Programmable multifrequency tone receiver

Details Programmable multifrequency tone receiver Programmable multifrequency tone receiver

H - Electricity

03

H

328/0.3

H03H 17/02 (2006.01) H04L 27/30 (2006.01) H04Q 1/457 (2006.01)

Patent

CA 1150783

Abstract A multifrequency tone receiver is disclosed for detecting simultaneous tone signals in a sampled digital signal. The tone receiver includes a microprogrammed sequence controller, a time-multiplexed digital filter and a signal processing microcomputer. For each sample of the digital signal, the sequence controller is pro- grammed to time multiplex the digital filter for perform- ing three cascaded second order filtering operations (two bandpass filter operations and one low pass filter opera- tion) for each of six tone signals to provide correspond ing energy estimates and one additional filtering operation to provide a total energy estimate. The signal processing microcomputer processes a number of sets of the seven energy estimates and provides an indication when a multifrequency tone pair has been detected. The digital filter, when enabled by a filter start signal from the sequence controller, asynchronously performs a single multiplication like filtering operation to implement each second-order filter, and provides a filter done signal upon completion of the filtering operation. Full-wave rectifying capability is provided during low pass filtering operations by logically complementing the digital filter input signal. Limit cycles may be sup- pressed in the digital filter output signal by rounding the output signal and clamping positive and negative overflows to the largest allowable positive and negative signals, respectively. The tone receiver may be advan- tageously utilized in a PCM communication system for detecting multifrequency tone signalling used for dialing and supervisory control. Moreover, the inventive tone receiver may be adapted to receive many different types of tone signalling simply by changing firmware there- within,

365623

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