>> That will give you a value with an error towards whatever level is used
>> for the "discharge" (instead). I do not see how that is better then a
>> value that is somehowe baised on interference from another channel.
>>
>> If you have two channels with, say, 3.0V and 3.1V on each, and you
>> *do* have problems with aquisision time, you will get a larger error if
>> you always discharge to 0V between each channel switch.
>>
>> Besides, I do not remember reading about that discharge for each
>> conversion either. :-)
>>
>> Jan-Erik.
>
> The discharge phase is not implemented on the smaller PICs (well, maybe o=
n
> some newer devices, I don't know them all).
>
> For example, the PIC18F4550 *does* have such a discharge phase (see
> datasheet DS39632D-page 267):
>
>   21.7  Discharge
>
>   The discharge phase is used to initialize the value of
>   the capacitor array. The array is discharged before
>   every sample. This feature helps to optimize the
>   unity-gain amplifier as the circuit always needs to
>   charge the capacitor array, rather than charge/discharge
>   based on previous measurement values.
>
>
> -Andries

Is "the array" the input sample capacitor? I think the ADC uses an array
of capacitors in a charge balance mechanism. It is, I think, like an R2R
ADC, but is instead C2C. I don't think the capacitor being discharged is
the input sample/hold capacitor.

Harold


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