How to Use Programmable Logic Devices (PLD) in Digital Circuit Design

You can use programmable logic devices to make special digital circuits for your needs. These devices are flexible because you can change the design without making a new board. You save money by using the same hardware for many projects. You can test new ideas quickly, so you finish projects faster. Many engineers like programmable logic devices because they make board layout easy and let you make changes easily.

Key Takeaways

• Programmable logic devices (PLDs) let you make custom digital circuits. You do not need new hardware for every design change.

• Using PLDs saves both time and money. You can quickly test ideas and finish projects faster.

• There are different types of PLDs, like SPLDs, CPLDs, and FPGAs. Each type has special features for different project needs. Some are for simple jobs, and some are for harder ones.

• You need to learn programming languages like Verilog or VHDL. These help you tell the PLD how your circuit should work.

• You should test your design with simulation tools before building it. This makes sure your circuit works right and helps you find mistakes early.

What Are Programmable Logic Devices

Definition

Programmable logic devices help you make digital circuits for your needs. A programmable logic device is a circuit you can set up to do certain logic jobs. You can change how it works many times. You do not have to build a new board every time you want a new design. This makes programmable logic devices useful in many areas like computers, cars, and communication systems. There are different types you can pick from. These include Simple Programmable Logic Devices (SPLDs), Complex Programmable Logic Devices (CPLDs), and Field-Programmable Gate Arrays (FPGAs). Each type lets you control your project in different ways.

Key Features

Tip: Programmable logic devices give you many good things. They help you design faster and easier.

Feature	Description
Flexibility	You can change the device to fit new designs.
Rapid Prototyping	You can test ideas fast without waiting for new parts.
Cost-Effectiveness	You save money because you do not need special hardware.
Integration	You can put many jobs into one device.
Custom Logic Functions	You can make the device do special tasks for your project.

You use these features when you work with digital circuits. You can change your design and try new ideas. You save time and money. Programmable logic devices help you fix problems and make better products.

How Programmable Logic Devices Work

Configuration Process

You can set up programmable logic devices in a few ways. Each type has its own way to be set up. You pick the device that fits your project best. The table below shows how SPLDs, CPLDs, and FPGAs are set up.

Device Type	Configuration Process	Key Features
SPLDs	Uses fuses or non-volatile memory for logic definition.	Up to 24 macrocells, reprogrammable, low power consumption.
CPLDs	Centralized memory architecture with Flash or EEPROM.	Fixed design, supports combinational and limited sequential logic.
FPGAs	Distributed memory architecture with SRAM and embedded Flash.	Highly configurable, supports complex digital systems, volatile memory.

You use SPLDs for simple logic jobs and easy changes. SPLDs have macrocells that do basic Boolean logic. You can change them many times. CPLDs have a set design with macrocells joined by a matrix. You use CPLDs for simple logic and they keep their setup when power is off. FPGAs have many logic blocks and are very flexible. You use FPGAs for hard digital jobs, but you must set them up again if power is lost.

When you set up a programmable logic device, you do these steps:

1. You set up the device by picking input and output logic.

2. You make product terms with the AND gate array.

3. You make sum terms with the OR gate array to get the output.

Tip: SPLDs let you change your design without a new board. CPLDs are good for simple logic and keep their setup after power loss. FPGAs can do hard jobs and give you many ways to set them up.

Logic Design Aspects

Programmable logic devices help you design faster and easier. You can change logic functions quickly. You do not need new hardware for every change. This saves you time and money.

• Flexibility lets you test ideas and fix problems fast.

• You save money because you do not need special circuits.

• You make your design better by matching it to your project.

You can make good digital circuits with programmable logic devices. You change the logic to fit your needs. You make your product better without extra hardware. You finish projects faster and spend less money.

Types of Programmable Logic Devices

You can pick from different programmable logic devices. Each type has its own features and uses. The main types are SPLDs, CPLDs, and FPGAs.

SPLDs

Simple Programmable Logic Devices (SPLDs) help you make basic logic. SPLDs work well for small projects with simple needs. They have a simple design and do not handle much logic. You often use SPLDs in easy control systems or switching jobs.

Note: SPLDs are good for people who are new. You can learn to program logic without hard tools.

CPLDs

Complex Programmable Logic Devices (CPLDs) are stronger than SPLDs. CPLDs are good when you need steady timing and more logic blocks. You use CPLDs for big control jobs, address decoding, and state machines. CPLDs keep their setup even if the power goes off.

• CPLDs help you with larger projects.

• You use them for jobs that need quick and steady answers.

FPGAs

Field-Programmable Gate Arrays (FPGAs) are the most flexible. You use an FPGA for advanced digital systems. FPGAs have lots of logic and many connections you can change. You can build test models, handle fast data, or make final products with FPGAs. Many engineers choose FPGAs for projects that need lots of logic and quick changes.

Tip: FPGAs let you try new ideas fast. You can change your design many times without new parts.

Here is a table that shows the main types of programmable logic devices and what they do:

Device Type	Characteristics	Typical Applications
SPLD	Simple design, not much logic	Basic logic jobs, simple control tasks
CPLD	Medium complexity, steady timing, more logic blocks	Big control jobs, address decoding, state machines
FPGA	Very flexible, lots of logic, many connections	Test models, register-heavy jobs, fast data work, final products

Many companies make programmable logic devices. The table below shows how much of the market each company has:

Company Name	Estimated Market Share (%)
Xilinx (AMD)	30-35%
Intel (Altera)	25-30%
Lattice Semiconductor	15-20%
Microchip Technology	10-13%
QuickLogic Corporation	5-7%
Other Companies (combined)	7-12%

You can see Xilinx (AMD) and Intel (Altera) have the biggest share. Lattice Semiconductor and Microchip Technology are also important. When you pick a programmable logic device, you often choose from these companies.

Programming Programmable Logic Devices

Languages

You use special languages to tell programmable logic devices what to do. These languages help you explain how your circuit works. The two most popular hardware description languages are:

• Verilog

• VHDL

Verilog is a lot like the C programming language. You write easy code to show how signals move and change. VHDL uses a style that is similar to Ada. You use it to explain logic and timing in your circuit. Both languages let you make designs for many programmable logic devices, including fpga chips.

Tip: You can learn Verilog or VHDL by starting with small projects. Try making simple logic gates or counters first.

Tools

You need special tools to design and program programmable logic devices. These tools help you write code, check your design, and make files for your device. Two big companies have strong software for this job.

Company Name	Year Founded	Country	Description
Altera Corp.	1983	United States	Supplies programmable logic devices and software for high-speed, high-density applications.
Xilinx, Inc.	1984	United States	Designs programmable logic solutions, including fpga chips and advanced development tools.

Altera and Xilinx give you software to draw circuits, write code, and test ideas. You use these tools to turn your design into a file that programs your device.

Example: 4-Digit Combination Lock

You want to build a 4-digit combination lock using programmable logic devices. Here is how you do it:

1. Write your design in Verilog or VHDL. Explain how the lock checks each digit.

2. Use the CAD tool from Altera or Xilinx. Enter your code and connect the inputs and outputs.

3. Simulate your design. Make sure the lock works as you want.

4. Make the programming file. This file tells your device what to do.

5. Load the file into your programmable logic device. Test the lock with real buttons.

Note: You can change your design anytime. If you want a 6-digit lock, you only need to update your code and reload the device.

Implementing PLDs in Digital Circuits

Design Steps

You can use simple steps to add programmable logic devices to your digital circuits. First, figure out what you want your circuit to do. Write down the logic functions you need. Decide how many inputs and outputs your circuit will have. Try to make your design as simple as possible. This helps you use fewer gates and flip-flops. Using fewer parts saves space and money.

Here is a table that shows how making your logic simple and picking states helps your design:

Advantage	Description
Minimized Logic Gates	Picking states first can use fewer logic gates.
Simplified Implementation	Gray coding makes circuits easier and helps stop mistakes.
Reduced Complexity	Fewer states mean less complex circuits and fewer flip-flops.
Cost Efficiency	Simple designs cost less to build.
Improved Performance	Better speed and less power are possible.

After you make your logic simple, give each state a name or number. You can use Gray coding to help make your design easier and avoid mistakes. Next, write your design using Verilog or VHDL. Put your code into the design tool and connect the inputs and outputs.

You can put inputs and outputs wherever you want. This makes it easy to change your design fast. You can try different ideas and see what works best. Here are some ways flexible input and output placement helps you:

• CPLDs let you change your design many times, so you can meet new needs.

• You can try out different logic ideas, which helps you build test models quickly.

If you use an fpga, you can test many ideas without changing the hardware. This helps you finish your project faster.

Testing

Testing checks if your programmable logic devices work the way you want. You should use the design tool to test your design before putting it on the device. Try all the inputs to see if your logic works. Fix any problems you find during this test.

After testing in the tool, program your device and test it with real signals. Make sure the outputs are correct. If you find mistakes, you can fix your code and load it again. This helps you make your design better step by step.

You might have some problems when you use programmable logic devices in your circuit. The table below shows some common problems and what they mean:

Challenge	Description
PCB Space Conservation	Analog and other parts use most of the board space, making it hard to fit everything.
Increased I/O Density	More inputs and outputs make the design harder and need better power use.
Security Threats	PLCs on the internet can be attacked, so you need strong security in hardware.

You can fix these problems by planning your design well. Use the flexibility of programmable logic devices to put inputs and outputs where you want. Try to keep your design simple and safe.

Tip: Always test your design in the tool and on real hardware. This helps you find mistakes early and make better circuits.

Advantages of Programmable Logic Devices

Flexibility

Programmable logic devices let you change your design easily. You can update your circuit after you build it. You do not need to make a new board for each change. This helps you keep up with new ideas. FPGAs let you add new features fast. You can test changes quickly. In fast industries, this is very helpful.

Feature	FPGAs	Fixed Logic Circuits
Reconfigurability	Can be programmed after manufacturing	Fixed after production
Adaptability	Cost-effective updates possible	Requires new hardware
Rapid Prototyping	Supports iterative design processes	Limited to initial design

Tip: You can reprogram high-density programmable logic devices after you install them. This means you can make your system better without new hardware.

Cost Savings

Programmable logic devices help you save money. You can put many jobs into one chip. You do not need lots of parts. This can make your board much smaller. Smaller boards use less power and cost less. For small projects, you do not pay for custom chips. FPGAs cost less to set up than ASICs if you only need a few.

Aspect	ASICs	FPGAs
Non-Recurring Engineering Costs	High NRE costs for custom design and making.	Lower NRE costs since no custom making needed.
Per-Unit Costs	Lower per-unit costs if you make many, but higher for a few.	Higher per-unit costs, but lower NRE for small numbers.
Manufacturing Complexity	Making is harder and takes more time.	You can buy and use FPGAs right away, and change them.
Design Flexibility	Hard to change after making; needs new design.	Very flexible; you can change them after making.

Rapid Prototyping

You can build and test ideas faster with programmable logic devices. CPLDs and FPGAs let you try new designs in minutes. You do not wait for long chip-making steps. You can fix problems and make your design better quickly. Many teams use these devices to finish products faster.

• CPLDs help you finish projects sooner than custom chips.

• You can change and test your design right away.

• Companies use programmable logic devices to make machine vision, gear sorting, and factory work faster.

Case Study	Description
Lee et al.	Made a machine vision part for PLCs, making systems cheaper and easier to use.
Darekar & Kulkarni	Used wireless PLCs and computer vision to sort gears faster and with fewer mistakes.
Al Fahim et al.	Built an automated cell with PLCs, showing better speed and flexibility in real factories.

Note: Rapid prototyping lets you make your product better step by step. This saves time and resources.

You can use programmable logic devices to make digital circuits for your needs. These devices are small and easy to change. They can check for problems by themselves. You save money when you use them in big control systems.

Many experts say you should read guides, join online groups, and do hands-on projects to learn faster.

• Use virtual tools and PLC kits to practice.

• Try new areas like IoT, AI, and 5G, where PLDs help make smart and fast solutions.

Keep learning and trying new things. Your ideas can help make automation better in the future.

 

 

 

 

 

Written by Jack Elliott from AIChipLink.

 

AIChipLink, one of the fastest-growing global independent electronic   components distributors in the world, offers millions of products from thousands of manufacturers, and many of our in-stock parts is available to ship same day.

 

We mainly source and distribute integrated circuit (IC) products of brands such as Broadcom, Microchip, Texas Instruments, Infineon, NXP, Analog Devices, Qualcomm, Intel, etc., which are widely used in communication & network, telecom, industrial control, new energy and automotive electronics. 

 

Empowered by AI, Linked to the Future. Get started on AIChipLink.com and submit your RFQ online today!