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In this paper, we propose a method to fully characterize noise in operational amplifiers (op-amps). The method allows the extraction not only of the spectra of the equivalent input current noise (EICN) and equivalent input voltage noise generators but also of their cross-correlation coefficients, which are routinely discarded in noise analysis of op-amps. The method is applied to extract all noise parameters of the low-noise bipolar-input op-amp OP27 and is validated through noise measurements in a test circuit. A key finding is that neglecting the cross-correlation coefficient between the two EICN generators can lead to severe errors in noise analysis.