Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
CISPR 22: Information Technology Equipment – Radio Disturbance Characteristics
Limits and measurement methods for conducted and radiated radio disturbance from IT equipment in the 0.15 MHz to 1 GHz range
Introduction to CISPR 22
CISPR 22 specifies limits and methods of measurement for radio disturbance characteristics of Information Technology Equipment (ITE). This standard applies to a broad range of devices including personal computers, servers, printers, network equipment, telecommunications terminal equipment, and associated peripherals. The frequency range covers 0.15 MHz to 1 GHz for both conducted and radiated emissions. CISPR 22 is one of the most widely referenced EMC standards globally, forming the basis for the European EMC Directive’s ITE emission requirements (EN 55022) and serving as the foundation for many national ITE EMC regulations. Compliance with CISPR 22 is typically mandatory for placing ITE on the market in most countries.
CISPR 22 distinguishes between Class A ITE (industrial/commercial environments) and Class B ITE (residential environments). Class B limits are 6-10 dB more stringent than Class A, reflecting the closer proximity of residential equipment to radio and television receivers.
Measurement Setup and Test Methods
CISPR 22 specifies detailed measurement procedures for both conducted emissions (0.15-30 MHz on AC power ports) and radiated emissions (30-1000 MHz). Conducted emission measurements use a 50 µH/50 Ω Line Impedance Stabilization Network (LISN) placed between the AC mains and the equipment under test (EUT). Radiated emission measurements are performed in a fully anechoic room (FAR) or on an open area test site (OATS) at a measurement distance of 10 m (Class B) or 30 m (Class A). The standard defines specific tabletop and floor-standing equipment configurations, cable routing, and peripheral connections to ensure reproducible results across different test laboratories.
| Emission Type | Class | Frequency Range | Limit (Quasi-Peak/Average) | Measurement Distance |
|---|---|---|---|---|
| Conducted (AC port) | Class B | 0.15 – 0.50 MHz | 66-56 dBµV / 56-46 dBµV | — |
| Conducted (AC port) | Class B | 0.50 – 5.0 MHz | 56 dBµV / 46 dBµV | — |
| Conducted (AC port) | Class B | 5.0 – 30 MHz | 60 dBµV / 50 dBµV | — |
| Radiated | Class B | 30 – 230 MHz | 30 dBµV/m (QP) | 10 m |
| Radiated | Class B | 230 – 1000 MHz | 37 dBµV/m (QP) | 10 m |
| Conducted (AC port) | Class A | 0.15 – 0.50 MHz | 79-73 dBµV / 66-60 dBµV | — |
| Radiated | Class A | 30 – 230 MHz | 30 dBµV/m (QP) | 30 m (or 40 dBµV/m at 10 m) |
Switching power supplies in ITE are the dominant source of conducted emissions. The fundamental switching frequency (typically 50-200 kHz) and its harmonics often appear as narrowband spectral lines that can exceed limits if not properly filtered. Pay special attention to the 0.15-1 MHz range where the fundamental and first few harmonics reside.
Engineering Design for ITE EMC Compliance
Designing ITE to meet CISPR 22 requires a multi-layered approach. At the PCB level, careful layout with dedicated ground planes, proper decoupling of each IC power pin (0.1 µF ceramic capacitor placed within 5 mm of each pin), and separation of high-speed traces from I/O boundaries are fundamental. Clock generation and distribution deserve particular attention — spread-spectrum clocking can reduce peak emission levels by 8-15 dB by distributing the clock energy over a wider frequency range.
Enclosure design plays a critical role in radiated emissions control. Metal enclosures with proper bonding of seams (conductive gaskets at intervals ≤ λ/20 at the highest frequency of concern) provide 20-40 dB of shielding effectiveness. For plastic enclosures, conductive coatings (nickel-copper spray, vacuum metalization, or conductive paint) with surface resistivity below 0.5 Ω/sq are necessary. Cable filtering at I/O ports using ferrite chokes or LC filters prevents internal noise from coupling onto external cables that act as efficient radiating antennas.
A systematic pre-compliance testing approach — using a near-field probe set and spectrum analyzer during development — can identify and fix 90% of emission issues before formal compliance testing. This typically reduces the total EMC development cost by 30-50% compared to troubleshooting failures in a certified lab.
Classification and Product Marking
CISPR 22 requires ITE to be classified and marked according to its emission class. Class B equipment is suitable for use in residential environments and is marked with a symbol indicating compliance with applicable EMC requirements. Class A equipment, intended for industrial/commercial use, must carry a warning notice stating that it may cause radio interference in residential environments. The classification is based on the equipment’s intended environment, not its technical characteristics — however, many manufacturers design all products to meet Class B limits to avoid market access restrictions.
Q: Does CISPR 22 apply to DC-powered ITE?
A: Yes, but conducted emission measurements are performed on the DC power port using a specific LISN or impedance stabilization network appropriate for DC lines.
A: Yes, but conducted emission measurements are performed on the DC power port using a specific LISN or impedance stabilization network appropriate for DC lines.
Q: Can software configuration affect emission measurements?
A: Absolutely. CISPR 22 requires the EUT to be exercised in a representative worst-case operating mode. Processor-intensive tasks, memory access patterns, and I/O activity all affect emission levels.
A: Absolutely. CISPR 22 requires the EUT to be exercised in a representative worst-case operating mode. Processor-intensive tasks, memory access patterns, and I/O activity all affect emission levels.
Q: What is the typical margin required for production compliance?
A> Most manufacturers target 3-6 dB below the limit during type testing to account for production variation. A 6 dB margin corresponds to approximately 50% reduction in emission amplitude.
A> Most manufacturers target 3-6 dB below the limit during type testing to account for production variation. A 6 dB margin corresponds to approximately 50% reduction in emission amplitude.
