Phased locked loop to provide precise frequency and phase tracking of two signals

摘要

A device and method are presented which allows the precise generation of signals within an integrated circuit that are calibrated to an external reference signal. The device consists of a ring oscillator which generates a calibration signal oscillating at a first frequency and a power source that supplies a compensated power signal to the ring oscillator. The first frequency is variable based on the voltage of the compensated power signal. A phase detector is used to detect the relative phase of the calibration signal and the external reference signal. The compensated power signal is also used for critical data paths within the integrated circuit where precise timing is required. In a tester, a plurality of signals may be extracted from the ring oscillator using a series of taps. These signals will oscillate at the same frequency as the calibration signal, but will be phase shifted. The signals may be combined with multiplexors to form a test signal which is applied to a device under test (DUT). Further, in order to make transparent propagation delay, delayed calibration signals may be generated.