Ken Kundert
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When running SpectreRF's PNoise analysis within Artist, the environment provides a "Phase Noise" button as part of its direct-plot capability. The label on this button is misleading, which has caused a substantial amount of user confusion.
It is important to know that when you press this button you are actually plotting the normalized voltage noise, or L, and not the phase noise (this is why the result has units of dBc). This function was added when we added support for oscillators. Oscillator designers use L as a way of characterizing the phase noise of their oscillators. This works because for oscillators the phase noise dominates, especially close to the carrier, and so they need not distinguish between phase noise and voltage noise. Furthermore, in oscillators the values of L and Sphi (the phase noise) are actually the same in most cases, which adds to the confusion.
However, problems arise when engineers who are not designing oscillators use the phase noise direct plot function thinking that this function is decomposing the total noise into amplitude and phase noise components and plotting only the phase noise. It is not doing that. Rather it is plotting L = Sv(df)/V12, where Sv is the power spectral density of the voltage at an offset frequency of df and V1 is the amplitude of the fundamental. Thus, it is plotting the noise power normalized to the power of the fundamental.
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