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# How to do the ac stability simulation of bandgap circuit?

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#### holddreams

##### Full Member level 6
Any one can give me a file and a plot?

Thanks.

Re: How to do the ac stability simulation of bandgap circuit

maybe you could inject a small signal current on top of a constant current loading on the bandgap and measure the resulting small signal deviations in the bandgap voltage. You can also look for large signal stability by stepping the load current from the max->min->max or min->max->min and see how the voltage recovers due to these.

Best regards,
v_c

Re: How to do the ac stability simulation of bandgap circuit

I would try for instance to feed the circuit with a modulated clock(predifined values ... let's say a triangle modulator of x Mhz),
and at the output I would aplly a FFT and see if the can observe the same values.

Best regards!

I think using the ota ac simulation may be possible

Re: How to do the ac stability simulation of bandgap circuit

Basicly, the tran. simulation is the sure way to verify the stability of a system.

But, if you want to do ac simulation to verify your system stability, such as bangap,

I think you have to break the loop(Both positive feedback & negative feedback), and get the loop gain every time for one type feedback, and compare the gain and bandwidth of two type loop to determine the stability.

If the negative feedback loop gain > postive feedback loop gain , and
the negative feedback loop bandwidth > postive feedback loop bandwidth,

you can get the conclusion that the bandgap is stable.

break the loop at sigle point, add stimulas and watch reponse at the other end

Re: How to do the ac stability simulation of bandgap circuit

montage2000 said:
break the loop at sigle point, add stimulas and watch reponse at the other end

Re: How to do the ac stability simulation of bandgap circuit

Hi
Can you please elaborate the same. I think we need to have the Transfer function of BG circuit. Any comments will be appreciated.
rellutzu said:
I would try for instance to feed the circuit with a modulated clock(predifined values ... let's say a triangle modulator of x Mhz),
and at the output I would aplly a FFT and see if the can observe the same values.

Best regards!

Re: How to do the ac stability simulation of bandgap circuit

break the loop at one point,in the opamp inputs in the feedback path.,and check the phase margina nd gain for every iteration.
transient simulations wud be enough to find the response time.

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