I understand your situation.
In your case, QPSS is also not suitable.
You should use Envelope Analysis with fudamental frequency of 1/(20*Tclk).
Envelope Analysis of Agilent ADSsim and GoldenGate support small signal noise analysis.
I recommend you to use RFDE2008U2 or GoldenGate-4.3.0. GoldenGate-4.3.0 is more recommended since convergence is very robust.
But GoldenGate-4.3.0 might not be suitable for your purpose.
So you might have to use RFDE2008U2 not GoldenGate-4.3.0 since we can't evaluate Time_Averaged_Noise_Power_Density(freq).
http://eesof.tm.agilent.com/products/goldengate_main.html#whats_newBy using these simulators, you can observe small signal noise Noise_Power_Density or Noise_Power around any harmonics you specify.
RFDE2008U2 calculates
Time_Averaged_Noise_Power_Density(freq).
GoldenGate-4.3.0 calculates
Ensemble_Averaged_Noise_Power(time).
So you can observe time behavior of small signal Noise_Power by using GoldenGate-4.3.0.
This is a little similar to Pnoise/TDnoise Analysis of Cadence Spectre where Ensemble_Averaged_Noise_Power_Density(time,freq) is evaluated.
About monte carlo type noise analysis similar to transient noise analysis, it is also available in Envelope Analysis of RFDE2008U2.
But it is not available in Envelope Analysis of GoldenGate-4.3.0.
Although you can evaluate small signal transfer function by using Envelope Analysis of RFDE2008U2, you can not evaluate it by using Envelope Analysis of GoldenGate-4.3.0.
Envelope Analysis of GoldenGate-4.3.0 doesn't support small signal analysis although it supports small signal noise analysis.
But you might be able to evaluate a transfer function by using two tones Envelope Analysis of GoldenGate-4.3.0 where one is N*1/(20*Tclk), the other is small input signal tone.
I don't know whether Envelope Analysis of Cadence Spectre supports small signal noise analysis although it can calculate AC charactersitics at specific envelope time.
http://www.cadence.com/Community/blogs/rf/archive/2009/01/14/tip-of-the-week-mms...