®
ISO
2
-CMOS
MT88L70
3 Volt Integrated DTMF Receiver
Features
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•
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2.7 - 3.6 volt operation
Complete DTMF receiver
Low power consumption
Internal gain setting amplifier
Adjustable guard time
Central office quality
Power-down mode
Inhibit mode
Functionally compatible with Mitel’s MT8870D
ISSUE 2
May 1995
Ordering Information
MT88L70AC
18 Pin Ceramic DIP
MT88L70AE
18 Pin Plastic DIP
MT88L70AS
18 Pin SOIC
MT88L70AN
20 Pin SSOP
MT88L70AT
20 Pin TSSOP
-40 °C to + 85 °C
Description
The MT88L70 is a complete 3 Volt, 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.
Applications
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Paging systems
Repeater systems/mobile radio
Credit card systems
Remote control
Personal computers
Telephone answering machine
VDD
VSS
VRef
INH
PWDN
Bias
Circuit
VRef
Buffer
Q1
Chip Chip
Power Bias
IN +
IN -
GS
Dial
Tone
Filter
High Group
Filter
Zero Crossing
Detectors
Low Group
Filter
Digital
Detection
Algorithm
Code
Converter
and Latch
Q2
Q3
Q4
to all
Chip
Clocks
St
GT
Steering
Logic
OSC1
OSC2
St/GT
ESt
STD
TOE
Figure 1 - Functional Block Diagram
4-23
MITEL [ MITEL NETWORKS CORPORATION ]
