DD276376A1 - MONOLITHIC CRYSTAL FILTER - Google Patents

Abstract

The invention relates to narrow-band monolithic quartz filters with juxtaposed structures, the application of which is used in electronic circuits for the mid-frequency range 30 MHz, preferably in IF amplifiers. In the inventive device an improved Stoerresonanzdaempfung, a reduction in the time and material costs in the production and the Pruefaufwandes are to be achieved. The solution according to the invention is based on the fact that the adjacent resonators located on a substrate are offset perpendicularly to the coupling direction and / or these resonators of the resonator pair have differently sized resonator structures or resonator electrodes, ie. H. that they differ both in the dimensions in the direction of the other resonator and perpendicular thereto. At the same time, the electrode of one resonator has a metal layer with a layer thickness which is larger than the other resonator with the larger resonator surface.

Description

For this 3 pages drawings

Field of application of the invention

The invention relates to an electrical frequency filter made of piezoelectric material for use in the mid-frequency range above 30 MHz, especially for intermediate frequency amplifiers. The structure of this monolithic quartz filter (MQF) operating with vertical waves is described according to the harmonic principle, in particular of a dual-circuit filter.

Characteristic of the known state of the art Medium frequency MQFs> 30MHz usually consist of one or more double resonators and other passive ones

electronic components together. They work mainly according to the overtone principle, also called harmonic principle.

The high operating frequencies can also be generated by the fact that the quartz disk in the area in which

later the two resonators are structured, is removed locally.

By this method, the work ability in the fundamental wave can be ensured even at higher frequencies. From the Literature is known that this in addition to a larger bandwidth improved suppression of disturbing Secondary waves is achieved (DE 2 255432, DE 2 256624, DE 2416085). Due to this high technical effort in the production of this MQF and the often unsatisfactory quality values

So far, such crystal filters could not prevail.

In addition to crystal filters and ceramic filters are known which also work on the basis of volume waves. PS-DD 240296 introduces such an electronic component. Here the arrangement of the resonator electrodes takes place

a ceramic strip so that the distance between the outer Eoktrodenränder each filter base element to its associated strip ends is unequal and each filter base element has the same defined distance from a .lektrodenrand to its associated strip edge. However, a frequency filter constructed in this way requires additional material in order to avoid deterioration of the characteristics of the useful mode. For this increased

Cost of materials results in an increase in the component dimensions and the component weights. With crystal filters, in particular MQF, the material, however, costs a considerable cost factor. As further possibilities

The secondary wave suppression prove the large-scale application of damping mass and the local vaporization by point-like damping mass. Naci.teilig is when using these possibilities, however, that this deteriorate the parameters of Nutzmode.

As can be seen from theoretical work, is below a critical size of the electrode surface or

below a certain layer thickness of the electrode (while maintaining a material-dependent ratio of

Electrode thickness to electrode surface) to expect an improved spurious suppression. These theories

However, neither basic manufacturing costs nor manufacturing tolerances (eg crowning or wedge shape of the

Qrirzsubstrate, technical limits due to technological problem, locally different thicknesses of applied

Layers).

The development of MQF usually involves numerous compromises between the various Filtei parameters. With the current theoretical design methods, it is often not possible, dio for the spurious suppression

to comply with favorable areas.

A minimization of the disturbing noise waves is often only possible by increased efforts (for example PS-DD 2313955). The document US Pat. No. 3,517,350 describes another possibility for spurious suppression. Here it is recognized that

Different fundamental resonators form different side wave spectra, but not the need to compensate for the resulting frequency differences between the resonators.

Object of the invention

The aim of the invention is to improve the technical parameters of the overtone MQF, in particular with regard to the attenuation, which is to be reduced in the passband and increased in the stopband. Furthermore, with this new technical solution in the production of MQF a reduction in the time and material costs and in the functional test a lesser amount of time can be achieved.

Explanation of the essence of the invention The burglaries that occur in the blocking area of the filters as a result of disturbing Neb'inwollen must be minimized. The realization of this task requires a stronger attenuation of the spurs without an application of Damping compounds, through which a further operation would be necessary for the hardening of the cement. Eifindungsgemäß the object is achieved in that the arrangement of the resonators of a Resonatorpaares in vertical Displacement is performed to the coupling direction and further by combining different Electrode designs an effective reinforcement of secondary wave attenuation and Nutzmode results. It has been found that by an offset of the resonators perpendicular to the coupling direction an improvement in the Side wave attenuation can be achieved. This fact is due, for example, to the fact that the second symmetric mode (which is generally the most interfering Nebenwelle) in this direction forms three oscillation zones; with the vibration zones on the edge

out of phase with the zone in the middle. The middle vibration zones are over another

Effect mechanism not effectively vaporize, without damaging the Nutzmode also. An additional Damping the äußei of vibration zones can z. B. continue to be achieved by means of known damping masses. It is known that considerably different resonator structures differ widely from one another

form. This makes it possible to dimension adjacent resonators so that the most pronounced

Side waves of the first resonator of a resonator pair occur where the second resonator has a low Has oscillation capability. It has also been found that it is not necessary to vary significantly Resonantorstrukturen use, ν / ο η η on the electrodes of the resonator with the smaller resonator surface opposite

this surface area smaller metal layer is applied.

Gs is further noted that even by displacement of this additionally applied metal layer influencing the Oscillation behavior of the spurs is possible. It succeeds by the transmission of the spurious waves of a resonator

to hinder the other resonator or to counteract a coupling between the secondary waves.

Using a special fine-adjustment mask, z. B. the resonator 1 are steamed again, in addition

The layer applied to the resonator is smaller than the basic structure of the resonator 1. As a result, the distance between the secondary waves formed by the two resonators can be sufficiently shifted relative to each other even if the

Resonators have almost the same Resonatorflächen. It has been experimentally confirmed that, despite the different structures of the resonators, the energy capture Mochanism

at dor Nutzmode remains.

AusfOhrungibeisplele The invention will be explained in more detail with reference to two Ausfihrungsbeispielen. Figures 1 and 3 illustrate an invention Resonator pair or a Doppelreson-gate in front view. The first embodiment with Figure 1 is used to demonstrate the effect of a slight misalignment of the baiden Resonators in the direction perpendicular to the original desired propagation direction of the shaft. The resonators 1 and 2 with the leads 5 are located on a quartz disk 3, which is clamped in a quartz holder 4

is. The mechanical attachment and electrical contacting of the quartz disk 3 in the quartz holder 4 takes place essentially by means of the cemented areas 6.

The resonators 1 and 2 are offset by V "their height and thus perpendicular to the coupling direction against each other

arranged.

Although the resonator dimensions deviate greatly from the theoretical optimum, an improvement of the Spurious wave suppression achievable. FIG. 2 shows for this purpose the comparison of the selection behavior between the double resonator described above (with

mutually offset resonators) and a double resonator with unsubstituted resonators. Both resonators were co-evaporated and all of the electrodes applied had the same dimensions.

Finally, the invention is documented in a second embodiment. Figures 3 and 4 provide a

Dop, elresona or or, in which both novelties were combined.

The quartz disk 3 is located in the resin holder 4. On the quartz disk 3, both the resonator 1 and the resonator 2 are

structured. The resonators 1 and 2 with the leads 5 are connected to the resin holder 4 via cemented areas 6 (eg silver conductive cement), whereby electrical contacting takes place.

The left resonator 1 initially oscillates at a higher frequency than the resonator 2 due to the small resonator area. The compensation of this asymmetry is achieved by the additional metal layer 7. Figure 4 shows the horizontal section through the central part of the Doppelrcsonators. Here is the quartz disk thickness

shown enlarged. The vapor-deposited layers are exaggerated.

From the figures it is apparent that the resonator 1 is arranged slightly higher in order to improve the secondary wave suppression

as the resonator 2. For the same reason is located on the resonator 1, a metal layer 7, which has a substantially smaller area than the resonator 1 and is also offset.

Claims (3)

1. Monolithic crystal filter, which consists of one or more filter base elements, for. B. double resonators and other passive electronic components and the Filtergrundelemerite work with bulk waves on the energy capture principle and the adjacent Resoantorelektroden are arranged on the filter base element so that the distance between the electrode edges to the associated outer edge of the filter element is unequal, characterized in that the Resonators of a pair of resonators perpendicular to the coupling direction are offset from each other and or each adjacent resonator located on a substrate resonator electrodes of different sizes both in thickness and surface, wherein the resonator (1) with the smaller resonator surface locally has a greater layer thickness than the resonator ( 2) with the larger resonator surface. 2. Arrangement according to claim 1, characterized in that the electrode of the resonator (1) at the same time a metal layer (7) having a substantially smaller area relative to the resonator surface of the resonator (1). 3. Arrangement according to claim 1 or 2, characterized in that the centers of mass of the metal layer (7) and the resonator are offset.