While the isolated probe may be the best—way to measure high-side GaN gate voltages, but they are expensive. Passive probes are a cheaper option, so it’s useful to see how well they work.
Passive probes can measure GaN gate signals using two probes and A–B subtraction or pseudo differential technique, but they have several limitations.
They often show high common‑mode noise because GaN switches very fast, and their input capacitance (typically 3.9 pF to 10 pF) can cause Probe loading, which can make the measured gate voltage appear 17% to 30% lower than the actual value.
Even when using better low‑impedance passive probes (5 kΩ // <2 pF), there is still residual noise—around 2.7 V peak‑to‑peak—which reduces accuracy.
Although high‑impedance passive probes performed better than expected, the low‑impedance passive probes produced results much closer to those of a trusted isolated probe, making them the preferred choice among passive options.
In short:
Isolated probes are the best option for GaN gate measurements because they provide:
- Highest CMRR
- Lowest loading
- Most accurate true VGS
- Cleanest waveforms
- Best performance at high dv/dt
Among passive probe methods:
- A–B method: Acceptable but noisy and error‑prone
- Single‑probe two‑step: Best passive‑only option; closer to isolated probe accuracy
Oscilloscope Probes
DC DC Switching Controllers | Power Management (PMIC) |DigiKey
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