A 40Gb/s PAM4 Transmitter with 3-tap FSE for Serial Link System

This paper presents a 40Gb/s PAM4 transmitter with a 3-tap fractionally-spaced equalizer (FSE) in 65nm CMOS technology. In order to improve the signal quality, a FSE instead of a symbol-space equalizer (SSE) is realized. In addition, the nonlinearity between the high and low bit output current is reduced by employing low-voltage cascode current source. Post simulation result shows that by boosting the high frequency components effectively, PAM4 signals with clear eye-diagram can be obtained at receiver for a channel with 6.45 dB attenuation @10 GHz. The minimum vertical and horizontal opening of the eye diagram is about 154 mVpp and near 0.6UI. The total area of the transmitter is about 705μm × 495μm including I/O pads and the power consumption is about 72mW under 1.2V power supply.