RF Generator monitor circuit

DETAILED DESCRIPTION An RF generator monitor circuit is provided for checking for variation in frequency of an RF generator outside predetermined limits.
The circuit includes means for sampling the output of an RF generator, means for clamping the sample signal to prevent damage to the circuit from an exceptionally strong signal, means for converting the clamped sample signal to a positive going square wave and for amplifying the square wave.
Also included is a phase locked loop integrated circuit having the amplified square wave as an input.
The phase locked loop integrated circuit includes a linear voltage-controlled oscillator and two different phase comparators.
The input square wave signal is compared to the voltage controlled oscillator and an error voltage proportional to phase differences is produced.
The error voltage is used as a control for the voltage controlled oscillator.
When the input square wave signal is within the predetermined frequency limits the error voltage causes the voltage controlled oscillator to be adjusted to a frequency equal to that of the input signal.
When the input signal is outside the predetermined limits the phase comparators provides output signals indicative thereof.