High Performance
16-/18-Bit ⌺⌬ Stereo ADCs
a
AD1878/AD1879*
FEATURES
FUNCTIO NAL BLO CK D IAGRAM
Fully Differential Dual Channel Analog Inputs
103 dB Signal-to-Noise (AD1879 typ)
–98 dB THD+N (AD1879 typ)
0.001 dB Passband Ripple and 115 dB Stopband
Attenuation
Fifth-Order, 64 Tim es Oversam pling ⌺⌬ Modulator
Single Stage, Linear Phase Decim ator
LRCK
BCK
S0
WCK
1
2
3
4
5
6
7
8
9
28
SERIAL OUTPUT
INTERFACE
27 DATA
DIGITAL
CHIP
26
CLOCK
S1
25
24
64/32
SINGLE-STAGE,
SINGLE-STAGE,
4k-TAP
FIR DECIMATION
FILTER
4k-TAP
FIR DECIMATION
FILTER
DV
DD
RESET
APPLICATIONS
DGND
NC
23 DGND
Digital Tape Recorders
Professional, DCC, and DAT
A/ V Digital Am plifiers
CD-R
ANALOG
CHIP
22 DV
DD
D
A
C
D
A
C
D
D
A
C
A
C
21
20
AV
1
AV
AV
1
2
SS
SS
Sound Reinforcem ent
AV
2
SS
DD
DD
19 AV
1
AGND 10
APD 11
P RO D UCT O VERVIEW
AGND
VINL–
VINL+
REFL
18
17
16
15
T he AD1879 is a two-channel, 18-bit oversampling ADC based
on ∑∆ technology and intended primarily for digital audio appli-
cations. T he AD1878 is identical to the 18-bit AD1879 except
that it outputs 16-bit data words. Statements in this data sheet
should be read as applying to both parts unless otherwise noted.
VINR–
VINR+
REFR
12
13
14
VOLTAGE
REFERENCE
Each input channel of these ADCs is fully differential. Each
data conversion channel consists of a fifth order one-bit noise
shaping modulator and a digital decimation filter. An on-chip
voltage reference provides a voltage source to both channels sta-
ble over temperature and time. Digital output data from both
channels is time-multiplexed to a single, flexible serial interface.
T he AD1878/AD1879 accepts a 256 × FS input master clock.
phase and a narrow transition band that permits the digitization
of 20 kHz signals while preventing aliasing into the passband
even when using a 44.1 kHz sampling frequency. Passband
ripple is less the 0.001 dB, and stopband attenuation exceeds
115 dB.
Input signals are sampled at 64 × FS on switched-capacitors,
eliminating external sample-and-hold amplifiers and minimizing
the requirements for antialias filtering at the input. With simpli-
fied antialiasing, linear phase can be preserved across the passband.
The AD1878/AD1879’s proprietary fifth-order differential
switched-capacitor modulator architecture shapes the one-bit
comparator’s quantization noise out of the audio passband. T he
high order of the modulator randomizes the modulator output,
reducing idle tones in the AD1878/AD1879 to very low levels.
T he AD1878/AD1879’s differential architecture provides in-
creased dynamic range and excellent common-mode rejection
characteristics. Because its modulator is single-bit, AD1878/
AD1879 is inherently monotonic and has no mechanism for
producing differential linearity errors.
T he flexible serial output port produces data in twos-complement,
MSB-first format. Input and output signals are to T T L and
CMOS-compatible logic levels. T he port is configured by pin
selections. T he AD1878/AD1879 can operate in either master
or slave mode. Each 16-/18-bit output word of a stereo pair can
be formatted within a 32-bit field as either right-justified, I2S-
compatible, or at user-selected positions. T he output can also be
truncated to 16-bits by formatting into a 16-bit field.
T he AD1878/AD1879 consists of two integrated circuits in a
single ceramic 28-pin DIP package. T he modulators and refer-
ence are fabricated in a BiCMOS process; the decimator and
output port, in a 1.0 µm CMOS process. Separating these func-
tions reduces digital crosstalk to the analog circuitry. Analog and
digital supply connections are separated to further isolate the
analog circuitry from the digital supplies.
T he digital decimation filters are single-stage, 4095-tap finite
impulse response filters for filtering the modulator’s high fre-
quency quantization noise and reducing the 64 × FS single-bit
output data rate to a FS word rate. T hey provide linear
T he AD1878/AD1879 operates from ±5 V power supplies over
the temperature range of –25°C to +70°C.
*P rotected by U.S. P atent Num bers 5055843, 5126653, and others pending.
REV. 0
Inform ation furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assum ed by Analog Devices for its
use, nor for any infringem ents of patents or other rights of third parties
which m ay result from its use. No license is granted by im plication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norw ood, MA 02062-9106, U.S.A.
Tel: 617/ 329-4700
Fax: 617/ 326-8703