A Sub-Nanosecond Gate Bias-Switching Circuit for GaN RF Power Amplifiers

In this letter, we present a design of a fast gate-switching power amplifier (GSPA) aimed at reducing its power consumption. This GSPA features a dedicated fast gate-switching circuit that commutates the gallium nitride (GaN) transistor between a nominal gate bias voltage (GSPA ON) and a strong negative voltage (GSPA OFF), thereby generating two discrete output power levels in an RF-pulsewidth modulation (PWM) fashion. A fast gate-switching circuit, including a commercial digital voltage isolator, is designed to switch between two gate bias voltages. The gate stability resistor and transmission line (TL) are carefully placed and designed to reduce the GSPA parasitic bias line and enable fast switching. Measured results provided a rise and fall time of 750 and 950 ps, respectively, and achieved RF pulsewidths as narrow as 5.88 ns, thus corresponding to a 170-MHz bandwidth.