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bandgap dc analysis and tran analysis (Read 3110 times)
A.D.J
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bandgap dc analysis and tran analysis
Jan 22nd, 2017, 9:02pm
 
Hi, everyone.
Recently I designed a resistorless bandgap. In the DC analysis, it works good enough.
But when I simulate the Tran analysis, no matter how long it is, the reference voltage will be unstable in the final simulation time in 100ns period. But the value is very small.
I don't know why.
Thank you.

PS: is this simulator issue?

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« Last Edit: Jan 23rd, 2017, 7:01am by A.D.J »  

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ULPAnalog
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Re: bandgap dc analysis and tran analysis
Reply #1 - Jan 23rd, 2017, 1:04am
 
Quote:
But when I simulate the Tran analysis, no matter how long it is, the reference voltage will be unstable in the final simulation time in 100ns period. But the value is very small.


Could you explain this in more detail as I do not completely follow it. Are you saying that bandgap is unstable in tran simulation, no matter what and the output of BGR is small?

In general, DC analysis tries to find an equilibrium point and it is not necessary that the equilibrium is a stable one. In a transient analysis, the simulator perturbs the system by moving it away from the equilibrium point. If the circuit is stable, it will return back to its equilibrium position. Going by what I understood from your post, it appears that the BGR is indeed unstable. I do not know which simulator was used to simulate this particular circuit, but I would be hard pressed to believe that it is a simulator issue.

For more details, you might be interested in taking a look at http://kenkundert.com/docs/bctm98-MSsim.pdf pg 5 in particular.

Thanks and regards
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A.D.J
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Re: bandgap dc analysis and tran analysis
Reply #2 - Jan 23rd, 2017, 7:01am
 
This is the simulation result for 500ns tran analysis.
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12.PNG

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A.D.J
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Re: bandgap dc analysis and tran analysis
Reply #3 - Jan 23rd, 2017, 7:02am
 
This is for 1us tran analysis
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22.PNG

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ULPAnalog
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Re: bandgap dc analysis and tran analysis
Reply #4 - Jan 24th, 2017, 1:40am
 
It is hard to say what might be going on without looking at the schematics of the BGR. If you have not tried already, I would suggest you to try ramping up the supply from 0 to Vdd and see if the BGR remains stable. How does the behavior look like after a long time, say 100 us. Does it stabilize or continues to exhibit oscillations?
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A.D.J
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Re: bandgap dc analysis and tran analysis
Reply #5 - Feb 20th, 2017, 2:45pm
 
Thank you. You are right.
People used to use ramp to test the startup time for BGR.
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