If you go through page 1 of CN-0129 is explains what the F is and why the Resistors are needed. In its simplest form, you need to attenuator the excitation voltage so you can sense capacitances that are larger than the input range of the part. Q = CV, we need to reduce V to keep the max Q within the range of the part for large C values.

I have sketched out this equation derivation. I have attached my understanding of it. The best way to break it down is to think about the two different excitation signals separately at first then subtract them. See the attached.

Hi Angela,

If you go through page 1 of CN-0129 is explains what the F is and why the Resistors are needed. In its simplest form, you need to attenuator the excitation voltage so you can sense capacitances that are larger than the input range of the part. Q = CV, we need to reduce V to keep the max Q within the range of the part for large C values.

Regards,

Eric.