I checked quite some ADC datasheets and am a bit confused regarding the actual achievable accuracy of an ADC.
Let's take this ADC for this example (ADC MCP3422): http://ww1.microchip.com/downloads/en/devicedoc/22088c.pdf
The most important specs:
- 18 Bit ADC (for 3.75 SPS, no missing codes)
- On-Board Voltage Reference (VREF): Accuracy: 2.048V ± 0.05%
- INL: 10 ppm of Full Scale Range
- GAIN ERROR 0.05 to 0.35% (PGA = 1, Includes all errors from on-board PGA and VREF)
An instrumentation amplifier will provide a signal in the range of 0-2V to this ADC (single ended). This ADC will not use the PGA (so: PGA = 1) By only taking the spec 'Gain Error' it can be off up to 0.35%, so regarding the conversion table I attached below, would already yield only a 10 Bit ADC max. I did not include all other errors from the specs i posted so far. Am I looking at it the wrong way and could I still get a decent accuracy out of this ADC (actual useful bits 14=<)?