Phase interpolator linearity through adjustments to unit current step

An apparatus comprising:

• means for driving a differential output of a phase interpolator, including a plurality of source-coupled transistor pairs configured to receive different phase shifted versions of an input signal, each source-coupled transistor pair being coupled to the differential output of a phase interpolator;
• and
• means for supplying a tail current to one or more source-coupled transistor pairs in the plurality of source-coupled transistor pairs, including a plurality of current sources, each current source being configured to supply a portion of the tail current at a level defined by a codeword that is configured based on total tail current supplied to the one or more source-coupled transistor pairs,
• wherein step changes in amplitude of the tail current occur in response to incremental changes in the codeword, wherein the step changes in amplitude vary with the amplitude of the tail current, and wherein an amplitude of step changes in the tail current corresponds to a unit current level when a value encoded in the codeword lies within a first range of values, is decreased by a first fraction of the unit current level when the value encoded in the codeword lies within a second range of values, and is increased by a second fraction of the unit current level when the value encoded in the codeword lies within a third range of values.

A method for operating a phase interpolator, comprising:

• receiving different phase shifted versions of an input signal at a plurality of source-coupled transistor pairs, a differential output of each source-coupled transistor pair being coupled to a differential output of the phase interpolator;
• and
• configuring a current source to supply a portion of a tail current to one or more source-coupled transistor pairs in the plurality of source-coupled transistor pairs at a level defined by a codeword that is configured based on total tail current supplied to the one or more source-coupled transistor pairs, the current source being one of a plurality of current sources,
• wherein step changes in amplitude of the tail current occur in response to incremental changes in the codeword, and wherein the step changes in amplitude vary with the amplitude of the tail current, and wherein an amplitude of step changes in the tail current corresponds to a unit current level when a value encoded in the codeword lies within a first range of values, is decreased by a first fraction of the unit current level when the value encoded in the codeword lies within a second range of values, and is increased by a second fraction of the unit current level when the value encoded in the codeword lies within a third range of values.