FPGA Development All--FPGA selection

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FPGA Practical Development Tips (1)

The fifth chapter, the FPGA actual combat development skill5.1 FPGA Device Selection Knowledge

Peng Tong, Hu Yihua/CAS Shanghai Institute of Technical Physics

The selection of FPGA devices is very important, unreasonable selection will lead to a series of follow-up design problems, and sometimes even make the design failure, reasonable selection can not only avoid design problems, but also can improve the system cost-effective, extend the product life cycle, to achieve unexpected economic results. FPGA Device Selection has the following 7 principles: The device's supply channel and development tool support, device hardware resources, the device's electrical interface standards, device speed rating, device temperature rating, device package and device price.

Support for supply channels and development tools for 5.1.1 devices

At present, the main FPGA supplier has Xilinx company, Altera Company, Lattic Company and Actel company, etc., FPGA development speed is very fast, many models of FPGA devices are not mainstream products, in order to improve the product life cycle, it is best in the supply of more than the mainstream device select. Xllinx's mainstream devices are spartan-3e, spartan-3a, VIRTEX-4LX, Virtex-4 SX, Virtex-4 FX, Virtex-5 LX, VIRTEX-5SX, Virtex-5 FX, Spartan-6 and Virtex-6 series, wherein the SPARTAN-3E and SPARTAN-3A series are mainly used in logic design and simple digital signal processing, Virtex-4 LX and Virtex-5 LX series are mainly used in high-speed logic design, Virtex-4 S The X and Virtex-5 SX series are primarily used for high-speed complex digital signal processing, and the Virtex-4 FX and VIRTEX-5 FX series are mainly used in embedded systems.

Xilinx has an integrated development environment Ise,altera Company has integrated development environment Quartusⅱ, two integrated development environment to support the design and development of all parts of our company. The integrated development environment is not only powerful, user-friendly, but also has many third-party partners providing the appropriate technical support to enable the device to achieve higher performance. Therefore, if there are no special application requirements, it is advisable to select the device in these two companies.

Hardware Resources for 5.1.2 devices

Hardware resources are important criteria for device selection. Hardware resources include logical resources, I/O resources, cabling resources, DSP resources, memory resources, phase-locked loop resources, serial transceiver resources, and hard-core microprocessor resources.

The need for logical resources and I/O resources is the most common concern of every designer, but the problems that may arise from excessive consumption of I/O resources and cabling resources can easily be overlooked. In the mainstream FPGA devices, the logical resources are rich, which can meet the needs of the application generally. However, in a more complex digital system, the consumption of excessive I/O resources can lead to 2 problems: The FPGA load is too heavy, the device is very hot, seriously affect the device's speed performance, work stability and life, the design should consider the thermal problem of the device, the local wiring resources are insufficient, the speed of the circuit is significantly reduced, Sometimes the design fails to fit the device even if it is not fitted. According to my application experience:

(1) in the process of complex digital signal processing, the multiplier and divider with higher bit number are more expensive to the global cabling resource;

(2) In the logic design, the two-way I/O port to the local wiring resources consumption is relatively large;

(3) in the use of memory resources to design the application of the filter, the consumption of local wiring resources is relatively large;

(4) in the electrical interface standard is more, and logic more complex applications, the consumption of local wiring resources is relatively large.

In the case of multiplication and more high speed performance requirements, it is better to choose a device with more DSP resources, for example, Altera's Statixⅱ and Statixⅲ series, Xilinx Company's Virtex-4 SX and Virtex-5 SX series.

The memory resources in the device are mainly used for 2 kinds of applications: high-performance filter and small-capacity high-speed data cache. This is a relatively valuable hardware resources, general device memory resources are not too much, memory resources more devices logical capacity is also very large, use less, supply channels are not many, device prices are very high. Therefore, in the device selection, it is best not one-sided pursuit of design integration and choose this device, you can consider the selection of low-end devices + external expansion memory design.

At present, PLL is integrated in mainstream FPGA, and PLL is used to lock the clock, which can make the circuit achieve more stable performance. Xilinx offers a digital phase-locked loop, which has the advantage of being able to obtain more accurate phases control, the disadvantage is that the lower operating frequency is higher, generally above 24MHz; Altera offers analog phase-locked loops, with the advantage that the lower operating frequency is lower, generally at more than MHz, the mainstream device Statix The enhanced phase-locked loops in the Ⅱ and Statixⅲ series are only required to operate at more than 4 MHz, with the disadvantage that the control accuracy of the clock phase is relatively poor.

In the field of communication, the transmission of high-speed data with optical fiber is a more common solution. A1tera's STATIXⅡGX and STATIXⅢGX series, Xilinx's Virtex-4 FX and VIRTEX-5 FX series are integrated with high-speed serial transceivers (note: Xilinx V5 with T products have high-speed serial transceiver, V4, v2p some models also have high (Fast serial transceiver), which is generally priced at a relatively high price. At present, national and Maxim and other companies to provide high-performance dedicated serial transceiver chip price is not high, therefore, if only for optical fiber data transmission is not counted, large can not choose this device, if it is fiber data transmission + logic or algorithm more complex applications, it is best to compare the two scenarios, Then consider whether the device is selected.

Embedded development using FPGA devices with integrated hard-core microprocessors represents One direction for embedded applications. Xilinx offers integrated powerpc™ Virtex-4 FX and virtex-5 FX series devices. As the device prices continue to decline, in many applications, without increasing the cost, the choice of the device and the traditional FPGA+MCU of the application scheme, can greatly improve the system performance and reduce the complexity of hardware design. At this time, the selection of the device is more ideal.

5.1.3 Electrical Interface Standard

At present, there are many electrical interface standards for digital circuits. In complex digital systems, a variety of electrical interface standards are often present. At present, the mainstream FPGA devices support the electrical interface standards are: 1. 5 v,1. 5-v and so on, can meet most application design needs.

Xilinx's FPGA is ideal for almost all of its pins that support the SSTL-2 Classⅱ electrical interface standard at this time.

Speed ratings for 5.1.4 devices

With regard to the selection of device speed grade, a basic principle is: In order to meet the needs of the application, as far as possible the use of low-speed devices. The selection principle has the following advantages:

(1) Because of the transmission line effect, high-speed devices are more likely to produce signal reflection, design to the integrity of the signal to spend more energy;

(2) High-speed devices generally used relatively little, the price is often multiplied, and the high-speed device supply channels generally less, the device's ordering cycle is generally relatively long, often delay the product development cycle, reduce product listing rate.

Temperature rating of the 5.1.5 device

In some applications, there is a high demand for the device's ambient temperature adaptability, which should be chosen in industrial or even military-grade or aerospace-grade devices. According to the research, Altera company each type of FPGA has industrial-grade products, Xllinx company each type of FPGA has industrial-grade products, some models of FPGA to provide military-grade and aerospace-grade products.

Encapsulation of 5.1.6 devices

At present, the main components of the package form: QFP,BGA and FB-GA,BGA and FBGA packaging devices, the pin density is very high, the design must use multilayer board, PCB cabling is very complex, the design cost is high, the device welding cost is relatively high, therefore, the design can not use as much as possible.

However, when the density is very high, the integration is very high and the PCB board volume requirements of high applications, as far as possible to choose BGA and FBGA packaging devices. In another case, in applications where the circuit speed is very high, it is best to choose BGA and FBGA package devices, which are 2 kinds of package devices because the device pin lead inductance and distribution capacitance is relatively small, is conducive to high-speed circuit design.

Price of 5.1.7 devices

Device integration continues to improve, performance continues to rise, and the price is declining is the development of the general trend of FPGA devices, therefore, in the introduction of the new device selection is a basic law. In the case of Xilinx's new Virtex-5, the performance was increased by 30% compared to Virtex-4, while the relative price was reduced by 35%.

FPGA Development All--FPGA selection