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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

Lecture 1: Introductory Topics

Prof. Park

ELC 222

Essex County College

ELC 222

modulation
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
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

ELC 222

electrical noise
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.

ELC 222

external noise
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.

ELC 222

internal noise
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
  • 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.

ELC 222

thermal noise1
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

ELC 222

example 1 4
Example 1-4

Determine the noise voltage produced by a 1Mohm resistor

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

ELC 222

signal to noise ratio
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

ELC 222

example 1 6
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

ELC 222

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

ELC 222

information and bandwidth
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

ELC 222

am vs fm
AM vs. FM

ELC 222

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

ELC 222

example 1 12
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.

ELC 222

example 1 13
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.

ELC 222

example 1 14
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.

ELC 222