Noise performance analysis of bipolar operational amplifier based on the noise matrix superposition expression

Noise analysis of an operational amplifier is not simple, because there are many noise sources inside the circuit. Usually, the equivalent input noise is calculated by superposition of individual noise sources inside the circuit, neglecting the correlation between noise voltage and current sources of the operational amplifier, or omitting the noise current source for a CMOS operational amplifier. Since the noise current source in a bipolar operational amplifier is larger than that in a CMOS operational amplifier, and it is correlated with the noise voltage source, the conventional method will introduce a significant error. The equivalent input noise matrix of an operational amplifier is presented, based on the noise matrix method. The benefits of the noise matrix superposition expression used in this method are that correlation between the noise voltage and current of an operational amplifier can be considered completely, and analysis of the noise contribution of an individual noise source inside the circuit to the equivalent input noise model can be obtained.