Microwave amplifier linearizer

Abstract

There is disclosed a system for linearizing an RF amplifier by the application of suitable load impedances to its 2nd, 3rd, and higher order output signals, thereby reducing output distortion products and improving performance. Intermodulation Distortion (IMD) reduction results from controlled termination of harmonic tuned filters produced by impedance selection and/or filter detuning. Preferably the apparatus comprises parallel band-pass filters including a filter passing the fundamental signals only; a filter passing 2nd harmonics; and a filter passing the 3rd harmonics. These, and optionally higher order filters, are employed for suppressing harmonic frequencies and reducing IMD. Preferably all filters have sufficient isolation to prevent serious interaction between filters. Therefore a selected mismatch provided at each of the harmonic output ports linearizes the amplifier's output. In some applications it is useful to mistune the filter to create a load impedance mismatch to cause the desired Intermodulation Distortion reduction. The system may be at the front end and/or output of an RF amplifier. Utilizing a suitable probing device the system may be used as a testing tool or for screening MIMIC RF amplifiers still in wafer form, or may be used to select a suitable load impedance for the MIMIC for later correction of IMD time or for selecting MIMICS which exhibit better IMD characteristics.