JPH0584660B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a capacitor, and more particularly to a capacitor connected in series to a piezoelectric vibrator and used to adjust the load resonance frequency of the piezoelectric vibrator.

BACKGROUND ART Conventionally, as shown in FIG. 8, this type of capacitor has a structure in which rectangular electrodes 203 are formed on both surfaces of a flat dielectric 201 over the entire surface.

Problems to be Solved by the Invention In the conventional capacitor described above, the load resonance frequency of the piezoelectric vibrator connected in series with the capacitor is adjusted by partially shaving the electrode. Since the load resonance frequency changes greatly with a small change in capacitance, adjustment is difficult and the defective rate is high, and fine adjustment requires time for adjustment, resulting in a high price. Furthermore, since the change in the load resonance frequency is not proportional to the interval at which the electrodes are shaved, the workability is poor and automation is difficult.

Means for solving the problem When a capacitor having a capacitance Cx is connected in series with a piezoelectric vibrator having a resonance frequency r, an equivalent parallel capacitance C ₀ , and a capacitance ratio γ as shown in Fig. 6a, the equivalent circuit is The result is as shown in FIG. 6b (γ=C ₀ /C ₁ ), and the load resonance frequency x is expressed by the following equation.

x-r/r=1/2γ(1+Cx/Co)...(1) Here, x is the load resonance frequency when capacitors with capacitance Cx are connected in series.

By changing this capacitance Cx, the load resonance frequency x can be adjusted.

When adjusting the load resonance frequency using a capacitor composed of flat parallel plate electrodes, it is possible to make the load resonance frequency r rise at equal intervals by scraping the capacitor's electrodes at regular intervals. , the drawbacks of the above-mentioned conventional methods can be eliminated.

It is assumed that the two orthogonal sides of the capacitor electrodes are defined as the X axis and the Y axis, and that the capacitor electrodes are made in the shape shown in FIG. That is, it is assumed that the shape of the first electrode of the two electrodes is o abdo in the figure, and the shape of the second electrode is o lmno (rectangle). When the first electrode is divided into equally spaced lines perpendicular to the Consider what kind of curve should be used for curve bd in order to make the change linear.

If the X-axis coordinate value is x, then the load resonance frequency x
Since this means changing linearly with respect to x, x−lm=kx...(2) where lm is the load resonance frequency when the capacitor of the present invention is connected before frequency adjustment, and k is a constant (2) Substituting the equation into equation (1) and solving for Cx, we get Cx=r/2γ(kx+lm-r)-1) C ₀ ...(3) Returning to Figure 7, since the curve bd is a function of x If this is set as S(x), then the capacitance of the capacitor Cx
is Cx＝h∫a xS(x)dx ...(4) where h is the capacitance per unit area and x＜a Substituting equation (4) into equation (3) to find S(x), S( x) = C ₀ kr / 2γh (kx + lm - r) ² ... (5) If the curve ba in Figure 7 is a curve expressed by the above equation (5), then the electrode should be connected to a line perpendicular to the X axis. By cutting the width, the load resonance frequency decreases in proportion to the width
x can be changed.

In addition, in equation (5), C ₀ , k, r, γ, h,
Since lm and r are all constants, the equation representing the curve bd can be expressed as follows.

S(x)=K ₁ /(x+K ₂ ) ² ...(5') where K ₁ and K ₂ are constants.Next, the present invention will be explained with reference to the drawings.
FIGS. 1a and 1b show the front and back surfaces of a capacitor according to an embodiment of the present invention, respectively.
(The distinction between a and b is the same up to Figure 5.)
This uses a flat ceramic 1 as a material, and has an electrode 10 on its surface expressed by the function S(x) shown in equation (5) above. By cutting the electrode perpendicular to side 0X from the point 0 side, the shaved electrode 0X
The load resonance frequency of the piezoelectric vibrator connected in series with the capacitor increases in proportion to the above length.

In Figure 2, the electrodes represented by the function S(x) in Figure 1 are separated at regular intervals perpendicular to the side 0X to form interdigital electrodes 21, 22, 23... This is a capacitor which is connected with a lead wire 100. By cutting the lead wires connected to each interdigital electrode one by one from the point 0 side, the load resonance frequency increases in proportion to the number of cut interdigital electrodes.

Figure 3 shows the interdigital electrode 2 of the capacitor in Figure 2.
1, 22, 23, . . . instead of using lead wires, electrode leads 20 are formed by vapor deposition on the back surface of the capacitor and are electrically connected to each interdigital electrode.

FIG. 4 shows the capacitor shown in FIG. 3, in which rectangular interdigital electrodes 31, 32, 33, etc., which are equivalent to the capacitance of each interdigital electrode 21, 22, 23, etc., are formed on the end face of the capacitor by vapor deposition, etc. Electrode leads 30 are formed and electrically connected capacitors to facilitate connection to a circuit board.

FIG. 5 shows a case where two capacitors having the function of the capacitor of the present invention are formed on one ceramic plate.

Effects of the Invention As explained above, in the present invention, in a capacitor in which electrodes are formed on both sides of a flat dielectric, when the electrodes on one side are shaved at equal intervals, the load resonance frequency is The shape of the electrode on one side is formed by a function that increases in proportion to the Therefore, the amount of change in the load resonance frequency is proportional to the length of the capacitor in the direction in which it is cut, making it easier to adjust the load resonance frequency and shortening the adjustment time, resulting in a lower defective rate and lower prices. There is. Also, since the intervals at which the electrodes are shaved are constant,
This has the advantage of making the work easier and easier to automate. Furthermore, by forming the electrodes represented by functions into a blind shape, the portion of the electrodes to be removed is reduced, which has the effect of shortening the adjustment time.

[Brief explanation of drawings]

Figures 1 to 5 each show each implementation of the present invention, where a is a view seen from the front, b is a view seen from the back, and Figures 6 a and b are illustrations for explaining the present invention, respectively. Electrical circuit diagram and its equivalent circuit diagram,
FIG. 7 is a diagram explaining the principle, and FIG. 8 is a perspective view of an example of a conventional capacitor. 1... Ceramic plate, 11... Surface electrode, 12
...Back electrode, 21, 22, 31, 32, 41,
42, 51, 52... interdigital electrode, 20, 3
0, 40, 50...Lead electrode, 100...Lead wire.

Claims (1)

[Claims] 1. In a capacitor constituted by a pair of parallel plate electrodes, at least one of the electrodes has a line y=0 and a line x=0 in orthogonal X and Y axis coordinates.
0, straight line x = a and curve y = K ₁ / (x + K ₂ ) ² , where x and y are X and Y coordinates, respectively. a, K ₁ and K ₂ have shapes similar to the area surrounded by constants. A capacitor characterized by: 2. The capacitor according to claim 1, wherein at least one electrode is divided into a webbing shape at regular intervals perpendicular to the X-axis.