a
LC MOS
Complete, 12-Bit, 100 kHz, Sampling ADCs
AD7870/AD7875/AD7876
FUNCTIONAL BLOCK DIAGRAM
2
FEATURES
Complete Monolithic 12-Bit ADC with:
2 s Track/Hold Amplifier
8 s A/D Converter
On-Chip Reference
Laser-Trimmed Clock
Parallel, Byte and Serial Digital Interface
72 dB SNR at 10 kHz Input Frequency
(AD7870, AD7875)
57 ns Data Access Time
Low Power: –60 mW typ
Variety of Input Ranges:
3 V for AD7870
0 V to +5 V for AD7875
10 V for AD7876
GENERAL DESCRIPTION
The AD7870/AD7875/AD7876 is a fast, complete, 12-bit A/D
converter. It consists of a track/hold amplifier, 8
µs
successive-
approximation ADC, 3 V buried Zener reference and versatile
interface logic. The ADC features a self-contained internal
clock which is laser trimmed to guarantee accurate control of
conversion time. No external clock timing components are re-
quired; the on-chip clock may he overridden by an external
clock if required.
The parts offer a choice of three data output formats: a single,
parallel, 12-bit word; two 8-bit bytes or serial data. Fast bus ac-
cess times and standard control inputs ensure easy interfacing to
modern microprocessors and digital signal processors.
All parts operate from
±
5 V power supplies. The AD7870 and
AD7876 accept input signal ranges of
±
3 V and
±
10 V, respec-
tively, while the AD7875 accepts a unipolar 0 V to +5 V input
range. The parts can convert full power signals up to 50 kHz.
The AD7870/AD7875/AD7876 feature dc accuracy specifica-
tions such as linearity, full-scale and offset error. In addition,
the AD7870 and AD7875 are fully specified for dynamic perfor-
mance parameters including distortion and signal-to-noise ratio.
The parts are available in a 24-pin, 0.3 inch-wide, plastic or her-
metic dual-in-line package (DIP). The AD7870 and AD7875
are available in a 28-pin plastic leaded chip carrier (PLCC),
while the AD7876 is available and in a 24-pin small outline
(SOIC) package.
PRODUCT HIGHLIGHTS
1. Complete 12-Bit ADC on a Chip.
The AD7870/AD7875/AD7876 provides all the functions
necessary for analog-to-digital conversion and combines a
12-bit ADC with internal clock, track/hold amplifier and
reference on a single chip.
2. Dynamic Specifications for DSP Users.
The AD7870 and AD7875 are fully specified and tested for
ac parameters, including signal-to-noise ratio, harmonic dis-
tortion and intermodulation distortion.
3. Fast Microprocessor Interface.
Data access times of 57 ns make the parts compatible with
modern 8- and 16-bit microprocessors and digital signal pro-
cessors. Key digital timing parameters are tested and guaran-
teed over the full operating temperature range.
REV. B
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
which 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: 617/329-4700
World Wide Web Site: http://www.analog.com
Fax: 617/326-8703
© Analog Devices, Inc., 1997
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