"For each measurement the ADC uses 40,000 clock cycles ( counts ) to carry out the Auto zero, Integrate(10,000 counts) and de-integrate (20,000 counts). And in the process of de-integration, if the comparator is unable to "zero" the refernce capacitor even after 20,000 counts have elapsed, then the over range bit is set."

Correct, but in the Integrate phase the converter also determines and latches the polarity of the signal. At the start of the De-integrate phase, this polarity information is used to determine the correct polarity of the reference current, so that the integrator output returns to zero. So those 20,000 counts can represent either positive or negative inputs, as indicated by the POLARITY output.

Let's say you want to measure a voltage between 0 and 2V. Assume the signal is 0.5V. This will give you a reading of 5,000 counts , which equals a resolution of 0.5V/5,000 = 100µV.
Now if you scale your input by 2 and add an offset of -2V, the input of the converter will see -2 to +2V. The same 0.5V input signal will give a reading of 10,000 counts (negative), which means a resolution of 0.5V/10,000 = 50µV.
All you have to do is correct for the scale and offset in your software and you have a 40,000 count converter. QED.


Rob.