A Baseband Impedance Cancellation Technique for Wideband Multitransistor Amplifiers

A new baseband (BB) impedance cancellation technique is presented for broadband multitransistor amplifier designs. By placing a BB transformer in between the Doherty main and auxiliary amplifier, the BB component of a two-tone signal can be canceled out, resulting in improved efficiency, output power, and linearity over two-tone bandwidth. A 20-W, 6-dB back-off 3.5-GHz Doherty is designed and its performance is measured with and without this cancellation technique. The prototype shows significant improvements for all metrics for tone spacing above 130 MHz when the transformer is used, and it has an efficiency enhancement up to 15% points at 300-MHz tone spacing.