DTFM signal generation and detection (1)

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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