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One of the design activities often left
to the end of a project is verifying that
the product meets electro-magnetic
compatibility
(EMC)
emissions
requirements. EMC regulations help to
ensure unintentional electro-magnetic
conducted and radiated emissions
do not interfere with other electronic
devices.WhiledelayingEMCcompliance
testing until the end of the project is
a common practice, unexpected costs
and project delays can be avoided by
considering EMC compliance earlier in
the design process.
Electro-magnetic conducted and
radiated emissions are the radio
frequency (RF) energy emitted by a
product. The level of RF emissions are
regulated to ensure they do not cause
unreasonable harm to other electronic
products. At low frequencies (less
than about 30 MHz) the conductors
and cables of most electronic devices
Considering EMC Emissions Early
in the Design Process
Bruce Rose, Applications Engineer, CUI
15. Similar standards for products
sold in Europe are governed by
European regulations CISPR 22/EN
55022. Both sets of these regulations
describe limits for conducted and
radiated emissions and are applied
to the final system, including the
internal or external power supply.
While these two sets of regulations
are created and administered by
separate organizations they have
been constructed to be similar
or “harmonized”. One benefit of
harmonizing these regulations is that
designing a product to meet one set
of regulations typically ensures it
will also satisfy the requirements set
forth in the other set of regulations.
Conducted radiation specifications
cover emissions in the frequency
range of 150 kHz through 30 MHz.
A separate set of radiated emissions
specifications covers the spectrum of
are ineffective as antennas and
thus radiated emissions are not an
issue. At these low frequencies the
conductors and cables can conduct RF
energy through shared power sources
or loads and cause issues with other
electronic products, while at high
frequencies (above about 30 MHz)
the impedances of the conductors
and cables attenuate the conducted
energy sufficiently to prevent it from
being an issue. However, at these
higher frequencies the conductors
and cables can serve as antennas and
radiate the RF energy with the ability
to cause interference with nearby
electronic products.
Most industrial and consumer
electronic products sold in the United
States are required to meet conducted
and radiated emissions standards as
described in FCC regulations Title 47
Part 15, often referred to as FCC Part
56 l New-Tech Magazine Europe