A new differential CMOS current pre-amplifier for optical communications

This paper presents a new low-voltage fully differential CMOS current-mode pre-amplifier for optical communications. The number of transistors between the power and ground rails is minimum so that the minimum supply voltage is only V_T + V_sat. The pre-amplifier is a balanced two-stage configuration such that the effect of bias-dependent. mismatches is minimized. This configuration also achieves wide bandwidth and high current gain with reduced power consumption and transistor sizes. To lower the input impedance and increase the bandwidth, a new differential current-current negative feedback is introduced. In addition, a current-current common-mode feedback is employed to increase the common-mode rejection ratio (CMRR). The pre-amplifier is designed using a 0.18 μm 1.8 V CMOS technology. Simulation results from SPICE demonstrate that with a 0.5 pF photo diode capacitance, the pre-amplifier provides 31 dB current gain or equivalently 65 dB trans-impedance gain at 2.53 GHz.