Improving Power Integrity Measurement
Testing power distribution networks and improving power integrity measurements can be a bit of a bother. Power distribution networks are connected to all devices that require power so any transients or noise on the power rails also gets distributed to all systems.
The result, coupling and noise on the power rails is a common source of system jitter. On the opposite end, measuring power integrity is tough for a number of reasons. So you can only imagine the problems faced by custom power supplies manufacturers.
Oscilloscope offsets are not enough to calculate tiny vertical sensitivities. The probe and oscilloscope noise often buries the noise generated by the lower power rails.
The behavior of the power rail can also change when you connect a coax cable or probe. It can even hide signal detail. But embedded engineers should know that there are certain ways to measure power integrity.
First, begin with the probe and scope that has the lowest noise. If you are only going to measure a few millivolts, you can’t go with multiple mVs of noise.
Second, you have to use noise reduction techniques. Broadband noise is one of the biggest sources of noise in some scopes. So use broadband filters to bring broadband noise down and improve the accuracy of your measurements.
Third, use probes with high DC input impedance. If you take these steps, the system noise will reduce drastically and you can take more accurate measurements.