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The effects of random variations during the manufacturing process on devices can be simulated as a variation of transistor parameters. Device degradation, due to temperature or voltage stress, causes a shift of device parameters, for example threshold voltage V th, which can also be modeled as a degradation of transistor parameters. Therefore, in order to design circuits, which are robust and reliable, analysis and optimization of their sensitivity to variations in model parameters is important. Furthermore, constraints on the operating regions and voltage differences of transistors are used in order to keep operating points stable over a large temperature range. In this work, using two circuits for automotive applications and current process development kits (PDK), we show how design centering software can be used to consider both sensitivity reduction towards model parameter variation and constraints to control safe operating areas (SOA). Beyond that a comparison of the constraint matrix method with two established methods of SOA checking is done.
Date of Publication: May 2009