Bandgap output impedance...Pls help...

[bharatsmile2007]

Hi ...

How to reduce the output impedance to improve the load regulation of the BGR?

Pls find the schematic i used....as attachment...

Thanks

 

[PaloAlto]

Use a small opamp. Just a diff pair with current mirrror as load to convert to single ended. That should do the job

 

[saro_k_82]

Looks like you are trying to build a 1.2V reference., other architecture would have given you a better o/p impedance straightaway. With this circuit, you need to add a buffer to reduce the o/p impedance.

 

[bharatsmile2007]

Thanks saro_k_82 and PaloAlto...

PaloAlto,

I am using any OTA in the circuit.Would you pls explain me,if i use a diff pair,will i
get a low output impedance?

Saro_k_82,

Yes saro_k_82,i wanted to generate 1.2V ref...

 

[PaloAlto]

If you take any OTA from your circuit, just put feedback around it and you have low impedance at the output. In that way you buffer the voltage level lowering the impedance

 

[kishore2k4]

I would like to suggest a small extension to PaloAlto's post.

You can use an OTA with a pass transistor at the output and tap the reference at its source so it will be low impedance.

 

[analog_match]

Kishore,

What you are suggesting is the same thing as a common drain buffer, correct?

 

[kishore2k4]

Kishore,

What you are suggesting is the same thing as a common drain buffer, correct?

Yes it is a common drain stage with feedback. As it uses an NMOS transistor one has to check for voltage compliance. As the op-amp should produce a positive signal (wrt to output) to drive the NMOS. I think it can be done with a PMOS transistor too, you should check out some LDO topologies.

 

[bharatsmile2007]

hi

thanks for the suggestions...But if i use an LDO kind of circuit.The supply variation will effect the output voltage.

iam looking for BGR with low impedance ..

any other suggestion will be very helpful..

Thanks

 

[saro_k_82]

But if i use an LDO kind of circuit.The supply variation will effect the output voltage.

Why?
Use LDO or HDO if the supply voltage room permits.

 

[bharatsmile2007]

hi saro_k_82,

Thanks for the reply..

If the supply voltage room doesnt permit..what do suggest for getting low impedance BGR...?

Thanks again...

 

[jesseyu1984918]

should plus a buffer for LDO somthing to reduce it