Making noise

摘要

Friday nights, I play bass in a jazz trio. The sound of my upright acoustic bass easily fills our small club, so I con- stantly have to think about the level of noise I'm making, and that brings me to the subject of this column. I recently concluded some power-supply immunity testing on an IC. The test fixture directly injects intentional noise into the power terminal of the DUT (device under test) to see how much it can take without failing. Ordinarily, I place an impedance in series with the power terminal of the DUT, severely weakening the power system at that point and making it easy to inject substantial quantities of intentional noise into the chip's power terminal. This time a special requirement complicated my test: that the power system feeding the DUT remain unaltered during testing. Making matters even worse, the power system for this layout was hefty. Analysis of the design revealed a power-to-ground impedance of about 0.0211 at all frequencies as high as 1 GHz.