ACMatch Analysis (acmatch)

Description

ACMatch analysis linearizes the circuit about the DC operating point and computes the variations of AC responses due to the statistical parameters defined in statistical blocks. Only mismatch parameters are taken into account.

Syntax

Name  [node1]  [node2] acmatch parameter=value ...

Parameters

Analysis parameters


`mth`	`1e-3`	Threshold of the relative contribution to be exported in output file. The ratio is determined by individual contribution divided by total contribution. Both magnitude and phase are taken into account.
`oprobe`		The mismatch variations of the current signal through this component is chosen as the output. It can be one of the following: vsource, inductor, switch, tline, iprobe, ccvs, vcvs, pccvs, and pvcvs.

AC frequency sweeping parameters


`start`	`0`	Start sweep limit.
`stop`		Stop sweep limit.
`center`		Center of sweep.
`span`	`0`	Sweep limit span.
`step`		Step size, linear sweep.
`lin`	`50`	Number of steps, linear sweep.
`dec`		Points per decade.
`log`	`50`	Number of steps, log sweep.
`values`	`[...]`	Array of sweep values.
`valuesfile`		Name of the file containing the sweep values.

Output parameters


`groupby`	`param`	Choose the way of how to group the total sigma. Total sigma of each contributor can be grouped either by statistics parameters or by subckt instances. Possible values are param and inst.
`where`	`screen`	Specifies where the results should be printed. Possible values are screen, logfile, file and rawfile.
`file`		The name of the file in which the results are printed, if where=file.
`save`		Signal levels in output. Possible values are all, lvl, allpub, lvlpub, selected, none and nooutput.
`oppoint`	`no`	Determines whether operating point information should be computed. If yes, specifies where should it be printed (screen or file). Operating point information is not printed if the operating point computed in the previous analysis remains unchanged. Possible values are no, screen, logfile and rawfile.
`write`		DC operating point output file at the first step of the sweep.
`writefinal`		DC operating point output file at the last step of the sweep.

Initial condition parameters


`readns`		File that contains an estimate of DC solution (nodeset).
`prevoppoint`	`no`	Determines whether to use the operating point computed in the previous analysis. Possible values are no and yes.
`force`	`none`	The set of initial conditions to use. Possible values are none, node, dev and all.
`readforce`		File that contains the initial conditions.
`skipdc`	`no`	Skip DC analysis. Possible values are no and yes.
`useprevic`	`no`	If set to yes or ns, use the converged initial condition from the previous analysis as ic or ns. Possible values are no, yes and ns.
`restart`	`yes`	Restart the DC solution from scratch if any condition has changed. If not, use the previous solution as an initial guess. Possible values are no and yes.

Annotation parameters


`annotate`	`sweep`	Degree of annotation. Possible values are no, title, sweep, status and steps.
`title`		Analysis title.

ACMatch takes each parameter defined in the statistics blocks and applies variation one at a time to find the sensitivity of the output with respect to the parameter. Based on the sensitivities computed by this procedure, the total variation of the output is computed by adding up variation contributions from each parameter, assuming that the parameters are mutually independent.

You can define sweep limits by specifying the end points or the center value and span of the sweep. Steps can be linear or logarithmic, and you can specify the number of steps or the size of each step. You can specify a step size parameter (step, lin, log or dec) to determine whether the sweep is linear or logarithmic. If you do not specify a step size parameter, the sweep is linear when the ratio of stop to start values is less than 10 and logarithmic when this ratio is 10 or greater. All frequencies are in Hertz.

The small-signal analysis begins by linearizing the circuit about an operating point. By default, this analysis computes the operating point, if it is not known, or recomputes it if any significant component or circuit parameter has changed. However, if an operating point was computed during a previous analysis, you can set prevoppoint=yes to avoid recomputing it. For example, if prevoppoint=yes and the previous analysis was a transient analysis, the operating point is the state of the circuit at the final time point.

Nodesets help find the DC or the initial transient solution. You can specify nodesets in the circuit description file with nodeset statements or in a separate file by using the readns parameter. When nodesets are specified, Spectre computes an initial guess of the solution by performing DC analysis, while forcing the specified values on to nodes by using a voltage source in series with a resistor whose resistance is rforce. Spectre then removes these voltage sources and resistors and computes the required solution from this initial guess.

Nodesets have two important uses. First, if a circuit has two or more solutions, nodesets can bias the simulator towards computing the required solution. Second, this is a convergence aid. By estimating the solution of the largest possible number of nodes, you might be able to eliminate a convergence problem or significantly speed up convergence.

When you simulate the same circuit multiple times, it is recommended that you use both write and readns parameters and assign the same file name to both parameters. DC analysis then converges quickly even if the circuit has changed since the last simulation, and the nodeset file is automatically updated.

During the initial operating point DC analysis, you may force some of the circuit variables to the values given in the ic file, ic statements, or ic parameter on the capacitors and inductors. The ic parameter controls the interaction of various methods of setting the force values. The effects of individual settings are as follows:

force=none: All initial conditions are ignored.

force=node: The ic statements are used, and the ic parameters on the capacitors and inductors are ignored.

force=dev: The ic parameters on the capacitors and inductors are used, and the ic statements are ignored.

force=all: Both ic statements and ic parameters are used, with the ic parameters overriding the ic statements.

If you specify an ic file with the readforce parameter, force values from the file are used and any ic statements are ignored.

After you specify the initial conditions, Spectre computes the DC operating point with the specified nodes forced to the given value by using a voltage source in series with a resistor whose resistance is rforce (see spectre -h options).

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Spectre Circuit Simulator ReferenceProduct Version 23.1, September 2023