Capturing Crosstalk-Induced Waveform for Accurate Static Timing Analysis Masanori Hashimoto, Yuji Yamada, Hidetoshi Onodera Kyoto University
How cope with crosstalk- induced waveform? Never provide accurate waveforms
Problems of Conventional Methods Conventionally crossing-point approach Calculate crossing timing of reference voltage e.g. 50% delay, 20-70% transition time, etc. Estimate large delay difference in error almost the same waveforms
Gate Waveform Calculation Table look-up model Huge characterization cost Difficult to increase #parameter of waveform Characterization has to assume a typical waveform.
Related Works Sasaki, ASIC/SoC Conf., 1999 Estimate delay change vs transition timing at receiver output by circuit simulation Simulation is necessary for every instance Sirichotiyakul, DAC, 2001 Estimate delay change at receiver output by look-up tables Library extension and characterization increase
Proposed Equivalent Waveform Approach Propose equivalent waveform propagation that makes output waveforms equal Adjust both arrival time and slew Characterization uses typical waveforms.
Derivation of Equivalent Waveform Fitting waveforms using least square method Approximate entire outline Work well? NO!!
Problem of LSM Uniform fitting weight even for unnecessary region misleads equivalent waveform. Adaptive fitting for critical region is necessary. Transition finishes before noise injection.
Proposed Method Improved LSM with weight coefficient To consider output behavior slope Noiseless waveforms Vout vs Vin curve High gain sensitive to input Critical Region Higher weight
Strength of Proposed Method No library extension No additional characterization No additional calculation except fitting Implemented easily with conventional STA tools
Experimental Conditions True delay change is evaluated at Gate3 output. Conventional Method: delay change is evaluated at Gate2 input 100nm process, semi-global wire, 1mm coupled
Experimental Result ( Crosstalk ) Agg., vic. drivers 4x, 4x, load(C1,C2)=100fF Accurate delay variation curve is obtained.
Equivalent and Actual Waveforms Proposed method is not misled by meaningless noise. Cross 0.5Vdd Conventional method shifts waveform in error.
Agg.=vic. =4x, C1=C2=10fF Agg.=vic. =8x, C1=C2=100fFAgg.=vic. =8x, C1=C2=10fF Proposed method estimates more accurate curves than conventional methods. Worst case in our experiments.
Experimental Result (Crosstalk, two aggressors) Proposed method works even when multiple aggressors.
Computational Cost Numerical integration is necessary. #segments: accuracy vs CPU time CPU time increase is evaluated. Path delay calculation of inverter chain File I/O and RC reduction are excluded. 3-20 #segments is accurate enough. #segments CPU time conventional method: 1.00
Conclusion Propose equivalent waveform propagation scheme Cope with non-monotonic waveforms Familiar with conventional STA tools Experimentally verify our method improves much accuracy just with 30% CPU time increase.