a
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
AV
DD
14
LC MOS
16-Bit A/D Converter
AD7701
FUNCTIONAL BLOCK DIAGRAM
DV
DD
15
AV
SS
7
DV
SS
6
SC1
4
SC2
17
2
AD7701
CALIBRATION
SRAM
CALIBRATION
MICROCONTROLLER
13
CAL
A
IN
9
16-BIT A/D CONVERTER
ANALOG
MODULATOR
6-POLE GAUSSIAN
LOW-PASS
DIGITAL FILTER
12 BP/UP
V
REF
10
11 SLEEP
AGND
8
CLOCK
GENERATOR
SERIAL INTERFACE
LOGIC
20 SDATA
19 SCLK
DGND
5
3
CLKIN
2
CLKOUT
1
MODE
16
CS
18
DRDY
GENERAL DESCRIPTION
PRODUCT HIGHLIGHTS
The AD7701 is a 16-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 16-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 a crystal-controlled on-
chip clock 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 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 insures low power dissipation, and a power
down mode reduces the idle power consumption to only 10
µW.
1. The AD7701 offers 16-bit resolution coupled with outstand-
ing 0.0015% accuracy.
2. No missing codes ensures true, usable, 16-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 synchronous/asynchronous interface allows the
AD7701 to interface directly to UARTs or to the serial ports
of industry-standard microcontrollers.
5. Low operating power consumption and an ultralow power
standby mode make the AD7701 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
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 617/329-4700
Fax: 617/326-8703
AD [ ANALOG DEVICES ]
