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Prof. ParkELC 2221 Lecture 1: Introductory Topics Prof. Park ELC 222 Essex County College

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Prof. ParkELC 2222 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.

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Prof. ParkELC 2223 Mathematical Representation of Sine Wave v = V p sin( t + ) Where v = instantaneous value V p = peak value = angular velocity = 2 f = phase angle AM: Amplitude Modulation FM: Frequency Modulation PM: Phase Modulation

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Prof. ParkELC 2224 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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Prof. ParkELC 2225 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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Prof. ParkELC 2226 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.

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Prof. ParkELC 2227 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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Prof. ParkELC 2228 Thermal Noise P n = 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 Prof. ParkELC 2229 Determine the noise voltage produced by a 1Mohm resistor at room temperature (17C) over 1MHz bandwidth.

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Prof. ParkELC 22210 A communication system block diagram

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Prof. ParkELC 22211 Noise effect on a receiver’s first and second amplifier stages

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Prof. ParkELC 22212 Resistance noise generator

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Prof. ParkELC 22213 Device noise versus frequency

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Prof. ParkELC 22214 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 Prof. ParkELC 22215

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Noise Due to Amplifiers in cascade Friiss’s formula NR = NR Prof. ParkELC 22216

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Prof. ParkELC 22217 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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Prof. ParkELC 22218 AM vs. FM AMFMAnalog TV Low Limit535 kHz88 MHz High Limit1605 kHz108 MHz Channel BW10 kHz200 kHz6 MHz Baseband BW5 kHz15 kHz Max. Stations107100

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Prof. ParkELC 22219 Example 1-11 Determine the resonant frequency for the circuit below. Calculate its impedance at f = 12 kHz.

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Prof. ParkELC 22220 Example 1-12 Determine the resonant frequency for the circuit when R 1 = 20 , R 2 = 1 , L = 1mH, C = 0.4µF, and e in = 50 mV. Calculate e out at f r and at f = 12 kHz.

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Prof. ParkELC 22221 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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Prof. ParkELC 22222 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) f r, (b) Q, (c) Z max, and (d) BW.

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