Auto-tracking Method with Optimal Reference Voltage for PAM-4 Receiver

This paper presents an auto-tracking method with an optimal reference voltage for a PAM-4 receiver. The auto-tracking optimal reference voltage circuit includes a center detector and a counter circuit that automatically finds optimal reference voltage directions in additions, three samplers, and a phase interpolator (PI) used in the existing normal operation of PAM-4. The key feature of the proposed circuit is to find a direction of the reference voltage of three samplers in a PAM-4 receiver and apply the final determined reference voltage of the sampler in normal operation. The circuit is implemented in 40-nm CMOS technology, and the area added to the existing PAM-4 receiver for finding reference voltage operation is 30x100 um². The simulated proposed circuit consumes an average power of 221uW with a 4-GHz auto-tracking sampling clock.