1. FIELD OF THE INVENTION
This invention relates generally to photodetectors and circuits for coupling the output of photodetectors to amplifiers, oscilloscopes, or other circuitry for sensing and analyzing light inputs to the photodetectors.
2. BRIEF DESCRIPTION OF THE PRIOR ART
Many analytical systems and instruments utilize a photodetector to convert light energy into electrical energy and the electrical energy is measured or analyzed to determine the characteristics of the impinging light beam. The emergence of optical systems in new technologies or existing technologies that have given designers capability of having higher speed systems and systems with higher bandwidth has generated a need for developing photodetectors and photodetector circuits that have higher capabilities in analyzing the light energy that impinges upon the photodetector.
In most systems for sensing small optical signals, the photodetector output is coupled to a suitable amplifier. The optimum amplifier design would depend upon the speed of the response needed. A requirement for high speed of response results in higher amplifier noise and therefore poorer sensitivity. A requirement for less speed of response allows lower amplifier noise and therefore better sensitivity. The selection of the amplifier that is optimized for speed or sensitivity causes some tradeoff balancing these two Parameters. If a slow signal and a fast signal are sensed at the same time by the same photodetector, the preamplifier is traditionally optimized for the faster signal while extra noise due to the wideband amplifier is tolerated in recovering the slow signal.
It is an object of this invention to provide circuitry which allows the derivation of signals from both sides of a photodetector so that two different requirements can be met simultaneously with the same photodetector.