How to calculate effective resolution of ciruit

Discussion in 'General Electronics Chat' started by, Jun 10, 2014.


    Thread Starter Member

    Feb 27, 2014
    I am using 24 bit adc ADS1247 to measure voltage drop across thermsistor by passing current through it.

    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.

    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

    Last edited: Jun 10, 2014
  2. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
    Why don't you use some of the linearizion IC's, like TI's PGA309?
  3. dougc314


    Dec 20, 2013
    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