The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design >> Analog Design >> transient load for bandgap voltage reference
https://designers-guide.org/forum/YaBB.pl?num=1239680303

Message started by misc on Apr 13^th, 2009, 8:38pm

Title: transient load for bandgap voltage reference
Post by misc on Apr 13^th, 2009, 8:38pm

Dear forumites,

i am designing a bandagap voltage reference for and ADC. When i check for load current simulation for my architecture i found the bandgap voltage switching between certain voltages. i am expecting this to be constant with load current variations. I have attached transient load current response for reference, any inputs how to make my output constant with load current varions is of great help.

TIA
Raags

Title: Re: transient load for bandgap voltage reference
Post by misc on Apr 13^th, 2009, 8:40pm

also i am attaching the block level schematic for the reference

thanks in dvance
raags

Title: Re: transient load for bandgap voltage reference
Post by raja.cedt on Apr 14^th, 2009, 2:47am

hi Raags,
you should not draw current from the band gap,if you want draw put a buffer and then connect load,because when you are trying to draw current from the load it will come from the M1,then op amp will increase its bias and hence Mo current will also increase, then perfect cancellation of temp coefficients is impossible.
From your graph at zero current band gap voltage is at where it has to be.when you are trying to draw current it will increase because of op amp output increment. For convince your self add a dc current source at the load and see how your voltage will vary with temp,i guess it will vary a lot...
Another point i am trying to bring out is if you are connecting some thing at one side of the BG,connect other side also , this is the principle behind factional band gap.

Thanks,
Rajasekhar.