Changing Capacitance values

How can I change the value of a capacitor during a spctre transient
simulation ?

I have found 'vccap' in analogLib, but it does not have parameters, nor a
spectre view.

What is the solution ?

 

Hi Guenther,

VCCAP should be a feasible way to change the capacitor value during
Transient simulation. For Spectre, you need to use 'vccs' in AnalogLib,
not 'vccap'.

Refer to Spectre device model file "spectremod.pdf" for more info about
vccs.

Hope it helps.

Regards,
Yuchun

Guenther Sohler 写é“：

 

Hallo,

Thank you for your answer. I read spectremod.pdf .
I realize vccs and even zvccs.

Unfortunately I cannot find out, how I can use vccs to change
a capacitance over time.

Can you explain me ?

 

Hi Guenther,

This is kind of work-around. You know, vccs can be used as VCCAP,
right? You can define the control voltage for Transient simulation,
then finally change the capacitance of VCCAP. Here is an example,

***************************
v1 (vc 0) vsource type=pwl wave=[0 1 10n 1 10.001n 0.5 20n 0.5 20.001n
3 30n 3 ]
v2 (out 0 vc 0 ) vccs type=vccap pwl=[0 1f 0.9 1f 0.91 100f 1.9 100f 2
10p 2.1 10p]
r1 (vdd out) resistor r=1k
vvdd (vdd 0) vsource type=pulse period=5n val0=0 val1=5

tran1 tran stop=40n
***************************

in the above example. Let me know if anything is unclear.

Regards,
Yuchun

Guenther Sohler 写é“：

 

Hallo,

thank you very much for the information.
I will try it.

Just a little question:
once the capacitance is changed during transient simulation:

Q=C*U

Whats the Situaion.
Does Q remain constant and U is scaled
or

Does U remain constant and Q is scaled

?

 

Hallo,

Thank you for the answer.

Just a cursious question: Are the actual values of v1(vc) wave vector
important ?

the pwl of v2 says everything, but obviously vccs needs to have 4
terminals this using a dummy voltage source.


right ?

 

Hi Guenther,

v(vc) is used to control the capactance value of 'v2', so it should be
well defined to meet your requirement. For 'v2', you can regard it as a
capacitor. In my example, it is connected to a resistor and voltage
source. You can see the different charging curve when the control value
v(vc) changed.

Thanks,
Yuchun

Guenther Sohler 写é“：