The digital multiplexer is a logical combined device that is designed for the controlled transmission of information from several data sources to the output channel. In fact, this device consists of several digital position switches. It turns out that the digital multiplexer is a switch of input signals to one output line.
This device has three groups of inputs:
- address, binary code on which determines which information input must be connected to the output;
- informational;
- permissive (gating).
In the manufactured integrated circuits, the digital multiplexer has a maximum of 16 information inputs. If the designed device requires more, in this case the structure of the so-called multiplexer tree is built from several microcircuits.
A digital multiplexer can be used to synthesize almost any logic device, which significantly reduces the number of logic elements used in circuits.
Rules for the synthesis of devices based on multiplexers:
- Carnot map is built for the output function (according to the values of variable functions);
- the order of use in the multiplexer circuit is selected;
- a masking matrix is built, which should correspond to the order of the multiplexer used;
- it is necessary to superimpose the resulting matrix on the Carnot map;
- after that, the function is minimized separately for each area of the matrix;
- based on the results of minimization, it is necessary to construct a scheme.
Now let's move on from theory to practice. Consider where such devices are used.
Flexible multiplexers are designed for the formation of digital streams (primary) with a speed of 2048 kbit / s from analog signals (speech), as well as data of digital interfaces for cross-switching electronic channels with a speed of 64 kbit / s, transmission of a digital stream over IP / Ethernet and for conversion linear signaling and physical joints.
Using such a device, you can connect up to 60 (in some models this figure may be more) analog terminations in 1 or 2 E1 streams or 128 subscriber sets for four E1 streams. Typically, the analog lines are PM lines with in-band signaling, or the signaling is implemented on a separate channel. Voice channel data can be compressed up to 32 or 16 kbit / s per channel, for this, ADPCM encoding is used.
Flexible multiplexers allow you to use broadcast connections, that is, to send signals from one of the digital or analog channels to several others. Often used to deliver broadcasting programs simultaneously to several different points.
Optical multiplexers are devices designed to work with data streams using light beams, which differ in amplitude or phase diffraction grating, as well as wavelength. The advantages of such devices include resistance to external influences, technical safety, protection against hacking of transmitted information.