Introduction to 4 to 16 Line Decoder ICs
A decoder is a combinational circuit that converts binary information from the input lines to a specific output line. 4 to 16 line decoders have 4 input lines and 16 output lines. They take a 4-bit binary input and activate one of the 16 output lines.
Decoders are used in various applications like memory addressing, multiplexing, and seven segment displays. Some common ICs used as 4 to 16 line decoders are 74154, 74LS154, CD4514B, MC14514, etc.
How 4 to 16 Line Decoders Work
A 4 to 16 decoder has 4 input lines (A, B, C, D) and 16 output lines (Y0 to Y15). The truth table below shows the working of a 4 to 16 decoder:
| A | B | C | D | Output |
|---|---|---|---|---|
| 0 | 0 | 0 | 0 | Y0 |
| 0 | 0 | 0 | 1 | Y1 |
| 0 | 0 | 1 | 0 | Y2 |
| 0 | 0 | 1 | 1 | Y3 |
| 0 | 1 | 0 | 0 | Y4 |
| 0 | 1 | 0 | 1 | Y5 |
| 0 | 1 | 1 | 0 | Y6 |
| 0 | 1 | 1 | 1 | Y7 |
| 1 | 0 | 0 | 0 | Y8 |
| 1 | 0 | 0 | 1 | Y9 |
| 1 | 0 | 1 | 0 | Y10 |
| 1 | 0 | 1 | 1 | Y11 |
| 1 | 1 | 0 | 0 | Y12 |
| 1 | 1 | 0 | 1 | Y13 |
| 1 | 1 | 1 | 0 | Y14 |
| 1 | 1 | 1 | 1 | Y15 |
Based on the binary input at A, B, C, D pins, the corresponding output line is activated HIGH while other lines are LOW.
Features of 4 to 16 Line Decoder ICs
Some notable features of 4 to 16 line decoder ICs are:
- All outputs are active LOW, i.e. output is LOW when selected
- Output enable pin (E) to disable all outputs
- Complementary outputs in some ICs
- Ability to cascade two 4 to 16 decoders to obtain a 8 to 256 decoder
- Wide operating voltage range (3V to 18V)
- High current drive capacity (25mA)
- High speed operation (10MHz)
- Low power consumption
Applications of 4 to 16 Line Decoder ICs
Some major applications of 4 to 16 line decoder ICs include:
- Memory addressing – To decode address bus bits for memory chip selection
- Seven segment displays – To decode BCD inputs and drive seven segment displays
- Demultiplexing – Converting multiple inputs into a single output line
- Peripheral selection – Choosing between various peripheral devices
- Waveform generation – Generating different waveforms from binary inputs
Comparison Between Popular 4 to 16 Decoder ICs
| Parameter | 74LS154 | CD4514B | MC14514 |
|---|---|---|---|
| Supply Voltage | 4.5V to 5.5V | 3V to 18V | 3V to 15V |
| Propagation Delay | 15ns | 50ns | 100ns |
| Output Current | 25mA | 25mA | 5mA |
| Power Dissipation | 135mW | 330mW | 100mW |
| Temperature Range | 0°C to 70°C | -55°C to 125°C | -55°C to 125°C |
Frequently Asked Questions
What is the difference between a decoder and a demultiplexer?
A demultiplexer converts one input into multiple outputs whereas a decoder converts binary inputs into a single output. Demultiplexer is mostly used for data routing while decoder is used for memory addressing.
How do I cascade two 4 to 16 decoders?
The outputs of the first 4 to 16 decoder can be fed as inputs to the second decoder. An enable pin can be added between the decoders. This results in a total of 16*16 = 256 outputs with 8 input pins.
Can unused outputs of the decoder be left floating?
No, unused outputs should be connected to ground through a resistor. A floating output may oscillate and cause unwanted transitions.
What are the advantages of active low outputs in decoders?
Active low outputs allow the outputs to be ORed or NORed if required. This is useful in memory decoding to select multiple chips. Active high outputs cannot be directly ORed.
How do I choose the right decoder IC for my application?
Consider voltage levels, output drive capacity, speed, power dissipation, and cost. Analyze the loading on each output to determine the drive needed. Also look for complementary outputs if active high levels are needed.
