Hey guys,
I try to verify with a simple SH block the kT/C noise equation using PSS and PNoise analysis with SpectreRF.
I use a simple MOS switch and a 800fF capacitor, see attached file. (Thus I assume at room temperature 71.9uV noise.)
The switch has an on-resitance of <100Ohm.
I follow the guidelines in
http://www.designers-guide.org/Analysis/sc-filters.pdfI adjust the maxacfreq and nr of sidebands (200) such that the error is fairly small.
In order to get the sampled noise power I use the time domain Pnoise simulation as proposed.
But dependend on the switch resistance I got different noise voltages.
Typically I obtain 44-48uV instead of 72uV!?
Where is my mistake? What I have to change in the setup.
Thanks much for you help!
Friedel
PS I notice that if I decrease the cap size below a certain value ca. 50f Spectre terminates with an error!
See below!
......
Order 2 used in 54 subintervals.
Order 8 used in 3 subintervals.
Order 10 used in 1 subintervals.
Order 16 used in 314 subintervals.
Conv residual norm = 1.56e-06.
Conv solution-change norm in fdtd = 211e-09.
Number of refinements using multi-interval Chebyshev polynomial spectral algorithm = 1. Total steps = 5166
MIC-PSA finite-difference refinement finished, took 420 ms.
pss: The steady-state solution was achieved in 4 iterations.
Number of accepted pss steps = 5166.
Total time required for pss analysis `pss' was 2.86 s.
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Periodic Noise Analysis `pnoise': freq = (100 kHz -> 100 MHz)
*************************************************************
Using the operating-point information generated by PSS analysis `pss'.
Working on time-domain noise timepoint 1 of 1 (time=0).
Internal error found in spectre at freq = 100 kHz during PNoise analysis `pnoise'. Please run `getSpectreFiles' or send the netlist, the spectre log file, the behavioral model files, and any other information that can help identify the problem to support@cadence.com.
Assertion failed in file `qptv_qpnoise.c' at line 1471.
Assertion failed.