Automatic sweep acquisition circuit for a phase-locked-loop

Abstract

An automatic sweep acquisition circuit for a phase-locked-loop using a positive feedback network coupled between a non-inverting input of an operational amplifier and an output of the operational amplifier is provided. The operational amplifier serves as a loop filter for the PLL and has a negative feedback network configured as a lead-lag integrator. The positive feedback network forms a Wein-bridge oscillator that automatically oscillates at a predetermined frequency when phase lock does not exist. A negative feedback path also supplies a portion of the phase shift required to activate the Wein bridge oscillator in order to provide sweep acquisition. When the circuit operates within the bandwidth of the PLL or within the lock-in range of the PLL the positive feedback network provides minimal feedback and thus creates no oscillation or sweeping voltage. The locked-in range of the PLL is increased to the pull-in range of the voltage controlled oscillator used in the phase-locked loop.

Dependencies are inferred from the claim text.