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HB tstab randomly giving bad results compared to regular transient

MatanR 8 months ago

Spectre version: 23.1.0.403_ISR6

Virtuoso: 23.1.ISR6

*can't upload images for some reason.

While running a harmonic balance configured like this:

1. Run transient - Decide automatically.

2. Run Envelope tstab - no.

3. 1 Tone - fundamental freq. is LO.

11 harmonics.

oversample factor = 4

freqdivide Ration for Tone1 = 1

For random points - tstab outputs wrong results - for example a DC circuit has it's output on the wrong voltage.

while running regular transient (in Cx) I get the right results for all points.

sometimes HB tstab gets it right.

what am I doing wrong?

Tawna 8 months ago

This is best handled by Customer Support. Please consider filing a Case on https://support.cadence.com . There are too many questions I'd need to ask to verify your setup is correct. Also, if there is a problem, you'd need to contact Customer Support anyway to get a CCR (Cadence Change Request) filed.

The purpose of the transient assist (tstab) is to get hb (or pss) to a point where Spectre can calculate the periodic steady state operating point of your circuit.

See this Article on COS: Getting the Most out of Spectre® X-RF 23.1 Maximizing Performance . It discusses Spectre RF best practices, accuracy, setting oversample and number of harmonics, what to do when your circuit has square waves, what to do when your circuit contains nports (check all s-parameter files using the new S-parameter checking and fitting tool).

best regards,

Tawna
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