eldo_user

Setting Up An Analysis
Transient Noise Analysis
When a .NOISETRAN simulation is requested with multiple run MRUN specified, transient
analysis extracts (or extracts without any analysis type) will by default return only nominal
values in the .chi file. Specify option DEFRMSNTR to dump both RMS values (computed by
the transient noise analysis) and nominal values (computed by the nominal transient analysis).
Use the analysis type NTR on the .EXTRACT command to select computation based on RMS.
If a single-run .NOISETRAN is performed, then the .EXTRACT command without any
analysis will be interpreted only for the transient run, not for the transient noise analysis.
Specify option DEFRMSNTR to report the nominal and the transient noise analysis (on RMS
waves). Use the keyword NTR on the extract to obtain the RMS extract value.
Spikes may appear in noisy runs of .NOISETRAN with the single-run algorithm. This is
because the circuit (a latch for example) has a very non-linear behavior with respect to noise.
Tip
See “.NOISETRAN” in the Eldo Reference Manual.
Related Topics
Transient Noise Analysis
Example: Extraction of the Phase Noise Spectrum at the
Output of a PLL Circuit
This example illustrates the use of a transient noise analysis to compute the phase noise
spectrum at the output of a PLL circuit.
The transient noise analysis is set in a single noisy run configuration without the nominal
(noiseless) simulation.
1. The following commands instruct the simulator to run a transient analysis up to the
steady-state and save the results:
.tran 0 5u
.save pll.sav end
.plot tran V(CP_VCNT)
.optwind vntol=(2.9u, 5u, 1e-6)
.optwind reltol=(2.9u, 5u, 1e-6)
The following actions are performed:
o
o
o
Run the transient simulation up to 5μs.
Save the state of the circuit at the end of the simulation, to the file pll.sav.
Plot the control node of the VCO. This is used to verify that the PLL is in the steadystate.
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Eldo® User's Manual, 15.3