Efficient phase encoding for clock recovery

A phase interpolator for interpolating four input clock signals phase-offset by 90 degrees to span 360 degrees, the phase interpolator comprising:

• two primary mixer to each interpolate between a pair of the input clock signals by:
• adjusting a phase value based on most-significant-bit (MSB) thermometer bits;
• and
• adjusting the phase value based on least-significant-bit (LSB) thermometer bits and LSB binary bits;
• and
• two secondary mixers to each interpolate between a pair the of input clock signals by:
• adjusting a phase value based on MSB thermometer bits and boundary bits;
• and
• adjusting the phase value based on LSB thermometer bits and LSB binary bits;
• and
• wherein each primary and secondary mixer:
• generates a first output clock signal at the phase value of the respective mixer;
• and
• generates a second output clock signal offset from the first output clock signal by 180 degrees,
• thereby generating eight output clock signals phase-offset by 45 degrees to span 360 degrees.

A method for controlling a phase interpolator to interpolate four input clock signals to generate eight output clock signals, the four input clock signals being phase-offset from each other by increments of 90 degrees to span 360 degrees, each of the eight output clock signals being phase-offset from each other by increments of 45 degrees to span 360 degrees, the phase interpolator comprising two primary mixers and two secondary mixers, the method comprising:

• generating a mixed thermometer-binary phase interpolator code configured to cause the generation of a first output clock signal of the eight output clock signals by a first one of the primary mixers, and to cause the generation of a second output clock signal of the eight output clock signals by a first one of the secondary mixers, a phase value of the second output clock signal being offset from a phase value of the first output clock signal by 45 degrees;
• and
• transmitting the mixed thermometer-binary phase interpolator code to the phase interpolator,
• wherein:
• the first one of the primary mixers determines the phase value of the first output clock signal by:
• interpolating between a pair of input clock signals of the four input clock signals based on a mixed thermometer-binary phase interpolator code by:
• adjusting the phase value between phases of the pair of input clock signals by a number of steps based on a plurality of most-significant-bit (MSB) thermometer bits of the mixed thermometer-binary phase interpolator code;
• and
• adjusting the phase value by a number of half-steps based on at least one least-significant-bit (LSB) thermometer bit and at least one LSB binary bit of the mixed thermometer-binary phase interpolator code;
• and
• the first one of the secondary mixers determines the phase value of the second output clock signal by:
• interpolating between a pair of input clock signals of the four input clock signals based on the mixed thermometer-binary phase interpolator code by:
• adjusting the phase value between phases of the pair of input clock signals by a number of steps based on a plurality of MSB thermometer bits and a plurality of boundary bits of the mixed thermometer-binary phase interpolator code;
• and
• adjusting the phase value by a number of half-steps based on at least one LSB thermometer bit and at least one LSB binary bit of the mixed thermometer-binary phase interpolator code.