When confronted with a multilayer circuit card or subsystem for which spares are all but unobtainable, and documentation is wishful thinking, the use of forward looking design options can be limited. ?Often we are required to use legacy production test equipment as part of final qualification,? Notes Patrick Antaki, lead engineer at PHT Aerospace. ?This means that we must go beyond functional compatibility and achieve something close to real timing equivalence despite the fact that newer FPGA?s and other components are capable of much faster speeds.?
Challenges in reproducing legacy avionics systems don?t stop there. Experienced engineers will be familiar with level shifters, off card signal buffering, overshoot correction and load tuning, emi reduction, and pcb design rule specification as just some of the tricks required to make 21st century electronics look and behave like a 30 or even 50 year old legacy system.
What is required in every case, is a proven process that is both comprehensive and detail oriented enough to insure that use cases both inside and external to our system (a system that may not even be documented) are not missed or mischaracterized in any way.
PHT?s Reverse Engineering Processes
Through years of avionic system reengineering, the team at PHT has developed a process that remains mostly intact at a high level, when confronted with most reverse engineering challenges. An example of this process applied to the recent reverse engineering of a 12 layer CCA used in the radar solution of a jet fighter, goes something like this:
- Capture the complete design in digital simulation, including timing parameters
- Develop our own simulation vectors
- Apply these simulation vectors as test patterns (using a newly developed tester) to the legacy CCA to try to match-up our simulation with the physical legacy CCA. These vectors may not match the in-situ use of the CCA, but they are a first step for confirmation of our logic design.
- Build our new CCA and implement the design based on our own generated test / simulation vectors set. Note that our design mostly resides within the FPGA logic, rather than being significantly dependent on the rest of the hardware PCB design.
- When we gain physical access to a radar system (or to a legacy tester), we will capture actual digital patterns as applied to, and responded by, the legacy CCA (as well as our prototype CCA). This is one of the engineering functions of the new tester we will design, which will allow engineers to extract that data easily, on-the-fly and in-situ during radar operation. Our design will extract data that includes both digital patterns as well as parametric data (voltage levels, rise/fall times, etc.)
- We will then use the extracted “real” functional vectors in our tester to continue to verify, adjust, and reconfirm our CCA design (as well as its matching the legacy CCA).
- A few iterations of this process will lead to a complete and highly repeatable new CCA design (with FPGA program).
- The same tester is versatile enough to use in engineering prototype testing, in-situ testing and vector data acquisition, as well as for manufacturing testing.
- As a design philosophy, we intend to achieve a match for all three “CCAs”: digital simulation, legacy CCA and the new design CCA (including production units). This is the only means of “gaining control” over the design with confidence, and ensuring that no small details fall-through, even if the new CCA functions within the radar system.
Add to this process the details of electrical and environmental testing, burn-in, as well as field qualification, and you have a skeleton understanding of the level of detail and careful design considerations that are front of mind during analysis and design.
These considerations and test equipment are often carried forward on location for the various in-situ testing stages where we bring with us all development tools, including CCAs and our tester and associated technical equipment to allow for immediate changes, updates, improvements to the new CCA design or tester as needed.
Legacy system qualification and design requires significant experience and deep understanding of the nature of legacy system reproduction.
Call PHT Aerospace to discuss your Reverse Engineering or Obsolescence challenges, today.