VCCAP Usage and Documentation

Hi Mingqiang,

We already talked before about plotting the capacitor value via :lx0. So plot two signals - one is the period (versus time) that you asked about, and the other is the capacitor value (lx0). 

Then over the x-axis, click right mouse->Y vs Y. Pick the trace that you want to be the x-axis (the capacitor value, lx0) and you'll then get a new graph of the period versus the capacitor value.

Does that answer your question?

Andrew

Hi Andrew,

Thank you so much! This is now clear.

Because lx0 I plotted is only against time and I am wondering how to relate it to period.

Now your explanation is in more detail!

Sorry for my bad understanding!

Thanks,

Mingqiang

Hi Mr. Andrew,

I am really sorry to disturb you again, but the picture I get is not a discrete graph as shown below. This is confusing as I set all capacitor values at discrete values at certain time point in the dynamic variable vector. However, the results give me continuous graph in oppoint against time. I set infotimes to save these oppoint. May I ask if there is any way of plotting frequency against discrete lx0?

Thank you very much!

Best Wishes,

Mingqiang

Dear Mingqiang,

EEE student said:

May I ask if there is any way of plotting frequency against discrete lx0?

Did you right click on your plot of capacitance versus time and choose "Type->Points" and, also from a right click, "Symbols on". This will only display the values without any line between data points.

Shawn

Thank you very much! I will do it tomorrow! I will update if I succeed.

I don't really understand what you're doing here - why are you using a vccap and then using a dynamic parameter to change the capacitor value? Why not just use a capacitor with a variable as the value and use the dynamic parameter to change it?

It's unclear to me what you're really doing here - seeing the input.scs netlist would really help as it's hard to understand otherwise.

Potentially you could take the trace that is supposed to be "discrete" and use right mouse->type->sample and hold, but that will only help if it is truly discrete, which I'm not convinced is the case here. Similarly Shawn's suggestion won't help either in that case.

Andrew

Hi Mr. Andrew,

Sorry to confuse you. Let me show you the graph below:

As you can see, the hysteresis opamp's oscillation frequency is determined by this vccs cap. If I did directly parameter sweep, that would be in the dc analysis and every change would be against this vccs value. 

However, hysteresis opamp will never run because it takes time to oscillate. Therefore, we must do the transient analysis to see its actual period and then treat the vccs as a dynamic variable to observe how this period changes as the vccs value increases. Hence I calculate period using 1/freq(). Then using opt() to plot vccs value against the time.

For your reference, I have attached the netlist here:

// Library name: Lab1
// Cell name: schmitt_trigger
// View name: schematic
I13 (vdd! 0 capout vfeedback schmitt_out) opamp_sch
R3 (vdd! vfeedback) polyhres_pcell_1 sl=156.76u w=1.2u
R2 (capout schmitt_out) polyhres_pcell_1 sl=160.17u w=1.2u
R1 (vfeedback 0) polyhres_pcell_1 sl=156.76u w=1.2u
R0 (vfeedback schmitt_out) polyhres_pcell_1 sl=156.76u w=1.2u
C1 (out 0) capacitor c=1p
I10 (0 schmitt_out out vdd!) Inverter
V0 (vdd! 0) vsource dc=1.8 type=pulse val0=0 val1=1.8 rise=100n
V1 (net15 0) vsource dc=dc_cap type=dc
G1 (capout 0 net15 0) vccs gm=1p type=vccap inputtype=single delta=0
simulatorOptions options reltol=1e-3 vabstol=1e-6 iabstol=1e-12 temp=27 \
tnom=27 scalem=1.0 scale=1.0 gmin=1e-12 rforce=1 maxnotes=5 maxwarns=5 \
digits=5 cols=80 pivrel=1e-3 sensfile="../psf/sens.output" \
checklimitdest=psf
tran tran stop=200u param=dc_cap param_vec=[0 1 10u 1.5 20u 2 30u 2.5 40u \
3 50u 3.5 60u 4 70u 4.5 80u 5 100u 4.5 110u 4 120u 3.5 130u 3 140u 2.5 \
150u 2 160u 1.5 170u 1] write="spectre.ic" writefinal="spectre.fc" \
annotate=status infotimes=[5u 15u 25u 35u 45u 55u 65u 75u 85u 95u 105u \
115u 125u 135u 145u 155u 165u 175u] maxiters=5 infoname=tran_Info
finalTimeOP info what=oppoint where=rawfile
tran_Info info what=oppoint where=rawfile
modelParameter info what=models where=rawfile
element info what=inst where=rawfile
outputParameter info what=output where=rawfile
designParamVals info what=parameters where=rawfile
primitives info what=primitives where=rawfile
subckts info what=subckts where=rawfile
saveOptions options save=allpub

Thank you for your patience!

Mingqiang

Hi there, 

Here is a quick update. I successfully plotted the stuff using your method. I have attached it for your reference! Thank you very much!