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

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.

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

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.

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.

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.

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 White Noise: Another name for thermal noise because its frequency content is uniform across the spectrum.

Prof. ParkELC 2228 Thermal Noise P n = kT  f k = Boltzmann’s constant (1.38  J/K) T = Resistor temperature in kelvin (K)  f = Frequency bandwidth of the system The rms noise voltage en has a maximum at

Example 1-4 Prof. ParkELC 2229 Determine the noise voltage produced by a 1Mohm resistor at room temperature (17C) over 1MHz bandwidth.

Prof. ParkELC A communication system block diagram

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

Prof. ParkELC Resistance noise generator

Prof. ParkELC Device noise versus frequency

Prof. ParkELC 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

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

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

Prof. ParkELC 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

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

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

Prof. ParkELC 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.

Prof. ParkELC 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.

Prof. ParkELC 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.