===Noise Test===
The Noise Test analyzes the device-generated noise over a range of frequencies. For this test you provide an input source, an output port and a range of frequencies. [[B2RF.Spice A/D]] calculates the noise contributions of each device (and each noise generator within each device) to the output port voltage. The program also calculates the equivalent to the output noise referred back to the specified input source. This is what is meant by the "Input Noise". The calculated value of the noise over the specified range of frequencies corresponds to the spectral density of the signal viewed as the square root of a stationary Gaussian stochastic process. After calculating the spectral densities, the simulator integrates these values over the frequency range to arrive at the total noise voltage/current over this frequency range. This calculated value corresponds to the variance of the circuit variable viewed as the square root of a stationary gaussian process.
As for the specific noise sources, they include the "shot" noise associated with the DC currents in semiconductor devices and the "thermal" noise associated with resistance. Semiconductors also display "flicker" (1/f) noise. However, due to the lack of a unified model, [[B2RF.Spice A/D]] handles this type of noise on a "case by case" basis. There are flicker noise [[parameters]] available for transistors in the list of model [[parameters]]. The program can also provide the noise gain associated with the 1/f source.
The [[parameters]] of the noise test are specified using the setup dialog of the Test Panel. The input noise source can be either a voltage or current source, which you can select from the drop-down list labeled "Noise Source". The output port must be specified as a pair of node numbers, the "Output Node" and the Reference Node". The rest of the [[parameters]] specify the frequency interval over which the noise analysis will be performed. They are similar to an AC analysis. If you check the checkbox labeled "Include Noise Generator Contributions", then noise contributions of all the individual devices will be shown as well. If not checked, the input noise and output noise will be shown only.