FPGA digital clock circuit analysis

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FPGA digital clock circuit analysis

Posted Date: 2024-01-26

What is FPGA

FPGA (Field Programmable Gate Array), field programmable gate array, a semi-customized digital integrated circuit. FPGA is widely used in communications, image processing, medical and other fields due to its high flexibility, short development cycle, and strong processing performance (parallel). With the advancement of technology, FPGA also has a place in fields such as artificial intelligence, 5G and autonomous driving.

FPGA is a product further developed on the basis of programmable devices such as PAL, GAL, and CPLD. It appears as a semi-custom circuit in the field of application-specific integrated circuits (ASIC), which not only solves the shortcomings of custom circuits, but also overcomes the shortcomings of the limited number of original programmable device gate circuits.

For example, use a breadboard to build a digital clock circuit; although the circuit is a digital clock, it contains a crystal oscillator, a buzzer, a digital tube, and various 74 series small chips. The functions that these small chips can achieve are equivalent to a few logic Door, if you build it yourself, you will definitely know that it is very troublesome to build this circuit. You have to connect it one wire at a time and constantly compare it with the schematic diagram. You are afraid that if you connect the wrong wire, your mentality will collapse.

This is just a lot of wiring to build a simple digital clock. If we want to implement more complex functions, then we will have difficulties, because we need to use dozens or hundreds of such dedicated small chips to complete it, which will make the layout and wiring of the circuit board difficult. It will also greatly affect the performance of the entire system, and the built circuit is bulky, unsightly, and extremely poor in practicality, so this method is undoubtedly not feasible.

In order to change this situation, everyone came up with a way, which is to implement it through application-specific integrated circuits (ASIC). We can hand over the specific needs to be realized to ASIC manufacturers and let them design an application-specific integrated circuit chip, so that This problem is solved.

For example, if we hand over the digital clock function requirements to the ASIC manufacturer, the ASIC manufacturer will design an application-specific integrated circuit chip based on the digital clock function requirements. This small chip actually completes the function of our digital clock circuit. Although this method is good, it also brings many other problems, such as long generation cycle, difficulty in verifying the chip, and the inability to change the internal circuit of the chip, etc. So people began to continue to explore to see if there was any way to achieve the function well while solving the shortcomings of the customized circuit.

So FPGA came into being, invented by Ross Freeman, one of the founders of Xilinx, in 1985. It is a type of programmable logic device (PLD).

Xilinx A7 series FPGA chips

The first FPGA chip in the true sense, XC2064, was invented by Xilinx. This time is almost 20 years later than the famous Moore's Law. However, once FPGA came out, the subsequent development speed was faster than most people's imagination.

We need to know that the function of a dedicated ASIC custom integrated circuit chip has been determined before leaving the factory. Take the above digital clock as an example. If I get a brand new digital clock chip now, then I only need to look at it. According to the data sheet provided by the manufacturer, to see how it operates, I may just need to power it on and simply configure it to work.

Its function cannot be changed, it can only run a digital clock, and I don’t know what its internal circuit is like. Although it is simple to use, it lacks flexibility, but FPGA is different. It is shipped from the factory. At that moment it does not have any function, it can be said to be a blank sheet of paper. You can create whatever you want on this piece of white paper. If you want it to realize the function of a digital clock, you can write the logic of the digital clock through a specific editing language, such as Verilog, VHDL and other hardware description languages, and download it to the FPGA. It will generate a digital clock circuit to complete the function of a digital clock. When you no longer want this feature, no problem, you can erase the internal program at any time, or overwrite the original design with a new one. Theoretically, we can use FPGA to generate any function we want. It is precisely based on this powerful editability that FPGA has become more and more recognized by the market in recent years. In the future, the scope of application of FPGA will become wider and wider. .

What are FPGAs used for?

The fields in which FPGA can be applied can be roughly divided into six categories:

1) Communication field

The application of FPGA in the field of communications can be said to be omnipotent. Thanks to the characteristics of the internal structure of FPGA, it can easily implement distributed algorithm structures, which is very beneficial for realizing high-speed digital signal processing in wireless communications. Because in wireless communication systems, many functional modules usually require a large number of filtering operations, and these filtering functions often require a large number of multiplication and accumulation operations. By implementing distributed arithmetic structures through FPGA, these multiplication and accumulation operations can be effectively implemented. In particular, Xilinx's FPGA integrates a large number of resources suitable for the communication field, such as: baseband processing (channel card), interface and connection functions, and RF (radio frequency card) three categories:

(1) Baseband processing resources

Baseband processing mainly includes channel coding and decoding (LDPC, Turbo, convolutional code and RS code coding and decoding algorithms) and the implementation of synchronization algorithms (WCDMA system cell search, etc.).

(2)Interface and connection resources

The interface and connection functions mainly include the implementation of the wireless base station's external high-speed communication interface (PCI Express, Ethernet MAC, high-speed AD/DA interface) and the corresponding internal backplane protocols (OBSAI, CPRI, EMIF, LinkPort).

(3)RF application resources

RF applications mainly include modulation/demodulation, up/down conversion (single-channel, multi-channel DDC/DUC of WiMAX, WCDMA, TD-SCDMA and CDMA2000 systems), peak clipping (PC-CFR), and predistortion (Predistortion). Implementation of technology.

All in all, as long as you learn FPGA well, you can definitely show your talents in the field of communications.

2) Digital signal processing field

FPGA is also invincible in the field of digital signal processing, mainly because of its high-speed parallel processing capabilities. The biggest advantage of FPGA is its parallel processing mechanism, which uses parallel architecture to implement digital signal processing functions. This parallel mechanism makes FPGA particularly suitable for completing repetitive digital signal processing tasks such as digital filtering such as FIR. For high-speed parallel digital signal processing tasks, FPGA performance far exceeds the serial execution architecture of general-purpose DSP processors. It also The voltage and drive capability of its interface are programmable and configurable. Unlike traditional DSP, which needs to be controlled by the instruction set, because of the limitation of the clock cycle of the instruction set, it cannot handle signals that are too high-speed. For LVDS with a rate level of Gbps, It is difficult to deal with class signals. Therefore, the application of FPGA in the field of digital signal processing is also very extensive.

3) Video image processing field

As the times change, people are pursuing higher and higher image stability, clarity, brightness and color. For example, the previous standard definition (SD) has gradually evolved into high definition (HD), and now people are even pursuing Blu-ray quality. Image. This makes the amount of data that the processing chip needs to process in real time becomes larger and larger, and the image compression algorithm becomes more and more complex, so that simply using ASSP or DSP can no longer meet such a large amount of data processing. At this time, the advantages of FPGA are highlighted. It can process data more efficiently. Therefore, after considering the cost in the field of image processing, FPGA is becoming more and more popular in the market.

4) High-speed interface design field

In fact, after looking at the performance of FPGA in the field of communications and digital signal processing, I think everyone should have guessed that FPGA must also have a place in the field of high-speed interface design. Its high-speed processing capabilities and hundreds of thousands of IOs determine its unique advantages in the field of high-speed interface design.

For example, I need to interact with the PC for data, send the collected data to the PC for processing, or send the processed results to the PC for display. PCs have rich interfaces for communicating with external systems, such as ISA, PCI, PCI Express, PS/2, USB, etc. The traditional approach is to use corresponding interface chips for corresponding interfaces, such as PCI interface chips. When I need many interfaces, I need multiple such interface chips. This will undoubtedly make our hardware peripherals more complicated and larger. It is huge and inconvenient, but if you use FPGA, the advantages will come out immediately, because different interface logic can be implemented inside the FPGA. There is no need for so many interface chips. With the use of DDR memory, our interface Data processing becomes more convenient.

5) Artificial intelligence field

If you prefer to pay attention to news in the technology sector, you will definitely be flooded with 5G communications and artificial intelligence recently. Indeed, the 21st century has unknowingly reached 2020. During these 20 years, artificial intelligence has developed rapidly, and the smooth research and development of 5G has also made Artificial intelligence is even more powerful, and it is foreseeable that the future will be dominated by artificial intelligence.

FPGA is also widely used in the front-end part of artificial intelligence systems. For example, autonomous driving requires the collection of various traffic signals such as driving routes, traffic lights, roadblocks, and driving speeds. It requires the use of a variety of sensors to integrate these sensors. Driver and fusion processing can use FPGA. There are also some intelligent robots that need to collect and process images, or process sound signals, which can be completed using FPGAs. Therefore, FPGAs are easy to use in front-end information processing of artificial intelligence systems.

6) IC verification field

When you hear the word IC, you may think it is very profound and beyond the reach of ordinary people, and IC design is a job that only some gods can do. It is undeniable that the threshold for IC design is indeed relatively high, but we do not need to make it too mythical. In fact, to put it simply, we can compare it with PCB design. PCB is built with components on a printed circuit board. A circuit combination with a specific function, and IC design is to use MOS tubes and PN nodes on a silicon-based substrate to build a circuit combination with a specific function, one macro and one micro. If the PCB design is scrapped, it will not cause much loss if it is redesigned and re-prototyped. However, if the IC design is scrapped and then redesigned, the losses will be heavy. As the saying goes, once the cannon is fired, there will be ten thousand taels of gold, so in the IC field** *It’s not just a matter of money. Photoresist is extremely expensive, and photolithography is not cheap. In addition, there are hundreds or thousands of other processes, including manpower, material resources, machine losses, and machine maintenance. It is a painful loss, so IC design must emphasize the success of the first version. To ensure the success of the first version of the IC, sufficient simulation testing and FPGA verification are required. Simulation verification is to run simulation software on the server for testing, similar to ModelSim/VCS software; FPGA verification mainly involves transplanting the IC code to the FPGA and using FPGA synthesis The tool performs synthesis, layout and routing to finally generate bit files, and then downloads them to the FPGA verification board for verification. For complex ICs, we can also split them into several functional parts for verification respectively, and place each functional module on an FPGA. ,The circuit generated by FPGA is very close to the ,real IC chip. This greatly facilitates our IC designers to verify their IC designs.

FPGA manufacturer

The two giants: Xilinx and Altera.

A group of juniors: Unisoc, Jingwei Yage, Gowin Semiconductor, Shanghai Anlu, Xi'an Zhipoly, etc. Compared with leading foreign manufacturers, domestic FPGA manufacturers have greater performance, power consumption, and functions. gap.


ZYNQ = FPGA + ARM core, you can customize the circuit yourself, and you can also do ordinary embedded development.

The Zynq-7000 series is a fully programmable system-on-chip launched by Xilinx, including PS (Processing System) and PL (Programmable Logic). Zynq SoC integrates the ARM dual-core cortex-A9 processor and the Xilinx 7 series FPGA architecture, which not only has the advantages of ASIC in terms of energy consumption, performance and compatibility, but also has the advantages of FPGA hardware programmability.

PYNQ: Python Productivity for Zynq = Python + ZYNQ, is an open source framework launched by Xilinx that uses the Python language and libraries to allow designers to take advantage of programmable logic and microprocessors in zynq to quickly build high-performance Embedded applications.


PLD: Programmable Logic Device, programmable logic device.

SoC: System on Chip, system on a chip.

Review Editor: Huang Fei

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