Decoder

A decoder or decoder is generally understood to be a converter , converter or converter for digital or analog signals . With a converter or a coding unit, also called an encoder or encoder , it can form a logical unit or a functional chain . A device which can generate the original input signals for the decoder from output signals of the decoder, the encoder or encoders (English).

A decoder does not necessarily have to have the task of completely restoring the original information of the coding unit or of making it available to another system, since the conversion of the information or signals can be redundant or lossy.

The following picture represents an encoder (encoder) / decoder (decoder) system:

Secure signal transmission with coding and decoding

In communications engineering , the English term decoder is generally used as a decoder and the term encoder is used for the encoder.

In cryptography , people and tools for decrypting messages are often referred to as decoders.

Depending on the type of signal, a distinction is made between these two signal structures: analog decoders, digital decoders and transfers.

Analog decoders

One of the common decoder for analog signals is for the stereo reception decoder used in the VHF - FM - receivers . PAL and SECAM analog decoders are also used in Europe for receiving analog color television .

Digital decoders

Decoders can be implemented using pure hardware (e.g. in code converters ), pure software (e.g. in codecs ) or in DSPs .

The digital signal processing can be used to build decoders.

Digital decoders can use:

being constructed.

In multimedia applications , decoders and codecs are often used to reconstruct data after transmission or compression .

Typical applications of digital decoders in technology are conversion of signals for measuring devices, control of digital counters with different counting logics and conversion of signals from parallel transmission methods for serial data transmission , e.g. B. for the RS-232 interface.

Examples of digital decoders in circuit technology

A decoder can be a switching network that, depending on the implementation, generates minimum or maximum terms from n inputs (or fewer) . Every function can be expressed by these terms and therefore the decoder is suitable for implementing any switching function by combining the terms that occur on the output side. ${\ displaystyle 2 ^ {n}}$

Example of a switching network as a digital decoder

A 3 × 8 decoder
• Inputs: s0, s1, s2
• Outputs: Minterme m0, m1,…, m7
s2 s1 s0 m0 m1 m2 m3 m4 m5 m6 m7
0 0 0 1 0 0 0 0 0 0 0
0 0 1 0 1 0 0 0 0 0 0
0 1 0 0 0 1 0 0 0 0 0
0 1 1 0 0 0 1 0 0 0 0
1 0 0 0 0 0 0 1 0 0 0
1 0 1 0 0 0 0 0 1 0 0
1 1 0 0 0 0 0 0 0 1 0
1 1 1 0 0 0 0 0 0 0 1

1-out-of-n decoder

The 1-out-of-n decoder switches exactly one of n outputs to 1, where n is a power of 2, since n must be present at the inputs in binary representation. For inputs e0, e1, e2, e3 with 0 1 1 0 bin = 6 dec, the output would be y6 = 1 and all others would be y0, y1,…, y5, y7, y8,…, y15 = 0.

With the help of 1-out-of-n decoders, for example, the individual flip-flops in a memory are selected to be written to by applying the address to the inputs of the 1-out-of-n decoder and the outputs y0, ..., yn and the flip-flop inputs f0,…, fn are connected with an AND.

Realization of decoder circuits with minter terms / max terms:

Minterm Max term
0 NOR gate AND gate
1 OR gate NAND gate

Code conversion between analog and digital

Analog-to-digital converters are used to convert analog to digital signals and digital-to-analog converters are used for the reverse direction . The main parameters of these converters are the accuracy, linearity and speed of implementation. The main area of ​​application for these decoders is measurement technology . But also in entertainment electronics, digital signals z. B. converted from a CD, DVD or from a digital radio or television receiver into analog signals.