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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

LC2MOS 16-Bit A/D Converter AD7701 FUNCTIONAL BLOCK DIAGRAM AVDD

DVDD

AVSS

DVSS

SC1

SC2

14

15

7

6

4

17

AD7701 CALIBRATION SRAM

AIN

CALIBRATION MICROCONTROLLER

16-BIT A/D CONVERTER

9

AGND

DGND

CAL

12 BP/UP

ANALOG MODULATOR

6-POLE GAUSSIAN LOW-PASS DIGITAL FILTER

CLOCK GENERATOR

VREF 10

13

SERIAL INTERFACE LOGIC

11 SLEEP

8

5

3

2

1

16

CLKOUT

MODE

CS

19 SCLK

18

CLKIN

20 SDATA

DRDY

GENERAL DESCRIPTION

PRODUCT HIGHLIGHTS

The AD7701 is a 16-bit ADC which uses a sigma-delta conversion 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 frequency and output word rate are set by a master clock input that may be supplied externally, or by a crystal-controlled onchip clock oscillator.

1. The AD7701 offers 16-bit resolution coupled with outstanding 0.0015% accuracy.

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.

4. A flexible synchronous/asynchronous interface allows the AD7701 to interface directly to UARTs or to the serial ports of industry-standard microcontrollers.

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.

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.

5. Low operating power consumption and an ultralow power standby mode make the AD7701 ideal for loopowered remote sensing applications, or battery-powered portable instruments.

CMOS construction insures low power dissipation, and a power down mode reduces the idle power consumption to only 10 µW.

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


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