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4 to 2 Encoder ICs: An Overview

4 to 2 Encoder ICs An Overview

Introduction to 4 to 2 Encoders

4 to 2 encoders are digital circuits that take a 4-bit binary input and encode it to a 2-bit output. They are a type of data compressor, allowing 4 input states to be represented by just 2 output states. This reduces the number of transmission lines needed, at the cost of some loss of information.

Some common applications of 4 to 2 encoders include:

  • Reducing the pin count of microcontrollers or other ICs
  • Simplifying the wiring for interface buses like I2C
  • Encoding audio or video data to reduce bandwidth

How 4 to 2 Encoders Work

A 4 to 2 encoder has 4 input pins labeled A, B, C, and D. These pins can take on a binary input value from 0000 to 1111 (0 to 15 decimal).

The encoder then converts this to a 2-bit output according to the following logic:

InputOutput
000000
000101
001010
001111
010000
010101
011010
011111
100000
100101
101010
101111
110000
110101
111010
111111

As you can see, the encoder combines inputs 0 to 3, 4 to 7, 8 to 11, and 12 to 15 into just 2 output states each. This compresses the data while preserving some of the information about the input value.

4 to 2 Encoder ICs

Several integrated circuits provide 4 to 2 encoding in compact, easy to use packages:

74LS148

One of the most popular 4 to 2 encoder ICs is the 74LS148 made by various manufacturers like Texas Instruments. This 8-pin chip includes active-low enables and accepts inverted or non-inverted inputs.

CD74HC148E

The CD74HC148E from TI is a more modern CMOS version of the 74LS148 but with non-inverted outputs. It has higher speed and lower power consumption.

MC74VHC148AFT1G

ON Semiconductor’s MC74VHC148AFT1G is an ultra low power 4 to 2 encoder in a small SOT-363 surface mount package. It runs on just 1.65-5.5V.

HEF4794

Nexperia’s HEF4794 is actually a 4 to 3 encoder but can be easily adapted to 4 to 2 operation if one output is ignored. It comes in compact 8-pin SOIC and DIP formats.

Conclusion

4 to 2 encoders are simple but useful ICs for compressing data and minimizing interconnects. With devices like the 74LS148, CD74HC148E, MC74VHC148AFT1G, and HEF4794, engineers have several solid options to choose from depending on their design requirements. These encoders continue to find widespread use in many digital applications today.

Frequently Asked Questions

What are the advantages of using a 4 to 2 encoder?

The main advantages are reducing pin count and wiring complexity by compressing 4 bits into 2. This minimizes PCB trace routing and can reduce interconnect costs in some applications.

What are some disadvantages of 4 to 2 encoders?

Since they compress the data, some original information is lost. This could introduce errors if the encoded data is not decoded properly. They also add some logic delay compared to direct interconnects.

What is priority encoding?

Some 4 to 2 encoders use priority encoding, meaning inputs with a binary value of 1 are given priority over 0 bits. This ensures that each input value maps to a unique output code.

Can 4 to 2 encoders be cascaded or used in reverse?

Yes, the outputs of multiple 4 to 2 encoders can be chained together to encode larger input widths. They can also be reversed to implement 2 to 4 decoders.

Are there other common data encoder ICs besides 4 to 2?

Yes, other versions like 8 to 3, 16 to 4, binary to BCD, and binary to Gray code encoders are also readily available. These follow the same basic principles but have different input/output widths.