Download ECEN 2612 Two-Port Circuits

ECEN 2612
Two-Port Circuits (20.0 points)
Lab #9
Name:
Partner:
Objective: Using experimental means, determine values of two-port z parameters and compare with
theory. Using OrCAD PSpice, determine a circuit’s two-port parameters.
Read through Chapter 18 of the course
textbook on Two-Port Circuits to gather an
understanding of background information
for this lab. Take notes as necessary to aid
your lab work. (Refer to instructor supplemental notes online for more details.)
Figure 1: Two-Port Circuit
Procedure:
1. Set-up and find z parameters.
z11 
V1
I1
z 22 
I 2 0
(5 points)
V2
I2
z 21 
I1  0
V2
I1
z12 
I 2 0
V1
I2
I1  0
(a) Build the two-port circuit shown in Fig. 1 by wiring together the components on the Cadet II
breadboard. Make sure to record measured component values using the DMM. After the circuit is
built, begin by experimentally determining the four z parameters z11, z12, z21, and z22 as described
below. Use the DMM and Agilent DC power supply as necessary.

For example, the impedance parameter z11 can be determined by opening port 2 and finding the resistance as seen at
port 1. Impedance parameter z22 can be found by opening port 1 and finding the resistance as seen at port 2.
 To find the transfer impedance z21 assume that port 2 is open, so I2 is 0. Then apply a test voltage across port 1.
Measure the current I1 and the voltage V2 while holding the test voltage V1 constant. A test voltage of 10V will
work for these measurements.
 To find the transfer impedance z12 assume that port 1 is open, so I1 equals 0. Then supply a test voltage across
port 2. Measure the current I2 and the voltage V1 while holding the test voltage V2 constant.
(b) A two-port circuit is reciprocal if the interchange of an ideal voltage source at one port and an
ideal ammeter at the other port (while maintaining +/- connections) produces the same ammeter
reading. If a two-port circuit is reciprocal then only three calculations or measurements are needed
to determine a set of parameters. Determine if the circuit in Fig. 1 is a reciprocal two-port circuit.
Provide measurements to support your result.
(c) A reciprocal two-port circuit is symmetric if its ports can be interchanged without disturbing the
values of the terminal currents and voltages. A symmetric two-port circuit needs only two calculations or measurements to determine a set of parameters. Determine if the circuit in Fig. 1 is a
symmetric reciprocal two-port circuit. Provide measurements and descriptions to support your
result.
(d) Check the experimentally determined values for the four z parameters in part (a) against an
analytical solution. Show all work done to compute these values. Be sure to use measured
element values, and use KVL/KCL equations as necessary. See text example 18.1 for reference.
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2. Analysis of a terminated two-port circuit
(4 points)
Figure 2: Terminated Two-Port Circuit
(a) The two-port circuit shown in Fig. 2 has a “signal generator” (Vg) connected to port 1. Zg might be
the internal impedance of the signal generator (use 1k), and ZL is the impedance of a load. Adjust
your circuit so that it now represents the circuit in Fig. 2. Measure the input impedance Zin = V1/I1,
the load voltage V2, and the output current I2. Discuss the methods chosen to measure each of
these three quantities.
(b) Compare these measured quantities to the analytical values you obtain using the following sets of
theoretical equations and the experimental values of z parameters found in step 1. Use your DMM
values. Calculate percent differences as necessary.
3. OrCAD PSpice
(5 points)
(a) Build the circuit of Fig. 1 in PSpice. Do you need a ground in the circuit? Using PSpice and the
methods discussed in part 1 determine the values of the four z parameters z11, z12, z21, and z22.
Describe the steps you take to determine each of the different z parameters. Include printouts of
the results obtained based on the methods of measurement chosen.
(b) Adjust the circuit from part (a) so that it now represents the terminated two-port circuit shown in
Fig. 2. Use PSpice to measure the three quantities Zin, V2, and I2. Describe the steps taken to
determine Zin, V2, and I2. Include printouts of the results obtained based on the methods of
measurement chosen.
4. Tabulation and summary of results
(4 points)
(a) Discuss and summarize in a table the experimental, theoretical, and PSpice-simulation results for
the four z parameters, z11, z12, z21, and z22.
(b) Discuss and summarize in a table the experimental, theoretical, and PSpice-simulation results for
the input impedance Zin, load voltage V2, and the load current I2 for the terminated two-port circuit
in Fig. 2.
Normally with PSpice work, at least one example schematic, one or two printed .OUT files, and Probe outputs should be
printed and included. Be sure to write notes on your PSpice files to indicate what you see.
REPORT: Keep a complete record of all data, results, observations, and answers to questions, written neatly and legibly
on the unlined side of standard engineering paper. Attach the lab sheet as a cover.
(2 points)
This is due at the end of next lab session!
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