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

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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