Patent ID: 6320334
Filing Date: 2001-11-20
Classification: H01J,H05H

Abstract:
A controller for controlling a phase shift between a reference signal and a measured signal in an rf resonator having an rf power supply, the controller comprising:an oscillator for providing a reference sinusoidal signal having a reference phase;a detector for generating a transduced signal from the rf resonator, the transduced signal having a detected phase;a phase shifter apparatus including:a quadrature signal generator arranged to shift the phase of the reference sinusoidal signal by 90.degree. relative to the reference phase so as to generate a reference cosinusoidal signal;a phase demand signal generator arranged to generate a first phase demand signal representing the sine of a desired angle of phase shift of the said reference sinusoidal signal plus an additional 90.degree., and to generate a second phase demand signal representing the cosine of the said desired angle of phase shift plus an additional 90.degree.;a first multiplier arranged to multiply the said cosinusoidal reference signal with the first phase demand signal representing the sine of the desired angle of phase shift plus 90.degree. to generate a first composite signal;a second multiplier to multiply the said sinusoidal reference signal with the second phase demand signal representing the cosine of the desired angle of phase shift plus 90.degree. to generate a second composite signal; anda summer arranged to sum the first and second composite signals to generate a phase shifter output signal which is a second sinusoidal signal that is shifted in phase relative to the reference phase of the reference sinusoidal signal by the said desired angle of phase shift plus 90.degree., the second sinusoidal signal being equivalent to a second cosinusoidal signal that is shifted in phase relative to the reference phase of the reference cosinusoidal signal by the said desired angle of phase shift;a third multiplier arranged to multiply the transduced signal with the second cosinusoidal signal and to generate a phase error signal having a dc component from the resultant product; anda processor arranged to generate a control signal on the basis of the dc component of the phase error signal, to control the output of the said rf power supply so as to minimize the phase error signal.