A 66dBΩ 5 GHz and 44.88 √Hz/(pA·pW) Inductorless TIA in 65 nm CMOS

High-speed optical applications demand broadband transimpedance amplifiers (TIA) for efficient current-to-voltage conversion of photodiode signals. The inherent junction capacitance of photodiodes limits TIA bandwidth. This work proposes an inductorless design strategy for broadband CMOS TIAs. To mitigate the deteriorating effect of photodiode capacitance, a cross-coupled impedance negator integrated with an auxiliary amplifier to form the modified regulated cascode structure (RGC) is utilized at the input stage and, a capacitive degeneration stage is incorporated to improve the bandwidth. The TIA is designed for a high transimpedance gain of 66 dBΩ and is implemented in standard 65nm CMOS technology. The simulation results exhibit a -3 dB bandwidth of 5 GHz, input-referred noise current of 17.74 pA/√Hz, and power consumption of 3.2 mW. This design approach renders the TIA input insensitive to the input photodiode, exhibiting a stable frequency response over a range of photodiode capacitance from 50 fF to 300 fF.