AD1870| Datasheet

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FEATURES Single 5 V Power Supply Single-Ended Dual-Channel Analog Inputs 92 dB (Typ) Dynamic Range 90 dB (Typ) S/(THD + N) 0.006 dB Decimator Pass-Band Ripple Fourth Order, 64 Oversampling - Modulator Three-Stage, Linear-Phase Decimator 256 fS or 384 fS Input Clock Less than 100 W (Typ) Power-Down Mode Input Overrange Indication On-Chip Voltage Reference Flexible Serial Output Interface 28-Lead SOIC Package APPLICATIONS Consumer Digital Audio Receivers Digital Audio Recorders, Including Portables CD-R, DCC, MD, and DAT Multimedia and Consumer Electronics Equipment Sampling Music Synthesizers
LRCK WCLK BCLK DVDD1 DGND1 RDEDGE S/M 384/256 AVDD 1 2 3 4 5 6 7 8 9

Single-Supply 16-Bit - Stereo ADC AD1870*
FUNCTIONAL BLOCK DIAGRAM
SERIAL OUTPUT INTERFACE CLOCK DIVIDER 28 27 26 THREE-STAGE FIR DECIMATION FILTER THREE-STAGE FIR DECIMATION FILTER 25 CLKIN TAG SOUT DVDD2

24 DGND2 23 RESET MSBDLY RLJUST AGND VINR CAPR1 CAPR2 AGNDR VREFR

DAC

22 21 20 19 18

VINL 10 CAPL1 11 CAPL2 12 AGNDL 13 VREFL 14 SINGLE-TODIFFERENTIAL INPUT CONVERTER SINGLE-TODIFFERENTIAL INPUT CONVERTER

17 16 15

VOLTAGE REFERENCE

AD1870

PRODUCT OVERVIEW

The AD1870 is a stereo, 16-bit oversampling ADC based on sigma-delta ( - ) technology intended primarily for digital audio bandwidth applications requiring a single 5 V power supply. Each single-ended channel consists of a fourth order one-bit noise shaping modulator and a digital decimation filter. An on-chip voltage reference, stable over temperature and time, defines the full-scale range for both channels. Digital output data from both channels are time multiplexed to a single, flexible serial interface. The AD1870 accepts a 256 fS or a 384 fS input clock (fS is the sampling frequency) and operates in both serial port Master and Slave Modes. In Slave Mode, all clocks must be externally derived from a common source. Input signals are sampled at 64 fS onto internally buffered switched capacitors, eliminating external sample-and-hold amplifiers and minimizing the requirements for antialias filtering at the input. With simplified antialiasing, linear phase can be preserved across the pass band. The on-c
hip single-ended-to-differential signal converters save the board designer from having to provide them externally. The AD1870's internal differential architecture provides increased dynamic range and excellent power supply rejection characteristics. The AD1870's proprietary fourth order differential switched-capacitor - modulator architecture
*Protected by U.S. Patent Numbers 5055843, 5126653; others pending.

shapes the one-bit comparator's quantization noise out of the audio pass band. The high order of the modulator randomizes the modulator output, reducing idle tones in the AD1870 to very low levels. Because its modulator is single bit, the AD1870 is inherently monotonic and has no mechanism for producing differential linearity errors. The input section of the AD1870 uses autocalibration to correct any dc offset voltage present in the circuit, provided that the inputs are ac-coupled. The single-ended dc input voltage can swing between 0.7 V and 3.8 V typically. The AD1870 antialias input circuit requires four external 470 pF NPO ceramic chip filter capacitors, two for each channel. No active electronics are needed. Decoupling capacitors for the supply and reference pins are also required. The dual-digital decimation filters are triple-stage, finite impulse response filters for effectively removing the modulator's high frequency quantization noise and reducing the 64 fS single-bit output data rate to an fS wo
rd rate. They provide linear phase and a narrow transition band that properly digitizes 20 kHz signals at a 44.1 kHz sampling frequency. Pass-band ripple is less than 0.006 dB, and stop-band attenuation exceeds 90 dB.
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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 Analog Devices, Inc., 2002