A clock generating circuit includes a phase comparison circuit that generates a delay control signal corresponding to the relative phases of an output clock signal and a reference clock signal. A voltage controlled delay circuit generates the delayed clock signal by inverting a signal applied to its input and delaying the signal by a delay that is determined by a delay control signal. A selection circuit couples either the reference clock signal or the delayed clock signal to the input of the voltage controlled delay circuit. When the reference clock signal is coupled to the input of the voltage controlled delay circuit, the clock generating circuit functions as a delay-lock loop. When the delayed clock signal is coupled to the input of the voltage controlled delay circuit, the voltage controlled delay circuit operates as a ring oscillator so that the clock generating circuit functions as a phase-lock loop.