What is power integrity?
Power integrity is the assurance that power applied to a circuit or device is appropriate for the desired performance of the circuit or device.
Such sensitive electronic designs require modern test solutions. When measuring power rails, for instance, there are usually two common challenges: lower rail voltages and smaller tolerances. Industry dynamics are driving both a decrease in rail voltage values as well as tighter tolerances across a wide range of power rails. The graph shows, that making an accurate ripple measurement on a rail value of 1.2 V with 2 % tolerance, for example, is difficult to measure on all oscilloscopes.
So how should we set up an oscilloscope to get the best accuracy for power integrity measurements?
Tip 1: Adjust viewing characteristics
Waveform intensity: Default – 50 % à Adjusted to 90 %
Infinite persistence
Tip 2: Lower noise
Noise leads to a large measurement deviation. It can mask or hide anomalies or causes Measured Vpp to be much greater than the Actual Vpp is. Consequently, you should choose the signal path that has the lowest noise and use the most sensitive vertical scale. In order to do that, you need to use the smallest V/div setting.
Chose the right probe (attenuation, BW and connection): With a 1:1 attenuation probe such as the R&S
RT-ZPR20 or the R&SRT-ZPR40 power rail probe you can benefit from a few advantages. These probes are designed specifically to measure small perturbations on power rails. They are active and single-ended, provide low noise, best in class offset compensation capability, good dynamic range and have a built-in DC meter. When coupled with such a 1:1 probe, oscilloscope demonstrates superior measurement quality.
Tip 3: Achieve sufficient offset
When using probes with built-in offset, (e.g. R&SRT-ZPR20 with ±60 V built-in offset) you can zoom in on a wide range of DC power rail standards.
Tip 4: Evaluate switching and EMI
In order to follow one of power integrity measurements top concerns, a frequency domain evaluation of coupling and switching is recommended. Adding frequency domain view enables users to quickly find and isolate coupled signals.
Tip 5: Accelerate measurement time
The update rate has an impact on speed of power integrity measurements: Fast update rates up to 1 MWFS/S show modulated signal on power rail. They let users test power rails more quickly. The graphic visualizes the impact of measurements, memory depth increases, and the use of an FFT on the update rate of the R&SRTO oscilloscopes (log scale).
Making accurate power integrity measurements continues to increase in importance, as rail voltages get lower and tolerance get tighter. Therefore, we suggest following the above-recommended tips.