Patent ID: RE42917

Claim:
A VHF generator for delivering rf power to a plasma, comprising, a) a variable rf signal generator including a power amplifier connected to a directional coupler; b) the directional coupler having one output connected to a matching network wherein power is delivered to plasma in a processing chamber; c) at least one output of the directional coupler disposed to sample a forward power signal of the rf signal generator and at least one output of the directional coupler disposed to sample a reflected power signal of the rf signal generator; d) each of the sampled forward and reflected signals is connected to mixers for mixing with an intermediate frequency of an oscillator; e) the mixed forward and reflected signals are passed through low pass filters; f) the filtered forward and reflected signals are connected to amplifiers and detectors; and g) the detected forward and reflected signals are fed back to a power control circuit wherein the power delivered to the plasma is monitored without interference from spurious frequency signals generated by the plasma.