[volt-nuts] Voltage Reference Mini-Oven

[WarrenS]

I did not forget about the opamp, It need not be a limiting factor, which is 
why I did not include it in MY count.
True, it does need to be included in the basic "careful analog design 
considerations", and for many designs I've seen it can be a major source of 
error.
There are many options to insure it is not a problem.
Which one or ones are used depends on what is being made, ones skill level, 
and the amount of time and money available.


1) Lots of choices for selecting a better opamp.

2) Many opamps can be zero TC using there offset adjustment, A very OLD 
trick.

3) In the 6.2 volt version the effect of the op amp's offset is down  about 
100 to 1 so it is NOT critical
1uv change at the op amp causes a 0.002 PPM change at the 6.2 volt zener.

4) IN the manual A-Cal 10 volt version, the error of the opamp is removed 
completely by using the Manual A-Cal method.

5) The effect of the opamp's TC drift can be zero out (over a limited 
temperature range)  at the same time the Zener is Zero TCed, by changing the 
current thru the Zener .

6) And there are other less simple solutions to insure that the OpAmp does 
not become a critical part when building a precision voltage reference.

ws

*********************
>m k m1k3k1 at hotmail.com  wrote:

>Dont forget that you can have 1uV per C just from the opamp offset voltage. 
>That makes three critical parts.

*********************
> From: warrensjmail-one at yahoo.com
>
> Using a circuit similar to
> http://www.febo.com/pipermail/volt-nuts/attachments/20110903/b7da2eca/attachment-0001.gif
>
> A 10 reference standard can be built so that there are only TWO really
> critical parts that limit its performance.
> The reference  Zener and the 5/3 gain matched resistors.
> The rest just takes careful analog design considerations.
> The way I hope to remove the resistor matching limitation is to do that 
> part
> digital.
>
> As far as more details on the Mini-Oven, nothing else to say. It is just
> three small parts "Taped" together.
> One is the device to be controlled, one is the heater and the last is the
> temperature sensor. Same as any oven, just smaller.
> I don't know how this mini-oven would apply to a standard cell.
>
> ws
>