Daily Archives: 15-February-2011

Drive-By Math

Occasionally I have an engineer come by my cube and unexpectedly present me with an opportunity to do math. A few years ago one of the engineers stopped by with a VERY common type of electrical engineering problem. He had an LVPECL logic device that needed to connect to a CML logic device. Of course, these two logic families have different voltage levels and cannot communicate with one another unless some sort of voltage-level shifting (Figure 1) is performed between the devices. We had been using a level-shifting circuit recommended by an IC vendor, but that circuit had turned out to have some problems (I do not know what these problems were). The engineer posing the question had spent a few hours grinding through the math manually and eventually decided that it was too painful to continue. He knew that I use computer algebra systems like Mathematica and Mathcad, so he asked if I could help. Using Mathcad, the following analysis was performed and we had a solution within five minutes. It was quite a demonstration of the power of modern computer algebra systems. Continue reading

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