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The Shaughnessy Report: A Handy Look at Rules of Thumb
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Quiet Power: Cable Quality Matters
In my August column, we looked at the importance of properly terminating the cables that connect a measuring instrument to our device under test. We may be surprised to learn that even if we use the correct termination at the end of the cable, the measured waveform may depend on the quality of the cable we use.
To illustrate the point, we will use the same DC-DC converter evaluation board with an LTM4604 buck converter. To eliminate any possibility of ground loops, the converter is powered from a small battery pack with three AA batteries. The load is a small incandescent bulb, taking approximately 1A DC current from the output. We use a 50-ohm coaxial cable with BNC connectors at both ends. One end of the cable is connected to CH1 input of a Tektronix TDS540B oscilloscope. The input is switched to 50-ohm input impedance. The other end of the cable is connected to the BNC socket on the evaluation board, which directly monitors the output voltage. Read the full column here.Editor's Note: This column originally appeared in the October 2013 issue of The PCB Design Magazine.
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