Phase interpolator and method of phase interpolation with reduced phase error

A method of phase interpolation comprising:

• providing a first, a second, a third, and a fourth differential pair each including a first and a second transistor having sources coupled with each other to form a source coupled node;
• providing a plurality of current sources;
• supplying a first operating current to the source coupled node of a first selected one of the first and second differential pairs and a second operating current to the source coupled node of a second selected one of the third and fourth differential pairs by switching connection between the source coupled nodes of the differential pairs and the plurality of current sources;
• inputting a first input signal having a first phase and a second input signal having a second phase opposite to the first phase to gates of the first and second transistors, respectively, in the first differential pair;
• inputting the second input signal and the first input signal to gates of the first and second transistors, respectively, in the second differential pair;
• inputting a third input signal having a third phase between the first and second phases and a fourth input signal having a fourth phase opposite to the third phase to gates of the first and second transistors, respectively, in the third differential pair;
• inputting the fourth input signal and the third input signal to gates of the first and second transistors, respectively, in the fourth differential pair;
• outputting a differential output signal from a first and a second output node, which are formed by commonly connecting drains of the first transistors in the differential pairs to a first load resistor and by commonly connecting drains of the second transistors in the differential pairs to a second load resistor, respectively;
• and
• reducing an amplitude of voltage fluctuation at the source coupled node of each of the differential pairs by connecting a stabilizing capacitor between the source coupled nodes of each of the differential pairs and a reference voltage.