What does this equation mean?

The quantization step itself has a clean expression once gain and reference voltage are fixed. For an ADC with N effective bits resolving a full-scale reference voltage $V_{ref}$ , the size of one quantization step is $q = \frac{V_{ref}}{2^{N}}$. and, treating quantization error as uniformly distributed over one step, the resulting quantization noise power has a root-mean-square value of q / $\sqrt{12}$ . This is the textbook derivation behind every “effective number of bits” figure a converter data sheet reports, and it is the reason oversampling helps: spreading the same quantization noise power across a wider sampled bandwidth before filtering it back down effectively lowers the in-band noise floor without changing the converter’s physical resolution. This is analysis grounded in a standard result, not a claim from either vendor’s marketing copy — both data sheets report measured effective noise in microvolts or nanovolts RMS directly, and those measured numbers are what a systems designer should budget against, not the nominal bit count printed on the package.