First‐Order Opamp Integrator and Differentiator Circuits

Summary

This chapter presents basic opamp integrator and differentiator circuits, which have a long history in analog circuits including analog computers. It starts with an RC integrator circuit, which shows how a series capacitor can integrate a signal current source. The chapter discusses the calculation of the step response of a series RC circuit. An opamp integrator circuit integrates a current over time to get voltage for capacitor voltage in terms of current. The chapter discusses the properties of an ideal opamp model: input voltage is zero, input current is zero, and the output voltage is whatever it needs to be to keep the input voltage equal to zero. The output voltage of the opamp differentiator circuit is proportional to the derivative of the input voltage. The chapter discusses the derivation of the behavior of the ideal opamp differentiator circuit by considering Kirchhoff's current law for the currents entering the voltage node.