Suppression circuit for suppressing unwanted transmitter output

A multi-frequency suppression circuit for suppressing unwanted outputs at multiple frequencies from an amplifier having an input and an output, the input receiving an input and the amplifier operable over a frequency band and operable to amplify the input signal to produce an amplified output signal, the multi-frequency suppression circuit connected between the input of the amplifier and the output of the amplifier, the multi-frequency suppression circuit comprising:

• a signal coupler coupled to the output of the amplifier, and arranged to provide a feedback signal derived from the amplified output signal;
• a signal splitter configured to split the feedback signal into a plurality of feedback signals;
• a plurality of sets of signal processing circuits, the sets respectively arranged to receive one of said plurality of feedback signals, and configured to process said one of said plurality of feedback signals to generate a respective negative feedback signal at a selected frequency within the frequency band of the amplifier;
• a signal combiner configured to combine said generated negative feedback signals from said signal processing circuits to produce a combined negative feedback signal;
• and
• a further signal coupler coupled to the input of the amplifier, and arranged to receive the input signal and the combined negative feedback signal, and arranged to couple the combined negative feedback signal to the input signal, such that when the input signal is amplified by the amplifier any signal at the selected frequencies can be suppressed.

A method of suppressing unwanted transmitter output in a radio frequency (RF) amplifier, comprising:

• obtaining a feedback signal from the output of the RF amplifier;
• downconverting an excision frequency band of the feedback signal to one or more feedback signal baseband components, the excision frequency band being a band that it is desired to remove from the output of the RF amplifier;
• low pass filtering the feedback signal baseband components to remove signals outside the excision frequency band;
• upconverting the filtered feedback signal baseband components to RF;
• and
• feeding back the unconverted feedback signal to an input of the RF amplifier;
• the method further comprising inverting the feedback signal at any point in the signal processing chain to provide a negative feedback signal to the input of the RF amplifier.