US 3,943,446 AGranted

Power and modulation control system

AssigneeWestinghouse Electric Corp.

InventorVaughn L. Quidort

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Abstract

A system for controlling and maintaining the power output of a broadcast transmitter under varying line voltage conditions, including a pulse width modulator wherein a triangular wave acting as a reference input is compared to the audio input. Power is controlled by varying the amplitude of the triangular wave relative to the audio input which additionally includes a DC bias thereby increasing or decreasing the comparator square wave output duty cycle which output is used to control the transmitter's RF power amplifier. Three separate DC control inputs, respectively, for automatic power control, remote or local manual power control, and a slow start control are summed and fed to an operational DC amplifier which provides a composite DC output which is fed to a triangular waveform generator in order to control the amplitude of the triangular waveform generated thereby.

Claims12

Dependent claims

A system for controlling the power output of a transmitter in response to the operation of a modulation switch turned on and off by a pulse width modulated substantially square wave, comprising in combination:

a. a comparator circuit coupled to said modulation switch and having first and second inputs respectively coupled to receive a DC biased modulating input signal and a regularly repetitive variable amplitude reference signal and producing said substantially square wave signal consisting of a pulse train in which the width and consequently the duty cycle of the pulses are proportional to the instantaneous amplitude of said DC biased modulating signal relative to the amplitude of the reference signal;
b. a waveform generator, adapted to produce said regularly repetitive variable amplitude reference signal of a predetermined frequency, coupled to said second input of said comparator circuit, said waveform generator being operable in response to an initiating signal of said predetermined frequency and additionally receiving a control signal which is adapted to vary the amplitude of said reference signal;
c. first circuit means responsive to the power output of said transmitter to generate at least a first signal indicative of the power output of said transmitter;
d. second circuit means responsive to an external signal to generate at least a desired power output signal indicative of the desired power output of said transmitter;
and
e. combining circuit means for combining a plurality of signals to generate said control signal, said plurality of signals including at least said signal indicative of the power output of said transmitter and said desired power output signal, said control signal being coupled to said waveform generator such that the power output of said transmitter is controlled at the desired level.

3 more elements

A modulator for modulating and controlling the average power output of an RF amplifier comprising in combination:

a comparator circuit having first and second inputs respectively coupled to receive a DC biased modulating input signal and a regularly repetitive variable amplitude reference signal and producing a substantially square wave signal consisting of a pulse train in which the width and consequently the duty cycle of the pulses are proportional to the instantaneous amplitude of said DC biased modulating signal relative to the amplitude of the reference signal;
input circuit means for providing said modulating input signal including means for providing said DC bias to produce said DC biased modulating input signal, said DC bias establishing a first DC position of said modulating input signal relative to said reference signal and accordingly a gross power output setting of said RF amplifier;
a waveform generator, for producing said regularly repetitive variable amplitude reference signal of a predetermined frequency, coupled to said second input of said comparator circuit, said waveform generator being operable in response to an initiating signal of said predetermined frequency and additionally receiving a control input signal for varying the amplitude of said reference signal;
control circuit means operable in response to a second power output setting of said RF amplifier, generating said control input signal including circuit means coupling said control input signal to said waveform generator;
and
filter means coupled to receive said pulse train and produce therefrom a composite signal having an AC and a DC component with the DC component being primarily determined by the average duty cycle of said pulse train and the amplitude of the AC portion being determined by instantaneous duty cycle of said pulse train;
and
means for coupling said composite signal to said RF amplifier such that the average power of the output signal of said RF amplifier is determined by said DC component and is modulated by said AC component.

5 more elements

Dependencies are inferred from the claim text.