Novel Capacitors
Murata’s New ESR Capacitors
Tackle Anti-Resonance
A
s consumers continue to seek out
more innovative and attractive products, manufacturers keep coming up
with more advanced electronic
equipment. High-performance LSIs play a central role in those electronic products, starting
from the communication equipment underpinning our lifestyles, and extending to end-user
devices, such as personal computers, TVs, and
mobile phones. Monolithic ceramic capacitors
provide vital support for these high-performance LSIs. A number of these monolithic ceramic capacitors are placed near LSIs as decoupling devices for eliminating noise and absorbing load fluctuations during operation.
Basic noise suppression measures have usually been based on the idea of reducing the
impedance of a target line. Monolithic ceramic
capacitors, which have a low resistive component called equivalent series resistance (ESR),
are the best noise suppression device for this
purpose, which is why many circuits employ
these capacitors. However, nowadays, in some
circuits, the concept of reducing the impedance
no longer applies. When the ESR value is too
low, an impedance peak known as anti-resonance is generated and the decoupling performance in the peak frequency region declines.
To resolve this problem, Murata
Manufacturing Co., Ltd. developed low-ESL
controlled ESR capacitors with ESR values that
have been purposely increased. These are
Murata’s LLR Series capacitors.
Selectable ESR in LLR
Capacitors
The main feature of the LLR capacitors is
that their ESR values have been purposely increased. The ESR is selectable among four values from 100mΩ to 1,000mΩ. (Table 1)
Fig. 1: Impedance curve of capacitor
Table 1: LLR series product lineup
Ideally, the electrical characteristics of a capacitor are quoted only by equivalent series capacitance (ESC), which indicates capacitance. In reality,
however, dielectric (material)
loss and internal electrode loss
produce a coil component
called equivalent series inductance (ESL), and a resistive
component called ESR. For this
reason, the impedance characteristics express a dipping Fig. 2: Circuit configuration of circuit board mounted with LSI
curve (Fig. 1). Although monolithic ceramic capacitors have
the advantage of a low ESR
value (high Q value), this low
ESR in some cases causes antiresonance with capacitors of
different capacitances or with
the capacitance component of
LSI packages. The advantage
of the LLR Series is its bathtub-curve impedance characteristics, which is achieved by increasing the ESR value of the
capacitor (by reducing the Q
value) to prevent anti-resonance. An ideal way to control Fig. 3: Circuit impedance simulation data
the load fluctuations of an LSI
port.
is to reduce the ESL value of the capacitor and
In a circuit configuration, such as the one in
improve the charge and discharge characteristhis figure, the area between the LSI package
tics. However, the conventional ESR control
and the on-package capacitors (C01) is susceptimethod, which changes the internal electrode
ble to anti-resonance. Anti-resonance is generatpatterns of a monolithic ceramic capacitor, has
ed there because of LC resonance caused by an
a downside because it causes the ESL value to
extremely small capacitance component of an
increase at the same time. Murata has adopted
LSI package and an ESL component of a capacits own design to successfully control the ESR
itor (C01) mounted on the package.
value while the ESL value remains the same.
Three methods are available to control this
In this way, Murata’s new LLR Series achieves
anti-resonance. One is to increase the capacithe capacitor performance for operating in the
tance contained in an LSI package. Another
broadband region.
method is to reduce the ESL value of the capacitor. The third is to increase the ESR value of
Using LLR Capacitors
the capacitor. The values for the first and second
Anti-resonance can be generated when the
methods are determined by the components seESR value of a capacitor is too low. In the case
lected during the equipment design phase.
of a standard circuit configuration, various caTherefore, the third method, which increases the
pacitors are placed between a high-performance
ESR value, is the easiest way to control anti-resLSI and a DC-DC converter that supplies power
onance. The LLR Series has been developed to
to this LSI (Fig. 2). The on-package capacitors,
achieve this purpose.
or capacitors mounted on an LSI package board,
Fig. 3 shows simulation data of the circuit
(shown as C01 in Fig. 2) are used as decoupling
impedance profile when all capacitors (C01)
devices for high-frequency
mounted on the LSI package are replaced with
range support, whereas the highthe LLR Series capacitors. This graph shows
capacitance ceramic capacitors
that the higher the resistance value, the lower
and aluminum electrolytic cathe anti-resonance peak. In this simulation, the
pacitor with a capacitance of
peak value of the LLR series is reduced by a
more than 100µF (shown as C02
factor of one-fiftieth. Therefore, noise reduction
and C03, respectively) are used
in a target frequency range can be expected.
as decoupling devices for lowand mid-frequency range sup(Continued on page 24)
JEI November 2010, 11
Copyright2010 Dempa Publications, Inc.
Company on the Move
MediaTek
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stablished
stablished in
in 1997,
1997, MediaTek
MediaTek Inc.,
Inc., aa
leading
leading Taiwanese
Taiwanese fabless
fabless semiconducsemiconductor
tor company,
company, has
has been
been promoting
promoting the
the
leading-edge
leading-edge system-on-a-chip
system-on-a-chip (SoC)
(SoC)
solutions
solutions relating
relating to
to digital
digital consumer
consumer electronelectronics,
ics, including
including high-definition
high-definition (HD)
(HD) TVs,
TVs, optical
optical
storages
storages and
and DVD
DVD and
and Blu-ray-Disc
Blu-ray-Disc (BD)
(BD) prodproducts,
ucts, along
along with
with wireless
wireless communication
communication dedevices.
vices. The
The company
company has
has been
been stepping
stepping up
up as
as
well
well its
its presence
presence in
in the
the global
global market.
market.
The
The company
company posted
posted sales
sales of
of US$3.5
US$3.5 billion
billion
in
in 2009.
2009. “MediaTek
“MediaTek not
not only
only provides
provides silicon
silicon
chips
chips to
to our
our customers
customers but
but we
we also
also provide
provide marmarket-proven
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says Ryan
Ryan Chen,
Chen, General
General
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Manager, Digital
Digital TV
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MediaTek.
Taking
Taking TV
TV products
products as
as an
an example,
example,
MediaTek
MediaTek proposes
proposes to
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customers either
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chipset and
and aa driver-based
driver-based platform
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solution, or
or aa more
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MediaTek constantly
constantly invests
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trends of
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Chen
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says, “Consumer
“Consumer electronics
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says Ryan
Ryan Chen,
Chen, General
General
Manager,
Manager, Digital
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TV BU
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at MediaTek
MediaTek Inc.
Inc.
leading
leading technologies
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and make
make tremendous
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investments.”
“Our
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technologies.”
Commenting
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the Japanese
Japanese market,
market, Chen
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says,
says, “Competition
“Competition in
in the
the TV
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become
increasingly
increasingly fiercer.
fiercer. Choosing
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Inaddition
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manufacturers in
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early
early stage.
stage. By
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leveraging MediaTek’s
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resources
and
and technologies,
technologies, Japanese
Japanese manufacturers
manufacturers can
can
exert
exert R&D
R&D resources
resources more
more effectively
effectively and
and shorten
shorten
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the time
time to
to market.
market. MediaTek
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determined to
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manufacturers.”
JEI
JEI
Murata’s New ESR Capacitors Tackle...
(Continued from page 11)
Preventing DC-DC Converter
Oscillation
A capacitor is used at the output side of the
step-down DC-DC converter to control the output voltage fluctuations (ripple voltage fluctuations). An LC low-pass filter is also provided at
the output side to smooth the voltage output
from the DC-DC converter (Fig. 4). When a
monolithic ceramic capacitor with a low ESR
value is used for the corresponding location,
oscillation occurs. To prevent the oscillation,
the ESR value of a capacitor is increased to
provide a phase margin. This function can be
achieved by using the LLR Series, which can
24, JEI November 2010
Copyright2010 Dempa Publications, Inc.
resolve the oscillation problem stemming from
a low ESR value of a monolithic ceramic capacitor. Murata believes that the LLR Series
can give circuit designers more options.
Fig. 4: Step-down type DC-DC converter
Emergence of ESR Control
In the past, the only requirements for
monolithic ceramic capacitors have been
large-capacitance and low-ESR characteristics
for maintaining the power supply line and I/O
line at low impedance. As more functions are
added to electronic equipment, the new idea of
ESR control has emerged. Murata believes
that the value of monolithic ceramic capacitors as an easy-to-use passive component can
be further improved through flexible responses to such new needs.
Murata intends to further develop the LLR
Series and extend the lineup featuring this
product.
❑
About this Article
The author is Masayuki Tsuruzono, Product
Development Section 3, Product Development
Department 2, Fukui Murata Manufacturing Co., Ltd.