Efficient Output Power Configuration in a K-Band Power Amplifier Using a Split-Gate Layout

A multi-finger RF transistor has been divided into multiple gate sections which can be biased independently. This provides a system designer the ability to dynamically reconfigure the output power and power gain of the device while maintaining good power efficiency and without changing the input drive power. By selectively switching the gate biases below pinch-off to effectively reduce the device’s active periphery, the maximum current of the device can be tuned to "follow" a reduced drain bias voltage, so that the optimum impedance at lower power remains similar to the one at full power, and a fixed matching network can be used to accommodate all power modes. The concept has been implemented in a K-Band PA prototype. Simulation show the achievement of two power modes, with ≃6dB of maximum output power tuning while maintaining an efficiency >35% in both modes. Initial small signal measurement results show the tuning capability being effective in tuning the gain of the PA.