# How to calculate equivalent cap. of a Vacator using Hspice?

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#### leonken

##### Full Member level 3 smic varactor

I made a varactor by using a mosfet.
The question is how to calculate the equivalent capacitor of the varactor varying with biased voltage?
thanks!!!

#### wenty

##### Junior Member level 1 acm=12 gate ps pd

You should be able to require the lib for the foundry. following is the SMIC 018 process varactor model

.subckt pvar18_ckt 1 2 lr=l wr=w nf=finger
* mos varactor scalable model parameters
Risod 3 0 1E12
Risos 4 0 1E12
MAIN 3 1 4 2 pvar18 L=lr W='wr*nf' AD=0 AS=0 PD=0 PS=0
* MOS Varactor Model
.MODEL pvar18 PMOS
+LEVEL = 49 VERSION = 3.2 TNOM = 25
+CAPMOD = 3 VOFFCV = 0.5 K1 = 0.88
+VTH0 = -1.573 ACDE = 1.596 TOX = 4.105E-9
+TOXM = 4.105E-9 NCH = 1.106E+17 ACM = 12
+CALCACM = 1 BINUNIT = 2 K2 = 0
+KT1 = 0.05
.ends pvar18_ckt

#### flushrat

##### Full Member level 3 hspice cggbo

print the total capacitance of the gate bias voltage
eg. print cap(node)
print CGGBO(m1)

#### leonken

##### Full Member level 3 how to calculate varactor cap

wenty said:
You should be able to require the lib for the foundry. following is the SMIC 018 process varactor model

.subckt pvar18_ckt 1 2 lr=l wr=w nf=finger
* mos varactor scalable model parameters
Risod 3 0 1E12
Risos 4 0 1E12
MAIN 3 1 4 2 pvar18 L=lr W='wr*nf' AD=0 AS=0 PD=0 PS=0
* MOS Varactor Model
.MODEL pvar18 PMOS
+LEVEL = 49 VERSION = 3.2 TNOM = 25
+CAPMOD = 3 VOFFCV = 0.5 K1 = 0.88
+VTH0 = -1.573 ACDE = 1.596 TOX = 4.105E-9
+TOXM = 4.105E-9 NCH = 1.106E+17 ACM = 12
+CALCACM = 1 BINUNIT = 2 K2 = 0
+KT1 = 0.05
.ends pvar18_ckt

The process is a pure digital CMOS process. The foundary didn't provide us the model such as varactor, parastic pnp transistor....

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