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

  • From: Steve Weir <weirsi@xxxxxxxxxx>
  • To: arpad.muranyi@xxxxxxxxx, <group_delay@xxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
  • Date: Fri, 28 Jan 2005 14:25:51 -0800

Arpad, let us suppose that we follow your intuition on this.  Then as a 
constant current source on the slopes, ie very high impedance, and an open 
on the flats, we should expect that little or none of the waveform couples 
through a series capacitor between two transmission line segments.  And 
that the incident wave reflects back to the source at nearly 2X 
amplitude.  However, that is not what we see in a real circuit, is it?  So, 
the intuition, however reasonable, is wrong.

Now, if we convert the TD representation into FD, the answer that we get 
correlates very well to experimental data.

Regards,


Steve
At 01:12 PM 1/28/2005 -0800, Muranyi, Arpad wrote:
>I enjoyed reading all the responses to this posting.
>The way I would look at it in the time domain is this:
>
>During the ramping part of the trapezoid waveform I
>would think of it as a constant current source, and
>during the horizontal portion of the trapezoid I
>would think of it as an open (or constant current source
>with a 0 A output).
>
>In terms of impedance, the AC (small signal) impedance
>of the constant current source is infinite, the DC
>impedance is V/I at any given time iteration.
>
>Arpad Muranyi
>Intel Corporation
>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
>=3D=3D=3D=3D=3D=3D
>
>-----Original Message-----
>From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
>On Behalf Of group_delay
>Sent: Tuesday, January 25, 2005 2:11 PM
>To: si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] capacitor impedance in time domain
>
>
>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 =3D 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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