This item checks for the distance and existence of bead component in signal
pattern.
In order to prevent noise coupling to or form other signals, the designer may assign
bead components in signal pattern. The distance from IC to bead component should be
kept as short as possible. A ferrite bead is a passive electric component used to
suppress high frequency noise in electronic circuits. It is a specific type of
electronic choke. Ferrite beads employ the mechanism of high dissipation of high
frequency currents in a ferrite to build high frequency noise suppression
devices.
In addition to small stray capacitance, ferrite bead inductors have another excellent
feature. At high frequencies, this type of inductor works not as an inductor but as
a resistor and dissipates noise in the form of heat.
Item: Enter item name.
Net: Select a target net group that nets in the group that needs bead
components.
Bead Comp: Select a component group that components in the group will be
used as bead components.
Start Comp: Select a starting component group.
Distance: Assign a reference distance of bead components from the starting
component.
Result
PollEx DFE reports No Filter if there is no bead
component.
PollEx DFE reports No Start Comp if there is no
starting component.
If there is a bead component but it is placed too far from the starting
component, PollEx DFE reports Distance Fail and
measured distance as well as the reference distance.
Bead component is an L-element type component of power line to protect noise from
power. To the signal which is very sensitive to noise, the designer can use bead
component for EMI to filter out unnecessary high frequency noise.
Figure 1.
Characteristics of ferrite bead inductors allow you to remove high frequency noises
by converting them to heat.
Table 1. EMI Filter Usage
Usage
Specification
Type
Recommentation
Power Line
BLM11P (0.5-1A)
Ferite Bead
IC Power Line
NFM2012P (2A)
3-Terminal Capacitor
BLM41P (1-6A)
Ferite Bead
Power Circuit
NFM46P (6A)
3-Terminal Capacitor
Signal Line
BLM10A (10~1kΩ)
Ferite Bead
Weak Ground Pattern
BLA3216A (30~1kΩ)
Array-Type Ferite Bead
PLM3216K (280Ω)
Common Mode Choke
GRM36
2-Terminal Capacitor
Strong Ground Pattern
NFM39R (22~2200pF)
3-Terminal Capacitor
NFM60R (22~2200pF)
T-Type 3 Terminal Capacitor
NFA3216D (22~2200pF)
Array Type
High Speed Line
NFM51R (10M~500MHz)
3-Terminal Capacitor
Normal Mode Noise
NFM839R (22~10Ω, 10~100pF)
RC-Type 3 Terminal Capacitor
NFA3216 (6.8~100Ω, 10~100pF)
RC Array Type
BLM11B (5~500MHz)
Ferite Bead
PLM250 (350~4kΩ)
Common Mode Choke
Common Mode Noise
Characteristics of Analog and Digital Signals
Because analog signal handles change of magnitude in signal, if noise is overlapped
on signal, it results in distortion of signal and changes the original signal. In
this case, it is impossible to recover the original signal. Digital signal can be
recovered from the changes made by noise.
