Hewlett-packard Company

Stefan Rohrer

Hubert Kuderer

A photodiode array comprises a plurality of n channels, each channel having a photodiode which is reverse biased such that it acts as a current source. Each channel further comprises an A/D converter for providing a digital output signal (DATA) which is representative o the photo current (Iph) provided by the photodiode and therefore of the intensity of the light impinging on the photodiode. The A/D converter comprises a controllable current source, an integrator circuit, a comparator for comparing the output signal (Vout) of the integrator with a predetermined signal (Vthreshold), a logic circuit for controlling the current source in response to the output signal (Vcomp) of the comparator such that Vout is kept within a certain range. Preferably, the current source provides current in the form of charge dumps to and/or from the integrator. The number of dumps in one direction is counted by a counter and is a digital measure of the photo current (Iph). The photodiode array is particularly useful in spectrophotometers since the provision of a separate A/D converter for each channel allow simultaneous processing of all the photosignals in the array so that spectra distortions arising from time delays in processing the photosignals are avoided.

Growing community of inventors

Schramberg, Germany

Stefan Rohrer