The combinational logic circuits are used in networking and telecommunication systems as it has n number of inputs and outputs. It does not have any memory, and hence the output of the circuit depends on the present input state and does not get affected by the previous input state. Decoder and Demultiplexer are the types of combinational logic circuits whose difference as follows.
Decoder vs Demultiplexer
The main difference between Decoder and Demultiplexer is that decoder has n number of inputs, whereas the demultiplexer takes only one input. The output of the decoder is double the number of inputs (2n). On the other hand, the output of the Demultiplexer depends on the number of selected output lines.
Decoder circuits are designed to convert binary information in applications like seven-segment display, multiplexing, address decoding in-memory systems. The decoders system takes multiple inputs and produces multiple outputs using the AND gates and NAND gates. If the circuit takes n inputs, then the decoder generates two to the power of n (2n) number of outputs. Decoders do not use any device to input the data as in demultiplexer.
The demultiplexer is the circuit designed to execute general logic along with a multiplexer. It is used to transmit signals from one destination to others and hence termed as a distributor. The demultiplexer takes an input signal using data routers and then converts it into multiple output signals based on the selected lines. If the user selects n lines, then the demultiplexer generates a 2n number of outputs.
Comparison Table Between Decoder and Demultiplexer
| Parameters of Comparison | Decoder | Demultiplexer |
| Definition | The circuit decodes the binary information by taking n input signals to 2n output signals. | It is a combinational logic circuit designed to convert a serial data signal at the input to parallel data at its several output lines. |
| Boolean Expression Implementation | It uses AND gate or NAND gates and NOT gates. | It uses six individual gates consisting of AND, NOT gates. |
| Input and output lines | It has n inputs lines and 2n output lines. | It has one input and 2n outputs of selected lines. |
| Opposite | The encoder is the inverse of the decoder. | The multiplexer is the inverse of Demultiplexer. |
| Application | Data routing, memory decoding | Data recovery in clocks, serial to parallel conversion |
What is Decoder?
Decoders are also a type of combinational circuit that changes the code into many signals when it is enabled. That is, the decoder detects the particular code. It is a simple logic circuit that has N inputs and 2n outputs. It converts the binary data to other codes like in 3-to-8 decoder, it converts binary to octal data, in 4-to-10 decoder it operates as BCD to decimal converter, and in the 4-to-16 decoder, it converts binary to hexadecimal data.
The decoder is also found in the control unit of the central processing unit. It is also used to decode program instructions and commands to activate the specific control line so that the ALU of the CPU is carried out for different operations.
Decoders are also used to implement the Boolean functions using AND gates and NAND gates. The internal circuit is the same for both the decoder and DEMUX. Some of the applications of decoders are it is used for high-performance memory decoding and for data routing that requires shorter transmission delays. Now a day, Decoders are used in networking and telecommunication systems.
What is Demultiplexer?
The demultiplexer is a digital logic circuit. It is also called a data distributor. The action of Demultiplexer or DEMUX is opposite to a multiplexer or MUX. For example, DEMUX transmits data from one to N output devise, whereas MUS transmits from N to one device. The DEMUX is mainly used to generate Boolean functions in decoder circuits by using AND gates and NOT gates. Different types of DEMUX are presently based on output configurations. They are 1-to-2, 1-to-4, 1-to-8, and 1-to-16 DEMUX. Some most commonly used DEMUX IC packages are
- TTC 74LS138à 1-to-8 output DEMUX
- TTC 74LS139à dual 1-to-4 output DEMUX
- TTC 74LS237à 1-to-8 output DEMUX with address latches
- TTC 74LS154à 1-to-16 DEMUX
- TTC 74LS159à1-to-16 DEMUX
- CMOS 4514à 1-to-16 DEMUX input with latches.
In this, some standard DEMUX IC packages have additionally implemented output pints which keep the lid on the input from being passed to the selected output. Some latches built in the output are used to maintain output logic levels after that addresses of input gets changed. The DEMUX IC packages are also used as decoder IC packages but with different names like 74159 are used for 4-to-16 line decoder. Some of the applications of DEMUX are it is used as a clock data recovery solution, packet broadcaster in ATMS, serial to parallel converter, wavelength router, stores the output of ALU.
Main Differences Between Decoder and Demultiplexer
- The decoder is a logical circuit that converts the binary information into different data formats like hexadecimal, octal, BCD, and others. On the other hand, Demultiplexer converts the serial data into parallel data.
- The decoder has n numbers of input lines, but the Demultiplexer takes only one input line.
- The decoder takes data as input, and the Demultiplexer takes signals as input.
- The decoders give 2n number of outputs, and the Demultiplexer gives several outputs based on selected lines.
- The decoder’s functions are opposite to encoders, whereas the Demultiplexer functions opposite to multiplexer.
Conclusion
Decoders and Demultiplexer are the types of combinational logic circuits used in different applications to convert the data or to control the signals. The decoders are the same as Demultiplexer but with special functionalities. The decoder does not have selection lines, but the Demultiplexer has selection lines. These two concepts are important to understand digital circuits. These concepts are used in telecommunication networks to improve the performance of the signals and reduce delays.
References
- https://www.google.co.in/books/edition/Digital_Design/JCfNBQAAQBAJ?hl=en&gbpv=1&dq=digital+design:+basic+concepts+and+principles+john+f+wakery&pg=PP1&printsec=frontcover
- https://www.google.co.in/books/edition/Digital_Electronics/Ljsr7UA83ScC?hl=en&gbpv=1&dq=digital+electronics+by+anil&printsec=frontcover