[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 18:00:00 -0800
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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