a
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 Passband Ripple
Fourth-Order, 64 Oversampling - Modulator
Three-Stage, Linear-Phase Decimator
256 f
S
or 384 f
S
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
DV
DD
1
DGND1
RDEDGE
S/M
384/256
AV
DD
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
DV
DD
2
24 DGND2
23
RESET
MSBDLY
RLJUST
AGND
V
IN
R
CAPR1
CAPR2
AGNDR
V
REF
R
DAC
DAC
DAC
DAC
22
21
20
19
18
V
IN
L 10
CAPL1 11
CAPL2 12
AGNDL 13
V
REF
L 14
SINGLE-TO-
DIFFERENTIAL INPUT
CONVERTER
SINGLE-TO-
DIFFERENTIAL INPUT
CONVERTER
17
16
15
VOLTAGE
REFERENCE
AD1870
PRODUCT OVERVIEW
The AD1870 is a stereo, 16-bit oversampling ADC based on
sigma-delta (鈭?鈭? 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
脳
f
S
or a 384
脳
f
S
input
clock (f
S
is the sampling frequency) and operates in both serial
port 鈥渕aster鈥?and 鈥渟lave鈥?modes. In slave mode, all clocks must
be externally derived from a common source.
Input signals are sampled at 64
脳
f
S
onto internally buffered
switched-capacitors, eliminating external sample-and-hold ampli-
fiers and minimizing the requirements for antialias filtering at the
input. With simplified antialiasing, linear phase can be preserved
across the passband. The on-chip single-ended to differential signal
converters save the board designer from having to provide them
externally. The AD1870鈥檚 internal differential architecture provides
increased dynamic range and excellent power supply rejection
characteristics. The AD1870鈥檚 proprietary fourth-order differen-
tial switched-capacitor
鈭?鈭?/div>
modulator architecture shapes the
*Protected
by U.S. Patent Numbers 5055843, 5126653; others pending.
one-bit comparator鈥檚 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鈥檚 high
frequency quantization noise and reducing the 64
脳
f
S
single-bit
output data rate to an f
S
word rate. They provide linear phase
and a narrow transition band that properly digitizes 20 kHz signals
at a 44.1 kHz sampling frequency. Passband ripple is less than
0.006 dB, and stop band attenuation exceeds 90 dB.
(Continued
on Page 7)
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
漏 Analog Devices, Inc., 2001
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