NF band

NF – Noise Figure Meter, must be used in transient mode.

As known, the noise sources can be described by a summation of distinct sinusoids in the

following form:

where Ω s is noise sideband frequency, Ω0 is the fundamental frequency. To carry out noise analysis, the circuit is perturbed around the noiseless steady-state solution. Then a perturbation equation is obtained. Since envelope transient treats an arbitrary signal in the form of time varying phasor (amplitude, phase and frequency), the noise perturbation is considered as one of the modulation signals. Solving the perturbation equation, one gets the carrier referred amplitude perturbation and the total phase perturbation in the time domain. Then the frequency spectrum of above perturbations are obtained through Fourier transform, and the corresponding AM noise and PM noise can be easily computed. With envelope transient method, one has a direct access to the amplitude and phase modulation, so the AM and PM noise can be explicitly separated. In addition, the absolute voltage noise spectrum can also be calculated by solving the above perturbation equation.

Then it is possible to calculate the Noise in the bandwdth of interest and to obtained the NF value.