Digitally assisted power levelling circuit for rf power generator

Claim 1

In an RF generator that provides RF output energy at a predetermined frequency and at an output power level that corresponds to a power demand voltage applied thereto, wherein an RF signal is applied from an RF source to controllable RF power amplifier means which has a control input and an output at which metering circuit means provides a measured power voltage that represents a measured power level of the RF output energy, and in which an analog feedback circuit includes an analog control loop with an input provided with said measured power voltage and an output that provides a control voltage to one input of a summer circuit, the latter having a second input provided with said power demand voltage and an output coupled to the control input of the RF power amplifier means such that the output power level thereof corresponds to the power demand voltage; the combination, with said analog feedback circuit, of a digital levelling assist circuit to compensate for non-linearities in said metering circuit means in its measuring of said RF output energy, thereby to increase the accuracy of control of the RF output energy with respect to said power demand voltage, the digital levelling assist circuit comprising digitizing means with inputs coupled to receive said measured power voltage and said power demand voltage and an output providing digital representations of said measured power voltage and said power demand voltage, a digital control element which derives a digital correction factor based on said digital representations of the measured power and power demand voltages, d/a converter means coupled to said digital control element for providing a correction voltage corresponding to said digital correction factor, and said summer circuit including means coupled to said d/a converter means for combining said correction voltage with said power demand voltage and said control voltage.