Power and Area Efficient Transimpedance Amplifier Driving Large Capacitive Loads Based on Modified RGC Structure

Abstract

In this brief, an additional modification to the modified regulated cascode (RGC) transimpedance amplifiers (TIA) is applied which can greatly improve the bandwidth when the TIA has to drive a relatively large capacitive load. The cross-coupled input stage of the modified-RGC TIA is utilized as a negative capacitance converter without employing any additional active circuit and by only using an extra compensation capacitor. The method is cost-effective with no extra power budget and with very low area headroom. To confirm the efficiency of the technique, two modified-RGC TIA with and without the proposed technique are designed in a standard 0.18 $\mu \text{m}$ CMOS process. Post-layout simulation results with a 250 fF photodiode capacitance and a 120 fF loading capacitance show that the bandwidth without and with a compensation capacitor of 90 fF are 1.2 GHz and 3.7 GHz, respectively. The power consumption (of both cases) is about 3 mW and the area is $15\,\,\mu \text{m}\,\,\times $ 27 $\mu \text{m}$ , which is increased by about 56% compared to the conventional one.