In a recent meeting with a vendor about their new product, the product engineer emphasized that their part had guaranteed “four-corner performance”, unlike some of their competitors. That's a phrase I occasionally hear, and it says everything about the design challenge, especially on the analog side.
What is four-corner performance? It means meeting specifications anywhere within the four extreme pairings of high/low voltage and high/low temperature. Each of these corners stresses the electrical parameters due to drift, temperature coefficients, ability to source and sink current, and many other factors. Meeting performance at 25 degree C ambient temperature and nominal supply voltage is not the same as meeting it everywhere within the extremes.
Even if all the ICs in your design meet the four-corner criteria, the board- and system-level design still may not. Linear and nonlinear changes in primary and secondary parameters of the passive components, connectors, the PCB itself, display, and just about everything else, can sum to out-of-spec overall performance.
Achieving four-corner system-level performance poses some strategic engineering decisions. Should you use only qualified components and safety margins, so the end product meets specs by its inherent design? Or should you accept some performance shortfall in the hardware design, and compensate for it by factory and field software-based calibration? Or perhaps it's better to use feedback and calibration, centered on a single near-perfect component, such as a premium voltage reference? Decisions like this are what thorough engineering is all about.
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