The amplitude of each pulse is directly proportional to instantaneous modulating signal amplitude at the time of pulse occurrence and then keeps the. No information is lost, but the energy is redistributed in the frequency domain. Sampling theorem and pulse amplitude modulation pam reference stremler, communication systems, chapter 3. Figure 36 spectrum of a pam waveform with flattop sampling. Pulseamplitude modulation pam, is a form of signal modulation where the message information is encoded in the amplitude of a series of signal pulses. Flattop sampling is the process in which, the sampled signal can be represented in pulses for which the amplitude of the signal cannot be changed with respect to the analog signal, to be sampled. Flat top sampling or pam pulse amplitude modulation 1. Pam pulse amplitude modulated modulation ve demodulation. It is a modulation system in which the signal is sampled at regular intervals and each sample is made proportional to the amplitude of the signal at the instant of sampling. Depth of amplitude modulation m when you have completed the previous work you will be displaying a picture like that of e in table 1. Study on performance analysis of pulse code modulation pcm. In pam the amplitude of the message or modulating signal is mapped to a series of pulses with two possible variant. The output of the modulator is provided to the pulse reshaping circuit.
As the amplitude of message is reduced then the depth of modulation is reduced. User manual for pulse amplitude modulation and demodulation. An example of a ir uwb carrier is a gaussian monopulse, shown in fig. It is based on creating a sequence of short pulses, modulated by pulse amplitude modulation pam or pulse position modulation ppm. The flattop pam signal is shown in the following figure. Thus the amplitude of the pulse after sampling is kept constant and the top of the sampled pulse do not follow the contour of the modulating signal unlike natural sampling.
The pam method is not normally used for direct signal transmission. Comparing the reconstructed output of 2 nd order low pass butterworth filter for all three types of sampling, it is observed that the output of the sample and hold is the better when compared to the outputs of natural sampling and the flat top sampling. To convert an audio signal 020khz to digital form, the minimum sampling frequency is 40khz. Pulse amplitude modulation pam, is a form of signal modulation where the message information is encoded in the amplitude of a series of signal pulses. There are two types of sampling techniques for transmitting a signal using pam. In analog pulse modulation some parameter of each pulse is modulated. Sampling theorem determines the necessary conditions which allow us to change an analog signal to a discrete one. Thus, x pam t consists of narrow pulses with the amplitudes of the signal within the pulse width for narrow pulses, the pulse amplitude can be approximated by the signal amplitude at the sampling timethis is called flattop pam.
Analog communication pulse modulation tutorialspoint. Pulse amplitude modulation pam is a type of pulse modulation in which the signal is sampled at regular intervals, with each sample proportional to the amplitude of the signal at the time of sampling. Pulse amplitude modulation pulse code modulation sampling. The proposed alloptical quantization and coding scheme, combined with existing alloptical sampling techniques, will enable ultrafast ad conversion at operating speed of hundreds of gss with at. The key pulse takes on the current sampling instant to the amplitude value of the information. The following safety and common symbols may be used in this manual and on the equipment. Pulse amplitude demodulation september 4, 20 by ashutosh bhatt 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. Sampled uniformly and then timedivision multiplexed are 24 voice signals.
Which is better flat top or natural top pulse amplitude. This process is known as pulse amplitude modulation pam. Flattop sampling time domain appearance of a pam signal. Pulse amplitude modulation an overview sciencedirect. The flattop pam means the instantaneous sampling, i. It is an important precursor for the production of other types of pulse modulation, such as pulse code pcm pulse duration pdm and pulse phases ppm modulation. It is an analog pulse modulation scheme in which the amplitudes of a train of carrier pulses are varied according to the sample value of the message signal. Introduction to pulse amplitude modulation pam sample and hold, flat top sampling. Natural a pulse of short width with varying amplitude.
Flat top sampling pam a sampleandhold circuit is used in conjunction with the chopper to hold the amplitude of each pulse at a constant level during the sampling time 23 flattop sampling generation of pam signals. Flat top sampling is the process in which sampled signal can be represented in pulses for which the amplitude of the signal cannot be changed with respect to the analog signal, to be sampled. Sampler extract samples of a continuous signal, it is a subsystem ideal sampler produces samples which are equivalent to the instantaneous value of the continuous signal at the specified various points. The flat top pam means the instantaneous sampling, i. Producing pulse amplitude modulation via sampling consider what happens when we sample a signal s t with a pulse train c n s t q t nt rather than a function. During transmission, noise is introduced at top of the transmission pulse which can be easily removed if the pulse is in the form of flat top. Sinusoidal amplitude modulation amplitude demodulation. For fm, the maximum frequency deviation occurs at peak values of mt.
In flat top sampling, the amplitude of the samples remain constant at an instant of time unlike in natural sampling where the amplitude of the samples vary in accordance with the amplitude of the input signal that is to be sampled. Analog communicationpulse amplitude modulation and demodulation trainer is proposed to user friendly to process the experiments and the trainer had all internal features like message signal, carrier signal, power supply etc. Natural sampling s s f d f null at 3 pam and pcm pam pulse amplitude modulation. Discuss advantages and disadvantages of pam using natural and flat top sampling. The amplitude of each pulse is directly proportional to instantaneous modulating signal amplitude at the time of pulse occurrence and then keeps the amplitude of the. Communication theory flattop sampling easy to implement using sample and hold operation. Pulse amplitude modulation pam in pulse amplitude modulation, a pulse is generated with an amplitude corresponding to that of the modulating waveform.
Principles of communication systems 20022003 10 chapter 7. The sampled pulses can be achieved either by natural or flat top sampling. The sampling process generates flat top pulse amplitude modulated pam signal. Pulse amplitude modulation pam is one of several forms of single modulation in which data is transmitted through varying the amplitude of the pulses in regular timed sequence of electrical or electromagnetic pulses. This is described as a 100% amplitude modulated signal.
Amplitude modulation definition, types, solved examples. Communication is a process by which information is exchanged between. Amplitude modulation this experiment examines the characteristics of the amplitude modulation am process. The sampling operation involved flattop samples with 1. Fig 3 flat top sampling as shown in fig 3, the output obtained after sampling an analog signal is a pulse amplitude modulated signal. The following figures explain the pulse amplitude modulation. Sampling with sample and hold d1 91 flat top sampling takes a slice of the waveform, but cuts off the top of the slice horizontally. They are particularly easy to implement if the channel is assumed to be flat, so. Flattop sampling sample and hold, like natural but with single amplitude value. However, it is the first step in another very popular conversion method called pulse code modulation. Mcnames portland state university ece 223 communications ver. Theory and application of pulse amplitude modulated.
Hence, it is called as flat top sampling or practical sampling. Study of pulse amplitude modulation experiment no 04. In this video, i have explained flat top sampling or pam pulse amplitude modulation by following outlines. The top of the slice does not preserve the shape of the waveform. The flat top pam signal is shown in the following figure. Using the circuit from part 3, connect the oscilloscope as shown in figure 4. Pulse modulation of two types analog pulse modulation pulse amplitude modulation pam. Properties of joint cumulative distribution function. The amplitude of the signal cannot be changed with respect to the analog signal to be sampled. Principles of communication part i professor aditya k. Pulse modulation timedivision multiplex tdm continued time multiplexing of two pam signals graphic interpretation assume all input signals are lowpass and bandlimited to. In flat top sampling, the top of the samples remains constant and equal to the instantaneous value of the modulating signal at the start of the sampling. There are two types of pam sampling natural sampling gating flattop or sampleandhold.
The amplitude of each pulse is directly proportional to instantaneous modulating signal amplitude at the time of pulse occurrence and then keeps the amplitude of the pulse for the rest of the half cycle. A sample symbol sequence and corresponding continuoustime signal are also. Additional info pulse wave modulation pam, pwm, ppm do not convert baseband msg signal to bandpass, whereas continuos wave modulation am, fm, pm converts baseband into bandpass msg signal. Flattop sampling is the process in which, the sampled signal can be. Overmodulated am signals and its requirement for coherent detection are also considered. The pulse may take any real voltage value that is proportional to the value of the original waveform. The top of the slice does not preserve the shape of the. Natural sampling is a practical method of sampling in which pulse have finite width equal to sampling is done in accordance with the carrier signal which is digital in nature.
Oct 22, 2017 pam pulse amplitude modulated modulation ve demodulation sample and hold flat top mode hacettepe university ee telecommunication lab. Pulse amplitude modulation signal there are two types of sampling techniques for transmitting messages using pulse amplitude modulation, they are flat top pam. Pulse amplitude modulation pam, quadrature amplitude modulation qam 12. Two possible outcomes natural sampling and flattop sampling. Sampling techniques communication engineering notes in. The sampling takes place at rising edge of carrier signal, so the solution is quite straightforward. Their are basically three types of sampling techniques, namely. Two possible outcomes natural sampling and flat top sampling. The process is referred to as pulse amplitude modulation pam. Pulse amplitude modulation using flat top sampling.
For the baseband digital transmission, pulse amplitude modulation pam is the most efficient in terms of power and bandwidth utilization. In practice, sampling frequency for encoding music into cd is 44. Flat top sampling is the process in which, the sampled signal can be. Pulse amplitude modulation natural and flattop sampling. Sampling theorem and pulse amplitude modulation pam. Flat top sampling or pam pulse amplitude modulation in. The amplitude of each pulse is directly proportional to modulating signal amplitude at the time of pulse occurrence. Flat top sampling takes a slice of the waveform but cuts off the top of the slice horizontally. Multiple choice questions and answers on analog communication.
Set the amplitude of the carrier signal generator output voltage to 2 vpp, and the frequency to 100 khz, and set the amplitude of the em generator to 6 vpp. Pulse amplitude modulation pam theory of and its applications. In cw modulation schemes some parameter of modulated wave varies continuously with message. The modulator generates a pulse amplitude modulated signal. Aug 05, 2018 in this video, i have explained flat top sampling or pam pulse amplitude modulation by following outlines. Though the pam signal is passed through a lpf, it cannot recover the signal without distortion. In the case of analog pulse amplitude modulation signals, the number of pulse amplitudes can be infinite. It is often called as am and is commonly used in transmitting a piece of information through a radio carrier wave. Pulse amplitude modulated pam fluorometry provides one of the most versatile techniques for monitoring and assessing zooxanthellae health, as it can measure the photophysiological state of zooxanthellae in a non. Flat top sampling makes use of sample and hold circuit.
Pulse amplitude modulation has some applications, but it is not used by itself in data communication. This basically shapes the pulses so that it can be easily detected at the receiver. In this article, you will find the study notes on types of modulation and demodulation which will cover the topics such as introduction to communication systems, amplitude and demodulation, classification of am, angle modulation and demodulation, generation of fm and pulse modulation. Pam pulse amplitude modulated modulation ve demodulation sample and hold flat top mode hacettepe university ee telecommunication lab. Sampling and reconstruction ee 442 spring semester 1 lecture 8 ideal sampling flattop sampling natural sampling reading. Sampling frequency 2b, where b is the maximum frequency of the message signal nyquist rate minimum sampling frequency 2b samplesec nyquist interval 1 2b sec types of sampling there are three sampling types available, these are a ideal sampling b natural sampling c flat top sampling. Pam is the simplest of all pulse modulation technique.
Jul 10, 20 pulse amplitude modulation pam in pulse amplitude modulation, a pulse is generated with an amplitude corresponding to that of the modulating waveform. For the generation of a pam signal we use a flat top type pam scheme because during the transmission,the noise is interfered at top of the transmission. The demodulation is performed by an envelope detector. In analog pulse modulation some parameter of each pulse is modulated by a particular sample value of the message. What is the difference between pulseamplitude modulation. Flattop sampling is the process in which sampled signal can be represented in pulses for which the amplitude of the signal cannot be changed with respect to the analog signal, to be sampled. Pulse amplitude modulation is a technique in which the amplitude of each pulse is controlled by the instantaneous amplitude of the modulation signal. Flat top sampling or pam pulse amplitude modulation in digital communication by engineering funda duration. Amplitude modulation is a process by which the wave signal is transmitted by modulating the amplitude of the signal. Flat top uses sample and hold, like natural but with single. A brief discussion about pulse code modulation and demodulation. The input sequence b k consists of binary digits bits 1 and 0 with a bit duration of t b and a bit rate of r b 1 t b.