DTFM signal generation and detection (1)
The key technology of DSP to realize DTMF signal generator
Overview
The DTMF signal generator converts the button or digital signal into a two-tone signal. Information in the dual tone signal of the DTMF signal detector. The following figure shows the dual-tone frequency of a general dual-tone multi-frequency phone.
The key technology of DSP to realize DTMF signal generator
1 Sinusoidal signal algorithm and frequency control
There is a system: its transfer function H (z) has no zero point, but only a pair of conjugate poles on the unit circle, then the unit impulse response is a constant amplitude oscillation, which produces a sinusoidal signal.
2 DTMF dual tone signal generation
ROW frequency: 697, 770, 852, 941Hz COLUMN frequency: 1209, 1336, 1477, 1633Hz Sampling frequency: fs = 8kHz
3 DTMF signal timing control
According to AT & T technical specifications:
(1) The maximum transmission speed of digital numbers is 10, that is, one number occupies 100ms time slice.
(2) The dual-tone multi-frequency signal lasts no less than 45ms and no more than 55ms within a 100ms time slice.
(3) A digital button has two jobs: Tone Task and Quiet Task.
4 Process description
Key interruption will start a job (Start Task). Execute Quiet Task: Insert the interval between two-tone signals. Set the Tone Task count size. Unpack New Digit Execute Tone Task: output the two-tone signal according to the specified time slice.
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