THE DESIGN BRIEF

Issue #010 · Thursday, April 23, 2026 · Engineering Intel

Your conducted emissions headroom is shrinking. I'm seeing more failures in the 9-30 MHz range as switching frequencies push higher. Class B limits are 10 dB stricter than Class A — that's the difference between 40 dBμV and 50 dBμV at 30 MHz conducted.

Rule of thumb: Keep your fundamental switching frequency below 150 kHz if possible. Above that, you're fighting harmonics in the CISPR conducted band. I measured a 15 dB improvement on radiated emissions (30 MHz-1 GHz) just by dropping from 200 kHz to 120 kHz switching on a recent SMPS design.

The frequency extension in CISPR 32 up to 6 GHz means your old "good enough at 1 GHz" approach won't work for multimedia gear anymore.

• • MIL-STD-461G (2015 revision) still current — no updates despite platform changes
• • Medical devices under IEC 60601-1-2 reference CISPR 11 for 150 kHz-1 GHz emissions
• • Automotive CISPR 12 stops at 1 GHz radiated — inadequate for modern vehicle electronics
• • ESD immunity (IEC 61000-4-2) requirements unchanged but contact/air discharge voltages hitting harder

• • Gap between automotive standards (1 GHz ceiling) and actual vehicle RF content pushing into 5G bands
• • Medical device EMC lagging behind — IEC 60601-1-2 Edition 2.1 from 2001 with 2004 amendments still referenced

Have you tested CISPR 32 equipment beyond 1 GHz recently? Reply with what you found above 3 GHz — I'm collecting field data.

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