A complete operational amplifier noise model: analysis and measurement of correlation coefficient

In contrast to the general operational amplifier (op amp) noise model widely used, we propose a more complete and applicable noise model, which considers the correlation between equivalent input voltage noise source e_n and current noise source i_n. Based on the super-position theorem and equivalent circuit noise theory, our formulae for the equivalent input noise spectrum density of an op amp noise are applied to both the inverting and noninverting input terminals. By measurement, we demonstrate that the new expressions are significantly more accurate. In addition, details of the measurement method for our noise model parameters are given. A commercial operational amplifier (Burr-Brown OPA37A) is measured by means of a low-frequency noise power spectrum measuring system and the measured results of its noise model parameters, including the spectral correlation coefficient (SCC), are finally given