A variable-threshold digitizer for photodiode arrays

A versatile digitizer circuit for a photodiode-array output has been developed. Because of a dual-threshold system, the circuit can compensate for the inadequate slew rate of the photodiode output amplifier. The adaptable nature of the thresholds provides a functional digitizer for pictures having slowly changing local characteristics. The adaptive nature of this digitizer is an essential feature for many biological slides such as those of liver cells because the stain density can vary considerably across the slide.