AD7703 Datasheet, PDF (1/16 Pages) Analog Devices – LC2MOS 20-Bit A/D Converter

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FEATURES
Monolithic 20-Bit ADC
0.0003% Linearity Error
20-Bit No Missed Codes
On-Chip Self-Calibration Circuitry
Programmable Low-Pass Filter
0.1 Hz to 10 Hz Corner Frequency
0 to +2.5 V or +2.5 V Analog Input Range
4 kSPS Output Data Rate
Flexible Serial Interface
Ultralow Power
APPLICATIONS
Industrial Process Control
Weigh Scales
Portable Instrumentation
Remote Data Acquisition
LC²MOS
20-Bit A/D Converter
AD7703
FUNCTIONAL BLOCK DIAGRAM
DV_DD 15
AV_DD 14
AV_SS
7
DV_SS
6
SC1
4
SC2
17
AD7703
CALIBRATION
SRAM
CALIBRATION
MICROCONTROLLER
13 CAL
A_IN 9
V_REF 10
AGND 8
DGND 5
20-BIT CHARGE BALANCE A/D
CONVERTER
ANALOG
MODULATOR
6-POLE GAUSSIAN
LOW-PASS
DIGITAL FILTER
12 BP/UP
11 SLEEP
CLOCK
GENERATOR
SERIAL INTERFACE
LOGIC
20 SDATA
19 SCLK
3
2
1
16
CLKIN CLKOUT MODE CS
18
DRDY
GENERAL DESCRIPTION
The AD7703 is a 20-bit ADC which uses a sigma delta conver-
sion technique. The analog input is continuously sampled by an
analog modulator whose mean output duty cycle is proportional
to the input signal. The modulator output is processed by an
on-chip digital filter with a six-pole Gaussian response, which
updates the output data register with 20-bit binary words at
word rates up to 4 kHz. The sampling rate, filter corner fre-
quency and output word rate are set by a master clock input
that may be supplied externally, or by an on-chip gate oscillator.
The inherent linearity of the ADC is excellent, and endpoint
accuracy is ensured by self-calibration of zero and full scale
which may be initiated at any time. The self-calibration scheme
can also be extended to null system offset and gain errors in the
input channel.
The output data is accessed through a serial port, which has two
synchronous modes suitable for interfacing to shift registers or
the serial ports of industry standard microcontrollers.
CMOS construction ensures low power dissipation, and a power
down mode reduces the idle power consumption to only 10 ␮W.
PRODUCT HIGHLIGHTS
1. The AD7703 offers 20-bit resolution coupled with
outstanding 0.0003% accuracy.
2. No missing codes ensures true, usable, 20-bit dynamic range,
removing the need for programmable gain and level-setting
circuitry.
3. The effects of temperature drift are eliminated by on-chip
self-calibration, which removes zero and gain error. External
circuits can also be included in the calibration loop to remove
system offsets and gain errors.
4. A flexible synchronization allows the AD7703 to interface
directly to the serial ports of industry standard
microcontrollers and DSP processors.
5. Low operating power consumption and an ultralow power
standby mode make the AD7703 ideal for loop powered
remote sensing applications, or battery-powered portable
instruments.
REV. D
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.
© Analog Devices, Inc., 1996
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