FET Amplifier MCQ Quiz in తెలుగు - Objective Question with Answer for FET Amplifier - ముఫ్త్ [PDF] డౌన్‌లోడ్ కరెన్

JFET common drain amplifier is sometimes considered as a source follower and has voltage gain less than unity.

⇒ 

Putting the value of g_m, we get

⇒ 

Concept:

The lower-3dB frequency, fL in the given amplifier is given by:

Calculation:

R_i = 10k + 1MΩ = 1.01 MΩ

C_G = 1.576 nF

Concept:

Transconductance indicates the amount of control the gate has on the drain current.

Mathematically, the transconductance (gm) is defined as:

It is given the name transconductance because it gives the relationship between the input voltage and the output current.

Given: Δ V_GS = 1 V and Δ I_D = 10 mA

∴ 

= 0.01 mho

• In capacitively coupled amplifiers, the coupling and bypass capacitors affect the low-frequency cut-off. These capacitors form a high-pass filter with circuit resistances.
• Coupling and bypass capacitors are also called external capacitors.
• For high-frequency response, it is determined by the device’s internal capacitance and the Miller effect.
• Device internal capacitance is shunted and also called as Junction capacitors.

The correct answer is option 1
In the given figure input signal is applied at the source terminal and the output is drawn at the drain terminal. hence it is a common gate configuration
Concept:
FET : Field Effect Transistor

The transistor that uses the electric field or voltage to control flow of current in semiconductor. 

Generally it supports 3 modes of operation :

1. Common Gate :

In this input signal is applied at the source terminal and output is drawn at the drain terminal.

Gate is kept common or generally common terminal is grounded.

2. Common Drain :

In this input signal is applied at the gate terminal and output is drawn at the source terminal.

Drain is kept common or generally common terminal is grounded.

3. Common Source :

In this input signal is applied at the gate terminal and output is drawn at the drain terminal.

Common drain Amplifies with voltage divider bias and its small-signal equivalent circuit is as shown below:

Calculation:

Given:

R₁ = 1.5 MΩ, R₂ = 1 MΩ

So,

R_in = 600 kΩ 

Concept:

The Miller effect refers to the increase in equivalent capacitance that occurs when a capacitor is connected from the input to the output of an amplifier with a large, negative gain.

Miller capacitance is given by:

CMi = (1 + Av) Cgs

The output miller capacitance =  

Calculation:

Given that, Av = 20

Cgs = 2 pF

CMi = (1 + 20) × 2 = 42 pF

CONCEPT: 

Amplifier:

• An amplifier is a device by which the amplitude of the input ac signal (voltage/current/power) can be increased.
•  Transistors can act as amplifiers while they are functioning in the active region or when it is correctly biased.

Transistor as an amplifier (CE configuration):

• In this configuration, the emitter is common for both input and output.
• The input signal is connected in series with the voltage applied to the base-emitter junction.
•  For proper functioning of a transistor, the emitter-base junction must be forward-biased and the collector-base junction must be reverse-biased.
• The current gain is given as,

• Voltage gain is given as,

• Power gain is given as,

Where ΔIC = change in collector current, ΔIB = change in base current, Vout = output voltage, Vin = input voltage, RL = signal resistance in the Collector, RE = signal resistance in the Emitter

Calculation:

Power gain = 40 × 25 = 1000

Given that λ = 0, so the small-signal output resistance will be:

r0 = ∞

Therefore, we draw the small-signal equivalent circuit as:

From the circuit, we have

v0 = gm vgs RD      ---(1)

At input, vgs = -vi

Substituting the value of vgs in equation (1), we get:

v0 = -gm vi RD

So, the voltage gain will be:

= -2.6 m × 6k = -15.6

Voice frequency range: 300 to 3.5 kHz

Audio frequency range: 20 to 20 kHz

Video frequency range: 0 to 4.5 MHz