Abstract
AbstractIn electronic measurement, industrial measurement, medical instrumentation and industrial control, there are several practical problems in dc amplifier characteristics such as initial offset voltage, temperature drift, time drift, noise and input bias current. In some applications, a dc amplifier with a good long‐term stability is required. This paper presents a method for realizing a dc amplifier suitable to these applications. After characteristics of the components used are matched as much as possible, a thermal feedback is introduced that suppresses the effect of the ambient temperature fluctuation. First, a model of the system is introduced and the thermal coupling stage of the first stage affecting the drift is analyzed so that the parameters necessary for suppression of the temperature drift are obtained. Next, this model is used for derivation of the degree of suppression of the drift by the present method. A method of selecting the parameters and a design procedure are discussed. It is found that the temperature drift can be suppressed by 40 dB at an extremely low‐frequency range in the test amplifier and the temperature coefficient is 0.36 μV/°C. At specific frequencies, the improvement is 16 dB at 0.27 mHz and 10 dB at 0.6 mHz.
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