[SI-LIST] Re: Zo vs Zin
- From: "Loyer, Jeff" <jeff.loyer@xxxxxxxxx>
- To: <edpc108@xxxxxxxxx>
- Date: Thu, 13 Mar 2003 09:34:34 -0800
I don't know if you were looking for the mathematically intensive =
answer, or a more qualitative one. In case you're interested in the =
qualitative analysis, I would look to Eric Bogatin, and the =
www.gigatest.com website. He covers it very well in his classes, and =
there's probably relevant papers on the website somewhere.
My quick 'n dirty overview (and some of this is identical to how Eric =
states it):
Characteristic Impedance (Z0) is the "instantaneous" impedance a signal =
sees as it propagates down a trasmission line. It is independent of =
features which occur before or after the current moment. Z0 is usually =
graphed as a function of Z vs. time (or easily translated to Z vs. =
position). It is measured with a TDR (Time Domain Reflectometer). It =
is also largely frequency independent - you typically measure the same =
Z0, regardless of rise-time of the TDR, but you can only discern fine =
features with a short rise-time.
Input impedance, on the other hand is the "total" impedance of the =
circuit. It is very frequency dependent, especially concerning =
fractions of the wavelength of the circuit. It is typically measured =
with a VNA (Vector Network Analyzer), and is usually not graphed =
directly, but rather Vo/Vin (both amplitude and phase) are graphed vs. =
frequency.
Characteristic Impedance is used when talking in the time domain; input =
impedance implies we're talking in the frequency domain.
This is a very simplistic representation, and may raise more questions =
than it answers - a detailed answer could go on for pages. Eric gives =
an entire class on the subject. I would also look at Agilent's and =
TEK's websites.
Jeff Loyer
-----Original Message-----
From: Jayaprakash Balachandran [mailto:edpc108@xxxxxxxxx]
Sent: Wednesday, March 12, 2003 6:14 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Zo vs Zin
Dear SIers,
What is the difference between characteristic
impedance and input impedance in a transmission line?
Thanks in advance,
Jayaprakash.=20
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