Device for setting minimal and maximal frequencies of a frequency

Abstract

A frequency control apparatus automatically sets minimum and maximum reference frequencies (f.sub.min and f.sub.max) of a frequency modulated video luminance signal. An insertion circuit receives first and second reference voltages corresponding to f.sub.min and f.sub.max output from an AGC amplifier of a video tape recorder, wherein f.sub.min and f.sub.max are synchronized with first and second control signals. A discriminator receives one of the reference frequencies, f.sub.min or f.sub.max, together with the frequency modulated video signal from a voltage controlled oscillator of the video tape recorder and generates two voltage levels related to the input frequencies. A comparator receives one of the two voltage levels from the discriminator, generating a difference voltage corresponding to the difference between the two input voltage levels. An output of the comparator is provided to a switch which is controlled by third and fourth control signals so that the output level of the comparator controls either (a) the setting of the gain of a variable gain amplifier of the video tape recorder or (b) feeds one of the inputs of an adder of the video tape recorder. The switch is responsive to the reference frequency supplied to the discriminator to servo-control the video signal output by the voltage controlled oscillator either by f.sub.min or f.sub.max.