[SI-LIST] Re: Differential mode impedance of common mode filter
- From: steve weir <weirsi@xxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Mon, 21 Jan 2013 04:33:18 -0800
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, 李晖 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
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