[SI-LIST] Re: A question about how fast the step pulse we need in measuring impedence
- From: David Instone <dave.instone@xxxxxxxxxx>
- To: art_porter@xxxxxxxxxxx
- Date: Fri, 01 Aug 2008 16:38:53 +0100
Unless of course you don't meet the spec, in which case the extra
resolution of the faster pulse can help you decide which of all the
'summed' discontinuities is/are the ones to concentrate on fixing.
Regards
Dave Instone
+44 (0)1235 824963
OXFORD SEMICONDUCTOR LIMITED
25 MILTON PARK
ABINGDON
OXFORDSHIRE
OX14 4SH
Registered in England no 2733820
Registered Address: As above
art_porter@xxxxxxxxxxx wrote:
> TDR normalization is the solution to this problem. See app note
> http://cp.literature.agilent.com/litweb/pdf/5988-2490EN.pdf.
>
> Testing with a "real-world" rise time is always best; no point in worrying or
> wasting precious design time on reflections or perturbations that will never
> exist in your real design due to a slower rise time.
>
> Art Porter
> Agilent Technologies
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
> Behalf Of DAVID CUTHBERT
> Sent: Friday, August 01, 2008 8:23 AM
> To: huang.jian2@xxxxxxxxxx
> Cc: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: A question about how fast the step pulse we need in
> measuring impedence
>
> In the case of FR-4 PCB material the relative dielectric constant decreases
> at approximately 0.1 per decade of frequency. The 70 ps rise time vs. the
> 200 ps risetime will result in the Er being measured approximately 0.05
> lower. If you are measuring a 50 ohm line it may measure as 50.3 ohms.
> Dave Cuthbert
> SI, EMC, Analog, RF, Antennas, Pwr (unemployed)
>
> On Fri, Aug 1, 2008 at 4:50 AM, <huang.jian2@xxxxxxxxxx> wrote:
>
>
>> Must we need to filtering the default step pulse that the impedence
>> analyer generates so that the rise time of the filtered step pulse
>> is matching the real condition in the transmission line? For example, the
>> default rise time of step pulse that that the impedence
>>
>> analyer generates is 70ps, and the real rise time of applicable high speed
>> signal in the tranamission line is 200ps.
>>
>> What if the default step pulse with rise time of 70ps used in measuring
>> iimpedence?
>>
>> Thanks in advance
>>
>>
>>
>>
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