Overview of Programmable Logic Devices (PLD), FPGA, and CPLD: History, Types, Architecture, and Development Tools

Programmable Logic Devices (PLD) originated in the 1970s as a configurable hardware platform derived from ASICs, allowing users to program functionality via software, which shortens design cycles, improves flexibility, and reduces cost.

Common PLD families include PROM, FPLA, PAL, GAL, EPLA, CPLD, and FPGA, which can be further divided by granularity (small, medium, large) and programming technology (fuse, antifuse, EEPROM, SRAM).

The development history of PLDs is divided into four stages: early PROM/EPROM/EEPROM devices, the emergence of PAL/GAL, the introduction of FPGA and CPLD by Xilinx and Altera, and the current era of SOPC/SOC integration that merges PLD and ASIC technologies.

CPLD Architecture : Based on product‑term structures, CPLDs consist of macro cells, programmable interconnect (PIA), and I/O control blocks. Macro cells contain a product‑term array (AND) and a product‑term selection matrix (OR), optionally a programmable D‑flip‑flop.

FPGA Architecture : Modern FPGAs use SRAM‑based lookup tables (LUTs) as configurable RAM cells. Each LUT implements a truth table for up to four inputs, enabling flexible combinational logic. FPGAs also contain programmable I/O blocks, configurable logic blocks (CLBs), digital clock managers (DCM), embedded block RAM (BRAM), routing resources, and embedded hard IP cores such as DSP, PLL/DLL, and soft/hard CPUs.

Key FPGA modules include:

Programmable I/O (IOB) – configurable electrical standards and high‑speed I/O.

Configurable Logic Blocks (CLB) – contain slices with multiple LUTs, flip‑flops, and carry logic.

Digital Clock Management (DCM) – PLL/DLL for precise clock generation and phase control.

Embedded Block RAM (BRAM) – configurable as single/dual‑port RAM, ROM, FIFO, or CAM.

Rich routing resources – global, long, short, and distributed networks.

Embedded hard IP – dedicated multipliers, SERDES, and CPU cores for SOC‑level designs.

Development of PLDs relies heavily on Electronic Design Automation (EDA) tools that perform synthesis, placement, routing, and programming. Essential EDA components are the synthesis engine and the device‑specific adapter, which translate HDL or schematic descriptions into configuration bitstreams.

Effective PLD tools should accurately map designs to hardware, efficiently use resources, provide fast compilation, offer extensive IP libraries, and present a user‑friendly interface.

IP cores (soft, hard, and firm) are reusable modules that accelerate design; soft IP is RTL‑level and highly portable, hard IP is pre‑implemented in silicon, and firm IP includes placement information for higher reliability.

Overall, PLDs—especially FPGA and CPLD—serve as versatile platforms for prototyping and low‑to‑medium volume production, bridging the gap between custom ASICs and fixed‑function logic devices.