The 'h' in h-parameters stands for "Hybrid" because they are a mix of different units (impedance, admittance, ratios), unlike Z or Y parameters which have consistent units.
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2In the hybrid model of a transistor, which parameter represents the input impedance?
Two Port Devices and the Hybrid model
Easy
A.
B.
C.
D.
Correct Answer:
Explanation:
The parameter represents the input impedance of the transistor in the common-emitter configuration. The 'i' stands for input and 'e' for common-emitter.
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3A two-port network has how many terminals?
Two Port Devices and the Hybrid model
Easy
A.Four
B.Three
C.Two
D.Six
Correct Answer: Four
Explanation:
A two-port network has an input port (with two terminals) and an output port (with two terminals), making a total of four terminals.
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4Which h-parameter represents the forward current gain in a common-emitter configuration?
Two Port Devices and the Hybrid model
Easy
A.
B.
C.
D.
Correct Answer:
Explanation:
is the forward current gain (ratio of output current to input current) in a common-emitter configuration. The 'f' stands for forward and 'e' for common-emitter. It is also known as .
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5How is the h-parameter determined from the input characteristics (a graph of vs )?
Determination of the h parameters from the characteristics
Easy
A.By finding the x-intercept
B.By finding the reciprocal of the slope of the curve
C.By finding the y-intercept
D.By finding the area under the curve
Correct Answer: By finding the reciprocal of the slope of the curve
Explanation:
is the input impedance, defined as the change in input voltage () divided by the change in input current () at a constant output voltage (). This is calculated as the reciprocal of the slope () of the input characteristic curve.
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6The h-parameter is calculated from which set of characteristics?
Determination of the h parameters from the characteristics
Easy
A.Transfer characteristics
B.Input characteristics
C.Power characteristics
D.Output characteristics
Correct Answer: Output characteristics
Explanation:
is the forward current gain (). It is calculated from the output characteristics (a graph of vs ) by observing the change in collector current () for a given change in base current () while keeping constant.
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7To determine the h-parameter from the output characteristics, what condition must be met?
Determination of the h parameters from the characteristics
Easy
A.Output voltage () is kept constant
B.Input voltage () is kept constant
C.Output current () is kept constant
D.Input current () is kept constant
Correct Answer: Input current () is kept constant
Explanation:
is the output admittance, defined as the ratio of the change in output current () to the change in output voltage () while the input current () is held constant. This is found from the slope of the output characteristic curves.
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8What is the unit of the h-parameter ?
Analysis of a Transistor Amplifier circuit using h-parameters
Easy
A.Siemens (S) or Mho
B.It is unitless
C.Volts (V)
D.Ohms ()
Correct Answer: Siemens (S) or Mho
Explanation:
represents the output admittance, which is the reciprocal of impedance. Its unit is Siemens (S), also formerly known as Mho.
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9Which of the following h-parameters is a unitless quantity?
Analysis of a Transistor Amplifier circuit using h-parameters
Easy
A.
B.
C.None of the above
D.
Correct Answer:
Explanation:
(forward current gain) and (reverse voltage gain) are ratios of similar quantities (current/current and voltage/voltage respectively), making them unitless or dimensionless.
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10The input voltage () of a two-port network described by h-parameters is given by which equation?
Analysis of a Transistor Amplifier circuit using h-parameters
Easy
A.
B.
C.
D.
Correct Answer:
Explanation:
The standard defining equation for the input voltage () of a two-port network using general h-parameters is , where is input impedance and is reverse voltage gain.
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11The output current () of a two-port network described by h-parameters is given by which equation?
Analysis of a Transistor Amplifier circuit using h-parameters
Easy
A.
B.
C.
D.
Correct Answer:
Explanation:
The standard defining equation for the output current () of a two-port network using general h-parameters is , where is forward current gain and is output admittance.
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12Which transistor amplifier configuration provides a high voltage gain and a high current gain?
comparison of Transistor Amplifier configuration
Easy
A.Common Base (CB)
B.Common Emitter (CE)
C.Common Gate (CG)
D.Common Collector (CC)
Correct Answer: Common Emitter (CE)
Explanation:
The Common Emitter (CE) configuration is the most widely used because it provides both significant voltage gain and significant current gain, resulting in the highest power gain.
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13Which amplifier configuration is also known as an "emitter follower"?
comparison of Transistor Amplifier configuration
Easy
A.None of the above
B.Common Collector (CC)
C.Common Emitter (CE)
D.Common Base (CB)
Correct Answer: Common Collector (CC)
Explanation:
The Common Collector (CC) configuration is called an emitter follower because the output voltage taken from the emitter "follows" the input voltage applied to the base. It has a voltage gain of approximately 1.
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14Which transistor configuration has the lowest input impedance?
comparison of Transistor Amplifier configuration
Easy
A.Common Collector (CC)
B.Common Emitter (CE)
C.All have the same input impedance
D.Common Base (CB)
Correct Answer: Common Base (CB)
Explanation:
The Common Base (CB) configuration is characterized by a very low input impedance and a very high output impedance.
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15The Common Collector (CC) amplifier provides a:
comparison of Transistor Amplifier configuration
Easy
A.Low voltage gain (approx. 1) and high current gain
B.High voltage gain and low current gain
C.Low voltage gain and low current gain
D.High voltage gain and high current gain
Correct Answer: Low voltage gain (approx. 1) and high current gain
Explanation:
The main characteristics of a Common Collector (CC) or emitter follower amplifier are a high current gain, high input impedance, low output impedance, and a voltage gain that is approximately unity (1).
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16What is the primary reason for cascading amplifiers?
Cascading Transistor Amplifiers
Easy
A.To increase the overall gain
B.To reduce power consumption
C.To decrease the overall bandwidth
D.To simplify the circuit design
Correct Answer: To increase the overall gain
Explanation:
A single amplifier stage may not provide sufficient gain. By connecting multiple amplifier stages in series, or "cascading" them, the overall gain becomes the product of the individual stage gains, resulting in a much higher total amplification.
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17Which type of coupling is most commonly used for cascading amplifiers in integrated circuits (ICs)?
Cascading Transistor Amplifiers
Easy
A.Transformer coupling
B.RC coupling
C.Impedance coupling
D.Direct coupling
Correct Answer: Direct coupling
Explanation:
Direct coupling, where the output of one stage is connected directly to the input of the next, is preferred in ICs because it avoids the need for bulky and frequency-dependent components like capacitors and transformers.
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18What is the main disadvantage of RC coupling in a cascade amplifier?
Cascading Transistor Amplifiers
Easy
A.Poor low-frequency response
B.High cost and bulkiness
C.Excellent frequency response
D.High power consumption
Correct Answer: Poor low-frequency response
Explanation:
The coupling capacitor in an RC-coupled amplifier has a high reactance at low frequencies, which blocks or attenuates low-frequency signals. This leads to a poor low-frequency response.
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19If three identical amplifier stages, each with a voltage gain of 10, are cascaded, what is the total voltage gain?
n-Stage Cascaded Amplifier
Easy
A.1000
B.10
C.30
D.100
Correct Answer: 1000
Explanation:
The total gain of a cascaded amplifier is the product of the individual stage gains. Therefore, the total gain is .
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20When amplifier stages are cascaded, what generally happens to the overall bandwidth compared to a single stage?
n-Stage Cascaded Amplifier
Easy
A.It becomes infinite
B.It remains the same
C.It decreases
D.It increases
Correct Answer: It decreases
Explanation:
Cascading amplifier stages increases the overall gain, but at the cost of reduced bandwidth. The overall upper and lower cutoff frequencies move closer together, narrowing the range of frequencies that are effectively amplified.
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21In the hybrid model of a BJT, the parameter represents the ratio of which two quantities when the output is AC short-circuited ()?
Two Port Devices and the Hybrid model
Medium
A.Change in collector current to change in base voltage,
B.Change in collector current to change in base current,
C.Change in base current to change in collector current,
D.Change in collector voltage to change in base voltage,
Correct Answer: Change in collector current to change in base current,
Explanation:
is the small-signal forward current gain, defined as . It measures how much the output collector current changes for a given change in input base current, with the output voltage held constant (AC short circuit).
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22The hybrid parameter (reverse voltage gain) is measured under what specific input condition?
Two Port Devices and the Hybrid model
Medium
A.Output is short-circuited ()
B.Input is short-circuited ()
C.Input is open-circuited ()
D.Output is open-circuited ()
Correct Answer: Input is open-circuited ()
Explanation:
The hybrid equations are and . To measure , which is defined as , we must make the term with zero. This is achieved by setting the input current , which means the input port is open-circuited.
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23If is the current gain in a common-emitter (CE) configuration, how is the current gain in a common-base (CB) configuration, , approximately related to it?
Two Port Devices and the Hybrid model
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
The relationship between the current gains is derived from the basic transistor current equations (). The exact formula is . Since is typically large (e.g., 100), is very close to -1.
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24From the output characteristics of a CE transistor, for a fixed base current , the collector current changes from to when changes from to . What is the value of the output admittance, ?
Determination of the h parameters from the characteristics
Medium
A.40 kΩ
B.25 mS
C.40 µS
D.25 µS
Correct Answer: 25 µS
Explanation:
The output admittance is defined as the slope of the output characteristic curve: with constant. Here, and . Therefore, .
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25The input characteristic of a BJT in CE configuration shows that for a constant , the base-emitter voltage changes from to as the base current changes from to . Calculate the input impedance, .
Determination of the h parameters from the characteristics
Medium
A.1 kΩ
B.2 kΩ
C.4 kΩ
D.500 Ω
Correct Answer: 2 kΩ
Explanation:
The input impedance is defined as the slope of the input characteristic curve: with constant. Here, and . Therefore, .
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26On the output characteristics of a CE amplifier, at a constant , the collector current is for a base current . When the base current is increased to , the collector current becomes . What is the value of the forward current gain, ?
Determination of the h parameters from the characteristics
Medium
A.120
B.80
C.150
D.100
Correct Answer: 120
Explanation:
The forward current gain is defined as with constant. Here, and . Therefore, .
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27A common-emitter amplifier has , , and is driving a load of . Neglecting the effects of and for a simplified analysis, what is the approximate voltage gain ()?
Analysis of a Transistor Amplifier circuit using h-parameters
Medium
A.-200
B.-800
C.-100
D.-400
Correct Answer: -400
Explanation:
The voltage gain of a CE amplifier can be approximated by the formula when is negligible and . Substituting the given values: .
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28For a CE amplifier with , , and a load resistance , calculate the current gain .
Analysis of a Transistor Amplifier circuit using h-parameters
Medium
A.100
B.50
C.80
D.64
Correct Answer: 64
Explanation:
The current gain of a CE amplifier is given by the formula . Substituting the given values: .
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29A transistor in a CE configuration has , , , and . It is connected to a load of . What is the input impedance () of the amplifier?
Analysis of a Transistor Amplifier circuit using h-parameters
Medium
A.1.5 kΩ
B.2.23 kΩ
C.2 kΩ
D.1.77 kΩ
Correct Answer: 1.77 kΩ
Explanation:
The input impedance is given by the exact formula . First, calculate the denominator term: . Then, calculate the fraction: . Finally, .
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30For a transistor amplifier, the voltage gain from base to collector is . The amplifier has an input resistance of and is driven by a voltage source with an internal resistance of . What is the overall voltage gain ?
Analysis of a Transistor Amplifier circuit using h-parameters
Medium
A.-180
B.-100
C.-150
D.-125
Correct Answer: -125
Explanation:
The overall voltage gain accounts for the voltage divider effect at the input between the source resistance and the amplifier's input resistance . The relationship is . Substituting the values: .
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31For a BJT amplifier with a source resistance , the output admittance is given by . If , what is the output resistance ?
Analysis of a Transistor Amplifier circuit using h-parameters
Medium
A.11.1 kΩ
B.28.9 µS
C.34.5 kΩ
D.25 kΩ
Correct Answer: 34.5 kΩ
Explanation:
The correct option follows directly from the given concept and definitions.
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32Which transistor amplifier configuration is characterized by a very low input impedance, a very high output impedance, and a high voltage gain but a current gain of approximately unity?
Comparison of Transistor Amplifier configuration
Medium
A.Common Collector (CC)
B.Emitter Follower
C.Common Emitter (CE)
D.Common Base (CB)
Correct Answer: Common Base (CB)
Explanation:
The Common Base (CB) configuration has a very low input impedance (typically tens of ohms) and a high output impedance. It provides high voltage gain similar to CE, but its current gain is slightly less than 1 (). It is often used for high-frequency applications.
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33You need to design an amplifier that provides a high input impedance to avoid loading a sensitive source, and you also require a significant voltage gain. A single-stage solution is not possible. Which two-stage cascade would be most suitable?
Comparison of Transistor Amplifier configuration
Medium
A.Two CE stages
B.CB followed by CC
C.CC followed by CE
D.CE followed by CB
Correct Answer: CC followed by CE
Explanation:
To get a high input impedance, the first stage should be a Common Collector (CC) amplifier. To get a high voltage gain, the second stage should be a Common Emitter (CE) amplifier. This combination, known as a Darlington pair if integrated, provides both high input impedance and high overall gain.
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34Which of the following statements correctly compares the phase relationship of the output voltage with respect to the input voltage for the three basic BJT configurations?
Comparison of Transistor Amplifier configuration
Medium
The Common Emitter (CE) configuration is an inverting amplifier, producing a 180° phase shift. Both the Common Base (CB) and Common Collector (CC) configurations are non-inverting, meaning their output voltage is in phase (0° shift) with their respective input voltages.
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35A specific application requires an amplifier with a moderate input impedance, high voltage gain, and an inverted output signal. Which configuration is the best fit?
Comparison of Transistor Amplifier configuration
Medium
A.Common Base (CB)
B.Cascaded CC-CB
C.Common Collector (CC)
D.Common Emitter (CE) with emitter resistor
Correct Answer: Common Emitter (CE) with emitter resistor
Explanation:
The standard Common Emitter (CE) configuration provides high voltage gain and an inverted output. While its input impedance can be low, adding an unbypassed emitter resistor increases the input impedance to a moderate level, making it a better fit for the requirements than the other configurations.
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36Two non-identical amplifier stages are cascaded. The first stage has a voltage gain of 20 dB, and the second stage has a voltage gain of 5. What is the total voltage gain of the cascaded amplifier in dB?
Cascading Transistor Amplifiers
Medium
A.25 dB
B.27 dB
C.100 dB
D.34 dB
Correct Answer: 34 dB
Explanation:
When cascading amplifiers, the overall gain in dB is the sum of the individual stage gains in dB. First, convert the gain of the second stage to dB: . The total gain is the sum: .
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37In a two-stage RC-coupled CE amplifier, the effective load of the first stage is calculated by considering its collector resistor () in parallel with what other resistances?
Cascading Transistor Amplifiers
Medium
A.The parallel combination of the second stage's biasing resistors and its input impedance ()
B.Only the input impedance of the second stage ()
C.The series combination of and
D.Only the biasing resistors of the second stage ()
Correct Answer: The parallel combination of the second stage's biasing resistors and its input impedance ()
Explanation:
The AC signal from the collector of the first stage sees three paths to AC ground: through its own collector resistor , through the biasing network of the second stage (which is a parallel combination ), and into the input of the second transistor (). Therefore, the effective load is .
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38A cascode amplifier is a two-stage amplifier consisting of a CE stage followed by a CB stage. What is a key advantage of this configuration over a single-stage CE amplifier?
Cascading Transistor Amplifiers
Medium
A.Greatly increased bandwidth by reducing the Miller effect
B.Lower power consumption
C.Much higher input impedance
D.Significantly higher current gain
Correct Answer: Greatly increased bandwidth by reducing the Miller effect
Explanation:
The main advantage of the cascode configuration is its improved high-frequency response. The CB stage has a very low input impedance, which acts as the load for the CE stage. This results in a very low voltage gain for the CE stage, which significantly reduces the Miller effect (the apparent multiplication of the base-collector capacitance). This reduction leads to a much wider bandwidth.
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39If three identical amplifier stages, each with a lower 3-dB frequency of Hz, are cascaded, what is the approximate overall lower 3-dB frequency () of the 3-stage amplifier?
n-Stage Cascaded Amplifier
Medium
A.33.3 Hz
B.300 Hz
C.51 Hz
D.196 Hz
Correct Answer: 196 Hz
Explanation:
When identical stages are cascaded, the overall lower cutoff frequency increases. The formula is . For n=3, the denominator is . Therefore, .
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40Consider an n-stage cascaded amplifier made of identical stages. As the number of stages 'n' increases, what is the general effect on the overall voltage gain and the overall bandwidth?
n-Stage Cascaded Amplifier
Medium
A.Both gain and bandwidth decrease.
B.Gain increases, but bandwidth decreases.
C.Gain decreases, but bandwidth increases.
D.Both gain and bandwidth increase.
Correct Answer: Gain increases, but bandwidth decreases.
Explanation:
Cascading increases the overall gain, as the gains of the individual stages multiply (or add, in dB). However, cascading reduces the overall bandwidth. The upper cutoff frequency decreases and the lower cutoff frequency increases, resulting in a narrower frequency response. This represents a fundamental trade-off in amplifier design.
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41The standard low-frequency h-parameter model for a BJT assumes linearity around a Q-point. Under which condition does this model most significantly fail to represent the transistor's behavior, even if the Q-point is stable?
Two Port Devices and the Hybrid model
Hard
A.When the load resistance is purely reactive.
B.When the operating temperature deviates by more than 10°C from the temperature at which the parameters were measured.
C.When the input signal swing is large enough to cause significant variation in the small-signal parameters.
D.When the source impedance is perfectly matched to the input impedance.
Correct Answer: When the input signal swing is large enough to cause significant variation in the small-signal parameters.
Explanation:
H-parameters are small-signal parameters, derived from the slope of the characteristic curves at the Q-point. A large signal swing moves the operating point significantly, causing the slopes (and thus h-parameters) to change, violating the linearity assumption upon which the model is based.
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42If the collector current () of a BJT in a common-emitter configuration is increased, while keeping constant, how do the h-parameters and primarily change?
Determination of the h parameters from the characteristics
Hard
A.Both and decrease.
B. decreases and increases.
C. increases and decreases.
D.Both and increase.
Correct Answer: decreases and increases.
Explanation:
The input resistance is approximately . As collector current increases, decreases. The current gain, (or ), generally shows a slight increase with over a wide range of currents before it starts to drop at very high currents. Thus, the primary effect is a decrease in and an increase in .
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43For a common-emitter amplifier with an unbypassed emitter resistor and a source with internal resistance , what is the correct expression for the overall voltage gain ? Assume is negligible ().
Analysis of a Transistor Amplifier circuit using h-parameters
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
The input loop KVL equation is . Substituting gives . The output voltage is . The gain is found by dividing the two expressions, which yields the correct formula.
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44Consider a two-stage CE-CE cascaded amplifier. The voltage gain of the first stage, when measured with no load, is . When the second stage is connected to the output of the first stage, the effective voltage gain of the first stage () will be:
Cascading Transistor Amplifiers
Hard
A. because the stages are coupled by a capacitor which isolates the DC bias.
B. because the second stage provides additional amplification.
C.
D. because the input impedance of the second stage () shunts the collector resistor of the first stage ().
Correct Answer: because the input impedance of the second stage () shunts the collector resistor of the first stage ().
Explanation:
The voltage gain of a CE stage is proportional to its effective load resistance, . Initially, . When the second stage is connected, its input impedance is in parallel with . The new load is . Since a parallel combination is always smaller than either individual resistance, the effective load decreases, and consequently, the voltage gain of the first stage is reduced due to this loading effect.
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45For an application requiring a high-frequency buffer amplifier with maximum power transfer from a source with very high output impedance, which configuration is most suitable and why?
comparison of Transistor Amplifier configuration
Hard
A.Common Collector (CC), because it has high input impedance and low output impedance.
B.Common Emitter (CE) with an emitter resistor, because its input impedance can be precisely controlled.
C.Common Base (CB), because it has very low input impedance and high output impedance.
D.A Darlington pair in Common Collector configuration, because it provides extremely high input impedance.
Correct Answer: A Darlington pair in Common Collector configuration, because it provides extremely high input impedance.
Explanation:
To avoid loading a source with very high output impedance, the amplifier must have an extremely high input impedance. While a single CC amplifier has high input impedance, a Darlington pair CC amplifier offers a much higher input impedance (approximately ), making it far superior for this specific application. It also maintains the low output impedance characteristic of a buffer.
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46An n-stage cascaded amplifier is built using n identical, non-interacting stages. If each individual stage has an upper 3dB frequency of , what is the overall upper 3dB frequency, , of the cascaded amplifier?
n-Stage Cascaded Amplifier
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
The overall gain magnitude squared is the product of the individual stage gain magnitudes squared. At the overall 3dB frequency , the total gain magnitude squared is half its mid-band value. For n identical stages, this means . This leads to the relationship . Solving for gives the formula . This phenomenon is known as bandwidth shrinkage.
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47Given the h-parameters for a two-port network, what is the correct expression for the short-circuit output admittance, ?
Two Port Devices and the Hybrid model
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
The parameter is defined as with . From the h-parameter equations ( and ), setting gives . Substituting this into the second equation gives . Factoring out and finding the ratio yields , which simplifies to the given expression. Note that () is the open-circuit output admittance, not short-circuit.
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48Given the input characteristics ( vs ) of a BJT for two different values of ( and ), how would you determine the reverse voltage gain, ?
Determination of the h parameters from the characteristics
Hard
A.It is the slope of the vs curve at the Q-point.
B.It is the ratio for a constant between the two curves.
C.It is the reciprocal of the slope of the output characteristics ( vs ) at the Q-point.
D.It cannot be determined from the input characteristics alone; output characteristics are also required.
Correct Answer: It is the ratio for a constant between the two curves.
Explanation:
By definition, the reverse voltage transfer ratio is . For graphical determination, this is approximated as . You find the change in between the two curves ( and ) while keeping the base current at its Q-point value.
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49In the h-parameter analysis of a Common Emitter amplifier, the reverse voltage gain () is often neglected. In which of the following circuit conditions would this approximation lead to the most significant error in calculating the amplifier's input impedance ()?
Analysis of a Transistor Amplifier circuit using h-parameters
Hard
A.When the collector load resistance () is very large.
B.When the transistor is biased at a very low collector current.
C.When a large unbypassed emitter resistor () is used.
D.When the source resistance () is very small.
Correct Answer: When the collector load resistance () is very large.
Explanation:
The full expression for the input impedance of a CE amplifier is . The second term represents the feedback effect due to . This term is directly proportional to the load resistance (which is primarily ). If is very large, this term becomes significant compared to , and neglecting it will introduce a substantial error.
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50A three-stage amplifier has stage gains of 100, 200, and an attenuator stage with a gain of 0.1. What is the overall gain in decibels (dB)?
n-Stage Cascaded Amplifier
Hard
A.46 dB
B.66 dB
C.86 dB
D.60 dB
Correct Answer: 66 dB
Explanation:
The total linear voltage gain is the product of the individual stage gains: . The overall gain in dB is calculated as dB.
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51A cascode amplifier consists of a CE stage followed by a CB stage. What is the primary reason for this configuration's significant improvement in high-frequency performance over a single CE stage?
Cascading Transistor Amplifiers
Hard
A.The Miller effect in the input CE stage is drastically reduced because its voltage gain is approximately unity.
B.The CB stage has a much higher current gain, boosting the overall gain.
C.The overall output impedance is significantly lower, allowing it to drive heavy loads.
D.The input impedance of the CB stage perfectly matches the output impedance of the CE stage.
Correct Answer: The Miller effect in the input CE stage is drastically reduced because its voltage gain is approximately unity.
Explanation:
High-frequency response in a CE amplifier is limited by the Miller effect, where the base-collector capacitance () appears multiplied by the stage's voltage gain. In a cascode amplifier, the CE stage's load is the very low input impedance of the CB stage, resulting in a very low voltage gain () for the CE stage. This prevents the large multiplication of , thus reducing the effective input capacitance and extending the amplifier's bandwidth.
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52An amplifier design requires both high voltage gain and high input impedance, but a low output impedance is not critical. Which of the following configurations or combinations would be the most suitable compromise?
comparison of Transistor Amplifier configuration
Hard
A.A Darlington pair in a Common Emitter (CE) configuration.
B.A Common Base (CB) amplifier.
C.A single-stage Common Emitter (CE) with a large unbypassed emitter resistor.
D.A Common Collector (CC) followed by a Common Emitter (CE).
Correct Answer: A Darlington pair in a Common Emitter (CE) configuration.
Explanation:
A standard CE amplifier provides high voltage gain but has only moderate input impedance. A Darlington pair behaves like a single transistor with a much higher current gain () and much higher input impedance. Using this pair in a CE configuration leverages the high voltage gain property of the CE setup while providing the desired high input impedance, thus satisfying both main requirements.
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53Using the h-parameter model for a Common Emitter amplifier, what is the expression for the output impedance () looking back into the collector terminal, considering a source with internal resistance ?
Analysis of a Transistor Amplifier circuit using h-parameters
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
To find , set the independent source , apply a test voltage at the output, and find the current . The input loop equation becomes . The output loop equation is . By solving for from the first equation and substituting into the second, we can find the ratio . The result shows that the output impedance depends on the source resistance due to the internal feedback term .
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54Given the common-emitter h-parameters (), which expression correctly represents the common-base input impedance, ? Assume the standard approximations hold.
Two Port Devices and the Hybrid model
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
The exact conversion formula for is . Given that the reverse voltage gain and the product are both very small, the denominator simplifies to approximately . This yields the common and useful approximation , which relates the small CB input resistance to the larger CE input resistance.
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55A CE amplifier stage with a high output impedance () needs to drive a second CE stage with a relatively low input impedance (). To improve power transfer and overall gain, a buffer is inserted between them. What is the most suitable single-transistor amplifier configuration for this buffer?
Cascading Transistor Amplifiers
Hard
A.Common Collector (CC)
B.Common Base (CB)
C.Common Emitter (CE) with an emitter bypass capacitor
D.Common Emitter (CE) with a very small collector resistor
Correct Answer: Common Collector (CC)
Explanation:
An impedance-matching buffer placed between a high output impedance stage and a low input impedance stage should itself have a high input impedance and a low output impedance. The Common Collector (or Emitter Follower) configuration perfectly fits this requirement. It presents a high input impedance to the first stage, preventing loading, and provides a low output impedance to drive the second stage effectively, ensuring maximum signal transfer.
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56An n-stage RC-coupled amplifier is made from n identical stages. If the lower 3dB frequency of a single stage is , what is the overall lower 3dB frequency, , of the n-stage amplifier?
n-Stage Cascaded Amplifier
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
The gain of each stage decreases at low frequencies. The overall gain is the product of individual gains. At the overall lower 3dB frequency , the gain magnitude squared is half its mid-band value. For n identical stages, this requires . Solving this for based on the low-frequency transfer function yields . This shows that the overall lower cutoff frequency is always higher than that of a single stage.
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57If the ambient temperature of a BJT amplifier increases significantly, what are the most prominent changes in the common-emitter h-parameters and ? (Assume the bias point is not perfectly stabilized).
Determination of the h parameters from the characteristics
Hard
A.' increases, but decreases.
B.Both and increase.
C.Both and decrease.
D.' decreases, but increases.
Correct Answer: Both and increase.
Explanation:
An increase in temperature causes several effects. The current gain, (), increases significantly. The input resistance, , is related to the thermal voltage and emitter current . increases directly with absolute temperature. Additionally, leakage currents increase, which can shift the Q-point to a higher collector current. The dominant effects are the direct increase in and the influence of increased , both of which lead to an increase in as well.
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58Which statement most accurately contrasts the Common Base (CB) and Common Collector (CC) configurations in terms of signal phase and impedance transformation?
comparison of Transistor Amplifier configuration
Hard
A.CB is inverting while CC is non-inverting; both are high-to-low impedance transformers.
B.Both are non-inverting, but CC is a low-to-high impedance transformer while CB is a high-to-low impedance transformer.
C.CB is non-inverting while CC is inverting; CB is a low-to-high impedance transformer while CC is a high-to-low impedance transformer.
D.Both are non-inverting, but CB is a low-to-high impedance transformer while CC is a high-to-low impedance transformer.
Correct Answer: Both are non-inverting, but CB is a low-to-high impedance transformer while CC is a high-to-low impedance transformer.
Explanation:
Both CB and CC amplifiers have a positive voltage gain, meaning the output signal is in phase with the input (non-inverting). The CB amplifier has a very low input impedance and a high output impedance, making it a low-to-high impedance converter. Conversely, the CC amplifier has a high input impedance and a low output impedance, making it a high-to-low impedance converter (or buffer).
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59For a Darlington pair treated as a single device, what is the approximate overall forward current gain, , and input resistance, , in terms of the individual transistor parameters (), assuming identical transistors (, )?
Analysis of a Transistor Amplifier circuit using h-parameters
Hard
A.,
B.,
C.,
D.,
Correct Answer: ,
Explanation:
The overall current gain of a Darlington pair is approximately the product of the individual gains: . The input impedance is that of the first transistor () in series with the input impedance of the second transistor as reflected to the emitter of the first, which is . Therefore, . For identical transistors and large , this approximates to .
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60You need to design a three-stage amplifier with very high overall voltage gain, high input impedance, and low output impedance. Which of the following cascade sequences is the most logical choice?
Cascading Transistor Amplifiers
Hard
A.CE - CE - CE
B.CC - CE - CC
C.CE - CB - CC
D.CB - CE - CC
Correct Answer: CC - CE - CC
Explanation:
This is a classic system design problem. The first stage should provide high input impedance to avoid loading the source; a Common Collector (CC) stage is ideal. The middle stage should provide high voltage gain; a Common Emitter (CE) stage is the best choice. The final stage must provide a low output impedance to drive a load; a Common Collector (CC) stage is used for this buffering purpose. Therefore, the CC-CE-CC cascade effectively meets all three design requirements.