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Design >> Analog Design >> any passive r-c circuit which can filter CM noise in band.
https://designers-guide.org/forum/YaBB.pl?num=1414575531

Message started by yvkrishna on Oct 29^th, 2014, 2:38am

Title: any passive r-c circuit which can filter CM noise in band.
Post by yvkrishna on Oct 29^th, 2014, 2:38am

Hi,
I have a Diff signal and CM noise in band, is there any passive circuit which can filter the CM noise component without filtering the DM signal component.

Thanks,
yvkrishna

Title: Re: any passive r-c circuit which can filter CM noise in band.
Post by loose-electron on Nov 2^nd, 2014, 7:12pm

Process the signal though a differential amplifier that should have significant CMRR characteristics.

Keep the system fully differential end to end in any and all analog parts

Title: Re: any passive r-c circuit which can filter CM noise in band.
Post by yvkrishna on Nov 2^nd, 2014, 8:38pm

@loose-electron,

differential amplifier is probably the best way to address this, however my CM noise swing is about 4X larger the min. detectable DM signal present.

However I wonder if there exists any passive circuit which can do this job?
When I search for this on google I only get Commonmode choke.

I have also tried using a T network (shown in the pic)which offer different impedance for CM and DM picture, even here I am not able to achieve CM bandwidth < DM bandwidth.

looks like there is some fundamental limitation in what I am trying to achieve using passives.

Thanks,
yvkrishna

Title: Re: any passive r-c circuit which can filter CM noise in band.
Post by loose-electron on Nov 3^rd, 2014, 4:59pm

consider a common mode choke then. External to the chip if needed, or even internal to the chip if you have the freedom of doing some electromagnetics inside the chip. Will depend heavily on frequency range needed and the consequent size of the device.

Title: Re: any passive r-c circuit which can filter CM noise in band.
Post by yvkrishna on Nov 3^rd, 2014, 10:02pm

I doubt if there exists any simple r-c circuit which does this.

Or is this impossible without using electromagnetics ?

Title: Re: any passive r-c circuit which can filter CM noise in band.
Post by loose-electron on Nov 6^th, 2014, 4:01pm

plenty of active circuit methods

does it have to be passive? If so I think you are going to need some electromagnetics

Title: Re: any passive r-c circuit which can filter CM noise in band.
Post by hiSkill_11 on Sep 8^th, 2015, 11:57pm

How about using diff amp with high DM BW and low CM BW?

yvkrishna wrote on Oct 29^th, 2014, 2:38am:

Hi,
I have a Diff signal and CM noise in band, is there any passive circuit which can filter the CM noise component without filtering the DM signal component.

Thanks,
yvkrishna

Title: Re: any passive r-c circuit which can filter CM noise in band.
Post by loose-electron on Sep 10^th, 2015, 10:22am

Have you researched the concept of "Instrumentation Amplifiers" ???

Getting rid of big common mode signal content is what these are designed for.

Research time.