Download Question Paper (Link Below)

Question Paper Solution

1. (a) Explain the concept of energy bands in semiconductors.

(b) How do Energy band influence the electrical conductivity of a semiconductor material?

(c) Provide a detailed comparison between the valence band and the conduction band.

2. (a) Discuss the operation and characteristics of a semiconductor diode.

(b) Explain the forward and reverse bias conditions, and provide a mathematical relation for the diode current in each case.

(c) Illustrate your explanation with characteristic curves.

3. (a) Explain the basic operation of an NPN Transistor. What are the roles of the emitter, base and collector regions ? How does a small base current control a larger collector current?

In an NPN transistor, a small base current $(I_B)$ controls a much larger collector current $(I_C)$ due to the physical structure and design of the transistor, as well as the relationship between its three regions: Emitter, Base, and Collector.

• Small Base Current $(I_B)$ allows a larger number of electrons to flow from the emitter to the base.
• Minimal Recombination occurs in the thin base, meaning that only a small base current is needed to balance the recombined electrons.
• The Reverse-Biased Collector-Base Junction attracts most of the electrons from the emitter, creating a large collector current $(I_C)$.
• The transistor's current gain (β) amplifies the small base current into a larger collector current, allowing the transistor to control or amplify signals.

(b) Given a common emitter NPN transistor with a collector current ($I_C$) of 5 $\mu$A and a base current ($I_B$) of 50 $\mu$A, calculate the transistor's current gain ($\beta$).

The current gain ($\beta$) of a transistor is calculated using the formula:

$\beta = \frac{I_C}{I_B}$

where:

• $I_C = 5 \, \mu \text{A}$
• $I_B = 50 \, \mu \text{A}$

Substitute the values:

$\beta = \frac{5 \, \mu \text{A}}{50 \, \mu \text{A}} = 0.1$

The transistor's current gain ($\beta$) is 0.1.

4. Describe the working of a N-Channel Depletion MOSFET with a neat diagram. Also explain the different characteristics based on Gate-Source Voltage, Drain Voltage, Drain current, etc. with suitable diagrams.

6. (a) Discuss the concept of negative feedback in op-amp circuits. Explain how negative feedback improves the performance of amplifier and reduce distortion.

(b) Explain the operation of a non-inverting amplifier configuration using an op-amp. Provide the voltage gain equation for a non inverting amplifier and discuss its advantages over the inverting amplifier configuration.

7. Perform the following:

a. 259 + 641 using BCD

249 in Decimal

• 2 in BCD: 0010
• 5 in BCD: 0101
• 9 in BCD: 1001

So, 249 → 0010 0101 1001

641 in Decimal

• 6 in BCD: 0110
• 4 in BCD: 0100
• 1 in BCD: 0001

Adding:

  0010 0101 1001
+ 0110 0100 0001
  --------------
  1000 1001 1010

Result:

1000 1001 1010

Here,

• 1000 → 8
• 1001 → 9
• 1010 → 10

To correct 1010, we will add 6.

   1010
 + 0110
 -------
   0000 (with a carry of 1)

Final BCD Result

1000 1001 0000

So, the final corrected BCD result of the addition is 1000 1001 0000, which represents the decimal value 890 in BCD.

b. 3459 - 4367 using 9's complement

9's complement is obtained by subtracting each digit from 9.

• $9 - 4 = 5$
• $9 - 3 = 6$
• $9 - 6 = 3$
• $9 - 7 = 2$

So, the 9's complement of 4367 is 5632.

Add 9's complement to 3459

  1 1
  3459
+ 5632
  ----
  9091 

Binary: 1001 0000 1000 0001 → 9091

Since every digit is in the range 0 to 9 and less than 10,000

Since $9091 < 10,000$, the result is positive.

$10000 - 9091 = 909$

Thus, $3459 - 4367 = -909$.

c. 23-35 using 2's complement

8. (a) Discuss the purpose and function of a signal generator in electronic measurements. Provide examples of the types of signals a signal generator can produce. (with diagrams)

(b) Explain how a CRO can be employed to measure the phase difference between two AC signals. Provide a step-by-step procedure for phase measurement.

9. (a) What are the materials used for creating P-type semiconductor ?

(b) What are the difference between n-p-n and p-n-p transistor?

(c) What do you mean by resonance in a Oscillator?

A phenomenon in which an external force or a vibrating system forces another system around it to vibrate with greater amplitude at a specified frequency of operation.

Resonant frequency is the natural frequency where a medium vibrates at the highest amplitude. Resonant frequency is usually denoted as $f_0$. Resonance is witnessed in objects in equilibrium with acting forces and could keep vibrating for a long time under perfect conditions.

$v = \lambda f$

where $v$ is the wave velocity and $\lambda$ is the distance of the wavelength.

(d) Convert the following binary numbers to Grey Code:

1. 101101
2. 111001

$101101$

• MSB → 1

  1 - - - - -

  • $1 \oplus 0 \to 1$

  1 1 - - - -

  • $0 \oplus 1 \to 1$

  1 1 1 - - -

  • $1 \oplus 1 \to 0$

  1 1 1 0 - -

  • $1 \oplus 0 \to 1$

  1 1 1 0 1 -

  • $0 \oplus 1 \to 1$

  1 1 1 0 1 1

  Answer: $\textbf{111011}$

$111001$

• MSB → 1

  1 - - - - -

  • $1 \oplus 1 \to 0$

  1 0 - - - -

  • $1 \oplus 1 \to 0$

  1 0 0 - - -

  • $1 \oplus 0 \to 1$

  1 0 0 1 - -

  • $0 \oplus 0 \to 0$

  1 0 0 1 0 -

  • $0 \oplus 1 \to 1$

  1 0 0 1 0 1

  Answer: $\textbf{100101}$

(e) Perform the following conversions:

$(FAB.9A)16=(?)_{10} = (?)_{2}$

1. Integer Part
   $15\ 10\ 11$

   $(1 \times 16^5) + (5 \times 16^4) + (1 \times 16^3) + (0 \times 16^2) + (1 \times 16^1) + (1 \times 16^0) = 1380369$

2. Fraction Part
   $0.910$

   $(9 \times 16^{-1}) + (1 \times 16^{-2}) + (0 \times 16^{-3})$

   $= (0.5625) + (0.00390625) + 0 = 0.5664065$

3. Adding Integer & Fractional Parts

   $= 1380369.5664065$

(f) Why is input impedence of Op-Amp generally high?

The input impedance of an operational amplifier (op-amp) is generally high to minimize the amount of current drawn from the input signal source, ensuring accurate signal amplification without significant loading effects.

(g) What is the primary function of Collector in BJT?

The primary function of the collector in a BJT is to collect the charge carriers from the base, allowing a controlled current to flow from the collector to the emitter. This function enables the BJT to amplify signals and act as a switch. Additionally, the collector handles most of the power dissipation and is thus designed to manage heat effectively.

(h) What is the basic difference between N-Channel and P-Channel MOSFET?

(i) What is the operational principle of an CRO.

A Cathode Ray Oscilloscope (CRO) works by using a high-speed electron beam that is deflected by an electric or magnetic field to produce a visual display of an electrical signal.

(j) Find the complement of the Boolean expression F = A'B + CD'