How to simulate noise in bandgap voltage reference?

[melodyseu]

I got a problem. I want to simulate the noise in bandgap voltage reference using spice or spectre, but both of them must choose a input voltage. The problem is the bandgap voltage reference has no input port, how to simulate it? Thanks.

 

[jiangwp]

You can add a ac soure in the power supply. So you can get the transfer function of Vout/VDD.
So you can evulate the PSRR of the Bandgap.

 

[melodyseu]

You can add a ac soure in the power supply. So you can get the transfer function of Vout/VDD.
So you can evulate the PSRR of the Bandgap.

But I want to simulate the noise of bandgap, not the PSRR.

 

[field_catcher]

PSRR is only one of measurements you can do by using thhe method jiangwp described.

The reason spectre asks for a input noise is so that it can calculate input-referred noise from any points in circuit to the input.

If you don't care the input-referred noise, you can put a 0v DC voltage source as the input noise source in series with any branch in your circuit, and click on the output point of interest. The 0v DC voltage source wouldn't have any effect on the noise calculation. You will see you will get the same result on the same output no matter where you put the input noise source.

Hope it helps.

 

[cetc1525]

I think it's the model's problem.

 

[melodyseu]

I think it's the model's problem.

Which model? Can you explain more in detail?

 

[borodenkov]

Everything should be ok with your model

In periodic noise (PNoise) it is possible to have an option 'None' for input noise source if you do not need input-reffered noise or NF. I do not know why there's not such option in Noise analyses. But you can do as field_catcher has written - select some noiseless source for input probe and look at output noise.

 

[ccw27]

So I put a voltage source in series with the output and an input port somewhere in the bandgap circuit. Do I need to put any AC magnitude? Because I am not getting any output noise simulation.

Added after 7 minutes:

Nevermind ... I selected probe instead of voltage for output.

Now for bandgap, what is considered a good output noise voltage number?

Thanks

 

[melodyseu]

I'v tried the methord field_catcher told, and it works well.
Thank all of you

 

[jiangwp]

To melodyseu：

If you want to find some input reffered noise, i think you should find the transfer function between the input point and the output point. In other words, the GAIN between the input point and the output point is must.

As is known,
Y(s)=Vi(s)*|H(s)|

The noise calculation aso obeys the law.