LC2MOS
Complete 14-Bit, Sampling ADCs
AD7871/AD7872
Data Sheet
FEATURES
FUNCTIONAL BLOCK DIAGRAMS
AGND
CREF
22
Complete monolithic 14-bit ADC
Twos complement coding
Parallel, byte, and serial digital interface
80 dB SNR at 10 kHz input frequency
57 ns data access time
Low power: 50 mW typ
83 kSPS throughput rate
23
VDD
REF OUT VIN
25
26
21
TRACKAND-HOLD
R
R
COMP
3V
REFERENCE
CLK
APPLICATIONS
14-BIT
DAC
CLOCK
5
SAR +
COUNTER
14/8/CLK 28
CONTROL
LOGIC
CONVST 1
PARALLEL
AND SERIAL
INTERFACE
2
GENERAL DESCRIPTION
CS
4
6
20
14
27
DB13
RD BUSY/INT
DB0
DGND
VSS
Figure 1.
The AD7871/AD7872 are fast, complete, 14-bit analog-todigital converters (ADC). They consist of a track-and-hold
amplifier, successive approximation ADC, 3 V buried Zener
reference, and versatile interface logic. The ADC features a selfcontained, laser trimmed internal clock, so no external clock
timing components are required. The on-chip clock may be
overridden to synchronize ADC operation to the digital system
for minimum noise.
AGND
CREF
12
11
REF OUT VIN
13
VDD
3V
REFERENCE
3
16
TRACKAND-HOLD
R
CLK
VDD
9
14
R
The AD7871 offers a choice of three data output formats: a
single, parallel, 14-bit word; two 8-bit bytes or a 14-bit serial
data stream. The AD7872 is a serial output device only. The two
parts are capable of interfacing to all modern microprocessors
and digital signal processors.
COMP
14-BIT
DAC
CLOCK
SAR +
COUNTER
CONVST 2
CONTROL
LOGIC
SERIAL
INTERFACE
4
5
AD7872
6
SSTRB SCLK SDATA
8
15
DGND
VSS
12889-002
CONTROL 1
The AD7871/AD7872 operate from ±5 V power supplies,
accept bipolar input signals of ±3 V and can convert full power
signals up to 41.5 kHz.
In addition to the traditional dc accuracy specifications, the
AD7871/AD7872 are also fully specified for dynamic
performance parameters including distortion and signal-tonoise ratio.
3
AD7871
12889-001
Digital signal processing
High speed modems
Speech recognition and synthesis
Spectrum analysis
DSP servo control
Figure 2.
Both devices are fabricated in Analog Devices, Inc., LC2MOS
mixed technology process. The AD7871 is available in 28-pin
PDIP, PLCC, and CERDIP packages. The AD7872 is available in
a 16-pin PDIP, CERDIP, and SOIC packages.
PRODUCT HIGHLIGHTS
1.
2.
3.
Rev. E
Complete 14-Bit ADC on a Chip.
Dynamic Specifications for DSP Users.
Low Power.
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