The capacitor model contains process information that may be used to compute the capacitance from strictly geometric information.
name | parameter | units | default | example
|
CAP | model capacitance | F | 0.0 | 1e-6
|
CJ | junction bottom capacitance | F/meters^2 | - | 5e-5
|
CJSW | junction sidewall capacitance | F/meters | - | 2e-11
|
DEFW | default device width | meters | 1e-6 | 2e-6
|
DEFL | default device length | meters | 0.0 | 1e-6
|
NARROW | narrowing due to side etching | meters | 0.0 | 1e-7
|
SHORT | shorting due to side etching | meters | 0.0 | 1e-7
|
TC1 | first order temperature coeff. | F/^oC | 0.0 | 0.001
|
TC2 | second order temperature coeff. | F/^oC^2 | 0.0 | 0.0001
|
TNOM | parameter measurement temperature | ^oC | 27 | 50
|
DI | relative dielectric constant | F/m | 0.0 | 1
|
THICK | insulator thickness | meters | 0.0 | 1e-9
|
The capacitor has a capacitance computed as:
If value is specified on the instance line then
Cnom = value * scale * m
If model capacitance is specified then
Cnom = CAP * scale * m
If neither value nor CAP are specified, then geometrical and physical parameters are take into account:
C0 = CJ (l - NARROW) (w - NARROW) + 2 CJSW (l - SHORT + w - NARROW)
CJ can be explicitly given on the .model line or calculated by physical parameters. When CJ is not given, is calculated as:
If THICK is not zero:
DI * eps 0 CJ = --------- if DI is specified THICK eps SiO 2 CJ = --------- if DI is not specified THICK with: eps = 8.854214871e-12 F/m 0 eps = 3.4531479969e-11 F/m SiO 2
Cnom = C0 * scale * m
After the nominal capacitance is calculated, it is adjusted for temperature by the formula:
2 C(T) = C(TNOM) [1 + TC (T - TNOM) + TC (T - TNOM) ] 1 2 where C(TNOM) = Cnom
In the above formula, `T' represents the instance temperature, which can be explicitly using the temp keyword or os calculated using the circuit temperature and dtemp, if present.