A 56Gbps PAM-4 optical receiver front-end

A 56Gbps PAM-4 optical receiver front-end is presented. In order to reduce the input-referred current noise of the receiver front-end, the shunt feedback resistor Rf of the TIA is enlarged. And, the equalizer is inserted to boost the high-frequency gain and extend the bandwidth. The AGC amplifier using the proposed dB-linear VGAs is further to lower the noise. This PAM-4 optical receiver front-end is fabricated in a 40 nm CMOS process. Its power is 120mW from a supply of 1.2V excluding the output buffers. Its core area is 0.21mm
²
.