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In modern embedded design, choosing between an MCU (Microcontroller Unit) and an FPGA (Field-Programmable Gate Array) is one of the most fundamental engineering decisions. While both can control circuits, process signals and enable intelligent systems, they do so in fundamentally different ways.
- The MCU is the microcontroller brain of an embedded circuit, running code that has already been flashed on its ROM. It provides control over sensors, motors, and communication peripherals.
- The FPGA is a combination of sequential logic gates that an engineer can program to create project-specific digital logic that runs in parallel.
This article will compare the internal structures, performance differences, applications, and design trade-offs of microcontrollers and FPGAs. A real-world case study is provided as well.
What is MCU? What is FPGA?
A microcontroller unit is a standalone embedded controller. Essentially, it is a processor core with integrated memory and peripherals all within one chip. An engineer writes software instructions in high-level languages such as C or C++, and the microcontroller unit will execute these commands sequentially, with no consideration of how many they are.
- Common Architectures: ARM Cortex-M series (STM32, NXP, Renesas, etc.)
- Advantages: Low cost, low power consumption, high integration, low development barrier (C language development is sufficient)
FPGAs are programmable at the “hardware” level, unlike pre-programmed hardware. Inside it are thousands of logic blocks and thousands of interconnects that can be configured (or “wired”) in software to achieve desired digital operations. Hardware logic can be defined by designers using hardware description languages (HDLs such as Verilog/VHDL) to implement fully customized circuits.
Core characteristics:
- Hundreds or thousands of logic units execute tasks simultaneously
- Can be ‘rewired’ at the circuit level
- Fixed logic paths make them suitable for applications with high real-time requirements
Components of a Microcontroller and FPGA
Although both can serve the role of driving electronics, their internal construction differs immensely.
MCU Internal Construction
A microcontroller unit is a mini computer in a single chip. It has everything you need to run your program from the start:
- CPU Core: the component that performs instructions sequentially, one at a time.
- Flash Memory: the equivalent of a hard drive; it holds your program permanently.
- RAM: It’s a fast and temporary memory for real-time tasks in the stack.
- Peripherals: components such as communication protocols, timers, and digital and analog converters that enable the MCU to interface.
- Clock System: enables synchronized passage of time for operating tasks on time.
An MCU is a toolbox waiting to be put to use. Your program operates, and it can immediately control a machine, sensor, or basic electronic piece without any extra work needed.
FPGA Internal Construction
An FPGA does not provide you with a complete setup. Instead, it gives you:
- Configurable Logic Blocks (CLBs): digital building blocks that act as digital “Legos” with which you create whatever logic function you desire.
- Interconnects: the wiring to connect various logic parts.
- I/O Blocks: pins that can be configured for input or output to connect the FPGA with the external world.
- Digital Signal Processor Slices: configured units that can handle math operations for filtering or similar processes.
- Block RAM (BRAM): distributed RAM located within different parts of the chip.
- Clock Management Units (PLLs, DCMs): ensure that all logic blocks stay in sync with each other at faster-than-necessary speeds.
FPGA acts like a box of Lego. Do you want to make a CPU? Or a signal processor? Or something else? Once configured, it runs everything in parallel.
Difference between MCU and FPGA
Both microcontroller units and FPGA can control electronics, but they follow completely different design philosophies. The table below summarizes their main technical differences.
MCU vs FPGA Comparison Table:
| MCU | FPGA | |
Architecture | Runs on a fixed CPU to interpret and execute instructions in order. | Made of reconfigurable logic blocks that operate to perform tasks in parallel. |
Performance | Limited based on CPU clock speed. | Capable of very high throughput and ideal for real-time applications. |
Flexibility | Has fixed peripherals and functions that cannot be adjusted. | Entirely customizable hardware; the exact needs of the application are met. |
Power Consumption | Typically, lower power consumption; ideal for battery-operated devices. | Typically higher power consumption; however, newer ones are more power-efficient. |
Cost | Less expensive to create the chip and initial development tools. | More costly devices and more expensive design tools. |
Ease of Development | Programmed in C/C++ languages with a standard toolchain easily found. | Programmed in HDL (VHDL/Verilog), requiring someone who knows how to design hardware. |
Applications | Consumer electronics, IoT, motor control, and industrial automation applications. | 5G technology, aerospace applications, AI acceleration, video/image processing. |
MCU vs FPGA: Which should I Choose?
How to select is a performance consideration based on the required application.
- An MCU is suitable for applications where low power and cost-critical designs are required, such as sensor controls, motor drivers, or small IoT boards. From the PCB perspective, this often means one power rail, basic clock requirements, and minimal decoupling considerations. A layout is often straightforward beyond proper grounding and signal routing.
- An FPGA offers much more performance and flexibility, but requires more design effort. PCs will need multiple power rails for core and I/O, specialized oscillators for clocking applications, and power integrity will need high-speed considerations for DDR or PCIe connections. Significant pin counts in BGAs require fan-out considerations and potentially HDI stackups and microvias. Power and thermal considerations have become mandatory.
In some instances, the two components coexist, with the FPGA doing heavy parallel processing and the MCU doing the control and communication. Thus, designers also need to consider the interconnects between the two domains in an added layer of complexity.
When Should You Consider Upgrading or Adding an FPGA?
You may need to switch from a microcontroller to an FPGA when your project shows signs of performance limitations, such as:
-
High CPU utilization or insufficient real-time performance
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Requirements for multi-channel parallel processing or deterministic timing
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Complex control loops or multiple ADC inputs
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Latency jitter or custom high-speed interface demands
How to Migrate from MCU to FPGA
Typically, direct replacement is a very risky leap; a safer and more sensible way is to employ a gradual migration strategy.
There are several ways to accomplish this. The first one is High Level Synthesis, which involves creating FPGA code in C language. Another option is to utilize an FPGA with a processor or processors embedded inside it.
The following steps can serve as a reference:
- Use a performance profiler to identify functional modules that have high CPU utilization, long execution times, and strong parallelism (e.g., filters and FFTs).
- Abstract these hotspot functions into modules, design them as portable logic modules (HDL/HLS), offload them to the FPGA, and enable communication and collaboration with the microcontroller unit.
- Place the acceleration modules on the FPGA, and implement a soft-core CPU on the FPGA so that you can continue running part of the MCU code.
- Use high-level synthesis (HLS) tools to convert existing C/C++ code segments into hardware modules, thereby reducing the need for manual HDL coding.
- Once the prototype has passed testing and has been shown to operate stably, consideration can be given to either large-scale migration or the integration of MCU functionality into the FPGA.
Case Study: Fragment of Motor Control Migration from MCU to FPGA
Let’s take a motor control system as a real-world example.
Originally developed on an MCU in C/C++ for closed-loop control, PID computations, feedback filtering, PWM driving, and so on. Under high-performance conditions, the MCU’s response time, jitter, and interference become bottlenecks.
The migration path goes as follows:
- Identify the important modules: Examples include speed loops, current loops, filtering, and PWM output control.
- Use HLS to encapsulate these modules as hardware blocks and create an HDL implementation.
- The FPGA is used to control speed and current, whereas the MCU is only responsible for upper-layer scheduling, parameter changes, and communication management.
- Check to see if latency, jitter, resource utilization, and other parameters satisfy requirements. If the results are favorable, gradually migrate more submodules.
Conclusion
This article compared microcontroller units and FPGAs with respect to architecture, efficiency, and design implications.
- MCUs are best for compact, cost-effective, and power-sensitive designs.
- FPGAs unlock higher performance, parallelism, and real-time capabilities, though they require more complex design and layout considerations.
Whether it’s a small application based on an MCU or a sophisticated design that relies on an FPGA and HDI stackups, ELEPCB can help you. Our engineering and PCB manufacturing staff will align your needs with performance, reliability, and cost thresholds regardless of the application. Contact us today to choose suitable platform for your embedded design!
FAQ
A1: An MCU is easier to design because it generally requires one rail of supply, fewer decoupling capacitors, and simpler routing. FPGAs require multiple rails, impedance control, and proper fan-out due to high pin counts of BGAs.
A2: MCUs come in QFP or small enough BGAs that are fairly easy to route. FPGAs use large BGAs with hundreds if not thousands of pins that require HDI technology, microvias, and fine stackup configuration.
A3: Yes. Designs often use an MCU for control and communication while the FPGA runs at a higher frequency for data. However, interconnects must be planned to ensure no problems occur between the two devices.
A4: Yes. FPGAs typically require external oscillators, configuration memory, and more robust power regulation. MCUs come with these requirements internally better integrated.
A5: Not always. While FPGAs are great at high-speed parallel tasks, PCB placement for stack-up, impedance matching and controlled routing is just as important and can give the edge to the MCU.
References
[1] Intel. (n.d.). FPGA vs. Microcontroller: Choosing the Right Solution for Your Application. Retrieved from https://www.intel.com
[2] Microchip Technology. (n.d.). FPGA vs MCU Guide. Retrieved from https://www.microchip.com
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