Inductor-less bandwidth-extension technique applied to CMOS differential trans-impedance amplifier

Abstract

To achieve a large bandwidth without inductor peaking, this work presents an inductor-less bandwidth-extension technique to establish Multi-Level Active Feedback (MLAF) structure that is used in a CMOS differential Trans-Impedance Amplifier (TIA). The proposed TIA consists of a trans-impedance stage, a low-pass filter, a gain stage, and an output buffer. The trans-impedance stage adopts the regulated cascode structure. In the gain stage, the MLAF structure which has four cascaded amplifiers and three active feedbacks in a hierarchical feedback topology is employed to effectively increase the bandwidth under a Butterworth response without inductor. The TSMC 0.18μm CMOS technology was used to implement the proposed differential TIA with a core size of 0.05mm 2 . Without the use of inductor peaking to enlarge the bandwidth, the proposed TIA was measured to have a bandwidth of 7.2GHz, a differential trans-impedance gain of 1.8kΩ and a minimum input sensitivity of 25μA at a bit error rate of 10 -12 under 2 31 -1 PRBS. Comparing with conventional TIAs, the proposed TIA apparently exhibits a low hardware cost and fairly good performance for applications of 10Gbps optical communications.