Podcast
Questions and Answers
If an amplifier's AC load line operation extends 15µA above and below its Q-point base current of 40µA, how does this affect the signal handling capability, assuming symmetrical clipping?
If an amplifier's AC load line operation extends 15µA above and below its Q-point base current of 40µA, how does this affect the signal handling capability, assuming symmetrical clipping?
- Reduces maximum possible signal swing. (correct)
- The AC load line does not affect signal handling.
- Increases maximum possible signal swing.
- Maintains the signal swing, but shifts the Q-point.
What does the stability of voltage gain in a BJT amplifier primarily ensure?
What does the stability of voltage gain in a BJT amplifier primarily ensure?
- The amplifier operates at the highest possible gain.
- The amplifier can amplify signals of any frequency without distortion.
- The voltage gain remains constant regardless of temperature or transistor variations. (correct)
- The amplifier consumes minimal power.
In a voltage-divider bias configuration, what is the main advantage of designing it such that it is 'stiff'?
In a voltage-divider bias configuration, what is the main advantage of designing it such that it is 'stiff'?
- The power consumption of the circuit is significantly reduced.
- The base voltage is relatively independent of the transistor's beta. (correct)
- The collector current becomes more sensitive to temperature variations.
- The base voltage is highly dependent on the transistor's beta.
In a BJT amplifier circuit, if the DC beta ($\beta_{DC}$) increases due to a temperature change, and the bias is not particularly stiff, how will this primarily affect the collector current ($I_C$)?
In a BJT amplifier circuit, if the DC beta ($\beta_{DC}$) increases due to a temperature change, and the bias is not particularly stiff, how will this primarily affect the collector current ($I_C$)?
What is the primary effect of increasing the value of a bypass capacitor connected in parallel with the emitter resistor in a common-emitter amplifier?
What is the primary effect of increasing the value of a bypass capacitor connected in parallel with the emitter resistor in a common-emitter amplifier?
What is the most likely consequence of removing the emitter bypass capacitor in a common-emitter amplifier circuit?
What is the most likely consequence of removing the emitter bypass capacitor in a common-emitter amplifier circuit?
Why is it important to consider the 'r'e' (AC emitter resistance) of all transistors in a multi-stage amplifier circuit when calculating the overall gain?
Why is it important to consider the 'r'e' (AC emitter resistance) of all transistors in a multi-stage amplifier circuit when calculating the overall gain?
In a class AB amplifier, what is the primary purpose of the biasing network that sets a small quiescent current?
In a class AB amplifier, what is the primary purpose of the biasing network that sets a small quiescent current?
What is crossover distortion in a power amplifier, and which class of amplifier is most susceptible to it?
What is crossover distortion in a power amplifier, and which class of amplifier is most susceptible to it?
Which characteristic distinguishes a Class A power amplifier from Class B and Class AB amplifiers?
Which characteristic distinguishes a Class A power amplifier from Class B and Class AB amplifiers?
In a negative feedback amplifier, if the feedback network returns a fraction of the output signal to the input, what effect does this generally have on the amplifier’s bandwidth?
In a negative feedback amplifier, if the feedback network returns a fraction of the output signal to the input, what effect does this generally have on the amplifier’s bandwidth?
Which of the following is a primary advantage of using negative feedback in an amplifier circuit?
Which of the following is a primary advantage of using negative feedback in an amplifier circuit?
In an amplifier circuit, what is the effect of the Miller capacitance, and how does it typically impact the high-frequency response?
In an amplifier circuit, what is the effect of the Miller capacitance, and how does it typically impact the high-frequency response?
What is the primary reason for using cascading amplifier stages in electronic circuit design?
What is the primary reason for using cascading amplifier stages in electronic circuit design?
How does the addition of a source/emitter follower stage typically affect the overall performance of a multi-stage amplifier?
How does the addition of a source/emitter follower stage typically affect the overall performance of a multi-stage amplifier?
Flashcards
Stability of Voltage Gain
Stability of Voltage Gain
The extent to which the voltage gain of a BJT amplifier remains constant despite variations in temperature, transistor parameters, or operating conditions.
Stiff Voltage-Divider Bias
Stiff Voltage-Divider Bias
A bias circuit where the base voltage is largely independent of the transistor's beta, providing stable operation.
Cross-Over Distortion
Cross-Over Distortion
A distortion that occurs in class B amplifiers when the input signal is near zero, causing the transistors to be cut off and the output signal to be missing a portion around the zero-crossing point.
Cut-off Region
Cut-off Region
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Active Region
Active Region
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Q-Point
Q-Point
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Characteristic Curves
Characteristic Curves
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DC (BDC) and AC (Bac) Beta
DC (BDC) and AC (Bac) Beta
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Study Notes
- This is a fill-in paper test for Electronics 2, module code EEELE2A.
- The test is set for March 15, 2024, and the duration is 90 minutes.
- Only non-programmable calculators are allowed.
- The marks total 37, and the question paper consists of 10 typed pages.
Instructions Summary
- A valid student card is required.
- Student number needs to be written clearly.
- Answers have to be numbered correctly.
- SMS/texting language and TIP-EX are not allowed.
- Answers must be in pen, sketches in pencil.
- All work must be submitted before leaving.
- Cell phones and other mobile devices must be switched off and kept away.
Disciplinary Actions
- Possession of undocumented material can lead to disciplinary hearing/disqualification.
- Communication with others (excluding the invigilator) is prohibited.
- Offensive matter is prohibited.
- Committing irregularities is prohibited.
- Unsatisfactory conduct is prohibited.
Prohibitions
- Leaving the assessment venue without permission.
- Asking for explanations of questions.
- Borrowing anything from other candidates.
Question 1
- This pertains to the characteristic curves of a certain amplifier.
- The AC load line operation extends 10 µA above and below the Q-point base current of 35 µA.
Question 1.1
- Determine the resulting peak-to-peak values of the collector current and collector-to-emitter voltage from the graph.
Question 1.2
- Determine dc beta (BDC) and ac beta (Bac) from the graph.
- Explain what is meant by the stability of the voltage gain for a BJT amplifier.
Question 2
- The amplifier circuit is provided in Figure 2.
Question 2.1
- Determine whether the voltage-divider bias circuit is stiff and justify the answer.
- Calculate VB, IE, and VCE.
Question 2.2
- Amplifier circuit is shown in Figure 3, with Bac = BDC = 150 for all transistors.
- All transistor ré considerations are a must.
- IE1 is stated as 6.468mA in Figure 3.
- Calculate Vout.
Question 3
- Given the load line in Figure 4, label the Q-points in the figure with their corresponding power amplifier class
- Given the power amplifier circuit in Figure 5, draw a fully labelled and improved version of this circuit to eliminate cross-over distortion.
Equations
- IE = IC + IB
- Ic/IB = BDC
- VBE = 0.7 V
- IB = (VBB - VBE) / RB
- VCE = VCC - ICRC
- VCB = VCE - VBE
- A = RC / re
- VCE(cutoff) VCC
- IC(sat) (VCC - VCE(sat)) / RC
- IB(min) IC(sat) / BDC
- IC = BDCIB
- VB = VCC * (R2 / (R1 + R2))
- VE = VB - VBE
- IC = IE = VE / RE
- VC = VCC - ICRC
- RIN(BASE) = BDCRE
- IE = (VTH - VBE) / (RE + RTH/BDC)
- IE = (-VEE - VBE) / (RE + RB/BDC)
- VCE = VCC - ICRC
- IC = BDC(VCC - VBE) / (RE + RB/BDC)
- IE = (VCC - VBE) / (RB/BDC)
- VCE = VCC - ICRC
- re = 25mV / IE
- Ap = A'Ai
- R = R ∥ R ∥ R in(base) 1 2 in(base)
- Rout = Rc
- Av = RC / re
- Rin(source) = 1/gm
- A0 = RC /RE1
- For FET: R = RG (VGS) / IGSS in
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