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Capacitors

General Form:
cname n+ n- [value | modname] [c=expr] [ic=val] [temp=temp [tc1=tcoeff1]
[tc2=tcoeff2] [l=length] [w=width]
cname n+ n- poly c0 [c1 ...] [ic=val]

Examples:
cload 2 10 10p
cmod 3 7 cmodel l=10u w=1u

The capicatance value can be specified as a bare number, if it is the first parameter following the node list. This token can also be a capacitor model name. The paramaters that can follow are:

c=expr
This can also be given as ``cap=expr'', or ``capacitance=expr'', where expr is an expression yielding the capacitance in farads. This is the partial derivative of charge with respect to voltage, possibly as a function of other circuit variables. This form is applicable when the first token following the node list is not a capacitance value or model name. It also applies when a model is given, it overrides the geometric capacitance value.

This is the default keyword, so actually the parameter name and equals sign are optional, a bare expression is acceptable.

ic=val
The optional initial condition val is the initial (time zero) voltage across the capacitor. The initial condition (if any) applies only when the uic option is specified in transient analysis.

temp=temp
The temp is the Celsius operating temperature of the capacitor, for use by the temperature coefficient parameters.

tc1=tcoeff1
The first-order temperature coefficient. This will override the first-order coefficient found in a model, if given.

tc2=tcoeff2
The second-order temperature coefficient. This will override the second-order coefficient found in a model, if given.

l=length
The length of the capacitor. This applies only when a model is given, which will compute the capacitance from geometry.

w=width
The width of the capacitor. This applies only when a model is given, which will compute the capacitance from geometry.

The second form allows specification of a polynomial capacitance, which will take the form

Capacitance = c0 + c1 . v + c2 . v2...
where v is the voltage difference between the positive and negative element nodes. There is no built-in limit to the number of terms.

The n+ and n- are the positive and negative element nodes, respectively, and value is the capacitance for a constant valued capacitor. Alternatively, a capacitor model modname can be specified which allows for the calculation of the actual capacitance value from strictly geometric information and the specifications of the process. If value is specified, it defines the capacitance. If modname is specified, then the capacitance is calculated from the process information in the model modname and the given length and width. If value is not specified, then modname and length must be specified. If width is not specified, then it will be taken from the default width given in the model. Either value or modname, length, and width may be specified, but not both sets.


next up previous contents index
Next: Capacitor Model Up: Passive Element Lines Previous: Passive Element Lines   Contents   Index
Stephen R. Whiteley 2017-02-22