Parameter space analysis of a phase-locked loop voltage-controlled oscillator circuit

Phase-locked loop circuits are widely used for communications applications such as frequency synthesizers for missile tracking. These systems often become unstable due to the vibrations and large g-forces experienced during a missile launch. We consider a phase-locked loop circuit modified by an additional RC low-pass filter for improved noise stability. To analyze the robust stability of this circuit, a parameter space analysis was performed with the components of the RC filter and the circuit gain K as adjustable parameters. The analysis shows the resistor and capacitor values that lead to stable circuit behavior for given values of gain and desired noise attenuation.