2020 041404

B.Tech Examination, 2020

Time 3 hours

Full Marks 70

Instructions:

The marks are indicated in the right-hand margin.
There are NINE questions in this paper.
Attempt FIVE questions in all.
Question No. 1 is compulsory.

Questions

Q1

Answer the following:

a)

Explain the characteristics of ideal voltage amplifier.

[2 Marks]

b)

Which FET amplifier offers a high-input impedance and a low-output impedance?

[2 Marks]

c)

Explain about diffusion capacitance in BJT amplifier.

[2 Marks]

d)

In common-base BJT amplifier, what is the phase difference between AC collector voltage to emitter voltage?

[2 Marks]

e)

Explain how $h_{fe}$ is frequency dependent in high frequency response of a BJT amplifier.

[2 Marks]

f)

What is the gain bandwidth product?

[2 Marks]

g)

Why does current gain of a bipolar transistor drop at high frequencies?

[2 Marks]

h)

On which parameters the bandwidth of an RF-tuned amplifier depends?

[2 Marks]

i)

Why is negative feedback employed in high gain amplifiers?

[2 Marks]

j)

Which oscillator is used for audio-frequency applications?

[2 Marks]

Q2

Answer the following:

a)

Draw the approximate small-signal equivalent circuit at low frequency for common-base amplifier with load resistance $R_L$ . Compute the current gain in terms of $h$ parameters.

[8 Marks]

b)

Explain the frequency distortion in amplifier and list the various causes for distortion.

[6 Marks]

Q3

Answer the following:

a)

Draw and explain the working of low-frequency small-signal equivalent circuit of common-collector BJT.

[6 Marks]

b)

For the given hybrid $\pi$ model of a transistor shown in figure below, compute the (i) parameters of low-frequency hybrid model, (ii) quiescent collector current at the room temperature, (iii) frequency $f_T$ at which the CE short-circuit current gain is unity.

[8 Marks]

Q4

Answer the following:

a)

Draw the small-signal equivalent circuit at high frequency for common-drain FET amplifier with load resistance $R_L$ . Compute the expression for current gain.

[8 Marks]

b)

Draw and explain the working of bootstrapped Darlington circuit.

[6 Marks]

Q5

Answer the following:

a)

What must be the relationship between $t_r$ and high 3-dB frequency $f_H$ in order to amplify the pulse without excessive distortion?

[5 Marks]

b)

Sketch the high-frequency step response of a low-pass single-pole amplifier and explain the intermediate steps required to achieve the output.

[9 Marks]

Q6

Answer the following:

a)

Calculate the overall lower 3-dB and upper 3-dB frequencies for five non-interacting stages amplifier having an individual stage lower 3-dB $f_1 = 50\text{ Hz}$ and upper 3-dB $f_2 = 5\text{ MHz}$ .

[8 Marks]

b)

Define tilt and how the tilt is related to the low 3-dB frequency $f_L$ .

[6 Marks]

Q7

Answer the following:

a)

Draw a small-signal equivalent circuit model for common-source FET amplifier and derive an expression for a 3-dB bandwidth of its frequency response.

[9 Marks]

b)

Compute overall noise figure of 8 cascaded amplifiers having equal individual power gain = $50\text{ dB}$ and noise factor = $4\text{ dB}$ .

[5 Marks]

Q8

Answer the following:

a)

Explain the working of class AB power amplifier.

[7 Marks]

b)

Derive an expression for the oscillation frequency of a Colpitts oscillator and compute its value for given $L = 12\text{ mH}$ , $C_1 = 30\text{ nF}$ and $C_2 = 300\text{ nF}$ .

[7 Marks]

Q9

Answer the following:

a)

Compute the bandwidth for single tuned BJT amplifier uses one parallel-tuned circuit as load.

[14 Marks]

2019 041404

B.Tech 4th Semester Exam., 2019

Time 3 hours

Full Marks 70

Instructions:

The marks are indicated in the right-hand margin.
There are NINE questions in this paper.
Attempt FIVE questions in all.
Question No. 1 is compulsory.

Section 1

Q1

Choose the correct answer from the following (any seven) :

a)

If the $Q$ of a single-stage single-tuned amplifier is doubled, the bandwidth will

a)

remain the same

b)

become half

c)

become double

d)

become four times

b)

Which of the following oscillators is suitable for frequencies in the range of mega hertz?

a)

RC phase shift

b)

Wien bridge

c)

Hartley

d)

Both (i) and (iii)

c)

An R-C coupled amplifier has an open loop gain of 200 and a lower cutoff frequency of $50 \text{ Hz}$ . If negative feedback with $\beta = 0.1$ is used, the lower cutoff frequency will be

a)

about $50 \text{ Hz}$

b)

about $5 \text{ Hz}$

c)

about $2.38 \text{ Hz}$

d)

about $70.5 \text{ Hz}$

d)

The load impedance $Z_L$ of a CE amplifier has $R$ and $L$ in series. The phase difference between output and input will be

a)

$180^\circ$

b)

$0$

c)

more than $90^\circ$ but less than $180^\circ$

d)

more than $180^\circ$ but less than $270^\circ$

e)

The gain of an FET amplifier can be changed by changing

a)

$r_m$

b)

$g_m$

c)

$R_d$

d)

None of the above

f)

In class C operation of an amplifier circuit, the collector current exists for

a)

$360^\circ$ of input wave

b)

$180^\circ$ of input wave

c)

more than $180^\circ$ of input wave

d)

less than $180^\circ$ of input wave

g)

Which resistance in hybrid $\pi$ model of transistor represents the bulk resistance present between the external base terminal and the virtual base?

a)

Collector-to-emitter resistance ($r_{ce}$)

b)

Base spreading resistance ($r_{bb'}$)

c)

Virtual base to emitter resistance ($r_{b'e}$)

d)

None of the above

h)

Which among the following represents the frequency at which short-circuit CE current gain acquires unit magnitude?

a)

$f_\alpha$

b)

$f_\beta$

c)

$f_T$

d)

None of the above

i)

Which type of amplifiers exhibits the current gain approximately equal to unity without any current amplification?

a)

CE

b)

CB

c)

CC

d)

None of the above

j)

Which among the below stated notations of $h$-parameters is used to represent the short-circuit forward current transfer ratio?

a)

$h_{11}$

b)

$h_{12}$

c)

$h_{21}$

d)

$h_{22}$

[14 Marks]

Section 2

Q2a

Explain the amplitude distortion in amplifier and list the various causes for distortion.

[6 Marks]

Q2b

Draw the approximate small-signal equivalent circuit at low frequency for common-emitter amplifier with load resistance $R_L$ . Compute the current gain in terms of $h$-parameters.

[8 Marks]

Q3a

Explain why input resistance is increased by adding the emitter resistance $R_E$ in common-emitter amplifier. Discuss with the help of small-signal equivalent circuit at low frequency.

[6 Marks]

Q3b

For the given hybrid $\pi$ model of a transistor shown in Fig. below, compute (i) parameters of low-frequency hybrid model, (ii) the quiescent collector current at the room temperature, (iii) the frequency $f_T$ at which the CE short-circuit current gain is unity. [Diagram: Hybrid-pi model with $r_{bb'} = 700 \Omega$ , $r_{b'e} = 1.5 \text{ k}\Omega$ , $C_{b'e} = 10 \text{ pF}$ , $C_{b'c} = 5 \text{ pF}$ , $r_{b'c} = 14 \text{ M}\Omega$ , $g_m = 0.08 \text{ A/V}$ , $r_{ce} = 70 \text{ k}\Omega$ .]

[8 Marks]

Q4a

Explain the working of bootstrapped Darlington circuit. How is the input resistance increased by bootstrapping?

[8 Marks]

Q4b

Draw the small-signal equivalent circuit at high frequency for common-source FET amplifier with load resistance $R_L$ . Compute the expression for voltage gain.

[6 Marks]

Q5a

Sketch the high-frequency step response of a low-pass single-pole amplifier and explain the intermediate steps required to achieve the output.

[8 Marks]

Q5b

Define the rise time $t_r$ . Explain the relationship between $t_r$ and the high 3-dB frequency $f_H$ .

[6 Marks]

Q6a

Draw the hybrid-$\pi$ model for a transistor in the CE configuration. Compute the frequency at which the short-circuit CE current gain attains unit magnitude.

[7 Marks]

Q6b

Calculate the overall lower 3-dB and upper 3-dB frequencies for five non-interacting stages amplifier having an individual stage lower 3-dB $f_1 = 40 \text{ Hz}$ and upper 3-dB $f_2 = 2 \text{ MHz}$ .

[7 Marks]

Q7a

Write the Friis cascade formula and explain its different terms. Compute overall noise figure of 10 cascaded amplifiers having equal individual power gain = $60 \text{ dB}$ and noise factor = $5 \text{ dB}$ .

[7 Marks]

Q7b

Derive the expression for the oscillation frequency of a Hartley oscillator and compute its value for given $L_1 = 1.2 \text{ }\mu\text{H}$ , $L_2 = 6.8 \text{ }\mu\text{H}$ , and $C = 10 \text{ nF}$ .

[7 Marks]

Q8a

How are power amplifiers categorized? Explain the working of class A power amplifier.

[6 Marks]

Q8b

A single-tuned transistor amplifier is used to amplify the modulated RF carrier of $600 \text{ kHz}$ and bandwidth of $15 \text{ kHz}$ . The circuit has total output resistance, $R_o = 20 \text{ k}\Omega$ and output capacitance $C_o = 50 \text{ pF}$ . Calculate values of inductance and capacitance of the tuned circuit.

[8 Marks]

Q9a

Explain the working of cascaded BJT amplifier and list its advantages.

[6 Marks]

Q9b

State the Barkhausen criterion for sustained oscillation and derive the expressions for the frequency of oscillation and condition of stable oscillation in case of Wien bridge oscillator.

[8 Marks]

2019 041504

B.Tech 5th Semester Exam., 2019

Time 3 hours

Full Marks 70

Instructions:

The marks are indicated in the right-hand margin.
There are NINE questions in this paper.
Attempt FIVE questions in all.
Question No. 1 is compulsory.

Section 1

Q1

Answer any seven of the following questions briefly :

a)

The ear is not sensitive to which type of distortion in the amplifier?

b)

Write the condition for approximate model of BJT in CE configuration.

c)

What is the phase difference between input and output currents in CE configuration?

d)

Why is the Bootstrap principle used in emitter follower circuit?

e)

What is Gain Bandwidth Product?

f)

Which of the BJT transistor currents is always the largest?

g)

What are the main purposes for which a CC amplifier may be used?

h)

What is the purpose of transformer coupling in transistor amplifier?

i)

Why is CB amplifier used as constant current source?

j)

Explain the Barkhausen criterion.

[14 Marks]

Section 2

Q2a

Explain the phase distortion in amplifier and list the various causes for distortion.

[6 Marks]

Q2b

Draw the approximate small-signal equivalent circuit at low frequency for common-base amplifier with load resistance $R_L$ . Compute the output resistance in terms of h parameter.

[8 Marks]

Q3a

The BJT is connected as a CE amplifier. Determine $Z_i, Z_o, A_I$ and $A_V$ using complete hybrid model.

[7 Marks]

Q3b

For an emitter bias BJT circuit (capacitor is bypassed), determine $r_e, Z_i, Z_o$ and $A_V$ . Given: $R_B = 470 \text{ k}\Omega, R_C = 2.2 \text{ k}\Omega, V_{CC} = 20 \text{ V}, R_E = 0.56 \text{ k}\Omega, C_E = 10 \text{ }\mu\text{F}, \beta = 120, r_o = 40 \text{ k}\Omega, C_C = 10 \text{ }\mu\text{F}$ .

[7 Marks]

Q4a

Draw the single stage RC coupled BJT amplifier and discuss the effect of (i) input capacitance $C_s$ , (ii) emitter bypass capacitor $C_e$ and (iii) output capacitor $C_c$ , on the frequency response.

[8 Marks]

Q4b

Derive an expression for percentage tilt (P) in the output waveform for square symmetrical wave applied as input to an amplifier that behaves as high-pass circuit at low-frequency signal.

[6 Marks]

Q5a

Derive the expressions for input and output resistances in case of emitter follower BJT amplifier using its hybrid model.

[8 Marks]

Q5b

Derive the expressions for voltage gain in case of low-frequency common-drain FET amplifier and prove why voltage gain is less than unity.

[6 Marks]

Q6a

Find the mean-square value $V_0^2$ of the output noise voltage for the circuit shown in the figure given below. The circuit represents a generator supplying Johnson noise to the RC combination. Prove that $\frac{1}{2} C V_o^2 = \frac{1}{2} kT$ . [Diagram: Noise source $V_n$ with resistor $R$ and capacitor $C$ .]

[9 Marks]

Q6b

Compute overall lower 3-dB frequency for four interacting stages amplifier having individual stage lower 3-dB frequency, $f_1 = 40 \text{ Hz}, f_2 = 100 \text{ Hz}, f_3 = 50 \text{ Hz}$ and $f_4 = 10 \text{ Hz}$ .

[5 Marks]

Q7a

With a neat circuit diagram, explain the operation of a transformer coupled class A power amplifier.

[6 Marks]

Q7b

Compute the expression for current gain using small-signal equivalent circuit at high frequency for common-drain FET amplifier with load resistance $R_L$ .

[8 Marks]

Q8a

Derive the relationship between $t_r$ and high 3-dB frequency $f_H$ in order to amplify the pulse without excessive distortion.

[7 Marks]

Q8b

Derive the frequency and condition of oscillation for FET phase-shift oscillator.

[7 Marks]

Q9a

Explain the working of a class B push pull amplifier. Prove that the maximum efficiency is 78.5%.

[7 Marks]

Q9b

Derive the expressions for frequency and condition of oscillation in case of Wien bridge oscillator. Determine the maximum and minimum frequency of oscillations of a Wien bridge oscillator circuit having a resistor of $10 \text{ k}\Omega$ and a variable capacitor of $1 \text{ nF}$ to $1000 \text{ nF}$ .

[7 Marks]

2018 011404

B.Tech 4th Semester Exam., 2018

Time 3 hours

Full Marks 70

Instructions:

The marks are indicated in the right-hand margin.
There are NINE questions in this paper.
Attempt FIVE questions in all.
Question No. 1 is compulsory.

Section 1

Q1

Choose the correct answer from the following (any seven) :

a)

When there is no base current in a transistor switch, the output voltage from the transistor is

a)

low

b)

high

c)

unchanged

d)

unknown

b)

If the emitter resistance increases, the collector voltage

a)

decreases

b)

stays the same

c)

increases

d)

breaks down the transistor

c)

Consider 49 cascaded amplifiers having individual rise time as 2 n sec, 3 n sec, ..., 50 n sec. The input waveform rise time is 1 n sec. Then the output signal rise time is given by (assume output signal rise time is measured within 10 percent range of the final output signal)

a)

39-28 $\mu$ sec

b)

2.28 $\mu$ sec

c)

0.228 $\mu$ sec

d)

39.28 $\mu$ sec

d)

Which capacitance(s) in hybrid $\pi$ model represent(s) the storage of excess minority carriers at the base emitter junction?

a)

Diffusion capacitance

b)

Transition capacitance

c)

Both (i) and (ii)

d)

None of the above

e)

Why do the internal capacitances of transistor at low frequencies treated as open circuits by completely neglecting their effects in analysis?

a)

Due to high reactance

b)

Due to low reactance

c)

Due to moderate reactance

d)

None of the above

f)

Which among the below assertions is not a salient feature/property of CE amplifier?

a)

High voltage gain

b)

High current gain

c)

High input resistance

d)

High output resistance

g)

In a power amplifier, the collector current flows for $270^\circ$ of the input cycle. The operation is

a)

class A

b)

class B

c)

class AB

d)

class C

h)

Which capacitor is used to block DC portion by allowing to pass only AC portion of the amplified signal to load?

a)

Input coupling capacitor

b)

Bypass capacitor

c)

Output coupling capacitor

d)

All of the above

i)

When the circuit is switched on, the loop gain of an Wien bridge oscillator is

a)

1

b)

more than 1

c)

less than 1

d)

about 0.5

j)

If Q of an L-C circuit increases, then bandwidth

a)

increases

b)

decreases

c)

remains the same

d)

Insufficient data

[14 Marks]

Section 2

Q2a

Explain the frequency distortion in amplifier and list the various causes for distortion.

[7 Marks]

Q2b

Draw the approximate small-signal equivalent circuit at low frequency for common-collector amplifier with load resistance $R_L$ . Compute the input resistance in terms of $h$ parameters.

[7 Marks]

Q3a

Draw and explain the working of low-frequency small-signal equivalent circuit of common base BJT.

[6 Marks]

Q3b

Compute the input impedance $R_i'$ using the equivalent circuit diagram given in figure below at frequency $f = 30 \text{ MHz}$ , where $g_m = 50 \text{ mA/V}$ , $R_L = 2 \text{ k}\Omega$ and $C_L = 20 \text{ pF}$ . [Diagram: Hybrid-pi model with $V_s$ , $50 \Omega$ , $100 \Omega$ , $1 \text{ k}\Omega$ , $R_L$ , $C_L$ , $V_i$ , $V_o$ , $100 \text{ pF}$ and $3 \text{ pF}$ capacitances, and current source $g_m V_{b'e}$ .]

[8 Marks]

Q4a

Draw and explain the working of Bootstrapped Darlington circuit.

[7 Marks]

Q4b

Explain the $f_\beta$ and $f_T$ , which are bandwidths of the circuit and short circuit current-gain bandwidth product respectively.

[7 Marks]

Q5a

The input to a low-pass amplifier is a pulse of width $t_p$ . Sketch the output waveform and explain the intermediate steps involved to achieve the output.

[10 Marks]

Q5b

What must be the relationship between $t_p$ and high 3-dB frequency $f_H$ in order to amplify the pulse without excessive distortion?

[4 Marks]

Q6a

Compute overall upper 3-dB frequency for four interacting stages amplifier having individual stage upper 3-dB frequency, $f_1 = 4 \text{ MHz}$ , $f_2 = 4.2 \text{ MHz}$ , $f_3 = 4.1 \text{ MHz}$ and $f_4 = 3.9 \text{ MHz}$ .

[8 Marks]

Q6b

Define tilt. How is the tilt related to the low 3-dB frequency $f_L$ ?

[6 Marks]

Q7a

Explain thermal and shot noises associated to the amplifier and briefly discuss the thermal-resistance noise voltage and mean-square shot-noise current in the context of thermal and shot noises respectively.

[7 Marks]

Q7b

Compute the expression for current gain using small-signal equivalent circuit at high frequency for common-source FET amplifier with load resistance $R_L$ .

[7 Marks]

Q8a

Explain the working of phase-shift oscillator.

[7 Marks]

Q8b

Derive expression for the oscillation frequency of a Colpitts oscillator and compute its value for given $L = 10 \text{ mH}$ , $C_1 = 24 \text{ nF}$ and $C_2 = 240 \text{ nF}$ .

[7 Marks]

Q9a

Explain the working of class-B push-pull amplifier and compute the maximum conversion efficiency.

[7 Marks]

Q9b

Compute the bandwidth for single-tuned BJT amplifier using one parallel tuned circuit as load.

[7 Marks]

2018 041404

B.Tech 4th Semester Exam., 2018

Time 3 hours

Full Marks 70

Instructions:

The marks are indicated in the right-hand margin.
There are NINE questions in this paper.
Attempt FIVE questions in all.
Question No. 1 is compulsory.

Section 1

Q1

Choose the correct answer from the following (any seven) :

a)

When there is no base current in a transistor switch, the output voltage from the transistor is

a)

low

b)

high

c)

unchanged

d)

unknown

b)

If the emitter resistance increases, the collector voltage

a)

decreases

b)

stays the same

c)

increases

d)

breaks down the transistor

c)

Consider 49 cascaded amplifiers having individual rise time as 2 n sec, 3 n sec, ..., 50 n sec. The input waveform rise time is 1 n sec. Then the output signal rise time is given by (assume output signal rise time is measured within 10 percent range of the final output signal)

a)

39-28 $\mu$ sec

b)

2.28 $\mu$ sec

c)

0.228 $\mu$ sec

d)

39.28 $\mu$ sec

d)

Which capacitance(s) in hybrid $\pi$ model represent(s) the storage of excess minority carriers at the base emitter junction?

a)

Diffusion capacitance

b)

Transition capacitance

c)

Both (i) and (ii)

d)

None of the above

e)

Why do the internal capacitances of transistor at low frequencies treated as open circuits by completely neglecting their effects in analysis?

a)

Due to high reactance

b)

Due to low reactance

c)

Due to moderate reactance

d)

None of the above

f)

Which among the below assertions is not a salient feature/property of CE amplifier?

a)

High voltage gain

b)

High current gain

c)

High input resistance

d)

High output resistance

g)

In a power amplifier, the collector current flows for $270^\circ$ of the input cycle. The operation is

a)

class A

b)

class B

c)

class AB

d)

class C

h)

Which capacitor is used to block DC portion by allowing to pass only AC portion of the amplified signal to load?

a)

Input coupling capacitor

b)

Bypass capacitor

c)

Output coupling capacitor

d)

All of the above

i)

When the circuit is switched on, the loop gain of an Wien bridge oscillator is

a)

1

b)

more than 1

c)

less than 1

d)

about 0.5

j)

If Q of an L-C circuit increases, then bandwidth

a)

increases

b)

decreases

c)

remains the same

d)

Insufficient data

[14 Marks]

Section 2

Q2a

Explain the frequency distortion in amplifier and list the various causes for distortion.

[7 Marks]

Q2b

Draw the approximate small-signal equivalent circuit at low frequency for common-collector amplifier with load resistance $R_L$ . Compute the input resistance in terms of $h$ parameters.

[7 Marks]

Q3a

Draw and explain the working of low-frequency small-signal equivalent circuit of common base BJT.

[6 Marks]

Q3b

Compute the input impedance $R_i'$ using the equivalent circuit diagram given in figure below at frequency $f = 30 \text{ MHz}$ , where $g_m = 50 \text{ mA/V}$ , $R_L = 2 \text{ k}\Omega$ and $C_L = 20 \text{ pF}$ . [Diagram: Hybrid-pi model with $V_s$ , $50 \Omega$ , $100 \Omega$ , $1 \text{ k}\Omega$ , $R_L$ , $C_L$ , $V_i$ , $V_o$ , $100 \text{ pF}$ and $3 \text{ pF}$ capacitances, and current source $g_m V_{b'e}$ .]

[8 Marks]

Q4a

Draw and explain the working of Bootstrapped Darlington circuit.

[7 Marks]

Q4b

Explain the $f_\beta$ and $f_T$ , which are bandwidths of the circuit and short circuit current-gain bandwidth product respectively.

[7 Marks]

Q5a

The input to a low-pass amplifier is a pulse of width $t_p$ . Sketch the output waveform and explain the intermediate steps involved to achieve the output.

[10 Marks]

Q5b

What must be the relationship between $t_p$ and high 3-dB frequency $f_H$ in order to amplify the pulse without excessive distortion?

[4 Marks]

Q6a

Compute overall upper 3-dB frequency for four interacting stages amplifier having individual stage upper 3-dB frequency, $f_1 = 4 \text{ MHz}$ , $f_2 = 4.2 \text{ MHz}$ , $f_3 = 4.1 \text{ MHz}$ and $f_4 = 3.9 \text{ MHz}$ .

[8 Marks]

Q6b

Define tilt. How is the tilt related to the low 3-dB frequency $f_L$ ?

[6 Marks]

Q7a

Explain thermal and shot noises associated to the amplifier and briefly discuss the thermal-resistance noise voltage and mean-square shot-noise current in the context of thermal and shot noises respectively.

[7 Marks]

Q7b

Compute the expression for current gain using small-signal equivalent circuit at high frequency for common-source FET amplifier with load resistance $R_L$ .

[7 Marks]

Q8a

Explain the working of phase-shift oscillator.

[7 Marks]

Q8b

Derive expression for the oscillation frequency of a Colpitts oscillator and compute its value for given $L = 10 \text{ mH}$ , $C_1 = 24 \text{ nF}$ and $C_2 = 240 \text{ nF}$ .

[7 Marks]

Q9a

Explain the working of class-B push-pull amplifier and compute the maximum conversion efficiency.

[7 Marks]

Q9b

Compute the bandwidth for single-tuned BJT amplifier using one parallel tuned circuit as load.

[7 Marks]

2018 041504

B.Tech 5th Semester Exam., 2018

Time 3 hours

Full Marks 70

Instructions:

The marks are indicated in the right-hand margin.
There are NINE questions in this paper.
Attempt FIVE questions in all.
Question No. 1 is compulsory.

Section 1

Q1

Choose the correct answer (any seven) :

a)

For the BJT circuit (Fig. 1) shown below, assume that the $\beta$ of the transistor is very large and $V_{BE} = 0.7 \text{ V}$ : [Diagram Fig. 1: BJT with $10 \text{ k}\Omega$ collector resistor, $1 \text{ k}\Omega$ emitter resistor, $10 \text{V}$ collector supply, $2 \text{V}$ base supply.] The mode of operation of the BJT is

a)

cut-off

b)

saturation

c)

normal active

d)

reverse active

b)

Assuming $V_{CE, Sat} = 0.2 \text{ V}$ and $\beta = 50$ , the minimum base current ($I_B$) required to drive the transistor in the given figure (Fig. 2) to saturation is: [Diagram Fig. 2: BJT with $1 \text{ k}\Omega$ collector resistor, $3 \text{V}$ collector supply.]

a)

$56 \text{ } \mu \text{A}$

b)

$140 \text{ } \mu \text{A}$

c)

$60 \text{ mA}$

d)

$3 \text{ mA}$

c)

In the transistor amplifier circuit shown in Fig. 3 the transistor has the following parameters: $\beta_{DC} = 60$ , $V_{BE} = 0.7 \text{ V}$ , $h_{ie} = \infty$ , $h_{fe} = \alpha$ . [Diagram Fig. 3: BJT with $1 \text{ k}\Omega$ collector resistor, $53 \text{ k}\Omega$ feedback resistor, $5.3 \text{ k}\Omega$ source resistor, $12 \text{V}$ supply.] The capacitance $C_C$ can be assumed to be infinite. Under DC conditions, the collector to emitter voltage drop is

a)

$4.8 \text{ V}$

b)

$5.3 \text{ V}$

c)

$6 \text{ V}$

d)

$6.6 \text{ V}$

d)

In Fig. 3, if $\beta_{DC}$ is increased by 10%, then collector to emitter voltage drop

a)

increases by less than or equal to 10%

b)

decreases by less than or equal to 10%

c)

increases by more than 10%

d)

decreases by more than 10%

e)

The small-signal gain of the amplifier $V_c/V_s$ is

a)

$-10$

b)

$-5.3$

c)

$5.3$

d)

10

f)

The value of $C$ required for sinusoidal oscillations of frequency $1 \text{ kHz}$ in the circuit shown in Fig. 4 is: [Diagram Fig. 4: Op-amp oscillator with $1 \text{ k}\Omega$ and $2.1 \text{ k}\Omega$ resistors.]

a)

$\frac{1}{2\pi} \mu \text{F}$

b)

$2\pi \mu \text{F}$

c)

$\frac{1}{2\pi\sqrt{6}} \mu \text{F}$

d)

$2\pi\sqrt{6} \mu \text{F}$

g)

For the JFET circuit shown in Fig. 5: [Diagram Fig. 5: JFET with $R_D, R_S$ , $2 \text{ M}\Omega$ gate resistor, $20 \text{V}$ supply.] Given $r_d = 20 \text{ k}\Omega$ , $I_{DSS} = 10 \text{ mA}$ , $V_P = -8 \text{ V}$ , $Z_i$ and $Z_o$ of the circuit are, respectively

a)

$2 \text{ M}\Omega$ and $2 \text{ k}\Omega$

b)

$2 \text{ M}\Omega$ and $\frac{20}{11} \text{ k}\Omega$

c)

infinity and $2 \text{ k}\Omega$

d)

infinity and $\frac{20}{11} \text{ k}\Omega$

h)

$I_D$ and $V_{DS}$ in Fig. 5 under DC conditions are, respectively

a)

$5.625 \text{ mA}$ and $8.75 \text{ V}$

b)

$7.5 \text{ mA}$ and $5 \text{ V}$

c)

$4.5 \text{ mA}$ and $11 \text{ V}$

d)

$6.250 \text{ mA}$ and $7.5 \text{ V}$

i)

In Fig. 5, transconductance in millisiemens (mS) and voltage gain of the amplifier are, respectively

a)

$1.875 \text{ mS}$ and $3.41$

b)

$1.875 \text{ mS}$ and $-3.41$

c)

$3.3 \text{ mS}$ and $-6$

d)

$3.3 \text{ mS}$ and $6$

j)

The cascade amplifier is a multistage configuration of

a)

CC-CB

b)

CE-CB

c)

CB-CC

d)

CE-CC

[14 Marks]

Section 2

Q2a

Explain class B transformer-coupled amplifier with circuit diagram.

[7 Marks]

Q2b

A transformer-coupled class A amplifier supply... [text incomplete in original] / In a BJT-based RC phase-shift oscillator, $R = 200 \text{ k}\Omega$ , $C = 200 \text{ pF}$ . Find the frequency of the BJT-based oscillator.

[7 Marks]

Q3

It is required to design a tuned amplifier of the type shown in Fig. 6, having $f_o = 1 \text{ MHz}$ , 3 dB bandwidth $= 10 \text{ kHz}$ , centre frequency gain $= -10 \text{ V/V}$ . The FET available has at the bias point $g_m = 5 \text{ mA/V}$ and $r_o = 10 \text{ k}\Omega$ . The output capacitance is negligibly small. Determine $R_L, C_L$ and $L$ . [Diagram Fig. 6: Tuned MOSFET amplifier.]

[14 Marks]

Q4

Draw the small-signal equivalent circuit of common-emitter amplifier and derive the expression for (a) current gain, (b) input resistance and (c) voltage gain.

[14 Marks]

Q5

Draw the hybrid-$\pi$ model for a transistor in the CE configuration and discuss about each parameter.

[14 Marks]

Q6

Explain the effect of an emitter bypass capacitor on low frequency response of a BJT-based basic amplifier.

[14 Marks]

Q7

Explain the operation of common-base configuration of BJT and draw the input-output characteristics. Also explain the early effect.

[14 Marks]

Q8a

Write short notes on Ideal voltage amplifier.

[7 Marks]

Q8b

Write short notes on Ideal transconductance amplifier.

[7 Marks]

2017 041404

B.Tech 4th Semester Exam., 2017

Time 3 hours

Full Marks 70

Instructions:

The marks are indicated in the right-hand margin.
There are NINE questions in this paper.
Attempt FIVE questions in all.
Question No. 1 is compulsory.

Section 1

Q1

Choose the correct answer of the following (any seven) :

a)

Early effect in BJT refers to

a)

avalanche breakdown

b)

thermal runaway

c)

base-width modulation

d)

Zener breakdown

[2 Marks]

b)

When a BJT is employed as an amplifier, it operates

a)

in cutoff

b)

in saturation

c)

in the active region

d)

well into saturation

[2 Marks]

c)

Thermal runaway is not possible in FET because, as the temperature of FET increases

a)

the mobility decreases

b)

the transconductance increases

c)

the drain current increases

d)

None of the above

[2 Marks]

d)

If the output of a logic gate is '1' when all its inputs are at logic '0', the gate is either

a)

a NAND or a NOR

b)

an AND or an EX-NOR

c)

an OR or an NAND

d)

an EX-OR or an EX-NOR

[2 Marks]

e)

In a tuned-amplifier, the bandwidth can be decreased by

a)

increasing the quality factor $Q$

b)

decreasing the quality factor $Q$

c)

increasing resonant frequency

d)

None of the above

[2 Marks]

f)

Feedback factor $\beta$ of an amplifier is

a)

always greater than 1

b)

less than or equal to 1

c)

always zero

d)

None of the above

[2 Marks]

g)

Class-C amplifier is mostly used

a)

in tuned amplifier

b)

in RC coupled amplifier

c)

as audio amplifier

d)

as high-voltage amplifier

[2 Marks]

h)

The overall efficiency of a cascaded system is generally

a)

equal to the efficiency of the most efficient stage

b)

equal to the efficiency of the least efficient stage

c)

greater than the efficiency of any individual stage

d)

less than the efficiency of any individual stage

[2 Marks]

i)

RC phase-shift oscillators are suitable for

a)

audio frequencies

b)

radio frequencies

c)

microwave frequencies

d)

None of the above

[2 Marks]

j)

Which of the following is true for an RC phase-shift oscillator?

a)

It does not require feedback

b)

It operates at audio frequencies

c)

It operates at radio frequencies

d)

It uses an inductor

[2 Marks]

[14 Marks]

Section 2

Q2a

Given the $V_{CE}$ vs $I_C$ curves of a typical transistor. How do we determine the value of $\alpha$ and $\beta$ ? Discuss.

[7 Marks]

Q2b

Derive an expression for small-signal voltage gain $A_V$ , input resistance $R_i$ and output resistance $R_o$ of an emitter-follower amplifier.

[7 Marks]

Q3a

Discuss why efficiency is a major issue in power amplifiers. Delineate the advantages of class-B and class-C amplifiers over their class-A counterpart. Draw respective frequency response curves.

[7 Marks]

Q3b

Draw the low-frequency equivalent circuit of a typical RC-coupled CE amplifier and derive an expression for the lower-cutoff frequency $f_L$ . Sketch the frequency response curve.

[7 Marks]

Q4

Discuss the method of determining the output voltage, current and gain of cascaded amplifier. Mention the main factors restricting the performance of such a practical system.

[14 Marks]

Q5

Explain the concept of negative feedback in amplifiers. What is the effect of negative feedback on the input and output impedances of a voltage series feedback amplifier?

[14 Marks]

Q6

Find the transfer function for an amplifier having low-frequency gain $A_L = \frac{s \cdot A_{mid}}{s + \omega_L}$ and high-frequency gain $A_H = \frac{A_{mid}}{1 + \frac{s}{\omega_H}}$ . Find its output when a step input of $1\text{ V}$ is applied to it.

[14 Marks]

Q7a

Explain the operation of a class-A power amplifier and calculate its efficiency.

[7 Marks]

Q7b

Explain the working of $RC$ phase-shift oscillator using transistor. Also write the expression for frequency of oscillation.

[7 Marks]

Q8

Discuss how impedance matching limits the performance of a Colpitts oscillator system. Given a standard Colpitts oscillator, can you propose a method of tuning it to higher or lower frequencies? Provide analytical arguments.

[14 Marks]

Q9

Write short notes on any two of the following:

a)

Tuned amplifiers

b)

Crystal oscillator

c)

Ideal voltage and transresistance amplifiers

[14 Marks]

2016 041404

B.Tech 4th Semester Exam., 2016

Time 3 hours

Full Marks 70

Instructions:

The marks are indicated in the right-hand margin.
There are NINE questions in this paper.
Attempt FIVE questions in all.
Question No. 1 is compulsory.

Section 1

Q1

Choose the correct answer (any seven) :

a)

Early effect in BJT refers to

a)

avalanche breakdown

b)

thermal runaway

c)

base-width modulation

d)

Zener breakdown

[2 Marks]

b)

For a BJT, the common-base current gain $\alpha = 0.98$ and the collector base junction reverse bias saturation current $I_{CO} = 0.6 \text{ \mu A}$ . This BJT is connected in the common-emitter mode and operated in the active region with a base drive current $I_B = 20 \text{ \mu A}$ . The collector current $I_C$ for this mode of operation is

a)

$0.98 \text{ mA}$

b)

$0.99 \text{ mA}$

c)

$1.0 \text{ mA}$

d)

$1.01 \text{ mA}$

[2 Marks]

c)

When a BJT is employed as an amplifier, it operates

a)

in cutoff

b)

in saturation

c)

in the active region

d)

well into saturation

[2 Marks]

d)

A transistor amplifier has a measured S/N ratio of 10 at its input and 5 at its output. Its noise figure is

a)

$10 \text{ dB}$

b)

$3 \text{ dB}$

c)

$2 \text{ dB}$

d)

$1 \text{ dB}$

[2 Marks]

e)

Refer to the circuit of figure, the values of upper and lower cutoff frequencies are respectively [Diagram: RC filter circuit diagram with two stages]

a)

$\frac{1}{2\pi \times 10^{-6}}$ and $\frac{1}{2\pi \times 10^{-3}}$

b)

$\frac{1}{2\pi \times 10^{-6}}$ and $0$

c)

$\frac{1}{2\pi \times 10^{-6}}$ and $10^6$

d)

$0$ and $\frac{1}{2\pi \times 10^{-6}}$

[2 Marks]

f)

When an amplifier is provided with current series feedback, its

a)

input impedance increases and output impedance decreases

b)

input and output impedances both decrease

c)

input impedance decreases and output impedance increases

d)

input and output impedances both increase

[2 Marks]

g)

A power amplifier delivers $50 \text{ W}$ output at $50\%$ efficiency. The maximum power dissipated by the transistor is

a)

$25 \text{ W}$

b)

$50 \text{ W}$

c)

$100 \text{ W}$

d)

$300 \text{ W}$

[2 Marks]

h)

What determines the lowest frequency in a tuned-amplifier?

a)

Turn-off time

b)

Turn-on time

c)

Time constant

d)

Modulation

[2 Marks]

i)

The voltage gain of an amplifier without feedback and with negative feedback respectively are 100 and 20. Determine the percentage of negative feedback ($\beta$).

a)

$0.04$

b)

$0.05$

c)

$0.4$

d)

$0.8$

[2 Marks]

j)

Which of the following is true for an RC phase-shift oscillator?

a)

It does not require feedback

b)

It operates at audio frequencies

c)

It operates at radio frequencies

d)

It uses an inductor

[2 Marks]

[14 Marks]

Section 2

Q2a

Given the $V_{CE}$ vs $I_C$ curves of a typical transistor. How do we determine the value of $\alpha$ and $\beta$ ? Discuss.

[7 Marks]

Q2b

Enlist all the values of typical h-parameters for a general purpose transistor. Write two differences between CE and CB configuration of a bipolar junction transistor.

[7 Marks]

Q3a

Given the $r_e$ model, derive an expression for the voltage gain $A_V$ for a common base configuration.

[7 Marks]

Q3b

How does one construct a hybrid $\pi$-model of a transistor from the physical parameters? Draw and explain.

[7 Marks]

Q4

Draw the low-frequency equivalent circuit of a typical RC-coupled CE amplifier and derive an expression for the lower-cutoff frequency $f_L$ . Sketch the frequency response curve.

[14 Marks]

Q5

Discuss the method of determining the output voltage, current and gain of cascaded amplifier. Mention the main factors restricting the performance of such a practical system.

[14 Marks]

Q6a

Derive an expression for the effect of negative feedback on input impedance of an amplifier.

[7 Marks]

Q6b

Derive the fundamental requirement of an oscillator system. Explain.

[7 Marks]

Q7

Discuss how impedance matching limits the performance of a Colpitts oscillator system. Given a standard Colpitts oscillator, can you propose a method of tuning it to higher or lower frequencies? Provide analytical arguments.

[14 Marks]

Q8

Discuss why efficiency is a major issue in power amplifiers. Delineate the advantages of class-B and class-C amplifiers over their class-A counterpart. Draw respective frequency response curves.

[14 Marks]

Q9

Write short notes on any two of the following:

a)

Tuned amplifiers

b)

Hybrid $\pi$-capacitances

c)

FET as an amplifier

[14 Marks]

2016 041504

B.Tech 5th Semester Exam., 2016

Time 3 hours

Full Marks 70

Instructions:

The marks are indicated in the right-hand margin.
There are NINE questions in this paper.
Attempt FIVE questions in all.
Question No. 1 is compulsory.

Section 1

Q1

Answer the following questions (any seven) :

a)

Current mirror circuit is used to

a)

establish constant current

b)

establish constant voltage

c)

increase output current

d)

decrease input current

[2 Marks]

b)

Output of a common-collector amplifier is taken from

a)

emitter

b)

base

c)

collector

d)

none of the above

[2 Marks]

c)

Early effect in BJT refers to

a)

avalanche breakdown

b)

thermal runaway

c)

base-width modulation

d)

Zener breakdown

[2 Marks]

d)

Slew rate of an ideal op-amp is

a)

infinite

b)

zero

c)

1

d)

0.5

[2 Marks]

e)

RC phase-shift oscillators are suitable for

a)

audio frequencies

b)

radio frequencies

c)

microwave frequencies

d)

None of the above

[2 Marks]

f)

Feedback factor $\beta$ of an amplifier is

a)

always greater than 1

b)

less than or equal to 1

c)

always zero

d)

None of the above

[2 Marks]

g)

Negative feedback in an amplifier decreases

a)

stability

b)

input impedance

c)

voltage gain

d)

bandwidth

[2 Marks]

h)

The value of modulation index $m_f$ in FM is

a)

$m_f = 0$

b)

$m_f > 1$

c)

$m_f < 1$

d)

Both (ii) and (iii)

[2 Marks]

i)

Which stage follows the mixer in a typical superheterodyne receiver?

a)

IF amplifier

b)

Audio amplifier

c)

Demodulator

d)

Local oscillator

[2 Marks]

j)

Monostable multivibrator is also called

a)

bistable multivibrator

b)

astable multivibrator

c)

free-running multivibrator

d)

one-shot multivibrator

[2 Marks]

[14 Marks]

Section 2

Q2a

Derive an expression for small-signal voltage gain $A_v$ , input resistance $R_i$ and output resistance $R_o$ of an emitter-follower amplifier.

[7 Marks]

Q2b

Discuss the necessity of cascading of amplifiers. Explain the meaning of half-power frequency.

[7 Marks]

Q3

Draw the small-signal model of FET and find expressions for $g_m$ and voltage gain.

[14 Marks]

Q4a

Explain how bias stabilization is achieved in a BJT by the use of self-bias circuit.

[7 Marks]

Q4b

Write short notes on Darlington-pair amplifier.

[7 Marks]

Q5

Derive an expression for close-loop gain of a non-inverting amplifier. Also design a practical differentiator circuit to differentiate a $1\text{ kHz}$ sinusoidal signal of amplitude $2\text{ V}$ .

[14 Marks]

Q6

What is 555 timer? Explain in brief. Write four practical applications of 555 timer. Also draw a circuit diagram of monostable multivibrator using 555 timer.

[14 Marks]

Q7

What is modulation? Why is it required? Give some differences between FM and AM.

[14 Marks]

Q8a

Derive an expression for the effect of negative feedback on input impedance of an amplifier.

[7 Marks]

Q8b

Derive the fundamental requirement of an oscillator system. Explain.

[7 Marks]

Q9

Write short notes on any two of the following:

a)

Current mirror

b)

Wideband amplifiers

c)

Tuned amplifiers

[14 Marks]

2015 041404

B.Tech 4th Semester Exam., 2015

Time 3 hours

Full Marks 70

Instructions:

The marks are indicated in the right-hand margin.
There are NINE questions in this paper.
Attempt FIVE questions in all.
Question No. 1 is compulsory.

Section 1

Q1

Choose the correct answer of the following (any seven) :

a)

A transistor in common-emitter configuration has

a)

a high input resistance and a low output resistance

b)

a low input resistance and a high output resistance

c)

a low input resistance and a low output resistance

d)

a high input resistance and a high output resistance

[2 Marks]

b)

At room temperature, the value of thermal voltage $V_T$ is

a)

26 V

b)

26 mV

c)

2.6 mV

d)

None of the above

[2 Marks]

c)

Early effect in BJT refers to

a)

avalanche breakdown

b)

thermal runaway

c)

base-width modulation

d)

Zener breakdown

[2 Marks]

d)

Output of a common-collector amplifier is taken from

a)

emitter

b)

base

c)

collector

d)

none of the above

[2 Marks]

e)

The coupling capacitors $C_C$ in an amplifier

a)

only affect the low-frequency response

b)

only affect the high-frequency response

c)

have no effect on frequency response

d)

Both (i) and (ii)

[2 Marks]

f)

Feedback factor $\beta$ of an amplifier is

a)

always greater than 1

b)

less than or equal to 1

c)

always zero

d)

None of the above

[2 Marks]

g)

Class-C amplifier is mostly used

a)

in tuned amplifier

b)

in RC coupled amplifier

c)

as audio amplifier

d)

as high-voltage amplifier

[2 Marks]

h)

A simple capacitor filter cannot be used for high-load current because

a)

the ripple increases with load

b)

it uses a large capacitor

c)

it is very costly

d)

None of the above

[2 Marks]

i)

The voltage gain of an amplifier without feedback and with negative feedback respectively are 100 and 20. Determine the percentage of negative feedback ($\beta$).

a)

0.04

b)

0.05

c)

0.4

d)

0.8

[2 Marks]

j)

RC phase-shift oscillators are suitable for

a)

audio frequencies

b)

radio frequencies

c)

microwave frequencies

d)

None of the above

[2 Marks]

[14 Marks]

Section 2

Q2a

Derive an expression for small-signal voltage gain $A_V$ , input resistance $R_i$ and output resistance $R_o$ of an emitter-follower amplifier.

[7 Marks]

Q2b

Describe output characteristics of a common-base amplifier.

[7 Marks]

Q3a

What is difference between ideal and practical constant-voltage source and constant-current source? Explain.

[7 Marks]

Q3b

Consider the circuit shown in the figure below: [Diagram: Circuit diagram of a BJT voltage-divider bias circuit with $+V_{CC} = 15\text{ V}$ , $R_1 = 100\text{ k}\Omega$ , $R_2 = 50\text{ k}\Omega$ , $R_C = 5\text{ k}\Omega$ , $R_E = 3\text{ k}\Omega$ . Transistor $\beta = 100$ .] Determine the coordinates of the operating point.

[7 Marks]

Q4a

Derive expressions for lower and upper cutoff frequencies of an $RC$-coupled amplifier.

[7 Marks]

Q4b

Write short notes on Darlington-pair amplifier.

[7 Marks]

Q5a

Explain how bias stabilization is achieved in a BJT by the use of self-bias circuit.

[7 Marks]

Q5b

Discuss the necessity of cascading of amplifiers. Explain the meaning of half-power frequency.

[7 Marks]

Q6a

Explain the concept of negative feedback in amplifiers. What is the effect of negative feedback on the input and output impedances of a voltage series feedback amplifier?

[7 Marks]

Q6b

Find the transfer function for an amplifier having low-frequency gain $A_L = \frac{s \cdot A_{mid}}{s + \omega_L}$ and high-frequency gain $A_H = \frac{A_{mid}}{1 + \frac{s}{\omega_H}}$ . Find its output when a step input of $1 \text{ V}$ is applied to it.

[7 Marks]

Q7a

Explain the operation of a class-A power amplifier and calculate its efficiency.

[7 Marks]

Q7b

Explain the working of $RC$ phase-shift oscillator using transistor. Also write the expression for frequency of oscillation.

[7 Marks]

Q8a

State and explain Barkhausen's criterion for sustained oscillations.

[7 Marks]

Q8b

With the help of suitable diagrams, explain the operation of Colpitts oscillator.

[7 Marks]

Q9

Write short notes on any two of the following:

a)

Early effect

b)

Crystal oscillator

c)

Wideband amplifiers

[14 Marks]

2015 041504

B.Tech 5th Semester Exam., 2015

Time 3 hours

Full Marks 70

Instructions:

The marks are indicated in the right-hand margin.
There are NINE questions in this paper.
Attempt FIVE questions in all.
Question No. 1 is compulsory.

Section 1

Q1

Choose the correct answer of the following (any seven) :

a)

Current mirror circuit is used to

a)

establish constant current

b)

establish constant voltage

c)

increase output current

d)

decrease input current

[2 Marks]

b)

When $V_{BE} = 0.7\text{ V}$ and $V_{CE} = 0.2\text{ V}$ , a silicon NPN transistor is operating in

a)

active region

b)

cutoff region

c)

saturation region

d)

reverse active region

[2 Marks]

c)

Slew rate of an ideal op-amp is

a)

infinite

b)

zero

c)

1

d)

0.5

[2 Marks]

d)

For low bias current op-amp, the input stage should use

a)

differential amplifier using BJT

b)

differential amplifier using FET

c)

common-emitter amplifier

d)

common-collector amplifier

[2 Marks]

e)

Monostable multivibrator is also called

a)

bistable multivibrator

b)

astable multivibrator

c)

free-running multivibrator

d)

one-shot multivibrator

[2 Marks]

f)

Integrator uses

a)

active-low pass filter

b)

active-high pass filter

c)

band-pass filter

d)

all-pass filter

[2 Marks]

g)

Negative feedback in an amplifier decreases

a)

stability

b)

input impedance

c)

voltage gain

d)

bandwidth

[2 Marks]

h)

The value of modulation index $m_f$ in FM is

a)

$m_f = 0$

b)

$m_f > 1$

c)

$m_f < 1$

d)

Both (ii) and (iii)

[2 Marks]

i)

The number of $10\text{ kHz}$ voice channels can be routed over a broadband $5\text{ MHz}$ microwave channel is

a)

$200$

b)

$500$

c)

$5000$

d)

$10000$

[2 Marks]

j)

Which stage follows the mixer in a typical superheterodyne receiver?

a)

IF amplifier

b)

Audio amplifier

c)

Demodulator

d)

Local oscillator

[2 Marks]

[14 Marks]

Section 2

Q2

Explain the terms:

a)

Thermal runaway

b)

Thermal resistance

c)

Input bias current

d)

CMRR

[14 Marks]

Q3

Draw the small-signal model of FET and find expressions for $g_m$ and voltage gain.

[14 Marks]

Q4a

Derive an expression for close-loop gain of a non-inverting amplifier.

[7 Marks]

Q4b

Design a practical differentiator circuit to differentiate a $1\text{ kHz}$ sinusoidal signal of amplitude $2\text{ V}$ .

[7 Marks]

Q5

Define oscillators. Derive an expression for the frequency of oscillation of an RC phase-shift oscillator. Explain the principle of operation of RC phase-shift oscillator using Op-Amp 741.

[14 Marks]

Q6

What is a 555 timer? Explain in brief. Write four practical applications of 555 timer. Also draw a circuit diagram of monostable multivibrator using 555 timer.

[14 Marks]

Q7

What is modulation? Why is it required? Give some differences between FM and AM.

[14 Marks]

Q8

With the help of block diagram, explain the operation of superheterodyne radio receiver. State the advantages and disadvantages of superheterodyne radio receiver.

[14 Marks]

Q9

Write short notes on any two of the following:

a)

Active filters

b)

Current mirror

c)

Early effect

[14 Marks]