Electronic Devices and Circuits MCQ Quiz - Objective Question with Answer for Electronic Devices and Circuits - Download Free PDF

Concept

When designing an active filter for high-frequency applications, it is crucial to consider various factors to ensure the filter's performance and efficiency. The operational amplifier (op-amp) used in the active filter plays a significant role in determining the overall performance of the filter. One of the most critical specifications of the op-amp for high-frequency applications is the slew rate.

Solution

• The slew rate of an operational amplifier is defined as the maximum rate of change of the output voltage per unit time.
• It is typically measured in volts per microsecond (V/µs). In high-frequency applications, the signals change rapidly, and the op-amp must be able to keep up with these changes without distortion.
• A higher slew rate ensures that the op-amp can handle fast-changing signals effectively, which is essential for maintaining the integrity of the signal in high-frequency applications.

Additional Information

Option 1: The power supply voltage of the operational amplifier

While the power supply voltage is an important factor in the operation of an op-amp, it is not as crucial for high-frequency performance as the slew rate. The power supply voltage primarily affects the maximum output voltage swing and the overall power consumption of the op-amp.

Option 2: The open-loop gain of the operational amplifier

The open-loop gain of an op-amp is the amplification provided by the op-amp when no feedback is used. Although a high open-loop gain is generally desirable for precision applications, it is not the most critical factor for high-frequency performance. The open-loop gain tends to decrease at higher frequencies, and other factors like the slew rate become more significant.

Option 3: The value of the input resistor

The value of the input resistor can affect the input impedance and noise characteristics of the filter, but it does not directly impact the high-frequency performance of the op-amp. The slew rate is a more critical factor for ensuring that the op-amp can handle fast signal changes.

Option 4: The slew rate of the operational amplifier

The correct answer. The slew rate is a key specification for high-frequency applications because it determines how quickly the op-amp can respond to rapid changes in the input signal. A higher slew rate allows the op-amp to accurately follow fast signals without introducing distortion.

The correct option is 4

• The output of the oscillator will not depend upon input voltage because there is no input voltage for an oscillator
• An oscillator is an amplifier circuit with positive feedback in which a part of the output is feedback to the input via a feedback circuit
• It should satisfy Barkhausen criteria |Aβ| = 1, where A is the amplifier gain and β is the feedback gain 
   

Barkhausen Criterion 'or' Conditions for Oscillation:

The circuit will oscillate when two conditions, called Barkhausen’s criteria are met. These two conditions are:

• The loop gain must be unity or greater.
• The feedback signal feeding back at the input must be phase-shifted by 360° (which is the same as zero degrees). In most of the circuits, an inverting amplifier is used to produce 180° phase-shift and an additional 180° phase shift is provided by the feedback network.

Concept

An operational amplifier (op-amp) is a high-gain electronic voltage amplifier with a differential input and typically a single-ended output. In a non-inverting amplifier configuration, the input signal is applied to the non-inverting input of the op-amp. The voltage gain of the non-inverting amplifier is determined by the feedback network connected between the output and the inverting input.

In a non-inverting amplifier, the voltage gain (A_v) is given by:

\(A_v = 1 + \frac{R_f}{R_{in}}\)

where R_f is the feedback resistor and R_in is the input resistor.

Solution

The question asks about the factor that determines the voltage gain in a non-inverting amplifier using an operational amplifier. The correct answer is option 1.

The voltage gain of a non-inverting amplifier is given by the formula:

\(A_v = 1 + \frac{R_f}{R_{in}}\)

Therefore, the voltage gain is determined by the ratio of the feedback resistor (R_f) to the input resistor (R_in).

Hence, the correct answer is option 1.

Explanation:

LED Brightness and Current

Introduction:

Light Emitting Diodes (LEDs) are semiconductor devices that emit light when an electric current passes through them. The brightness of an LED is primarily determined by the current flowing through it. Understanding the relationship between current and brightness is crucial for designing circuits that utilize LEDs effectively.

Correct Option Analysis:

The correct option is:

Option 3: Current; greater

This option correctly indicates that the brightness of an LED depends on the current flowing through it. When the source voltage is much greater than the diode voltage, the brightness of the LED becomes approximately constant. This phenomenon can be explained through the electrical characteristics of LEDs.

The correct answer is ​Germanium.

Key Points

• Silicon and germanium are not suitable because those junctions produce heat and no appreciable IR or visible light.
  • Hence Germanium is NOT suitable for the fabrication of a light-emitting diode structure.

Additional Information

• The LED (light-emitting diode) is a PN junction device that emits light when a current passes through it in the forward direction, i.e. when LED is forward biased, it emits light.
• In an LED, this energy lies in the visible region of electromagnetic radiation, and the photon released is perceived as light.

• The compound semiconductor Gallium Arsenide – Phosphide is used for making LEDs of different colours.
• Gallium Arsenide is used for making infrared LED.
• Gallium phosphide, Indium gallium nitride, and Gallium arsenide are used for the fabrication of a light-emitting diode.
• LEDs are generally fabricated with Direct Band Gap (DBG) semiconductors like GaAs, GaAsP, and GaP.

TRIAC allows the current in both directions and thus it is bidirectional.

SCR, GTO (Gate Turnoff Thyristor) and BJT allow the current in only one direction.

TRIAC:

• A TRIAC is equivalent to two SCRs joined together in parallel; It has two main terminal and one gate

• In the TRIACs, there will be single gate control conduction in both the directions
• It is a bidirectional device and in both the directions it will conduct
• It is available in high voltage ratings
• TRIAC is a  5-layer device

The UJT is a three-terminal, semiconductor device which exhibits negative resistance and switching characteristics for use as a relaxation oscillator in phase control applications.

​

• We observe that the emitter terminal is p-type.
• The structure of a UJT is quite similar to that of an N-channel JFET.
• In a unijunction transistor, the emitter is heavily doped while the N-region is lightly doped, so the resistance between the base terminals is relatively high, typically 4 to 10 kilo Ohm when the emitter is open.

The basic differences between the UJT and the BJT are as follows:

Op-amp:

This IC is Dual Inline Package and it is represented as 741 IC.

The pin diagram is shown below:

Pin 2 and 3 are input terminals.

Inverting terminal:

If we apply the input at this terminal the output will have a 180° phase shift.

Non-inverting terminal:

If we apply the input at this terminal the output will not have any phase shift at the output.

Kirchhoff’s Voltage law:

This law states that the algebraic sum of all voltages in a closed loop will be zero.

\(\sum {V_{loop}} = 0\)

Virtual ground:

Both the terminal voltages will be equal for an op-amp.

Here we are discussing the voltage and in a loop, it will be zero.

V₁ = V₂

V₁ – V₂ = 0

Crystal Oscillator:

A crystal oscillator is the most stable frequency oscillator.

Advantages:

• The crystal oscillator is possible to obtain a very high precise and stable frequency of oscillators
• It has very-low-frequency drift due to change in temperature and other parameters
• The Q is very high
• It has automatic amplitude control

Disadvantages:

• These are suitable for high-frequency application
• Crystals of low fundamental frequencies are not easily available

• Hartley and Colpitts's oscillators are LC oscillators.
• LC oscillators are unstable oscillators.
• Phase shift oscillator is suitable for oscillations in AF range up to 1 kHz
• Crystals like quartz have high-quality factors, Q (range: 104 - 106). The high-quality factor will result in high-frequency stability.

A transistor can be operated in one of the three modes: 

1) Active Region

2) Saturation Region

3) Cut-off Region

The biasing for different mode of operation is as shown in the table:

∴ For a transistor operating in the saturation region, both the junctions need to be forward bias.

Operational Amplifier (OP-AMP)

An operational amplifier (op-amp) is an integrated circuit (IC) that amplifies the difference in voltage between two inputs. 

It has two terminals i.e. inverting and non-inverting terminals.

The output of the OP-AMP is:

\(V_{OUT}=A_V({V_{NI}-V_I})\)

Properties of OP-AMP

• High input impedance
• Low output impedance
• High CMRR
• High gain
• High slew rate
• Low input offset voltage
• High bandwidth

Clamper circuit:

• A clamper is an electronic circuit that changes the DC level of a signal to the desired level without changing the shape of the applied signal.
• The Clamper circuit moves the whole signal up or down to set either the positive feedback or negative feedback of the signal at the desired level.
• It consists of capacitors and diodes to shift the voltage level.

In a Voltage doubler circuit, the output voltage is double the input voltage with the circuit diagram as shown:

Important Points

• Clipper circuits are used to remove the part of a signal above or below some defined reference level.
• One example of a clipper circuit is a half-wave rectifier that clips off the negative-going waveform.

Explanation:

An oscillator is: An amplifier with positive feedback

• An oscillator is a circuit that generates a continuous, periodic waveform without the need for an external input signal.
• It achieves this by using positive feedback, where a portion of the output is fed back to the input with a phase shift of 360 degrees (positive feedback).
• This continuous feedback loop sustains and regenerates the oscillations, producing a waveform such as a sine wave, square wave, or triangle wave.
• Oscillators are commonly used in electronic circuits for generating signals in applications such as radio frequency (RF) communication, audio synthesis, and clock generation.