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Capacitor, Frequency-Dependent (Netlist Only)

Capacitor, Frequency-Dependent (Netlist Only)

Instead of the standard capacitor syntax with a specified capacitance value, you can define the capacitance by an expression involving the frequency, using the syntax given in this section.

Notes

The frequency-dependent capacitor is available for use in netlists, but is not supported in the Components window of the Designer Schematic Editor.

The frequency-dependent capacitor is supported only for frequency-domain analyses such as AC and LNA. Running a time-domain analysis such as TRAN on a circuit including a frequency-dependent capacitor is an error.

Frequency-Dependent Capacitor Instance Netlist Syntax

The general form for a frequency-dependent capacitor instance is:

Cxxxx n1 n2 [modelname] [C=]'freq_dependent_expr'

[M=val] [DTEMP=val] [TRAN_EVAL_FREQ=val]

n1 is the positive node and n2 is the negative node of the capacitor. The current is assumed to flow from n1 through the capacitor to n2. If a model statement is provided for the capacitor, the modelname is its name. The modelname is identified by matching it to the .MODEL statements in the netlist.

The frequency-dependent expression should be enclosed in single quotation marks. The token HERTZ can be used in the expression to indicate the frequency as supplied by the analysis. The circuit frequency is available to the model each time the model equations are evaluated. The label C= is optional. The first unlabeled value after a modelname is taken to be the capacitance.

When the parameter TRAN_EVAL_FREQ is provided, Nexxim can run a transient (time-domain) analysis, substituting the value of TRAN_EVAL_FREQ for the variable HERTZ to produce a constant capacitance value for the transient analysis.

**Frequency-Dependent Capacitor Instance Parameters**
Instance Parameter	Description	Unit	Default
C	Capacitance	Farad	Calculated from frequency expression
DTEMP	Difference between capacitor and circuit temperatures	Celsius	0.0
M	Multiplier to simulate parallel capacitors	None	1.0
TRAN_EVAL_FREQ	Frequency to use for transient analysis	Hertz	0.0

Frequency-Dependent Capacitor Netlist Examples

Frequency-domain analysis:

C1 1 2 capacitorF1 C='1e-12*sqrt(HERTZ)' M=2

.LNA LIN 100 1e6 10e6

.MODEL capacitorF1 C TC1=0.1 TC2=0.05

Time-domain analysis:

C23 11 22 capacitorF1 C='1e-12*sqrt(HERTZ)' TRAN_EVAL_FREQ=1e8

.TRAN -.01ns 10ns

.MODEL capacitorF1 C TC1=0.1 TC2=0.05

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