Low-noise current preamplifier for photodiodes with DC-current rejector and precise intensity meter suited for optical light spectroscopy

A low-noise large dynamic-range current preamplifier for photodiode current signals is presented. The circuit is equipped with a smart device for automatic removal of the DC current of the photodiode. This device sinks away the exact amount of DC current from the preamplifier input, yielding auto zeroing of the output-voltage offset, while introducing the minimum electronic noise possible. As a result the measurement dynamic-range is maximized. An auxiliary inspection point is provided which precisely tracks the DC component of the photodiode current. This auxiliary signal may be used for precise beam alignment and diagnostic purposes. The excellent gain stability and linearity make the circuit perfectly suited for optical-light pulse spectroscopy. Applications include two-dimensional characterization of semiconductor detectors, ultra-precise characterization of laser beam stability, particle sizing in the 100 nm range, confocal microscopy.