Hello Everyone,

I'm sorry if this question is repetitive, but I tried to find similar questions on the whole forum and couldn't find anything, so I decided to start a new thread.

I was looking up the AD8232 datasheet and it suggests some circuits to implement a High Pass Filter (using the OPAMP labeled HPA) following the Transconductance based instrumentation amplifier (made up of transconductance amplifiers GM1 and GM2, and an integrator). However, the circuits look like they're implementing a low-pass Sallen-Key configuration, and not a high-pass one.

I'm sure I'm missing something here, but I can't zero-in on what I'm getting wrong. (I'm talking particularly about the figure number 56 in the datasheet.)

Could anyone quickly point out where I might be going wrong?

Thanks!

Lyapunov,

Was there a particular figure on the AD8232 data sheet you were asking about?

From control system theory, if you have a forward path, G, and a feedback path, H,

the closed loop transfer function is:

G/(1+G*H)

So if H is a low pass, it is in the denominator, and you wind up with a high pass.

Harry