From the datasheet for the Atmega328P, in the ADC input circuit the sample-and-hold capacitor (14 pF) is connected to Vcc/2. Why that and not ground?
My guess* is that this allows for a faster charging time. With a 5V input (and assuming Vcc is 5V) then the capacitor only has to charge up to 2.5V (being 2.5V over Vcc/2). And with a 0V input the capacitor charges (negatively) to -2.5V.
Or is there another reason?
- Which I am starting to think is nonsense.