Photodiode Does Position Sensing

Using a quadrant silicon photodiode with a total active diameter of 7.89 mm for a total active area of 50 mm2, QD50-0-SD photodiode has each quadrant connected to a transimpedance amplifier with a gain of 10,000 ohms, with higher gains available. The width of the quadrant separator is 0.2 mm with smaller separations available. The circuit contains all of the amplifier elements needed to provide the sum of the outputs of all four quadrants and difference outputs-the latter consist of the upper minus lower quadrants and the left minus right quadrants to make this circuit combination well-suited for light beam nulling and position applications. The circuit requires ±15V supply and draws less than 50 mA in its quiescent state.