REV. B

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.

a

Complete, 12-Bit Analog I/O System

AD7868

© 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

RO DAC

RI DAC

DGND

AD7868

R

R

RO ADC

AGND

CLOCK

R

R

12-BIT

DAC

DAC SERIAL

INTERFACE

ADC SERIAL

INTERFACE

12-BIT

ADC

DAC 3V

REFERENCE

ADC 3V

REFERENCE

TRACK/HOLD

LDAC

TFS

TCLK

DT

CONTROL

RFS

RCLK

DR

CLK

CONVST

FEATURES

Complete 12-Bit I/O System, Comprising:

12-Bit ADC with Track/Hold Amplifier

83 kHz Throughout Rate

72 dB SNR

12-Bit DAC with Output Amplifier

3

s Settling Time

72 dB SNR

On-Chip Voltage Reference

Operates from

5 V Supplies

Low Power – 130 mW typ

Small 0.3" Wide DIP

APPLICATIONS

Digital Signal Processing

Speech Recognition and Synthesis

Spectrum Analysis

High Speed Modems

DSP Servo Control

GENERAL DESCRIPTION

The AD7868 is a complete 12-bit I/O system containing a DAC

and an ADC . The ADC is a successive approximation type

with a track-and-hold amplifier having a combined throughput

rate of 83 kHz. The DAC has an output buffer amplifier with a

settling time of 3

µs to 12 bits. Temperature compensated 3 V

buried Zener references provide precision references for the

DAC and ADC.

Interfacing to both the DAC and ADC is serial, minimizing pin

count and giving a small 24-pin package size. Standard control

signals allow serial interfacing to most DSP machines. Asyn-

chronous ADC conversion control and DAC updating is made

possible with the CONVST and LDAC logic inputs.

The AD7868 operates from

±5 V power supplies, the analog in-

put/output range of the ADC/DAC is

±3 V. The part is fully

specified for dynamic parameters such as signal-to-noise ratio

and harmonic distortion as well as traditional dc specifications.

The part is available in a 24-pin, 0.3" wide, plastic or hermetic

dual-in-line package (DIP) and in a 28-pin, plastic SOIC

package.

PRODUCT HIGHLIGHTS

1. Complete 12-Bit I/O System.

The AD7868 contains a 12-bit ADC with a track-and-hold

amplifier and a 12-bit DAC with output amplifier. Also

included are separate on-chip voltage references for the DAC

and the ADC.

2. Dynamic Specifications for DSP Users.

In addition to traditional dc specifications, the AD7868 is

specified for ac parameters including signal-to-noise ratio

and harmonic distortion. These parameters along with im-

portant timing parameters are tested on every device.

3. Small Package.

The AD7868 is available in a 24-pin DIP and a 28-pin SOIC

package.