
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.
a
LC
2
MOS
20-Bit A/DConverter
AD7703
Analog Devices, Inc., 1996
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 617/329-4700
Fax: 617/326-8703
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
FUNCT IONAL BLOCK DIAGRAM
5
DGND
AV
DD
DV
DD
AV
SS
DV
SS
SC1
SC2
14
15
7
6
4
17
AGND
A
IN
V
REF
10
8
13
CALIBRATION
SRAM
CALIBRATION
MICROCONTROLLER
CAL
BP/UP
SLEEP
20
19
CLOCK
GENERATOR
SERIAL INTERFACE
LOGIC
SDATA
SCLK
3
2
1
16
18
CLKIN
CLKOUT
MODE
CS
DRDY
AD7703
9
ANALOG
MODULATOR
12
11
6-POLE GAUSSIAN
LOW-PASS
DIGITAL FILTER
20-BIT CHARGE BALANCE A/D
CONVERTER
PRODUCT HIGHLIGHT S
1. T he 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. T he 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.
GE NE RAL DE SCRIPT ION
T he AD7703 is a 20-bit ADC which uses a sigma delta conver-
sion technique. T he analog input is continuously sampled by an
analog modulator whose mean output duty cycle is proportional
to the input signal. T he 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. T he 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.
T he 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. T he self-calibration scheme
can also be extended to null system offset and gain errors in the
input channel.
T he 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
m
W.