Hello,

I'm currently looking at a product that uses the AD8232 with the high-pass filtering configuration described in the datasheet Figure 56 i.e. an alternative two-pole high-pass filter using C2 and Rcomp.

I would like to generate the transfer function for this section of filtering to understand it further, but I'm struggling to figure out how to derive this and hence how the cutoff frequency becomes = 10 / (2pi (sqrt(R1xC1xR2xC2)) as stated on page 22 of datasheet.

I've attached a re-drawn diagram to try and understand this circuit, but please give any comments.

Any help would be much appreciated!

Tom

Hi Tom,

You can derive the transfer function using KCL at the node where R1, R2, and Rcomp meet (let's call it Vx), and then again at the -IN of HPA. You can solve for Vx in one equation so you can sub it into the other to find HPDRIVE/IAOUT. If you check out the "Eliminating Electrode Offsets" section on page 21 of the datasheet, it explains that the in-amp feedback causes the cutoff equation to be modified by the G=100 of the in-amp. The second-order filter just gets you there 10X faster.

Feel free to post here again if you get stuck.

Regards,

Jordyn