Depletion Type MOSFET MCQ Quiz - Objective Question with Answer for Depletion Type MOSFET - Download Free PDF

Explanation:

Correct Option Analysis:

The correct option is:

Option 4: 1.8 mA

We are given an N-channel E-MOSFET with the following parameters:

• ID(ON) = 5 mA at VGS = 10 V
• VGS(th) = 5 V

We need to calculate its drain current (ID) for VGS = 8 V.

The drain current for an E-MOSFET in the saturation region can be calculated using the following equation:

ID = ID(ON) * ((VGS - VGS(th)) / (VGS(ON) - VGS(th)))^2

Given:

• ID(ON) = 5 mA
• VGS(ON) = 10 V
• VGS(th) = 5 V
• VGS = 8 V

Substitute the given values into the equation:

ID = 5 mA * ((8 V - 5 V) / (10 V - 5 V))^2

Calculate the terms inside the parentheses first:

(8 V - 5 V) = 3 V

(10 V - 5 V) = 5 V

Now, substitute these values back into the equation:

ID = 5 mA * (3 V / 5 V)^2

Simplify the fraction:

ID = 5 mA * (0.6)^2

Calculate the square of 0.6:

(0.6)^2 = 0.36

Now, multiply this by 5 mA:

ID = 5 mA * 0.36

ID = 1.8 mA

Therefore, the drain current for VGS = 8 V is 1.8 mA, making option 4 the correct answer.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 1: 3.2 mA

Using the same method, if we substitute the values into the equation:

ID = 5 mA * ((8 V - 5 V) / (10 V - 5 V))^2

ID = 5 mA * (3 V / 5 V)^2

ID = 5 mA * (0.6)^2

ID = 5 mA * 0.36

ID = 1.8 mA

Clearly, the calculation shows that the correct drain current is 1.8 mA and not 3.2 mA, so option 1 is incorrect.

Option 2: 4 mA

Again, using the same method:

ID = 5 mA * ((8 V - 5 V) / (10 V - 5 V))^2

ID = 5 mA * (3 V / 5 V)^2

ID = 5 mA * (0.6)^2

ID = 5 mA * 0.36

ID = 1.8 mA

The calculation confirms that 1.8 mA is the correct value, so option 2 is incorrect as well.

Option 3: 2.6 mA

Using the same method:

ID = 5 mA * ((8 V - 5 V) / (10 V - 5 V))^2

ID = 5 mA * (3 V / 5 V)^2

ID = 5 mA * (0.6)^2

ID = 5 mA * 0.36

ID = 1.8 mA

The calculation clearly shows that 2.6 mA is not the correct drain current, thus option 3 is also incorrect.

Conclusion:

Understanding the operation of an N-channel E-MOSFET and the application of the drain current equation are crucial for correctly identifying the drain current for a given gate-source voltage. By carefully substituting the given values and performing the calculations, we have determined that the correct drain current for VGS = 8 V is 1.8 mA. This confirms that option 4 is the correct answer.

Concept

It is a common gate amplifier where output is taken from the drain terminal and input is given to the source.

The input terminal is also connected to GND, hence V_in = 0

Calculation

The equivalent AC model is:

The gate to source voltage (V_gs) is given by:

\(V_{gs}={R_o\over R_o+R_o}\times V_o={V_o\over 2}\)...........(i)

Applying KCL at V_o, we get:

\({V_o-V_d\over R_o}={V_o\over 2R_o}+gV_{gs}\)...........(ii)

Putting the value of equation (i) in (ii), we get:

\({V_o-V_d\over R_o}={V_o\over 2R_o}+{gV_{o}\over 2}\)

\({V_o\over V_d}=\rm \left(\frac{g_mR_0}{2}+\frac{3}{2}\right)^{-1}\)

MOSFET:

MOSFET stands for Metal Oxide Semiconductor Field Effect Transistor.

It is a majority carrier device and also called as Voltage controlled current device (VGS control the current ID)

Operation of the MOSFET:

The drain characteristics or the plot between ID and VDS is shown below

The drain characteristics are shown in below tabular form.

VGS = Gate-Source voltage

ID = Drain current

VDS = Drain-Source voltage

Calculation:

Let us assume that MOSFET is biased in the saturation region.

ID = k (VGS – VT)2

Given, I_D = 10 mA

VGS = 8 V

VT = 2 V

\(k = \frac{I_D}{(V_{GS}-V_T)^2} = \frac{10\times 10^{-3}}{(8-2)^2} =0.278\times 10^{-3}\)

∴ The device constant k is 0.278 mA/V2.

Important Points

• MOSFET is a voltage-driven/controlled device.
• The current through the two terminals is controlled by a voltage at the third terminal (gate)
• It is a unipolar device (current conduction is only due to one type of majority carrier either electron or hole)
• It has a high input impedance.

MOSFET (Metal Oxide Semiconductor Field Effect Transistor)

MOSFET transistor is a semiconductor device which is used for amplifying and switching electronic signals in electronic devices.

MOSFET is of two types:

1. Enhancement MOSFET:

MOSFET:

MOSFET stands for Metal Oxide Semiconductor Field Effect Transistor.

It is a majority carrier device and also called as Voltage controlled current device (VGS control the current ID)

Operation of the MOSFET:

The drain characteristics or the plot between ID and VDS is shown below

The drain characteristics are shown in below tabular form.

VGS = Gate-Source voltage

ID = Drain current

VDS = Drain-Source voltage

Concept:

The drain current in saturation for a D-MOSFET is given by:

\({{I}_{D}}={{I}_{DSS}}{{\left( 1-\frac{{{V}_{GS}}}{{{V}_{p}}} \right)}^{2}}\)

IDSS = Saturation Drain Current

Vp = Pinch Off Voltage

Calculation:

Given: I_DSS = 10 mA,

V_P = VGS(off) = -4 V, and

VGS = + 2 V

Putting on the respective values, we get the drain current as:

\({{I}_{D}}=10m{{\left( 1+\frac{2}{{4}} \right)}^{2}}\)

\({{I}_{D}}=10\times \frac{9}{4} ~mA\)

I_D = 22.5 mA

Calculation:

Let us assume that MOSFET is biased in the saturation region.

ID = k (VGS – VT)2

Given, I_D = 10 mA

VGS = 8 V

VT = 2 V

\(k = \frac{I_D}{(V_{GS}-V_T)^2} = \frac{10\times 10^{-3}}{(8-2)^2} =0.278\times 10^{-3}\)

∴ The device constant k is 0.278 mA/V2.

Concept

It is a common gate amplifier where output is taken from the drain terminal and input is given to the source.

The input terminal is also connected to GND, hence V_in = 0

Calculation

The equivalent AC model is:

The gate to source voltage (V_gs) is given by:

\(V_{gs}={R_o\over R_o+R_o}\times V_o={V_o\over 2}\)...........(i)

Applying KCL at V_o, we get:

\({V_o-V_d\over R_o}={V_o\over 2R_o}+gV_{gs}\)...........(ii)

Putting the value of equation (i) in (ii), we get:

\({V_o-V_d\over R_o}={V_o\over 2R_o}+{gV_{o}\over 2}\)

\({V_o\over V_d}=\rm \left(\frac{g_mR_0}{2}+\frac{3}{2}\right)^{-1}\)

Important Points

• MOSFET is a voltage-driven/controlled device.
• The current through the two terminals is controlled by a voltage at the third terminal (gate)
• It is a unipolar device (current conduction is only due to one type of majority carrier either electron or hole)
• It has a high input impedance.

MOSFET (Metal Oxide Semiconductor Field Effect Transistor)

MOSFET transistor is a semiconductor device which is used for amplifying and switching electronic signals in electronic devices.

MOSFET is of two types:

1. Enhancement MOSFET:

MOSFET:

MOSFET stands for Metal Oxide Semiconductor Field Effect Transistor.

It is a majority carrier device and also called as Voltage controlled current device (VGS control the current ID)

Operation of the MOSFET:

The drain characteristics or the plot between ID and VDS is shown below

The drain characteristics are shown in below tabular form.

VGS = Gate-Source voltage

ID = Drain current

VDS = Drain-Source voltage

Important Points

• MOSFET is a voltage-driven/controlled device.
• The current through the two terminals is controlled by a voltage at the third terminal (gate)
• It is a unipolar device (current conduction is only due to one type of majority carrier either electron or hole)
• It has a high input impedance.

Concept:

The drain current in saturation for a D-MOSFET is given by:

\({{I}_{D}}={{I}_{DSS}}{{\left( 1-\frac{{{V}_{GS}}}{{{V}_{p}}} \right)}^{2}}\)

IDSS = Saturation Drain Current

Vp = Pinch Off Voltage

Calculation:

Given: I_DSS = 10 mA,

V_P = VGS(off) = -4 V, and

VGS = + 2 V

Putting on the respective values, we get the drain current as:

\({{I}_{D}}=10m{{\left( 1+\frac{2}{{4}} \right)}^{2}}\)

\({{I}_{D}}=10\times \frac{9}{4} ~mA\)

I_D = 22.5 mA