> Thinking about it this way,

> I would have to agree with an integration range from 0 to f0.

> If we were only to cover half that range,

> we would neglect the portion that occurs at negative frequencies

> (and also folded to the range f0/2 - f0).

No, integration range has to be from 0 to PSSfund/2.

Since PSD of Spectre is 1-sided view spectrum

which is twice of 2-sideded view spectrum.

For example, integration range is from 0 to fmax

for normal noise analysis. This is because PSD is 1-sided view.

Here you don't have to integrate from -fmax to +fmax.

Cadence will revise TDnoise explanation in SpectreRF manual soon.

You will see the reason why both analysis range and

integration range are from 0 to PSSfund/2.

If you integrate from 0Hz to PSSfund,

then you will include the same noise many times,

so an integral range should be limited to 0Hz~PSSfund/2.

About noise folding, see below.

(3) Folding and Alias.

When inputing noise into a linear time periodic varying (LTPV) system,

because of frequency translation, the output noise at f has contribution

from input noise at f+n*PSSfund (-infinity<n<+infinity).

This is noise folding. It is physical.

When sampling the above output noise from LTPV at t0+n*T, and do

PSD for it, the PSD repeats every PSSfund.

This is aliasing. It is not physical.