PERFORMANCE OF TRANSFER RESISTANCE AMPLIFIERS WITH CAPACITIVE SOURCES IN OPTICAL APPLICATIONS

Transfer resistance amplifiers using standard operational amplifiers are often employed when moderate bandwidths and low noise are required from capacitive current sources, such as photodetectors for optical imaging and the samples which are used in the OBIC and EBIC techniques of semiconductor microscopy. Analytic design equations are derived that predict bandwidth and noise performance as a function of source capacitance and allow the selection of the most suitable amplifier for specified conditions. Both the noise performance and frequency response will change if the source capacitance departs from its design value, as it will when the reverse bias on a photodiode is altered, and the significance of these changes is calculated. Results from specific design examples, based on standard low-noise operational amplifiers, are discussed.