Biomedical Engineering Reference
In-Depth Information
Figure 4.2 The characteristic voltage spectrum envelope of emissions by every logic gate is highly
dependent on the technology being used.
integrated
filters are available for dc power lines. For example, Figure 4.3 shows the way
in which muRata BNX002 block
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filter the raw dc power outputs pro-
duced by two C&D Technologies' HB04U15D12 isolating dc/dc converters. In the circuit,
each dc/dc (IC1 and IC2 ) produces unregulated 24 V (
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filters are used to
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12 V if the center-tap common is
used), which is isolated from the
15 V dc power input by an isolation barrier rated at
3000 V dc (continuous, tested at 8 kV, 60 Hz for 10 s). The outputs of the dc/dc converters
are
lters
implemented with feed-through capacitors, monolithic chip capacitors, and ferrite-bead
inductors. Each of these
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filtered via
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filters FILT1 and FILT2, which internally incorporate multiple EMI
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filters attenuates RF by at least 40 dB in the range 1 MHz to
1 GHz. C1/C4 and C7/C10 are used to reduce ripple, and the circuits following these
capacitors are linear regulators that yield regulated
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24 V at 50 mA to the applied part for
which this isolation power supply was designed.
Another
filter worth mentioning is muRata's PLT x R53C common-mode choke coil.
This family of modules is ideal for suppressing noise from a few megahertz (1 to 5 MHz,
depending on the model) to several hundred megahertz (10 MHz to 1 GHz, depending on
the model) from dc power supplies. This module is useful in suppressing noise radiated
from the cable connecting a device to an external wall-mounted or “brick” ac adapter.
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ELECTROMAGNETIC FIELDS
EMI standards establish that radiated-emissions test measurements should be performed at
a distance of 10 to 30 m, depending on the device's classi
cation. For compliance testing,
the device under test should be placed on a nonconductive table 0.8 m above a ground
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