2
LC MOS
20-Bit A/D Converter
a
AD7703
FEATURES
FUNCTIO NAL BLO CK D IAGRAM
Monolithic 20-Bit ADC
0.0003% Linearity Error
AVSS
DVSS
SC1
SC2
17
20-Bit No Missed Codes
On-Chip Self-Calibration Circuitry
Program m able 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 Pow er
7
6
4
AD7703
15
14
DVDD
AVDD
CALIBRATION
MICROCONTROLLER
CALIBRATION
SRAM
13
CAL
20-BIT CHARGE BALANCE A/D
CONVERTER
AIN
9
12
11
BP/UP
SLEEP
6-POLE GAUSSIAN
ANALOG
MODULATOR
VREF
10
LOW-PASS
DIGITAL FILTER
APPLICATIONS
Industrial Process Control
Weigh Scales
Portable Instrum entation
Rem ote Data Acquisition
AGND
DGND
8
5
20 SDATA
19
CLOCK
SERIAL INTERFACE
GENERATOR
LOGIC
SCLK
3
2
1
16
18
MODE
CLKIN CLKOUT
CS
DRDY
GENERAL D ESCRIP TIO N
P RO D UCT H IGH LIGH TS
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.
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.
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.
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.
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 W.
REV. D
Inform ation furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assum ed by Analog Devices for its
use, nor for any infringem ents of patents or other rights of third parties
which m ay result from its use. No license is granted by im plication or
otherwise under any patent or patent rights of Analog Devices.
© Analog Devices, Inc., 1996
One Technology Way, P.O. Box 9106, Norw ood, MA 02062-9106, U.S.A.
Tel: 617/ 329-4700
Fax: 617/ 326-8703