Filter after amplifier in the ECg block diagram

Hi

I am attaching a ECG block diagram. I have a question in my mind In the lock diagram a pre-amplifier is placed before the filter block but when we try to design a filter normally OTA-C filter then we try to take small vgs so that we can achieve linearity. If pre-amplifier is placed before filter the pre-amplifier will provide a large amplified signal which will go to the filter and the filter input will be large. For reducing the input signal in filter different attenuation techniques are used so that we can get low vgs and improved linearity. Why a filter block is placed after a pre-amplifier because first we increase the signal by using pre-amplifier then we try to decrease the amplified signal to get low vgs to improve linearity in filter.

First increasing and then using techniques to decrease signal I can understand. Cant a filter be placed directly then amplify may be.


Can some one help me in understanding this.

Why is your filter non-linear? Most filters have excellent linearity. Maybe the gain of the preamp is too high and is clipping? You do not attenuate the signal, instead you set the gain so that the output level is not too high.

Your last post came to me as an alert but is not in this thread, maybe you deleted it.
It sounds like you are re-inventing an ECG amplifier circuit by using a Mosfet??
But usually an instrumentation amplifier IC is used with common-mode negative feedback fed to the patient to cancel AC and DC interference. Here is one of many similar circuits:

n OTA-C filter the OTA is nonlinear. We have to increase linearity to make filter linear.

My question is when we hv increased the amplitude of ECG signal by a pre amplifier than for designing the filter the amplitude of the amplified signal is reduced to decrease vgs because low vgs increases linearity.

First increasing the signal by pre amplifier than decrease it by using different techniques in filter design to decrease vgs. I cant understand. The small ECG signal can directly be send to filter instead of first amplifying

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Thankyou for your reply. I am not re-inventing the ECG amplifier. I have seen many research articles in which an OTA-C filter is designed for ECG acquisition system. I have attached the block diagram attachd in my first post above. The OTA-C filter is designed by frst designing the OTA and increasing the OTA linearity then use it in OTA-C filter.

OTA-C filters have limited linearity by design. They realize a tradeoff between linearity and dynamic range.

If you want best linearity, use different filter topologies than OTA-C.