hspice book hspice ch20 1 Thu Jul 23 19 10 43 1998 Chapter 19 Performing Cell Characterization Most ASIC vendors use Star Hspice to characterize their standard cell libraries and prepare data sheets by using the basic capabilities of the MEASURE statement Input sweep parameters and the resulting measure output parameters are stored in the measure output data files design mt0 design sw0 and design ac0 Multiple sweep data is stored in this file and you can plot it by using AvanWaves This lends itself to generating fanout plots of delay versus load The slope and intercept of the loading curves can be used to calibrate VHDL Verilog Lsim TimeMill and Synopsys models This chapter covers Determining Typical Data Sheet Parameters A series of typical data sheet examples show the flexibility of the MEASURE statement Performing Data Driven Analysis Automates cell characterization including timing simulator polynomial delay coefficient calculation There is no limit on the number of parameters simultaneously varied or the number of analyses to be performed Convenient ASCII file format for automated parameter input to StarHspice Using Digital File Input Stimuli You can use logic state transition tables to produce the input stimuli for the characterization The D2A model in Star Hspice provides a 28 state logic simulator interface for rapid figuring of a cell characterization testbed Star Hspice Manual Release 1998 2 19 1 hspice book hspice ch20 2 Thu Jul 23 19 10 43 1998 Determining Typical Data Sheet Parameters Performing Cell Characterization Determining Typical Data Sheet Parameters This section describes how to determine typical data sheet parameters Rise Fall and Delay Calculations The following example first calculates vmax using the MAX function over the time region of interest Then it calculates vmin using the MIN function Finally the measured parameters can be used in subsequent calculations for accurate 10 and 90 points in the determination of the rise and fall time Note that the RISE 1 is relative to the time window formed by the delay TDval Finally the delay Tdelay is calculated using a fixed value for the measure threshold Example MEAS TRAN vmax MAX V out FROM TDval TO Tstop MEAS TRAN vmin MIN V out FROM TDval TO Tstop MEAS TRAN Trise TRIG V out val vmin 0 1 vmax TD TDval RISE 1 TARG V out val 0 9 vmax RISE 1 MEAS TRAN Tfall TRIG V out val 0 9 vmax TD TDval FALL 2 TARG V out val vmin 0 1 vmax FALL 2 MEAS TRAN Tdelay TRIG V in val 2 5 TD TDval FALL 1 TARG V out val 2 5 FALL 2 volts Trise 5v V in Tfall V out Tdelay TDval Tstop time Figure 19 1 Rise Fall and Delay Time Demonstration 19 2 Star Hspice Manual Release 1998 2 hspice book hspice ch20 3 Thu Jul 23 19 10 43 1998 Performing Cell Characterization Determining Typical Data Sheet Parameters Ripple Calculation This example performs the following Delimits the wave at the 50 of VCC points Finds the midpoint Tmid Defines a bounded region by finding the pedestal voltage Vmid and then finding the first time that the signal crossed this value Tfrom Measures the ripple in the defined region using the peak to peak PP measure function from Tfrom to Tmid Example MEAS MEAS MEAS MEAS MEAS MEAS TRAN TRAN TRAN TRAN TRAN TRAN Th1 WHEN V out 0 5 vcc CROSS 1 Th2 WHEN V out 0 5 vcc CROSS 2 Tmid PARAM Th1 Th2 2 Vmid FIND V out AT Tmid Tfrom WHEN V out Vmid RISE 1 Ripple PP V out FROM Tfrom TO Tmid ripple defined region V out Vmid 5v vcc 2 5 v 0v Th1 Tfrom Tmid Th2 time Figure 19 2 Waveform to Demonstrate Ripple Calculation Star Hspice Manual Release 1998 2 19 3 hspice book hspice ch20 4 Thu Jul 23 19 10 43 1998 Determining Typical Data Sheet Parameters Performing Cell Characterization Sigma Sweep versus Delay This file is set up to sweep sigma of the model parameter distribution while looking at the delay giving the designer the delay derating curve for the model worst cases This example is based on the demonstration file in installdir demo hspice cchar sigma sp This technique of building a worst case sigma library is described in Performing Worst Case Analysis on page 10 33 Example tran 20p 1 0n sweep sigma 3 3 5 meas m delay trig v 2 val vref fall 1 targ v 4 val vref fall 1 param xlnew polycd sigma 0 06u toxnew tox sigma 10 model nch nmos level 28 xl xlnew tox toxnew Figure 19 3 Inverter Pair Transfer Curves and Sigma Sweep vs Delay 19 4 Star Hspice Manual Release 1998 2 hspice book hspice ch20 5 Thu Jul 23 19 10 43 1998 Performing Cell Characterization Determining Typical Data Sheet Parameters Delay versus Fanout This example sweeps the subcircuit multiplier to quickly generate a family of five load curves By buffering the input source with one stage more accurate results are obtained The example calculates the mean variance sigma and average deviance for each of the second sweep variables m delay and rms power This example is based on the demonstration file installdir demo hspice cchar load1 sp Input File Example tran 100p 2 0n sweep fanout 1 10 2 param vref 2 5 meas m delay trig v 2 val vref fall 1 targ v 3 val vref rise 1 meas rms power rms power x1 in 2 inv x2 2 3 inv x3 3 4 inv m fanout Output Statistical Results meas variable m delay mean 273 8560p varian 1 968e 20 sigma 140 2711p avgdev 106 5685p meas variable rms power mean 5 2544m varian 8 7044u sigma 2 9503m avgdev 2 2945m Star Hspice Manual Release 1998 2 19 5 hspice book hspice ch20 6 Thu Jul 23 19 10 43 1998 Determining Typical Data Sheet Parameters Performing Cell Characterization Figure 19 4 Inverter Delay and Power versus Fanout Pin Capacitance Measurement This example shows the effect of dynamic capacitance at the switch point It sweeps the DC input voltage pdcin to the inverter and performs an AC analysis each 0 1 volt The measure parameter incap is calculated from the imaginary current through the voltage source at the 10 kilohertz point in the AC curve not shown The peak capacitance at the switch point occurs when the voltage at the output side is changing in the opposite direction from the input side of the Miller capacitor adding the Miller capacitance times the inverter gain to the total effective capacitance Example mp out in 1 1 mp w 10u l 3u mn out in 0 0 mn w 5u l 3u vin in 0 DC pdcin AC 1 0 ac lin 2 10k 100k sweep pdcin 0 5 1 measure ac incap find par 1 ii vin hertz twopi AT 10000hertz 19 6 Star Hspice Manual Release 1998 2 hspice book hspice ch20 7 Thu Jul 23 19 10 43 1998 Performing Cell Characterization Determining Typical Data Sheet Parameters Figure 19 5 Graph of