HT9172

DTMF Receiver

Block Diagram

Rev. 1.00

1

March 30, 2006

Features

General Description

The HT9172 is a Dual Tone Multi Frequency (DTMF) re-

ceiver device which includes an integrated digital de-

coder and band split filter functions as well as

power-down and inhibit mode operations. The device

uses digital counting techniques to detect and decode

the full range of 16 DTMF tone pairs into a 4-bit code

output. Highly accurate switched capacitor filters are uti-

lised to divide the DTMF dual tone frequencies into low

and high group signals. An integrated dial tone rejection

circuit is provided to eliminate the need for pre-filtering.

O P A

X 2

X 1

3 . 5 8 M H z

C r y s t a l

O s c i l l a t o r

V r e f

G e n e r a t o r

L o w G r o u p

F i l t e r

H i g h G r o u p

F i l t e r

S t e e r i n g C o n t r o l C i r c u i t

P r e - F i l t e r

V P

V N

G S

F r e q u e n c y

D e t e c t o r

C o d e

D e t e c t o r

L a t c h

&

O u t p u t

B u f f e r

O E

V R E F

R T / G T

E S T

D V

D 0

D 1

D 2

D 3

I N H

B i a s

C i r c u i t

P W D N

D V B

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