Stability analysis and improvement of transimpedance amplifiers for precision optical sensing

Transimpedance amplifiers (TIAs) are essential for converting weak photocurrents in precision optical sensing, yet concurrent demands for bandwidth, gain, and low noise often induce instability. Existing literature lacks comprehensive stability analysis incorporating parasitic effects and load capacitance. This work derives, for the first time, complete analytical expressions for noise gain, loop gain, and closed-loop gain that explicitly include input parasitic capacitance (C_ip), feedback path additional capacitance (C_fa), op-amp output resistance (R_o), and load capacitance (C_ol). The individual and combined impacts on phase margin are rigorously quantified. Simulations using OPA817 validate the theory, identifying R_o-C_ol interaction as the primary instability driver. To mitigate these effects, T-type capacitor and resistor networks are analyzed for suppressing C_fa effects. Two stabilizing resistor (R_st) placements, external and internal to the feedback loop, are compared. Results demonstrate that the external R_st configuration robustly suppresses C_ol effects across a wide load range, while the internal configuration is unsuitable for high-performance TIAs. Experimental validation on printed circuit boards confirms that the external R_st design operates stably, whereas the internal configuration exhibits destructive oscillation. This work provides crucial design guidelines and compensation strategies for reliable, high-performance TIAs.