Hello Tom
Actually, I am checking the differential mode of ADC in MSP432. It clearly define the CMRR for the ADC in differential mode.
I think it should be full differential. But I need the S/H stage digram(Analog input equivalent cicuit) to confirm this.
Thanks!
I have requested an equivalent circuit model, but you should be also be able to confirm this. For example, if Vin+ swings from 0 to 2.5V (where Vref+ = 2.5V and Vref- = 0V) and Vin- also swings from 0 to 2.5V but is 180 degrees out of phase, the differential waveform measured by ADC will swing from +/- 2.5V (full-scale).
Regards,
Chris
Hello,
At this time we can only provide the following for the equivalent circuit.
The switches used to apply the differential voltage (Vin+ - Vin-) are not shown. By inspection you will find that the conversion time is the same between single-ended and differential modes indicating that both capacitors are sampled and converted simultaneously and not sequentially. Furthermore, the datasheet shows that the full range is supported per the classical definition of true differential.
Please let me know if some additional evidences can be provided (instead of a more detailed circuit). I have done a couple of quick experiments to hopefully give more insite: In this first case the input on Vin+ is a 60hz sine wave which swings from 0 to 2.4V (Vref+ is 1.2V and Vref- is 0V). On Vin- is 1.2V. Please note that when Vin+ exceeds the rail it saturates.
In this second diagram the inputs Vin+ and Vin- swing from 0 to 1.2V but are 180 degrees out of phase.
Regards,
Chris
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