US Patent 7199630 Delay locked loops and methods using ring oscillators

Delay locked loops include a ring oscillator having serially connected inverters and a feedback path around the serially connected converters. The ring oscillator is configured to generate an output clock signal that is a delayed version of an input clock signal, in response to the input clock signal and to a control signal that is applied to the ring oscillator. A phase responsive circuit is configured to generate the control signal in response to a phase difference between the input clock signal and the output clock signal. Analogous methods of delaying a clock signal also are described.