What is the application of FPGA in the aerospace field
1. Features of FPGA
FPGA (Field programmable gate arrays) is a programmable signal processing device, the user can define its function by changing the configuration information to meet the design requirements. Compared with traditional digital circuit systems, FPGA has the advantages of programmability, high integration, high speed and high reliability. By configuring the internal logic functions and input/output ports of the device, the original board-level design is carried out in the chip. , improve the circuit performance, reduce the workload and difficulty of the printed circuit board design, and effectively improve the flexibility and efficiency of the design. Advantages for designers using FPGAs:
- Reduce the demand for the required device varieties, which helps to reduce the volume and weight of the circuit board;
- Increases the flexibility to modify the design after the circuit board is completed;
- Flexible design modification helps to shorten product delivery time;
- With fewer devices, fewer solder joints can improve reliability. In particular, it is worth mentioning that in the case of higher and higher operating frequencies of circuits, the use of complex circuit functions implemented by FPGA reduces the electromagnetic interference problem caused by improper PCB wiring on board-level circuits and helps to ensure circuit performance.
FPGA is also the best way to realize aerospace application specific integrated circuit at this stage. Using commercial off-the-shelf FPGAs to design on-board electronic systems for spacecraft such as microsatellites can reduce costs. Using the abundant logic resources in the FPGA to carry out on-chip redundant fault-tolerant design is a good way to meet the reliability requirements of the spaceborne electronic system.
At present, with the continuous development of satellite technology, the continuous improvement of user technical indicators and the increasingly fierce market competition, functional integration and light miniaturization have become a mainstream trend of on-board electronic equipment. The use of miniaturization technology can reduce the volume, weight and power consumption of spaceborne electronic equipment, and improve the ability of spacecraft to carry payloads and the power efficiency ratio.
The use of high-function integrated miniaturized devices can reduce the size of the printed board, reduce the number of pads, and make full use of redundancy technology to improve the fault tolerance of the system. The key to the miniaturization of spaceborne digital circuits is the selection of devices, including the selection of embedded high-integration devices. Among them, the selection of high-density programmable logic devices FPGA is an important implementation method.
At present, in the design of aerospace remote sensors, FPGA is widely used in the function expansion of the CPU of the main control system, the generation of the driving sequence of the CCD image sensor and the high-speed data acquisition. This paper reviews the development of FPGA, analyzes its main structure, and summarizes the aerospace application FPGA. The requirements for FPGA and its design in aerospace applications are pointed out, the influence of space radiation effect on the reliability of FPGA is analyzed, and the reliability design method to improve the radiation resistance of FPGA is summarized. Finally, the development of FPGA for aerospace application is prospected.
2. The application of FPGA in the aerospace field
Programmable logic devices have been more and more widely used in aerospace and space fields because of their convenient design, easy design modification, and easy expansion of functions. One is a one-time programming anti-fuse FPGA represented by Actel’s products, and the other is a SRAM-based reconfigurable FPGA represented by Xilinx’s products.
2.1 Classification of FPGAs for Aerospace Applications
FPGA According to its programmability, there are currently two types of FPGAs with successful aerospace application experience: one is a one-time programming FPGA that can only be programmed once. The other type is a reprogrammable FPGA that can be programmed multiple times, such as SRAM-type FPGA and Flash-type FPGA. Such FPGAs generally have in-system programming capabilities.
2.1.1 One-time programming FPGA
This kind of product adopts anti-fuse switching element, which has the characteristics of small size, small layout area, low radiation resistance and anti-interference, and low characteristic impedance of interconnection lines. It does not require external PROM or EPROM, and the configuration data of the circuit will not be lost after power failure. , can work after power-on, suitable for aerospace, military, industry and other fields. Among such products, the representative product that has achieved successful experience in aerospace applications is ACTEL’s radiation-hardened anti-fuse FPGA.
Different from the layout of logic modules, wirings, and switch matrices scattered in the traditional FPGA plane, the anti-fuse FPGA adopts a compact, grid-dense layout of plane logic modules. Devices are connected by metal-to-metal programmable anti-fuse internal connection elements located between the upper and lower logic module layers, reducing the space occupied by channels and routing resources. Before programming, the connection element is in an open state. During programming, a small local area of the anti-fuse structure has a sufficiently high current density, which instantly generates large thermal power consumption and melts the insulating layer medium to form a permanent path.
2.1.2 Reprogrammable FPGA
Such products use SRAM or FlashEPROM-controlled switching elements, which have the advantage of being reprogrammable. The configuration program is stored in the memory outside the FPGA. When the system is powered on, the configuration program is loaded into the FPGA to complete the customization of hardware functions. Among them, the SRAM-type FPGA can also change the configuration during system operation to realize the dynamic reconfiguration of system functions.
However, the user configuration logic stored in such FPGAs will be lost after power down, and can only be reloaded from external memory after power up. FlashEPROM type FPGA has the dual advantages of non-volatile and reconfigurable, but it cannot be dynamically configured, and its power consumption is higher than that of SRAM type FPGA.
Because the configuration data of this type of FPGA is stored in the SRAM memory in the FPGA, the programmable logic switch is realized by a multiplexer, and the internal logic function is realized by a look-up table based on the SRAM structure. These parts belong to the single-event flip effect sensitive semiconductor structure. . Therefore, special attention should be paid in aerospace applications. A representative product with successful experience in aerospace applications is Xilinx’s FPGA products based on the SRAM-type Virtex series.
2.2 Current Situation of FPGA Aerospace Applications
FPGA has been widely used in aerospace and space fields at home and abroad, especially commercial satellites. According to statistics, FPGAs are used in a total of 60 projects in deep space exploration, scientific and commercial satellites at home and abroad, and there are also many projects in military satellite projects that use FPGAs.
2.2.1 Aerospace application of ActeFPGA
Actel’s radiation-hardened and radiation-hardened FPGAs have continued to be used in NASA and ESA’s Mars exploration missions since the success of the 1997 Mars Pathfinder and subsequent Spirit and Opportunity missions. Actel’s radiation-tolerant and radiation-hardened devices are used in the control computer of the Mars rover, which performs the navigation function for the six-month flight from Earth to Mars.
Actel devices are used in the cameras and wireless communication equipment of the Mars Explorer Rover. More than 20 ActelFPGA devices are used in the solid-state recorder in ESA’s Mars Express orbiting satellite. Actel’s FPGA devices have been used in the German Aerospace Field (DLR) Dual Spectral Infrared Detection (BIRD) satellite.
BIRD is the world’s first satellite to use infrared sensor technology to detect and study high-temperature events on Earth, such as forest fires, volcanic activity, and oil well and coal seam burning. More than 20 high-reliability FPGAs are used in satellite payload data processing, memory management, interfacing and control, co-processing, and sensor control for infrared cameras in several key functions.
2.2.2 Aerospace application of Xilinx FPGA
Compared with ACTEL, Xilinx’s products for aerospace and space fields are developed relatively late. However, the transition from its powerful, high-performance, reconfigurable civilian plastic-encapsulated products to aerospace-grade products, and the overall improvement of space radiation resistance, gradually It has become a commonly used FPGA product in the design of space electronic products, and will be more and more widely used.
Xilinx’s Virtex radiation-tolerant FPGA is used in OptusCL, an Australian military-civilian mixed communication satellite launched in 2003. In the satellite’s UHF payload, XilinxVirtexFPGA (XQVB300) is used to implement signal processing algorithms for earth data, and IP provided by Xilinx is used nuclear.
Xilinx’s ruggedized FPGA XQR4062XL was used in the high-performance computing payload of the Australian science satellite Fedsat (Joint Satellite, used to study the magnetosphere) launched in 2002. HPC-1 is the first example of using FPGA to implement the configurable computing technology RCT in the standard operation of an on-board computer system. The RHC-II currently under development will use XilinxFPGA to realize on-board data processing.
In addition, the XQR4O36XL product is used in the sensor of GRACE (NASA). XilinxFPGA products have been successfully applied in Mars exploration rovers Discovery and Spirit. Two pieces of aerospace FPGAVirtexTMFPGAXQVR100O are used in the wheel motor control, robotic arm control and other instruments of the Mars rover, and four pieces of radiation-resistant 4000 series FPGAXQR4062XL are used to control the key ignition equipment of the Mars lander to ensure that the lander descends according to the prescribed procedures and Landed successfully. Europe’s first comet orbiter and lander ROSETTA have a total of 45 FPGAs, all of which use ACTELRT14I00A, which undertakes important functions such as control, data management, and power management, and any FPGA must not be powered off during flight.
The latest release of Xilinx Virtex-5QVFPGA has very high radiation resistance, TID resistance is more than 700kraD, SEU (Sin-gleEventUpset, single event upset) latch (LatchUp) resistance exceeds 100MeV · cM2/Mg, mainly for artificial satellites and the universe Remote sensing processing, image processing and navigator applications on the spacecraft.
Therefore, the FPGA-based system configuration does not need to add redundancy for radiation measures, and it is possible to reduce the time and cost required for system development. Its scale also reaches 130,000 logic units, integrates high-speed transceivers with a maximum speed of 3.125Gbit/s, and strengthens DSP functions. As an FPGA used in the aerospace field, it is the highest level in the industry.
3. The radiation effect of FPGA in the aerospace field and its influence
Aerospace and space electronic equipment are affected by radiation differently due to their different orbits and usage environments. Generally speaking, the radiation effects that have a greater impact on FPGAs mainly include: total dose effect, single-event flip, single-event latch-up, single-event function interruption, single-event burnout, and single-event transient pulse effects. , the failure forms of the FPGA are also different.
TID：Total ionizing Dose
Photons or high-energy ions are ionized in the materials of integrated circuits to generate electron-hole pairs, which eventually form oxide trap charges or interface trap charges at the interface between the oxide layer and the semiconductor material, which reduces the performance of the device or even fails.
SPF：Single Particle Flip
The heavy particles with a certain energy collide with the storage device or the PN junction of the logic circuit. The charges formed around the trajectory of the heavy particles are collected by the sensitive electrodes and form a transient current. If the current exceeds a certain value, the logic circuit will be triggered to form a logic state. flip. The single-event flip-sensitive area refers to the area in the FPGA that is easily affected by the single-event effect, including the configuration memory, DCM, CLB, and block storage area of the FPGA.
SEL：Single Event Latchup
The PNPN structure of the CMOS device has become a thyristor structure. The incidence of protons or heavy particles can trigger the conduction of the PNPN junction into a high-current regeneration state, resulting in single-event latch-up. The latch state can only be exited by reducing the supply voltage.
SEFI：Single Event Functional Interrupt
The incident protons or heavy particles cause the device’s control logic to malfunction, thereby interrupting normal control functions. The sensitive parts of single event function interrupt in FPGA are configuration memory, power-on reset circuit, SelectMAP interface and JATAG interface.
SEB：Single Event Burnout
Transient currents generated by incident particles cause sensitive parasitic bipolar junction transistors to turn on. The regenerative feedback mechanism of the bipolar junction transistor causes the collector junction current to continuously increase until secondary breakdown occurs, resulting in a permanent short circuit between the drain and the source, which burns the circuit. The probability of single event burnout of FPGA is small.
SET：Singl Eevent Tran
The transient current pulse generated by the incident of charged particles affects the input of the logic circuit of the next stage, causing the output of the logic circuit to be disordered. Single-event transient pulses may cause short-term errors in the internal logic circuits of the FPGA. Single-event transient pulses have a greater impact on FPGAs with <0.25μM technology.
Some of the above radiation effects on FPGA are permanent, such as total dose effect, single-event burnout, and displacement damage; some can be recovered, such as single-event overturn, single-event function interruption, and single-event transient pulse.
Among the above single event effects, SEL, SEB and SEGR may cause permanent damage to the device. Therefore, generally on-board systems will use SEL-resistant devices. Although SEU and SET are transient effects, their incidence is much higher than those of the above three types, and more attention should be paid to them. Next, according to the analysis of the above radiation effects, the reliability design method to improve the radiation resistance effect of FPGA is studied.
With the improvement of the process level, the increase of the scale and the reduction of the core voltage of the device, the anti-total dose effect performance of SRAM-type FPGAs has been continuously improved, but it is more susceptible to the influence of SEU and SET.
In response to the problem of single event effects, the report submitted by the MAPLD, NSREC, and RADECS conferences believes that the total dose radiation resistance of Virtex-II series products reaches 200krad, and the anti-SEL ability is below LET160MeV cm/mg without latch-up. At the same time, it is necessary to consider Single event effects such as SEU, SET, SEFL
4. Application of FPGA in Aerospace Field
FPGA reliability design In aerospace and space electronic equipment, FPGA is mainly used to replace standard logic, and also used in SOC technology to provide embedded microprocessors, memories, controllers, and communication interfaces. Among them, reliability is the main requirement of FPGA design.
According to the different functions and their importance, the design of space electronic systems is divided into two categories: critical and non-critical. Spacecraft control is the critical category, and scientific instruments are non-critical. General requirements for FPGAs in spacecraft control systems: high reliability, radiation hardening, and failsafe.
The design requirements of scientific instruments for FPGAs are generally high performance, radiation resistance and fail-safe, and their reliability is determined by performance requirements. The requirements for FPGAs also vary from system to system, such as measurement resolution, bandwidth, high-speed storage, and fault tolerance. ability etc.
The reliability design of aerospace FPGA is mainly realized through the hardware design and software design of the device itself.
4.1 FPGA hardware reliability design
The hardware reliability design of FPGA is mainly aimed at the influence of space radiation effect, and the single event effect protection problem is completely solved with the help of manufacturing process and design technology. Generally, the design is carried out from the following aspects: the overall design of the FPGA is strengthened, the internal design of the self-checking module for indirect detection of radiation effects, and the introduction of an external high-reliability monitoring module.
The overall reinforcement design refers to the use of a certain thickness of material on the outside of the electronic equipment for overall radiation shielding to reduce the radiation effect of the equipment. The commonly used materials are aluminum, tantalum and lipid compounds. This method is widely used in aerospace electronic components and is relatively mature.
For example, Honeywell, a major supplier of U.S. military microelectronics, has a broad coverage of ruggedized ASIC technology. Aeroflex provides ruggedized ASIC products with advanced performance in the way of “design reinforcement, commercial IC process line tape-out”, and has the ability to develop digital-analog hybrid ruggedized ASICs. This kind of technical circuit using commercial wire tape to produce military and reinforced microelectronic products is not only conducive to getting rid of the constraints of process reinforcement on device development, but also conducive to meeting users’ needs for advanced reinforced devices, reducing costs and shortening delivery time.
Atmel provides users with process resources for various devices with high performance, small size, and low power consumption, including radiation-resistant high-speed, low-power digital-analog hybrid CMOS processes for aerospace and CMOS processes with embedded EEPROM.
There are many domestic units engaged in the development of military microelectronic devices, including state-owned scientific research units and non-state-owned IC development companies. However, there are not many units that can complete the development of radiation-hardened ICs. Domestic self-developed reinforced ASIC products have been successfully applied in satellites.
The use of bulk silicon epitaxial layers can also prevent SEI from occurring. For example, Xilinx’s virtex-II radiation-resistant products are further designed with epitaxial substrates on the basis of military-grade devices, and the ability to resist total dose ionization effects is subject to batch sampling and assessment in accordance with MIL-STD-883Method1019.
The purpose of the self-test module is to predict the normality of the entire FPGA operation through the normal operation of some modules. The self-checking module is implemented by simple logic circuits distributed near the important wiring areas of the FPGA, and can also directly provide output from the voting results of the multi-mode redundant module or other results generated by the remainder detection method and the parity check method.
4.2 FPGA software reliability design aerospace applications
The software reliability design of FPGA refers to the application of software program configuration to shield the malfunction caused by radiation effects. Among them, the redundant design method is recognized as a relatively reliable method to deal with radiation effects. Commonly used redundant designs include three-modular redundancy (TMR, Triplemoduleredundancy) and partial triple-modular redundancy (PTMR, ParTIaltriplemoduleredundancy). While TMR can improve system reliability, it also reduces module speed, consumes resources, and increases power. Taking into account other design indicators, the partial three-mode redundancy method can be used for key parts according to the actual situation.
Although the redundant structure can ensure the reliability of the system, it cannot detect and correct errors in time, or introduce too many combinational logics to detect errors. When applied to FPGA, the possibility of fault-tolerant circuit itself is increased. In addition, the unattended operation of the spaceborne system makes system reconstruction and fault recovery very difficult.
Readback checksum of configuration memory and reconfiguration (or partial reconfiguration) is an effective way to resist radiation effects, and the effects of SEU effects can be repaired by reloading part of the configuration, the frequency of which should be the worst case 10 times the incidence of the SEU effect. In the design of reloading logic, it is necessary to carefully design the implementation method of reloading and the content to be loaded. Not all content can be reloaded, and not all content needs to be reconfigured.
In the system design, the high-reliability anti-fuse FPGA is used to read the configuration data of XilinxFPGA from the non-volatile large-capacity memory to configure it. During operation, the configuration memory that is most susceptible to radiation effects is read column by column, then compared with standard data, and the erroneous column is partially reconfigured.
The programmable IO of the FPGA is also susceptible to radiation particles to generate SEUs and SELs. It is a very effective method to design the three-mode redundant design method for the input and output pins, but this method will require three times the I/O resources. If SET acts on the clock circuit or other data and control lines, it is easy to produce short pulse jitter, which may cause false triggering of the circuit or data latching errors. In the design, synchronous reset can be used to design the internal reset circuit and control line enable Signal line, logic data should match the enable signal as much as possible when latching.
5. FPGA aerospace application development trend
At present, under the deep micro-submicron semiconductor process, the traditional FPGA design technology faces challenges in terms of device yield, power consumption, interconnection delay, signal integrity, and testability design. FPGAs based on traditional technologies are still developing in the direction of high density, high performance and low power consumption, making FPGAs develop from general-purpose semiconductor devices to platform-based system-level devices. FPGA design based on asynchronous circuits, 3D integration technology, and the application of new semiconductor structures will be the hotspots in the development of FPGA technology.
In terms of aerospace and space applications, the summary and forecast analysis of FPGA space applications by foreign aerospace companies show that the selection of FPGAs for space applications presents the following trends:
- The working voltage of the device changes from 5V to 3.3V, 2.5V or even 1.8V;
- From the use of total dose reinforcement FPGA to the use of total dose resistant FPGA products;
- From the application of SEU-sensitive register FPGA to the FPGA using the built-in register TMR structure;
- Development from an anti-fuse FPGA that uses only one-time programming to a resettable FPGA based on SRAM/EEPROM.
The prominent problems brought about by this trend of selection are: from register sensitive to SEU to FPGA sensitive to SEU; the design complexity of configuration storage FPGA has been equal to the complexity of ASIC.
The above is all about the application of FPGA in the aerospace field. This paper summarizes the use of FPGA in aerospace applications, analyzes the structural characteristics of FPGA, and analyzes the failure mode and reliability design method of FPGA in aerospace applications according to the irradiation conditions of aerospace and space environment. Finally, the development of aerospace application FPGA and its reliability design technology is prospected.
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