Test & measurement
Figure 2. Measuring load-step response in multiple channels simultaneously.
visible. If there is enough offset adjustment to reduce the influence of the DC voltage, the oscilloscope vertical sensitivity in mV per division can be set to isolate the AC ripple component and so allows more precise assessment. The MXO 5 oscilloscope is built primarily for high-accuracy power supply testing and has a large offset adjustment range, up to 15V, in the vertical sensitivity range of 120mV to 3V per division. Achieving such a large offset in a 50-Ohm termination is an outstanding feat of engineering and is the major factor here that enables even a small ripple component in the output of a DC switching regulator to be measured accurately.
Proper probe selection and grounding techniques also play a crucial role in accurate power measurements, such as ripple. A low-noise probe tends to have limited bandwidth and can therefore fail to show high-frequency transients and, as a result, can under-report Vpp measurements. This can obscure sources of ripple that could be detected using a probe with wider bandwidth, such as a purpose-built power-rail probing solution.
VIEWING NOISE IN THE FREQUENCY DOMAIN
Data transmissions across high-speed lanes, such as between the processor and memory, can couple noise into the power supply lines. With many scopes, viewing those coupled sources
30
in the frequency domain can be a challenge. The Fast Fourier Transform (FFT) engine of the MXO 5 is capable of 45,000 FFTs per second, helping identify noise at their specific frequencies including harmonics of the power supply switching frequency. If high-speed signal lines from the processing subsystem are becoming coupled onto the power supply lines, the scope’s FFT analysis can help to identify the coupled frequencies. Moreover, with the built-in math functions, which are hardware accelerated and thus permit retaining the high acquisition rate without requiring post-processing, engineers can distinguish common-mode noise from differential noise. If excessive noise of either type is discovered, that knowledge then helps to work out how to add filters and chokes to remove these sources.
MULTIPHASE TRANSIENT RESPONSE In addition to testing the static conditions under various loads, analysis should also include applying load step scenarios appropriate to the application then checking the reactions of the buck converter stages.
When working with multiphase converters, where each phase operates with a time shift, being able to measure multiple power phases simultaneously helps make an accurate assessment of the load step response (figure 2). The MXO 5 oscilloscope used to capture this image has eight channels that let users
analyse individual phases to check correct synchronization and help track down causes of any noise and instability. The multi-channel scope helps analyse individual contributions to voltage ripple and transient response and can capture phase-specific details.
When measuring the load transient response, ensuring the undershoot and overshoot are both within tolerances is extremely important. It is also important to verify that each phase of the converter reacts to load steps with low latency, as required, as well as checking for correct phase management.
CONCLUSION
Activity patterns in AI processors are driving up overall power consumption as well as causing large fluctuations in power demand with dynamically changing workloads and frequent interactions with memory to exchange data. Multiphase converters are becoming widely used to meet these demands and testing them requires careful attention to detail, assisted by an oscilloscope designed for power measurements and selected probes such as a power-rail, 1:1, isolated, or current probe. Multi-channel capability, a high acquisition rate, large voltage offset range, and low noise are preferred features in scopes for this purpose.
Rohde & Schwarz UK
www.rohde-schwarz.com/uk/ January 2026 Instrumentation Monthly
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73
