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Lecture 1: Introductory Topics

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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  1. Lecture 1: Introductory Topics Prof. Park ELC 222 Essex County College ELC 222

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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

  9. Example 1-4 Determine the noise voltage produced by a 1Mohm resistor at room temperature (17C) over 1MHz bandwidth. ELC 222

  10. A communication system block diagram ELC 222

  11. Noise effect on a receiver’s first and second amplifier stages ELC 222

  12. Resistance noise generator ELC 222

  13. Device noise versus frequency ELC 222

  14. 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

  15. 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

  16. Noise Due to Amplifiers in cascade • Friiss’s formula • NR = NR ELC 222

  17. 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

  18. AM vs. FM ELC 222

  19. Example 1-11 • Determine the resonant frequency for the circuit below. Calculate its impedance at f = 12 kHz. ELC 222

  20. 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

  21. 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

  22. 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

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