Capacitors for RF Applications Michael P. Busse Vice President

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Capacitors for RF ApplicationsMichael P. Busse
Vice President

• Dielectric Laboratories, Inc
• 2777 Rte. 20 East
• Cazenovia, NY 13035
• 315-655-8710
• 315-655-8179
• www.dilabs.com

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Purpose

• To familiarize users with the basic properties of
  Ceramic Capacitors and
• To demonstrate CapCad, a modeling and selection
  methodology.

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Outline

• Application of Capacitors
• Capacitor Structures
• Terminology and Definitions
• Electrical Properties
• Physical Characteristics
• Mounting Considerations
• Capacitor Models
• CapCad
• Conclusions

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Applications

• Ceramic Capacitor technology covers a wide range
  of product types, based upon a multitude of
  dielectric materials and physical configurations.
  All are basically storage devices for electrical
  energy which find use in varied applications in
  the electronics industry including the following
• Discharge of Stored Energy
• Blockage of DC Current
• Coupling of Circuit Components
• By-Passing of an AC Signal
• Frequency Discrimination
• Transient Voltage and Arc Suppression

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Structures

• Multi Layer MLC
• A parallel array of capacitors in a common
  structure.
• High C/V can be achieved
• More complex to manufacture
• Cap Ranges of .10 PF to ?5100 pf

• Single Layer SLC
• Two plates separated by a dielectric.
• Simple to fabricate
• Area/thickness limited
• Cap Ranges of .05 pf to ?2000 pf

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Definitions

• Capacitor A device for storing electrical
  energy. The simplest form is two separate
  parallel plates with a non-conducting
  (dielectric) substance between them. The amount
  of energy that can be stored depends on the Area
  (A), Dielectric Constant (K), and the Thickness
  (t) of the dielectric. CKA(.2246)/t (.2246 is a
  conversion factor in English, for Metric 0.0884).
  The area can be manipulated by the structure.
• Capacitance A unit of measure describing the
  electrical storage capacity of a capacitor.
  Capacitance is measured in farads, microfarad
  (millionth of a farad), nanofarad (billionth of a
  farad or 10-9), or in picofarad (trillionth of a
  farad or 10-12).

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Definitions

• Dielectric Any material which has the ability
  to store electrical energy. In a DLI capacitor,
  it is non-conducting ceramic between the plates.
  In general, capacitors can utilize any
  dielectrics such as air, or naturally occurring
  dielectrics such as mica.
• Classes of Dielectrics Two basic groups (Class
  1 and Class 2) are used in the manufacture of
  ceramic chip capacitors.
• Class 1 dielectrics display the most stable
  characteristics of frequency, voltage, time and
  temperature coefficients (TC). TC is expressed as
  a of capacitance change from a reference or
  parts per million per degree C (ppm/ºC).
• Class 2 dielectrics offer much higher dielectric
  constants but with less stable properties with
  temperature, voltage, frequency, and time. TC is
  expressed as a change from a reference (- 15
  over some range of temperature)

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Common Dielectrics
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Definitions

• Dielectric Constant (K) The calculated
  measurement of a material which defines its
  capacity to store electrical energy. A higher
  K signifies a higher capacitance per unit at
  the test temperature.
• Electrode The metallic plates that are the top
  and bottom of a single dielectric layer. In a
  SLC (Single Layer Capacitor), the outer
  metallized plates form the electrodes. In an MLC
  (Multi Layer Capacitor), the metal print that
  alternates between the ceramic layers form the
  electrodes.

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Electrical Properties

• IR Insulation Resistance
• DC Resistance which is a function of the
  dielectric. It is the ability of the capacitor
  to oppose the flow of electricity at a given
  direct voltage.
• DF Dissipation Factor
• Loss Tangent is the ratio of energy used up by
  a working capacitor divided by the amount of
  energy stored over a definite period of time. It
  is a measure of the capacitors operating
  efficiency.
• ESR Equivalent Series Resistance
• The effective resistance to the passage of RF
  energy

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Electrical Properties

• Dielectric Withstanding Voltage (DWV) is a
  measurement of the electrical strength of the
  dielectric at 2½ times the rated voltage.
• Temperature Coefficient (TC) is a measure of how
  the capacitance changes with temperature.
• Tolerance is the amount of variation allowed from
  a target value. It is normally expressed as an
  Alpha character, for example a J tolerance
  would be 5.
• Voltage Conditioning is a test that applies heat
  and voltage to the parts for a set number of
  hours to accelerate failure mechanisms and
  identify rejects.

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Q

• Q Quality Factor is a numeric expression of the
  relative loss of a capacitor. Most commonly
  described as the storage factor of a capacitor
  and is the reciprocal of the Dissipation Factor.
• Q is defined as
• Q1/2pFC(ESR)
• Ffrequency
• Ccapacitance
• For any given capacitance at a given frequency,
  the highest Q part will have the lowest ESR

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Physical Considerations

• Size equates to Voltage Rating
• Larger case sizes have greater voltage
  capabilities
• Smaller case sizes have higher series resonance
  characteristics
• The separation between the internal electrodes
  dominates voltage rating
• The dielectric has to be an insulator
• The dielectric will determine the properties of
  the capacitor.

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Mounting Considerations
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Capacitor Models

• Reasonable prediction to the first series
  resonance
• Predicted behavior above series resonance doesnt
  match observed results.

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Transmission Line Model

• Treats the capacitor as an open circuited
  transmission Line
• Results closely match measured data

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CapCad V3

• Modeling software to simplify the selection of
  the right capacitor.
• Easy to use graphical interface
• Export and Import s2p files
• Smith chart graphing
• Includes Spice Modeling

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Conclusion

• Capacitors present more of a challenge to
  selection than just the capacitance
• The Physical as well as the Electrical properties
  must be taken into consideration
• Proper Modeling Tools can simplify the selection
• Thank You !

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DLI Overview

• Company was established in 1974
• Cazenovia, NY, USA
• Company Headquarters
• Manufacturing Facility
• Design Center
• Other Locations
• US Sales Offices - California and Connecticut
• Asia Sales Distribution Center open 3Q02,
  Shanghai
• Inspection and Packaging contractor qualified,
  Bangkok
• Board and Package Assembly contractor 3Q02,
  Taipei
• Europe Sales Office under development

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Single Layer Capacitors (SLC)

• Worlds Most Respected Name
• Worlds Broadest Offering
• DiCap - T-cap - Border Cap
• Bar Cap - Gap Cap - Bi Cap
• Milli-Cap - Broadband Solution As The Ideal
  Capacitor

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Multi Layer Products (MLC)

• Common Case Sizes 0603 up to 3838
• High Q Ceramic
• High-Fire Reliability
• Newly Introduced
• Ultra-Low ESR C07
• Lead-Free MLC
• 0402 Case Size Under Development
• RF Power Performance Line (C22 and C40)
• Opti-Cap - Broadband DC Block from lt20 KHz to
  60 GHz

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Custom Thin Film Products

• Enhanced High Performance, Flexible Process
  Capabilities
• Broad Range of Ceramics and Metal Systems
• Traditional Alumina, Alumina Nitride, and Fused
  Silica
• Proprietary higher K, Class I dielectrics
• Titanates and Zirconias
• Expert with all Common Metallization Systems
• Organizational Focus with Product Team
• Products Include
• BP Filters, Frequency Equalizers, Hybrid Circuits
  and Components
• Bias Filter Self Bias Networks, Heat
  Sinks/Stand-Offs

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DiPak MMW Power Packaging

• Superior materials provide best millimeter wave
  power performance
• Low K loss tangent
• Virtually No X-Y shrinkage
• High thermal conductivity with Cu/Mo base
• Surface Mount Device
• Patent pending
• Lowest loss concept in market
• Applications
• Millimeter Wave Digital Radios
• Satellite Broadband
• MMIC/ MCMs

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