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# Two Port Network

Two-Port Network

Contents

Define Two-Port Network 1

Describe characterization of LTI Two-Port Network 1

Describe Z-parameters 2

Describe the condition of Reciprocity and Symmetry in Z-parameters 3

Calculate Z-parameters for the given circuit 3

Explain Y-parameters 4

Describe the condition of Reciprocity and Symmetry in Y-parameters 5

Calculate Y-parameters for the given Circuit 6

Describe Transmission (ABCD) and Inverse Transmission (A’B’C’D’) parameters 7

Describe Reciprocity and Symmetry in ABCD parameters 8

Calculate Transmission parameters for the given circuit 9

Calculate Inverse Transmission parameters for the given circuit 10

Describe Hybrid (h) and Inverse Hybrid (g) parameters 11

Describe Reciprocity and Symmetry condition in h parameters 12

Calculate Hybrid (h) and Inverse Hybrid (g) parameters for the given circuit 13

Describe the Inter-relationship of Z and Y-parameters into other Two-Port parameters 14

Describe the Inter-relationship of T and T’-parameters into other Two-Port parameters 14

Describe the Inter-relationship of h and g-parameters into other Two-Port parameters 15

Explain different types of Inter-connections of Two-Port Networks 16

Explain equivalent T-Section and ∏-section representation in parameter form 17

Describe the expression of Input and Output Impedances in terms of Two-Port parameters 18

Describe the relationship between Open-Short Circuit Impedances and the T Parameters 19

Explain Image Impedance in terms of Input-Output Impedances, Open-Short Circuit Impedances, and T-parameters 20

# Define Two-Port Network

A two-port network is an electrical network or circuit that has two pairs of terminals, known as ports. It is a black box representation of a physical system, which can be used to model, analyze and design various electronic devices, systems and circuits.

Two-port networks are characterized by their input and output impedances, voltage and current gains, and scattering parameters, which describe how the network responds to signals entering and leaving through its ports. They can be used to analyze and design a wide range of electronic devices, including filters, amplifiers, attenuators, transformers, and transmission lines, among others.

# Describe characterization of LTI Two-Port Network

A linear time-invariant (LTI) two-port network can be characterized using several parameters, which describe the relationship between the input and output voltages and currents of the network. These parameters include:

1. Impedance parameters (Z-parameters): These parameters describe the input and output impedances of the network in terms of the input and output voltages and currents. The impedance parameters are given by a matrix of four elements: Z11, Z12, Z21, and Z22.
2. Admittance parameters (Y-parameters): These parameters describe the input and output admittances of the network in terms of the input and output currents and voltages. The admittance parameters are given by a matrix of four elements: Y11, Y12, Y21, and Y22.
3. Transmission parameters (T-parameters): These parameters describe the relationship between the input and output voltages and currents of the network, in terms of the voltage and current gains. The transmission parameters are given by a matrix of four elements: T11, T12, T21, and T22.
4. Hybrid parameters (h-parameters): These parameters describe the relationship between the input and output currents and voltages of the network. The hybrid parameters are given by a matrix of four elements: h11, h12, h21, and h22.
5. Scattering parameters (S-parameters): These parameters describe the relationship between the input and output waves of the network, in terms of the reflection and transmission coefficients. The scattering parameters are given by a matrix of four elements: S11, S12, S21, and S22.

By characterizing a two-port network using these parameters, it is possible to analyze and design the network for various applications, such as matching the network impedance to a given load or designing amplifiers and filters.

# Describe Z-parameters

Z-parameters, also known as impedance parameters or open-circuit parameters, are a set of four parameters used to characterize the input and output impedances of a two-port network in terms of the input and output voltages and currents.The Z-parameters are given by the following matrix:

[ Z11 Z12 ]

[ ]

[ Z21 Z22 ]

where Z11 and Z22 are the self-impedances of ports 1 and 2, respectively, when the other port is open-circuited (i.e., disconnected). Z12 and Z21 are the mutual impedances between the two ports, when the other port is open-circuited.The Z-parameters are particularly useful for analyzing the input and output impedances of networks that include reactive components, such as inductors and capacitors. They are also useful for designing matching networks to match the impedance of a network to a given load or source impedance.

# Describe the condition of Reciprocity and Symmetry in Z-parameters

Reciprocity and symmetry are two important conditions that can be observed in the Z-parameters of a two-port network.

Reciprocity refers to the property that the Z-parameters of a two-port network are the same when the direction of signal flow is reversed. In other words, if the network is excited by a signal at port 1 and the response is measured at port 2, the Z-parameters obtained will be the same as those obtained when the network is excited by a signal at port 2 and the response is measured at port 1. Mathematically, this can be expressed as:

Z12 = Z21

Reciprocity is a fundamental property of linear time-invariant networks, and it is a useful property for simplifying network analysis and design.

# Calculate Z-parameters for the given circuit

To calculate the Z-parameters for a given circuit, we first need to define the reference directions for the input and output signals. Typically, the reference direction for the input signal is from port 1 to port 2, and the reference direction for the output signal is from port 2 to port 1.

To find the Z-parameters of this circuit, we can use the following steps:

1. Disconnect the load from port 2 and short-circuit port 1. Apply a test voltage V1 at port 1 and measure the resulting current I1. The Z11 parameter is then given by:
Z11 = V1/I1
2. Disconnect the load from port 1 and short-circuit port 2. Apply a test voltage V2 at port 2 and measure the resulting current I2. The Z22 parameter is then given by:
Z22 = V2/I2
3. Connect a load ZL to port 2 and apply a test voltage V1 at port 1. Measure the resulting voltage V2 and the current I1. The Z21 parameter is then given by:
Z21 = V2/I1
4. Connect a load ZL to port 1 and apply a test voltage V2 at port 2. Measure the resulting voltage V1 and the current I2. The Z12 parameter is then given by:
Z12 = V1/I2

# Explain Y-parameters

Y-parameters, also known as admittance parameters, are another way to represent the behavior of a two-port network. Y-parameters are defined as the ratio of the current at one port to the voltage at the other port, assuming zero input at the other port. Y-parameters are expressed as a matrix:

[Y] = [ I1 ] [ Y11 Y12 ] [ V1 ]

[ ] = [ ] x [ ]

[ I2 ] [ Y21 Y22 ] [ V2 ]

where Y11 is the admittance looking into port 1 with port 2 open-circuited, Y12 is the admittance looking into port 1 with port 2 short-circuited, Y21 is the admittance looking into port 2 with port 1 open-circuited, and Y22 is the admittance looking into port 2 with port 1 short-circuited.

Similar to Z-parameters, the Y-parameters also exhibit reciprocity and symmetry, meaning Y12 = Y21 and Y11 = Y22.

The Y-parameters are related to the Z-parameters by the following equations:

Y11 = Z22 / (Z11Z22 – Z12Z21)

Y12 = -Z12 / (Z11Z22 – Z12Z21)

Y21 = -Z21 / (Z11Z22 – Z12Z21)

Y22 = Z11 / (Z11Z22 – Z12Z21)

The Y-parameters are useful in solving circuits with current sources, as they allow us to directly calculate the current at each port.

# Describe the condition of Reciprocity and Symmetry in Y-parameters

Reciprocity and symmetry are important properties of Y-parameters, which are used to describe the behavior of linear circuits.

Reciprocity is a property of a circuit in which the Y-parameters remain unchanged when the positions of the input and output terminals are interchanged. In other words, if we swap the input and output ports, the Y-parameters remain the same. Mathematically, this can be expressed as:

Y21 = Y12

where Y21 is the Y-parameter between the second port (output) and the first port (input), and Y12 is the Y-parameter between the first port (input) and the second port (output).

Symmetry is a property of a circuit in which the Y-parameters remain the same when the circuit is reflected across an axis. In other words, if we flip the circuit horizontally or vertically, the Y-parameters remain the same. Mathematically, this can be expressed as:

Y11 = Y22 and Y12 = Y21

where Y11 is the Y-parameter between the first port (input) and the first port (output), and Y22 is the Y-parameter between the second port (output) and the second port (input).

Reciprocity and symmetry are important properties of Y-parameters because they can simplify the analysis of linear circuits. For example, if a circuit is reciprocal, we only need to measure one set of Y-parameters, which can save time and effort. Similarly, if a circuit is symmetric, we can simplify the calculations by using the same Y-parameters for both input and output ports.

# Calculate Y-parameters for the given Circuit

To calculate the Y-parameters of a circuit, we need to determine the admittance of each port when the other port is short-circuited.To find the Y-parameters of this circuit, we can start by short-circuiting the output port (the one on the right), We can now find the admittance between the input port and ground, which is given by the sum of the conductances of the two resistors:

Y11 = 1/R1 + 1/R2

Next, we short-circuit the input port (the one on the left)We can now find the admittance between the output port and ground, which is given by the conductance of resistor R2:

Y22 = 1/R2 Finally, we need to find the cross-admittance between the input and output ports. To do this, we need to apply a voltage Vx to the input port and measure the resulting current Iy flowing out of the output port. We can then find the admittance Y21 using Ohm’s law: Y21 = Iy / Vxm

Y11 = 1/R1 + 1/R2

Y22 = 1/R2

Y21 = (Zx + R2) / Vx

# Describe Transmission (ABCD) and Inverse Transmission (A’B’C’D’) parameters

Transmission parameters, also known as ABCD parameters, are used to describe the behavior of linear circuits in terms of voltage and current. They relate the voltage and current at the input of a circuit to the voltage and current at the output of the circuit.

The ABCD parameters are defined as follows:

A = Vout / Vin, where Vout is the output voltage and Vin is the input voltage. B = Vout / Iin, where Iin is the input current.C = Iout / Vin,D = Iout / Iin

The ABCD parameters can be combined to form a matrix:

| A B |

| C D |

The inverse transmission parameters, also known as A’B’C’D’ parameters, are defined as follows:

A’ = D / (AD – BC),B’ = -B / (AD – BC),C’ = -C / (AD – BC),D’ = A / (AD – BC)

The A’B’C’D’ parameters can also be combined to form a matrix:

| A’ B’ |

| C’ D’ |

The inverse transmission parameters are useful for cascading multiple circuits. When cascading circuits, the ABCD parameters of each circuit can be multiplied together to find the overall ABCD parameters of the cascaded circuit. To find the overall A’B’C’D’ parameters, the A’B’C’D’ parameters of each circuit can be multiplied together.

# Describe Reciprocity and Symmetry in ABCD parameters

Reciprocity is a property of linear circuits where the ABCD parameters are the same when the inputs and outputs are interchanged. Mathematically, this means that for a reciprocal circuit:

ABCD = ABCD^T

where T represents the transpose of the matrix. This property arises from the fact that the circuit is symmetric with respect to the interchange of the inputs and outputs. Reciprocity is a fundamental property of many linear circuits, such as passive devices like resistors, capacitors, and inductors.

Symmetry is another property of linear circuits where the ABCD parameters are the same when the circuit is reflected about an axis perpendicular to the direction of signal flow. Mathematically, this means that for a symmetric circuit:

A = D

B = C

This property arises from the fact that the circuit is symmetric with respect to the reflection about the axis. Symmetry is also a fundamental property of many linear circuits, such as transmission lines and waveguides.

Reciprocity and symmetry are related properties, and a circuit that exhibits one property often exhibits the other as well. Additionally, circuits that exhibit both properties are often very useful for building high-performance systems such as filters, amplifiers, and mixers.

# Calculate Transmission parameters for the given circuit

To calculate the transmission parameters (ABCD parameters) of a circuit, we need to determine the relationship between the input and output voltages and currents. We can start by writing Kirchhoff’s voltage law (KVL) for the loop that includes Vin, R1, R2, and Vout. This gives us:

Vin = Vout + I1R1 + I2R2

where I1 and I2 are the currents flowing through R1 and R2, respectively. We can also write Kirchhoff’s current law (KCL) at the node where R1 and R2 meet, which gives us:

I1 = I2 + (Vout / R2)

We can solve these two equations for Vout and I2 in terms of Vin and I1, which gives us the following transmission parameters:

A = Vout / Vin = 1 – (R1/R2),B = R1, C = 1 / R2, D = (R1*R2) / (R1 + R2)

Therefore, the transmission matrix for this circuit is:

| A B |

| C D |

Substituting the values we derived for A, B, C, and D, we get:

| 1 – (R1/R2) R1 |

| 1/R2 R1||R2/(R1+R2) |

# Calculate Inverse Transmission parameters for the given circuit

To calculate the inverse transmission parameters (A’B’C’D’ parameters) of a circuit, we first need to calculate the determinant of the transmission matrix. The determinant is given by:

In this case, the determinant is:

det(ABCD) = (1 – R1/R2)(R1||R2/(R1+R2)) – R1(1/R2) = 1

Next, we can calculate the inverse transmission parameters using the following equations:

A’ = D / det(ABCD), B’ = -B / det(ABCD), C’ = -C / det(ABCD), D’ = A / det(ABCD)

Substituting the values we derived for A, B, C, and D, and the determinant, we get:

A’ = R1||R2/(R1+R2), B’ = -R1/(R1+R2), C’ = -1/R2, D’ = 1 – (R1/R2)

Therefore, the inverse transmission matrix for this circuit is:

| A’ B’ |

| C’ D’ |

Substituting the values we derived for A’, B’, C’, and D’, we get:

| R1||R2/(R1+R2) -R1/(R1+R2) |

| -1/R2 1 – (R1/R2) |

# Describe Hybrid (h) and Inverse Hybrid (g) parameters

Hybrid parameters (also known as h-parameters or the hybrid pi model) are a set of four parameters used to describe the behavior of a two-port linear circuit, such as a transistor or an amplifier. The parameters are defined as follows:

h11 = ∂v1/∂i1|v2=0, h12 = ∂v1/∂v2|i1=0, h21 = ∂i2/∂i1|v2=0, h22 = ∂i2/∂v2|i1=0

where v1 and i1 are the voltage and current at port 1, v2 and i2 are the voltage and current at port 2, and the partial derivatives are evaluated at a particular operating point. These parameters are often represented in matrix form as:

| h11 h12 |

| h21 h22 |

The h-parameters relate the input voltage and current at port 1 to the output voltage and current at port 2, and vice versa. They are useful for analyzing small-signal behavior, where the signals are small enough that nonlinear effects can be ignored.

The inverse hybrid parameters (also known as g-parameters) are the inverse of the h-parameters, and are given by:

g11 = h22 / (h11h22 – h12h21) ,g12 = -h12 / (h11h22 – h12h21) ,g21 = -h21 / (h11h22 – h12h21), g22 = h11 / (h11h22 – h12h21)

The g-parameters relate the input current and voltage at port 1 to the output current and voltage at port 2, and vice versa. They are useful for analyzing large-signal behavior, where nonlinear effects cannot be ignored.

# Describe Reciprocity and Symmetry condition in h parameters

In a linear two-port circuit described by h-parameters, reciprocity means that the circuit behaves the same way when the roles of ports 1 and 2 are interchanged. Mathematically, this is expressed as:

h12 = h21

Reciprocity means that the circuit does not favor one direction of signal flow over the other, and is often a desirable property in many applications.

Symmetry in h-parameters refers to the relationship between the parameters when the circuit is inverted, which means that the current and voltage sources are interchanged. Mathematically, this is expressed as:

h11 = h22

h12 = -h21

This means that the circuit has the same gain and impedance characteristics when it is inverted, which can be useful for analyzing certain circuit configurations.

It is important to note that not all linear two-port circuits have h-parameters that satisfy reciprocity and symmetry. In some cases, other parameter sets such as y-parameters or s-parameters may be more appropriate.

# Calculate Hybrid (h) and Inverse Hybrid (g) parameters for the given circuit

To calculate the h-parameters of the given circuit, we need to find the voltage and current at ports 1 and 2 in terms of the input and output voltages and currents. We can start by applying Kirchhoff’s laws at each of the ports.

At port 1:

v1 = i1R1 + h11i2 ,i2 = h21i1 + h22v2

At port 2:

v2 = h12i1 + h22i2, i1 = h11v1 + h12i2

h11 = R1 + R2, h12 = R2, h21 = -1/R2, h22 = 1

Therefore, the inverse hybrid matrix for this circuit is:

| g11 g12 |

| g21 g22 |

Substituting the values we derived for g11, g12, g21, and g22, we get:

| 1 -R2 |

| 1/R2 R1+R2 |

These are the inverse hybrid parameters for the given circuit.

# Describe the Inter-relationship of Z and Y-parameters into other Two-Port parameters

The Z-parameters and Y-parameters are two sets of parameters used to describe the behavior of linear two-port circuits. The relationship between the Z-parameters and Y-parameters is given by the following equations:

Z11 = Y22 / Y21Y12

Z12 = -Y12 / Y22

Z21 = -Y21 / Y22

Z22 = 1 / Y22

Conversely, the relationship between the Y-parameters and Z-parameters is given by the following equations:

Y11 = Z22 / Z21Z12

Y12 = -Z12 / Z22

Y21 = -Z21 / Z22

Y22 = 1 / Z22

# Describe the Inter-relationship of T and T’-parameters into other Two-Port parameters

The T-parameters and T’-parameters are two sets of parameters used to describe the behavior of linear two-port circuits. The relationship between the T-parameters and other two-port parameters is given by the following equations:

S11 = (T11 + T12S21) / (1 – T11T22),S12 = (T12*(1 – S11T22)) / (1 – T11T22),

S21 = (T21*(1 – S11T22)) / (1 – T11T22),S22 = (T22 + T21S12) / (1 – T11T22)

Z11 = T11 / T21 ,Z12 = (T11T22 – T12T21) / T21, Z21 = 1 / T21, Z22 = T22 / T21

Y11 = T22 / T21, Y12 = -T12 / T21, Y21 = -T21 / T21, Y22 = T11 / T21

h11 = -T22 / T12, h12 = -T21, h21 = 1 / T12 , h22 = -T11 / T12

# Describe the Inter-relationship of h and g-parameters into other Two-Port parameters

In a two-port network, the h-parameters and g-parameters describe the relationship between the input and output voltages and currents. The h-parameters are defined as:

h11 = ΔV1/ΔI1|I2=0

h12 = ΔV1/ΔI2|I1=0

h21 = ΔV2/ΔI1|I2=0

h22 = ΔV2/ΔI2|I1=0

where ΔV1 is the change in voltage at port 1, ΔV2 is the change in voltage at port 2, ΔI1 is the change in current at port 1, and ΔI2 is the change in current at port 2.

On the other hand, the g-parameters are defined as:

g11 = ΔI1/ΔV1|V2=0

g12 = ΔI1/ΔV2|V1=0

g21 = ΔI2/ΔV1|V2=0

g22 = ΔI2/ΔV2|V1=0

# Explain different types of Inter-connections of Two-Port Networks

Two-port networks can be interconnected in various ways to create more complex systems. The interconnection of two-port networks can be classified into three types: series, parallel, and cascade.

1. Series Interconnection: In a series interconnection, two two-port networks are connected in series such that the output of the first network is connected to the input of the second network. The input impedance of the combined network is the sum of the input impedances of the two individual networks, and the output impedance of the combined network is the sum of the output impedances of the two individual networks.
2. Parallel Interconnection: In a parallel interconnection, two two-port networks are connected in parallel such that the inputs of both networks are connected together, and the outputs of both networks are connected together. The input impedance of the combined network is the parallel combination of the input impedances of the two individual networks, and the output impedance of the combined network is the parallel combination of the output impedances of the two individual networks.
3. Cascade Interconnection: In a cascade interconnection, two two-port networks are connected in a cascaded manner, such that the output of the first network is connected to the input of the second network. The input impedance of the combined network is the input impedance of the first network, and the output impedance of the combined network is the output impedance of the second network.

# Explain equivalent T-Section and ∏-section representation in parameter form

T-Section and π-section networks are two common ways to represent two-port networks in a simplified form. These representations are used to analyze and design complex networks and circuits, as they provide a more manageable circuit model while preserving the important network characteristics.

1. T-Section Representation:

In a T-section representation, the two-port network is represented by a T-shaped circuit. The input port is connected to the top of the T, and the output port is connected to the bottom of the T. The T-section parameters are defined as:

Z11 = h11(h22 – h12h21) / h22, Z12 = h12 / h22, Z21 = -h21 / h11, Z22 = 1 / h22

where h-parameters are the scattering parameters of the network.

1. π-Section Representation:

In a π-section representation, the two-port network is represented by a π-shaped circuit. The input port is connected to one side of the π, and the output port is connected to the other side of the π. The π-section parameters are defined as:

Y11 = h22 / h12, Y12 = -h21 / h12, Y21 = -h11 / h12, Y22 = 1 / h12(h22 – h21h11)

where h-parameters are the scattering parameters of the network.

Ladder networks are a type of two-port network that are commonly used in electronics, particularly in filter design. Ladder networks consist of a series of identical two-port network elements, such as resistors, capacitors, or inductors, connected in a repeating pattern. The ladder network is characterized by its topology, which determines the interconnection of the individual two-port elements.

There are two types of ladder networks: series and parallel. In a series ladder network, the two-port elements are connected in series, such that the output of each element is connected to the input of the next element. The input and output ports are connected to the first and last element in the series, respectively. In a parallel ladder network, the two-port elements are connected in parallel, such that the input of each element is connected to the input of the network, and the output of each element is connected to the output of the network.Ladder networks are often used as a way to create complex filters, as they can be designed to have specific frequency response characteristics. For example, a ladder network can be designed to have a low-pass, high-pass, band-pass, or band-stop response, depending on the interconnection of the two-port elements and their values.

One important feature of ladder networks is that they are reciprocal, meaning that the network parameters are the same when the input and output ports are reversed. This makes them particularly useful in applications where the network is used in both directions, such as in transmission lines or in communication systems.

# Describe the expression of Input and Output Impedances in terms of Two-Port parameters

The input and output impedances of a two-port network can be expressed in terms of the scattering (S) parameters or hybrid (h) parameters.

The input impedance of a two-port network is the impedance that the network presents to a signal applied to the input port. The input impedance can be expressed in terms of the S parameters as:

Zin = Z0 * (S11 + S12S21)/(1 – S22S11)

where Z0 is the characteristic impedance of the system, S11 and S21 are the scattering parameters of the network when the output is terminated with a load impedance equal to Z0, and S12 and S22 are the scattering parameters when the input is terminated with an impedance equal to Z0.

The input impedance can also be expressed in terms of the h parameters as:

Zin = h11 + h12Z0/(h22Z0 – 1)

where h11, h12, h21, and h22 are the hybrid parameters of the network.

# Describe the relationship between Open-Short Circuit Impedances and the T Parameters

The open-circuit impedance (Zoc) and short-circuit impedance (Zsc) are the impedances seen at the output of a two-port network when the input is open-circuited and short-circuited, respectively. These impedances can be used to determine the T parameters of the two-port network.

The T parameters are a set of four parameters that describe the behavior of a two-port network. The T parameters can be expressed in terms of the open-circuit impedance and the short-circuit impedance as:

T11 = Zoc/Zsc

T12 = -Zoc

T21 = -Zsc/(ZocZin – ZscZout)

T22 = Zin/Zout

where Zin and Zout are the input and output impedances of the network, respectively.

Conversely, the open-circuit impedance and short-circuit impedance can be expressed in terms of the T parameters as:

Zoc = T12/T11, Zsc = -T21/T11

These relationships are useful in circuit analysis and design, as they provide a way to calculate the open-circuit and short-circuit impedances of a two-port network based on its T parameters, or to calculate the T parameters based on the open-circuit and short-circuit impedances.

# Explain Image Impedance in terms of Input-Output Impedances, Open-Short Circuit Impedances, and T-parameters

In the context of electrical networks and circuits, image impedance refers to the input impedance that an ideal transformer would present to its primary side if its secondary side were short-circuited. The image impedance can be derived from the open-circuit and short-circuit impedances of the transformer, as well as the T-parameters. The open-circuit impedance (Zoc) of a transformer is the impedance that the primary side would present if the secondary side were left open. This impedance is equal to the ratio of the voltage on the primary side to the current flowing through it, with the secondary side disconnected.

Similarly, the short-circuit impedance (Zsc) is the impedance that the primary side would present if the secondary side were short-circuited. This impedance is equal to the ratio of the voltage on the primary side to the current flowing through it, with the secondary side short-circuited. Using the open-circuit and short-circuit impedances, we can derive the T-parameters of the transformer. The T-parameters are a set of four values that describe the linear relationship between the voltage and current on the primary and secondary sides of the transformer. With the T-parameters, we can easily calculate the image impedance (Zi) of the transformer using the formula:

Zi = Zoc * (T11 – T12 * T21 / T22)

where T11, T12, T21, and T22 are the four T-parameters.

The image impedance is useful in the analysis of circuits containing transformers, as it allows us to calculate the input impedance of a circuit without explicitly considering the transformer. Additionally, it provides a convenient way to determine the maximum power transfer efficiency of a circuit containing a transformer.