A question about bandgap reference,please help me.

[jonneylu]

I designed a bandgap reference circuit,as is shown in the attached picture.The circuit is based on the amplifier feedback to build reference voltage.In ac simulation,it's loop gain and phase margin is enough,but in transient simulation,it will fluctuate with amplitude 0.2mV. I dont know which caused it.
Please help me to solve it ,thanks!

 

[transbrother]

i do not see an attached fig

 

[iamxo]

what is the fluctuation? Vref or opamp's step resonse.

if it is Vref's, I think it may come from your simulation power supply rise time or the parasitic cap between Vdd and Vref. you can use low rise time (1ms) to simulate.

if it is opamp's, I think you should simulate your opamp in the loop, not breaking it from the whole circuit , to see whether it is stable.

 

[suria3]

If the 0.2mV is at the voltage reference output, then it could be due to the poor PSRR of your opamp or the overall bandgap. Putting some cap at the output will also reduce some ripples.

 

[jonneylu]

to transbrother:
Sorry, when i attach the pic,encountered some trouble.
to iamxo:
Vref flucutation.And what you said is write,when the rise time is longer,the vref is better.
to suria:
the psrr is 90 db at DC.

 

[holddreams]

to transbrother:
Sorry, when i attach the pic,encountered some trouble.
to iamxo:
Vref flucutation.And what you said is write,when the rise time is longer,the vref is better.
to suria:
the psrr is 90 db at DC.

If possible you can paste your circuit and simulation file here,
then someone can give you answers or suggestions about the problem.

 

[jankin]

Please upload the circuits.

 

[mingjie]

don't see your circuit

 

[paley]

pls upload your schematic and simulation files

 

[niezimei]

In my opinion, it is caused by the simulation options. ues method=gear, the parastic ring will disappear.