Apparatus and method for reducing distortion in amplification

Apparatus according to claim 19 wherein the offset means comprises

• a signal generator having an output frequency at the required reduced frequency of the control means input signals, and two outputs in phase-quadrature with one another,
• first and second pairs of offset mixers, each pair having an input terminal connected to applies signals in quadrature to the respective mixers of the pair, and being connected to receive the control-means input signals for that processing means, respectively,
• the mixers of the first pair being connected to receive respective outputs of the signal generator and having an output terminal connected to combine the output signals of the mixers,
• the mixers of the second pair being connected to receive the combined output signals of the first pair and having separate output terminals, and
• means for selecting the lower sidebands of the mixers of the second pair as the reduced frequency control-means input signals.

A method of reducing the distortion produced by an amplifier circuit comprising the steps of

• deriving an error signal dependent on the output signals of the amplifier circuit and inputs signals supplied to the amplifier from which it is required to provide undistorted output signals,
• cancelling the distortion produced by the amplifier circuit using the error signal, to provide a corrected signal,
• automatically making separate amplitude adjustments and phase adjustments of at least one of:
• the error signals, a signal used in generating the error signal and a signal used in providing the corrected signal, in response to respective simultaneously derived first and second control signals to give substantially improved cancellation of the said distortion, and
• generating the first and second control signals in dependence upon signals representative of the said input signals and signals derived therefrom.

Apparatus for reducing the distortion produced by an amplifier circuit, comprising

• error-signal generating means for connection to the input and output of an amplifier circuit for deriving an error signal dependent on the output of the amplifier circuit and input signals supplied to the amplifier from which it is required to provide undistorted output signals.
• correction means for cancelling the distortion in the amplifier output signals by using the error signal to provide a corrected signal,
• the error-signal generating means comprising independently acting first, amplitude, and second, phase adjustment means for carrying out automatic, respective, adjustment of the amplitude and phase of at least one of:
• the error signal, a signal used in generating the error signal, and a signal used in providing the corrected signal,
• the automatic adjustment being carried out in response to respective first and second simultaneously derived control signals to give improved cancellation of the said distortion, and
• control means for generating each of the first and second control signals from at least two signals, one of which depends on one of the said input signals, and signals derived therefrom, and the other of which depends on the said error signal.

A method of reducing the distortion produced by an amplifier circuit comprising the steps of

• deriving an error signal dependent on the output signals of the amplifier circuit and inputs signals supplied to the amplifier from which it is required to provide undistorted output signals,
• cancelling the distortion produced by the amplifier circuit using the error signal, to provide a corrected signal,
• automatically making separate amplitude adjustments and phase adjustments of at least one of:
• the error signals, a signal used in generating the error signal and a signal used in providing the corrected signal, in response to respective simultaneously derived first and second control signals to give substantially improved cancellation of the said distortion, and
• generating each of the first and second control signals from at least two signals, one of which depends on one of the said input signals, and signals derived therefrom, and the other of which depends on the said error signal.