| 摘要 |
A digital pushbutton (PB) signalling receiver having reduced sampling frequency for reducing the operations required by digital filters. The PB receiver is responsive to an in-band audio signal digitized at a conventional sampling frequency (e.g., 8 KHz) and detects two PB frequencies, one from a lower group and one from a higher group of frequencies. The input signal is successively digitally filtered and sampled, with each sampling frequency being reduced by 1/2 from the preceeding sampling frequency. This results in two digitized outputs, both of which are much lower sampled digitized signals than the input, and each of which contains information corresponding to said lower and higher groups of frequencies, respectively. The two outputs are then applied to two banks of frequency detectors, comprising digital band-pass filters and energy calculating circuits, for providing an indication of the presence of the lower and higher group of frequencies in the original input signal.
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