[SI-LIST] Re: Propagation delay difference
- From: istvan novak <Istvan.Novak@xxxxxxx>
- To: jpoltz@xxxxxxxxx
- Date: Sat, 10 Mar 2007 11:53:20 -0500
Jongbae and All,
As Julius pointed out, in 'normal' coupled microstrips a
considerable portion of the differential field goes through
free space above the traces, whereas in common mode
most of the field is confined to between the traces and
plane inside the dielectric material. It should be noted
however that this 'normal' construction is not the only
possibility: with layered dielectrics above and/or below
the traces, or just by shaping properly the facing contours
of the vertical trace walls, it is possible to make up for
the 'missing' coupling capacitance. All of these tricks
obviously require either extra material or processing, so
in regular digital applications we just live with the different
propagation delays.
Regards,
Istvan Novak
SUN Microsystems
Juliusz Poltz wrote:
>Hello Jongbae,
>
>
>
>The differential mode in inhomogeneous line (microstrip) propagates
>significant portion of electric energy through free space, whereas the
>common mode uses mostly the dielectric (located between strips and the
>ground plane). As a result, the effective dielectric constant of the
>differential mode is lower and differential signal travels faster. This
>phenomenon is common for all kinds of designs since we normally attach
>signal lines to ground planes using dielectric materials. In circuit terms,
>the difference is distribution of electric and magnetic field can be
>discussed as the difference in ratios of Cm/C and Lm/L for both modes.
>
>
>
>Best regards
>
>
>
>Julius
>
>
>
>----- Original Message -----
>From: <jbtera77@xxxxxxxxx>
>To: <si-list@xxxxxxxxxxxxx>
>Sent: Friday, March 09, 2007 4:06 AM
>Subject: [SI-LIST] Propagation delay difference
>
>
>
>
>>Hi, all
>>As all know, in homogeneous strip line, the propagation speed is the same
>>for both differential and common mode.
>>
>>However, in inhomogeneous microstrip line, the propagation speed of
>>differential mode is faster than that of common mode.
>>In specific, the value of Cm/C is higher than Lm/L in inhomogeneous
>>microstrip line while the values are same in homogeneous strip line?
>>
>>Could somebody let me know why it physically is?
>>
>>
>>Thanks in advance,
>>Jongbae Park.
>>
>>
>>
>>--
>>--------------------------------------------------------Ph.D Candidate
>>StudentTerahertz Interconnection & Package Laboratory,Department of
>>Electrical Engineering, Korea Advanced Institute of Science and Technology
>>(KAIST),373-1, Kusong-dong, Yusong-ku, Taejon 305-701,
>>KoreaFax)+82-42-869-8058Tel)+82-42-869-5458Mobile)+82-11-9787-7966E-mail)
>>pjb77@xxxxxxxxxxxxxxxxxxxxxx URL)
>>
>>
>>
>http://tera.kaist.ac.kr/----------------------------------------------------
>----
>
>
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