Understand RF Pickup When Measuring Power Rails

Figure 1: Teledyne LeCroy's
HDO8108A sports a very low
noise floor of about 145 μV 

Measuring the noise on a power rail seems to be a straightforward task. However, there are some basic pitfalls that can cause incorrect, or even downright strange, results. Let's look at one of these challenges: RF pickup. We'll demonstrate the effect of RF pickup on a power-rail measurement, and then we'll show you an effective means of mitigating that effect.