How does the opamp bandwith affect the bandgap voltage reference source?

[jc2]

Many bandgap voltage sources have a opamp.

Is the opamp bandwith important? why?
Is necesary a high bandwith?
How does the opamp bandwith affect the bandgap voltage reference source?

thanks

 

[huanchou]

Re: Bandgap Opamp

In my opinion, the bandgap opamp bandwidth is not important,
because the bandgap just process the DC signal, but its gain is very important.
The opamp DC gain relatice to its input offset and it should be as small as possible.

 

[scottieman]

Re: Bandgap Opamp

In my opinion, the bandgap opamp bandwidth is not important,
because the bandgap just process the DC signal, but its gain is very important.
The opamp DC gain relatice to its input offset and it should be as small as possible.

Yes, I agree with huanchou.
In general cases, the higher the bandwidth of your op-amp, higher the chance your bandgap to oscillate.

Scottie

 

[Humungus]

Re: Bandgap Opamp

On the other hand, a large bandwidth helps to have a large PSRR over a wider range of fraquencies as the opamp reacts to any posible change of the voltages on the bandgap branches.

Oscillation MUST be avoided by properly compensating the bandgap.

Also having an opamp in your bandgap reduces offset of the bandgap branches compared to the solution when two follower transistors are used. Reducing offset makes your bandgap to be more stable over temperature.

 

[limingchou]

Bandgap Opamp

i agree with you
the bandgap op gain and input offest is important

 

[gajen]

Re: Bandgap Opamp

Lower bandwidth will help in reducing the device noise but increase your startup time.

Lower bandwidth will also degrade PSRR at higher frequencies. At around 3bB of opamp PSRR will start degrading. So higher bandwidth will push this degradation to higher frequencies.

 

[xwcwc1234]

Re: Bandgap Opamp

But what is the optimized opamp bandwidth for bandgap op? Is there any rule of thumb to follow ?