A circuit includes a first transistor in a common-collector configuration and a heterojunction bipolar transistor (HBT) in a common-emitter configuration. The first transistor has a base coupled to an input node for receiving a pulsed signal. A collector of the first transistor is coupled to a first voltage source node. A base of the HBT is coupled to an emitter of the first transistor. A collector of the HBT is coupled to a second voltage source node configured to bias the HBT normally off. The HBT operating isothermally when the pulsed signal has a short-pulse width and a low duty cycle. The first transistor drives the HBT when the pulsed signal is received at the base of the first transistor to output an amplified pulsed signal at the collector of the HBT.