I am using 24 bit adc ADS1247 to measure voltage drop across thermsistor by passing current through it.
http://www.digikey.com/product-detail/en/PR103J2/615-1069-ND/2651611

Since thermistor value gets very large so I connected a 20K fixed resistor in parallel with it.


1. Now my current source is 50uA with initial error is +-6% with temperature drift +-100ppm/C.

2. Voltage reference is 2.048V with +-10mV & drift is +-15ppm/C.

3. Resistor = 20K +-0.01% with drift +-5ppm/C.

4. PGA = 2, operating range = -40C to +60C.

5. Minimum voltage step need to measure = 75uV.


Questions:
1. How to calculate effective resolution I will get finally.

2. Do I need any other factors to consider besides I mentioned above.

3. Do final resolution is equal to ENOB?

4. Will I be able to achieve minimum voltage step = 75uV with this adc




Crosspost:
http://www.eevblog.com/forum/beginners/how-to-calculate-effective-resolution-of-ciruit/

 

Why don't you use some of the linearizion IC's, like TI's PGA309?

 

The thermistor has a non-linear resistance change with temperature. In order to calculate resolution you will need to generate on expression for resistance as a function of temperature. There are good articles on Wikipedia for this. Also most Thermistor vendors publish a table of resistance vs temperature for their thermistors and you could simply use the table to determine the dR/dT at various temperatures. I think the most important AD parameter you are looking for is differential non-linearity, check that out on Wikipedia as well