An integrated position sensor using JFETs as a buffer for PSD output signal

Abstract

Abstract A novel compact integrated linear position sensor has been developed. The sensor chip, fabricated by bipolar IC technology, includes a PSD and its peripheral circuitry. In order to eliminate the dependence of the position signal on light intensity, the difference of the two output currents of the PSD was divided by their sum using a simple conversion circuit of a differential pair of NPN transistors. JFET buffers were incorporated to reduce conversion error caused by the input current of the transistors. A leakage current canceller with an optically shielded PSD was also integrated on the same chip. The output characteristics were measured and the nonlinearity was less than 1% over the temperature range −20-+100 °C.