NASA Office of Logic Design

NASA Office of Logic Design

A scientific study of the problems of digital engineering for space flight systems,
with a view to their practical solution.


The NASA ASIC Guide: Assuring ASICs for SPACE

Section Three: ASIC Design

Introduction

Section Objective:

To describe, for ASIC managers and designers, the tasks essential to producing high-reliability computer-based circuit design and tests that model all ASIC function, test and performance requirements.

The NASA ASIC Guide assumes that all technical readers have experience with board-level electronic design. To create ASIC designs, designers must master microelectronic component design. To meet the extensive requirements of space applications, designers must also master design for high-reliability.

Successful microelectronic component design fundamentally consists of creating a set of computer files that accurately reflect the required ASIC function and performance. An ASIC vendor then uses these files to build parts that meet all device requirements. The design methodology used must supply all needed information so the ASIC vendor can properly do his job. We strongly recommend that ASIC designers adopt only tools and design approaches supported by their selected ASIC vendor. By doing so, designers will receive much better design support from their vendor and greatly enhance their chances of a first-pass working device.

The ASIC "Technical Specification" and the "ASIC Design Process" chapters summarize general microelectronic component design (they apply to both commercial & space ASIC work) from the ASIC user/designer perspective. The "ASIC Design Process" chapter is further broken into generation of a complete and accurate specification, logic synthesis/implementation, design verification, test generation, and packaging-influenced design.

Both the "Design for Test" and "Design for Radiation Tolerance" chapters summarize ASIC design for space applications. Design for natural space radiation environments is truly unique to space ASICs. While design for test (DFT) is not unique to space devices, it is a very important part of satisfying space ASIC high-reliability requirements.

Successful ASIC design, especially successful high-reliability ASIC design, depends upon thorough ASIC management and informed ASIC vendor evaluation. Then, even the best ASIC design must rely on the right fabrication, assembly, and part acceptance for good ASIC parts.

Before we begin the main part of the section, we will present a sample of designer responsibilities in some of these other areas of an ASIC program.

Design in ASIC Management, Section One

ASIC managers must supply adequate resources, realistic goals, and unambiguous requirements for ASIC designers to do their jobs. ASIC designers must, in turn, support ASIC management with accurate estimates of their needs and then regular, measurable status information as their work proceeds.

Most managers faced with using ASICs in a board design for the first time will have some experience with off-the-shelf component board design. What they won't have is experience in board design where one or more components (ASICs) also have to be designed. Designers have a responsibility to educate managers without ASIC experience about these differences.

The guide's management section discusses scheduling and resource management as well as the system/board development flow in relation to the development of an ASIC. Quite a bit of detail is available there for your review.

Design in ASIC Vendor Evaluation, Section Two

ASIC designers have a vested interest in good vendor evaluation. Selecting the right ASIC vendor not only brings a design partner with the right tools, but also enhances the chances of an excellent final part. Correct tool selection is a large part of vendor evaluation. You, as a designer, need to work hard in this area for the right tools to do your job.

Design in Part Acceptance, Section Four

Designers and manages without much ASIC experience are unaware that legal obligations only require ASIC vendors to deliver parts that pass contracted-for tests. It is extremely unusual for a vendor to be contractually-bound to deliver a part that implements a particular netlist or schematic. This doesn't mean that vendors don't use the designed netlist or schematic, but, if another, cheaper structure can pass the tests you give them, that's what you'll get. Therefore, we cannot over-emphasize that a designer's responsibility must include complete and accurate testing. What you test for is what you get.

Design in Procurement Support, Appendix Five

The most important deliverable for the support of an ASIC procurement is a good contract. This requires a complete technical specification from the designer. In conjunction with any general specification and statement of work (SOW), the technical specification forms the major documentation which supports the ASIC procurement.

ASIC designers are frequently called upon to support various phases of an ASIC procurement. This support may include evaluation of contract elements, negotiation evaluations, review of technical bids, etc. Designers and their managers must allocate sufficient time to these activities or ASIC quality will suffer.


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Last Revised: February 03, 2010
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