How to simulate the stability of a bandgap?

[jake]

Hi,
Who can tell me how to simulate the stability of a bandgap?

 

[Humungus]

As in every case, open the loop at an appropriate node. Remember to connect the rigth load to your open loop output node.

 

[sunking]

add ideal inductor and cap for opening loop while keep the dc point

 

[scottieman]

Hi,
Who can tell me how to simulate the stability of a bandgap?

If you want to see whether your bandgap is stable or not, the best method is using transient simulation.

For example:
applying a step source at the input of your bandgap, and then probe the output of your bandgap. If ringing occurs, it means your bandgap is unstable.

Please adjust your input step to be as fast as possible (e.g. 1V/ns). Otherwise, you can get a stable output even your bandgap IS UNSTABLE

Scottie

 

[nuiscet]

I think of that first what you should do is to confirm whether the o.p.amp have enough phase magin (>=45), then confirm the start-characteristic of the circuit.

 

[GDF]

Is 45° phase margin enough? I think we make the phase margin larger than 65° is better.

 

[nuiscet]

Usually 45℃ is just the lowest phase magin. Otherwise the bandgap circuit can oscillate and can't acquire an accurate voltage.

 

[zenisle]

cut off a node for open loop first.

 

[wanily1983]

give a step signal to Vdd, do a complete trans analysis with start-up circuit, check the bandgap output to see if has large overshoot.

 

[jake]

Hi,
Who can tell me how to simulate the stability of a bandgap?

If you want to see whether your bandgap is stable or not, the best method is using transient simulation.

For example:
applying a step source at the input of your bandgap, and then probe the output of your bandgap. If ringing occurs, it means your bandgap is unstable.

Please adjust your input step to be as fast as possible (e.g. 1V/ns). Otherwise, you can get a stable output even your bandgap IS UNSTABLE

Scottie

scottieman, when my input step is 1v/ns, the startup circuit is oscillated. However, there is an 80 degree phase margin in the op amp. What's the matter?