a method for a phase - locked loop , which circuit includes , in a preferred embodiment , a resistor to unbalance phase detector outputs to an operational amplifier to cause the voltage output of the operational amplifier to sweep and thus cause the frequency output of a voltage controlled oscillator to sweep . simple circuitry detects correct lock and terminates sweeping ; or , if lock is not achieved , causes the output of the operational amplifier to remain at a low level until the operational amplifier is reset and then permits resweep . very little auxiliary circuitry is required .