For decades, power system stability has been measured in the frequency domain: inject a signal, sweep across frequency, and read phase margin off a Bode plot. It’s a proven method — but today’s DC-DC converters are nonlinear and time-variant, and that traditional approach is starting to show its limits on exactly the designs engineers care about most.
In a new video — a collaboration between Picotest and Tektronix — Steve Sandler, Managing Director of Picotest, previews a faster, more accurate alternative.
Steve introduces SEPIA — Step-Load Enhanced Power Integrity Analysis — a new measurement technique designed for today’s nonlinear, time-variant DC-DC converters, demonstrated on a Tektronix 6 Series oscilloscope.
Rather than relying on traditional frequency-domain Bode plots, SEPIA works entirely in the time domain. From a single high-speed step-load response, it extracts three things at once:
- Phase margin — the core stability number, without a frequency sweep
- Equivalent circuit models — a working model of the power system’s behaviour
- Stability insight — a direct read on how the converter actually responds
In other words, the way a converter recovers from a fast load step already carries the stability information engineers need. SEPIA reads it directly from that transient, rather than reconstructing it from a swept-frequency plot.
Why step-load response is superior to the Bode plot
The heart of the video is a simple argument: for modern power systems, the step-load response tells you more, faster, than a Bode plot can.
Traditional Bode-plot analysis assumes a linear, time-invariant system — an assumption that modern, nonlinear, time-variant converters increasingly break. As designs get more complex, frequency-domain measurements take longer to run and become harder to trust. Measuring the step-load response instead captures the converter behaving the way it really does, and delivers phase margin and a circuit model together from one fast measurement — on an oscilloscope engineers already have on the bench.
Power integrity measurement is evolving
The bigger takeaway is where measurement is heading. As power systems grow more demanding, the tools have to keep pace — and SEPIA is a look at that shift: away from the assumptions of the frequency domain, and toward what a high-speed step-load response can reveal directly.
Watch the video
See Steve preview SEPIA and explain why step-load response is superior to the traditional Bode plot:
▶ Modern Stability Analysis with SEPIA and without Bode Plots
Talk to us about step-load measurement
A step-load technique is only as good as the current step behind it — fast, clean, and precisely controlled. If you’re exploring step-load-based stability analysis for your own designs, contact Picotest to talk through the Load Stepper and how it fits your bench.
A Picotest and Tektronix collaboration.
