On Some Reliability Implications of Electronic Circuit Design

Practical approaches to improved reliability have been made difficult to develop at least in part because reliability is an interdisciplinary art involving solid-state physics, circuit theory, and information engineering. In this paper, I delineate some of the factors that must be considered in improving reliability at the design stage. A major factor in achieving this result is the demonstration that the levels of power dissipation in discrete active devices can be reduced by up to at least a factor of 10, with actual improvement in overall circuit operation. The key to this improvement is the fact that with most active devices, the characteristics displayed in a circuit are very sensitive to output current level, but much less sensitive to output supply voltages as long as they exceed a minimum value. As supply voltages are reduced, the power dissipated decreases proportionately, but operating characteristics need not be changed. A series of ``paper´´ designs can quickly verify the independence of operating conditions with respect to the output supply voltage. The result is less waste power, less cooling requirement, and, because of the sensitivity of MTBF (mean time between failure) to device temperature, increased overall MTBF, allowing systems to approach their life expectancy more closely. The subject of electron tube circuit reliability is also included in the discussion, first because the same principles that apply to bipolar and field-effect transistors apply to electron tubes as well, and because high-power transmitters still must use electron tubes in their final stages.