> So are you saying that Vref does not need to be stable as I thought?

No, quite the opposite (if I'm correct in my thinking). Vref source
impedance would appear to me to be as important a factor as any
other for a good result. Note that its specified impedance is only 250
ohms, vs 2k5 or 5k for the analogue input souce impedance

What I often do is jack up a 78L05 to 5.12V and use that for both
Vcc and Vref. Output Z of a 78L05 is around 0.2 ohms. I have no
figures to suggest it rises appreciably when jacked up. I have no
figures to suggest it doesn't either, but its current-sourcing capability
is similar, if not the same, as a straight regulator

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