ADC Differential 16bit channels

[fbaglivo]

Hi! I have a doubt on K64 series ADC channels resolution. This paragraph is unclear:

The 16-bit accuracy specifications listed in Table 30 and Table 31 are achievable on the differential pins ADCx_DP0, ADCx_DM0. All other ADC channels meet the 13-bit differential/12-bit single-ended accuracy specifications.

Reading this I understand that there is only one ADC differential channel that meets 16bit accuracy specs. I guess that the rest are 13 bits ADC channels. Is that correct? 

Best!

[mjbcswitzerland]

Hi

All channels can work in either 8, 10, 12 or 16 bit modes, however the "accuracy" achieved depends on the settings (speeds, HW averaging etc.) and the practical limit (when no extra noise from PCB etc.) tends to be between around 12..13 bits.
The differential inputs can achieve sightly better accuracy than the single-ended ones (possibly up to 14.5 effective bits with maximum HW averaging enabled).

Specific to your question; I expect that all differential inputs (and not just the ADC0_DP0/DM0 and ADC1_DP0/DM0) would be equivalent but the data sheet does indeed only precise the improvement on ADCx_DP0/DM0, which may be true for specific reason but could also be just that the 0 should be a y. We will need to wait to see whether the person who wrote the data sheet can confirm which it is to be absolutely sure (or try it and find out - which will need a very good/low noise circuit HW to be practical).

Regards

Mark

[fbaglivo]

Hi Mark! Thanks for your quick answer. The thing i do not get is why NXP announces 16 bit ADCs if it never reachs that accuracy. It´s not clear at all and makes difficult HW selection.  It seems  to me like a tricky selling strategy.

Best!

Fabricio

[egoodii]

I'm afraid ALL ADC (and DAC) devices are marketed at their physical "number of bits" handled.  The 'basic figure' for inherent realized resolution for an ADC is Equivalent Number Of Bits (ENOB).  But as in all things analog, there are a NUMBER of error factors to consider in overall 'accuracy' for your application.