ADC Vref

Wish to measure three small voltages (<1V) on a 16f676. Set Vref to 1.023V, but found the reading fluctutes with an injected voltage of 100mV on AN1. Checked AN1 ok with internal vref. This raises two questions:

1. What is the lowest practical value of Vref for the ADC to work correctly?

2. Does Vref require a buffer or filter capacitor - Checked with scope and Vref looked smooth?

Thanks

Any code and schematic are welcome ;)

Microchip's web site ahs an excellent 20 minute video on designing AD circuits. I can't place a direct link due to their .aspx, but search their site for "Techniques that Reduce System Noise in ADC Circuits"

Quote:

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Originally Posted by JD123

Microchip's web site ahs an excellent 20 minute video on designing AD circuits. I can't place a direct link due to their .aspx, but search their site for "Techniques that Reduce System Noise in ADC Circuits"

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Go to http://techtrain.microchip.com/webse...QuickList.aspx and search for "Techniques That Reduce System Noise in ADC Circuits". You'll find the information JDM123 is referring to.