Multiplexer And Demultiplexer Theory Pdf

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multiplexer and demultiplexer theory pdf

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The major factor that differentiates multiplexer and demultiplexer is their ability to accept multiple input and single input respectively. The multiplexer also known as a MUX operates on several inputs but provide a single output.

In electronics , a multiplexer or mux ; spelled sometimes as multiplexor , also known as a data selector , is a device that selects between several analog or digital input signals and forwards the selected input to a single output line. A multiplexer makes it possible for several input signals to share one device or resource, for example, one analog-to-digital converter or one communications transmission medium , instead of having one device per input signal. Multiplexers can also be used to implement Boolean functions of multiple variables. Conversely, a demultiplexer or demux is a device taking a single input and selecting signals of the output of the compatible mux , which is connected to the single input, and a shared selection line. A multiplexer is often used with a complementary demultiplexer on the receiving end.

Frequency-division multiplexer and demultiplexer for terahertz wireless links

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The development of components for terahertz wireless communications networks has become an active and growing research field. However, in most cases these components have been studied using a continuous or broadband-pulsed terahertz source, not using a modulated data stream. This limitation may mask important aspects of the performance of the device in a realistic system configuration. We report the characterization of one such device, a frequency multiplexer, using modulated data at rates up to 10 gigabits per second.

We observe that the far-field spatial variation of the bit error rate is different from that of the emitted power, due to a small nonuniformity in the angular detection sensitivity. This is likely to be a common feature of any terahertz communication system in which signals propagate as diffracting beams not omnidirectional broadcasts.

The volume of wireless data traffic is increasing exponentially and will surpass 24 exabytes per month by 1 To accommodate this trend, future generations of wireless networks will require much higher capacity for data throughput. Recent years have witnessed rapidly growing interest in the development of components to enable wireless communications in the terahertz THz range.

One of the earliest examples is modulators, first discussed almost 20 years ago 6 , with rapid improvements continuing to be reported 7 , 8 , 9 , Despite these efforts, many important components of such networks remain at a very immature stage of development, including components for mux and demux. In the THz range, where frequency bands may not be continuous over a broad spectral range due to atmospheric attenuation 24 or regulatory restrictions 25 , frequency-division multiplexing is even more of a compelling need.

This concept exploits the highly directional nature of THz signals, which are much more like beams than omnidirectional broadcasts. A particular client in a network would be assigned a spectral band based on its location, such that only signals within that spectral band are sent to the location of the particular client. The device can accommodate mobility by tuning the carrier frequency to account for changes in the client location; this process would likely rely on beam-sounding techniques using legacy bands at lower frequencies The operating principle of the leaky-wave device is straightforward.

It is based on a metal parallel-plate waveguide PPWG , which has proven to be a versatile platform for manipulation of THz signals 27 , The waveguide has a narrow slot opened in one of the metal plates, which in the demux configuration allows some of the guided wave to leak out into free space.

Similar leaky-wave designs have been used in the RF community for many years 29 , but their use in the THz range has so far been limited 21 , 30 , The frequency of the emitted radiation at a given angle is determined by a phase-matching constraint:.

Substituting Eq. For an incoming wave, the situation is simply reversed; an incident wave at a given frequency only couples into the waveguide if it arrives at the appropriate angle determined by Eq. Thus, the design supports both mux and demux capabilities. Characterization of the performance of these devices in the context of a communication system, using data modulated at high bit rate, has for the most part not been demonstrated, and little consideration has yet been given to the enormous challenge of integration into a larger system.

Meanwhile, there have also been several recent single-input single-output SISO THz link demonstrations 3 , 23 , 32 , 33 , 34 , 35 , which have achieved impressive data rates but have so far not progressed to the integration of any of the aforementioned signal processing components. We use modulated data to characterize bit error rates and power penalties for this subsystem, as a function of data rate and source power.

The numerical simulation in Fig. This suggests that a detector with sufficient aperture to collect most of the carrier wave will also capture the modulation information required for signal transmission.

However, our experimental results, described below, reveal a surprising sensitivity of the signal quality to the angular position of the receiver, resulting from a small angular nonuniformity in the detection sensitivity. Demultiplexing of modulated THz channels for different data rates.

The horizontal plane shows the intensity in a plane centered between the metal plates i. The vertical out of plane arc shows the radiated power as a function of angle.

The solid green line indicates the angle predicted by Eq. The angular spread of these sidebands is smaller than the angular width of the carrier wave diffracting through the slot. Both are normalized to unity and plotted on a log scale BER plotted as the negative log , to facilitate comparison of the angular widths. Here, the plate separation b is 0.

Results for several different data rates all show the same optimum angle of In this plot, the colors correspond to the same data rates as in c.

We first explore the performance of the device in the demux configuration, with a single data-modulated input wave. We generate the THz signal by photomixing two infrared optical signals modulated using an optical modulator, resulting in a an amplitude-modulated signal amplitude shift keying, ASK with a carrier frequency determined by the optical frequency difference. The input aperture of the waveguide is tapered to improve the input coupling efficiency The collection and detection system is mounted on a rotation arm, to characterize the output as a function of the angular position of the receiver.

After electrical amplification, the bit error rate BER is determined in real-time, i. This figure demonstrates several important results. This is consistent with previous work demonstrating the low-loss and low-dispersion characteristics of TE 1 mode propagation in parallel-plate waveguides 27 , We also note that the optimum BER and maximum power are always obtained at the same angle, regardless of the modulation rate.

This is not surprising, as the angle is determined by the carrier frequency and the plate separation, according to Eq. The most surprising aspect of Fig. This is considerably smaller than the measured angular width of the power distribution as shown clearly in Fig. Moreover, at a given BER, the widths of the curves in Fig.

This strong and anomalous angular dependence suggests that the BER is significantly influenced by the angular sensitivity of the detection of modulation sidebands, which co-propagate with the carrier frequency at slightly different angles, as shown in Fig. Using a simple model for the angular filtering of the receiver, we can qualitatively understand both the observed angular widths and the data-rate dependence shown in Fig.

We imagine that, regardless of the details of the detection system, its sensitivity when it is located at a particular angular location is a slowly varying function of the propagation angle of the THz signal, with a maximum sensitivity when the beam propagation angle is equal to the detector angle so that the beam hits the center of the detector.

If the detector is moved so that it is not centered on the diffracting beam i. Even if this spectral asymmetry is small, it will lead to a decrease in the overall signal-to-noise of the detection, and thus a degrading of the BER. We note that this effect will not impact the detection of the overall signal power, which explains why the angular width of the power curve is significantly larger than that of the BER curve in Fig. Modulation at a higher data rate produces sidebands that are more widely spaced in frequency and therefore also in angle.

These are more sensitive to the angular filtering as they sample the filter at larger angles away from the optimal central angle. Thus, the angular degradation of the BER is more rapid at higher modulation rates, consistent with our observations. Given the highly directional nature of THz signals, this angular sensitivity is likely to be a quite general feature of any THz wireless network in which frequency multiplexing is used and in which beam widths are diffraction-limited.

Another important parameter is the insertion loss, which induces a power penalty for error-free operation. To explore this issue, we compare the measured BER values for demuxed signals at the optimal receiver angular location to those measured without demux; in that latter case the detector is placed directly at the location of the demux input port, bypassing the demux waveguide entirely.

This result, shown in Fig. This penalty is probably due almost entirely to the efficiency of the coupling into and out of the waveguide, and not to propagation losses or dispersion inside the waveguide, which are known to be small Demultiplexing of modulated THz channels as a function of detected power.

Before demultiplexing, all the curves have about the same slope. The waveguide is at the bottom left , where the red arrow indicates the propagation direction for the guided wave.

Interference fringes are clearly evident due to interference between the bit emerging from the far end of the waveguide and the previous bit, which radiated through the slot. We speculate that this increased noise arises from signals emerging from the far end of the waveguide rather than from the slot, as intended. The impedance mismatch to free space is not large 39 , so most of the remaining power is emitted into air, and then can scatter from this abrupt waveguide termination to cause interference at the detector.

Such scattered signals are delayed by their extra travel time inside the waveguide. If this delay exceeds the duration of a single bit, then this coherent interference can leak over into the subsequent bit, thus degrading the eye diagram.

Therefore, one could expect a higher BER for signals with data-modulation rate larger than a certain threshold value determined by the inverse of the extra travel time of the scattered interference signal. This idea is supported by the numerical time-domain simulation shown in Fig. This simulation is somewhat limited in accuracy as it is only a 2D simulation; nevertheless one can clearly see the fringes due to ISI between a bit emerging from the slot and one emerging from the end of the waveguide.

To demonstrate the real-time mux and demux operation, we use two independent transmitters as shown in the schematic in Fig. In this case, one channel is the photomixer-based THz source described above, and the other one is a frequency multiplication chain. These two signals with carrier frequencies of We use one of the slots to couple two different signals into the waveguide mux , and the other slot to couple them out demux. The input angles of the two signals into the first slot are adjusted according to the criterion of Eq.

At the output, the receiver is rotated through a range of angles to characterize the angular distribution of the output, as in Fig. We measure both the power Fig. In other words, we achieve error-free mux and demux for each channel, whether or not the other channel is simultaneously propagating in the waveguide. The small changes in each BER curve when the other channel is present can be understood by noting the small overlap between the two demuxed beams as show in Fig.

Nevertheless, it is clear that error-free mux-demux can be achieved for both channels. We further demonstrate this remarkable result by modulating the two channels using real video data from two different television broadcasts. When the receiver is rotated from one optimum angular position to another, the received video shown on the monitor switches from one channel Fig. Power pattern and BER performance for both real-time links at Error-free operation can be achieved in both channels even with both signals on.

In the monitor connected to the detector, the channel switches when the angular position of the receiver changes. Finally, we explore the efficacy of higher order modulation schemes, which can provide increased data rates while using less spectral bandwidth.

For this measurement, the photomixer THz source is driven by an optical signal modulated using quadrature phase shift keying QPSK at To preserve the phase information contained in the QPSK signal, we detect the signals using a sub-harmonic mixer. The down-converted signals are analyzed to recover the constellation diagrams and BER performance for both channels. The degraded BER relative to the results shown in Fig.

Novel Quaternary Quantum Decoder, Multiplexer and Demultiplexer Circuits

In large scale digital systems, a single line is required to carry on two or more digital signals — and of course! But, what is required is a device that will allow us to select; and, the signal we wish to place on a common line, such a circuit is referred to as a multiplexer. The function of a demultiplexer is to inverse the function of the multiplexer. The shortcut forms of the multiplexer and demultiplexers are mux and demux. Some multiplexers perform both multiplexing and demultiplexing operations.

multiplexer and demultiplexer pdf

A Multiplexer is a device that allows one of several analog or digital input signals which are to be selected and transmits the input that is selected into a single medium. Multiplexer is also known as Data Selector. A multiplexer of 2n inputs has n select lines that will be used to select input line to send to the output. Multiplexer is abbreviated as Mux. MUX sends digital or analog signals at higher speed on a single line in one shared device.

Thank you for visiting nature. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser or turn off compatibility mode in Internet Explorer. In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript. The development of components for terahertz wireless communications networks has become an active and growing research field.

Carlos H. Silva-Santos 1. Vitaly F. Hugo E. Directional couplers DC are devices composed by two parallel dielectric waveguides, where the optical power transfers from one guide to another guide [ 1 ].

Multiplexer and Demultiplexer : Types and Their Differences

multiplexer and demultiplexer pdf

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Applications of demultiplexers. 5 Summary. Learning objectives. 1. Get familiar with principles of Multiplexing and Demultiplexing. 2. Study the logic diagram.


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5 Comments

  1. Constance L. 30.01.2021 at 12:28

    In a demux, we have n output lines, one input line, and m select lines.

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  5. Lcomcesupy 07.02.2021 at 04:58

    Multiplexer and Demultiplexer. A multiplexer is a circuit that accept many input but give only one output. A demultiplexer function exactly in the reverse of a.