I see. Yes, I agree. The impedance is quite important with regards to both stability and noise control. 0.2 ohms is excellent and better than a Zener. I also noticed something about the PCB layout. Indeed it is often critical, especially for high resolution-high speed converters. ----- Original Message ----- From: "Jinx" To: "Microcontroller discussion list - Public." Sent: Wednesday, August 13, 2008 11:45 PM Subject: Re: [PIC] A/D impedances >> 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 > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist