I can't find any design issue in your post.
Your question is not design issue but simple feature of specific vendor's EDA tool.
Please post to "The Designer's Guide Community Forum ≫ Simulators ≫ RF Simulators".nathanee wrote on Jul 3rd, 2008, 6:53am:Please help to clarify the following concept about noise and simulation method.
What do you mean by "concept" ?
nathanee wrote on Jul 3rd, 2008, 6:53am:1. Thermal, flicker, and KT/C noise CAN NOT be simulated by using spectre/hspice transient method.
Apart from accuracy, you can evaluate these noise using transient noise analysis in Spectre.
I don't think HSPICE supports transient noise analysis. So you can't evaluate these noise using HSPICE's transient analysis.
nathanee wrote on Jul 3rd, 2008, 6:53am:2. Thermal, flicker, and KT/C noise CAN be simulated by using spectre/hspice ac method.
For time invariant circuit, you can evaluate thermal and flicker noise using AC noise analysis in both Spectre and HSPICE.
But you can't evaluate KT/C noise directly using Spectre's AC analysis.
On the other hand you can evaluate KT/C noise using HSPICE's combination analysis of ".AC", ".Noise", and ".SAMPLE" analysis, although it is not accurate evaluation.
nathanee wrote on Jul 3rd, 2008, 6:53am:3. Thermal, flicker, and KT/C noise CAN be simulated by using spectreRF.
Yes, for periodically time varied circuit, you can evaluate these noise using Shooting Newton Method in both SpectreRF and HSPICE RF.