DSP Performance Analysis of FPGA

“With the continuous development of electronic chip technology, FPGAs are increasingly used in a variety of DSPs. We expect this trend to become more pronounced in the next few years.” The US research agency Berkeley Design Technology made the above prediction. The two major FPGA manufacturers, Xilinx and Altera, have been involved in DSP applications many years ago. In the past one or two years, with the development of 5G communication, video imaging and other fields, FPGA DSP has become a hot spot again.

How did FPGAs introduce industry-driven architectures

Why use FPGA as DSP? Wu Xiaodong, general manager of Xilinx China operations, analyzed the concept of DSP: DSP means digital signal processor, and it can also be expressed as digital signal processing—it does not represent a certain kind of chip. In fact, there are many different solutions for digital signal processing, which can be implemented by ordinary digital signal processors, MCUs (microcontrollers), etc. Similarly, FPGAs can also do digital signal processing. As the speed of digital signal processing continues to increase, the application of FPGA is increasingly prominent. That is, FPGA and DSP complement each other.

Mr. Wang Donggang, Altera’s Asia-Pacific market channel engineer, went a step further and even optimistically predicted that the two not only complement each other, but FPGA may compete with current high-end DSPs. He proposed: traditional DSP is facing the challenges of performance, power consumption and time to market, especially the following applications: next-generation wireless communication systems, high-end consumer electronics, multi-channel video systems. There are two major trends in implementing DSP with FPGA: first, as a traditional DSP co-processing, to meet the ultra-high performance requirements of system equipment for DSP; second, to directly replace traditional DSP to meet the system’s excess requirements for power consumption, cost and time-to-market .

What are the characteristics of FPGA for digital processing? For ordinary DSP, digital signal processing mainly uses one unit. The traditional DSP processor is a high-performance digital processor, which includes a high-performance unit that can run at a speed of several GHz, but it is only one unit, When you do a more complex operation, you may loop back and forth hundreds of times to complete the operation, so its speed is not very fast.

FPGA is a natural parallel processing structure. There are hundreds of units in FPGA. For example, Xilinx Virtex-5 SXT is 550MHz, but this complex operation can be quickly completed in one unit, so the performance of FPGA is actually is much higher than the traditional DSP.

According to convincing independent third-party benchmarks: Altera’s devices have 10x/$ DSP performance. The system architecture using FPGA co-processor can offload the workload of traditional DSP, and effectively execute complex mathematical calculation algorithms to improve DSP system-level performance.

So, what is the relationship between FGPA for DSP (Digital Signal Processing) function and traditional DSP (Digital Signal Processor)? FPGA manufacturers believe that the traditional DSP is a programmable DSP, which is actually an ideal solution for signal processing; however, with the increasing complexity of current operations and changes in standards, the requirements for high-definition, multi-channel, and real-time are getting higher and higher. , so there is a performance gap in the process of applying their method, and more and more users in this place are using FPGA for processing, so it can be considered that FPGA and DSP are complementary to each other, especially in the multiplexing of logic and mergers.

When the multiplexing and merging of logic requires new peripherals and bus implementations with different bandwidths, using FPGA to implement digital signal processing gives engineers great flexibility. At the same time, FPGA has powerful parallel processing capabilities, which can help DSP to do a lot of performance acceleration , to solve the overload problem. In this regard, FPGA manufacturers and TI have a consensus. The two sides complement each other in many aspects and jointly provide customers with a better solution.

The evolution of FPGA’s DSP is like this: the logic is solidified and programmed as a solidified multiplier, and then it is promoted to a higher stage and becomes a multiply-accumulate unit (MAC). Why is this so? Because digital signal processing is not a simple multiplication, when doing digital signal processing, you will encounter a lot of multiplication and multiply-accumulate, as well as comparison, counting and matrix operations, etc. If these are done through multipliers, signal processing is required. Experts and experts familiar with FPGAs can do it.

Another advantage of FPGA’s DSP is that it can be guaranteed to run above 250MHz. The upper limit is not given. It depends on the user. For some experienced users, it can run to more than 300MHz. But for a DSP designer who is not very familiar with FPGA, it can easily run to 250MHz.

Xilinx currently has 8 FPGA DSPs. Among them, Sparten-3A DSP is a low-end product, which was just released on April 16 this year. High-end Virtex-DSP is divided into two product lines: Virtex-4 SX, Virtex-5 SXT using 65nm process. Many DSP engineers are very concerned about whether the performance of DSP is high enough? So Xilinx’s products range from 21 up to 352 GMAC/s (giga-multiply-add/s) to provide a different range of performance, while also increasing bandwidth in terms of memory. So the lowest speed products can run to 250MHz, the high speed products can run to 550MHz; MAC units from 84 to 640.

Altera uses high-density Stratix III devices to expand the DSP performance of FPGAs. With embedded DSP blocks running at 550Hz, these devices can achieve 492 giga-multiply-add (GMAC) per second performance and combine a good logic structure with a speed-optimized interconnect.

The benefits offered by low-cost Cyclone III FPGAs include DSP performance, flexibility, and faster time to market. The inexpensive Cyclone III ECP3C5 has enough embedded multipliers and logic resources for real-time 7×7 pixel filtering on 1080p high definition video. Cyclone III is the right choice for cost-sensitive DSP applications.

For high volume applications, Stratix II devices can be ported to HardCopy II structured ASICs with full pin compatibility, ensuring that the customer’s design functionality remains unchanged. Altera’s new generation of structured ASIC chips with logic equivalent to up to 2.2 million ASIC gates, DSP blocks equivalent to an additional 1.4 million gates, and more than 8 Mbits of embedded memory.

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