Pulsed Load Modulation (PLM) Technique for Efficient Power Amplification

A new concept of pulsed load modulation (PLM) is introduced for efficient power amplification. The proposed technique allows the power amplifier (PA) to maintain maximum efficiency until the output power of the amplifier is backed off by 6 dB. The PLM amplifier contains two pulse-biased PAs connected with a lambda/4 transmission line and a high-
Q
bandpass resonator. For maximum efficiency and linearity, the load impedance of the amplifier is digitally modulated using the switched-resonator concept. A prototype amplifier is implemented using two PAs and a diplexer for the 1.87-GHz band. The measured efficiency of the amplifier at peak output power is 51%. Compared with 25.5% of the conventional class-B amplifier, the PLM amplifier obtains an improved efficiency of 38% at 6-dB output power back-off.