AD7703_15 Datasheet, PDF (1/16 Pages) Analog Devices – 20-Bit A/D Converter

LC²MOS
20-Bit A/D Converter
AD7703
FEATURES
Monolithic 16-Bit ADC
0.0015% Linearity Error
On-Chip Self-Calibration Circuitry
Programmable Low-Pass Filter
0.1 Hz to 10 Hz Corner Frequency
0 V 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
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 that uses a S-D conversion tech-
nique. 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 16-bit binary words at word rates up to
4 kHz. The sampling rate, filter corner frequency, and output
word rate are set by a master clock input that may be supplied
externally, or by a crystal controlled on-chip clock oscillator.
The inherent linearity of the ADC is excellent and endpoint accu-
racy 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 flexible serial port, which
has an asynchronous mode compatible with UARTs and 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 µW.
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. Flexible synchronous/asynchronous interface 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. E
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