| abstract |
An optical operational amplifier is disclosed. The operational amplifier has a first photodiode with an anode and a cathode. A second photodiode with an anode coupled to the cathode of the first photodiode, and an anode coupled to the cathode of the first photodiode to form an output terminal. A resistor is coupled in parallel with the first and second photodiodes. The inputs to the operational amplifier are light sources which generate different currents in the first and second photodiodes. The output voltage from the output terminal is a function of the difference in currents across the first and second photodiode. The output voltage is amplified in proportion to the value of the resistor. The basic optical operational amplifier configuration may be used in a variety of useful circuits. One example is the use of the amplifier in a position sensing device which determines position of a light beam by the output of photodiode sensing elements. A second example is the use of the operational amplifier in a retinal stimulator device. The output waveform of the operational amplifier may be shaped by the resistor and added capacitative elements to be more compatible with retina cells. |