REV. D

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a

AD7701

16-Bit A/D Converter

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

GENERAL DESCRIPTION

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.

PRODUCT HIGHLIGHTS

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.

© 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

FUNCTIONAL BLOCK DIAGRAM

5

DGND

SC1

SC2

14

15

7

64

17

AGND

9

10

8

13

CALIBRATION

SRAM

CALIBRATION

MICROCONTROLLER

16-BIT A/D CONVERTER

ANALOG

MODULATOR

CAL

BP/UP

SLEEP

12

11

20

19

CLOCK

GENERATOR

SERIAL INTERFACE

LOGIC

SDATA

SCLK

3

2

1

16

18

CLKIN

CLKOUT

MODE

CS

DRDY

6-POLE GAUSSIAN

LOW-PASS

DIGITAL FILTER

AD7701