Filter circuitry for voltage controlled oscillator

1. Field of the Invention The controlling circuit element of a voltage controlled oscillator (VCO) for use in a phase lock loop (PLL) is a varactor connected between the terminals used to convey the power supply voltage and the frequency control voltage. The loop filter, implemented in a shunt configuration at the input of the VCO, is also connected between the power supply and frequency control voltage terminals. As a result, any variations in the power supply voltage appear at both terminals of the varactor due to the voltage coupling effect of the loop filter between the shared power supply and frequency control voltage terminals.