The Amplitude Responses of the Basic Connection Circuit of a Differential Difference Operational Amplifier in Analog Sensor Interfaces with Nonlinear Input Stages

The nonlinear modes of operation of the analog interface based on a differential difference operational amplifier (DDA), which is designed to process the sensor signals in automation devices and robotics, are investigated. The main versions of approximation of the transfer characteristics (TC) and derivatives of the corresponding functions for differential input stages (DS) of DDA (piecewise linear characteristic, hyperbolic tangent, integral polynomial function (IPF)) are considered. It is established that the approximation of the TC in the form of continuous IPF is the most universal and can be recommended for describing the DS properties in the structure of the DDA on small and large signals with different types of transistors (CMOS, JT, JFet). Mathematical analysis and computer simulation shows that the nonidentity of parameters of the input DS to the DDA and the low voltages of the TC limitation have a significant impact on the linearity of the amplitude response of the basic connection circuit of the DDA. The obtained results are recommended to be used not only when creating DDAs of new generation, but also when evaluating nonlinear distortions and fast response in analog devices of automation and computer technology with differential stages.