61 lines
2.2 KiB
Plaintext
61 lines
2.2 KiB
Plaintext
Adding transient simulation top generate the operating point of a circuit
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The operating point of a circuit has to be established before a transient, ac,
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or noise simulation may be started.
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The procedure, as found in cktop.c is as follows:
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1) Iterate the matrix with the starting values
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If this fails:
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2) Start gmin stepping
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If this fails:
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3) start source stepping
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If this again fails, bail out.
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In this branch a fourth method is added:
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4) Start a transient simulation for a specific amount of time.
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Keep all data local. Keep the matrix values as an
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operating point for the simulation that is following.
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If this fails, finally stop.
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A new command sets the flags for transient op calculation
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optran n1 n2 n3 n4 n5 n6
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This command has to be given before the simulation commands
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run, ac, tran, pz, or noise. Only the simulation commands will
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start the (modified) op calculation. Another 'optran' will
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override the previous flags.
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Step 1 (from above) may be skipped by
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option noopiter
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command optran n1 overrides noopiter
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Step 2 may be skipped by
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option gminsteps=0
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command optran n2 overrides gminsteps
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Step 3 may be skipped by
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option srcsteps=0
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command optran n3 overrides srcsteps
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n4 sets the step size for transient simulation towards the operating point.
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n5 sets the time for transient simulation towards the operating point.
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n6 set a ramp time to ramp all independent voltage or
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current sources until 100% is reached at opramptime.
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The transient op calculation uses the 'UIC' flag for its startup.
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Basically two applications come to mind: You may use this with
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constant voltage and current sources and simulate until the
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output is stable. A method to automatically stop the op transient
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simulation when all nodes have become stable, might be desirable,
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but has not yet been implemented.
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One also may use the optran for a first transient simulation, maybe
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with different step sizes, before the next (tran, ac, pz, noise)
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simulation is commencing. So you may reach a certain bias point
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quickly and with coarse time steps, and then continue with fine
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steps to see details. For example a power amp in electro-thermal
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simulation may run for some seconds (minutes?) until the final
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temperature is reached, and then the detailed transient or
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an ac simulation starts.
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