1
DTMF Design Description
DTMF Receiver Overview
DTMF Receiver Overview
In a telephone network, two basic techniques are used for transmitting
information between network entities: in-band and common channel
signalling. In-band signalling shares the transmission facility for signalling
and voice data. Common channel signalling uses one transmission facility for
all signalling functions for a group of voice channels.
One common form of in-band signalling is dual tone multifrequency, or
DTMF. DTMF signals are commonly generated by “Touch-Tone”
telephones; most of us probably have this type of telephone in our homes
today. Here is a layout of a standard DTMF keypad:
Notice that keys “A”, “B”, “C”, and “D” are not usually on telephones for
home use. They are mainly used in commercial applications with special
instruments. Pressing a key will cause the telephone to generate the indicated
pair of tones, one from the high frequency group, and one from the low
frequency group.
697Hz
770Hz
852Hz
941Hz
1200Hz 1336Hz 1477Hz 1633Hz
High Frequency Group
Low
Frequency
Group
1
23
A
4
56B
C
D
7
8
9
*
0#
