US Patent 7587012 Dual loop clock recovery circuit

A clock recovery circuit for digital data transmission includes a delay lock loop having a first loop which generates a phase difference signal which is indicative of a quantized phase difference between a data signal and a clock signal; and a second loop which generates a phase difference signal which is a smooth, continuous function of the phase difference between the data signal and the clock signal, such as a phase difference signal which is proportional to the phase difference. The delay lock loop may include two phase shifters in series, and one or both of these may include a phase interpolator.