Will adding these two capacitors help with common mode signal rejection

Sheldon He

Hi expert,

I'd like to know if any ways to increase common mode signal rejection by adding these two resistors in the circuit? How will they influence the CMRR?

If they can't, is there any other ways to improve CMRR?

Thanks

over 5 years ago

0 LeonardEllis over 5 years ago

TI__Guru 71526 points

Hello Sheldon,

When you say "in the circuit" please expand on what the circuit you are referring to might be. A schematic would be very helpful, as well as the type of device you are using "in the circuit".

Thanks,

~Leonard

0 kai klaas69 over 5 years ago

Guru 140200 points

Hi Sheldon,

to post a picture use the "Insert File" button (paper clip) in the header of text box.

Kai

0 Sheldon He over 5 years ago in reply to LeonardEllis

TI__Expert 8585 points

Hi Leonard and Kai,

Sorry for missing the file. They two capacitors are shown here!

0 Sheldon He over 5 years ago in reply to kai klaas69

TI__Expert 8585 points

Hi Kai,

I have upload a circuit diagram to ilustrate my question.

Thanks

0 Ron Michallick over 5 years ago in reply to Sheldon He

TI__Guru**** 165206 points

Sheldon,

Those capacitor make a low pass filter. So they reduce bandwidth. If the caps don't match then they could actually reduce CMRR.

0 kai klaas69 over 5 years ago in reply to Sheldon He

Guru 140200 points

Hi Sheldon,

the best common mode rejection is provided by the true instrumentation amplifier with three OPAmps. The common mode rejection of the simple differential amplifiers, on the other hand, usually suffers from the loss of symmetry caused by the manufacturing tolerances of the four resistors. And even with hand-selected resistors uneven temperature drifts and long term drifts will heavily limit the achievable common mode rejection. Unfortunately, the instrumentation amplifier can only show its advantage at higher gains.

Kai

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Will adding these two capacitors help with common mode signal rejection