Cut-off frequency of biomedical amplifier

[ali45]

Hello friends
I have designed an amplifier based on Differential Difference Amplifier (DDA) topology for biomedical application,
but in close loop i can't adjust high-pass cut-off frequency for first stage. the image of circuit and frequency response are shown below
please help me...
Thanks

Image of circuit & results:

1- https://imgur.com/CoHJQzB
2- https://imgur.com/NjzreTx

 

[KlausST]

Hi,

I can't se details like part calues in your pictures.

Please use picture export or screen shot with .png format.
And please try to use the "add image" button (with the "tree" icon) at the top of the editor window.

Klaus

 

[BradtheRad]

can't adjust high-pass cut-off frequency

1.
Your plot appears to have greatest signal strength below 100 Hz. Do you want high or low pass?

2.
Your second amplifier has capacitors connected directly to the inputs. It blocks DC however there is no definite current path for signal because internal impedance is invisible and unknown. It creates an error known as a floating input.

 

[d123]

Hi,

Not too familiar with compensation topologies, and maybe SMPS compensation can't work here, so excuse me. Could the filters around the first amp be made into Type III compensation to boost the frequency response across the range of interest and give a gain boost higher up f range or does it have to cover 0Hz to fc?