# Are Passive Probes Good Enough for GaN Gate Measurements?

**URL:** <https://forum.digikey.com/t/are-passive-probes-good-enough-for-gan-gate-measurements/64382>\
**Category:** Discrete Semiconductor Products\
**Tags:** faqs, transistors\
**Created:** [January 20, 2026, 5:48am UTC](https://forum.digikey.com/t/are-passive-probes-good-enough-for-gan-gate-measurements/64382 "2026-01-20T05:48:58Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![aayushi.nainwal](https://sea2.discourse-cdn.com/digikey/user_avatar/forum.digikey.com/aayushi.nainwal/32/62803_2.png) [@aayushi.nainwal](https://forum.digikey.com/u/aayushi.nainwal)\
**Post date:** [January 20, 2026, 5:48am UTC](https://forum.digikey.com/t/are-passive-probes-good-enough-for-gan-gate-measurements/64382/1 "2026-01-20T05:48:58Z")

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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.

 ![image](https://global.discourse-cdn.com/digikey/original/3X/4/0/406db1e1898aa71efd397aa7548cfad2f1f64d78.png)  
 ![image](https://global.discourse-cdn.com/digikey/original/3X/7/e/7ec6dcca19c5735035252fad49f41217869c7384.png)

**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

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