I'm trying to clarify my understanding of the relationship between ADC resolution and ENOB (Effective Number of Bits), particularly when it comes to practical calculations. From what I understand, ENOB represents the actual performance of an ADC accounting for real-world imperfections like noise and distortion, while the resolution is the theoretical bit depth of the converter. Since ENOB is invariably less than the stated resolution, I'm confused about which value should be used in calculations.

Specifically, when calculating the LSB (Least Significant Bit) step size, should I be using: 1 LSB = V_ref / 2^Resolution (the theoretical value) or 1 LSB = V_ref / 2^ENOB (based on effective performance)?

If ENOB is the more meaningful metric for actual performance, why do datasheets prominently feature the resolution specification? Is the resolution purely a marketing/theoretical spec, while ENOB tells the real story? Or do these two parameters serve different purposes in system design?

I'd appreciate any insights into when each specification is relevant and how you approach LSB calculations in your designs.

My current understanding:

Resolution defines the theoretical quantization - a 16-bit ADC has 2^16 discrete output codes, so with a 1V reference:

1 LSB = 1V / 2^16 = 15.26 µV (the step size between codes)

ENOB represents the actual usable performance accounting for real-world noise and distortion. If the same 16-bit ADC has ENOB = 14 bits, then:

Effective noise floor ≈ 1V / 2^14 = 61 µV RMS. Signals smaller than ~61 µV will be buried in the noise (hard to distinguish from random fluctuations)

This means that while the ADC outputs 16-bit codes with 15.26 µV steps, the inherent noise causes the readings to fluctuate by approximately ±2 LSB, making the effective resolution equivalent to a cleaner 14-bit converter.

Is this correct?