Use the spectrum analyzer to compare this modulator to the one in part 2. The simplest form of am demodulator consists of a diode which. Am modulation and demodulation with circuit and output slideshare. We can design the ask modulation circuit using a 555 timer ic in an astable mode. Diode envelope detector amplitude modulation am demodulation. The circuit that is widely used to demodulate am signals is called an envelope detector.
Considering the difficulties faced by the designer in terms of hardware for designing such systems we have used a system that uses less hardware for this process. Multiplying the am waveform by the carrier shifts the baseband spectrum down to 0 hz, but it also shifts it up to 2f c in this case 200 mhz, because as stated above multiplication moves the existing spectrum up by f c and down by f c. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. One of the easiest ways to implement qam with hardware is to generate and mix two sine waves that are 90 degrees out of phase with one another. Though it is theoretically possible to transmit baseband signals or information without modulating it, it is far more efficient to send data by modulating it onto a higher frequency carrier wave. When the modulation source is an audiofrequency oscillator and the destination is the gain of a vca in the audio signal path, we call the result amplitude modulation, or am for short. May 23, 20 in this article, i will explain quadrature amplitude modulation and demodulation in detail along with the necessary circuit diagram and frequency spectrum. As before, this may require a manual adjustment of the voltsdiv and secdiv to obtain a suitable waveform. The am signal is taken from the transistors collector. Pulse amplitude modulation circuit diagram circuit design. Content introduction what is modulation types of modulation amplitude modulation modulation index amplitude demodulation circuit diagram about project conclusion 3. Ee4512 analog and digital communications chapter 6 the analytical signal for double sideband, large carrier amplitude modulation dsblc am is. The demodulator is the circuit, or for a software defined radio, the software that is used to recover the information content from the overall incoming modulated.
For a perfect modulation, the value of modulation index should be 1, which implies the percentage of modulation should be 100%. Source called v1 generates the message to be transmitted. It was developed in the first few decades of the twentieth century. Amplitude demodulation or detector electronics tutorials. Introduction modulation is used in efficient radiation of signals. Its important to understand that the received signal could be from. Remember, for analysis purposes keep the modulation index and frequency the same as part 2, step 3. Pulseamplitude demodulation peak detection is used to detect pam.
Radio waves can carry audio, video, and digital information over great distances by using changes in a carrier waves amplitude, frequency, or phase to represent the information being transmitted. Amplitude modulation am, demodulation and their circuit. When the height is used, it is called pulseamplitude modulation pam. Understanding quadrature demodulation radio frequency. Mixer or sample mixer operates as a sample and hold circuit on the. Amplitude modulation and demodulation circuit simulation in multisim. A sine wave generator is used which is based on wien bridge oscillator circuit. Amplitude shift keying is a type of amplitude modulation in which digital signal is represented as a change in the amplitude of a. In this technique the amplitude of a high frequency signal is varied corresponding to the variation in the amplitude of the low frequency modulating signal.
In early am transmitters the amplitude modulator circuit was a key element of the transmitter. Mar 05, 2019 quadrature amplitude modulation qam requires changing the phase and amplitude of a carrier sine wave. The signal output from a demodulator may represent sound an. Quadrature amplitude modulation and demodulation in detail. Frequency division multiplexing, fdma amplitude modulation and demodulation. The am diode detector offers simplicity and low cost. Describe fm demodulation circuit operation for the phaseshift and gatedbeam discriminators and the ratiodetector demodulator.
The amplitude modulation and demodulation technique involved in this project comprises of three stages. Transmitters that transmit amplitude modulated signals require an am modulator circuit to produce the required signal. The simplest form of am demodulator consists of a diode. In quadrature demodulation, we are converting the existing modulation into the corresponding iq baseband signals. Implementing an amplitude demodulator with a product detector.
The process of demodulation for signals using amplitude modulation can be achieved in a number of different techniques, each of which has its own advantage. The resulting amplitude modulation am waveform is then demodulated using an envelope detector circuit. Demodulation of am signal as stated earlier, an envelope detector has been used here for demodulation. The process of demodulation or detection consists in getting back the original modulating voltage from the modulated carrier voltage. The demodulation of an am wave can be done with only few components and unlike most of the demodulation technique there is. Amplitude modulation definition, types, solved examples. As an example, the following figure shows the amplitude modulation with mtsin2. Adjust the carrier and modulated signals for a modulation index of 0. An interactive demo which enables you to both see and hear the result of multiplying a sine wave with a cosine amplitude envelope. As we mentioned before, well use dsbc modulation because of its ease in demodulation.
Adjusting only the amplitude of either signal can affect the phase and amplitude of the resulting. Dutton ee3 winter 2004 1 ee3 lab 1 amplitude modulation and demodulation 1 lab notes a word about power. Abstractthis project explores the robust design of amplitude modulation and demodulation using bjt amplifier and diode detector. The diode detector has been used for many years for detecting or demodulation signals using amplitude modulation, am.
We can define amplitude modulation by saying that a modulating signal, should produce an am wave of. Synchronous modulation and demodulation low dc current may be transformed into a high voltage dc by simple chopper action. Amplitude modulation and demodulation real time experiment. The demodulator is the circuit, or for a software defined radio, the software that is used to recover the information content from the overall incoming modulated signal. As was mentioned above, analog amplitude demodulation is simple enough as it uses an envelope circuit.
Am modulation and demodulation with circuit and output 1. Amplitude modulation and demodulation abstracta single tone sinusoidal signal is transmitted using amplitude modulation and is demodulated at the receivers end using an envelope detector and the attenuated signal is amplified using common source bjt amplifer i. This article is easy to understand, clear and with all the information. When the height is used, it is called pulse amplitude modulation pam. Here we use ic8038 as a signal generator to generate modulating and carrier signal. The audio signals used for modulation is called modulating signal or message signal or base band signal. Change the amplitude of fg1 to 2 v and capture the am signal and its spectrum, use a di. Two signal generators are used in this circuit, one representing a high frequency 200khz rf carrier, vg2, the other signal generator is used to inject a 1khz audio signal. We can define amplitude modulation by saying that a modulating signal, should produce an am wave of the form well use s instead of v or e to indicate that were talking about a modulated quantity and that it can be either a field or a voltage. Quadrature amplitude modulation qam requires changing the phase and amplitude of a carrier sine wave.
Here is the circuit used for modulation and its simulation. There are many types of modulation so there are many types of demodulators. It is often called as am and is commonly used in transmitting a piece of information through a radio carrier wave. Fm modulation and demodulation circuit multisim live. Amplitude modulation circuit implementation for use in. Demodulation is the process by which we can reconstruct the original. Basic concept of modulation the information source typically a low frequency signal referred to as the baseband signal carrier a higher frequency sinusoid example.
Amplitude modulation circuit implementation electrical. Cr1 is the input diode which allows capacitor c1 to charge to the peak value of the pam input pulse. A demodulator is an electronic circuit or computer program in a softwaredefined radio that is used to recover the information content from the modulated carrier wave. Aug 20, 2017 synchronous modulation and demodulation. Introduction in chapters 1 and 2 you studied how to apply intelligence modulation to an rfcarrier wave. Synchronous modulation and demodulation photo optical modulator. Thus, detection is a process reverse of the process of modulation. An62582 explains how to implement amplitude modulation am and. The simple pulse modulation technique called pulse amplitude modulation pam proved to be more power efficient than the pwm and consumes constant power for individual pulses like ppm. Amplitude modulation is a process by which the wave signal is transmitted by modulating the amplitude of the signal. The message signal is, for example, a function of the sound to be reproduced by a. Analog modulation and demodulation amplitude modulation pages 306309.
In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. Am modulation and demodulation with circuit and output. In pam the amplitude of the individual pulses are varied according to the amplitude of the modulating signals. As you can see, the rectifier stage chops the am signal in half letting only. There are different types of modulation and so are demodulators. In this article will will discuss about amplitude demodulation or detector, its type and details about linear diode detector. Demodulation is defined as extracting the original informationcarrying signal from a modulated carrier wave. We can vary the carrier signal by using r1, r2 and c. It requires that the amplitude of the dc a part of a t is equal to the amplitude of the ac part a. An envelope detector figure 6a is an electronic circuit that takes a highfrequency modulated signal as input and provides an output which is the envelope of the original signal. I find am a fascinating topic, not least because it has a quite unexpected result. Demodulation is extracting the original informationbearing signal from a carrier wave.
In this circuit, the carrierwave generated by an oscillator that isnt shown in the circuit is applied to the base of a transistor. In this article, i will explain quadrature amplitude modulation and demodulation in detail along with the necessary circuit diagram and frequency spectrum. There are many ways in which amplitude modulation can be generated and a variety of circuits that can be used. To code an analog signal in pulse form one can use the height of the pulse, the width or duration, or the position of the pulse relative to standard position. Am is a relatively simple way to add audio information to a carrier wave so that sounds can be transmitted.
This circuit uses two signal generators to simulate an amplitude modulated rf carrier wave. We have written the ngspice code for the modulator and. Understanding the principle of amplitude demodulation. Figure 321 includes a simplified circuit view a for this demodulator and its waveforms views b and c. The original method of electronically encoding sound information on radio waves is called amplitude modulation, or am. Then, the audio input is applied to the transistors emitter through a transformer. Amplitude modulation modulation is the process of varying a higher frequency carrier wave to transmit information. Quadrature amplitude modulation qam national instruments. The amplitude modulation is the simplest modulation technique among the wide verity of modulation techniques in use.
The math you have used assumes the transistor circuit is operating in the linear region i. The pam modulator and demodulator circuits simple compared to other kind of modulation and. Modulation allows us to transmit multiple signals in the same medium i. A demodulator is an electronic circuit that is mainly used to recover the information content from the modulated carrier wave. In other words, amplitude modulation allows the original carrier waveform through the vca, and also creates two new signals called the sum and the difference signals. Amplitude modulation is mostly used in the form of electronic communication. Digital demodulation can become complicated as you need to extract a discrete signal level from the carrier, and the extracted digital signal in amplitude demodulation has wide bandwidth. Circuit design of pulse amplitude modulation a pam is generated from a pure sine wave modulating the signal and a square wave generator which produces the carrier pulse and a pam modulator circuit. Synchronous modulation and demodulation photo optical. Sep 06, 2014 amplitude modulation and demodulation circuit simulation in multisim. May, 2016 am modulation and demodulation with circuit and output 1. In quadrature modulation, we use baseband iq signals to create an amplitude, frequency, or phasemodulated waveform that will be amplified and transmitted. Note that this is on the very low end of the recommended voltage range.
Demodulation is the process of reconstructing the original signal at the receiver level. The output can be used to simulate the response of lc and tank circuits. Describe phase demodulation circuit operation for the peak, lowpass filter, and conversion detectors. The circuit of figure 1 shows an am modulator circuit, whose carrier.1247 237 683 902 608 468 1041 1464 1240 789 653 1080 1549 1408 459 328 220 317 434 1172 508 1234 229 218 1068 1466 1251 752 95 1015 1115 1150 240 1478 167 40 1282 988 948 24 850 198