Raising itl4 to 100 or more may help to eliminate timestep too small errors improving both convergence and speed. Small floating resistors connected to high impedance nodes might cause convergence difficulties. Starhspice transient analysis computes the circuit solution as a. In general, spice uses an adaptive step size in transient simulations to minimize simulation time while maintaining accuracy. The circuits work fine when i test them for logical functionality with an input frequency measured in seconds, but. Even if the voltages are dc as in the previous tutorials, transient analysis must. Hello, i need to be able to run my circuit for about 50 ms but it shows that the time step is too small in ltspice. Minimum step size required to register an event on the input of the internal ad converters.
A transient analysis in eagle takes three variables, start time, stop time, and tmax. Mar 07, 20 eggn 281 lecture 23 transient analysis step by step procedure taught by dr. Smaller time steps in transient analysis improve measurement accuracy. I would like to know if there is a way when using pspice schematics to set a minimum time step when doing transient analysis.
Internal timestep too small can happen for any number of reasons, havingnothing whatsoever to do with the. I am running the following file and getting the error. When troubleshooting transient analysis failure, try setting. If you are not sure what values to enter, press the set defaults button on the page to automatically calculate the transient analysis parameters as follows.
This solution is not viable for performing an ac analysis because an operating point must precede the ac analysis. On that comp the simulation worked without a problem. Convergence error in transient analysis custom ic design. However, the simulation is very sensitive to the input values i enter. If you enter the time step size is larger than the recommended value, a message box will prompt you and ask you if you want to change the value. When spiceruns into a problem, it backs up and tries again. Abstolreltol lowest current magnitude in the circuit vntol reltol lowest voltage magnitude in the circuit raising the value of gmin may help with convergence, but decreases accuracy. This will allow the transient analysis to go through more iterations for each timestep before giving up.
Bolii dont know if i can help specifically, but here are a few comments. When circuit variables node voltages, for example are changing rapidly, it will take shorter time steps, and when circuit variables are changing slowly, it will take longer time steps. After running transient analysis, you can use the linearize command to interpolate the automatically chosen sample times to. For detailed information, please look at the page 383 of hspice user guide.
This analysis can be done after spice first calculates a dc bias point or with initial conditions the user specifies. Jul 12, 2015 transient analysis means analysing a system in unsteady state. The other two settings define when the transient analysis starts and stops. Dec 19, 2007 best regards, ray raymond anderson senior signal integrity staff engineer advanced platforms group advanced products division product technology department package design engineering xilinx inc. Advanced spice options online documentation for altium products. Transient analysis online documentation for altium products. With other oa simulation is ok, but with all microchip models, the same error.
For two reasons to improve accuracy and reduce long simulation times. A default time step size will be provided by the program and then used in the analysis. For a thermal only transient analysis, the time step size can be much larger. How do we take a collection of resistive and energystorage components, then find its time response to an arbitrary input waveform. Typically transient step time and transient max step time are set to the same value. Importing models into ltspice, time step too small error.
The internal timestep changes often throughout a simulation. Your transient analysis results waveform is stored in. The only parameter that is required is the run to time, which is entered in the. Transient analysis and operational amplifiers in pspice. Raising this value may help to eliminate timestep too small. Simulation with hspice university of texas at dallas. Stepbystep procedures help you solve spice convergence problems. Since transient analysis is dependent on time, it uses different analysis algorithms, control options with different convergencerelated issues and different initialization parameters than dc analysis. This means it would take about 8 hours to run a 1 second analysis with my processor speed. Back to search page click to download printable version of this guide. Hspice is just a program that takes in a netlist a simple text. How to select a time step size for a transient analysis in. The program determines the time step size using an internal.
One of the most complex and intriguing capabilities of the spice algorithm is the transient analysis. Transient analysis always begins at time 0, and assumes that only the dc sources were connected to the circuit prior to that time. Ravel ammerman, colorado school of mines recorded march 6, 20. Stepbystep procedures help you solve spice convergence. For the love of physics walter lewin may 16, 2011 duration. I am familiar with hspice and have done some of the analysis on it. Stop time in transient analysis custom ic design cadence. For detailed information, please look at the page 383 of.
Dec 24, 2016 for the love of physics walter lewin may 16, 2011 duration. Id appreciate if anyone could advise on what spice settings i could change to help stabilize it so that i can vary the input in 1 us time frames and test the slew rate bandwidth of the ic in the model. In a transient analysis, the error message internal timestep too small indicates that the. Simulation troubleshooting online documentation for altium. I beleive the circuit ive made available is the 8pf version. How do calculate time step size in ansys transient structural.
Instead, use voltage sources or iprobes to measure current. Tran tiner tstop startstval where tiner is the timestep, tstop is the final time value and stval is the initial time value. For nonlinear circuits, spice completes the nonlinear loop 26 at each time point of the transient analysis. It means that, because of the nature of your circuit, to achieve the required accuracy. Transient analysis of a cmos inverter using hspice youtube. Regards, vuk borich operating manager, arf simulation and models agilent technologies, eesof division 408 553 2605 original message from. A 1foot pipe with flow moving 1 fts needs a time step of between. A small step toward compatibility with hspice files was taken by allowing 3v1 to mean the same thing as 3v1. There are step by step design examples in the mmsim 12. Csv stands for comma separated values, the favored format for importing data into excel. Ensure that a complete set of parasitic capacitors is used on nonlinear devices to avoid. The time step will be reduced when circuit voltages and currents are changing rapidly.
I am assuming that this is an issue with convergence since this time step is extraordinarily small. Tmax defines the maximum allowed step time and can be useful for analyzing oscillators. Transient analysis means analysing a system in unsteady state. Tips for using hspice university of california, berkeley.
As a starting point set both of these parameters to. Use hb analysis if a sinusoidallchigh q oscillator or pss if a ring oscillator rather than transient analysis. Avoid very small floating resistors, particularly small parasitic resistors in semiconductors. Instantiating hspice subcircuits inside veriloga modules. Transient analysis always begins at time0, and assumes that only the dc sources were connected to the circuit prior to that time. Performing transient analysis understanding transient analysis star hspice manual, release 1997. Part of the spec is that the gates must drive a 1 or 8 pf capacitor to the output voltage within 1nsec. Advanced spice options online documentation for altium. Because they dont give us technical support web pages, i will give this information for your convenience. Eggn 281 lecture 23 transient analysis stepbystep procedure taught by dr. Hspice transient analysis university of texas at dallas. Acmag is the ac magnitude and acphase is the ac phase. I tried changing the solver in tools to alternate but it works only for 1 ms. In general, spice uses an adaptive stepsize in transient simulations to minimize simulation time while maintaining accuracy.
With the entire circuit properly biased by the dc supplies, the timevarying stimuli are switched on at time0, and the response of the circuit to them is calculated, time point by time point. Op and then performs a transient analysis of duration tstop seconds with a maximum time step of tincr. It looks like the time step too small fixes you found during your. Generally, the time step should be less than 120fmax in transient structural by ansys, where fmax is the highest frequency interested. The circuits work fine when i test them for logical functionality with an input frequency measured in seconds, but when.
Currently when i run transient with a particular circuit, the time step will stay at 1e12. This tutorial shows hspice simulation of a cmos inverter. Anyone know which options will help to solve this problem. I build it a couple of months ago on a different computer which i cant access anymore. The example project well be working with is an opamp circuit that uses. See setting up analyses on page 282 for a description of the analysis setup dialog box. Since transient analysis is dependent on time, it uses different analysis algorithms, control options with different convergencerelated issues and different initialization parameters. If the source value is zero both for dc and transient analyses, this value may be omitted. Abstolreltol lowest current magnitude in the circuit. Hspice rf does not support short names for internal subcircuits, such.
Transient analysis of a circuit in this section of the tutorial, you will learn to perform a transient analysis on a circuit. Overview hspice transient analysis computes the circuit solution as a function of time over a time range specified in the. Tran perform a transient analysis differential equation solver see p. With the entire circuit properly biased by the dc supplies, the time varying stimuli are switched on at time 0, and the response of the circuit to them is calculated, time point by time point. Chapter 7 performing transient analysis class home pages. If i am not mistaken, what it means is the timestep specified in the spice simulation file is too small. Dctran is the dc and transient analysis value of the source. A solid in motion may also be a driving factor for a time step size. Best regards, ray raymond anderson senior signal integrity staff engineer advanced platforms group advanced products division product technology department package design engineering xilinx inc.
Curves can now be saved in either csf or usr formats. If there is an event that is trying to be captured, the time step size needs to be small enough to capture the event. With the entire circuit properly biased by the dc supplies, the time varying stimuli are switched on at time0, and the response of the circuit to them is calculated, time point by time point. Hspice simulation and analysis user guide department of. If the variables involved in defining the state of a system doesnot vary with respect to time, then the system is said to be in steady state. Chapter 7 performing transient analysis starhspice transient analysis computes the circuit solution as a function of time over a time range specified in the. Tran tstep tstop this command performs a timedependent analysis starting from time0 sec to timetstop sec. The transient analysis is always used when you want to view a graph of a voltage or current as a function of time. Select download center hspice version number release notes. Ic and ic initialcondition statements to assist in the initial stages of the transient analysis. Understanding the simulation flow understanding transient analysis using the. Timestep too small is not actually due to nonconvergence. Hspice tutorial university of california, berkeley.