Modified photodiode equivalent circuit model considering coplanar waveguide electrodes

Accurate equivalent circuit models can assist in better analyzing the performance of photodetectors. This study proposes a modified photodiode (PD) equivalent circuit model that considers coplanar waveguide (CPW) electrodes. First, the CPW electrodes of the PD are analyzed using high-frequency structure simulation software and advanced design simulation software. Skin effect occurs inside the electrode at high frequencies, increasing the PD loss and reducing the bandwidth. Subsequently, the extraction formula for the proposed model is derived, and the proposed model is compared with two conventional CPW electrode models. The proposed model effectively eliminates the frequency-dependency issue in the parameter extraction process of previous models, thereby demonstrating its accuracy. Furthermore, simulation and experimental results validate the reliability of the proposed model. Among the entire frequency band, the proposed model has good stability and a low error rate and can achieve excellent fitting with the measured results. Compared with previous studies, the average error rate is reduced by over 10%, demonstrating a significant improvement. Finally, the influence of the skin effect and high-impedance transmission lines on PD performance is analyzed and a viable approach to improve the bandwidth of PDs is proposed. The proposed model provides a viable approach to model and optimize CPW structures and is significant for the design of high-performance PDs.