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AD7746 and Capacitance expansion technique

Question asked by Preetham on Jun 28, 2013
Latest reply on Jun 28, 2013 by seanbrown

We are doing a Project to measure a capacitance of range 300nF to 750nF using AD7746.


We are using Capacitance Extension technique to get 200pF and connecting a capacitor of 180pF in series with the capacitance we are measuring (so that effective capacitance can come in the range 180pF).


I have series of doubt while doing this!!!!


1. What will be the Range if capacity extension technique is implemented for 200pF. I think it will be


     resolution=200E-12 / 2^24= 1.192092896E-17= nearly 12aF


2. What are the registers value i have to program to activate the capacity extension technique of 200pF.

3. The concept behind the CAPDAC if explained correctly i would be very helpful. ( I really didnt get the concept behind the CAPDAC)

4. The square pulse coming out of EXCA and EXCB is AC or DC??? I mean whether it is Bipolar or Unipolar.


I would be very helpful to solve myself using answers. Expecting your reply.