Difference between decoder and multiplexer
Decoders and multiplexers are fundamental building blocks in digital circuits and play crucial roles in information processing. Although both devices serve distinct functions, they share similarities regarding input-output relationships. Understanding the workings of both these devices can help us design more efficient digital circuits and create more robust embedded systems.
Decoders
A decoder is a combinational circuit that takes multiple inputs and produces unique output combinations based on the input values. Essentially, it enables the selection of a specific output line by activating the corresponding input combination. Let’s look at a 2x4 decoder below:
Note: Notice how each input combination activates a unique output line. Each output combination has a unique and specific input combination, making their relation one-to-one.
Now, let’s examine these results in tabular form. A truth table is a way of expressing input and output relationships.
Input | Output | ||||
A | B | Q0 | Q1 | Q2 | Q3 |
0 | 0 | 1 | 0 | 0 | 0 |
0 | 1 | 0 | 1 | 0 | 0 |
1 | 0 | 0 | 0 | 1 | 0 |
1 | 1 | 0 | 0 | 0 | 1 |
We just looked at a 2x4 decoder, but decoders come in various input and output configurations. A decoder designed to have
Use cases
There are several circuits where decoders can be a useful tool. The following are a few of the most common uses of decoders:
Binary to decimal conversion: A 3x8-bit decoder can convert a 3-bit binary input into an 8-line output, representing decimal values from 0 to 7.
Address decoding: In memory systems, decoders often select specific memory locations based on the binary address input.
Seven-segment display drivers: Decoders are essential in driving seven-segment displays, where each input combination corresponds to lighting up a specific segment to display numbers or characters.
Multiplexers
On the other hand, a multiplexer, often referred to as a mux, is a combinational circuit that selects one of many input lines and directs it to a single output line. The selection is controlled by additional input lines known as control lines or select lines (denoted with
Note: Notice how each S-line combination sends a unique input line to the output. This means that a multiplexer acts as a routing switch, where the S-lines control which input flows ahead to the output.
Now, let’s look at the truth table for a 4x1 multiplexer. Instead of listing all 64 possible entries, we’ll focus on just a few to understand the relationship between inputs and output.
Select | Input | Output | ||||
S0 | S1 | A0 | A1 | A2 | A3 | Q0 |
0 | 0 | 1 | 0 | 0 | 0 | 1 |
0 | 1 | 1 | 0 | 1 | 1 | 0 |
1 | 0 | 1 | 1 | 0 | 1 | 0 |
1 | 1 | 1 | 0 | 1 | 0 | 0 |
Note: The inputs highlighted in the table are passed to the output. The S-line combination determines which input to pass.
Use cases
There are several circuits where multiplexers can be a useful tool. The following are a few of the most common uses of multiplexers:
Data transmission: Multiplexers are employed in communication systems to combine multiple data streams into a single channel for transmission, which is then demultiplexed at the receiving end.
Input selection: In digital systems, multiplexers select inputs from various sources and route them to a common output, optimizing resource utilization.
Analog signal sampling: Multiplexers are utilized in analog-to-digital converters to sample multiple analog signals and convert them into digital form.
Differences between decoders and multiplexers
The following table highlights the differences between decoders and multiplexers:
Decoder | Multiplexer | |
Function | Converts multiple inputs into a unique output combination. | Selects one of many inputs and directs it to a single output. |
Output | Typically has more output lines than input lines. | Selects one of many inputs and directs it to a single output. |
Input | Selection is based on the input binary code. | There are additional input lines control selection. |
Application | Commonly used in decoding binary information, memory addressing, and driving displays. | Applied in data transmission, input selection, and analog signal sampling. |
Conclusion
Decoders and multiplexers are integral components in digital electronics, each serving unique purposes. While decoders focus on decoding binary information and selecting specific output lines, multiplexers excel in dynamically routing data from multiple inputs to a single output. Understanding the distinctions between these two devices is crucial for designing efficient digital systems tailored to specific applications.
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