Push-pull amplifier output circuit

Claim 1

A high frequency amplifier, comprising in combination, a pair of transistors, each having base, emitter and collector electrodes, and being connected together in a push-pull circuit arrangement, the collector electrodes each exhibiting a collector to emitter capacitance, input means for applying an input signal to the base electrodes of the transistors, output transformer means for deriving an output signal in common from the collectors of the transistors, and capacitance means connected between the collector and emitter electrodes of each transistor, each of said capacitance means having a capacitance value which is in the order of magnitude of several times the collector to emitter capacitance of the transistor at the normal collector voltage, whereby the variation in the output capacitance of said transistors with respect to the collector voltage is minimized to reduce parametric oscillations, said amplifier further comprising a low pass filter coupled to said output transformer for providing harmonic suppression, said filter being so constructed and arranged to avoid presenting a series resonance to any harmonic of the output signal, and resistance termination means for in-phase signal components between said push-pull circuit arrangement and said low pass filter, said resistance termination means comprising a 180° hybrid network interconnected between said push-pull arrangement and said low pass filter, said hybrid network including a port terminated in a resistor.