CMOS adaptive TIA with embedded single-ended to differential conversion for analog optical links

A variable gain transimpedance amplifier (TIA) is presented featuring single-ended to differential conversion by means of negative feedback. The proposed topology also ensures stability when amplifier gain is varied. Furthermore, effective input capacitance of the TIA is reduced by using a positive capacitive feedback. The circuit is intended for intermediate frequency (IF) over fiber systems, but can be readily adapted for other applications. When simulated with a photodiode capacitance of 1.4 pF, the TIA exhibits a tunable gain range of 51 to 73dBΩ with a bandwidth of 550 MHz. The circuit designed in a standard 65nm CMOS process consuming 4mA from a 1.2V supply, achieves a spurious free dynamic range (SFDR) of 109dB·Hz^2/3 at 100 MHz.