# Decoder circuit

27.10.2020 By Mazusar

Decoder is a circuit which converts the digital signal into analog signal.

Its input will be in digital form while the output will be a continuous sine wave or analog wave. As shown in the given diagram there are four resistances connected to the input of the amplifier through switches. Whenever, the input bite is one the switch is closed while it is open for zero bite.

The ouput is given by. And is constant while the R in is the input resistances which changes every time according to the input bites. The value of R in depends upon the number of switches closed.

If the input is the input resistance R n becomes 75 K parallel to K. It is used to compare the two input values. If A is greater than B the output will be one. Otherwise it will be zero. It is an electronic device which counts the number in binary system. It increases by one number whenever high input pulse is given. The output of the AND gate is given to the counter which becomes the pulse for it.

This pulse is high whenever the output of the AND gate is one. The output of the counter is given to digital converter which produces analog output and is given to comparator. When input A is set it means that the counter is instructed to count up to that level at that time the counter output is As a result the B signal is 0 volt. The comparator compare A and B signals.

As A is greater than B so the output of the comparator is one. This input signal is given to the counter which counts the next number. This is converted to analog signal which is again less than three volt and the same process continuous till the B signal is equal or becomes high then A. Main menu. Decoder Decoder is a circuit which converts the digital signal into analog signal.In digital electronicsa binary decoder is a combinational logic circuit that converts binary information from the n coded inputs to a maximum of 2 n unique outputs.

There are several types of binary decoders, but in all cases a decoder is an electronic circuit with multiple input and multiple output signals, which converts every unique combination of input states to a specific combination of output states. In addition to integer data inputs, some decoders also have one or more "enable" inputs.

### Digital Circuits - Decoders

When the enable input is negated disabledall decoder outputs are forced to their inactive states. Depending on its function, a binary decoder will convert binary information from n input signals to as many as 2 n unique output signals. Some decoders have less than 2 n output lines; in such cases, at least one output pattern may be repeated for different input values.

A binary decoder is usually implemented as either a stand-alone integrated circuit IC or as part of a more complex IC. In the latter case the decoder may be synthesized by means of a hardware description language such as VHDL or Verilog. Widely used decoders are often available in the form of standardized ICs. A 1-of-n binary decoder has n output bits. This type of decoder asserts exactly one of its n output bits, or none of them, for every integer input value.

The "address" bit number of the activated output is specified by the integer input value. For example, output bit number 0 is selected when the integer value 0 is applied to the inputs. Code translators differ from 1-of-n decoders in that multiple output bits may be active at the same time. An example of this is a seven-segment decoderwhich converts an integer into the combination of segment control signals needed to display the integer's value on a seven-segment display digit.

One variant of seven-segment decoder is the BCD to seven-segment decoderwhich translates a binary-coded decimal value into the corresponding segment control signals for input integer values 0 to 9.

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## Binary decoder

Categories : Binary logic Digital circuits.Prerequisite- Binary DecoderMultiplexers. A Decoder is a combinational circuit that converts binary information from input lines to unique output lines. Apart from the Input lines, a decoder may also have an Enable input line. A Decoder with Enable input can function as a demultiplexer. A demultiplexer is a circuit that receives information from a single line and directs it to one of possible output lines. A demultiplexor receives as input, selection lines and one Input line.

These selection lines are used to select one output line out of possible lines. To implement a demultiplexor, we use a decoder with Enable input. The selection lines of the demultiplexer are the input lines that the decoder gets and the one input line of demulitplexer is the Enable input of the Decoder.

Making demultiplexer using Decoder with Enable input. Let A, B be the selection lines and EN be the input line for the demultiplexer. The decoder shown below functions as a demultiplexer when EN is taken as a data input line and A and B are taken as the selection inputs.

The single input variable E has a path to all four outputs, but the input information is directed to only one of the output lines, as specified by the binary combination of the two selection lines A and B. This can be verified from the truth table of the circuit. Truth Table. A decoder takes input lines and has output lines. These output lines can provide the minterms of input variables. Since any boolean function can be expressed as a sum of minterms, a decoder that can generate these minterms along with external OR gates that form their logical sums, can be used to form a circuit of any boolean function.

For example, if we need to implement the logic of a full adder, we need a decoder and OR gates. The input to the full adder, first and second bits and carry bit, are used as input to the decoder.

Let x, y and z represent these three bits. Sum and Carry outputs of a full adder have the following truth tables- Therefore we have- The following circuit diagram shows the implementation of Full adder using a Decoder and OR gates.

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Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below. Writing code in comment? Please use ide. Prerequisite- Binary DecoderMultiplexers A Decoder is a combinational circuit that converts binary information from input lines to unique output lines. Decoder as a De-Multiplexer —. Check out this Author's contributed articles.

Improved By : cmkmanwani. Load Comments.Prerequisite — EncoderDecoders. Binary code of N digits can be used to store 2 N distinct elements of coded information.

This is what encoders and decoders are used for. Encoders convert 2 N lines of input into a code of N bits and Decoders decode the N bits into 2 N lines. Encoders — An encoder is a combinational circuit that converts binary information in the form of a 2 N input lines into N output lines, which represent N bit code for the input. For simple encoders, it is assumed that only one input line is active at a time. As shown in the following figure, an octal-to-binary encoder takes 8 input lines and generates 3 output lines.

As seen from the truth table, the output is when D0 is active; when D1 is active; when D2 is active and so on. Implementation — From the truth table, the output line Z is active when the input octal digit is 1, 3, 5 or 7.

Similarly, Y is 1 when input octal digit is 2, 3, 6 or 7 and X is 1 for input octal digits 4, 5, 6 or 7. Hence, the Boolean functions would be:. One limitation of this encoder is that only one input can be active at any given time.

If more than one inputs are active, then the output is undefined. For example, if D6 and D3 are both active, then, our output would be which is the output for D7. To overcome this, we use Priority Encoders. Another ambiguity arises when all inputs are 0. In this case, encoder outputs which actually is the output for D0 active. In order to avoid this, an extra bit can be added to the output, called the valid bit which is 0 when all inputs are 0 and 1 otherwise.

Priority Encoder — A priority encoder is an encoder circuit in which inputs are given priorities. When more than one inputs are active at the same time, the input with higher priority takes precedence and the output corresponding to that is generated. Let us consider the 4 to 2 priority encoder as an example.

From the truth table, we see that when all inputs are 0, our V bit or the valid bit is zero and outputs are not used. Here, D3 has highest priority, therefore, whatever be the other inputs, when D3 is high, output has to be These are frequently used in communication system such as telecommunication, networking, etc. Similarly, in the digital domain, for easy transmission of data, it is often encrypted or placed within codes, and then transmitted.

Digital Logic - Decoders

At the receiver, the coded data is decrypted or gathered from the code and is processed in order to be displayed or given to the load accordingly.

An encoder is an electronic device used to convert an analogue signal to a digital signal such as a BCD code. It has a number of input lines, but only one of the inputs is activated at a given time and produces an N-bit output code that depends on the activated input. The encoders and decoders are used in many electronics projects to compress the multiple number of inputs into smaller number of outputs. The encoder allows 2 power N inputs and generates N-number of outputs.

For example, in encoder, if we give 4 inputs it produces only 2 outputs. The decoders and encoders are designed with logic gate such as an OR-gate. There are different types of encoders and decoders like 48, and 16 encoders and the truth table of encoder depends upon a particular encoder chosen by the user.

Here, a 4-bit encoder is being explained along with the truth table. The four-bit encoder allows only four inputs such as A0, A1, A2, A3 and generates the two outputs F0, F1, as shown in below diagram.

A normal encoder has a number of input lines amongst which only one of which is activated at a given time while a priority encoder has more than one input, which is activated based on priority. Which means that, the priority encoders are used to control interrupt requests by acting according to the highest priority request?

If two or more inputs are equal to one — at the same time, the input having the highest priority will be preferred to take. Internal hardware will check this condition and priority, which is set. The multiplexers and demultiplexers are digitalelectronic devices that are usedto control applications. A multiplexer is a device that allows multiple input signals and produces a single output signal. For example, sometimes we need to produce a single output from multiple input lines. Electronic multiplexer can be considered as a multiple input and single output lines.

In this case, the multiplexer used selects the input line to be sent to the output. The digital code is applied to the selected inputs to generate respective output. Each device in succession has a brief time to send and receive the data. This is the special advantage of using this MUX.

The decoder is an electronic device that is used to convert digital signal to an analogue signal. It allows single input line and produces multiple output lines. The decoders are used in many communication projects that are used to communicate between two devices. The decoder allows N- inputs and generates 2 power N-numbers of outputs.

For example, if we give 2 inputs that will produce 4 outputs by using 4 by 2 decoder.

### Types of Encoders and Decoders with Truth Tables & Applications

The encoders and decoders are designed with logic gates such as AND gate. There are different types of decoders like 4, 8, and 16 decoders and the truth table of decoder depends upon a particular decoder chosen by the user.One of these outputs will be active High based on the combination of inputs present, when the decoder is enabled. That means decoder detects a particular code. The block diagram of 2 to 4 decoder is shown in the following figure.

The Truth table of 2 to 4 decoder is shown below. Each output is having one product term. So, there are four product terms in total. The circuit diagram of 2 to 4 decoder is shown in the following figure. If enable, E is zero, then all the outputs of decoder will be equal to zero. In this section, let us implement 3 to 8 decoder using 2 to 4 decoders. We can find the number of lower order decoders required for implementing higher order decoder using the following formula.

Therefore, we require two 2 to 4 decoders for implementing one 3 to 8 decoder. The block diagram of 3 to 8 decoder using 2 to 4 decoders is shown in the following figure.

The complement of input A 2 is connected to Enable, E of lower 2 to 4 decoder in order to get the outputs, Y 3 to Y 0. These are the lower four min terms. The input, A 2 is directly connected to Enable, E of upper 2 to 4 decoder in order to get the outputs, Y 7 to Y 4. These are the higher four min terms. In this section, let us implement 4 to 16 decoder using 3 to 8 decoders. Therefore, we require two 3 to 8 decoders for implementing one 4 to 16 decoder.

The block diagram of 4 to 16 decoder using 3 to 8 decoders is shown in the following figure.

The complement of input, A3 is connected to Enable, E of lower 3 to 8 decoder in order to get the outputs, Y 7 to Y 0. These are the lower eight min terms. The input, A 3 is directly connected to Enable, E of upper 3 to 8 decoder in order to get the outputs, Y 15 to Y 8. These are the higher eight min terms.An Encoder is a combinational circuit that performs the reverse operation of Decoder.

It will produce a binary code equivalent to the input, which is active High. It is optional to represent the enable signal in encoders. The block diagram of 4 to 2 Encoder is shown in the following figure.

The Truth table of 4 to 2 encoder is shown below. We can implement the above two Boolean functions by using two input OR gates. The circuit diagram of 4 to 2 encoder is shown in the following figure. The above circuit diagram contains two OR gates.

These OR gates encode the four inputs with two bits. Octal to binary encoder is nothing but 8 to 3 encoder. The block diagram of octal to binary Encoder is shown in the following figure. The Truth table of octal to binary encoder is shown below. We can implement the above Boolean functions by using four input OR gates. The circuit diagram of octal to binary encoder is shown in the following figure. The above circuit diagram contains three 4-input OR gates.

These OR gates encode the eight inputs with three bits. There is an ambiguity, when all outputs of encoder are equal to zero.

Because, it could be the code corresponding to the inputs, when only least significant input is one or when all inputs are zero. If more than one input is active High, then the encoder produces an output, which may not be the correct code.

So, to overcome these difficulties, we should assign priorities to each input of encoder. Then, the output of encoder will be the binary code corresponding to the active High input swhich has higher priority. This encoder is called as priority encoder. Here, the input, Y 3 has the highest priority, whereas the input, Y 0 has the lowest priority.

We considered one more output, V in order to know, whether the code available at outputs is valid or not. In this case, the output, V will be equal to 1.

In this case, the output, V will be equal to 0. We can implement the above Boolean functions using logic gates. The circuit diagram of 4 to 2 priority encoder is shown in the following figure.

Hence, this circuit encodes the four inputs with two bits based on the priority assigned to each input. Digital Circuits - Encoders Advertisements.