REV. C
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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
LC
2
MOS 4-Channel, 12-Bit Simultaneous
Sampling Data Acquisition System
AD7874
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 617/329-4700 Fax: 617/326-8703
FUNCTIONAL BLOCK DIAGRAM
AGND
CLK
DGND
DB11
DB0
V
SS
CS
12-BIT
DAC
V
IN1
V
IN2
V
IN3
V
IN4
COMP
REFERENCE
BUFFER
INT
RD
AD7874
CONVST
V
DD
V
DD
REF IN
REF OUT
3V
REFERENCE
DATA
REGISTERS
SAR
MUX
CONTROL LOGIC
INTERNAL
CLOCK
TRACK/
HOLD 3
TRACK/
HOLD 4
TRACK/
HOLD 2
TRACK/
HOLD 1
GENERAL DESCRIPTION
The AD7874 is a four-channel simultaneous sampling, 12-bit
data acquisition system. The part contains a high speed 12-bit
ADC, on-chip reference, on-chip clock and four track/hold am-
plifiers. This latter feature allows the four input channels to be
sampled simultaneously, thus preserving the relative phase
information of the four input channels, which is not possible if
all four channels share a single track/hold amplifier. This makes
the AD7874 ideal for applications such as phased-array sonar
and ac motor controllers where the relative phase information is
important.
The aperture delay of the four track/hold amplifiers is small and
specified with minimum and maximum limits. This allows sev-
eral AD7874s to sample multiple input channels simultaneously
without incurring phase errors between signals connected to
several devices. A reference output/reference input facility also
allows several AD7874s to be driven from the same reference
source.
In addition to the traditional dc accuracy specifications such as
linearity, full-scale and offset errors, the AD7874 is also fully
specified for dynamic performance parameters including distor-
tion and signal-to-noise ratio.
The AD7874 is fabricated in Analog Devices’ Linear Compat-
ible CMOS (LC
2
MOS) process, a mixed technology process
that combines precision bipolar circuits with low-power CMOS
logic. The part is available in a 28-pin, 0.6" wide, plastic or her-
metic dual-in-line package (DIP), in a 28-terminal leadless ce-
ramic chip carrier (LCCC) and in a 28-pin SOIC.
FEATURES
Four On-Chip Track/Hold Amplifiers
Simultaneous Sampling of 4 Channels
Fast 12-Bit ADC with 8 ms Conversion Time/Channel
29 kHz Sample Rate for All Four Channels
On-Chip Reference
610 V Input Range
65 V Supplies
APPLICATIONS
Sonar
Motor Controllers
Adaptive Filters
Digital Signal Processing
PRODUCT HIGHLIGHTS
1. Simultaneous Sampling of Four Input Channels.
Four input channels, each with its own track/hold amplifier,
allow simultaneous sampling of input signals. Track/hold ac-
quisition time is 2 µs, and the conversion time per channel is
8 µs, allowing 29 kHz sample rate for all four channels.
2. Tight Aperture Delay Matching.
The aperture delay for each channel is small and the aperture
delay matching between the four channels is less than 4 ns.
Additionally, the aperture delay specification has upper and
lower limits allowing multiple AD7874s to sample more than
four channels.
3. Fast Microprocessor Interface.
The high speed digital interface of the AD7874 allows direct
connection to all modern 16-bit microprocessors and digital
signal processors.
