Phase margin of opamp in bandgap reference

[shaq]

Dear all,

Is it important that phase margin of opamp in bandgap reference?

And, I want to know what is the most important of opamp in bandgap reference.

Plz give me more suggestions.

Thanks so much!!!!

 

[nuiscet]

Phase magin is necessary. Gain is important to ensure that the voltages of the positive and negitive input terminals are equal, too. and other PSRR is also important for the bandgap voltage undepending on the supply voltage, i think.

 

[winsonpku]

i don't think phase margin is important for the opamp used in bandgap.
because bandgap is almost a dc circuit and dc gain and offset of the opamp maybe more important.

Dear all,

Is it important that phase margin of opamp in bandgap reference?

And, I want to know what is the most important of opamp in bandgap reference.

Plz give me more suggestions.

Thanks so much!!!!

 

[wonbef]

i think phase margin is important to stabilize the bandgap reference system.

 

[shaq]

oh my !!!

Someone says phase margin isn't important, the other says important.

Which one is correct?

I'm so confused.

 

[jordan76]

i don't think phase margin is important for the opamp used in bandgap.
because bandgap is almost a dc circuit and dc gain and offset of the opamp maybe more important.

Hi

First of all, for all systems with feedback to work properly, they should be stable otherwise you want an oscillator or something like that!

For the case of bandgap, dc gain, offset and PSRR are all very important parameters besides stability concerns.

Hope it helps!

regards,
jordan76

 

[shaq]

i don't think phase margin is important for the opamp used in bandgap.
because bandgap is almost a dc circuit and dc gain and offset of the opamp maybe more important.

Hi

First of all, for all systems with feedback to work properly, they should be stable otherwise you want an oscillator or something like that!

For the case of bandgap, dc gain, offset and PSRR are all very important parameters besides stability concerns.

Hope it helps!

regards,
jordan76

Thanks for your suggestion!!!

 

[jcpu]

Other than jordan76's suggestions,
allow me to remind that,
input stage matching of this OPamp is
always on top of the list because
this is one donimant factor of output voltage spread.

Have fun

 

[shaq]

Here, I have a little quetion that is how to minimize the vos of opamp in the bandgap reference circuit.

 

[iocx]

Phase margin is an important parameter to opamp. If you don't design well, the opamp will oscillate.AZ can reduce offset voltage.

 

[shaq]

Phase margin is an important parameter to opamp. If you don't design well, the opamp will oscillate.AZ can reduce offset voltage.

Dear iocx,

What is "AZ" ?

 

[flushrat]

Well matching in layout reduce offset
Besides, start up is important

 

[hubert008]

For any system, stablity is important, but when you consider it, you must make sure which loop you consider.

 

[eng_Semi]

Don't care with the PM of the opamp BUT take care of the PM of the loop

 

[shaq]

Don't care with the PM of the opamp BUT take care of the PM of the loop

Don't care about the PM but BJT?

 

[khaled fayed]

Hi All

The PM of the OpAmp itself is not so important however the PM of the whole loop should be considered carefully to avoid oscillations. Also the PSRR of the Opamp should be maximized as much as u can to obtain a supply independent BG reference. and when u r supplying RF circuits that are sensitive to noise u should consume larger current in the BG opamp to minimize the output noise. Also the mismatch of the opamp should be minimized as much as u can by layout and circuit considerations.

 

[jordan76]

Phase margin is an important parameter to opamp. If you don't design well, the opamp will oscillate.AZ can reduce offset voltage.

Dear iocx,

What is "AZ" ?

I guess "AZ" means auto-zero technique to eliminate the DC offset voltage.
You may search for more details in ieee journals or google in the web.

regards,
jordan76

 

[pseudockb]

Chopper stabilization can also reduce the offset voltage of the opamp.

 

[ipsc]

Here, I have a little quetion that is how to minimize the vos of opamp in the bandgap reference circuit.

Same techniques that apply to opamp also apply for Bandgap.
Some of them:
1. common centroid layout for input diff-pair
2. Low VDsat for input diff-pair.
3. Sizing of 2nd-stage input TR. & 1st stage load TRs in the ratio of their currents.

Regards

 

[winsonpku]

could you explain the second issue in details?
I can't understand low Vdsat can reduce the offest of opamp

Here, I have a little quetion that is how to minimize the vos of opamp in the bandgap reference circuit.

Same techniques that apply to opamp also apply for Bandgap.
Some of them:
1. common centroid layout for input diff-pair
2. Low VDsat for input diff-pair.
3. Sizing of 2nd-stage input TR. & 1st stage load TRs in the ratio of their currents.

Regards

Added after 3 minutes:

Why large current will reduce the output noise?

Hi All

when u r supplying RF circuits that are sensitive to noise u should consume larger current in the BG opamp to minimize the output noise.