Television transmitter employing klystron with nonlinearity correction circuit

摘要

A television transmitter includes a klystron power amplifier, a non- linearity pre-correction circuit in a stage preceding the klystron power amplifier, a non-linearity detection circuit for detecting the non- linearity of the output of the klystron power amplifier, a first level controlling circuit for controlling the level of the output of the non- linearity pre-correction circuit in response to the output of the non- linearity detection circuit, a hum frequency component detection circuit for detecting a hum frequency component of the output of the klystron power amplifier and a second level controlling circuit for controlling the level of either the input or the output of the non-linearity pre- correction circuit in response to the detected hum frequency component. The first and second level controlling level circuits are preferably variable attenuators. Preferably, the hum component detection circuit is an AGC circuit, which preferably detects the pedestal level in the output of the power amplifier, and then applies the detected level to a bandpass filter which passes a component of substantially 50 to 60 Hz contained in the pedestal level. A comparator compares the output of the bandpass filter against a reference level and generates an error signal, which is employed to control the second variable attenuator, which is either at the input or the output of the pre-correction circuit.