General form:

CXXXXXXX n+ n- <value> <mname> <m=val> <scale=val> <temp=val> 
+ <dtemp=val> <tc1=val> <tc2=val> <ic=init_condition>

Examples:

CBYP 13 0 1UF
COSC 17 23 10U IC=3V

Ngspice provides a detailed model for capacitors. Capacitors in the netlist can be specified giving their capacitance or their geometrical and physical characteristics. Following the original SPICE3 `convention', capacitors specified by their geometrical or physical characteristics are called `semiconductor capacitors' and are described in the next section.

In this first form n+ and n- are the positive and negative element nodes, respectively and value is the capacitance in Farads.

Capacitance can be specified in the instance line as in the examples above or in a .model line, as in the example below:

C1 15 5 cstd
C2 2 7 cstd
.model cstd C cap=3n

Both capacitors have a capacitance of 3nF.

If you want to simulate temperature dependence of a capacitor, you need to specify its temperature coefficients, using a .model line, like in the example below:

CEB 1 2 1u cap1 dtemp=5 
.MODEL cap1 C tc1=0.001

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.

Ngspice calculates the nominal capacitance as described below:

[\begin{array}{ll} {C_{nom} = {{{\lbrack font\ rm\ \lbrack char\ v\ mathalpha\rbrack\lbrack char\ a\ mathalpha\rbrack\lbrack char\ l\ mathalpha\rbrack\lbrack char\ u\ mathalpha\rbrack\lbrack char\ e\ mathalpha\rbrack\rbrack} \cdot {\lbrack font\ rm\ \lbrack char\ s\ mathalpha\rbrack\lbrack char\ c\ mathalpha\rbrack\lbrack char\ a\ mathalpha\rbrack\lbrack char\ l\ mathalpha\rbrack\lbrack char\ e\ mathalpha\rbrack\rbrack}} \cdot m}} & \ \end{array}]

The temperature coefficients tc1 and tc2 describe a quadratic temperature dependence (see equation77) of the capacitance. If given in the instance line (the C... line) their values will override the tc1 and tc2 of the .model line (3.2.7).