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a

AD7720

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© Analog Devices, Inc., 1997

CMOS Sigma-Delta Modulator

FUNCTIONAL BLOCK DIAGRAM

FEATURES

12.5 MHz Master Clock Frequency

0 V to +2.5 V or

1.25 V Input Range

Single Bit Output Stream

90 dB Dynamic Range

Power Supplies: AVDD, DVDD: +5 V

5%

On-Chip 2.5 V Voltage Reference

28-Lead TSSOP

GENERAL DESCRIPTION

This device is a 7th order sigma-delta modulator that converts

the analog input signal into a high speed 1-bit data stream. The

part operates from a +5 V supply and accepts a differential input

range of 0 V to +2.5 V or

±1.25 V centered about a common-

mode bias. The analog input is continuously sampled by the

analog modulator, eliminating the need for external sample and

hold circuitry. The input information is contained in the output

stream as a density of ones. The original information can be

reconstructed with an appropriate digital filter.

The part provides an accurate on-chip 2.5 V reference. A refer-

ence input/output function is provided to allow either the inter-

nal reference or an external system reference to be used as the

reference source for the part.

The device is offered in a 28-lead TSSOP package and designed

to operate from –40

°C to +85°C.

2.5V

REFERENCE

SIGMA-DELTA

MODULATOR

CLOCK

CIRCUITRY

CONTROL

LOGIC

AVDD

AGND

DVDD

DGND

REF1

REF2

DATA

SCLK

XTAL1/MCLK

XTAL2

DVAL

RESETO

RESET

VIN(+)

VIN(–)

MZERO

GC

BIP

STBY

AD7720