Patent ID: 8907723

Claim:
A power amplifier comprising: a switch element configured to comprise a first terminal, a second terminal, and a control terminal, to short a circuit between the first terminal and the second terminal in response to a first edge of an input drive pulse supplied to the control terminal, and to open the circuit between the first terminal and the second terminal in response to a second edge appearing in the input drive pulse alternately with the first edge; a variable passive element configured to be connected directly or indirectly to the first terminal and to serve to increase or reduce a resonant frequency of the amplifier; a sampler configured to sample a voltage of interest in response to the first edge, the voltage of interest being based on at least one of a first voltage between the first terminal and the second terminal and a second voltage obtained by subjecting an output current from the amplifier to a current-voltage conversion; and a comparator configured to compare the voltage of interest with a reference voltage and to output a control voltage for the variable passive element based on a difference between the voltage of interest and the reference voltage.