ICMR (Input common mode range) of OTA

[simplsoft]

Can anyone help me in designing an OTA (operational transconductance amplifier) that can be used in designing of filter used in biomedical low frequency application (ECG detection).

I want to design an OTA but I can understand what Input Common mode range (ICMR) do I have to select?

Another thing for finding the DC gain we apply ac input at the differential pair of OTA and find the gain VS frequency and we say its a DC gain why is it so? when the input applied at differential pair is ac?

Regards

 

[Ata_sa16]

you have to chose your topology first.

Input common mode range depends on your application.

DC gain is:

The gain of amplifier when you apply a very low frequency signal at the input (fin < f3db OTA).

If you increase your frequency your gain will decrease.

 

[simplsoft]

Thanx for your reply. I want to design an OTA for portable ECG detection system. As I am at initial stage so I am trying a simple OTA (differential pmos ). This ICMR (Input common mode range) is diffficult for me to find? Is ICMR different for different topologies? I am designing OTA with 180nm.

Second thing which I want to ask is at the differential pair of OTA we have to apply dc+ac input or just ac?because we do the biasing and apply dc voltages at the gate of the differential pair to set the transistor modes of operation (saturation mode). so we apply dc+ac input to both the input of differential pair. and are equal ac + dc voltages applied?

Regards

 

[mtwieg]

Search for the paper "A Low-Power Wide-Linear-Range Transconductance Amplifier" by Sarpeshkar et al. Basically you need to degenerate the gm of the input (which will increase your input referred noise).

 

[Ata_sa16]

Thanx for your reply. I want to design an OTA for portable ECG detection system. As I am at initial stage so I am trying a simple OTA (differential pmos ). This ICMR (Input common mode range) is diffficult for me to find? Is ICMR different for different topologies? I am designing OTA with 180nm.

Second thing which I want to ask is at the differential pair of OTA we have to apply dc+ac input or just ac?because we do the biasing and apply dc voltages at the gate of the differential pair to set the transistor modes of operation (saturation mode). so we apply dc+ac input to both the input of differential pair. and are equal ac + dc voltages applied?

Regards

equal DC voltage and differential ac.

for example 0.6+1mv * sin(wt) and 0.6-1mv * sin(wt)

and for AC simulation:

0.6 DC for both , +1v AC and -1v if your topology is differential +1v and 0v if its single ended.