 dBFS (see Table XVI). When Bit PRE is set, the peak reading per channel is stored in the appropriate peak register. Once the register is read, the register value is set to zero and is updated by subsequent conversions.
Table XVI. Peak Reading Result Format
The Master/Slave hardware select (Pin 5, CLATCH/[M/S]) is equivalent to setting the M/S Bit of Control Register II. If set low, the device is placed in Master Mode, whereby the LRCLK and BCLK signals are outputs from the AD1871. When M/S is set high, the device is in Slave Mode, whereby the LRCK and BCLK signals are inputs to the AD1871.
MCLK Mode Select
The MCLK Mode hardware select (Pin 2, CCLK/[256/512]) is a subset of the MCLK Mode selection that is determined by Bits CM1-CM0 of Control Register X. When the hardware pin is low, the device operates with an MCLK that is 256 fS; if the pin is set high, the device operates with an MCLK that is 512 fS.
Serial Data Format Select
AxP
5 0 0 0 1 1
Code 4321 0 0 0 1 1 0 0 0 1 1 0 0 0 1 1 0 0 1 1 1
0 0 1 0 0 1
Level 0 dBFS -1 dBFS -2 dBFS -62 dBFS -63 dBFS
The Serial Data Format hardware select (Pins 3 and 4, DF0/ COUT and DF1/CIN) is equivalent to setting Bits DF1-DF0 of Control Register II. See Table VIII. In External Control Mode, all functions other than those selected by the hardware select pins (Master/Slave Mode select, MCLK select, and Serial Data Format select) are in their default (power-on) state.
MODULATOR MODE
A Peak Reading Register read cycle is detailed in Figure 21.
EXTERNAL CONTROL
The AD1871 can be configured for external hardware control of a subset of the device functionality. This functionality includes Master/Slave Mode select, MCLK select, and serial data format select. External control is enabled by tying the XCTRL Pin high as shown in Figure 22.
VDD
When the device is in Modulator Mode (MME Bit is set to 1), the D[0-3] pins are enabled as data outputs, while the COUT pin becomes MODCLK, a high speed sampling clock (nominally at 128 fS). The MODCLK enables successive data from the left and right channel modulators with left channel modulator data being valid in the low phase of MODCLK, while right channel modulator data is valid under the high phase of MODCLK (see Modulator Mode Timing in Figure 6). The Modulator Mode is designed to be used for applications such as direct stream digital (DSD) where modulator data is stored directly to the recording media without decimation and filtering to a lower sample rate. DSD is specified at a rate of 64 fS, whereas the AD1871 outputs at 128 fS, requiring an intermediate remodulator that downsamples to 64 fS and generates a single-bit output steam.
AD1871
256/512
XCTRL
DF0 DF1 M/S
Figure 22. External Control Configuration
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AD1871
INTERFACING Analog Interfacing
The analog section of the AD1871 has been designed to offer flexibility as well as high performance. Users may choose full differential input directly to the ADC's - modulator via Pins CAPxP and CAPxN. Alternatively, when using the on-chip PGA section, it is also possible to multiplex single-ended inputs on Pins VINxP and VINxN or to use these pins for full differential input. Whichever input topology is chosen (direct or via mux/PGA section), the modulator input pins (CAPxP and CAPxN) require capacitors to act as dynamic charge storage for the switched capacitor input section. Component selection for these capacitors is critical as the input audio signal appears on or across these capacitors. A high quality dielectric is recommended for these capacitors multilayer ceramic, NPO or metal film, PPS for surface-mounted versions, and polypropylene for through-hole versions. Indeed, as a general recommendation, high quality dielectrics should be specified where capacitors are carrying the input audio signal.
Modulator Direct Input
Left Channel Control Register I = xx0xGGGxxx, where GGG = the Input Gain (see Table V). Control Register III = 00xx1x0Sxx, where S = the SE Channel Selection. Right Channel Control Register I = xx0xxxxGGG, where GGG = the Input Gain (see Table V). Control Register III = 00xxx1xx0S, where S = the SE Channel Selection.
CAPLN 100pF NPO 1nF NPO CAPLP 100pF NPO
AD1871
FERRITE 600Z 100pF NPO 10 F VINLP VINLN VREF 10 F 100nF
Figure 23 shows the connection of a single-ended source via an external single-ended-to-differential converter to the modulator input of the AD1871. The external amplifier/buffer should have good slew rate characteristics to meet the dynamic characteristics of the modulator input that is a switched-capacitor load. The output of the external amplifier/buffer should be decoupled from the input capacitors via a 250 W resistor (metal film). In order to configure the AD1871 for differential input via the CAPxP and CAPxN pins, the Mux/PGA section must be disabled by setting the MEL and MER Bits in Control Register III to 1.
120pF NPO 100pF NPO 237 1nF NPO 237 5.76k OP275 5.76k 750k 100pF NPO CAPLP
Figure 24. Single-Ended Input via PGA Section
PGA Input, Differential
Figure 25 shows the connection of a differential source to the PGA section of the AD1871. The PGA section is configured as a differential buffer. The buffered differential outputs are connected internally to the CAPxx pins via a 250 W series resistors. In order to configure the AD1871 for differential input via the Mux/PGA, the Control Registers must be configured as follows: Left Channel Control Register I = xx0xGGGxxx, where GGG = the Input Gain (see Table V). Control Register III = 00xx0x0xxx. Right Channel Control Register I = xx0xxxxGGG, where GGG = the Input Gain (see Table V). Control Register III = 00xxx0xx0x.
CAPLN 100pF NPO 1nF NPO CAPLP 100pF NPO
FERRITE 10 F 5.76k 100pF NPO
5.76k OP275
CAPLN
AD1871
VREF 10 F 100nF
Figure 23. Direct Connection to Modulator
PGA Input, Single-Ended
AD1871
10 F
2 3 1
Figure 24 shows the connection of a single-ended source to the PGA section of the AD1871. The PGA section is configured for single-ended-to-differential conversion. The differential outputs are connected internally to the CAPxx pins via 250 W series resistors. In order to configure the AD1871 for single-ended input, the Control Registers must be configured as follows:
VINLP 10 F VINLN VREF 10 F 100nF
Figure 25. Differential Input via PGA Section
REV. 0
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AD1871
LAYOUT CONSIDERATIONS
In order to operate the AD1871 at its specified performance level, careful consideration must be given to the layout of the AD1871 and its ancillary circuits. Since the analog inputs to the AD1871 are differential, the voltages in the analog modulator are commonmode voltages. The excellent common-mode rejection of the part will remove common-mode noise on these inputs. The analog and digital supplies of the AD1871 are independent and separately pinned out to minimize coupling between the analog and digital sections of the device. The digital filters will provide rejection of broadband noise on the power supplies, except at integer multiples of the modulator sampling frequency. The digital filters also remove noise from the analog inputs provided the noise source does not saturate the analog modulator. However, because the resolution of the AD1871's ADC is high, and the noise levels from the AD1871 are so low, care must be taken with regard to grounding and layout. The printed circuit board that houses the AD1871 should be designed so the analog and digital sections are separated and confined to certain sections of the board. The AD1871 pin selection has been configured such that its analog and digital interfaces are connected on opposite ends of the package. This facilitates the use of ground planes that can be easily separated. A minimum etch technique is generally best for ground planes as it gives the best shielding. Figure 26 is a view of the ground plane separation (between analog and digital) in the area surrounding the AD1871, taken from the layout of the AD1871 Evaluation Board (EVAL-AD1871EB).
the analog inputs. Traces on opposite sides of the board should run at right angles to each other. This will reduce the effects of feedthrough through the board. A microstrip technique is by far the best but is not always possible with a double-sided board. In this technique, the component side of the board is dedicated to the ground planes while the signals are placed on the other side.
Figure 27. Connecting Analog and Digital Grounds
Good decoupling is important when using high speed devices. All analog and digital supplies should be decoupled to AGND and DGND, respectively, with 0.1 mF ceramic capacitors in parallel with 10 mF tantalum capacitors. To achieve the best from these decoupling capacitors, they should be placed as close as possible to the device, ideally right up against it, as shown in Figure 28. In systems where a common supply voltage is used to drive both the AVDD and DVDD of the AD1871, it is recommended that the system's AVDD supply be used. This supply should have the recommended analog supply decoupling between the AVDD pins of the AD1871 and AGND and the recommended digital supply decoupling capacitors between the DVDD pin and DGND.
Figure 26. Ground Layout
*In the above figure, the black area represents the solder side of the layout. The silkscreen in white is included for clarity.
Digital and analog ground planes should be joined in only one place. If this connection is close to the device, it is recommended to use a short (0 W resistor) or ferrite bead inductor as shown in Figure 27. The pads for the ferrite are positioned on the solder side directly underneath the AD1871 device. Avoid running digital lines under the device as they may couple noise onto the die. The analog ground plane should be allowed to run under the AD1871 to avoid noise coupling. If it is not possible to use a power supply plane, the power supply lines to the AD1871 should use as large a trace as possible to provide low impedance paths and reduce the effects of glitches on the power supply lines. Fast switching signals, such as clocks, should be shielded with digital ground to avoid radiating noise to other sections of the board, and clock signals should never be run near
Figure 28. AD1871 Power Supply Decoupling
Another important consideration is the selection of components such as capacitors, resistors, and operational amplifiers for the ancillary circuits. The capacitors that are used should in the analog audio signal chain should be of NPO dielectric (if ceramic) or metal film. Figure 28 shows the placement of the CAPxx pin capacitors relative to the CAPxx pins. The placement is intended to keep the tracking between the capacitor and the pin as short as possible while also ensuring that the track length from CAPxP pin to its capacitor equals that of the CAPxN to its capacitor.
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AD1871
OUTLINE DIMENSIONS 28-Lead Shrink Small Outline Package [SSOP] (RS-28)
Dimensions shown in millimeters
10.50 10.20 9.90
28
15
PIN 1
1 14
5.60 5.30 5.00
8.20 7.80 7.40
2.00 MAX
1.85 1.75 1.65
0.10 COPLANARITY 0.25 0.09
0.05 MIN
0.65 BSC
0.38 0.22
SEATING PLANE
8 4 0
0.95 0.75 0.55
COMPLIANT TO JEDEC STANDARDS MO-150AH
REV. 0
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C02644-0-8/02(0)
PRINTED IN U.S.A.

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