JPH0641386Y2 - Monolithic crystal filter - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] The present invention relates to a monolithic crystal filter formed by vertically connecting a plurality of stages of a piezoelectric single crystal disk-type AT-cut thickness sliding oscillator such as a quartz oscillator. is there.

[Conventional technology]

Conventionally, AT-cut thickness sliding crystal units have been widely used for monolithic crystal filters (hereinafter referred to as MCF). The AT cut is obtained by cutting out the XZ plane, which is one of the crystal planes of quartz, with an inclination of about 35 ° around the X axis, and has a characteristic that the frequency-temperature characteristic is good near room temperature.

In such an AT cut thickness sliding oscillator, as shown in FIG.
It is known that a dual mode oscillator can be obtained by separately forming and forming the ground electrode 23 on the back surface.
Since it is difficult to obtain a filter having a sufficient attenuation amount by itself, the dual mode oscillator is often connected in two or more stages in series via the coupling capacitor 24 as shown in FIG.

[Problems to be solved by the device]

When constructing a filter by connecting oscillators in multiple stages as described above, oscillators with the same thickness and diameter are used.However, since spurious in contour mode also occurs at the same frequency, these spurs are intensified. There was a problem that it would result in a large unnecessary response.

Then, the objective of this invention is providing the MCF which can suppress the spurious of a contour mode at the time of multistage vertical connection.

[Means for Solving the Problems]

In order to achieve the above-mentioned object, the present invention forms a plurality of pairs of electrodes on a piezoelectric single crystal disk-type AT-cut thickness-sliding vibrator with a beveled surface at the peripheral edge, and connects the vibrators in multiple stages in a vertical direction. The MCF is characterized in that the slopes of the vibrators at each stage have different shapes.

[Action]

That is, in the case of a disk-type AT-cut thickness-sliding oscillator with a frequency of several MHz or higher, the vibration displacement is concentrated in the central part to improve the energy trapping efficiency and reduce the supporting loss at the peripheral edge of the oscillator. For this reason, the peripheral surface of the disc is gradually polished so that the peripheral end portion becomes thinner. This slope shape changes the spurious frequency of the contour mode. Utilizing this property, the present invention disperses contour mode frequencies and suppresses spurious by vertically connecting transducers having different slope shapes in multiple stages.

〔Example〕

 FIG. 1 shows an example of the MCF according to the present invention.

In the drawing, reference numeral 1 is a disk-type AT-cut thickness-sliding vibrator made of a piezoelectric single crystal such as quartz, lithium niobate, or lithium tantalate. The peripheral end portion of the vibrator 1 improves energy trapping efficiency. Moreover, in order to reduce the support loss at the peripheral end of the vibrator 1, the sloped surface 1a is beveled. An input electrode 2 and an output electrode 3 are separately formed on the front surface of the vibrator 1, and a ground electrode 4 is formed at a portion corresponding to the input and output electrodes 2 and 3 at the center of the back surface. Two pairs of electrodes are constituted by the electrodes 2 and 4 and the electrodes 3 and 4, and a dual mode oscillator having a symmetric mode in which the displacement distribution is line symmetrical with respect to the propagation axis direction and a point symmetric oblique symmetric mode is realized. It

Support wires 5, 6 and 7 are electrically connected to the lead-out portions of the electrodes 2, 3 and 4 led out to the peripheral end of the vibrator 1, and these support wires are fixed to the stem 8 by an external connection. For terminals 9,10,1
Connected to 1. The vibrator 1 is housed in a cap 12 attached to the stem 8 and hermetically sealed.

Since the oscillator 1 cannot obtain a sufficient MCF when used alone, it is usually made up of a plurality of stages connected vertically as shown in FIG. In the present invention, when a plurality of vibrators 1 are vertically connected, the vibrators of the respective stages having different sloped shapes at the peripheral ends are used.

That is, FIG. 2 is a cross-sectional view of the vibrator 1, where the diameter is d, the thickness of the central portion is t, the angle of the peripheral end slope 1a is θ ₁ , and the width of the slope 1a is w ₁ .

FIG. 3 shows another transducer 1 ', whose diameter d and thickness t are the same as those in FIG. 2, but the angle θ ₂ of the slope 1b is larger than that of FIG. _{2 and} the width w _{2 of the} slope 1b is It is narrower than that of FIG.

FIG. 4 shows yet another transducer 1 ″, in which case the diameter d and the thickness t are the same as in FIGS. 2 and 3,
The difference is that the shape of the inclined surface 1c is not a tapered surface but a curved surface.

As illustrated in FIGS. 2 to 4, when oscillators having different slope shapes are combined and connected in multiple stages in a vertical manner, spurious frequencies in the contour mode can be dispersed due to the difference in slope shape, and an MCF with less spurious noise can be obtained. can get.

It should be noted that FIGS. 2 to 4 merely exemplify the typical shape of the vibrator, and other vibrators having different slope shapes are also conceivable. In the present invention, the slope shape is a concept including the angle and width of the slope and the curvature of the slope as described above.

Further, the present invention can be applied not only to the tandem type MCF but also to the mixed type MCF.

[Effect of device]

As is clear from the above description, according to the present invention, it is possible to enhance the damping characteristics by connecting the vibrators in multiple stages, and to improve the energy trapping efficiency by providing the inclined surface at the peripheral end of the vibrators. By changing the slope shape of the oscillator, it is possible to obtain an MCF with less spurious.

[Brief description of drawings]

1 is a cross-sectional view of an example of the MCF according to the present invention, FIG. 2 is a cross-sectional view of an example of the vibrator, FIG. 3 is a cross-sectional view of another example of the vibrator, and FIG. 4 is a vibrator. FIG. 5 is a cross-sectional view of yet another example of FIG. 5, FIG. 5 is a front view of a conventional vibrator, and FIG. 6 is a circuit diagram of a filter in which a plurality of vibrators are vertically connected. 1,1 ′, 1 ″ ... Oscillator, 1a, 1b, 1c ... Slope, 2 ... Input electrode, 3 ... Output electrode, 4 ... Ground electrode.

Claims (1)

[Scope of utility model registration request] 1. A plurality of pairs of electrodes are formed on a disk-shaped AT-cut thickness sliding oscillator of a piezoelectric single crystal having a beveled surface at its peripheral end.
A monolithic crystal filter in which a plurality of stages of these oscillators are vertically connected, in which the slopes of the oscillators in each stage have different shapes.