A low-noise analog front-end circuit (AFE) was designed using UMC 28 nm CMOS technology for optical receivers operating at 80 Gbit/s PAM4. To address the tradeoff between the noise and bandwidth, we adopted a trans-impedance amplifier (TIA) cascaded continuous time linear equalizer (CTLE) and input inductor peaking. A VGA with trans-conductance and a trans-impedance (gm-TIA) structure was adopted to effectively control the low-frequency gain and further expand the bandwidth. The circuit achieves a trans-impedance gain of 48.5 dBΩ, a bandwidth of 36.1 GHz, an average equivalent input current noise of 22.6 pA/Hz, and a power consumption of 14.5 mW, under the conditions of an input capacitance of 100 fF and a supply voltage of 1.2 V.
