High swing reference current

230

02:08:45

Try to creat a high swing 1 uA reference current circuit. 

This circuit isinspired by a circuit engineer in my company. Nonetheless, the output currents(both sink and source) are still not stable enough against supply voltage fluctuation.

I think I need to re-design the opamp.
*Update*
I added start up circuit. This circuit can now start correctly.

published 4 years ago

Redstone_guy

4 years ago

Cannot find solution

KeenZa

4 years ago

@Redstone_guy I fogot to pull up the switch. I have just fixed it. Close the switch and this circuit will work ~

abobaker

4 years ago

Note that it's not the DC supply variation that causes changes in the reference current , but the high frequency ones in your case, so it's mostly a problem with PSRR not with power supply variations ... try to reduce the frequency of the AC source to 1~10Hz and then to 100MHz and notice how the variations saturate to a certain value vs. frequency

abobaker

4 years ago

this is a typical PSRR curve, and I think it's a good circuit ... BTW Cgs of transisitors here in every circuit is 10pF which is excessive compared to real transistors of that size, and this actually makes the PSRR even worse

abobaker

4 years ago

one final note BTW you need to add a startup circuit to this BG reference , because it does not start correctly every time

KeenZa

4 years ago

Thank you very much for the information ! 😃 I'll do deep study. BTW, I have never known about the start up circuit. I guess that I have homework now :)

will7

4 years ago

I am just leaarning about this field and will be in my second semester in August, so I don't know a whole lot. That said what is the purpose of this circuit? What type of things would it be used in? Thanks for putting it on there and any answers to my question,

KeenZa

4 years ago

@will7 From my experience, I see this circuit in a most analog part of an IC. It is used to bias other circuit using its output currents such as amplifier, comparator, LDO, TSD etc. These currents are temperature and supply voltage independent.

KeenZa

4 years ago

I try adding a start up circuit. Now, it can start correctly after closing the switch ~

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