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Multiple AC Conditions (Read 3066 times)
Dave F.
Ex Member




Multiple AC Conditions
May 01st, 2015, 10:20am
 
Hi,

I have a circuit that has amplifiers in it and I running a combined transient and switch open-loop AC analysis. I am using the method where I specify rac on resistors to cut the feedback and swap in an AC source so I can measure open loop gain/phase.

I am running with Spectre and am using the actimes parameter so I can run AC analysis at different times where the load conditions changed over time.

So my circuits look like this:
V_AC_MID (mid_ac_voltage vref) vsource dc=0 mag=1 type=sine
R_AC_MID (mid_ac_voltage mid_amp_input) resistor r=1T rac=1
R_TRAN_MID (mid_feedback mid_amp_input) resistor r=1 rac=1T

And my analysis looks like this:
parameters simulation_points=[(1.9*period) (5.9*period)]
tran_tt tran stop=(12*period) errpreset=conservative acnames=[ac_tt] actimes=simulation_points infoname=info_tt infotimes=simulation_points noiseon=[X1]
info_tt info save=selected
ac_tt  ac  start=100k stop=100G dec=50  save=selected

Question:

I have multiple amplifiers in my design and I would like to analyse them separately. You could imaging them like:

V_AC_MID (mid_ac_voltage vref) vsource dc=0 mag=1 type=sine
R_AC_MID (mid_ac_voltage mid_amp_input) resistor r=1T rac=1
R_TRAN_MID (mid_feedback mid_amp_input) resistor r=1 rac=1T

V_AC_HIGH (high_ac_voltage vref) vsource dc=0 mag=1 type=sine
R_AC_HIGH (high_ac_voltage high_amp_input) resistor r=1T rac=1
R_TRAN_HIGH (high_feedback high_amp_input) resistor r=1 rac=1T

V_AC_LOW (low_ac_voltage vref) vsource dc=0 mag=1 type=sine
R_AC_LOW (low_ac_voltage low_amp_input) resistor r=1T rac=1
R_TRAN_LOW (low_feedback low_amp_input) resistor r=1 rac=1T

Then I'd like to be able to specify my simulation similar to something like:
parameters simulation_points=[(1.9*period) (5.9*period)]
tran_tt tran stop=(12*period) errpreset=conservative acnames=[mid_ac_tt,high_ac_tt,low_ac_tt] actimes=simulation_points infoname=info_tt infotimes=simulation_points noiseon=[X1]
info_tt info save=selected
mid_ac_tt  ac  start=100k stop=100G dec=50  save=selected
high_ac_tt  ac  start=100k stop=100G dec=50  save=selected
low_ac_tt  ac  start=100k stop=100G dec=50  save=selected

But somehow for these 3 different AC analyses, I would like to either:
1. Activate one of the three AC sources
2. Manipulate the resistors to one of the three amplifiers

I haven't been able to figure out to do that.

Another possibility is that I'd like to save a transient checkpoint, then load it into three different AC analyses. That would look something like:
* Simulate TRAN while saving checkpoints
* Call ALTER to reconfigure circuit for Mid Amp
* Simulate AC using saved checkpoint 0
* Simulate AC using saved checkpoint 1
* Call ALTER to reconfigure circuit for High Amp
* Simulate AC using saved checkpoint 0
* Simulate AC using saved checkpoint 1
* Call ALTER to reconfigure circuit for Low Amp
* Simulate AC using saved checkpoint 0
* Simulate AC using saved checkpoint 1

I'm out of ideas at this point... I've been working on this a while. Does anyone have any suggestions?

Sorry for the wall of text...

Thanks
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Ken Kundert
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Silicon Valley
Re: Multiple AC Conditions
Reply #1 - May 2nd, 2015, 11:52am
 
Indeed, there is too much detail. Perhaps you should just have asked about what you wanted to know rather than provide so much detail. It is hard to know what is important.

It sounds like you want to know how to turn on and off AC sources?

You can do that with:

Code:
disableMid1 alter dev=V_AC_MID param=mag value=0
enableHigh1 alter dev=V_AC_HIGH param=mag value=1
high_ac_tt  ac  start=100k stop=100G dec=50
... 



-Ken
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Dave F.
Ex Member




Re: Multiple AC Conditions
Reply #2 - May 2nd, 2015, 3:55pm
 
Hi Ken,

Thanks for your reply. I'll try to be more concise

I want to:
* Run a transient simulation
* Stop at some point in time
* Run individual AC analyses on 3 different amplifiers given the conditions of the transient simulation at the stopping point
* Continue the transient simulation

The wall of text detailed my various attempts (using 'actimes' in transient simulation or loading transient checkpoints into ac analysis)  :-X

Thanks,
Dave
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Ken Kundert
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Re: Multiple AC Conditions
Reply #3 - May 3rd, 2015, 2:42pm
 
Well there is the actimes setting in the transient analysis (use 'spectre -h tran', for me it is parameter #72). You could use that.

I don't understand the three different amplifiers. Are they completely independent of each other?

-Ken
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Dave F.
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Re: Multiple AC Conditions
Reply #4 - May 4th, 2015, 12:37pm
 
Ken Kundert wrote on May 3rd, 2015, 2:42pm:
Well there is the actimes setting in the transient analysis (use 'spectre -h tran', for me it is parameter #72). You could use that.

I don't understand the three different amplifiers. Are they completely independent of each other?

-Ken

Hi Ken,

They are driving different nodes of an RC network, so they do affect each other somewhat.

Currently I am using actimes, but with only one amplifier at a time. If I try to analyze all three, then it must be the same AC analysis calculation and all three amplifiers must receive an AC source at the same time. I'd like to use actimes with three different AC analyses where in each one, a different AC source is enabled.

If I analyze one independently or all three at once, I do get different results (second order differences)

Thanks,
Dave

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