A 4×106 Gb/s Mixed-Signal PAM-4 Transceivers for Optical Direct-Detect Applications With Adaptive Linearity Compensation in 28-nm CMOS

Optical transmission has been widely employed in data-centers, but the complex impairments including the non-linearity induced by the laser modulator degrade the signal. Conventional optical modules use DSP-based transceivers to address these impairments, but they rely on advanced technology, consuming much power and area as well. A 4x106Gb/s mixed-signal PAM-4 transceivers fabricated in 28nm CMOS are proposed in this work to reduce cost, area and power consumption. The transceiver supports adaptive linearity compensation with analog PAM4 level pre-distortion technique in TX. 4-tap FFE and 7-tap DFE including 4 floating taps are implemented in RX to take DFE’s advantage of not amplifying noise thanks to the mixed-signal structure. The transceiver achieves an optical sensitivity of -8.7dBm, which is 0.7dBm better than the DSP-based equalization methods under the same optical test environment. The energy efficiency and single-channel area are 4.42pJ/bit and 0.28mm2 respectively, both of which are better than reported 100Gb/s counterparts.