RU2373636C1 - Piezoelectric filter - Google Patents

Abstract

FIELD: communication facilities.

SUBSTANCE: invention relates to the field of piezo engineering and can be used in frequency selection devices, portable communication devices, communication devices of moving objects, navigation systems etc. Technical result is achieved by means of development as multilevel internal, as and external structure of filter, containing inside the ceramic package set of piezoelectric plates and matching condensers. Furthermore, on internal and external surface of filter it is implemented metallisation layer in the form of conductively closed circuit.

EFFECT: manufacturing of diminutive compact high order filters in casing for surface mounting.

7 cl, 5 dwg, 3 ex

Description

The invention relates to electronics, in particular for piezoelectric technology, and can be used in frequency selection devices for volumetric acoustic waves in the frequency range from 8 to 160 MHz. More specifically, the invention relates to the structure of a piezoelectric surface mount filter.

Piezoelectric filters are a resonant acoustic system using the principle of energy capture and are designed to distinguish a certain frequency band from the general spectrum. Filters in their structure contain at least one rectangular piezoelectric plate with one or more pairs of exciting electrodes placed on its working faces with electrical leads forming resonators, while the number of resonators determines the so-called filter order.

The analysis of scientific, technical and patent literature shows that there is a tendency, on the one hand, to increase the order of the filter to reduce the squareness coefficient and increase the guaranteed relative attenuation, which, however, leads to an increase in the overall dimensions of the filter with the traditional approach to the structure filter and determining the ratio of the width of the piezoelectric plate to its thickness. On the other hand, in practice, to ensure frequency filtering in modern radio receivers, low-order piezoelectric filters (second or fourth order) are widely used, having the smallest possible overall dimensions, but not ensuring high values of guaranteed relative attenuation and having restrictions on the implementation of the nominal frequency below 21 MHz Known piezoelectric filters, although they have reduced overall dimensions, they are a semi-finished product that requires the consumer to install additional capacitors outside the filter housing and possible selection of the capacitance of the capacitors to obtain the required amplitude-frequency characteristic of the filters. Such capacitors in the technology of manufacturing piezoelectric filters are referred to as matching capacitors.

So, a piezoelectric filter of the 8th, 10th order is known, designed to operate in the frequency range from 8 to 80 MHz in a metal-glass case with wire leads inserted into the holes of a printed circuit board containing several strip-type piezoelectric plates with two pairs of electrodes on each piezoelectric plate (see, for example, V. A. Mostyaev and V. I. Dyuzhikov “Technology of piezoelectric and acoustoelectronic devices”, M., Jaguar, 1993, pp. 182-183). The known filter has high electrical parameters in terms of guaranteed attenuation (more than 85 dB) and a rectangular coefficient of less than 2.5 at a level of 80/3 dB, however, it has significant overall dimensions and cannot be used for surface mounting on a consumer board due to the absence of flat contacts .

US Pat. No. 5,023,580 discloses a fourth-order quartz filter design in a sintered metal casing for surface mounting designed to operate at frequencies from 21.4 to 100 MHz. The known filter contains a quartz piezoelectric plate with four pairs of exciting electrodes placed on its working faces and forming acoustically coupled resonators. With small overall dimensions (for example, 7 × 5 × 1.35 mm), the known monolithic quartz filter, however, has a small guaranteed relative attenuation (not more than 75 dB), and it is provided only in the lower frequency range of the delay band, as well as a low order filter (no more than the fourth) and the limitation of the nominal frequency in the direction of its reduction. The known filter is characterized by the impossibility of mounting a matching capacitor, necessary to obtain the desired amplitude-frequency characteristic of the filter, inside the housing.

Thus, from the prior art are known:

- either monolithic piezoelectric filters having a minimum overall dimensions, but of a low order (not more than a fourth),

- either monolithic piezoelectric filters of a high order (above the fourth), however, having large overall dimensions due to the need to place a large number of piezoelectric plates in one housing.

In the framework of this application, the task of developing the design of such a miniature compact piezoelectric filter designed for surface mounting, which would increase its order to a tenth, as well as obtain a guaranteed relative attenuation of more than 80 dB with the extension of the frequency range towards lower frequencies to 8 MHz, is being solved . There is a need to convert the piezoelectric filter into a high-pass or low-pass filter, and into a notch filter based on the developed internal and external structure of the piezoelectric filter. The problem of designing a piezoelectric filter having an effective cost is also being solved.

This goal is achieved by the fact that in a piezoelectric filter containing a ceramic-metal housing for surface mounting, having a detachable connection with a cover, as well as at least two external contact pads made on its base and placed in the housing, at least one pair piezoelectric plates with two pairs of exciting electrodes each and at least one matching capacitor, the housing has two systems of internal contact pads, one of which is designed to supply high frequency electrical signal, and the other is intended for grounding, these two systems of internal contact pads are placed in the same plane in two mutually parallel rows so that in each row the internal contact pads of one system alternate with the internal contact pads of the other system, and each internal contact pad of one row is located opposite the internal contact pad of another system from a different row, with each piezoelectric plate and each matching capacitor connected the inenes are electrically with the internal contact pad of each system, in addition, the housing has a metallization layer both on its outer surface and on the inner surface, with the exception of the areas occupied by the external contact pads and matching capacitors, while the metallization layer forms a closed loop electrically connected to a system of grounded internal pads.

It is advisable that the matching capacitors are located either between the piezoelectric plates in the case of a fourth-order filter, or they are located under the piezoelectric plates for filters of a higher order.

In addition, the number of matching capacitors is determined from the relation n = N-1, where N is the number of piezoelectric plates.

Preferably, the piezoelectric plates are made of piezoelectric materials in which shear thickness oscillations are excited.

The ratio of the width of the piezoelectric quartz plate to its thickness for a quartz crystal cut yzb / 35 ° 11 'value from the range of 17.2-17.5; 13.7-14.0. (one)

In this case, the ratio of the width of the piezoelectric plate to its thickness for the lithium tantalate slice xys / -49 ° value from the range: 22.4-22.8; 19.6-20.0; 15.8-16.1; 13.5-13.8; 8.9-9.3; 6.3-6.6; 5.9-6.2; 5.5-5.8; 4.8-5.2. (2)

The ratio of the width of the piezoelectric plate to its thickness for langasite slice yzb / + 1 ° 30 'is a value from the range of 26.2-26.5; 23.5-23.8; 20.2-20.5; 18.0-18.4; 14.9-15.2. (3)

This internal and external structure of a piezoelectric filter made using a miniature cermet casing, designed for surface mounting, is characterized by a multi-level arrangement of the main components of the device in the housing and, subject to the required relative positioning of the piezoelectric plates, capacitors and contact pads inside the casing, allows such a dense packaging of the main components filter, which at the same time provides both increase guaranteed of relative attenuation and increase the filter order.

The invention is illustrated by non-limiting examples of its implementation and the accompanying drawings, in which:

figure 1 depicts a view of the piezoelectric filter from the side of the base of the housing.

figure 2 depicts a filter of the eighth order from above without a cover.

figure 3 depicts a fourth-order filter view from above without a cover.

4 is a view of an eighth order filter without piezoelectric plates.

5 is a cross-sectional view of this eighth order filter.

To clarify the invention, the following notation is introduced in the drawings: 1 - housing; 2 - cover; 3 - metallization layer; 4 - external contact pads input-output, 5 - external contact pads; 6 - a series of piezoelectric plates; 7 - a pair of input electrodes (lower input electrodes are not shown); 8 - a pair of output electrodes (lower output electrodes are not shown); 9 - the internal contact pad is grounded; 10 - capacitor; 11 - internal contact pad for supplying a high-frequency signal; 12 - internal metallization; 13 - conductive mounting element; 14 - plot free from metallization; 15 - element detachable connection.

The piezoelectric filter operates as follows. The piezoelectric filter system consists of a series of individual strip-type piezoelectric plates 6 made, for example, of quartz (see FIG. 2). It should be understood that any other piezoelectric material in which thickness shear vibrations are excited can be used as the material of the piezoelectric plate. The relations between the width and thickness of the piezoelectric filter plate to ensure the required monofrequency and maximum quality factor are for quartz, lithium tantalate and langasite, respectively, the values determined by relations (1), (2) and (3). For example, lithium tantalate or langasite can also be used as the piezoelectric material of the plate. Each plate of the series of piezoelectric plates 6 is electrically connected to the internal contact pads for supplying a high-frequency signal 11 and to internal contact pads grounded 9, and each capacitor 10 is electrically connected at one end to the internal contact pads for supplying a high-frequency signal 11, and the other end is connected to internal metallization 12. When applying to the upper electrode a pair of electrodes of the input 7 of the piezoelectric plate 6 from the external contact pad of the input 4 high-frequency signal and with a frequency corresponding to the main oscillation of the shear in thickness, a shear standing wave is established in the sub-electrode region. Due to the acoustic coupling between the frequency resonators formed by the pair of input electrodes 7 located on the working sides of the piezoelectric plate 6, the shear vibrations of the input resonator are transmitted to the sub-electrode region of the output resonator formed by the pair of output electrodes 8. The high-frequency output signal from the first plate from the series of piezoelectric plates 6 arrives at the input resonator of the second plate from a series of piezoelectric plates 6. Next, similar transformations occur high-frequency of the signal to the filter output (external output contact pads). Capacitors 10 (the so-called matching capacitors), necessary to obtain the desired amplitude-frequency characteristic of the filter, are placed between the internal pads for supplying a high-frequency signal 11 and the internal metallization 12, as well as either between the piezoelectric plates 6 or under the piezoelectric plates 6 depending on filter order.

Example 1

The eighth-order piezoelectric filter at a frequency of 21.4 MHz, made according to the proposed structure, has four piezoelectric plates 6 made of quartz with dimensions of 6 mm × 1.7 mm, placed inside the ceramic-metal housing 1.

The housing 1 of the piezoelectric filter has a metallization layer 3, covering its outer surface, namely the base and side faces of the housing 1, and forming a closed loop electrically connected to the grounded internal contact pads 9 and internal metallization 12. The housing 1 has external contact pads of input and output 4, made on its basis and intended for input / output of a high-frequency signal. The housing 1 may also have external contact pads 5, which are, by their functional purpose, reserve contact pads electrically connected to the internal contact pads 11. The housing 1 also has internal metallization 12 with sections 17 free from metallization. A series of piezoelectric plates 6 with two pairs of electrodes 7 and 8 (the lower electrodes of each pair are not shown), as well as the so-called matching capacitors 10, located between the insulated contact pads 11 and the internal metallization 12, are installed inside the housing 1 using conductive fastening elements 16 this matching capacitors 10 are placed under a series of piezoelectric plates 6 (see figure 2).

The presence of external contact pads 5 as backup pads allows, on the basis of this structure of the piezoelectric filter, to convert it from a band-pass filter into a high-pass or low-pass filter, as well as into a notch filter by additional electrical connection of the external contact pads 5 of the filter with capacitors or inductors.

A filter of this design with a multi-level arrangement of the main nodes has a guaranteed attenuation of more than 85 dB, a passband of 3.5 to 90 kHz, an attenuation attenuation of less than 3 dB, an uneven attenuation in the passband of less than 2 dB and a squareness factor of less than 2.5 at 80 / 3 dB

Example 2

The eighth-order piezoelectric filter at a frequency of 10.7 MHz consists of the same units as in example 1, however, langasite plates yl / 1 ° + 30 'were introduced as piezoelectric plates, while the four piezoelectric plates 6 are 6 mm × 1.72 mm. The filter contains a ceramic-metal casing with the same geometric dimensions as in example 1. Matching capacitors 10 are located under a series of piezoelectric plates 6 between the internal contact pads 11 and the internal metallization 12.

This filter has a guaranteed attenuation of more than 85 dB, a passband of 50 kHz, an attenuation attenuation of less than 3 dB, a non-uniform attenuation in the passband of not more than 2 dB, a squareness factor of not more than 2.5 at 80/3 levels.

Example 3

The fourth-order filter at a frequency of 10.7 MHz is made in the same metal-ceramic case as in Example 1, however, two plates 6 of xys / -49 ° cut lithium tantalate are introduced as piezoelectric plates (see Fig. 3) with dimensions of 6 mm × 2.83 mm, placed in the housing 1, and one matching capacitor 10 located between the series of piezoelectric plates 6, as well as between the inner contact pad 11 and the inner metallization 12.

This filter has a guaranteed attenuation of more than 80 dB in the frequency range

f _nom - 1 MHz, bandwidth from 50 to 400 kHz, insertion loss of less than 3 dB, unevenness in the bandwidth of not more than 2 dB, the coefficient of squareness at a level of less than 3 at 40/3 levels.

The invention can be used in the manufacture of monolithic piezoelectric bandpass filters, which can be used as components of portable communication devices, in navigation systems, as well as for other devices, for example, in SAW filters or in multi-cavity systems with other end use.

A commercial advantage of the claimed piezoelectric filter is the possibility of both increasing the guaranteed relative attenuation, and increasing the order of the filter with its miniature overall dimensions and at an effective price. The internal and external structure of the filter allows you to convert it into a high-pass or low-pass filter, as well as into a notch filter using the additional electrical connection of the backup external contact pads with external capacitors or inductance elements.

Claims (7)

1. A piezoelectric filter containing a ceramic-metal casing for surface mounting, having a detachable connection with a cover, as well as at least two external contact pads made on its base and placed in the housing, at least one pair of piezoelectric plates with two pairs of exciting electrodes each and at least one matching capacitor, in addition, the housing has two systems of internal contact pads, one of which is designed to supply high-frequency electric signal, and the other is intended for grounding, these two systems of internal contact pads are placed in one plane in two mutually parallel rows so that in each row the internal contact pads of one system alternate with the internal contact pads of the other system, and each internal contact pad of one row is opposite the inner contact pad of another system from a different row, with each piezoelectric plate and each matching capacitor electrically connected to the inside the lower contact pad of both systems, in addition, the housing has a metallization layer, both on its outer surface and on its inner surface, with the exception of the areas occupied by the external contact pads and matching capacitors, while the metallization layer forms a closed loop, electrically connected to the grounded system internal contact pads. 2. The device according to claim 1, characterized in that the matching capacitors are either located between the piezoelectric plates in the case of a fourth-order filter, or are located under the piezoelectric plates for filters of a higher order. 3. The device according to claim 1, characterized in that the number of matching capacitors is determined from the ratio n = N-l, where N is the number of piezoelectric plates. 4. The device according to claim 1, characterized in that the piezoelectric plates are made of piezoelectric materials in which shear thickness oscillations are excited. 5. The device according to claim 1, characterized in that the ratio of the width of the piezoelectric plate to its thickness is for a quartz slice yzb / 35 ° 11 'a value from a range of 17.2-17.5; 13.7-14.0. 6. The device according to claim 1, characterized in that the ratio of the width of the piezoelectric plate to its thickness is for cut lithium tantalate
xys / -49 ° value from the range: 22.4-22.8; 19.6-20.0; 15.8-16.1; 13.5-13.8; 8.9-9.3; 6.3-6.6; 5.9-6.2; 5.5-5.8; 4.8-5.2. 7. The device according to claim 1, characterized in that the ratio of the width of the piezoelectric plate to its thickness for langasite slice yzb / + 1 ° 30 'is a value from a range of 26.2-26.5; 23.5-23.8; 20.2-20.5; 18.0-18.4; 14.9-15.2.

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