Transimpedance amplifier for LGAD noise measurements: design and characterization

A wideband low-noise transimpedance amplifier (TIA) is designed for the measurement of the noise power spectral density (NPSD) of the current of low-gain avalanche diodes (LGADs). The design focuses on minimization of system background noise and maximization of operating bandwidth. The diffusive line effect of the high value resistor used in the feedback network has been analyzed, and a compensation of its effect has been implemented. With a transimpedance of 200 MΩ, a background white noise of 9.5 fA/√(Hz) and an input current dynamic range up to 20 nA are achieved. The useful bandwidth ranges from 1 kHz up to 3 MHz depending on the noise level to be measured. An effective method for calibrating the system and measuring its transfer function with high accuracy over the full bandwidth is described. The designed TIA enables an accurate characterization of LGADs noise, which is a crucial step for the technology qualification and for the prediction of the performance of these devices as radiation and particle detectors.