Lecture 1: Introductory Topics

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# Lecture 1: Introductory Topics - PowerPoint PPT Presentation

Lecture 1: Introductory Topics. Prof. Park ELC 222 Essex County College. Modulation. Modulation is the process of putting information onto a high-frequency carrier for transmission. The low-frequency information is called the intelligence. The high-frequency medium is called the carrier.

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## Lecture 1: Introductory Topics

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### Lecture 1: Introductory Topics

Prof. Park

ELC 222

Essex County College

ELC 222

Modulation
• Modulation is the process of putting information onto a high-frequency carrier for transmission.
• The low-frequency information is called the intelligence.
• The high-frequency medium is called the carrier.
• The demodulation is the reverse process of modulation.

ELC 222

Mathematical Representation of Sine Wave
• v = Vp sin(t + )
• Where v = instantaneous value
• Vp = peak value
•  = angular velocity = 2f
•  = phase angle
• AM: Amplitude Modulation
• FM: Frequency Modulation
• PM: Phase Modulation

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Electrical Noise
• Electrical noise: Any undesired voltages or currents that ultimately end up appearing in a circuit.
• Static: Electrical noise that may occur in the output of a receiver.
• External Noise: Noise introduced by the transmitting medium.
• Internal Noise: Noise introduced by the receiver.

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External Noise
• Human-Made Noise: Noise produced by spark-producing system such as engine ignition systems, fluorescent lights, commutators in electric motors, and power lines.
• Atmospheric Noise: Noise caused by naturally occurring disturbances in the earth’s atmosphere.
• Space Noise: Noise produced outside the earth’s atmosphere.

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Internal Noise
• Thermal Noise: Noise caused by thermal interaction between free electrons and vibrating ions in a conductor.
• Shot Noise: Noise introduced by carriers in the pn junctions of semiconductors
• Excess Noise: Noise occurring at frequencies below 1khz, varying in amplitude inversely proportional to the frequence
• Transit-Time Noise: Noise produced in semiconductors when the transit time of the carriers crossing a junction is close to the signal’s period.

ELC 222

Thermal Noise
• Thermal Noise: Noise caused by thermal interaction between free electrons and vibrating ions in a conductor.
• Johnson Noise: Another name for thermal noise, first studied by J. B. Johnson in 1928.
• White Noise: Another name for thermal noise because its frequency content is uniform across the spectrum.

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Thermal Noise
• Pn = kTf
• k = Boltzmann’s constant (1.3810-23 J/K)
• T = Resistor temperature in kelvin (K)
• f = Frequency bandwidth of the system
• The rms noise voltage en has a maximum at

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Example 1-4

Determine the noise voltage produced by a 1Mohm resistor

at room temperature (17C) over 1MHz bandwidth.

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Signal-To-Noise Ratio
• Signal-To-Noise Ratio: Relative measure of desired signal power to noise power
• Noise Figure (NF): A figure describing how noisy a device is in decibels
• Noise ratio (NR): A figure describing how noisy a device is as a ratio having no units

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Example 1-6
• A transistor amplifier has measured S/R of 10 at its input and 5 at its output.
• A) Calculate the NR
• B) Calculate the NF

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Noise Due to Amplifiers in cascade
• Friiss’s formula
• NR = NR

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Information and Bandwidth
• Hartley’s Law:

information  bandwidth  time of transmission

• Fourier Analysis: Method of representing complex repetitive waveforms by sinusoidal components
• Fast Fourier Transform (FFT): A technique for converting time-varying information to its frequency component

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AM vs. FM

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Example 1-11
• Determine the resonant frequency for the circuit below. Calculate its impedance at f = 12 kHz.

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Example 1-12
• Determine the resonant frequency for the circuit when R1 = 20, R2 = 1, L = 1mH, C = 0.4µF, and ein = 50 mV. Calculate eout at fr and at f = 12 kHz.

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Example 1-13
• A filter circuit has a response as below. Determine (a) bandwidth, (b) Q, (c) L if C = 0.001µF, and (d) total circuit resistance.

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Example 1-14
• A parallel LC tank circuit is made up of an inductor of 3mH and a winding of 2. The capacitance is 0.47µF. Determine (a) fr, (b) Q, (c) Zmax, and (d) BW.

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