Does perceived ADC resolution, range and precision depend on fixed point format? What is the best way to deal with this for signal processing? I am working on a system that is implementing a digital filter that was designed for another system that had an FPU and a 12bit ADC. The system that I am working on is using the same filter without an FPU using a 12 ADC and fixed point arithmetic.

The ADC resolution is 3.3v / 2^12 = 0.000805664062v


With an FPU each ADC integer value could be scaled with the above resolution. 

On the system using fixed point where 

m2^-e, e = 10 


The resolution would be 

2^-10 = 0.0009765625


This leads me to think that the use of fixed point is giving me slightly lower resolution.

Looking at it differently and representing a delta between ADC integers with 14bits for the fraction the resolution could be

2^(-11) + 2^(-12) + 2^(-14) = 0.000793457031


but then the range would be perceived as less than 3.3V

Is this thinking correct?
it may turn out to be very inconvenient, but you can do essentially anything in fixed-point that you can do in floating.  as long as you got "Add-with-carry" as an instruction and enough MIPS to do all of the multiword instructions you may need.  the 12 bits that come from your ADC don't care if it's fixed or floating and your ADC resolution is the same regardless.  can't promise that the quality of code coming out of a C compiler will be any good.