AN2384 Freescale Semiconductor / Motorola, AN2384 Datasheet - Page 14

• Manufacturer Part Number: AN2384
• Description: Generic Tone Detection Using Teager-Kaiser Energy Operators on the StarCore SC140 Core
• Manufacturer: Freescale Semiconductor / Motorola

DTMF Detector on StarCore
4.2.4 Signal Reception Timing
14
•
Generic Tone Detection Using Teager-Kaiser Energy Operators on the StarCore SC140 Core, Rev. 1
To respect the signal timing condition, we must know the duration of the signal and the pause. To get
this information, we must detect an edge in the signal, which can correspond to the beginning or the
end of a key, as depicted in Figure 7.
0.26
0.24
0.22
0.18
0.16
0.14
0.12
0.08
0.2
0.1
60
2 . 5
1 . 5
0 . 5
Pause
3
2
1
0
Thresholds for the Twist
70
0
2
80
90
Figure 7. Transition Between Pause and DTMF Signal
2 0
100
2
110
1
Signal
4 0
2
Thresholds for the Twist
120
Figure 6. Plots of Test Results
1
130
for +8dB
for -4dB
6 0
140
150
8 0
Pause
Edge
1 0 0
2.55
2.45
2.35
2.6
2.5
2.4
20
40
1 2 0
1
1
2
Signal
Thresholds for the Twist
60
for +8dB
for –4dB
1 4 0
80
100
fo r + 8 d B
fo r -4 d B
1 6 0
120
Freescale Semiconductor
140
1 8 0
for +8dB
for -4dB
160