As the figure shows, each channel occupies a different 5-kHz portion from the total combined bandwidth that is equal to 20kHz. The bandwidth of 10kHz is the output of the balanced modulator in a double-sideband suppressed-carrier waveform. The double sideband waveform is converted to a single sideband signal when it passes through a bandpass filter BPF.
In Channel 1, signals amplitude modulates a kHz carrier in a balanced modulator that suppresses the kHz carrier. In Channel 2, signal amplitude modulates a kHz carrier in the balanced modulator.
This produces a double sideband signal, which is then converted to a single-sideband every time it passes through a bandpass filter tuned to give only the upper sideband. It is partly similar to FDM. It sends information signals that initially occupied the same band frequencies through the same fiber at the same time without interference. It is a cooperation of two or more discrete wavelengths into and out of an optical fiber. In WDM, the wavelength spectrum that is used is in the region or mm.
These are the two wavelength bands at which the optical fibers have the least amount of signal loss. It allows many optical signals to be transmitted simultaneously using a single fiber cable. In the above figure, the propagation of each channel takes place in the same transmission medium at the same time. However, each channel occupies a different wavelength, and each wavelength takes a different transmission path.
TDM is very much different from WDM since the transmissions from multiple sources happen in the same facility but not at the same time.
It allows the transfer of two or more streaming digital signals in a common channel. TDM is also known as digital circuit-switched. All the incoming signals are divided into equal fixed-length time slots and then transmitted over a shared medium and reassembled in its original form after de-multiplexing. As an input, the combination of selection inputs is giving to the AND gate with the corresponding input data lines. In a similar fashion, all the AND gates are given connection.
And, finally, by using OR gates, all the AND gates are added; and, this will be equal to the selected value. Multiplexers are used in various applications wherein multiple-data need to be transmitted by using a single line. A communication system has both a communication network and a transmission system.
By using a multiplexer, the efficiency of the communication system can be increased by allowing the transmission of data, such as audio and video data from different channels through single lines or cables. Multiplexers are used in computer memory to maintain a huge amount of memory in the computers, and also to reduce the number of copper lines required to connect the memory to other parts of the computer.
In telephone networks, multiple audio signals are integrated on a single line of transmission with the help of a multiplexer. The multiplexer is used to transmit the data signals from the computer system of a spacecraft or a satellite to the ground system by using a GSM satellite.
De-multiplexer is also a device with one input and multiple output lines. It is used to send a signal to one of the many devices. The main difference between a multiplexer and a de-multiplexer is that a multiplexer takes two or more signals and encodes them on a wire, whereas a de-multiplexer does reverse to what the multiplexer does. The 1-to-4 demultiplexer comprises 1- input bit, 4-output bits, and control bits. The 1X4 demultiplexer circuit diagram is shown below.
If the data bit D is low, the output Y1 is low. IF data bit D is high, the output Y1 is high. The value of the output Y1 depends upon the value of data bit D, the remaining outputs are in a low state. The best example of 1X4 demultiplexer is IC The demultiplexer is also called a data distributor as it requires one input, 3 selected lines, and 8 outputs.
De-multiplexer takes one single input data line and then switches it to any one of the output lines. The 1-to-8 demultiplexer circuit diagram is shown below; it uses 8 AND gates for achieving the operation.
The input bit is considered as data D and it is transmitted to the output lines. This depends on the control input value of the AB. If D is low, the F1 is low, and if D is high, the F1 is high.
So the value of the F1 depends on the value of D, and the remaining outputs are in the low state. Demultiplexers are used to connect a single source to multiple destinations. These applications include the following:. Similarly you can calculate for any higher order Multiplexers. Now, for example let us try to implement a Multiplexer using a Multiplexer.
To achieve the first two MUX is connected in parallel and then the output of those two are feeded as input to the 3 rd MUX as shown below. Thus finally we get a multiplexer with four inputs W0, W1, W2 and W3 and only one output f. The truth table for a Multiplexer is shown below. As you can see in the table above, for each set of value provided to the Control signal pins S0 and S1 we get a different Output from the input pins on our output pin. This way we can use the MUX to select one among the available four input pins to work with.
Normally these Control pins S0 and S1 will be controlled automatically using a digital circuit. There are certain dedicated IC which can act as MUX and make the job easy for us, so let us take a look at them.
It is always interesting to build and verify things practically, such that the theory we learn would make more sense. So let us build a Multiplexer circuit and check how it works. The MCB pinout is shown below. Here the pins X0, X1, X2 and X3 are the four input pins and the pin X is its corresponding output pin. The control pins A and B are used to select the required input to the output pin. The Vee pin is for enable which is an active low pin so we have to ground it to enable this IC.
The MC is an Analog Multiplexer meaning the input pins can also be supplied with variable voltage and the same can be obtained though the output pins. The below GIF image shows how the IC outputs variable input voltage based in the control signals provided.
The input pins has the voltage 1. We can also assemble this circuit over a breadboard and check if they are working. To do that I have used two push buttons are inputs for the control pins A and B. And used a series of potential divider combinations to provide variable voltages for the pins 12, 14, 15 and The output pin 13 is connected to an LED. The variable voltages supplied to the LED will make it to vary the brightness based on the control signals.
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