A Baseband Impedance Cancellation Technique For WidebandMulti-Transistor Amplifiers

A new baseband impedance cancellation techniqueis presented for broadband multi transistor amplifier designs. Byplacing a baseband transformer in between the Doherty Main andAuxiliary amplifier, the baseband component of a 2-tone signalcan be cancelled out, resulting in improved efficiency, outputpower and linearity over 2-tone bandwidth. A 20 W, 6dB back-off3.5 GHz Doherty is designed and its performance measuredwith and without this cancellation technique. The prototype showsignificant improvements for all metrics for tone spacing above130 MHz when the transformer is used, it has an efficiencyenhancement up to 15% points at 300 MHz tone spacing.