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Right answer is (a) Bias stabilization

For EXPLANATION I would say: Bias stabilization is a process which makes the operating (Q) point independent of change in temperature or any change in transistor parameters.

As Q-point exhibits its independent nature over the several variations, it PLAYS a major role in providing the stability to greater extent especially for self-bias, fixed-bias and collector to base bias circuits. Since the stability factor of circuit gets UNNATURAL due to several variations, bias stabilization has a provision of maintaining the Q-point condition irrespective of the changes in temperature or transistor parameters and in that way ensuring the confined LEVEL of bias stability to circuits.

Correct choice is (d) Impedance matching

Easy EXPLANATION: The high input impedance along with low output impedance makes the high frequency response of emitter follower amplifier ideal for impedance matching. Along with that, its key CHARACTERISTICS include a comparatively high CURRENT and POWER gain.

Right answer is (a) VCE < VCC / 2

To EXPLAIN I would say: Thermal runaway is a growing process which can ultimately harm the transistor due to unnecessary internal heating or increase in ambient temperature. It occurs due to increase in collector current ahead of the maximum specified value. Additionally, it also occurs due to excessive internal POWER dissipation above the maximum allowed value. Thermal runaway can be disallowed by maintaining the provision of thermal stability in addition to the treatment of heat sink.

According to thermal stability condition, VCE should be less than Vcc/2 results in the Q-point operation at a safe level. On the contrary, if the location of Q-point is at VCE > Vcc/2, then the transistor is more likely to get damaged due to thermal runaway.

Correct ANSWER is (a) Transistor with lower hfe

Easy explanation: In general, the short CIRCUIT CE gain of a transistor gets reduced to unity at f = fT. This IMPLIES that the transistor loses its capability of current amplification at f = fT.

As the gain-bandwidth PRODUCT always REMAINS constant, the transistor with lower hfe will definitely possesses higher bandwidth if the two transistors are made available with equal unity gain frequency.

The correct choice is (b) 4

The BEST explanation: There are four types of coupling mechanisms used. They are Resistance – CAPACITANCE coupling, thermal coupling, IMPEDANCE coupling and TRANSFORMER coupling. Resistance – capacitance coupling is the most vastly used mechanism.

Correct ANSWER is (B) 3.83 kΩ

Easy explanation: To calculate theimpedance in output port, given I1 = 20 mA, I2 = 30 mA and Z = 2.3 kΩ:

ZIN2 = (1 + α) × Z / α

α = I2 / I1 = 1.5

Zin2 = (1 + α) × Z / α = (1 + 1.5) × 2.3 / 1.5 = 3.83 kΩ

The correct ANSWER is (c) Low

To explain I would say: The structure of a high frequency response of emitter FOLLOWER circuit is ROUGHLY comparable to a normal amplifier. The low output impedance is ONE of the most prominent differentiating FEATURE of a high frequency response of emitter follower circuit.

The CORRECT option is (C) 50dB

The BEST I can explain: The total gain of a high frequency response of multistage amplifier is the sum of the multiple stages when the gain is calculated is DECIBELS. GIVEN, AV1 = 14dB, AV2 = 12dB and AV3 = 24dB

AV = AV1 + AV2 + AV3 = 14dB + 12dB + 24dB = 50dB.

The CORRECT answer is (d) 2.5

For explanation I would SAY: The total gain of a high frequency response of multistage AMPLIFIER is the ration of the output of second stage amplifier to the INPUT of first stage amplifier. Where, Voutput = 25V and VINPUT = 10V.

AV = Voutput / Vinput = 25V / 10V = 2.5.

The CORRECT choice is (c) Decibels

The explanation: The voltage gain is measured in terms of decibels. The TOTAL voltage gain is calculated as the product of individual stages or as a sum of all the stages if the gain calculated at each intermediate stage was measured in decibels as well.

Right choice is (b) Additional voltage source

Easiest explanation: Millers Theorem is APPLIED in an amplifier setting known as Millers amplifier. The amplifier can be utilized as an extra voltage source which changes over the REAL impedance into a VIRTUAL impedance. The virtual impedance can be considered as a PART associated in PARALLEL to the amplifier input.

The correct option is (a) Temperature compensation takes place by variation in forward voltage (VF)

To elaborate: In some of the negative FEEDBACK circuits, the AMPLIFICATION level of AC signals gets ablated suddenly. Since it becomes difficult for the circuits to tolerate the loss of signals, it is essential to reduce the drift in an OPERATING point by means of compensation and stabilization.

Compensation TECHNIQUES include diode compensation, bias compensation using thermistor, sensistor & so on. They play a major role in providing maximum bias in addition to the thermal stabilization to the circuits.

Right choice is (c) Decibels

To ELABORATE: The VOLTAGE gain is measured in TERMS of decibels. The total voltage gain is calculated as the PRODUCT of individual STAGES or as a sum of all the stages if the gain calculated at each intermediate stage was measured in decibels as well.

Right CHOICE is (d) High

To elaborate: The construction of a high frequency response of emitter follower circuit is APPROXIMATELY similar to a normal amplifier. One of the most important differentiating feature of a high frequency response of emitter follower circuit is its high input IMPEDANCE.

Right ANSWER is (c) ONE dependent voltage and one independent voltage

Easiest explanation: Miller compensation suggests that an impedance component is supplied by two random voltage sources that are CONNECTED in series through the common ground. Practically, one of them ACTS as an independent voltage source and the other acts a linearly dependent voltage.

Right answer is (B) Output VOLTAGE proportional to signal current

Easiest explanation: An amplifier which produces the output voltage in PROPORTION to the signal current where the PROPORTIONALITY factor is independent of source and load resistances, is known as ‘Transresistance amplifier’. For a practical transresistance amplifier, input resistance must be very less than source resistance and the output resistance must be very less than load resistance.

Generally, it is the RATIO of voltage to signal current. Conversely, the transconductance amplifier exhibits output current proportional to signal voltage. Voltage amplifier exhibits the output voltage proportional to input voltage & current amplifier exhibits the output current proportional to the signal current.

Correct choice is (a) Low

The EXPLANATION: As per the CONFIGURATION of CB amplifier, it is obvious that its input resistance is very low whereas its output resistance is extremely high.However, the lower value of input resistance allows the provision of source loading in common base amplifier circuit. Thus, there is no current amplification due to unity current GAIN. These all reasons ultimately CONTRIBUTE to high level of voltage gain.

Right option is (a) 60^o

Explanation: R-C phase shift oscillator CONSISTS of three identical basic R-C phase shifting kind of networks approved in the cascade configuration.

Thus, the total phase shift introduced by three stage R-C network is equal to 180^o, which implies that the output of network LEADS its input by 180^o. As a result, it infers that each phase-shift stage acquires the phase shift of about 60^o.

RC network is also renowned as ‘Ladder network’. The phase-shift of about 180^o is generated PARTICULARLY at one particular frequency, which is MEASURED to be the frequency of operation of the oscillator.

Right option is (a) True

Explanation: One of the main functions of the coupling device in a high frequency response of multistage amplifier is to block the DIRECT CURRENT from passing through to the input of next stage from the output of the first stage. Another function of the coupling device is to transfer the current from the output of first stage to the input of the SECOND stage.

Correct choice is (a) 1

To explain: The voltage GAIN of a high frequency response of emitter follower amplifier configuration is ROUGHLY equal to unity. AV is APPROXIMATELY equal to 1. This is due to the relatively high input IMPEDANCE and low output impedance.

The correct ANSWER is (b) 3.83 kΩ

Easy explanation: To calculate the impedance in output port, given I1 = 20 mA, I2 = 30 mA and Z = 2.3 kΩ:

Zin2 = (1 + α) × Z / α

α = I2 / I1 = 1.5

Zin2 = (1 + α) × Z / α = (1 + 1.5) × 2.3 / 1.5 = 3.83 kΩ.

Right option is (B) N – stage AMPLIFIER

Explanation: A single stage of amplifier provides an INSUFFICIENT current gain or voltage gain. Several amplifier STAGES CONNECTED in cascade are used instead. Hence it is known as an n – stage cascading amplifier or multistage amplifier.

Correct answer is (b) CE gain of transistor drops by 3 DB from its value at low frequency

The explanation: Cut-off frequency (fβ) is BASICALLY the frequency at which short circuit CE gain of transistor drops by 3dB from its value at low frequency.

Thus, the frequency range upto the cut-off frequency(fβ) is regarded as the bandwidth of circuit. ALSO, the current gain reduces to 70.7% of the low frequency current gain.

Likewise, the frequency at which short circuit CB gain of transistor drops by 3dB from its value next to low frequency is known as cut-off frequency (fα).

The RELATIONSHIP between these cut-off frequencies indicates that the 3dB frequency of CB configuration is (1 + hfe) times GREATER or higher as compared to that of CE configuration.

Correct answer is (C) Good high frequency operation

The explanation: The high frequency RESPONSE of multistage amplifiers circuit can be constructed with TWO configurations of a transistor that is CE (common – emitter) and CB (common base) . The CB (common base) configuration delivers a good high – frequency operation.

Right choice is (a) Zin2 = Z × K / K – 1

Explanation: According to Millers Theorem, to calculate the input impedance from the OUTPUT port we USE: Zin2 = Z × K / K – 1. Where, Z is the original circuit impedance and K is the ratio of the two nodal voltages V2 / V1.

Correct choice is (c) One dependent voltage and one independent voltage

Explanation: Miller THEOREM RECOMMENDS that an impedance segment is provided by two irregular voltage sources that are ASSOCIATED in arrangement through the common ground. For all intents and purposes, one of them GOES about as a free voltage SOURCE and the other acts a linearly dependent voltage.

The correct choice is (a) INCREASE voltage gain

To explain I would say: A circuit having a SINGLE transistor configuration does not PROVIDE suitable BANDWIDTH or gain. The purpose of a high frequency response of differential amplifier is to provide an increase in the voltage gain. The total gain of a high frequency response of differential amplifier is the product of the voltage gains of the DISCRETE stages.

Right ANSWER is (a) True

Easiest explanation: One of the main functions of the coupling DEVICE in a high frequency response of differential amplifier is to block the direct current from PASSING through to the input of next stage from the OUTPUT of the first stage. Another function of the coupling device is to transfer the current from the output of first stage to the input of the second stage.

Right choice is (d) Kirchhoff’s Current and Voltage Law

The best explanation: The MILLERS Theorem DEALS with the impedance supplied by two current / voltage sources connected in parallel. These two versions were derived by Kirchhoff’s two laws: Voltage and Current laws. The dual Millers Theorem is based mainly on the current laws while the other theorem focuses on the voltage law.

The CORRECT option is (a) 1

To explain I would SAY: The value of β in a high FREQUENCY response of EMITTER follower amplifier configuration can be calculated using β = Vf / VO. Given, Vf = 12V and VO = 12V:

β = Vf / VO = 12 / 12 = 1.

Right option is (c) Emitter

Easiest explanation: The HIGH frequency RESPONSE of multistage AMPLIFIER circuit can be constructed by connecting the emitters of two consecutive transistors. A resistor is placed between each stage to ACT as a COUPLING device.

Right option is (C) Zin1 = Z / 1 – K

Explanation: According to Millers COMPENSATION, to calculate the input IMPEDANCE from the input port we use: Zin1 = Z / 1 – K. Where, Z is the original circuit impedance and K is the ratio of the two nodal voltages V2 / V1.

Right choice is (d) 2

To explain I WOULD say: The total gain of a high frequency response of DIFFERENTIAL amplifier is the ratio of the output of second stage amplifier to the input of first stage amplifier. Where, Voutput = 100V and VINPUT = 50V.

AV = Voutput / Vinput = 100V / 50V = 2.

Correct option is (b) ADDITIONAL voltage source

The best I can explain: Miller compensation and pole splitting is APPLIED in an amplifier SETTING known as Millers amplifier. The amplifier can be used as an additional voltage source which converts the ACTUAL impedance into a virtual impedance. The virtual impedance can be thought of as a component connected in parallel to the amplifier INPUT.

The correct OPTION is (c) VO = Ad × Vd + AC × VC

Easiest explanation: The differential gain of a high frequency response of differential amplifier is defined as the gain obtained at the output signal with respect to the difference in the input signals applied. To calculate the output VOLTAGE of a high frequency response of differential amplifier we use Ad × Vd + AC × VC. Where, Ad is the differential gain and AC and VC represent the common mode gain.

Correct answer is (a) Common collector

For explanation: The high frequency response of emitter follower circuit configuration is also known as the common collector configuration as it PROVIDES a high input impedance and a LOW output impedance. The high frequency response of emitter follower circuit acts as a buffer stage, and in result is used in several circuits where there is a need to PREVENT the LOADING of a circuit.

The correct option is (c) Zin1 = Z / 1 – K

To explain I would say: According to Millers Theorem, to CALCULATE the input impedance from the input port we use: Zin1 = Z / 1 – K. Where, Z is the original CIRCUIT impedance and K is the ratio of the TWO NODAL voltages V2 / V1.

Right choice is (d) KIRCHHOFF’s CURRENT and VOLTAGE Law

The explanation: The Miller compensation and pole splitting deals with the IMPEDANCE supplied by two current / voltage sources connected in PARALLEL. These two versions were derived by Kirchhoff’s two laws: Voltage and Current laws. The dual Miller compensation and pole splitting is based mainly on the current laws while the other theorem focuses on the voltage law.