Optimum noise filter for d.c. measurements
P. R. Samways · Journal of Physics E Scientific Instruments · 1968
A circuit is described for filtering the noise from a photomultiplier d.c. output current. The filter is of conventional RC low-pass type, but with a time constant which increases linearly with time, giving the filter the characteristic of an integrator. This is accomplished by exploiting the resistance-time characteristic of a photo-conductive cell on being plunged into darkness after brief exposure to light.