What is the aim of the filters?

Thread Starter

bessou55

Joined Oct 14, 2022
13
Hi,
can someone please explain what is the exact role of the filters below.
The circuit is designed to amplify a low voltage signal( 0-10mV) 100 times.
But I dont see why are the filters exactly used?
Here is the circuit:
View attachment 279231
Thanks
 

ericgibbs

Joined Jan 29, 2010
18,837
hi niss,
The C1 blocks the DC component of the Vout signal, together with R5 as an intermediate load.

R8 and C2 are a low pass filter.
Where is the Vinp of the INA connected, is it a 'noisy' voltage.?
E

BTW: Is this Homework.?
 

Audioguru again

Joined Oct 21, 2019
6,688
C3 reduces power supply noise.
C1 blocks DC but passes frequencies above 3.2Hz (-3dB).
C2 and R8 might be a lowpass filter that passes low frequencies and cuts high frequencies.
 

Thread Starter

bessou55

Joined Oct 14, 2022
13
hi niss,
The C1 blocks the DC component of the Vout signal, together with R5 as an intermediate load.

R8 and C2 are a low pass filter.
Where is the Vinp of the INA connected, is it a 'noisy' voltage.?
E
Hi, thank you for your answer.
So are C1 and R6 high pass filters?
So do we consider both together as a bandpass?
Inputs are connected to electrodes placed on the skin to measure the voltage of the muscles.
(No it is part of a project Im working on)
 
Last edited:

Papabravo

Joined Feb 24, 2006
21,225
C1 and R6 is a single pole high pass filter. R8 and C2 are a single pole loww pass filter. They may work well in combination, but I can't tell by looking at them. That would take additional time to do an analysis.
 

ericgibbs

Joined Jan 29, 2010
18,837
hi niss,
We discussed this INA a week or so ago.
This is the response I see, assuming a skin/muscle resistance of say 10k.
E
EG57_ 149.png
 

ericgibbs

Joined Jan 29, 2010
18,837
hi niss,
R5/6 changed.
E

Update: @nissafha
To choose a suitable filter, you must have an idea what are the range of frequencies of interest that you expect from the Vin source, and then filter out any unwanted low or high frequencies.
Do you have an image showing the expected signal input?

EG57_ 150.png
 
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