A transmission-line approach for modeling feedback resistors in integrated transimpedance amplifiers

Based on the transmission-line model, the grounded uniformly distributed RC line (URC) is used to investigate the behavior of the feedback resistor used in transimpedance amplifiers (TIAs). Due to their strong capacitive coupling to substrate ground, polysilicon resistors used in the feedback circuit contribute to the frequency response of the overall amplifier. This may result in limitations in bandwidth, signal distortion and even instability. A simple and descriptive model is derived to find design formulas to optimize the overall amplifier including its feedback capacitor and to show an upper performance limit for an idealized amplifier with high gain. Simulation results based on the approximation model and on the exact URC model are delivered for both an idealized as well as for a real amplifier.