IR Drop and Electromigration Analysis with Ultrasim Power Network ...

Processor with CPU 2193.787MHz. Ultrasim A mode is used as golden reference.( Ultrasim a mode uses table model while keeping the whole design in one partition).Table 2. Performance for Ultrasim UPS, VAVO and VAEOULTRASIM A MODE ULTRASIM A MODE + UPSSimulation time 22 hours 3 hoursDatabase 6GB 2.4GBVAVO loading time 3.5hours 21 minVAEO loading time 4.5 hours 3 hoursThe IR drop of both VDD and VSS power nets from Ultrasim A mode + UPS werecompared with those of Ultrasim A mode, the results were within 5% of Ultrasim Amode for any voltage drop more than 3mV. UPS provided more than 7X speed up duringsimulation. The database created by UPS were significantly smaller (more than 2X).This was partially due to the fact that power networks consisted of R and C and they weresolved by UPS linear solver, so the time steps were relatively big. While in A mode allthe elements were solved together in one partition, the time steps were mainly controlledby all the nonlinear devices, causing much smaller time step in general, hence biggerdatabase. Thanks to the smaller size of the data base, the loading time for VAVO wasreduced significantly by 7X.VAEO’s loading time is the same for both cases, because the signal nets are essentiallysolved in the same way.Both Ultrasim A mode and Ultrasim A mode + UPS identified 112 EM violations. Fig. 4.shows the textual report of the EM analysis.6

Fig. 4 Textual report from VAEOBelow is an excerpt from the textual report for IR drop analysis.……….HIERARCHY = "/I0"SIMULATION RESULTS =‘’run/sim_results/COM_TOP16V07_sim/UltraSim/config_spectre_power_r"RESULTS TYPE = TRANSIENTTRANSIENT START = "0"TRANSIENT STOP = "10n"----------- "VDD_D" PIN -----------VOLTAGE ASSURA SIMULATIONDROP NETNAME NETNAME5.044K 8070:VDD_D I0.\_8070\:VDD_D4.524K 8067:VDD_D I0.\_8067\:VDD_D3.325K 8069:VDD_D I0.\_8069\:VDD_D1.447K 7517:VDD_D I0.\_7517\:VDD_D950.5 7516:VDD_D I0.\_7516\:VDD_D344.8 7536:VDD_D I0.\_7536\:VDD_D338.6 7538:VDD_D I0.\_7538\:VDD_D293.7 8014:VDD_D I0.\_8014\:VDD_D279.4 8013:VDD_D I0.\_8013\:VDD_D…….Section IV. ConclusionIn this paper, we discussed Ultrasim UPS + VAVO/VAEO flow, it is targeted at powergrid and signal integrity verification of analog and mixed signal designs. Ultrasim UPS isthe simulation engine while post-processing of the IR and EM data is done byVAVO/VAEO. VAVO analyzes the IR drops in the power net, while VAEO checks forEM problems on signal nets. Ultrasim UPS is well suited to handle power networkefficiently without much loss of accuracy. The small database enables faster loading timefor VAVO. IR drop and EM results are colored coded and are displayed on top of theextracted view or layout. Cross probing between textual reports and the color map greatlyimprove efficiency when debugging.Reference1) Virtuoso Analog VotageStorm and ElectronStorm User Guide, June 20052) Virtuoso Ultrasim Simulator User Guide, May 20053) Xiaohao Wu, Xiaodong Zhang, Lifeng Wu and Jun Kong, “ Fast and AccurateDynamic Power Net Solver with Fast SPICE Simulator Ultrasim”, CTC057