Multiplexer Calibration

A Multiplexer is a combinational circuit that accepts multiple data inputs or signals and provides a single output. Because of its ability to select one signal out of many inputs, a Multiplexer is also called a Many-to-one circuit. It is often denoted as “MUX” in logic boards as an abbreviation.

With the advancements in Automation, IoT, and multiple sensor-driven electronics, data from complex devices must be sorted and transmitted at a higher speed on a single shared medium or device. The combined signal should then be processed to pinpoint and select the data as required by the application. Thanks to MUX, the industry can now take any number of inputs and select lines based on pre-set codes. Because of its ability to accept analog and digital signals, and its fast digital signal switching capability, MUX is recognized as a crucial component within the communication system, with applications ranging from signal routing, data communications, and data bus control.


Design of Multiplexers:

A MUX functions as a multiple-input, single-output switch and can be designed with various inputs-output configurations according to the application. To select and control the input lines (at a pre-set time or condition), MUX contains the “Selection” line(s). Selection lines are fed with the controlling code as Binary input to select a particular input line. The output will be one of the inputs given to MUX, as decided by selection lines.

The design of a MUX with the number of input and selection lines should follow the equation . M indicates the number of selection lines, and N indicates the number of input lines or channels. For example, if a communication system has four inputs and a single output configuration, four-to-one (4:1) MUX can be selected. Similarly, a multiplexer with an 8:2 configuration can be selected for an eight-channel input and two-channel output. However, the selection should follow the equation mentioned above.

Due to its ability to select a defined input signal at a preset time or code controls. Within a MUX, several input signals share a single transmission conductor, often a copper wire or fiber optic cable, and the conversion is from Parallel to Serial. A Demultiplexer has an opposite function and converts signals from Serial to Parallel. Modern MUXs can also be integrated with Demultiplexers. The advantage is that only one serial data line will be required instead of multiple parallel data lines. With DeMUX, multiplexers are sometimes called “data selectors” as they select the data to the line.


MUX – Types and Operational Principle:

For any transmission channel, based on its application and use, there are two ways a signal bandwidth can be used – either by dividing the available bandwidth into wavelength or frequency spectrums or allocating all the available bandwidth to each channel for a fixed discrete period. Broady, these two techniques are grouped as Analog and Digital, as explained in Figure 1.

Figure1: Multiplexer Types

Frequency Division Multiplexing (FDM): Uses various frequencies to combine data streams over a MUX or a medium for communication purposes. Example of FDM: Television Transmitters.

Wavelength Division Multiplexing (WDM): An equivalent of FDM optical, WDM is an analog multiplexing technique mixing input signals of various frequencies through light signals and transmitted across to the receiver. Example of WDM: SONET or Synchronous optical networks.

Time Division Multiplexing (TDM): TDM is a method of transmitting and receiving signals over a common signal path using synchronized switches at the ends of transmission lines. Digital telephony is a typical application of the TDM multiplexing technique.


Multiplexer (MUX) Maintenance – Why is it essential:

Due to continual progress in lowering supply voltage, incorporating fault-protected inputs, clamping the output voltage, and reducing the switch resistances, Multiplexers have gained popularity and are proliferating. The latest of these advances is the inclusion of precision resistors to allow two-point calibration of gain and offset in precision data-acquisition systems. MUXes have thus gained prominence and are widely adopted as a piece of critical equipment in communication systems. And it is equally important to maintain the condition of MUX by calibrations and condition monitoring.


Need for Multiplexer (MUX) Calibration:

Industrial standards and MUX calibration procedures have laid out parameters sensitivity and acceptance criteria as follows:


  1. VSWR (Voltage Standing Wave Ratio): It is a measure of that signal reflection and is measured as the ratio of maximum to minimum amplitude in the resulting interference wave, as shown in the following formula: (1+)/(1+), where p is the reflection coefficient. For a standard MUX, VSWR should be less than or equal to 1.8.
  2. Insertion loss: Usually measured by dB, it is the total optical power loss caused by the insertion of optical components. Insertion loss should be measured for each channel using the multiplexer control box. For a working MUX, Insertion loss should be less than or equal to 2dBm.
  3. Delta value: Delta is the difference of insertion loss between the ports, and for each pass, for an accurate MUX, the delta should be less than or equal to 0.5dBm.
  4. Isolation value: The isolation value for a MUX should be less than or equal to 57dBm.


Though multiplexer (MUX) usage seems straightforward, the equipment needs to be calibrated and maintained following OEM operation guidelines. To comply with international standards, an annual calibration process should support the repeatability and accuracy of Multiplexers.


e2b calibration offers industry-leading ISO-certified multiplexer calibration services. Our labs are ISO/IEC 17025 accredited and operated by a team of qualified calibration experts to test and calibrate your multiplexers. Our verifiable services are unmatched in the industry. We are registered with ANAB. We are also ANSI/NCSL Z540-1-1994 certified. We have the NIST Traceable Wide scope of ISO/IEC 17025 accreditation. Contact e2b calibration for all your equipment calibration needs.



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