Analog Transmission Of Analog Data: AM And FM
1Analog Transmissionof Analog Data:AM and FMRequired reading: -CSE 3213, Fall 2010Instructor: N. Vlajic
Modulation of Analog Data2Why Analog-to-Analog – two principal reasons for combining anan analog signal with a carrier at freq. fc:Modulation?(1) higher freq. may be needed for effectivetransmission in wireless domain, it is virtually impossibleto transmit baseband signals – the requiredantennas would be many kilometres in diameter(2) modulation permits FDM (freq. divisionmultiplexing) more on this later example: radioanalog signals produced by radio stations arelow-pass, all in the same range - to be able to listento different stations, the low-pass signals need to beshifted, each to a different rangeFDM in time-domainFDM in frequency-domain
Modulation of Analog Data (cont.)Types of Analog-to-Analog Modulation3
Amplitude Modulation4Amplitude – amplitude of the carrier signal varies with thechanging amplitude of input/modulating signal;Modulationfrequency and phase remain unchangeds(t) [A c x(t)] cos(2 πfc t) A c [1 k a x(t)] cos(2 πfc t) Ac – carrier amplitudeka – amplitude sensitivity of the modulator, must be:k a x(t) 1to ensure that the function [1 kax(t)] is always positive otherwise the envelope will cross the time axis, and info. will be odam.htm
Amplitude Modulation (cont.)5AM Bandwidth – bandwidth of an AM signal 2x bandwidth of modulatingsignal, and covers a range centered on carrier frequency BWtotal 2*BW modulating-signal example: AM radio the bandwidth of an audio signal (speech only) is 5 kHz each AM radio station needs a min bandwidth of 10 kHz AM stations are allowed carrier frequencies anywherebetween 530 - 1700 kHz; each station’s carrier frequencymust be separated from those on either side by at least 10kHz, to avoid interferencelower sidebandupper sideband
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Frequency ModulationFrequency – frequency of carrier signal follows changes involtage level (amplitude) of modulating signalModulationts(t) A c cos(2 πfc t 2πk f x(t)dt ) A c cos(θ i (t))0fi (t) 1 dθ i (t) fc k f x(t)2π fm.htmThe actual frequency spectrum of a FM signal is “challenging” to find.(The spectrum contains multiple sideband on each side of the carrier frequency.)7
Frequency Modulation (cont.)8FM Bandwidth – bandwidth of an FM signal 10xbandwidth of modulatingsignal, and covers a range centered on carrier frequency BWtotal 10*BW modulating-signal example: FM radio the bandwidth of an audio signal (speech AND music) inis almost 15 kHz each FM radio station needs aminimum bandwidth of 150 kHz FM stations are allowed carrier frequencies anywherebetween 88 and 108 MHz; stations must be separated byat least 200 kHz to keep their bandwidths from overlapping
AM vs. FMAM Disadvantages9(1) Most natural & man made radio noise is AM in nature,and AM receivers have no means of rejecting that noise.(2) Also, weak signals have lower amplitude than strongones, which requires the receiver to have circuits tocompensate for the signal level differences.AM Advantages(1) AM signals can be reflected from the ionospheric layerback to earth, so that the signals can reach unintendedplaces that are thousands of miles away.FM Disadvantages(1) At the high(er)-frequency FM signals pass unreflectedthrough the ionosphere.FM Advantages(1) The effects of amplitude noise are minimized, since therecovered audio is dependent only on the frequency,and not the strength.(2) The FM bandwidth can easily cover entire musical rangeof the human ear of about 20 kHz, and that is why FMradio sounds better than AM radio.AM radio has wider coverage than FM radio;FM radio has better sound quality than AM radio.
AM vs. FM (cont.)sky-wave (AM signal) propagationground-wave (FM signal) propagation“Radio waves are generally unaffected by obstacles smaller than their wavelength. So it is easyto visualise the 300 meter (1000 feet) waves of a 1 MHz AM radio station being unaffected by thehills and city buildings which play havoc with the 0.5 metre waves of UHF television. html10
Modulation of Analog Data 2 Why Analog-to-Analog Modulation? – two principal reasons for combining an an analog signal with a carrier at freq. f c: (1) higher freq. may be needed for effective transmission in wireless domain, it is virtually impossible to transmit baseband signals – the requi
modulation equipment Analog data, digital signal – Permits use of modern digital transmission and switching equipme nt Digital data, analog signal – Some transmission media will only propagate analog signals – E.g., unguided media (air) Analog data, analog signal – Analog data in
Analog I/O 1 / 10 V or 0-10 V or 0-20 mA TIDA-01633 Analog I/O 2 / 10 V or 0-10 V or 0-20 mA Load fault feedback Current/Voltage output select Analog I/O select Analog input Analog input ref PWM Input Analog DAC x2 x2 x2 x2 x
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Introduction to Analog Verification Analog Verification 2 of 13 Designer’s Guide Consulting www.designers-guide.com 1 Analog Verification Currently, 90% of all SOCs contain analog circuitry, and the analog con‐ tent of these SOCs averages a relatively constant 20% of the area of the SOC.
Getting analog inputs to digital form D/A conversion “digital to analog” Getting digital inputs to analog form Digital I/O Sometimes you can fake analog values with digital (e.g., digital pulsing) 8 D/A Conversion “DAC” “D/A Converter” “Digital To Analog Converter
2. ANALOG IC DESIGN: OVERVIEW In order to locate analog IC sizing, a brief presentation of a typical analog IC design flow is shown, and the analog IC sizing task is described. 2.1 Design Flow A commonly well accepted design flow for analog and mixed-signal ICs is depicted in Figure 1. It was proposed by Gielen and
Oct 29, 2014 · Reasons for Analog Modulation ! Modulation of digital signals " When only analog transmission facilities are available, digital to analog conversion required ! Modulation of analog signals " A higher frequency may be needed for effective transmission " Modulation permits frequency division multi
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