[SI-LIST] Re: Differential mode impedance of common mode filter
- From: steve weir <weirsi@xxxxxxxxxx>
- To: lihuizju <lihuizju@xxxxxxxxx>
- Date: Mon, 21 Jan 2013 23:27:33 -0800
The way that a CM choke is normally specified any DM impedance greater
than zero is from mostly leakage inductance and attenuates your signal.
This particular part's data sheet does not spec. that way. They present
a couple of S parameter magnitude plots which for your application
should be far more useful.
Steve.
On 1/21/2013 8:57 PM, LiHui wrote:
> HiSteveï¼
> Thanks for your reply.
> I had contacted with FAEs of the vendor, but they didn't give me a
> satisfaction answer. What confused me is the differential
> mode(actually from Eric Bogatin's book, this is should be odd mode)
> impedance which is different with characteristic impedance, so why do
> we need differential mode impedance? Does it mean the larger
> differential mode impedance, the more attenuation of the input signal?
> Best Regards!
> ------------------------------------------------------------------------
> lihuizju@xxxxxxxxx
> *From:* steve weir <mailto:weirsi@xxxxxxxxxx>
> *Date:* 2013-01-21 20:33
> *To:* si-list <mailto:si-list@xxxxxxxxxxxxx>
> *Subject:* [SI-LIST] Re: Differential mode impedance of common mode filter
> A CM choke is essentially a transformer that in the ideal case inserts
> the magnetizing inductance twice over in series with CM noise appearing
> at the input to both windings, and no inductance due to perfect field
> cancellation to difference signals. However, like all transformers:
> neither the coupling nor the inductive responses are ideal and hence the
> performance curves to tell you what a given part really does under the
> stated test conditions.
> Quality manufacturers such as Laird provide substantial theory of
> operation and application note data for their devices that can assist
> you. "common mode choke tutorial" returns 43,000+ hits in Google. Good
> reading.
> Steve.
> On 1/21/2013 4:11 AM, ææ wrote:
> > Hi All:
> > I have a spec of Onsemi's EMI4182 common mode filter. There's a figure
> > which depicts its common and differential mode impedance vs Frequency. I'm
> > confused with it, why the differential mode impedance varies with
> > frequency? Please recommend some articles or books which can help to
> > clarify it. I know discontinuous impedance will induce refection of input
> > signal, if the input signal are the digital clocks of MIPI whose working
> > frequency is 500Mhz but its band width would be several GHz, dose it mean
> > the reflection of this signal is inevitable?
> > In such scenario, how to choose an appropriate common mode filter?
> > Yours.
> >
> >
> >
> >
> --
> Steve Weir
> IPBLOX, LLC
> 150 N. Center St. #211
> Reno, NV 89501
> www.ipblox.com
> (775) 299-4236 Business
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--
Steve Weir
IPBLOX, LLC
150 N. Center St. #211
Reno, NV 89501
www.ipblox.com
(775) 299-4236 Business
(866) 675-4630 Toll-free
(707) 780-1951 Fax
All contents Copyright (c)2012 IPBLOX, LLC. All Rights Reserved.
This e-mail may contain confidential material.
If you are not the intended recipient, please destroy all records
and notify the sender.
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