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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. While
delaying EMC compliance 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 are ineffective
Considering EMC Emissions Early in the Design Process
Bruce Rose, Applications Engineer, CUI
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 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
30 MHz and greater. Test procedures
and tools are slightly different
for conducted versus radiated
62 l New-Tech Magazine Europe