HICUM evaluation

1. HICUM evaluation Cedric Pujol – Analog and Mixed Signal Flows Jean Remy – Analog and Mixed Signal Flows

2. Aim • The aim of these tests is to verify the HICUM implementation on a « real life » design, and all the simulators supported by ST. HICUM evaluation - 2 C. Pujol, J. Remy

3. EDA Tools • The simulators used are the following: • Ams 2004.1 and 2004.2 beta4 • ADS 2003.C • Aplac 7.92c • Spectre 5.0.33.031104 • GoldenGate 3.3.14 • Hspice 2004.2-beta2 • Hsim 5.0_2004.20.7 HICUM evaluation - 3 C. Pujol, J. Remy

4. Outline • Evaluation of the implementation of the HICUM model in the simulators : RF simulations • Transient simulation experiences • Comparison between STBJT and HICUM • Conclusion HICUM evaluation - 4 C. Pujol, J. Remy

5. Outline • Evaluation of the implementation of the HICUM model in the simulators : RF simulations • Mixer • LNA • Transient simulation experiences. • Comparison between STBJT and HICUM • Conclusion HICUM evaluation - 5 C. Pujol, J. Remy

6. First design under test • The design is a four bipolars based up-mixer done by CRD on 60GHz Bicmos ST process. • The simulations peformed are: • One 2 tone Harmonic Balance for a low gain • A swept Harmonic Balance for 13 gain points • The conditions chosen are 15 harmonics for the LO and 8 for the IF. The temperature is set to 25 °C. • The outputs are the fundamental tone at 1.941GHz and the two 3d order intermodulation products at 1.937 GHz and 1.943 GHz. HICUM evaluation - 6 C. Pujol, J. Remy

7. Non-linear results (fundamental) HICUM evaluation - 7 C. Pujol, J. Remy

8. Non-linear results (3d order) HICUM evaluation - 8 C. Pujol, J. Remy

9. Non-linear results (sweep) HICUM evaluation - 9 C. Pujol, J. Remy

10. Outline • Evaluation of the implementation of the HICUM model in the simulators • Mixer • LNA • Comparison between STBJT and HICUM • Conclusion HICUM evaluation - 10 C. Pujol, J. Remy

11. Second design under test • The design is a six bipolars based Low Noise Amplifier done by CRD on 60GHz Bicmos ST process • The simulations peformed are: • A DC analysis • One 2 tone Harmonic Balance for the IP3 computation (spacing between the tones = 4MHz) • A swept Harmonic Balance for the IP1 computation • A noise analysis • The conditions chosen are 10 harmonics for the RF tone. The temperature is set to 27 °C. HICUM evaluation - 11 C. Pujol, J. Remy

12. DC results HICUM evaluation - 12 C. Pujol, J. Remy

13. Noise results HICUM evaluation - 13 C. Pujol, J. Remy

14. IP1 results HICUM evaluation - 14 C. Pujol, J. Remy

15. OIP3 results HICUM evaluation - 15 C. Pujol, J. Remy

16. ADS results • The simulation times given for ADS are stopwatch times and for others CPU times. So to compare thoroughly, ADS simulation times should be decreased. Moreover, they are so low that they are really impacted by the netlisting process. • The results seem correct and the simulation times are reasonable. • The self-heating implementation causes an estimated 20% simulation time overhead which seems quite reasonable. • The 3d order non-linearities (NL) are quite different in ADS from other simulators but seem more physical since the slopes for the 3d order NL are theoratically correct (3dB/dB). HICUM evaluation - 16 C. Pujol, J. Remy

17. Aplac results • A bug has been submitted to Aplac Solutions in the 7.91c release. It has not been corrected in the new release. Therefore, We used a work-around that the support gave us for the 7.91c release. • The results seem correct but the simulation times skyrocket (over 12 hours for the mixer sweep). • The self-heating implementation makes the simulation time multiplied by around 3 which is much too long. HICUM evaluation - 17 C. Pujol, J. Remy

18. Eldo results • The results seem correct, and the simulation times are correct. • The results match all the simulators but ADS but they seem not physical (slopes are 2dB/dB for a 3d order NL). • The self-heating implementation multiplies the simulation time by 1.5 to 3x. HICUM evaluation - 18 C. Pujol, J. Remy

19. GoldenGate results • The results seem most of the time correct but the simulation time overhead for HICUM is much too high. The mixer testcase will be sent to the support. • The results are quite pessimistic compared with other simulators without any convincing explanation. • The self-heating implementation is activated by adding a flag in the Spectre model card that is not necessary in Spectre. The time overhead is pretty high (around 40% for the LNA) HICUM evaluation - 19 C. Pujol, J. Remy

20. Spectre results • 2 analyses were performed for non-linearities : PSS+PAC and QPSS. The first one is fast but only returns the fundamental. The other is longer and the non-linearities given are not satisfying for the mixer. • Therefore, these tests is not very relevant for HICUM accuracy but the implementation seems correct. • The self-heating implementation causes an estimated 20% simulation time for the mixer overhead which seems quite reasonable. • For the LNA, the DC simulation times are multiplied by 30 when the self heating is activated ! HICUM evaluation - 20 C. Pujol, J. Remy

21. Outline • Evaluation of the implementation of the HICUM model in the simulators : RF simulations • Transient simulation experiences. • Comparison between STBJT and HICUM • Conclusion HICUM evaluation - 21 C. Pujol, J. Remy

22. Third design under test (1) • Simulation of an ECL 4GHz frequency divider • 60GHz Bicmos process, 32 bipolar devices, no self heating • HICUM model introduced as maturity design kit update, close to tape-out date • Many iterations were needed with EDA vendors to reach transient simulation convergence HICUM evaluation - 22 C. Pujol, J. Remy

23. Third design under test (2) • After non convergence corrections, we detected a design problem that STBJT could not show-up (too high bias and saturation). • Two versions of the design are simulated : • With the design problem • With its correction. HICUM evaluation - 23 C. Pujol, J. Remy

24. Transient simulation times HICUM evaluation - 24 C. Pujol, J. Remy

25. Transient simulation results • Hsim (semi-electrical) does not detect the design problem • For nanosim, wait Q2 2005 ! HICUM evaluation - 25 C. Pujol, J. Remy

26. Transient simulation conclusions (1) • Incomplete partial derivatives highly impact transient (and assimilated) simulation time, and cause simulation crashes • Many iterations with EDA vendors for partial derivatives implementation • A lot of energy spent to convince designers of HICUM interest after first bad contact. • Partial derivatives corrections modify AC behavior with bias > fTmax HICUM evaluation - 26 C. Pujol, J. Remy

27. Transient simulation conclusion (2) • Need to re-qualify all AC validation simulations • Porting of excess phase and non quasi static effects was difficult on some simulators • Transient simulation still not completely reliable on every simulator, with random effects HICUM evaluation - 27 C. Pujol, J. Remy

28. Outline • Evaluation of the implementation of the HICUM model in the simulators : RF simulations • Transient simulation experiences. • Comparison between STBJT and HICUM • Conclusion HICUM evaluation - 28 C. Pujol, J. Remy

29. Aim • The aim of these tests is to compare the STBJT M2 (DK 2.1) with the HICUM (DK 3.0) model. • The simulation (1 dB compression point) has been performed on ADS and Spectre on all the simulators. HICUM evaluation - 29 C. Pujol, J. Remy

30. Simulation times (LNA) HICUM evaluation - 30 C. Pujol, J. Remy

31. Simulation times (Mixer) HICUM evaluation - 31 C. Pujol, J. Remy

32. Mixer results HICUM is in blue and STBJT in red. The curves are very different. But HICUM curves seem more physical since the slopes are 3dB/dB for the third harmonics. The compression of the fundamental arrives ealier too in HICUM. HICUM evaluation - 32 C. Pujol, J. Remy

33. Outline • Evaluation of the implementation of the HICUM model in the simulators • Comparison between STBJT and HICUM • Conclusion HICUM evaluation - 33 C. Pujol, J. Remy

34. Results sum up (HICUM no SH) • The small signal implementation is fast and accurate in every simulator, at least before transient simulation corrections. • The non linear simulations exhibit problems in terms of simulation speed and convergence. • The differences computed by ADS between the STBJT and HICUM are quite large on one of the third harmonics (35 dB) but other simulators disagree. • STBJT was always optimistic compared with HICUM which could be annoying. HICUM evaluation - 34 C. Pujol, J. Remy

35. Results sum up (HICUM with SH) • The self-heating implementation depends a lot on the simulator in terms of speed. • Moreover we met some problems on the LNA (DC with Spectre) that we don’t have on the mixer. • Therefore, it should be wise not to activate by default the self-heating. HICUM evaluation - 35 C. Pujol, J. Remy

36. Actions and recommendations (1) • We have to push on some EDA vendors to improve the convergence for both standard and self-heating implementations. • DC for SPECTRE • Non convergence for APLAC • Simulation speed for GOLDENGATE • Self heating speed improvement for ELDO and ADS • We should warn the designers that the overhead on simulation time could be from 2x to 6x when switching from STBJT to the HICUM models for non linear analyses. HICUM evaluation - 36 C. Pujol, J. Remy

37. Actions and recommendations (2) • The ADS curves showing a 3dB/dB physical slope are in contradiction with what is predicted by all its competitors. It has to be explained to see which simulator is right. • Try other testcases to refine this evaluation… HICUM evaluation - 37 C. Pujol, J. Remy

38. Conclusion • We are still waiting a stabilized implementation of self-heating in all supported simulators before releasing this new feature • First designer contact was very negative • A lot of energy/credibility lost in partial derivatives implementation • Multiplication of DEVICE compatibility flags, and absence of a reference source code • No decision to drop-out of STBJT model HICUM evaluation - 38 C. Pujol, J. Remy