Abstract: A circuit is provided for detecting out-of-lock condition in a phase lock loop. The phase lock loop receives a first signal having a first frequency and a voltage controlled oscillator of the phase lock loop produces a second signal having a second frequency. The circuit comprises a first data flip-flop coupled to the phase lock loop for receiving the first signal and clocked by the second signal. The first flip-flop produces an inverted output of the first signal. A second flip-flop is coupled to the phase lock loop for receiving the second signal clocked by the first signal, and produces a non-inverted output of the second signal. Additionally, an EXCLUSIVE-OR gate is coupled to the first and second flip-flops for receiving the inverted and non-inverted output thereof and producing a signal indicative of an out-of-lock condition.