Application of MOSFET's in the temperature compensation of DC amplifiers

A new application of metal oxide silicon field-effect transistor (MOSFET) devices is presented for solving the problem of drift in the characteristics of DC amplifiers under the effect of temperature variations in the range of 20-75°C. Expressions for the bias voltages and drain currents for operation at zero temperature coefficient for linear and nonlinear devices were derived. The validity of the derived expressions was checked experimentally for various samples of MOSFETs. These expressions were used to design the MOSFET stage to compensate for the drift of the DC amplifier. The amplifier has proved to be very reliable and can be adjusted for practically zero drift over a narrow band of temperatures. The drift was about 40 μV/°C over the range of 20-75°C and about 10 μV/°C over the range of 50-70°C. The 3-dB point in the frequency response is about 1.7 MHz. The overall gain is about 750 and the amplifier is capable of supplying a peak-to-peak output voltage of 3.0 V.