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how to simulate the startup circuit for bandgap reference?

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triquent

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I tried to add the startup circuit for bandgap voltage reference circuit(Op-amp type). Without the startup circuit I got it work right. I also didn't use the .ic command to setup the initial condition. Now my question is. If I add the startup circuit, how can i simulate it and verify it work? I mean without the startup the circuit willnot work, after add starup it will work and the starup part will not effect the whole circuit. Is this right?
 

Re: how to simulate the startup circuit for bandgap referenc

I consider what you think is right. Without the startup circuit the bandgap reference circuit has two stable state, so you must use .ic command to set the circuit to another stable state. So with or without the startup circuit you can see the difference.
 

Re: how to simulate the startup circuit for bandgap referenc

My question is how to check the startup circuit is working or not? how to simulate it?
bear7679 said:
I consider what you think is right. Without the startup circuit the bandgap reference circuit has two stable state, so you must use .ic command to set the circuit to another stable state. So with or without the startup circuit you can see the difference.
Click to expand...
 

Re: how to simulate the startup circuit for bandgap referenc

Do a transient simulation with ramping VDD from zero with different slopes. From 1V/ns up to 1V/us. If it works in this condition it likely work for all practical situations.
 

Re: how to simulate the startup circuit for bandgap referenc

Ramp for 10us, 10ms and 100ms. Also vary Vdd, i.e. 0.9Vdd, Vdd and 1.1Vdd. Plus simulate for different corners and different temperatures.
 

Re: how to simulate the startup circuit for bandgap referenc

In tests that rfsystem and ccw mentioned, I'd recommend setting gmin=0, if this does not confuse your simulator.
 
Re: how to simulate the startup circuit for bandgap referenc

why do i need to change the vdd? I should add this if the specification require the circuit to operate at a certain vdd range?
ccw27 said:
Ramp for 10us, 10ms and 100ms. Also vary Vdd, i.e. 0.9Vdd, Vdd and 1.1Vdd. Plus simulate for different corners and different temperatures.
Click to expand...

Added after 1 minutes:

what is gmin?
steer said:
In tests that rfsystem and ccw mentioned, I'd recommend setting gmin=0, if this does not confuse your simulator.
Click to expand...
 

Re: how to simulate the startup circuit for bandgap referenc

triquent said:
why do i need to change the vdd?
Click to expand...

Because this is what happans with your circuit in real life.


triquent said:
what is gmin?
Click to expand...

It's simulator option. Setting it to 0 makes makes it closer to the real life, but also might cause convergence problems at low temp.
 

Re: how to simulate the startup circuit for bandgap referenc

Ramped VDD is a must in BGR simulation.
What is more, after settling, you should stop the circuit by setting STP or PDB and restart the circuit to check the function.
 

Re: how to simulate the startup circuit for bandgap referenc

what is STP or PDB signals???
does it comes in .options of simulator?
i m using hspice.. so do i have this option.. i hv searched but didnt find any..
help me out in this..
thnks in advance...
 

Ramping the Vdd? does this mean that positive slope ramp and then maintain the Vdd constant?
 

You need to challenge the startup circuit, which is in a
sense challenging your assumptions. This wants a few
angles exercised. I'd do a very slow transient ramp (PWL
source or pulse w/ long trise) and I'd do a DC sweep, and
insist that both of them produce the same result (a clean
start, and no clinging to the ankles afterward - i.e. the
startup must cease sourcing current into the ptat loop,
otherwise your tempco will be jacked at some process
corner).

If you can break it, you're not done. That's the drill. And
you must try everything you can, to break it.
 
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