Pdf high speed amplitude modulator with high modulation. It follows, then, that multiplying the modulated signal by the carrier frequency will transfer the spectrum back to its original positioni. Increase the modulated signal until an am waveform appears. Before we study in detail about pam lets know the concepts of modulation. No information is lost, but the energy is redistributed in the frequency domain. As before, this may require a manual adjustment of the voltsdiv and. Pdf development of highvoltage pulse generator with.
Multiple choice questions and answers on amplitude modulation. As illustrated in figure 5, the amplifier is biased class c and the output rf signal amplitude is modulated by causing the collector supply voltage to vary with the modulation voltage. Carrier communication requires the modulation of the message onto a carrier signal to. It is often called as am and is commonly used in transmitting a piece of information through a radio carrier wave. In am radio, the voltage or amplitude of a carrier with a fixed center frequency by the station is varied by the analog audio signal. The method of varying amplitude of a high frequency carrier wave in accordance with the information to be transmitted, keeping the frequency and phase of the carrier wave unchanged is called amplitude modulation. In am modulation the carrier signal changes almost. The concluding part will be spent looking at the more popular form of high level modulation known as collector modulation or heising, named after its inventor. This form of modulation is essentially derived from two carriers that are 90 out of phase and adding information, either analogue or digital. This results in an output voltage that will follow the peak of the am waveform. Low voltage graphenebased amplitude modulator for high e. What is amplitude modulation, am electronics notes.
Amplitude modulation is mostly used in the form of electronic communication. Amplitude modulation explained amplitude modulation waveform. Course projects are one of the seven high impact practices discussed by koh in 1. Analog amplitude modulation of a high voltage, solid state inductive adder, pulse generator using mosfets january 2002 power modulator symposium, 1994. The polarization insensitive modulator is designed to achieve a maximum experimental modulation depth of about 53% within 5 v of gate voltages using monolayer graphene. Modulation index is normally expressed as a percentage, and may be displayed on a meter connected to an am transmitter. Traditional linear am amplifiers are a form of efficiency modulation. Farshad lahouti january 20, 2003 winter 2003 uw, ece 318 lecture notes 2 information source signal modulator propagation channel signal demodulator information destination analog communication system analog signals may be transmitted directly via carrier modulat ion over. By boosting the voltage, less current is needed to deliver a given amount of power to a load, reducing the resistive loss through conductors. This form of modulation is referred to as highlevel modulation, and the audio power level must be 50% of that of the rf amplifier to provide 100% modulation.
Spectrum analysis amplitude and frequency modulation an 150. Describe phase demodulation circuit operation for the peak, lowpass filter, and conversion detectors. Amplitude modulation circuit implementation for use in a communication. The carrier frequency, fc, should be larger than the highest spectral component. Oma is defined as the difference between the high and low levels, which can be written mathematically as. In this paper, a high efficiency terahertz amplitude modulation device based on a fieldeffect transistor has been proposed. When we vary current in a device with fixed supply voltage, the device normally does not have a squarelaw power response. Oma p p 1 0 1 average power is simply the average of the two power levels, i. Peak value of carrier signal can also be computed using the peaktopeak value of the am waveform see fig. An amplitude modulated signal is composed of both low frequency and high frequency. This means that their ratio is unity at the output of the adder, which forces m to a.
It may be necessary to adjust the level and frequency of both v c and v m to achieve a suitable waveform and index of modulation. Amplitude modulation is also used in digital data, like quadrature amplitude modulation, where both amplitude and phase modulation are. The circuit model of a threephase sixswitch pwm vsi is shown in fig. Am is a relatively simple way to add audio information to a carrier wave so that sounds can be transmitted. Pdf analog amplitude modulation of a high voltage, solid. Dec 21, 2017 amplitude modulation is one of the earliest radio modulation techniques. By driving a diode with sufficient ac voltage it acts like a switch.
With the modulating voltage adjusted to zero amplitude, increase the carrier amplitude until v o has a value of 2 v pp. In this paper, a highefficiency terahertz amplitude modulation device based on a fieldeffect transistor has been proposed. First, we rely on the fast and strong nonlinearities of polymers infiltrated into silicon, rather than on the slower free. Naturally, the amplitude of the current pulses through transistor q1 will vary. Other duty cycles produce any voltage in the range of 0 to 100% of the high voltage, depending upon the pwm resolution. Peak value of carrier signal can also be computed using the. Amplitude modulation an overview sciencedirect topics. This method is capable of producing nearly 100% modulation with reasonable linearity. The duty cycle is defined as the percentage of digital high to digital low signals present during a pwm period.
Here, the envelope of the carrier can be seen to change in line with the modulating signal. This occurs because supply voltage is constant and does not vary with modulation. Collector modulation method is the example of high level amplitude modulation. A solidstate high voltage pulse generator with multipulse burst capability, very fast rise and fall times, pulse width agility, and amplitude modulation capability for use with high speed. Highlevel modulation is accomplished with a collector plate in vacuum tubes modulator that varies the collector supply voltage in accordance with the modulating signal. The method of varying amplitude of a highfrequency carrier wave in accordance with the information to be transmitted, keeping the frequency and phase of the carrier wave unchanged is called amplitude modulation. The original waveform amplitude is quantized with a resulting loss of information. Many many digital systems are powered by a 5volt power supply, so if you filter a signal that has a 50% duty cycle you get an average. It was developed in the first few decades of the twentieth century. This form of modulation is referred to as high level modulation, and the audio power level must be 50% of that of the rf amplifier to provide 100% modulation.
An amplitude modulation circuit which comprises a modulating circuit for applying a modulating signal to a modulated stage, and a voltage regulator arranged to regulate a d. Subjects include modulation methods, modulation degree and sideband amplitude, zero span and markers, the fast fourier transform, special forms of amplitude modulation, angular modulation, bandwidth of fm signals, fm measurements with the spectrum analyzer, and am plus fm incidental fm. This principle is at the heart of amplitude modulation. A high voltage pulse generator with variable amplitude 100v to 3000 v and duration 100 s to 2000 s has been designed and developed.
Optical modulation amplitude oma and extinction ratio. The idea is simple, though the notion that it can be used to modulate signals for transmission was hardly obvious before its discovery. The binary signal when ask modulated, gives a zero value for low input while it. The pulse may take any real voltage value that is proportional to the value of the original waveform. Moreover, the manufacturing processes are inexpensive. The modified carrier signal is called the modulated signal.
Commercial broadcast stations use this type and it is commonly known as jus t amplitude modulation am. The binary signal when ask modulated, gives a zero value for low input while it gives the carrier output for high input. Amplitude, frequency and phase modulation can be applied directly by software to the generated signals, which gives great flexibility where complicated and precise waveforms are required. The original method of electronically encoding sound information on radio waves is called amplitude modulation, or am. Changing the amplitude of the carrier am modulation is one type of modulation easy, cheap, lowquality used for am receiver and cbs citizen bands generally high carrier frequency is used to modulate the voice signal 300 3000 hz. Amplitude linear modulation modulation is a process by which a parameter of a high frequency sinusoid is modified in accordance with the message signal to be transmitted. It requires that the amplitude of the dc a part of at is equal to the amplitude of the ac part a.
In this way the audio modulates the voltage supplied to the final amplifier, and the level of the output signal is modulated in line with the audio. This 26page application note provides information on amplitude and frequency modulation. Long distance electrical transmission favors ac power, since the voltage can be boosted easily with the use of transformers. Amplitude modulation definition, types, solved examples. Amplitude and frequency modulation when all three components of the modulation signal are in phase, they add together linearly and form the maximum signal amplitude emax, as shown in animation 1. Typically a transformer is used to enable the output of the audio amplifier to drive the anode voltage of the final power amplifier within the transmitter. Amplitude modulation is also used in digital data, like quadrature amplitude modulation, where both amplitude and phase modulation are used to create different binary states for transmission. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that. High level modulation is the processes of amplitude modulating the final power amplifier of a transmitter. Amplitude modulation is a process by which the wave signal is transmitted by modulating the amplitude of the signal. Highlevel modulation is the processes of amplitude modulating the final power amplifier of a transmitter. In amplitude modulation, it is the voltage level of the signal to be transmitted. In this paper, a highe ciency terahertz amplitude modulation device based on a.
Quadrature amplitude modulation is widely used for carrying many digital signals, everything from wifi to mobile phone communications and very much more. Wherever there is a changing electrical current, a changing magnetic field accompanies it. Power amplifiers are used to boost the carrier and modulating signals before modulation d. When the modulation signal occurs, the ac voltage across the secondary of the modulation transformer will be added to and subtracted from the collector supply voltage. The modulation may be in the form of amplitude am, frequency. Percentage modulation aka modulation index or modulation factor measure of extend to which carrier voltage is varied by intelligence defined as. In this modulation, the signal is sampled at regular intervals and each sample is made proportional to the amplitude of the modulating signal. Pdf high voltage, solid state, inductive adder, pulse generators have found increasing application as fast kicker pulse modulators for charged. Osa highspeed lowvoltage electrooptic modulator with a. Thus, we can think of amplitude modulation as shifting the original spectrum upward by f c and downward by f c. Pulse width modulation using digital pulses to create some analog value other than just high and low signal levels. Am modulators base, collector, grid and plate modulators.
Carrier modulation allows the transmission of modulating frequencies without the use of transmission wire as a medium. Amplitude modulation explained amplitude modulation. Jun 01, 2008 more generally, the amplitude of the overall signal is varied in line with the incoming audio or other modulating signal, as shown in figure 32. Modulationtypesamplitude,frequency,phase modulation.
University of north carolina at charlotte department of. The information is considered as the modulating signal and it is superimposed on the carrier. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. Feedback can be used to achieve an output that matches exactly the control signal. Amplitude modulation and demodulation electrical and computer. This has changed the design of wireless and wireline transceivers. Amplitude modulation receiver circuit eeweb community. Pulse amplitude modulation pam theory of and its applications. Pulse amplitude modulation is the basic form of pulse modulation.
As such, ac power is more conventional than high voltage dc systems due to the ease of stepping up voltage for transmission and stepping voltage down to household outlet levels. Collector modulation method is high level amplitude modulation c. One can, as explained in chapters 9 and 10, map each 1 to a voltage v1 held. The variable duration pulse has been generated by adopting a simple and novel technique of varying the turn off delay time. The receivers used to listen to amdsbc are perhaps the simplest receivers of any radio modulation technique. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. High carrier frequency allows deeper and more comfortable. Modulation is done at high power of carrier and modulating signal b. This varying supply voltage is applied to the class c amplifier. With the modulating voltage adjusted to zero amplitude, increase the carrier. Sep 02, 2017 amplitude modulation may be defined as a system, where the maximum amplitude of the carrier wave varies, according to the instantaneous value amplitude of the modulating message or baseband. Scan amplitude modulation sweep frequency modulation.
Low voltage graphenebased amplitude modulator for high. In high level amplitude modulation system, modulation is done at high power of carrier and modulating signals so power amplifiers are used to boost the carrier and modulating signals before modulation. More generally, the amplitude of the overall signal is varied in line with the incoming audio or other modulating signal, as shown in figure 32. Amplitude shift keying ask is a type of amplitude modulation which represents the binary data in the form of variations in the amplitude of a signal. For the first part of the experiment you will model eqn. Amplitude modulation index an overview sciencedirect topics. The high frequency sinusoid is known as the carrier and the message signal is the modulating signal. Frenzeljr, in handbook of serial communications interfaces, 2016. For a perfect modulation, the value of modulation index should be 1, which implies the percentage of modulation should be 100%. Generally high carrier frequency is used to modulate the voice signal. High speed amplitude modulator with high modulation index based on plasmonic resonant tunable metasurface article pdf available in applied optics 5810 march 2019 with 199 reads. Pdf analog amplitude modulation of a high voltage, solid state. High level modulation is accomplished with a collector plate in vacuum tubes modulator that varies the collector supply voltage in accordance with the modulating signal.
Amplitude modulation may be defined as a system, where the maximum amplitude of the carrier wave varies, according to the instantaneous value amplitude of. Before we study in detail about pam lets know the concepts of. With fixed high voltage, only the supply current varies with drive. Such record data allow 100gbits transmission and can be achieved by exploiting a combination of several physical effects. Communication systemsamplitude modulation wikibooks, open. Amplitude modulation article about amplitude modulation by. Pulse width modulation traditional solenoid driver electronics rely on linear control, which is the application of a constant voltage across a resistance to produce an output current that is directly proportional to the voltage. The voltage or current spectrum of the bandpass signal is. Amplitude modulation is one of the earliest radio modulation techniques.
1349 254 1354 600 507 1321 92 681 5 1025 232 16 374 321 1170 425 890 717 670 1460 1245 203 301 1016 1196 1014 856 440 342 84 640 74 997 911 630 1269 325 160 1321 527 1155 136 125 1008