The Zin = 0 for that case. Makes sense; it's the reciprocal. (Same positive current defined as into CCVS.) The derivation is left as an exercise for .... Arpad. :-) The Thevenin source is solved with KVL and you get Zin=0. If you transform to Norton equivalent you get the original infinite Zin. These are just the native source impedances of the two types: ideal V source's Zin = 0, ideal I source's Zin = infinity. It seems that what either version of the problem is out to prove, by isolating the source from its load through the -1 control factor. -Agathon On 4/10/07, Kevin Ko <wy_k@xxxxxxxxx> wrote: > > > Will the answer be same/different with CCVS, instead of VCCS, parallel to > 1 > ohm? > > regards, > Kevin > > --- "Muranyi, Arpad" <arpad.muranyi@xxxxxxxxx> wrote: > > > Thanks for all the great replies! I enjoyed > > reading them. There are many ways to skin the > > cat, right? Another analysis would be to make > > a Thevenin equivalent of the circuit in which > > the Thevenin source generates the same voltage > > on one side of the resistor that exists on > > the other side, i.e. the current through the > > resistor is always zero. > > > > Now, regarding how this relates to the original > > topic of T-line impedance: > > > > The resistor in this "trick question" corresponds > > to the characteristic impedance of the T-line. > > > > The source (current for Norton, or voltage for > > Thevenin) corresponds to the reflected wave in > > the T-line (with zero delay). So the apparent > > impedance (which I also like to call "electrical > > impedance") can be calculated by looking at what > > the circuit does, i.e. taking all voltage and > > current relationships into account. I find this > > example a good way to illustrate what goes on > > in a T-line without having to go into Maxwell's > > wave equations. To extend this example for > > T-lines, all you have to do is add in some > > delays (or phase if you do it in the frequency > > domain), and you got it... > > > > By the way, you can turn a capacitor into an > > inductor with an op-amp, configured as a NIC, > > often used for making inductors on the die. > > Same thing as in the above discussion, right? > > You have a physical device, a capacitor, which > > looks completely different in the circuit. > > > > We could call all of this "electrical illusions"... > > > > The lesson from this, which is a big pet peeve > > of mine (and I have commented on this before > > in this list), is that when we talk about > > impedance, we must be clear which one we are > > talking about. RF engineers tend to talk about > > the electrical impedance as it is seen at a certain > > frequency, taking into account all of the reflection > > and standing wave effects, etc..., not mentioning > > this underlying assumption most of the time. > > Board layout guys or time domain thinkers tend > > to talk about the characteristic impedance (most > > often not mentioning that assumption either). > > > > Imagine what happens when you put these two types > > of guys into the same conversation... Or imagine > > what happens when a newbie takes two T-line basics > > classes, one from each of these guys. Mass confusion, > > total nightmare, which I have had the "pleasure" of > > experiencing way too many times... > > > > I hope this thread helped to clarify a few basics... > > > > Arpad > > > =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: Chris Padilla (cpad) [mailto:cpad@xxxxxxxxx]=20 > > Sent: Tuesday, April 10, 2007 9:01 AM > > To: Muranyi, Arpad; si-list@xxxxxxxxxxxxx > > Subject: RE: [SI-LIST] Re: impedance and Characteristic impedanece > > > > The main thing to notice in this simple circuit is the DEPENDENT SOURCE. > > The amps supplied by the current source depend on the voltage developed > > across the resistor. I'm sure too many folks glossed over that very > > important detail because it appears to be such a simple, "by inspection" > > circuit. In reality it is simple if you just note that small but very > > important detail! > > > > I'll generalize the circuit a tad more: > > > > Let the current source be Alpha*v. Note that Alpha is in dimensions of > > amps per volt. > > Let the voltage across the current source and the resistor be v. > > Let the resistor be R. > > > > Now, look into this circuit to figure out the input impedance. In > > sophomore circuits class, we did this by "hooking on" an arbitray V > > source with a labeled driving i. Figure out V/i and you have Zin. > > > > As my circuit theory professor would say: Now thrash around a bit! > > > > I did a Kirchoff's Current Law at the top node of the resistor to get: i > > =3D Alpha*v + v/R. Note that v =3D V. > > > > I find that V/i =3D R/(1 + R*Alpha). Plug in R =3D 1, and Alpha =3D -1 > = > > and > > sure enough, V/i =3D 1/0. =20 > > > > Note that Polarity is VERY important here!! > > > > Chris > > ------------------------------------------------------------------ > > To unsubscribe from si-list: > > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > > > > or to administer your membership from a web page, go to: > > //www.freelists.org/webpage/si-list > > > > For help: > > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > > > > > List technical documents are available at: > > http://www.si-list.net > > > > List archives are viewable at: > > //www.freelists.org/archives/si-list > > or at our remote archives: > > http://groups.yahoo.com/group/si-list/messages > > Old (prior to June 6, 2001) list archives are viewable at: > > http://www.qsl.net/wb6tpu > > > > > > > > > > > > ____________________________________________________________________________________ > Looking for earth-friendly autos? > Browse Top Cars by "Green Rating" at Yahoo! Autos' Green Center. > http://autos.yahoo.com/green_center/ > ------------------------------------------------------------------ > To unsubscribe from si-list: > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > > or to administer your membership from a web page, go to: > //www.freelists.org/webpage/si-list > > For help: > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > > List technical documents are available at: > http://www.si-list.net > > List archives are viewable at: > //www.freelists.org/archives/si-list > or at our remote archives: > http://groups.yahoo.com/group/si-list/messages > Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > > > ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu