hspice book hspice ch07 1 Thu Jul 23 19 10 43 1998 Chapter 7 Performing Transient Analysis Star Hspice transient analysis computes the circuit solution as a function of time over a time range specified in the TRAN statement This chapter covers the following topics Understanding the Simulation Flow Understanding Transient Analysis Using the TRAN Statement Understanding the Control Options Testing for Speed Accuracy and Convergence Selecting Timestep Control Algorithms Performing Fourier Analysis Using Data Driven PWL Sources Star Hspice Manual Release 1997 2 7 1 hspice book hspice ch07 2 Thu Jul 23 19 10 43 1998 Understanding the Simulation Flow Performing Transient Analysis Understanding the Simulation Flow Figure 7 1 illustrates the transient analysis simulation flow for Star Hspice Simulation Experiment DC Op Point DC Transient UIC Four FFT AC Time sweep simulation Options Method Tolerance BYPASS CSHUNT DVDT GSHUNT LVLTIM x MAXORD x METHOD ABSV x ABSVAR x ACCURATE BYTOL x CHGTOL x DELMAX x FAST MBYPASS MU RELQ x RELTOL RELV x RELVAR x SLOPETOL x TIMERES TRTOL x VNTOL Limit AUTOSTOP BKPSIZ DVTR x FS x FT x GMIN x IMAX x IMIN x ITL3 x ITL4 x ITL5 x RMAX x RMIN x VFLOOR Figure 7 1 Transient Analysis Simulation Flow 7 2 Star Hspice Manual Release 1997 2 hspice book hspice ch07 3 Thu Jul 23 19 10 43 1998 Performing Transient Analysis Understanding Transient Analysis Understanding Transient Analysis Since transient analysis is dependent on time it uses different analysis algorithms control options with different convergence related issues and different initialization parameters than DC analysis However since a transient analysis first performs a DC operating point analysis unless the UIC option is specified in the TRAN statement most of the DC analysis algorithms control options and initialization and convergence issues apply to transient analysis Initial Conditions for Transient Analysis Some circuits such as oscillators or circuits with feedback do not have stable operating point solutions For these circuits either the feedback loop must be broken so that a DC operating point can be calculated or the initial conditions must be provided in the simulation input The DC operating point analysis is bypassed if the UIC parameter is included in the TRAN statement If UIC is included in the TRAN statement a transient analysis is started using node voltages specified in an IC statement If a node is set to 5 V in a IC statement the value at that node for the first time point time 0 is 5 V You can use the OP statement to store an estimate of the DC operating point during a transient analysis Example TRAN 1ns 100ns UIC OP 20ns The TRAN statement UIC parameter in the above example bypasses the initial DC operating point analysis The OP statement calculates transient operating points at t 0 and t 20 ns during the transient analysis Although a transient analysis might provide a convergent DC solution the transient analysis itself can still fail to converge In a transient analysis the error message internal timestep too small indicates that the circuit failed to converge The convergence failure might be due to stated initial conditions that are not close enough to the actual DC operating point values Star Hspice Manual Release 1997 2 7 3 hspice book hspice ch07 4 Thu Jul 23 19 10 43 1998 Using the TRAN Statement Performing Transient Analysis Using the TRAN Statement Syntax Single point analysis TRAN var1 START start1 STOP stop1 STEP incr1 or TRAN var1 START param expr1 STOP param expr2 STEP param expr3 Double point analysis TRAN var1 START start1 STOP stop1 STEP incr1 SWEEP var2 type np start2 stop2 or TRAN tincr1 tstop1 tincr2 tstop2 tincrN tstopN START val UIC SWEEP var pstart pstop pincr Parameterized sweep TRAN tincr1 tstop1 tincr2 tstop2 tincrN tstopN START val UIC Data driven sweep TRAN DATA datanm or TRAN var1 START start1 STOP stop1 STEP incr1 SWEEP DATA datanm or TRAN DATA datanm SWEEP var pstart pstop pincr Monte Carlo TRAN tincr1 tstop1 tincr2 tstop2 tincrN tstopN START val UIC SWEEP MONTE val 7 4 Star Hspice Manual Release 1997 2 hspice book hspice ch07 5 Thu Jul 23 19 10 43 1998 Performing Transient Analysis Using the TRAN Statement Optimization TRAN DATA datanm OPTIMIZE opt par fun RESULTS measnames MODEL optmod Transient sweep specifications can include the following keywords and parameters DATA datanm data name referred to in the TRAN statement MONTE val produces a number val of randomly generated values that are used to select parameters from a distribution The distribution can be Gaussian Uniform or Random Limit np number of points or number of points per decade or octave depending on the preceding keyword param expr user specified expressions for example param expr1 param exprN pincr voltage current element or model parameter or temperature increment value Note If type variation is used the np number of points is specified instead of pincr pstart starting voltage current temperature any element or model parameter value Note If type variation POI is used list of points a list of parameter values is specified instead of pstart pstop pstop final voltage current temperature any element or model parameter value START time at which printing or plotting is to begin The START keyword is optional you can specify start time without preceding it with START Note If the TRAN statement is used in conjunction with a MEASURE statement using a nonzero START time can result in incorrect MEASURE results Nonzero START times should Star Hspice Manual Release 1997 2 7 5 hspice book hspice ch07 6 Thu Jul 23 19 10 43 1998 Using the TRAN Statement Performing Transient Analysis not be used in TRAN statements when MEASURE also is being used SWEEP keyword to indicate a second sweep is specified on the TRAN statement tincr1 printing or plotting increment for printer output and the suggested computing increment for the postprocessor tstop1 time at which the transient analysis stops incrementing by tincr1 If another tincr tstop pair follows the analysis continues with the new increment type specifies any of the following keywords DEC decade variation OCT octave variation the value of the designated variable is eight times its previous value LIN linear variation POI list of points UIC causes Star Hspice to use the nodal voltages specified in the IC statement or by the IC parameters in the various element statements to calculate the initial transient conditions rather than solving for the quiescent operating