1.
Calculate the Current Gain (β) and Emitter Current (Iₑ) for a BJT
Given:
Collector current (Iₖ) = 10 mA
Base current (Iᵦ) = 0.5 mA
Current Gain (β) is defined as the ratio of the collector current to the base
current:
\beta = \frac{I_C}{I_B} = \frac{10\text{ mA}}{0.5\text{ mA}} = 20
Emitter current (Iₑ) is the sum of the collector current and the base current:
I_E = I_C + I_B = 10\text{ mA} + 0.5\text{ mA} = 10.5\text{ mA}
Thus:
Β = 20
Iₑ = 10.5 mA
2. Basic Construction and Working of an NPN Transistor with Relevant
Diagram
Construction:
An NPN transistor consists of three layers of semiconductor material:
1. Emitter €: N-type semiconductor (which emits electrons).
2. Base (B): P-type semiconductor (which is thin and lightly doped).
3. Collector ©: N-type semiconductor (collects the electrons).
The base-emitter junction is forward biased, and the base-collector junction is
reverse biased in active operation.
Working:
When a small current flows from the base to the emitter, it allows a much larger
current to flow from the collector to the emitter.
The majority carriers (electrons in NPN) from the emitter are injected into the
base. A small number recombine with holes in the base, and the rest move to the
collector due to the reverse bias of the base-collector junction.
The transistor thus amplifies the base current to control a much larger collector
current.
Diagram:
C (Collector)
|
|
| P (Base)
| |
Emitter € - NPN Transistor
| |
| N (Emitter)
|
4. Comparison of FET and BJT
5. Basic Block Diagram of a Communication System and Explanation
Block Diagram:
Message Signal Transmitter Communication Channel Receiver Output
Signal
Explanation of each block:
1. Message Signal: This is the original information (audio, video, data) that
needs to be transmitted.
2. Transmitter: The transmitter takes the message signal and modulates it
onto a carrier wave. This can include encoding and signal processing to
prepare the signal for transmission.
3. Communication Channel: This is the medium through which the signal
travels. It can be a physical medium (like cables or fiber optics) or wireless
(radio waves, microwaves).
4. Receiver: The receiver captures the signal from the channel and
demodulates it, extracting the message signal.
5. Output Signal: The extracted message signal is output at the receiver side,
often requiring further processing (e.g., decoding, amplification).
6. Block Diagram of a Digital Communication System and Explanation
Block Diagram:
Digital Message Signal Encoder Modulator Transmission Channel
Demodulator Decoder Output
Explanation of each block:
1. Digital Message Signal: The input signal, which is in digital form (e.g., binary
data, text, images, etc.).
2. Encoder: The encoder converts the digital message into a suitable form for
transmission. This could involve error correction, formatting, or
compression.
3. Modulator: In digital communication, modulation involves varying the
carrier signal to represent digital data. Common modulation schemes are
PSK, QAM, etc.
4. Transmission Channel: This is the physical medium (cable, fiber, or air) that
carries the modulated signal.
5. Demodulator: The demodulator extracts the digital signal from the
modulated carrier at the receiver side.
6. Decoder: The decoder reverses the encoding process, recovering the
original digital message.
7. Output: The final digital data is output from the receiver, ready for use
(e.g., display, storage, or further processing).
7. Operation of Fiber Optic Communication System
Fiber Optic Communication System involves transmitting data as light pulses
through fiber-optic cables. Here’s an explanation of its operation:
1. Transmitter:
The transmitter converts electrical signals (data) into optical signals. Typically, this
is done using a laser diode or LED. The electrical signal modulates the light source,
creating pulses of light that correspond to the binary data.
2. Optical Fiber Cable:
The modulated light is transmitted through optical fiber cables. The cables consist
of a core made of glass or plastic that guides the light through total internal
reflection. The light signals travel with minimal loss of signal over long distances
due to the low attenuation of optical fibers.
3. Receiver:
The receiver at the other end of the fiber-optic cable detects the light pulses using
a photodiode or photodetector, which converts the light back into an electrical
signal.
4. Signal Processing:
The received electrical signal is processed to recover the original data. This can
involve amplification, error correction, and other signal processing techniques.
Advantages of Fiber Optic Communication:
High bandwidth: Can carry large amounts of data with high speed.
Low attenuation: Less signal loss over long distances compared to traditional
copper cables.
Immunity to electromagnetic interference: Fiber optics are not susceptible to
electromagnetic interference, unlike metal-based cables.
Security: Difficult to tap or intercept, providing secure data transmission.
Fiber optic communication is used in high-speed internet, telecommunications,
and cable TV, and plays a critical role in modern communication systems.
