[sdiy] A (slightly) better VRef?

[ASSI]

On Monday 20 February 2012, 17:49:28, Justin Owen wrote:
> For VRefs I've always used the 2xR voltage divider into an op-amp buffer
> shown in Ex. 1. It's simple, it works but I've been wondering if there
> might be a small step up?
> 
> Would there be any advantage in using Ex. 2 over Ex. 1?

It all depends on what you define a "reference".  If the rails are regulated 
and your reference is supposed to track them, then Ex.1 is fine.  You might 
want to filter both input and output and tack R1||R2 into the feedback loop 
to minimize offset drift, but the trait of that reference is that whatever 
the supply does, the reference will follow.  You should also keep an eye on 
where those voltages come from you feed the divider with, they should go 
back directly to the rail regulators.

If on the other hand you want an absolute reference voltage, then this is 
not the circuit to use.  In fact you shouldn't be using Ex.2, either.  These 
days there is little to no reason to employ something like this, a proper 
fixed reference IC (or adjustable is you prefer) will give you a much more 
stable reference.


Regards,
Achim.
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