Top 100 Analog Electronics Interview Questions And Answers

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Que. 26 Difference between Butterworth and Chebyshev filter.

Answer:

Butterworth Filter	Chebyshev Filter
1. This has a maximally flat passband. i.e Gain remains constant inside the passband.	1. Highest roll-off rate outside the passband. i.e gain decreased at a higher rate.
2. Width of the transition band is more.	2. Width if transition band is small.
3. Butterworth filter poles lie on a circle.	3. Poles lie in an ellipse.
4. No. of poles are more, more components are required	4. No. of poles is less so fewer components are required.

Que.31 What does an electronic circuit mean? Types of electronic circuits.

Answer: A circuit having at least one electronic device such as an amplifier, oscillators, etc. is known as an electronic circuit.

Types of the electronic circuit:

• Analog circuit:  a circuit that can process analog signals or a ckt whose o/p and i/p are analog signals. Example- amplifier, rectifier, etc.
• Digital circuit: a circuit that processes digital s/g or signals which are in form of 0 & 1. Example-  adder, shift register, etc.
• Mixed-signal circuit: which uses both analog and digital circuits. Example-  analog to digital converter and digital to analog converter.

Que.32 What is a power supply? What is a regulated power supply? What are the components of the power supply?

Answer:

• An electronic system that converts AC power into DC power is known as a power supply system.

• A regulated power supply means output remains constant even if input changes.

Components of power supply are:

• Rectifier: which converts pure AC signal to pulsating DC signal (AC+DC). 
• Filters: which coverts pulsating DC signal to fluctuating DC signal.
• Voltage regulator: which finally converts fluctuating DC to stable or regulated DC.

Que.33 What is the regulation factor in analog circuits? What should be its ideal value? Types of regulation.

Answer: It is the measure of change in DC output voltage due to a change in load current.

%Regulation=\frac{V_{DCNL}- V_{DCFL}}{V_{DCFL}}

• Ideally regulation factor should be 0 i.e. DC output voltage should not change with change in load current.

Types of regulation: 

1. Line regulation: refers to keeping output voltage constant irrespective of change in AC supply voltage. i.e. in this case load current is kept constant.
2. Load regulation: it is the process of keeping output voltage constant irrespective of variation in load current. i.e. input voltage is kept constant.

Que.34 What is peak inverse voltage? Why high PIV is undesired?

Answer:

• It is the maximum voltage that appears across a diode when it is a reverse bias state or non-conduction state in a rectifier.

• For safe operation of the diode, PIV should be less than the breakdown voltage.

• Higher PIV is undesired because it will require a higher breakdown voltage, which will be costlier.

Que.35 Define filters in power supply. Types of filters used in power supply.

Answer:

• Filters are frequency selective network, which passes a desired range of frequencies but eliminates unwanted frequencies. In the power supply, it is used to remove the unwanted AC component, which is present in the output of the rectifier.

• Filters in power supply consist of large capacitors( micro to milli farad) and large inductors( of a few henries).

Filters used in power supplies are:

1. Capacitive filters
2. Inductive filter
3. LC or L section filter
4. Inductor filter
5. C-L-C or pie section filter

Que.36 What is a Voltage regulator? and what types of voltage regulators?

Answer:

• Voltage regulator: A circuit that maintains the DC output voltage of a power supply irrespective of fluctuations in AC supply and variation in load current.

• Types of voltage regulators:

1. Linear regulator: IC regulators – these are IC regulators in which transistor operates in the linear or active region.

It includes: Fixed voltage IC regulator- 78XX, 79XX , Adjustable voltage regulator- IC-723

Regulator using direct components – 1. Shunt type 2. Series type 

2. Nonlinear regulator or switching regulator: in this type, the transistor is operated in a cut-off or saturation region. 

Que.37 Working of Zener diode-based regulator.

Answer:

• Zener diode is used which is connected in parallel with a load resistor, hence also known as a shunt regulator.

Here,

R_s: resistance is used to prevent the heavy flow of current flow through the Zener diode.

V_s: the unregulated supply voltage.

I_z: Zener current

I_L: load current

I_S=\frac{(V_S - V_Z)}{R_S}…… KVL

I_S=I_Z+I_L …… KCL

• For proper operation, the current through Rs should be at least equal to the sum of knee current and specified load current.

i.e. I_S\geq I_{Zmin} + I_L

• and for the safe operation of zener diode,

I_S\leq I_{Zmax} + I_L

Note: In a Zener diode shunt regulator, the maximum value of Rs is obtained by considering the minimum value of supply voltage and minimum Zener current, and the minimum value of Rs is calculated by considering maximum supply voltage and maximum Zener current.

Que.38 Disadvantage of Zener diode regulator.

Answer:

• The output voltage can vary with temperature as the Zener diode is temp. Dependent.
• A large change in load current cause a much change in Zener current and thereby output voltage may have considerable change.

Que.39 What are the Wave shaping circuits. Application of waveshaping circuits.

Answer:

• Circuits are responsible for changing the shape of the alternating waveforms.

• These are basically of two types:

1. Linear wave shaping circuits: it is performed by linear elements such as R, L, and C.

Example- low pass RC and High pass RC circuits.

2. Non-linear circuits: it is performed using non-linear elements such as diodes.

Example- clippers: it is a non-linear waveshaping ckt. which can remove or cut the unwanted portion of a signal.

Application of waveshaping circuits:

• Clipper can be used to limit the amplitude of a signal, hence also called amplitude limiter.
• It can be used to eliminate the noise from pulse waveforms in digital communications.

Que.40 What is clamper and its application?

Answer:

• Clamper is also called a DC restorer or DC reinserted as it is responsible for adding DC voltage to an AC waveform.

• It does not change the shape of the signal instead it shifts the signal in either an upward or downward direction. 

• DC restorer because it can restore the DC voltage level of a signal which has lost its DC value in electronic processing.

Que.41 What is the significance of form factor in rectifiers?

Answer:

• The form factor is given by the formula,

Form\; Factor=\frac{I_{rms}}{I_{DC}}

• It is the ratio of the RMS value of alternating current and DC current.

• It basically signifies the greater smoothness in the waveform or less ripple factor.

Que.42 Why BJT is called a current controlled device?

Answer:

• In a BJT, base current I_b is nearly the same as recombination current, which is provided by biasing supply. 

• If the supply of compensating electrons is increased then the base region becomes negative due to a surplus of electrons and it attracts a greater no. of holes from the emitter, therefore the flow of holes from emitter to collector increases, if the supply of compensating electrons is reduced, then base become positive due to electron deficiency and it attracts large no of the hole from the emitter, therefore, the flow of electron from emitter to collector decreases.

• Thus, it implies the supply of compensating electron or base current Ib controls the flow of current from emitter to collector, hence BJT is called a current controlled device.

Que.43 Why emitter is heavily doped and the collector moderately doped in BJT?

Answer:

• In a BJT, an emitter is a region that emits the majority of carriers. It is heavily doped so that it can emit large no. of carriers.

• While collector is moderately doped because if it is lightly doped, its conductivity becomes low and if it is heavily doped, the breakdown voltage of the collector junction becomes smaller, therefore to achieve better conductivity and higher breakdown voltage, the collector is moderately doped.

Que.44 What is the early effect or base width modulation in BJT? What are its consequences?

Answer:

• It refers to the decrease in effective base width due to a decrease in reverse bias voltage across the collector junction.

• The early effect has three consequences:

1. Large signal current (alpha) increase- as Vcb increases effective base width decrease which implies a decrease in no. of recombination or increase in collector current, hence alpha increases.
2. For small increases in alpha, beta(small-signal current gain) increases by a large amount.
3. Emitter current Ie increases due to an increase in hole concentration gradient.

Que.45 What is punch through effect?

Answer:

• At a large value of reverse bias at collector junction, depletion region fully occupies base and effective base width becomes zero. This is called the punch-through effect.

• When the punch-through effect occurs, the collector and emitter get electrically short-circuited. As the collector is at a strong negative potential, a large no. of holes travel from emitter to collector i.e. heavy current flow which can damage BJT. 

Que.46 What factors are responsible for instability in collector current? What are its consequences?

Answer: Factors responsible for instability in collector current,

\boxed{I_C=\beta_F I_B + I_{CEO} \approx \beta_F I_B}

• Variation in Ico: Ico is the reverse saturation current of the collector junction and it is temperature-dependent. By 1 degree rise in temp. Ico is increased by 7%.  A change in Ico will cause a change in Ic.

• Variation in V_BE: V_BE is the forward voltage of the emitter junction, it is also temp. Dependent. By 1 degree rise in temp, it increased by 2.5mV. A change in V_BE will cause a change in I_B, hence I_C change.

• Variation in \beta: \beta is common-emitter current gain, it can vary due to transistor replacement or due to changes in temp.

This instability in Ic has two undesired effects:

• The operating point does not remain at the center of the load line, which can cause distortion in the output signal.
• A thermal runaway can occur which damages a BJT.

Que.47 What is biasing? What are the different biasing circuits used for operating BJT as amplifiers?

Answer:

• Biasing refers to providing DC current & DC voltage to an electronic device so that the device works as desired. 

• A BJT is biased to operate in an active region so that it can be used as an amplifier.

BJT biasing circuits to operate it as an amplifier are- 

1. Fixed bias ckt
2. Collector to base bias ckt. 
3. Self-bias ckt.

Que.48 What is a thermal runaway condition? How it can be avoided?

Answer:

• It is the process of self-destruction or self-damage of BJT, because of overheating at the collector junction due to an increase in collector current with an increase in Ico. If temperature increases reverse saturation current which causes in collector current hence power dissipation increases at collector junction which increases heat produced at collector junction implies an increase in temperature. This is a thermal runaway. It occurs mostly in power amplifiers.

Condition to prevent thermal runaway:

• Thermal runaway can be avoided if the rate at which heat is produced at the collector junction is less than the rate at which heat is transferred or dissipated to the surroundings.

• If V_CE <= V_cc/2, then thermal runaway does not occur irrespective of the value of theta, Such a circuit is called a thermally stable circuit. 

• If V_CE > V_cc/2, then thermal runaway can be avoided.

Que.49 How BJT can act as an amplifier?

Answer:

• The amplifier is basically an electronic ckt. which increases the strength (power level) of a weak electronic signal without a change in its shape.

• BJT is able to act as an amplifier because of small change in voltage at the input terminal can cause a large change in voltage at the output terminal

Que.50 What are the advantages of BJT over MOSFET.

Answer:

Advantage of BJT over MOSFET: 

• BJT has higher transconductance therefore gain-bandwidth product is greater in BJT than in JFET & MOSFET, hence BJT is preferred in the high-frequency amplifiers.
• BJT has higher fidelity & better gain in the linear areas as evaluated with the MOSFETs.
• As compared to MOSFETs, BJTs are very faster because of low capacitances on the control pin.
• BJTs are a very good choice for voltage and low-power applications.

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