陶瓷滤波器“CERAFIL®”应用指南

CERAMIC FILTER (CERAFIL®) APPLICATION MANUAL Murata Manufacturing Co., Ltd. Please read CAUTION and Notice in this catalog for safety. This catalog has only typical specifications. Therefore you are requested to approve our product specification or to transact the approval sheet for product specification, before your ordering. P11E.pdf 02.10.30 Introduction Ceramic filters (CERAFIL®*) have now become an indispensable component in numerous electric equipments. The IC, having developed in military and space applications, has found wide use in the field of commercial equipment, such as stereo systems, TV sets, Automotive radios, etc. For this reason, new miniature integrated filters, with high performance, are extremely desirable for use in IF circuits. Moreover, radio wave disturbance due to remarkable sophistication of communication network and rapid progress of data transmitting rate have become significant problems. As a result, the demand for filters with high selectivity and wide pass band width has increased. The IC application of the active elements will continue its progress, and there will be a growing demand for highly selective, non-adjustable, miniature and wide pass band width IF circuit. Under such circumstances, CERAFIL® fits in a broad range of products as the most suitable component. However, when one comes to the application of CERAFIL®, one finds very little reference literature on application and design features. This CERAFIL® Application Manual has been compiled to help you design with the superior characteristics of CERAFIL®, to utilize them more effectively and without any problem. The edition explains the CERAFIL® principle, the features and the specific criteria for the application of CERAFIL®. We intend to assist you utilize all of these features effectively by matching the purpose and the application. *CERAFIL® is the brand name of the MURATA product. Please read CAUTION and Notice in this catalog for safety. This catalog has only typical specifications. Therefore you are requested to approve our product specification or to transact the approval sheet for product specification, before your ordering. P11E.pdf 02.10.30 1 Types of CERAFIL® 2 Filter 3 Operating Principle of CERAFIL® 4 Tecnical terms of CERAFIL® 5 Discriminator 6 Trap 7 Features for CERAFIL® 8 How to Use CERAFIL® 9 Ceramic Discriminator Application 10 Appendix CONTENTSTypes of CERAFIL ® YYYYYYYYYYYYYYYYYYYYYYYYYYY12 FilterYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY13 1. Filter ..............................................................................................03 2. Operating Principles and Features of Filters ............................03 Operating Principle of CERAFIL®YYYYYYYYYYYY14 1. What is Piezoelectric Effect? ......................................................04 2. What is Piezoelectric Ceramics? ................................................05 3. Electrical-Mechanical Transducer and its Equivalent Circuit ...........................................................05 1. Vibrating Mode ............................................................................05 2. Symbols in the Electrical Circuit of the Electrical-Mechanical Transducer and the Equivalent Circuit ........................................06 4. CERAFIL® ......................................................................................07 Tecnical terms of CERAFIL® YYYYYYYYYYYYYYYYY18 1. Frequency Characteristics of CERAFIL® and the Related Terminologies...................................................08 2. Other Terminologies ....................................................................09 1. Input/Output Impedance .............................................................09 2. Impedance Matching...................................................................09 3. dB (Decibel) ................................................................................09 4. dBµ..............................................................................................10 5. Group Delay Time Characteristic ................................................10 Discriminator YYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY11 1. Discriminator ...............................................................................11 2. Detection methods......................................................................12 1. Ratio detection ............................................................................12 2. Quadrature Detection..................................................................13 3. Differential Peak Detection .........................................................13 Trap YYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY14 1. Trap ...............................................................................................14 2. Ceramic Trap ................................................................................14 1. Two-Terminal Ceramic Trap .......................................................14 2. Three-Terminal Ceramic Trap.....................................................15 Features for CERAFIL® YYYYYYYYYYYYYYYYYYYYYYY16 1. Designing with a high-selectivity is easy ..................................16 2. No Peaking Needed .....................................................................16 3. A Very Suitable Component for Miniaturization........................16 4. A Very Suitable Component for Integrated Filter......................16 5. Optimum Component for Solid State Application ....................16 How to Use CERAFIL® YYYYYYYYYYYYYYYYYYYYYYYY17 1. Impedance Matching ...................................................................17 2. Countermeasure for Spurious Response ..................................18 3. Consideration for Gain Distribution ...........................................18 4. Bias Circuit ...................................................................................19 Ceramic Discriminator ApplicationYYYYYYYYYY20 Appendix YYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY22 1. Correct Use of Ceramic Discriminator .......................................22 2. Applied IC Reference Table for Ceramic Discriminator ...........22 1 2 3 4 5 6 7 8 9 10 Please read CAUTION and Notice in this catalog for safety. This catalog has only typical specifications. Therefore you are requested to approve our product specification or to transact the approval sheet for product specification, before your ordering. P11E.pdf 02.10.30 2 Please read CAUTION and Notice in this catalog for safety. This catalog has only typical specifications. Therefore you are requested to approve our product specification or to transact the approval sheet for product specification, before your ordering. P11E.pdf 02.10.30 2 1 Types of CERAFIL® 1 Types of CERAFIL® and applicable markets Types of CERAFIL® C er am ic F ilt er C er am ic D is cr im in at o r C er am ic T ra p Typical Center Frequency 450kHz 455kHz K K K K K K K K K K K K K K K K K K K K K K K K K K K K K K K K K K K K K K K K 10.7MHz 4.5MHz 5.5MHz 6.0MHz 6.5MHz 450kHz 455kHz 10.7MHz 4.5MHz 5.5MHz 6.0MHz 6.5MHz H i- F iA ud io R ad io C o m m un ic at io n E q ui p m en t C o d e Le ss P ho ne M o b ile P ho ne W ir e Le ss D at a co m m un ic at io n R K E / T P M S T V / V C R C ar A ud io P o rt ab le A ud io SMD Type Lead Type SMD Type Lead Type 3 Please read CAUTION and Notice in this catalog for safety. This catalog has only typical specifications. Therefore you are requested to approve our product specification or to transact the approval sheet for product specification, before your ordering. P11E.pdf 02.10.30 2 Filter 1. Filter An electrical component which has a function of passing (or stopping) a specific frequency. 2. Operating Principles and Features of Filters The filters have different names depending on the structures and the materials used. The types, the principles and the features of the filters which are currently used are shown in the table 1. Fig.2-1 graphically shows the relations between the applicable frequency range and the band width of each filter. !Table 1. Operating Principle and feature of each filter. Active Filter Mechanical Filter Crystal Filter Ceramic Filter LC Filter 100 10 1 10 10 10 -1 -2 -3 100 1k 10k 100k 1M 10M 100M 1G Frequency (Hz) Fr a ct io n a l B a n d W id th (% ) Filter Groups The Range of Applicable Frequency Function Operating Principle Feature 10kHz to 100MHz B.P. B.E. Utilizing a piezo-electrical ceramics as an electrical-mechanical transducer and as a mechanical resonator, a specific characteristic is obtained by simultaneously providing electrical and mechanical system within a single system. The dimensions are smaller than the LC filter. The frequency is fixed for both IF circuit and FM detector circuit, and high selectivity is obtained. The frequency stability is inferior to the crystal filter. It has some spurious response by mechanical vibration. Ceramic Filter 100Hz to 150MHz L.P. H.P. B.P. B.E. A specific characteristic is obtained by merging the positive and negative reactances of the coil (L) and the capacitor (C). The acceptable degree of vibration for choosing the center frequency, the pass band, the amplitude characteristic or delay characteristic is normally great. On the other hand, the dimensions are often larger compared with the vibrating type of filter and the shape factor is inferior. LC Filter 3kHz to 200MHz L.P. H.P. B.P. B.E. A specific characteristic is obtained by merging both series and parallel resonant frequency by using frequency characteristics near the resonant point of the crystal resonator. The loss is extremely small, the cut-off characteristic is very steep and the stability is great. It is hard to get the wide band because of a high Q. Crystal Filter 100Hz to 800kHz B.P. It consists of 3 portions of mechanically vibrating filter sections which have certain frequency characteristics. The mechanical electrical transducer section and the matching section which connects with the external electronic circuit. It converts energy by adhering the piezo-electric ceramics on the metallic resonant element. The loss is small, the cut-off characteristic is steep and the stability is great. The structure is rather complicated. It also has a spurious characteristic. The dimensions are large. Mechanical Filter 100Hz to 80kHz L.P. H.P. B.P. B.E. Although the operating principle differs by the type, each of them generally utilizes the characteristics of the OP-Amp., and it operates the circuit by corresponding the merging circuit of both the OP- Amp. And the RC to the transfer function. A hybrid IC is used because a respectively high accuracy is required for the RC. The characteristics of any filters are available with this type. Compared with both the LC and mechanical filter, a miniature and light-weight filter is available in the low frequency range. It has strong vibration and shock resistance. It requires the power source. Active Filter L.P. : Low Pass Filter, B.P. : Band Pass Filter, H.P. : High Pass Filter, B.E. : Band Eliminate Filter Fig. 2-1 The relations between the Applicable Frequency Range and the Band Width of Each Filter Type 2 4 Please read CAUTION and Notice in this catalog for safety. This catalog has only typical specifications. Therefore you are requested to approve our product specification or to transact the approval sheet for product specification, before your ordering. P11E.pdf 02.10.30 CERAFIL® (ceramic filter) is a filter which uses a piezoelectric ceramics (barium titanate ceramics, lead- zirconate-titanate ceramics, etc.) as an electrical- mechanical transducer and as a mechanical resonator. It provides simultaneously the electrical and the mechanical system within a single element. 1. What is Piezoelectric Effect? Distortion takes place in the crystal lattice when a stress is applied upon it, and the crystal group which has no symmetric center in the crystal groups causes a polarization in addition to the distortion. This phenomenon was found by the Curie brothers in 1880 and is called the piezoelectric direct effect (or Curie’s Effect). In other wards, it means that the mechanical force (stress) can be converted into an electrical signal (an electrical field) or the electrical signal into the mechanical force. These two phenomena are collectively called the piezoelectric effect, and any substance which has this nature is called the piezoelectric ceramics. The crystal group, the symmetry of which is inferior among all crystals having the characteristic of the piezoelectricity, has a native limited volume of polarization before some electric field or stress is applied. This is called spontaneous polarization. The crystal is distorted by a phenomenon like the thermal vibration of atoms according to the temperature change. The degree of the spontaneous polarization also changes according to the distortion of crystal and its variation appears as a potential difference. This is called the phenomenon of pyroelectricity. On the other hand, when such a crystal is applied with an electric field, a distortion or a stress occurs. It is called the piezoelectric inverse effect (or Lippman’s Effect). Also among the crystals which have a spontaneous polarization, those which can reverse its direction by the external electrical field are called ferroelectric substance. The relations among these effects may be expressed as Fig. 3-1. Fig. 3-1 Relations Among Piezoelectricity, Plroelectricity, and Ferroelectricity. Dielectrics Piezoelectricity Pyroelectricity Ferroelectricity 3 Operating Principle of CERAFIL® 3 5 Please read CAUTION and Notice in this catalog for safety. This catalog has only typical specifications. Therefore you are requested to approve our product specification or to transact the approval sheet for product specification, before your ordering. P11E.pdf 02.10.30 3. Electrical-Mechanical Transducer and its Equivalent Circuit 1. Vibrating Mode Since the ceramic resonator with which the polarization has been oriented is piezoelectric, as described earlier, it vibrates in a vibrating mode when the electrodes are provided with the ceramic resonator, a sine wave is applied across the both polarities and then excited. Table 2 shows the typical vibrating modes, the shapes and the applicable frequencies of such ceramic resonators. !Table 2. The Vibrating Modes and the Applicable Frequency Band Frequency Vibrating mode (Hz) Flexural mode Length mode Area expansion mode Thickness shear mode Thickness expander mode 1k 10k 100k 1M 10M 100M 1G Note : Arrows signifies the directions of the vibrations. Operating Principle of CERAFIL® 3 2. What is Piezoelectric Ceramics? Some of the piezoelectric crystal can be calcined into the polycrystal ceramics, though there is a spontaneous polarization in each of the fine crystals in the piezoelectric ceramics which is cancelled as a whole and shows no piezoelectricity. But when a high D.C. voltage is applied to such ceramics, the directions of the spontaneous polarizations are brought to an uniformity and a ferroelectricity ceramics is attained. With some additives, the material with extremely stable frequency, temperature and aging characteristics is being used by MURATA for CERAFIL®. Compared with the single crystal, the piezoelectric ceramics has various advantageous features as follows ; 1. Can be mass-produced at low cost. 2. Can be formed into any desirable shape. 3. The direction of the polarization is easily attainable. 4. Chemically and physically stable. 5. Easy for fabrication. 3 6 Please read CAUTION and Notice in this catalog for safety. This catalog has only typical specifications. Therefore you are requested to approve our product specification or to transact the approval sheet for product specification, before your ordering. P11E.pdf 02.10.30 3 Operating Principle of CERAFIL® 3 In an ideal electrical-mechanical transducer, the impedance change takes place as shown in Fig. 3-5, and each constant of these and each constant of the equivalent circuit in Fig. 3-3 are in the following relation of equations shown in Fig. 3-5. Fig. 3-5 Impedance Characteristic of the 2-terminal Type Za Zr fr Frequency fa fr fa Zr Za : Resonant Frequency : Anti-Resonant Frequency : Resonant Impedance : Anti-Resonant Impedance fr = 1 2p L1 × C1 fa = 1 2p L1 × C1 × C0 C0+C1 Fig. 3-3 Two-terminal Type Equivalent Circuit C1 C1 L1 R1 C0 : Equivalent Compliance : Equivalent Mass : Equivalent Resistance : Parallel Equivalent Capacity L1 R1 C0 Fig. 3-4 Relations Between Spring-Pendulum and Electrical-Mechanical Transducer Mass M.=.L1 Spring Constant k .=.1/C1 Wall Floor Friction Resistance ƒ.=.R1 Weight 2. Symbols in the Electrical Circuit of the Electrical-Mechanical Transducer and the Equivalent Circuit The symbols as shown in Fig. 3-2 are used for the electrical-mechanical transducer in an electrical circuit. The equivalent circuit with two-terminal type transducer near the resonating point is shown in Fig. 3-3 even if the vibrating mode used is different. Each parameters can be considered as spring-pendulum shown in Fig. 3-4. C0 : the capacitance between the electrodes is called the parallel equivalent capacitance. C1 : mechanically corresponds to the flexibility of rubber or a spring, and it is called the equivalent compliance. L1 : mechanically corresponds to the inertia (mass or moment) and is called the equivalent mass (or equivalent inductance). R1 : is a friction resistance, and is called the equivalent resistance. Fig. 3-2 Symbols in the Electrical Circuit for the Transducer Two-terminal Transducer Three-terminal Transducer 7 Please read CAUTION and Notice in this catalog for safety. This catalog has only typical specifications. Therefore you are requested to approve our product specification or to transact the approval sheet for product specification, before your ordering. P11E.pdf 02.10.30 4. CERAFIL® When the piezoelectric ceramics described above is polarized by providing a pair of electrodes so that it can be excited in a prescribed vibrating mode and if a suitable matching impedance is applied to operate it, a CERAFIL® is completed. A model example of 455 kHz CERAFIL® for AM is shown in Fig. 3-6. Fig.3-6 Model of the 455 kHz CERAFIL® for AM (Ceramics) Ground Input (Driving Electrode) Output (Pick-up Electrode) Operating Principle of CERAFIL® 3 3 8 Please read CAUTION and Notice in this catalog for safety. This catalog has only typical specifications. Therefore you are requested to approve our product specification or to transact the approval sheet for product specification, before your ordering. P11E.pdf 02.10.30 4 Frequency 0 3 20 [dB] Input Level (or 6) (or 40) q e r t y w u i At te n u a tio n Some specific terms are used with CERAFIL®. Let us explain those terms in this paragraph. 1. Frequency Characteristics of CERAFIL® and the Related Terminologies Refer to the frequency characteristic graph (Fig. 4-1) with particulars (Table 3). Fig. 4-1 An example of CERAFIL® frequency characteristic Numbers in Fig.4-1 Terminology Symbol Unit Explanation of the Term Center Frequency f0 Hz It signifies the frequency in the center of the pass band width. However, the centerfrequency for some product is expressed at the point where the loss is minimum.q Pass Band Width (3dB) B.W. Hz Signifies a difference between the two frequencies where the attenuation becomes 3dBfrom the level of the minimum loss point.w Insertion Loss Loss dB Expressed in the input and output level ratio at the point of minimum loss in dB. (The insertion loss for some product is expressed in the input and output level ratio at the center frequency.) e Ripple