Integrated Passive Components
Balanced Line EMI Chip
BLC
The Syfer Balanced Line EMI chip has a unique internal architecture
which provides unbeatable EMC performance for dual line data
transmission.
C1
LINE A
LINE B
C1
C2
The Balanced Line EMI chip replaces decoupling capacitors or 3
terminal feedthrough chips on a 1 for 2 basis and provides line to
line (differential mode) decoupling. Fig 2.
The internal structure furnishes a reduced inductance when
compared to that of a conventional capacitor. This is a result of the
novel internal electrode structure which inherently reduces the
inductance by the cancellation effect of opposing currents in close
proximity.
The capacitance line to ground (common mode) is closely matched
due to the symmetry within the design. As the device includes line
to ground capacitance for both lines, any temperature, ageing and
voltage effects will have an equal influence on both lines therefore
maintaining balanced decoupling.
The construction also allows a capacitance between lines as well as
to ground as shown in Fig 3.
INPUT 2
INPUT 1
INPUT 3
INPUT 4
CHIP CAPACITORS
EARTH
TRACKS
INPUT 2
INPUT 1
INPUT 3
INPUT 4
3 TERMINAL CHIPS
EARTH
TRACKS
BALANCED LINE
EMI CHIP
EARTH
TRACKS
INPUT 2
INPUT 1
INPUT 3
INPUT 4
Fig 1
Fig 2
Fig 3
C2, the line to line capacitance, is half the line to ground
capacitance thus providing coupling of high frequency interference
between balanced lines.
Because the part acts as a decoupling device, the current limitations
of a standard 3 terminal chip do not apply. The single line 3
terminal feedthrough chip carries the signal current through the
very thin feedthrough electrodes within the device which have
limited DC resistance and so can cause excessive heating, hence the
maximum permissible current is often limited to around 300 mA for
a 1206 device. The dual line 3 terminal chip is in by-pass across
two lines and so is unaffected by high signal currents.
Table 1 offers a comparison of decoupling devices and
demonstrates how the Balanced Line EMI chip extends the options
for EMC circuit protection.
Component
Advantages
Disadvantages
Applications
● Requires 1 per line
● By-pass
Chip capacitor
● Industry standard
● High inductance
● Low frequency
● Capacitance matching problems
3 terminal
● Feedthrough
feedthrough
● Lower Inductance
● Current limited
● Unbalanced lines
● High frequency
● Very low inductance
● By-pass
● Replaces 2 (or 3) components
● Balanced lines
Balanced line
● Negates the effects of
● Not for unbalanced signal lines
● High frequency
EMI chip
temperature, voltage and ageing
● DC electric motors
● Provides both common mode and
differential mode attenuation
Table 1
A typical application for dual line data transmission would see a
board layout using decoupling chip capacitors or 3 terminal
feedthrough chips as shown in Fig 1.
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