Minimization of Bias-Induced Memory Effects in UHF Radio Frequency High Power Amplifiers with Broadband Signals

If the biasing circuit of a class AB radio frequency power amplifier (RF PA) does not present a zero impedance at the envelope frequencies, undesired ac voltages will be added to the dc supply voltage, producing amplitude and phase modulation of the RF output signal. Unfortunately, the sidebands due to this bias modulation fall exactly where the intermodulation distortion (IMD) products occur, producing their reinforcement or attenuation. This paper presents an effective biasing technique that minimizes this bias modulation while providing, at the same time, high impedance at the carrier frequency and low impedance at the second harmonic