An octal clock phase interpolator

摘要

A set of variably rotated octal clocks is generated by rotating each of four quadrature input clocks by the same variable angle and feeding the four rotated clocks to a pair of further similar phase rotators that shift the four rotated clocks by plus and minus 22.5 degrees (pi/8 radians). The use of similar circuit blocks in each stage reduces design time. The octal clocks may be used for data capture in an oversampled clock/data (CDR) recovery system where the sampling frequency is twice that of the frequency of reference clock edges. The complementary rotations effected by the further rotators may optionally be variable.