[SI-LIST] Re: capacitor impedance in time domain

Chris,

 

While one could define a capacitor impedance for time varying signals ? this 
would also be time varying, signal dependent and not very useful. For portions 
of the signals that are fast changing the capacitor shows a small ?impedance?, 
for the slow varying parts a large one.

 

You can solve the time domain differential equation of your system (with 
progressive and regressive waves on the Tx line) and find the time domain 
reflected wave as a function of C, no impedance needed.

On the other hand one could work in Laplace domain in which case the capacitor 
impedance is Z(s)=1/sC. Perform a Laplace transform on the signal, solve the 
reflection from Z(s) and transform back to time domain. Or you could do the 
same with Fourier transforms as Steve suggested.

And of course there is spice?

 

Peter

 


steve weir <weirsp@xxxxxxxxxx> wrote:group_delay, you have two choices, work in 
the frequency domain and 
convolve, or work in the time domain. It is usually a matter of what is 
more convenient. If you want to work in the frequency domain, you will 
need to convert your pulse into its constituent parts, including phase 
relationship, and then to get a TD response back out convolve again. That 
seems an awful lot of work versus a first order differential equation 
representing the Tx line as a resistance and the capacitor without parasitics.

Steve
At 03:08 AM 1/26/2005 +0000, group_delay wrote:

>Hi Steve and others,
>I am actually trying to do some theoretical analysis and for that I
>am using ideal transmission line and ideal capacitor. In other
>words, no parasitics. It is a single pulse with zero initial
>conditions on the capacitor. So in this case Z = 1/jwC, but the
>question is how to pick w?
>
>Thanks,
>Chris
>
>
>--- In si-list@xxxxxxxxxxxxxxx, steve weir wrote:
> > No, the sine wave impedance is only Z = 1/jwC near DC where you
>probably
> > don't care. For moderate frequencies, and assuming that you want
>to look
> > right at the capacitor, then the R-L-C model is adequate. But,
>depending
> > on the type of dielectric, C may vary considerably across the
>waveform
> > amplitude. If you are just trying to pass a pulse, you can get
>around that
> > by making C large enough that variations are insignificant to the
>series
> > impedance. However, if you are building an equalizer, then the
>choosing a
> > suitable dielectric type like plastic that doesn't change Er
>noticeably
> > with bias voltage is probably an important choice.
> >
> > Then there is the little problem of the initial condition. Is
>this a
> > single pulse with the system starting at zero, or is it a pulse in
>the
> > midst of a train of pulses? Given your chosen moniker, hopefully
>you have
> > the initial conditions in mind.
> >
> > Steve
> >
> > At 10:11 PM 1/25/2005 +0000, group_delay wrote:
> >
> > >Hello,
> > >
> > >I am trying to see what kind of an impedance a capacitor will
>present
> > >to a trapezoidal signal (finite rise time square wave). For a sine
> > >wave, we all know it is Z = 1/jwC. I need to know this because, I
>want
> > >to find the reflected (from load) waveform magnitude in the
>following
> > >situation:
> > >
> > >source --> 50 ohm termintion--transmission line--capacitor
>shorted to
> > >GND.
> > >
> > >Thanks.
> > >
> > >
> > >
> > >------------------------------------------------------------------
> > >To unsubscribe from si-list:
> > >si-list-request@xxxx with 'unsubscribe' in the Subject field
> > >
> > >or to administer your membership from a web page, go to:
> > >http://www.freelists.org/webpage/si-list
> > >
> > >For help:
> > >si-list-request@xxxx with 'help' in the Subject field
> > >
> > >List FAQ wiki page is located at:
> > > http://si-list.org/wiki/wiki.pl?Si-List_FAQ
> > >
> > >List technical documents are available at:
> > > http://www.si-list.org
> > >
> > >List archives are viewable at:
> > > http://www.freelists.org/archives/si-list
> > >or at our remote archives:
> > > http://groups.yahoo.com/group/si-list/messages
> > >Old (prior to June 6, 2001) list archives are viewable at:
> > > http://www.qsl.net/wb6tpu
> > >
> >
> >
> > ------------------------------------------------------------------
> > To unsubscribe from si-list:
> > si-list-request@xxxx with 'unsubscribe' in the Subject field
> >
> > or to administer your membership from a web page, go to:
> > http://www.freelists.org/webpage/si-list
> >
> > For help:
> > si-list-request@xxxx with 'help' in the Subject field
> >
> > List FAQ wiki page is located at:
> > http://si-list.org/wiki/wiki.pl?Si-List_FAQ
> >
> > List technical documents are available at:
> > http://www.si-list.org
> >
> > List archives are viewable at:
> > http://www.freelists.org/archives/si-list
> > or at our remote archives:
> > http://groups.yahoo.com/group/si-list/messages
> > Old (prior to June 6, 2001) list archives are viewable at:
> > http://www.qsl.net/wb6tpu
>
>
>
>------------------------------------------------------------------
>To unsubscribe from si-list:
>si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
>or to administer your membership from a web page, go to:
>http://www.freelists.org/webpage/si-list
>
>For help:
>si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
>List FAQ wiki page is located at:
> http://si-list.org/wiki/wiki.pl?Si-List_FAQ
>
>List technical documents are available at:
> http://www.si-list.org
>
>List archives are viewable at:
> http://www.freelists.org/archives/si-list
>or at our remote archives:
> http://groups.yahoo.com/group/si-list/messages
>Old (prior to June 6, 2001) list archives are viewable at:
> http://www.qsl.net/wb6tpu
>


------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field

List FAQ wiki page is located at:
http://si-list.org/wiki/wiki.pl?Si-List_FAQ

List technical documents are available at:
http://www.si-list.org

List archives are viewable at: 
http://www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu




                
---------------------------------
Do you Yahoo!?
 Yahoo! Mail - now with 250MB free storage. Learn more.

------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field

List FAQ wiki page is located at:
                http://si-list.org/wiki/wiki.pl?Si-List_FAQ

List technical documents are available at:
                http://www.si-list.org

List archives are viewable at:     
                http://www.freelists.org/archives/si-list
or at our remote archives:
                http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
                http://www.qsl.net/wb6tpu

Other related posts: