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MT8870D

Ò

ISO 2 -CMOS

MT8870D/MT8870D-1

Integrated DTMF Receiver

Features

• Complete DTMF Receiver

• Low power consumption

• Internal gain setting ampliﬁer

• Adjustable guard time

• Central ofﬁce quality

• Power-down mode

• Inhibit mode

• Backward compatible with

MT8870C/MT8870C-1

ISSUE 5

March 1997

Ordering Information

MT8870DE/DE-1 18 Pin Plastic DIP

MT8870DS/DS-1 18 Pin SOIC

MT8870DN/DN-1 20 Pin SSOP

-40

°

C to +85

°

C

Description

Applications

• Receiver system for British Telecom (BT) or

CEPT Spec (MT8870D-1)

• Paging systems

• Repeater systems/mobile radio

• Credit card systems

• Remote control

• Personal computers

• Telephone answering machine

The MT8870D/MT8870D-1 is a complete DTMF

receiver integrating both the bandsplit ﬁlter and

digital decoder functions. The ﬁlter section uses

switched capacitor techniques for high and low

group ﬁlters; the decoder uses digital counting

techniques to detect and decode all 16 DTMF tone-

pairs into a 4-bit code. External component count is

minimized by on chip provision of a differential input

ampliﬁer, clock oscillator and latched three-state bus

interface.

VDD VSS

VRef

INH

PWDN

Bias

Circuit

VRef

Buffer

Q1

Chip

Power

Chip

Bias

High Group

Filter

Digital

Detection

Algorithm

Code

Converter

and Latch

Q2

IN +

Dial

Tone

Filter

Zero Crossing

Detectors

IN -

Q3

GS

Low Group

Filter

Q4

to all

Chip

Clocks

St

GT

Steering

Logic

OSC1

OSC2

St/GT

ESt

STD

TOE

Figure 1 - Functional Block Diagram

4-11

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