The key difference is that in AC analysis the signal generators are AC signal sources explicitly defined by the user whereas in noise analysis the signal generators are invisible noise sources attached to every noise-generating element in the circuit, such as to the resistor shown below:įigure 1: Noise model of a simple resistorĪdditionally, in AC analysis the AC signal source amplitude and direction are set explicitly by the user while in noise analysis the amplitude of the noise source is set through a formula representing the physical noise phenomena of the noise-generating element. The noise generators within the circuit are completely uncorrelated and therefore have no direction their additive effect on any circuit node is calculated in an RMS-manner. The mechanics are very similar to those of an AC analysis. Noise Analysis is a small signal analysis which is carried out at discrete frequencies using a linearized version of the circuit.
