Inductorless bandwidth extension using local positive feedback in inverter-based TIAs

This paper investigates an inductorless technique for bandwidth extension which uses local positive feedback in an optical receiver front-end based on an inverter-based transimpedance amplifier and Cherry-Hooper post-amplifiers. Small feedback inverters create negative resistance that boosts the output resistance of inverter-based amplifiers. Compared to a reference design having a TIA and a three-stage post-amplifier, the addition of equal local positive feedback, while keeping the gain unchanged at 85.8 dB, increased the bandwidth from 12.4 GHz to 18.3 GHz and the vertical eye opening by 8% at 26 Gb/s. The noise performance degraded from 9.67 pA/√Hz to 10.66 pA/√Hz, while power consumption increases minimally. Unequal positive feedback on each post-amplifier, while keeping gain and bandwidth unchanged, further improved performance. Guidelines for sizing the feedback inverters are given.