REV. A

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a

AD7878

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

Tel: 617/329-4700

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Fax: 617/326-8703

© Analog Devices, Inc., 1997

100 kHz Sampling ADC with DSP Interface

FUNCTIONAL BLOCK DIAGRAM

FEATURES

Complete ADC with DSP Interface, Comprising:

Track/Hold Amplifier with 2

s Acquisition Time

7

s A/D Converter

3 V Zener Reference

8-Word FIFO and Interface Logic

72 dB SNR at 10 kHz Input Frequency

Interfaces to High Speed DSP Processors, e.g.,

ADSP-2100, TMS32010, TMS32020

41 ns max Data Access Time

Low Power, 60 mW typ

APPLICATIONS

Digital Signal Processing

Speech Recognition and Synthesis

Spectrum Analysis

High Speed Modems

DSP Servo Control

GENERAL DESCRIPTION

The AD7878 is a fast, complete, 12-bit A/D converter with a

versatile DSP interface consisting of an 8-word, first-in, first-out

(FIFO) memory and associated control logic.

The FIFO memory allows up to eight samples to be digitized

before the microprocessor is required to service the A/D con-

verter. The eight words can then be read out of the FIFO at

maximum microprocessor speed. A fast data access time of

41 ns allows direct interfacing to DSP processors and high

speed 16-bit microprocessors.

An on-chip status/control register allows the user to program the

effective length of the FIFO and contains the FIFO out of

range, FIFO empty and FIFO word count information.

The analog input of the AD7878 has a bipolar range of

±3 V.

The AD7878 can convert full power signals up to 50 kHz and is

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

ratio and harmonic distortion.

The AD7878 is fabricated in Linear Compatible CMOS

(LC

bines precision bipolar circuits with low power CMOS logic.

The part is available in four package styles, 28-pin plastic and

hermetic dual-in-line package (DIP), leadless ceramic chip

carrier (LCCC) or plastic leaded chip carrier (PLCC).

PRODUCT HIGHLIGHTS

1. Complete A/D Function with DSP Interface

The AD7878 provides the complete function for digitizing

ac signals to 12-bit accuracy. The part features an on-chip

track/hold, on-chip reference and 12-bit A/D converter. The

additional feature of an 8-word FIFO reduces the high soft-

ware overheads associated with servicing interrupts in DSP

processors.

2. Dynamic Specifications for DSP Users

The AD7878 is fully specified and tested for ac parameters,

including signal-to-noise ratio, harmonic distortion and

intermodulation distortion. Key digital timing parameters

are also tested and specified over the full operating tempera-

ture range.

3. Fast Microprocessor Interface

Data access time of 41 ns is the fastest ever achieved in a

monolithic A/D converter, and makes the AD7878 compat-

ible with all modern 16-bit microprocessors and digital

signal processors.