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

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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