[volt-nuts] Making a Reference IC

[Dave M]

I was looking at the schematics for the Fluke 731 and 732 voltage 
references.  these, and several other brands and models of voltage 
references, use the same or similar reference ICs as their basis.  The 
reference ICs are a Zener/NPN transistor pair on a single substrate.

Please view in a fixed-width font such
as Courier.

        |
        |
      C |
        |
         \ |
          \|
           |----
           |  B
          /|
         / |
      E |
        |
        +---------------
        |
     /------/
       /  \
      ------
        |
        |

Just thinking... would it be possible to make a reference with similar 
characteristics with discrete components (a low tempco Zener and a 
transistor)?  They would likely have to be closely coupled thermally and 
maintained at a constant temperature within an oven or by a peltier device.

What criteria would apply to the selection of the parts?

Dave M