Abstract: An oscillation system includes a pair of differentially connected oscillator transistors having a resonant tank circuit connected between collector electrodes and a current source transistor connecting both emitter electrodes to ground. The collectors and base electrodes of the oscillator transistors are cross connected to provide regenerative feedback and matched resistors connect each collector to a source of operating potential. A shunt transistor is connected to the collector of one of the oscillator transistors and a series transistor connected to their common emitters. The currents of the shunt and series transistors are combined in a second current source transistor. Control signals applied to the base of the series transistor vary the oscillator current (and thereby its frequency), and produce opposite current changes in the shunt transistor, thus maintaining the DC component of the oscillator output signal at a constant.

Abstract: A color television receiver has a tuner converting the received signal to an intermediate frequency and fine tuning means for varying the converted frequency. An intermediate frequency filter couples the converted signal to a synchronous demodulator which includes a variable frequency reference oscillator in a closed loop control system which tracks the IF frequency thereby providing an extended range of tuning adjustment. A two pole switch is operable to couple the DC component of the closed loop control system error signal to the tuner and the AC component of the error signal to the reference oscillator thereby providing an "exact tuning" operation.