## Two Port Networks

## Two Port Networks

(OP)

Does anyone know if this circuit has a name, or better still have an idea of how to solve? If I have a known current and voltage I1 and V1, how is the current through each impedance element determined? I've searched through filter design literature without success, and have attempted deriving ABCD parameters... surely this has been seen and solved before.

Thanks

Thanks

## RE: Two Port Networks

Did you intend one or either of them to be fixed? If so, that may reduce the number of unknowns to the point where the problem becomes a lot easier.

Whatever is connected between the two terminals at the right hand edge of the diagram is going to form part of the network you want to analyse - defining that properly might help too.

A.

## RE: Two Port Networks

You mentioned whatever is connected externally will affect the circuit... that's why I was hoping to use ABCD parameters to define this circuit topology. Then I can simply multiply the ABCD matrix by that of whatever I'm connected to (I hope)

## RE: Two Port Networks

nevertheless, what you show is relatively trivial if the load is resistive

TTFN

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## RE: Two Port Networks

I attempted the ABCD derivation but something isn't coming out right. I'm curious if this is a commonly seen circuit by some. In my search I can't find a similar example

## RE: Two Port Networks

To find the value of B, evaluate V1/I2 with the right-hand side of the circuit shorted (therefore V2 = 0).

To find the value of C, evaluate I1/V2 with the right-hand side of the circuit open (therefore I2 = 0).

To find the value of D, evaluate I1/I2 with the right-hand side of the circuit shorted (therefore V2 = 0).

If it helps, you can break the circuit into three smaller two-port networks: the left shunt admittance, the two middle series impedances, and the right shunt admittance. Find the ABCD matrix representation of each, and then simply multiply the three ABCD matrices in order from left to right (remember, matrix multiplication order matters). That's how I solved your problem. If you post what you think the correct answer is, maybe someone will tell you if you've gotten it right.

By the way, I assumed both I1 and I2 go from left to right when I worked the problem, so I don't have the same sign convention in Figure 1 in the Wikipedia link. No big deal; it just means I don't need the negative signs when determining C and D.

xnuke

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## RE: Two Port Networks

Google: Kirchhoff's laws

## RE: Two Port Networks

A = (Z2+Z3+Z4) / Z3

B = (Z1^-1 + (Z2+Z3+Z4)^-1)^-1

C = (Z1+Z2+Z3+Z4) / Z1

D = ?

I'm stuck on D... I need to stare some more

## RE: Two Port Networks

M

_{in}has A = 1, B = 0, C = 1/Z1, D = 1The two-port network for the middle series components of Z2 and Z4 as you defined in the image is:

M

_{mid}has A = 1, B = Z2+Z4, C = 0, D = 1The two-port network for the shunt branch of Z3 as you defined in the image is:

M

_{out}has A = 1, B = 0, C = 1/Z3, D = 1Matrix multiplication of the three matrices should give you the correct answer for the overall network: M = M

_{in}*M_{mid}*M_{out}.xnuke

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## RE: Two Port Networks

## RE: Two Port Networks

## RE: Two Port Networks

xnuke

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## RE: Two Port Networks

A = 1 + (Z2 + Z4) / Z3

B = Z2 + Z4

C = 1/Z1 + (1/Z3)*(1+(Z2+Z4)/Z1)

D = 1 + (Z2+Z4)/Z1

A*D - B*C = 1

## RE: Two Port Networks

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## RE: Two Port Networks

Z