The general form of the instance of a capacitor is the following:

C<name> <node1(+)> <node2(-)> [value] [model name] [L=<length>] [W=<width>] [IC=<VC0>]

For standard capacitors:

C<name> <node1(+)> <node2(-)> <value> [model name] [IC=<VC0>]    

For semiconductor capacitors:

C<name> <node1(+)> <node2(-)> <model name> L=<length> [W=<width>] [IC=<VC0>]    

For nonlinear capacitors:

C<name> <node1(+)> <node2(-)> C=<expression>



Is the name of the component and the initial letter C identifies the capacitors.

node1, node2

The first node (node1) is defined as positive. The voltage across the component is therefore defined as the first node voltage minus the second node voltage. Current flow from the first node through the component to the second node is considered positive.


Is the capacitance (in farads) and may be positive or negative but not zero. If this parameter is omitted, then the capacitance may be calculated from the process information (CJ, CJSW and NARROW) in the model and the given length and width.

model name

The model can be omitted if the capacitance value is specified while must always be specified together with the length for the semiconductor capacitors.


Diffusion length in meters. Must always be specified together with the model for semiconductor capacitors.


Diffusion width in meters. Must be specified for the semiconductor capacitors. If width is not specified, then it is taken from the default width (DEFW) given in the model.


The (optional) initial condition is the initial (time-zero) value of capacitor voltage (in Volts). Note that the initial conditions (if any) apply 'only' if the UIC option is specified on the .TRAN control line.


Nonlinear capacitors can be generated by putting the expression directly on the element line. The expressions may be any function of voltages and currents through voltage sources in the system. In an AC analysis, only the DC component of a voltage or current source when the initial operating point was calculated is used. In a transient analysis, any voltages or currents are evaluated at each time point. See also Behavioral modeling expressions.


In some cases, to allow the simulator to determine the operating point of a circuit may be necessary to connect a resistor in parallel to the capacitor. In fact, in the DC analysis the capacitors are considered open circuits. The value of the resistor must be high enough (1Gohm) in order not to influence the behavior of the circuit.


C1 1 2 100n
C2 1 2 100n CMOD
C3 1 2 100n IC=5
C4 1 2 CMOD L=50u W=5u

See also

Capacitor model
Capacitor instance parameters