A multiplexor is a device that has several signal inputs, one or more control inputs and one output. The multiplexer allows you to transmit a signal from one of the inputs to the output; in this case, the selection of the desired input is carried out by applying the appropriate combination of control signals.
Analog and digital [1] [2] multiplexers vary significantly in operation. The first electrically connect the selected input to the output (while the resistance between them is small - of the order of hundreds or tens of ohms ). The latter do not form a direct electrical connection between the selected input and output, but only “copy” the logical level ('0' or '1') from the selected input to the output. Analog multiplexers are sometimes called keys [3] or switches.
A device opposite the multiplexer in its function is called a demultiplexer . In the case of using analog multiplexers (using keys on field-effect transistors), there is no difference between the multiplexer and the demultiplexer; such devices may be called switches.
Content
Device
Schematically, the multiplexer can be depicted as a switch, providing the connection of one of several inputs (they are called information ) to one output of the device. The switch is serviced by a control circuit in which there are address inputs and, as a rule, enable ( gate ).
The signals at the address inputs determine which specific information channel is connected to the output. If between the number of information inputs and the number of address inputs valid ratio , then such a multiplexer is called complete. If a , then the multiplexer is called incomplete.
The enable inputs are used to expand the functionality of the multiplexer. They are used to increase the capacity of the multiplexer, synchronize its operation with the work of other nodes. The signals at the enable inputs may enable, or may prohibit the connection of a specific input to the output, that is, they may block the operation of the entire device.
As a control circuit , a decoder is usually used. In digital multiplexers, the logic elements of a switch and a decoder are usually combined.
Generalized Multiplexer Circuit
The input logical signals X i go to the inputs of the internal switch and are transferred to the output Y through the switch. At the input of the control circuit, the word address signals A k (from the English Address ) is fed. The multiplexer can also have an additional control input E (from Eng. Enable ), sometimes this input is indicated on CS circuits (from Eng. Chip Select - “chip selection”), which allows or prohibits the passage of the input signal to output Y. The logical level of the enable signal in different specific models of multiplexers can be either logical 1 or logical 0, but in the overwhelming number of types of multiplexers produced by industry, the enable signal is logical 0. In different types of multiplexers with a forbidden state of transmission at input E , output Y may have a state 0 or 1.
In addition, some multiplexers have an output that can take three states: two logical states 0 and 1, and the third state is a disabled output ( high-impedance state , it is often said, Z- state - output resistance is large, the output internal logic gate is disconnected from the output by a special internal key). This technical solution facilitates the increase in the number of input signals of the multiplexer by cascading several multiplexer microcircuits, while the outputs of the microcircuits are simply electrically connected. The multiplexer is transferred to the third state by applying to the input OE (from the English Output Enable ) a logical 1, often a logical 0 - again depends on the model of a particular multiplexer.
Usage
Multiplexers can be used in frequency dividers , trigger devices, shifting devices, etc. Multiplexers can be used to convert parallel binary code to serial. For such a conversion, it is enough to submit a parallel binary code to the information inputs of the multiplexer, and to send signals to the address inputs in such a way that the inputs are connected to the output, starting from the first and ending with the last.
Designation
Multiplexers are designated by the combination of MUX (from the English multiplexer ), as well as MS (from the English multiplexer selector ).
See also
- Demultiplexer
Notes
- ↑ Basics of Digital Electronics, 2.6. Multiplexers (inaccessible link) . Archived on May 6, 2009.
- ↑ 2. Combination circuits, 2.5 Multiplexer
- ↑ 2.4.2. Keys and multiplexers (inaccessible link) . Date of treatment June 19, 2009. Archived October 20, 2008.