Varian Associates, Inc.

Continental Electronics Corporation

Bryan A Weaver

Gilmer L Hulsey

Daniel L Dickey, Sr

An amplifier has at least several stages activated only to one of two bi-level states controlled in response to the value of an input source exceeding a threshold for each stage. Each stage has a different threshold. The thresholds and source are arranged so that the stages change between the bi-level states as the value of the source changes relative to the thresholds of the different stages. Bi-level outputs of the stages are summed together. The values of the thresholds are continuously varied by a small amount relative to a predetermined maximum value for the source in response to a noise source that is independent of the signal source. A power supply for the stages includes an AC-DC converter having plural primary windings and several secondary windings, one for each of the stages. The windings are coupled together so that at all times loading of the primary windings by the secondary windings as a result of activation of the output stages is approximately equal. The stages are controlled so that the sum of the outputs of the stages remains a predetermined function despite one or a few of the stages failing.

Amplifier with multiple switched stages and noise suppression

A power amplifier for a plate load of an AM, RF transmitter includes plural switching stages each powered by a DC source. Each stage is switched from non-sourced to saturation in response to the amplitude of an analog source exceeding a threshold amplitude for the stage; each stage has a different threshold. The thresholds and analog source are arranged so that responses derived between output terminals of the stages change between zero and predetermined amplitudes as the source amplitude changes relative to the thresholds of the different stages. The responses of the different stages are summed. A triangular wave having a small constant maximum amplitude relative to the analog source maximum value effectively changes the threshold of each stage. From time to time the thresholds of different stages are changed so that at different times different stages are in non-sourced and conducting for the same amplitude of the modulating source, while providing the same summed response for the same amplitude of the modulating source.

Power amplifier having multiple switched stages and method of operating

An RF-AM transmitter of the type including a power pulse amplifier driving an RF amplifier with a modulating voltage via a low pass filter includes a pulse width modulator for deriving variable frequency pulses having a frequency that is a direct function of an RMS like function of the amplitude and frequency of an information source; the width of the pulses is determined by the instantaneous amplitude of the information signal source. The pulse width modulator includes a constant amplitude, variable frequency triangular wave voltage controlled oscillator responsive to a DC signal representing the frequency and amplitude of the information source. In response to amplitude crossovers between the variable frequency triangular wave and the information source, transitions in the pulse width modulated wave are derived.

Pulse width modulator for AM-RF transmitter

An RF-AM transmitter includes a pulse amplifier responsive to a pulse width modulated (PWM) signal derived in response to an information signal. A low pass filter converts pulses derived by the power amplifier into a variable amplitude signal that is DC coupled to a power supply for an RF amplifier. An amplifier system including the pulse and RF amplifiers has stray capacitance coupled to a modulator which derives the PWM signal; the stray capacitance lengthens narrow modulator output pulses so they are excessively long. The amplitude of only the narrow pulses is reduced by a resistor-capacitor timing circuit in series with a switch to substantially preserve the narrow pulse area. The switch provides a low impedance path from the timing circuit to a reference potential terminal when current initially flows in the circuit during pulse transitions and throughout the length of each of the short duration pulses. Thereby, the power amplifier is forward biased but not driven into saturation during the short duration pulses. The switch provides a higher impedance path from the timing circuit to the reference potential terminal after the transition has elapsed, enabling the power amplifier to be saturated during pulses longer than the short duration pulses. The RF power amplifier tube has a tendency to load the power amplifier tube out of saturation during wide pulses. The ampitude of the wide pulses is maintained substantially constant by a resistor shunted by an inductor between the modulator and the power amplifier.

RF-AM transmitter with pulse width modulator

An AM-RF transmitter includes a transmitter stage having a DC power supply terminal energized by an AC to DC converter including reactances having a resonant frequency approaching frequencies of an information, modulating signal. The voltage applied by the supply to the DC power supply terminal is reduced to such an extent as to induce distortion in the transmitted AM-RF carrier in response to the transmitter stage being modulated by positive amplitude variations having frequencies that approach the resonant frequency. The amplitude of the transmitter stage modulation is increased when the distortion would otherwise occur to substantially prevent the distortion. The information signal is modified in amplitude by only AC coupling a replica of the DC power supply voltage variations to one input of a four quadrant multiplier, having a second input responsive to the information signal.

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Dallas, TX, United States of America

Bryan A Weaver