[SI-LIST] Re: capacitor impedance in time domain
- From: steve weir <weirsp@xxxxxxxxxx>
- To: group_delay@xxxxxxxxx, si-list@xxxxxxxxxxxxx
- Date: Tue, 25 Jan 2005 19:28:08 -0800
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 <weirsp@xxxx> 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.
> > >
> > >
> > >
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