Noise measurement of triple LM399H with constant current supply and simple filtering (see pictures above):

Pass No1: 0.88 uV p-p;

Pass No2: 0.87 uV p-p.

Hello,

That's a very good result: what is the band with of the filter?

Generally I have also large differences on my LM399 references:

The theoretical value on buried zeners with around 1mA is around 0.6ppm (p-p).

So for a 7V reference the theoretical value should be 4.2uVpp.

LM399#1 (LM334 temperature compensated current source) av: 3.85 uVpp s: 0.36 uVpp

LM399#2 (LM334 temperature compensated current source) av: 6.55 uVpp s: 0.35 uVpp

LM399#3 (LT1013 bootstrap current source) av: 3.56 uVpp s: 0.42uVpp

CH6 + CH7 are simple resistor configurations. (But with low noise LT1763 voltage regulator).

But since the dynamic resistance of the LM399 is around 0.5 Ohms

the difference current source / resistor has only very low influence on the 0.1 - 10 Hz noise.

With best regards

Andreas