GATE Electrical – Analog Electronics

Practice Problems – Page 18

This section contains problems based on Oscillators and feedback principles.

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Problem 171

Question:

What is an oscillator?

Answer:

An oscillator is an electronic circuit that generates periodic signals without any external input signal.

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Problem 172

Question:

What are the two essential conditions for oscillation?

Answer:

• Loop gain must be equal to 1
• Total phase shift must be 360° or 0°

This is known as Barkhausen Criterion.

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Problem 173

Question:

Write the frequency formula of an RC phase shift oscillator.

Answer:

f = 1 / (2πRC√6)

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Problem 174

Question:

What is the frequency formula of Wien bridge oscillator?

Answer:

f = 1 / (2πRC)

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Problem 175

Question:

Which oscillator is commonly used for audio frequency generation?

Answer:

Wien Bridge Oscillator

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Problem 176

Question:

Why is positive feedback required in oscillators?

Answer:

To sustain continuous oscillations.

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Problem 177

Question:

If R = 10 kΩ and C = 0.01 μF, find frequency of Wien bridge oscillator.

Solution:

f = 1 / (2πRC)

RC = 10,000 × 0.01 × 10⁻⁶

f ≈ 1591 Hz

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Problem 178

Question:

Which oscillator uses three RC sections?

Answer:

RC Phase Shift Oscillator

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Problem 179

Question:

What type of feedback is used in oscillators?

Answer:

Positive feedback

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Problem 180

Question:

Which device is commonly used as amplifier in RC oscillator?

Answer:

Transistor or Operational Amplifier.

 

GATE Electrical – Analog Electronics

Practice Problems – Page 17

This section contains problems based on Active Filters using Operational Amplifiers.

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Problem 161

Question:

What is a low pass filter?

Answer:

A low pass filter allows low frequency signals to pass and attenuates high frequency signals.

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Problem 162

Question:

What is a high pass filter?

Answer:

A high pass filter allows high frequency signals to pass and blocks low frequency signals.

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Problem 163

Question:

Write the cut-off frequency formula of an RC filter.

Answer:

fc = 1 / (2πRC)

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Problem 164

Question:

If R = 10 kΩ and C = 0.01 μF, find the cut-off frequency.

Solution:

fc = 1 / (2πRC)

RC = 10,000 × 0.01 × 10⁻⁶

fc ≈ 1591 Hz

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Problem 165

Question:

What is a band pass filter?

Answer:

A band pass filter allows signals within a certain frequency range to pass.

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Problem 166

Question:

What is a band stop filter?

Answer:

It blocks a specific band of frequencies while allowing others to pass.

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Problem 167

Question:

Why are active filters preferred over passive filters?

Answer:

Because they provide amplification and better frequency control.

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Problem 168

Question:

Which component in a filter determines cut-off frequency?

Answer:

Resistor and Capacitor

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Problem 169

Question:

What is the slope of a first order filter?

Answer:

−20 dB/decade

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Problem 170

Question:

What is the slope of a second order filter?

Answer:

−40 dB/decade

 

GATE Electrical – Analog Electronics

Practice Problems – Page 16

This section contains problems based on Operational Amplifier Comparator and Schmitt Trigger circuits.

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Problem 151

Question:

What is a comparator circuit?

Answer:

A comparator compares two voltages and produces a high or low output depending on which input voltage is larger.

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Problem 152

Question:

What happens when Vin > Vref in a comparator?

Answer:

Output becomes positive saturation.

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Problem 153

Question:

What happens when Vin < Vref?

Answer:

Output becomes negative saturation.

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Problem 154

Question:

What is a Schmitt trigger?

Answer:

A Schmitt trigger is a comparator circuit with positive feedback that provides hysteresis.

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Problem 155

Question:

What is hysteresis in Schmitt trigger?

Answer:

It is the difference between upper and lower threshold voltages.

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Problem 156

Question:

Write the formula for hysteresis voltage.

Answer:

VH = VUT − VLT

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Problem 157

Question:

Why is Schmitt trigger used?

Answer:

To eliminate noise and produce clean digital signals.

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Problem 158

Question:

What is the output of a comparator if input is a sine wave?

Answer:

Square wave

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Problem 159

Question:

Which op-amp application converts analog signals to digital signals?

Answer:

Comparator

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Problem 160

Question:

What is the advantage of positive feedback in Schmitt trigger?

Answer:

It creates hysteresis which improves noise immunity.

 

GATE Electrical – Analog Electronics

Practice Problems – Page 15

This section contains problems based on Operational Amplifier Integrator and Differentiator circuits.

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Problem 141

Question:

What is an integrator circuit?

Answer:

An integrator is an op-amp circuit whose output voltage is proportional to the integral of the input voltage.

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Problem 142

Question:

Write the output voltage equation of an op-amp integrator.

Answer:

Vo = − (1/RC) ∫ Vin dt

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Problem 143

Question:

If R = 10 kΩ and C = 0.1 μF, find RC.

Solution:

RC = 10,000 × 0.1 × 10⁻⁶

RC = 0.001 sec

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Problem 144

Question:

What is the output waveform of an integrator if input is a square wave?

Answer:

Triangular waveform

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Problem 145

Question:

Define differentiator circuit.

Answer:

A differentiator produces an output proportional to the rate of change of input voltage.

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Problem 146

Question:

Write the output equation of an op-amp differentiator.

Answer:

Vo = − RC (dVin/dt)

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Problem 147

Question:

If input is a triangular waveform, what is the output of a differentiator?

Answer:

Square wave

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Problem 148

Question:

Why is practical differentiator used instead of ideal differentiator?

Answer:

To avoid excessive noise amplification and instability.

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Problem 149

Question:

Where are integrator circuits commonly used?

Answer:

Analog computers, signal processing and waveform generation.

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Problem 150

Question:

Where are differentiator circuits used?

Answer:

Edge detection and wave shaping circuits.

 

GATE Electrical – Analog Electronics

Practice Problems – Page 14

This section contains problems based on Operational Amplifier Applications including summing amplifier and difference amplifier circuits.

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Problem 131

Question:

What is a summing amplifier?

Answer:

A summing amplifier is an op-amp circuit that produces an output voltage proportional to the sum of multiple input voltages.

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Problem 132

Question:

Write the output equation of an inverting summing amplifier.

Answer:

Vo = −Rf (V1/R1 + V2/R2 + V3/R3)

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Problem 133

Question:

If Rf = 10 kΩ, R1 = R2 = 5 kΩ, V1 = 1 V, V2 = 2 V, find output voltage.

Solution:

Vo = −Rf (V1/R1 + V2/R2)

Vo = −10k (1/5k + 2/5k)

Vo = −6 V

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Problem 134

Question:

What is a difference amplifier?

Answer:

A difference amplifier amplifies the difference between two input signals.

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Problem 135

Question:

Write the output voltage equation of a difference amplifier.

Answer:

Vo = (Rf/R1) (V2 − V1)

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Problem 136

Question:

If Rf = R1 and V2 = 4 V, V1 = 1 V, calculate output voltage.

Solution:

Vo = (V2 − V1)

Vo = 4 − 1 = 3 V

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Problem 137

Question:

Which op-amp circuit performs addition of signals?

Answer:

Summing Amplifier

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Problem 138

Question:

Which op-amp circuit is used for signal subtraction?

Answer:

Difference Amplifier

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Problem 139

Question:

Where is summing amplifier commonly used?

Answer:

Audio mixers and signal processing circuits.

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Problem 140

Question:

Which op-amp application is used in digital to analog converters?

Answer:

Summing Amplifier

 

GATE Electrical – Analog Electronics

Practice Problems – Page 13

This section contains problems based on Non-Inverting Operational Amplifier circuits.

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Problem 121

Question:

Write the voltage gain formula of a non-inverting amplifier.

Answer:

Av = 1 + (Rf / R1)

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Problem 122

Question:

If Rf = 10 kΩ and R1 = 2 kΩ, calculate voltage gain.

Solution:

Av = 1 + (Rf / R1)

Av = 1 + (10000 / 2000)

Av = 6

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Problem 123

Question:

If input voltage = 0.5 V and gain = 6, find output voltage.

Solution:

Vo = Av × Vin

Vo = 6 × 0.5 = 3 V

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Problem 124

Question:

What is the phase shift of a non-inverting amplifier?

Answer:

0°

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Problem 125

Question:

What is the input impedance of a non-inverting amplifier?

Answer:

Very high (ideally infinite).

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Problem 126

Question:

If Rf = 20 kΩ and R1 = 10 kΩ, find gain.

Solution:

Av = 1 + (Rf / R1)

Av = 1 + (20k / 10k) = 3

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Problem 127

Question:

Which op-amp configuration is used as voltage follower?

Answer:

Non-Inverting Amplifier

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Problem 128

Question:

What is the gain of a voltage follower?

Answer:

Av = 1

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Problem 129

Question:

Why is voltage follower used?

Answer:

For impedance matching between circuits.

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Problem 130

Question:

Which amplifier configuration has highest input impedance?

Answer:

Non-Inverting Amplifier

 

GATE Electrical – Analog Electronics

Practice Problems – Page 12

This section contains practice problems based on Inverting Operational Amplifier circuits.

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Problem 111

Question:

An inverting amplifier has Rf = 10 kΩ and Rin = 2 kΩ. Find voltage gain.

Solution:

Av = −Rf / Rin

Av = −10000 / 2000

Av = −5

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Problem 112

Question:

If input voltage is 0.5 V and gain is −10, find output voltage.

Solution:

Vo = Av × Vin

Vo = −10 × 0.5 = −5 V

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Problem 113

Question:

What is the input impedance of an inverting amplifier?

Answer:

Input impedance ≈ Rin.

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Problem 114

Question:

If Rin = 5 kΩ and Rf = 25 kΩ, calculate voltage gain.

Solution:

Av = −Rf / Rin

Av = −25k / 5k = −5

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Problem 115

Question:

Why is the inverting input terminal called virtual ground?

Answer:

Because voltage at the inverting terminal is approximately zero due to negative feedback.

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Problem 116

Question:

What is phase shift of an inverting amplifier?

Answer:

180°

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Problem 117

Question:

If Rf = Rin, what is voltage gain?

Answer:

Av = −1

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Problem 118

Question:

Which op-amp circuit performs signal inversion?

Answer:

Inverting amplifier

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Problem 119

Question:

What happens if feedback resistor increases?

Answer:

Voltage gain increases.

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Problem 120

Question:

What is the main advantage of negative feedback in op-amp?

Answer:

It stabilizes gain and reduces distortion.