Programmable Logic Devices, PLDs: types and technologies

Programmable logic devices inluding SPLDs, CPLDs and FPGAs have become a widely used part of the electronic circuit designers toolkit - find out about them.

Programmable Logic Devices Includes:
Types of Programmable Logic Device FPGA: Field Programmable Gate Array

Programmable Logic Devices or PLDs have revolutionized the landscape of digital electronics, providing a versatile and adaptable platform for implementing complex logic functions.

As might be expected from their popularity and versatility, there are several types of programmable logic chip from the SPLDs through CPLDs to FPGAs.

Understanding PLDs: the very basics

PLDs are integrated circuits (ICs) that can be programmed after manufacturing to perform specific digital logic functions.

Unlike ASICs or Application-Specific Integrated Circuits, which are fixed-function devices, PLDs offer a degree of flexibility and customization.

Firmware, as it is called, is the software generated code that is used to configure the programmable logic device, and this is typically generated using a high level language to capture the logic requirements.

This is then converted into a bitstream that is loaded into the PLD to configure it as required to complete its function.

Types of PLDs

There are several types of PLD - they come in various forms, and each has its unique characteristics and is used in different types of application:

Simple Programmable Logic Devices, SPLDs:

SPLDs are the smallest form or programmable device and they are generally used in circuits to replace a number of standard logic components. Typically they consist of between 4 and 22 macrocells.

Basic Structure: SPLDs consist of a limited number of logic gates and flip-flops interconnected through a programmable logic array (PLA).

Applications: Suitable for small-scale logic functions and simple control circuits.

Limitations: Limited functionality and scalability due to the fixed structure of the PLA.

Complex Programmable Logic Devices (CPLDs):

This is a step up from an SLPD, but not as complicated as an FPGA.

Modular Architecture: CPLDs are composed of multiple programmable logic blocks (PLBs) interconnected through a programmable interconnect network, PIN.

Flexibility: Offer greater flexibility and scalability compared to SPLDs.

Applications: Widely used in various applications, including digital signal processing, communication systems, and control circuits.

Field-Programmable Gate Arrays (FPGAs):

FPGAs are the final step in the complexity of programmable logic devices.

Fine-Grained Structure: FPGAs consist of a vast array of configurable logic blocks (CLBs) interconnected through a programmable routing fabric.

Ultimate Flexibility: Provide the highest level of flexibility and customization, allowing for the implementation of complex digital systems.

Applications: Used in high-performance computing, artificial intelligence, networking, and other demanding applications.

How PLDs Work: A Simplified Explanation

PLDs utilize programmable logic elements to create custom digital circuits. These elements are typically interconnected using a programmable fabric, allowing designers to define the desired logic functions.

The programming process involves loading configuration data into the PLD, which determines the specific connections between the logic elements.

What do PLDs offer?

Programmable logic devices of all sizes are used in many different areas of electronics because they provide some significant advantages.

The days of having to design, build and debug complicated logic boards have almsot gone.

PLDs offer several advantages over traditional hardware design methods:

Flexibility: They can be reprogrammed multiple times, allowing for rapid prototyping and design iterations.

Time-to-Market: PLDs can significantly reduce development time compared to custom ASIC design.

Cost-Effectiveness: They are often more cost-effective for low-volume production or applications that require frequent changes.

Scalability: PLDs can be scaled to accommodate various levels of complexity, from simple control circuits to large-scale digital systems.

Choosing the right PLD is important, not only for the cost implications, but current consumption, difficulty in programming and many other aspects.

Some aspects to consider include:

Functionality: Determine the complexity of the logic functions to be implemented.

Performance: Consider the required speed and throughput of the circuit.

Scalability: Evaluate the potential for future growth and expansion.

Cost: Assess the cost implications of using a PLD compared to other options.

Development Tools: Evaluate the availability of development tools and support for the chosen PLD.

Programmable Logic Devices have revolutionized the way digital circuits are designed and implemented. Their versatility, flexibility, and time-to-market advantages make them invaluable tools in the modern electronics industry. Whether it's a simple control circuit or a complex digital system, PLDs provide the foundation for creating innovative and efficient solutions.