The class BD high-efficiency RF power amplifier

Class B and class D operation of the same RF power amplifier circuit is not normally possible because of constraints imposed by the tuned output circuit and DC power input circuit. The use of square-wave drive in a current switching class D RF amplifier circuit allows the amplifier to move gradually from current source to current switch operation. This amplifier, called class BD, has a linear transfer characteristic (drive envelope to output envelope) and an efficiency 1.23 times that of a class B RF amplifier with the same peak output. The addition of a resistive AC current path to ground in the DC power input circuit of the class BD RF amplifier allows operation with sinewave driving waveforms. While this lowers the efficiency at the peak output, it can raise it at lower outputs, making possible a factor of 1.57 improvement in efficiency in the amplification of signals with large peak-to-average ratios. The class BD RF amplifier may therefore be used as a broad-band replacement for a Doherty-type amplifier.