sweeping the value of a capacitor in a subcircuit

[Mohit]

Hi,

I have a testbench that has 3 instances of a subcircuit called
DTC_NEA. This subcircuit is basically a differential buffer and it has
a couple of ideal capacitors with identical values in it. The top
level testbench puts these three buffers in a chain and also has the
necessary bias and voltage sources needed to make it work.

What I need to do is to sweep the value of these caps from 5fF to 50fF
and see what effect it has on the delay. How do I go about doing this?
I don't use the ADE tool, but do everything on the command line.

Currently, in my schematic, I have given the caps a value of C, which
is a parameter. Here is my sweep statement:

sweep_cap sweep sub=DTC_NEA param=C start=5e-15 stop=50e-15
step=53-15 {
tran tran stop=5n maxstep=20p errpreset=moderate write="spectre.ic"
writefinal="spectre.fc" annotate=status maxiters=5
}


Also, my subcircuit definition for DTC_NEA looks like this:

subckt DTC_NEA IS ISb Ts odp VB6Q VCC3
parameters C=5e-15
C0 (VCC3 t0) capacitor c=C
C1 (VCC3 t0b) capacitor c=C
.......
ends DTC_NEA



I use the following command to run the spectre netlist (sp.scs):

spectre sp.scs > sp.raw/Spectre.out


When I run the test, I get the following error:

"Error found by spectre during Sweep analysis 'sweep_cap'.
Subckt instance 'DTC_NEA' does not exist.


Does this mean that I have to give the instance name of the buffer
rather than the subcircuit name in the sweep statement? If so, how do
I ensure that the cap value changes for all three instances and not
just for one?


Any help would be appreciated.

Thanks,

Mohit A.

 

[S. Badel]

Currently, in my schematic, I have given the caps a value of C, which
is a parameter. Here is my sweep statement:

sweep_cap sweep sub=DTC_NEA param=C start=5e-15 stop=50e-15
step=53-15 {
tran tran stop=5n maxstep=20p errpreset=moderate write="spectre.ic"
writefinal="spectre.fc" annotate=status maxiters=5
}

First note : step=53-15 seems a bit high

About the sweep, if you use sub=, it expects the name of a subcircuit instance. I do not think it is
possible to specify multiple instances here.

What you should do is define a global parameter and "propagate" it to all subcircuit instances.
Then, do not specify sub= in your sweep statement.

simulator lang=spectre
parameters C=5e.15 .....
....
I1 (...) DTC_NEA C=C
I2 (...) DTC_NEA C=C
I3 (...) DTC_NEA C=C
....
sweep cap sweep param=C start=5e-15 stop=50e-15 step=53-15 {
...
}


Hope this'll work,

Stéphane

 

[Mohit]

On Apr 5, 5:26 am, "S. Badel" <stephane.ba...@REMOVETHISepfl.ch>
wrote:

Currently, in my schematic, I have given the caps a value of C, which
is a parameter. Here is my sweep statement:

sweep_cap sweep sub=DTC_NEA param=C start=5e-15 stop=50e-15
step=53-15 {
tran tran stop=5n maxstep=20p errpreset=moderate write="spectre..ic"
writefinal="spectre.fc" annotate=status maxiters=5
}

First note : step=53-15 seems a bit high

About the sweep, if you use sub=, it expects the name of a subcircuit instance. I do not think it is
possible to specify multiple instances here.

What you should do is define a global parameter and "propagate" it to all subcircuit instances.
Then, do not specify sub= in your sweep statement.

simulator lang=spectre
parameters C=5e.15 .....
...
I1 (...) DTC_NEA C=C
I2 (...) DTC_NEA C=C
I3 (...) DTC_NEA C=C
...
sweep cap sweep param=C start=5e-15 stop=50e-15 step=53-15 {
...

}

Hope this'll work,

Stéphane

Thanks, that worked well for me! and the step size was meant to be
5e-15.

Mohit.