Application of FEI's in Temperature Compensation of DC Amplifiers

Expressions for biasing ajunction FET at zero temperature coefficient are derived and checked experimentally. Heating over a wide range of temperature at a fixed bias in this region will show both positive and negative coefficients of a very small value. This property is utilized in the design of a simple dc amplifier in which good overall drift performance is obtained by using a FET biased for nearly zero drift in the first stage. The FET bias is adjusted to provide a drift in the proper direction to compensate for the drift in the main amplifier. An overall drift of less than 20 μV/C° has been obtained when the gain is about 100. The complete circuit is described and the adjustment procedure is outlined.