Talk:Two-port network

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[edit] parameters definitions

Z_{ab} = \frac{V_a}{I_b} \bigg|_{I_{ ! b} = 0}

where !b means the value that b isn't (ie if b=1, !b=2, and if b=2, !b=1).

y_{ab} = \frac{I_a}{V_b} \bigg|_{V_{ ! b} = 0}

where !b means the value that b isn't (ie if b=1, !b=2, and if b=2, !b=1).

[edit] combining 2 port networks

When talking about cascading networks or putting them in series and parallel, we really should have diagrams (No Worries 23:18, 22 April 2007 (UTC))

[edit] Partial derivations of voltages and currents in defnition of h parameters

I've made some research - preparing for labs of transistor characteristics and I used here specified definition of h parameters. My professor said me that it is not applicable to AC analysis and regime. For AC it must be partial derivation of those voltages and currents. --Čikić Dragan 13:39, 3 December 2007 (UTC)

Two-port parameters are for linear networks, so partial derivatives are not necessary. Of course you can always perform a linear approximation of a nonlinear network and then find the two-port associated with the linearization. -Roger 15:53, 3 December 2007 (UTC)
I think Čikić Dragan is talking about small signal h parameters, Roger, which are indeed defined as the derivative by transistor manufacturer data sheets due to the essential non-linearity of semiconductors. They also use large signal parameters which are going to be rather non-linear. This is the difference between hFE and hfe for instance. But I think this is something for the transistor circuit articles rather than here. SpinningSpark 17:48, 4 May 2008 (UTC)

[edit] Scattering parameters subsection

It is unclear to me whether this subsection belongs here, because the variables V1+, V1−, … etc. appear unrelated to the two-port definition in terms of V1, I1, … etc. If there is some discussion that clarifies this relationship, OK, put this discussion in the subsection. If not, this subsection should be placed separate from the two-port article, and the "two-port" description should be amended. In addition, there is no definition provided for the S-matrix. This subsection also requires references. I'd recommend Choma and Chen, Chapter 3, isbn 981-02-2770-1 ; World Scientific (2007). The article Scattering parameters should be cited as a

Main article: Scattering parameters

I have removed the present subsection to the talk page (see below) until it is ready for prime time. Brews ohare (talk) 18:49, 13 March 2008 (UTC)

[edit] Under construction

[edit] Scattering Matrix for a 2 Port Network

 V1+         -----------------           V2+
 o-----------| 2 Port        |-----------o
             | Network       |
 o-----------|               |-----------o           
 V1-         -----------------           V2-
\left[ \begin{array}{c} V_{1-} \\ V_{2-} \end{array} \right] = \left[ \begin{array}{cc} \gamma & \Tau \\ \tau & \Gamma \end{array} \right] \left[ \begin{array}{c}V_{1+} \\ V_{2+} \end{array} \right] .

Where γ / Γ is the reflection coefficient, and τ / Τ is the transmission coefficient.

The scattering matrix

\mathbf{S} = \left[ \begin{array}{cc} S_{11} & S_{12} \\ S_{21} & S_{22} \end{array} \right] .
I'm not sure if there's any benefit to giving this form, especially since it seems pretty much the same as this one. -Roger (talk) 03:30, 19 March 2008 (UTC)

[edit] Combinations of two-port networks

I have a problem with this section. I do not believe it is true that the Z matrices can be simply added for series connected networks. Here is a counter example, take this simple network of two resistors;

Z_{11} = 2 \Omega\,\!

Connecting two of them together like this gives the expected result;

Z_{11} = 2 \Omega + 2 \Omega = 4 \Omega\,\!

But what about this one. Still the same two circuits with ports still connected in series but now;

Z_{11} = 2 \Omega\,\!

Or this one. Now we have;

Z_{11} = 3 \Omega\,\!

Same two circuits connected in the same configuration and three different answers. Only one of them agreeing with,

[Z]_1 + [Z]_2 = [Z]\,\!

Does not get much simpler than a two resistor network. The statement cannot possibly hold for the general case. Or am I missing something obvious?


SpinningSpark 02:01, 25 March 2008 (UTC)

I have found a text-book which divides two-port interconnections into correct and incorrect depending on whether or not output current flows between them (everything above is incorrect except the first case). Solves the problem with output transformers, but then that means the model in not useable for dc/lf on incorrect circuits. Seems obvious that a great deal more needs to be written in this article to bring it up to standard on this point. SpinningSpark 17:22, 4 May 2008 (UTC)

[edit] Test edit?

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