Power saturation control of class C bipolar amplifiers

A Class C bipolar transistor amplifier including circuit means having a non-linear, high-current, low-knee voltage transfer characteristic in series with the emitter RF choke of a common base bipolar transistor, which increases the emitter bias voltage, and in turn forces the amplifier deeper into Class C operation during overdrive, effectively limiting the output power. In one embodiment, a low ohmic resistor and a MOSFET device are connected in series with the emitter RF choke of a common base bipolar transistor Class C amplifier. An active feedback control loop implemented with conventional operational amplifier (OP AMP) circuitry controls the MOSFET device so as to operate in the knee region of its current-voltage characteristic during power overdrive. In a second embodiment, a single non-linear circuit element such as a constant current diode having a high-current, low-knee voltage transfer characteristic is connected in series with the emitter RF choke. The constant current diode consists of a depletion mode MOSFET or JFET having the gate directly connected to the drain.