Macromodelling operational amplifiers

Abstract

In order to utilize low voltage operational amplifiers in system designs macromodels are required. The specific parameters of low-voltage operational amplifiers are not modelled correctly in the existing macromodels. In this paper a new macromodel is presented for low-voltage bipolar opamps which is able to model the characteristics accurately. Rail-to-rail behavior is modelled at the input as well as at the output. The class AB behaviour of the output stage is modelled accurately together with the frequency characteristic of its output impedance by means of the nested Miller structure. The macromodel which is developed and presented in this paper is used to model the low-voltage operational amplifier NE5234 which is available on the market. However the model can also be used for other low-voltage opamps by means of changing the parameters of the macromodel. >