-by Akshat Garg, Analog Applications Engineer, Texas Instruments
Government of India’s new initiative “Make in India,” is gaining popularity across all domains in manufacturing. The Avionics & Defense sector is one of the sectors emerging in this arena. Home grown players like Indian Space Research Organisation (ISRO), Hindustan Aeronautics Limited (HAL) and Defence Research and Development Organisation (DRDO) have already proved their mettle in developing indigenous technologies and robust systems. With the opening up of this sector for private players, the sector will definitely witness a scale up in operations in the future.
However, the major challenges confronting the development of new systems in Avionics & Defence, within limited time and stringent costs are:
- Reliability and robustness
- Complexity and integration
- Increased processing power and bandwidth requirement.
To develop new systems that comply with the above requirements, the components used in these systems will themselves have to qualify for operation in harsh environments. For example – Picture yourself flying in a commercial aircraft at 33,000 ft. above sea level. The temperature outside your window will be around -50ᵒC. You are working on your new Tablet. Imagine if the tablet is put outside the aircraft, Will it work? No, because the components used inside the tablet are all commercial temperature grade or extended, which are operational only in the range 0 to 70ᵒC or -20 to 85ᵒC respectively. On the other hand, the components used inside the control, actuator electronics and sensor conditioning of the aircraft (engine, flaps, rudders, wings, winglets etc.) however, have to work reliably at those extreme conditions.
Texas Instruments Inc. (TI) has been a part of this market and has more than 30+ years of experience in working with Aerospace and Defence sector. As a result, it is constantly innovating to deliver robust and cost effective ICs for this segment.
Reliability & Robustness
Traditionally, for an IC to be used in Avionics and Defence products, it has to be qualified as per the MIL-STD- 883 (MIL-PRF-38535 for ICs) standards. This qualification comes at a huge cost to semiconductor manufacturers and as a result the ICs are expensive. To reduce this cost, TI has invested in technologies (or qualification methods) that enable its products to deliver the same performance, even at absolute extreme conditions. Given below is a glance to some of TI’s innovative products:
This is a complete family of commercial products that undergo additional testing/qualification, in order to support customers with applications in harsh environments. Currently, TI has an available portfolio of over 750 EP devices including Analog, Microcontrollers (MCU), Digital Signal Processors (DSP), Logic, Power and many more. Some of main features of TI Enhanced Products are:
- Long lifetime – No obsolescence of parts until now (Although it has been 10 years, since TI launched its EP program)
- Controlled baseline: Single Assembly/Test(A/T) Sites , Fab site (“sameness” of product)
- Extended temperature range (-55°C to 125°C, or customer defined)
- Highly Accelerated Stress Test (HAST), Environmental Testing and Additional Test Coverage added to test programs
- More than 90 per cent cost savings in comparison to MIL-STD-883 devices.
High Temperature(‘-HT’) Products
The‘–HT’ grade of devices are superior to ‘–EP’ grade and are used under the harshest of conditions. There are certain applications where, the ambient temperatures during operation will go beyond 125ᵒC (maximum temperature for MIL 883). ‘-HT’ products can operate at a temperature range between -65ᵒC to +210ᵒC.
Some of the additional qualification testing performed on ‘-HT’ grade is as follows –
- +200°C operation for 1,000 hours
- Temperature Cycle (-65°C/+150°C 1000 cycles)
- Acceleration, Vibration and Shock testing of products
- Operating Life vs Junction Temperature characterization (Fig 2)
- Availability of Ceramic Packaging and Known Good Die (KGD).
Radiation Tolerant/Hardened Products
Not all electronic subsystems in avionics can be made with ‘–EP’,’ –HT’ or military grade ICs, for instance, the main flight computer system. These are the most critical systems and have to meet the most stringent qualification standard. A common design approach is to make the main flight computer system triple redundant, implement voting schemes, and use ICs that are radiation tolerant or, even better, radiation hardened. The radiation (protons, neutrons, gamma rays) from space, entering the Earth can cause bit flips in memories and processor interfaces. This can lead to execution of wrong instructions and even a full system shutdown/reboot which could be lethal for any avionics product, for example, a commercial aircraft flying at 33000 ft.
TI’s Space grade (‘-SP’) products address these radiation challenges. Both Rad-tolerant and Rad-Hard ICs are available and already being used by almost all the space agencies & avionic companies worldwide.
Direct RF-sampling in High Reliability applications.
In a direct RF-sampling architecture, the data converter digitizes a large chunk of frequency spectrum directly at RF and hands it off to a signal processor to dissect the available information. This is a paradigm shift from the heterodyne architecture where the analog stages (mixers, local oscillators and their attendant filters and amplifiers) are replaced into the digital domain by an RF direct sampling ADC.
Advantages of this approach include:
- Small and light weight RF designs.
- Higher Level of integration by reducing active signal chain components and their supporting power supplies.
- Smaller Multi-Band Radio systems (One RF-ADC per band).
- Power efficient.
With the above features these RF ADC are ideal for Avionics and Defence applications where size, weight and power consumption are prime concerns.
Column Grid Array (CGA) Packaging in High Reliability applications.
Sometimes the density of pins is so high that RF ADCs have to be packaged in Ball grid array (BGA) packaging. Unfortunately, BGA’s low height between component and circuit board and the use of eutectic solder material, do not meet the reliability requirement of some applications. BGA technology is not suitable in cases where long product life, extreme temperature & mechanical stress persist.
CGA packaging is the solution for the above use case. It uses taller solder columns that are often made of more flexible or compliant low-tin solder, rather than solder balls.
Fig6: CGA vs BGA packaging