SRC Forum - Message Replies
Forum: Reliability & Maintainability Questions and Answers
Topic: Reliability & Maintainability Questions and Answers
Topic Posted by: Reliability & Maintainability Forum
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998
Posted by: Joni siipola
Date posted: Tue Aug 31 5:08:16 US/Eastern 1999
Subject: Frequency derating
Could anyone explain the Military requirement for derating digital microcircuits? Especially frequency.
Thank you for your help!
Reply Posted by: Bruce Dudley
Organization: Reliability Analysis Center
Date Posted: Tue Aug 31 11:24:24 US/Eastern 1999
When applying commercial mirocircuits, designers should consider the device performance characteristics over the expected life and then apply a degree of parametric deratng to compensate for functional loss. For mirocircuits, parameters depending directly on transistor beta, resistor value or junction leakage are most prone to shift during life. Other parameters depending on saturation voltages of junctions and on ratios of resistors are most likely to remain stable. With this in mind, one should consider derating the fan out and logic noise margin of digital circuits to increase full performance over the life. Delay times or rates do not vary greatly so are not usually derated. With regard to the frequency parameter, this is usually derated in a microprocessor so as to reduce the heat dissipated in the device and increase the expected life at designed to performance. Most devices can be operated at the manufacturers specification limits but the question that you need to consider is, HOW LONG IS THIS TIME?