Telephonic communications – Substation or terminal circuitry – For loudspeaking terminal
Patent
1993-06-04
1995-04-25
Dwyer, James L.
Telephonic communications
Substation or terminal circuitry
For loudspeaking terminal
379389, 330251, 330253, H04M 910
Patent
active
054105927
ABSTRACT:
An audio amplifier for providing a power boost for telephone-sourced audio signals that drive one or more paging speakers employs a class D amplifier and a state variable feedback network, which monitors voltage and current levels of an audio output filter to which the paging speakers are coupled, so as to adjust the operation of the amplifier circuit, as necessary, to compensate variations in the speaker loading of the audio output filter. The class D amplifier includes a pulse width modulator, which controls the switching of a power H-bridge-configured switching circuit. The switching circuit sources and sinks current with respect to the paging speaker load. The output of the power bridge switching circuit is a high energy square wave-type signal, which is filtered in a downstream audio filter to remove the switching transients and preserve the desired voice paging signal for application to the paging speakers. The state variable feedback network monitors variations in current flow and voltage at a plurality of circuit locations of the audio filter circuit and sums the monitored variations to produce an error signal, which is fed back to the input of the voice paging amplifier circuit and combined with the audio input signal.
REFERENCES:
patent: 4178556 (1979-12-01), Attwood
patent: 4720848 (1988-01-01), Akiyama
patent: 4885577 (1989-12-01), Nelson
patent: 5063332 (1991-11-01), El-Hamamsy et al.
patent: 5160896 (1992-11-01), McCorkle
patent: 5200711 (1993-04-01), Andersson et al.
Mistry Yogi L.
Wagner Randall M.
Dwyer James L.
Harris Corporation
Saint-Surin Jacques M.
Wands Charles E.
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