Design and Comparative Study of Voltage Regulation-Based 2-Tap Flexible Feed-Forward Equalizer for Voltage-Mode Transmitters

Herein, the analog-based, 2-tap feed-forward equalization (FFE) voltage-mode transmitter using dual supply/ground voltage regulation is presented. In an FFE data modulator, the data are divided into transition and non-transition segments, and are transmitted to the main- and post-tap drivers. By using dual voltage regulation, flexible FFE strength adjustment is possible without process dependency, and the short-current path is eliminated, thus improving the overall energy efficiency. Furthermore, this structure with independent impedance calibration loops has good on-resistance and return loss characteristics, thereby securing signal integrity. In addition, by regulating the supply/ground voltages, the output swing and common-mode voltage can be adjusted independently. Therefore, our transmitter can serve multiple standards and channel environments with a single design. To verify the effectiveness of our method, we designed a prototype of the source-synchronous transmitter in a 65 nm CMOS process, and its performance was compared with that of a conventional FFE design. The simulation results show that the proposed design has better on-resistance, return loss, and FFE controllability, and it has an energy efficiency of 2.23 pJ/bit at 20 Gb/s.