Amplitude modulation using digitally selected carrier amplifiers

Apparatus for generating an amplitude modulated carrier signal, comprising:

• means for receiving an input signal in accordace with which a carrier signal is to be modulated;
• means for providing a plurality of carrier signals of like frequency and phase, said means providing a first plurality of carrier signals, all of equal amplitude, and at least one second carrier signal, each said at least one second carrier signal having an amplitude which is a selected fraction of the amplitude of each of said first pluraltiy of carrier signals;
• and
• means for combining a selected number of said carrier signals in accordance with the level of said input signal whereby a combined carrier signal is provided which is modulated as a function of said input signal.

Apparatus for generating an amplitude modulated carrier signal, comprising:

• means for digitizing an input signal to provide a plurality of control signals wherein the number of control signals having a first level changes as the amplitude of said input signal changes;
• a plurality of carrier signal sources each responsive to an asociated one of said control signals for providing an associated carrier signal when said control signal has said first level, said carrier signals being of like frequency and phase, a first plurality of said sources providing first carrier signals which are all of equal amplitude, and at least one other of said sources providing a carrier signal having an amplitude which is a selected fraction of the amplitude of each of said first carrier signals;
• and,
• means for combining said associated carrier signals, whereby a combined carrier signal is provided having an amplitude which varies in accordance with said input signal.

Apparatus for generating an amplitude modulated carrier signal, comprising:

• means for digitizing an input signal, said digitizing means being responsive to said input signal for providing a multibit digital signal which changes in accordance with said input signal;
• a plurality of carrier signal sources each responsive to an associated bit of said digital signal for either providing or not providing an associated carrier signal in accordance therewith, said associated carrier signals being of like frequency and phase, where a first plurality of said carrier signals are of equal amplitude and at least one other carrier signal has an amplitude which is a selected fraction of the amplitude of each of said first plurality of carrier signals, said carrier signal sources collectively responding to said digital signal such that the number of said first plurality of carrier signals being provided varies in accordance with the value of said input signal and that said at least one other carrier signal is provided when the amplitude of said input signal is between values represented by discrete numbers of said first plurality of carrier signals;
• and
• means for combining said associated carrier signals provided by said carrier signal sources, whereby a combined carrier signal is provided having an amplitude which varies in accordance with said input signal.

Apparatus for generating an amplitude modulated carrier signal, comprising:

• means for providing an input signal;
• means responsive to said input signal for digitizing said signal to provide a plurality of bilevel control signals where the number of said control signals having a first level changes in accordance with the amplitude of said input signal;
• means for providing a carrier signal;
• a plurality of power amplifier means, each responsive to said carrier signal and to an associated one of said control signals for providing an amplified version of said carrier signal when said associated control signal has said first level and no signal otherwise;
• and,
• means for combining said amplified versions of said carrier signals provided by said plural power amplifier means so as to thereby provide a combined carrier signal having an amplitude which varies in accordance with said input signal;
• wherein each said power amplifier means comprises four switching elements connected in a bridge arrangement across a DC power supply, and means for operating said switching elements in accordance with said carrier signal such that said amplified version of said carrier signal appears across the output junctions of said bridge arrangement.

A method of generating an amplitude modulated carrier signal, comprising the steps of:

• selectively providing a first plurality of equal amplitude carrier signals of like frequency and phase where the number of carrier signals being provided varies with the amplitude of an input signal;
• selectively providing at least one second carrier signal, each said at least one second carrier signal having an amplitude which is a selected fraction of the amplitude of each of said first plurality of carrier signals;
• and,
• combining said first plurality of carrier signals and said at least one second carrier signal to thereby form a combined carrier signal having an amplitude which varies in accordance with said amplitude of said input signal

An amplitude modulation circuit comprising:

• a plurality of first radio frequency signal providing circuits each operative to provide a radio frequency signal at its output, all said radio frequency signals being of equal amplitude, each of said first providing circuits being rendered operative in response to control signals applied thereto;
• at least one other radio frequency signal providing circuit each operative to provide an other radio frequency signal at its output in response to a control signal applied thereto, said other radio frequency signal being a fraction of the amplitude of each of the radio frequency signals provided by said plurality of first providing circuits;
• combiner means for additively combining said radio frequency signals provided by said plurality of first radio frequency signal providing circuits and said at least one other radio frequency providing circuit;
• means for synchronizing said first and other radio frequency signal providing circuits so that the output signals of said circuits are in phase;
• and
• means responsive to the amplitude of an input signal for selectively applying control signals to said first and other providing circuits so that the radio frequency signal output by said combiner means is amplitude modulated in accordance with the amplitude variations of said input signal.