[SI-LIST] Re: A question about how fast the step pulse we need in measuring impedence
- From: "DAVID CUTHBERT" <telegrapher9@xxxxxxxxx>
- To: huang.jian2@xxxxxxxxxx
- Date: Fri, 1 Aug 2008 08:22:34 -0600
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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