CD22204
3.579545MHz
DTMF Dialing Matrix
COL 0
1209Hz
XOUT
V
DD
1M
XIN
10
ATB
11
9
CD22204
6
XEN
COL 1
1336Hz
2
5
8
0
COL 2
1477Hz
3
6
9
#
COL 3
1633Hz
A
B
C
D
ROW 0
697Hz
ROW 1
770Hz
ROW 2
852Hz
1
4
7
*
XIN CONNECTED TO V
DD
10
11
CD22204
XEN
6
ROW 3
941Hz
NOTE: Column 3 is for special applications and is not normally used
in telephone dialing.
UP TO 10 DEVICES
Digital Inputs and Outputs
All digital inputs and outputs of the DTMF receivers are
represented by the schematic below. Only the “analog in” pin
is different, and is described above. Care must be exercised
not to exceed the voltage or current ratings on these pins as
listed in the “maximum ratings” section.
V
DD
FIGURE 2. CRYSTAL OSCILLATOR
Outputs D1, D2, D4, D8 and EN
Outputs D1, D2, D4, D8 are CMOS push-pull when enabled
(EN high) and open circuited (high impedance) when
disabled by pulling EN low. These digital outputs provide the
hexadecimal code corresponding to the detected digit. The
digital outputs become valid after a tone pair has been
detected and they are then cleared when a valid pause is
timed. The table below describes the hexadecimal codes.
TABLE 1. OUTPUT CODES
DIGIT
1
2
3
4
5
6
7
8
9
0
*
#
A
B
C
D
D8
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
D4
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
D2
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
D1
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
DIGITAL
INPUT
CMOS
DIGITAL
CIRCUITRY
DIGITAL
OUTPUT
V
SS
FIGURE 3. DIGITAL INPUTS AND OUTPUTS
Input Filter
The CD22204 will tolerate total input noise of a maximum of
12dB below the lowest amplitude tone. For most telephone
applications, the combination of the high frequency
attenuation of the telephone line and internal band limiting
make special circuitry at the input to these receivers
unnecessary. However, noise near the 56kHz internal
sampling frequency will be aliased (folded back) into the
audio spectrum, so if excessive noise is present above
28kHz, the simple RC filter shown below may be used to
band limit the incoming signal. The cut off frequency is
3.9kHz.
DV
DV signals a detection by going high after a valid tone pair is
sensed and decoded at the output pins D1, D2, D4, and D8.
DV remains high until a valid pause occurs.
NOISY
SIGNAL
270kΩ
ANALOG
IN
CD22204
0.0015µF
33kΩ
N/C Pin
This pin has no internal connection and should be left floating.
FIGURE 4. FILTER FOR USE IN EXTREME HIGH
FREQUENCY INPUT NOISE ENVIRONMENT
4
INTERSIL [ INTERSIL CORPORATION ]
