Important factors in choosing RFI filter or AC coupling component values before in-amps

Vala

Other Parts Discussed in Thread: INA333, INA826

Hi all,

I want to know what parameters I should consider for choosing RFI filter or AC coupling component values before in-amps. I mean except cut-off frequency. I know a couple issues:

1- The bigger the resistors, larger the tolerance, and less efficient the common-mode-rejection of the in-amp is.

2- On the other hand, with small resistors large capacitors should be used which needs large packages that become electrolytic capacitors.

3- I think the settling time of the filters should be considered too.

Please correct me in the above items if I am wrong and suggest me other factors.

Appreciate any help,

Regards

over 10 years ago

0 Joseph Wu over 10 years ago

TI__Guru** 100225 points

V324O,

Is this in regards to a data converter? If so, do you have a particular data converter in mind? If this is for instrumentation amplifiers in general, I can move this to the precision amplifiers group to get a better answer.

Joseph Wu

0 Vala over 10 years ago in reply to Joseph Wu

Expert 1110 points

Joseph Wu,

Oops, sorry! No this isn't. I made a mistake in choosing the forum. Thanks.

Regards

0 Joseph Wu over 10 years ago in reply to Vala

TI__Guru** 100225 points

V324O,

I'm just going to move this to the Precision Amplifiers Forum. I'm sure they'll be able to come up with an answer for you.

Joseph Wu

0 Vala over 10 years ago in reply to Joseph Wu

Expert 1110 points

Thanks!

0 Pete%20Semig over 10 years ago

TI__Mastermind 25865 points

Hello V3240,

First, let me note that some newer instrumentation amplifiers have integrated EMI/RFI filtering. Please take a look at the INA826 and INA333.

You are correct...large filter resistors and their mismatch (due to tolerance) will create an offset voltage due to the device's input offset current. Concerning the capacitors, mismatch of the common-mode caps can also create a differential voltage. Therefore it is recommended that the differential-mode capacitor's value is 10 times the value of the common-mode capacitors. Alternately, you may want to evaluate X2Y capacitors which have better matching between the three capacitors. Finally, it is certainly wise to ensure the passive filtering does not negatively affect your input signal.

0 Vala over 10 years ago in reply to Pete%20Semig

Expert 1110 points

Hi Pete,

Yes, I will probably use those chips, but good information about this issue. Thanks.

Regards

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Important factors in choosing RFI filter or AC coupling component values before in-amps