JPS588605B2 - Easy mode filter - Google Patents

Description

Detailed Description of the Invention The present invention forms electrode portions on a piezoelectric crystal plate by using a technique such as vapor deposition or printing, and utilizes mechanical coupling of vibrational energy through the non-electrode portion between each electrode. This paper relates to an energy confinement type filter.

In general, non-pole energy confinement filters that do not have an attenuation pole on a finite frequency axis have slow cutoff characteristics.
There is an increasing need for a polarized energy confinement filter that has an attenuation pole on a finite frequency axis and can provide steeper cutoff characteristics.

A conventional polarized multimode filter has an odd number of electrodes E1, E2,...E on a piezoelectric crystal plate P as shown in FIG.
2n-1, and a capacitor C is connected in parallel between the signal input terminals 1 and 2 and the signal output terminals 3 and 4. Attenuation pole f-∞ can be realized only on the frequency domain side.

Also, by forming an odd number of electrodes, replacing the signal output terminals as shown in Figure 3, and connecting a capacitor in parallel to the electrodes, it is possible to output signals only in the high frequency region with respect to the center frequency of the bandpass filter, as shown in Figure 4. Attenuation pole f+∞ can be realized.

Furthermore, as shown in Fig. 5, an even number of electrodes E1...
・If E2n is formed and a capacitor C is connected in parallel to the electrode between the signal input terminal and the signal output terminal, it will be symmetrical in the high frequency region and low frequency region with respect to the center frequency of the bandpass filter as shown in Figure 6. It is possible to realize an attenuation pole.

However, the above method has the disadvantage that the frequency of the attenuation pole is easily influenced by external parasitic capacitance, especially when the frequency of the attenuation pole is near the cutoff frequency of the filter, and the number of electrodes is In the case of an even number, there is a drawback that only one attenuation pole can be realized symmetrically with respect to the center frequency.

Therefore, the present invention aims to improve the above-mentioned drawbacks of the prior art, and its object is to provide a polarized multimode filter having a stable attenuation pole on a finite frequency axis.

The features of the present invention to achieve this objective include three energy trapping electrodes formed on a single piezoelectric crystal plate.
a member having at least one set of paired electrodes and commonly connecting one set of electrodes on one side of the crystal plate; an input terminal connected to the electrode on the other side of the crystal plate; The purpose is to realize an attenuation pole on a finite frequency axis by utilizing the feedback effect of an electric signal by a capacitor or inductor connected between an output terminal, the above-mentioned member, and a common input/output terminal,
According to the present invention, the frequency position of the attenuation pole is determined by the dimensions of the electrodes, the spacing between the electrodes, the film thickness of the electrodes, and the reactance, and is therefore very stable.

Examples will be described below with reference to the drawings.

7 and 8 are structural diagrams of a polarized multimode filter according to the present invention.

In Figures 7 and 8, 1 and 2 are signal input terminals, 3,
4 is a signal output terminal, and 5, 6, and 7 are electrodes formed on the piezoelectric crystal plate.

The three electrodes on one surface of the piezoelectric crystal plate P are commonly connected by a common connection member 8 forming a common electric terminal as an electrode set.

C in FIG. 7 and L in FIG. 8 are a capacitor and an inductor connected in series to electrodes formed on the piezoelectric crystal plate to realize attenuation poles, respectively.

The electrical signals applied from the input terminals 1 and 2 in both FIGS. 7 and 8 are converted into mechanical vibrations by the piezoelectric action of the piezoelectric crystal plate P at the electrode 5, forming a standing wave, and forming a standing wave. It propagates through the electrode section and reaches the electrode 7.

The vibration wave that has reached the electrode 7 constitutes a standing wave and is converted into an electric signal again.

On the other hand, the electrical signals flowing out from the electrodes 5, 6, 7 are transmitted to the terminals 8, 9.
The voltage is applied to the capacitor C or inductor L between the two.

In that case, the structure is such that the voltage across the capacitor C or the inductor L is fed back between the input terminals 1 and 2.

When the operation of the system shown in FIG. 7 is represented by a lumped constant equivalent circuit, it becomes as shown in FIG. 9.

In FIG. 9, L1-C1, L2-C3, and L5-C5 represent the electrodes 5, 6, and 7 in FIG. 7, and K1 and K2 are surrounded by broken lines.
is the non-electrode portion between electrodes 5-6 and electrode 6-7 in FIG.
This is an imaginary gyrator that represents the electrodeless part between the two.

Further, C is a capacitor inserted in order to realize an attenuation pole in a higher frequency region side than the center frequency of the bandpass filter according to the present invention.

Next, if the operation of the system shown in FIG. 8 is expressed by a lumped constant equivalent circuit, it can be written as shown in FIG.

Also in Figure 10, L1-C1, L2-C3, L5-C
Reference numeral 5 represents electrodes 5, 6, and 7, and K1 and K2 surrounded by broken lines are imaginary gyrators representing a non-electrode portion between electrodes 5-6 and a non-electrode portion between electrodes 6-7.

-C6 is a negative capacitor inserted in order to realize an attenuation pole in a lower frequency region than the center frequency of the bandpass filter according to the present invention.

However, in the operating range of the narrowband filter, if the center frequency of the bandpass filter is f0, it can be expressed as L=-1/(ω20C6), so FIG. 10 can be expressed by the lumped constant equivalent circuit of FIG. 11.

The frequency of the attenuation pole expressed by the embodiment of FIG. 7 is calculated using the lumped constant equivalent circuit of FIG.
, C2, and C4, and is given by:

Further, the frequency of the attenuation pole realized by the embodiment of FIG. 8 is given by using the lumped constant equivalent circuit of FIG.

Therefore, the attenuation pole frequency of equation (1) is obtained from the lumped constant equivalent circuit shown in FIG. 9, and its characteristics are shown in FIG. 12, and the attenuation pole frequency of equation (2) is obtained from the lumped constant equivalent circuit of FIG. The characteristics are shown in FIG.

Although the embodiment described above is a case where the piezoelectric crystal plate has three pairs of electrodes, the above explanation can also be applied to a case where three or more pairs of electrodes are formed on the piezoelectric plate.

FIG. 14 shows an example in which three or more pairs of electrodes are formed on a piezoelectric crystal plate, and FIG. 15 shows the characteristics shown in FIG. 14.

In the device shown in FIG. 14, three or more electrodes are formed on one piezoelectric crystal plate P, a plurality of electrodes on one surface are connected as an electrode set by a connecting member, and one of the connecting members A capacitor C is connected between the common input/output terminal and the other one of the connecting members.
An inductance L is connected between the terminal and the common input/output terminal.

Opposing electrode groups are provided between the electrode group to which the capacitor C is connected and the electrode group to which the inductance is connected, and between the electrode group to which the inductance is connected and the output terminals 3 and 4. Both are connected to a common return line.

The device shown in FIG. 14 is a polarized multimode filter having one attenuation pole each on the high frequency side and the low frequency side with respect to the center frequency.

Here, a specific design example of the polarized multimode filter shown in FIG. 7 and having an attenuation pole on the high frequency side will be shown below.

During the design, the following conditions were used as design parameters.

f-1=8.06MHz f+1=8.06365MHz f+∞=8.063825MHz Impedance 750Ω In this case, the constant of the equivalent circuit in Fig. 9 is C3=8.9
354846×10-3PFC2=C4=36.637
266PF C=30.4850PF f2=8.063MHz, and by substituting these constants into the above equation (1), f
+∞=8.063825MHz is obtained.

The design of the mechanical system that satisfies the above conditions is as shown in Fig. 7, with an electrode shape of 3 mm width x 2.62 mm depth, and an inter-electrode distance of 1.
．． 232mm, crystal plate (piezoelectric plate) frequency 8.218M
Hz (AT cut plate).

Further, a specific design example of the polarized multimode filter having an attenuation pole on the low frequency side shown in FIG. 8 will be shown below.

During the design, the following conditions were used as design parameters.

f-1=8.06MHz f+1=8.06365MHz f-∞=8.059825MHz Impedance 750Ω In this case, the constants of the equivalent circuit shown in Figure 10 are: C3=8.9354846×10-3PFC2=C4=
36.637266PF C6=-118.6PF, and when the attenuation pole frequency is calculated by substituting the above constant into equation (2), it becomes f-∞=8.059825MHz.

Moreover, L6 in the equivalent circuit of FIG. 11 is 3.284
It is 0μH.

As explained above, the polarized multimode filter of the present invention has three or more pairs of electrodes formed on a single piezoelectric crystal plate, and at least one surface of the three adjacent pairs of electrodes has a common electric field. The filter is characterized in that it has a terminal, and a capacitor or inductor is connected between the common electric terminal and the common return wire of the filter to realize a stable attenuation pole on a finite frequency axis.

[Brief explanation of drawings]

1 to 6 are structure and characteristic diagrams of conventional polarized multimode filters, FIGS. 7 and 8 are structural examples of polarized multimode filters according to the present invention, and FIGS. 9 to 11. 12 and 13 are characteristic diagrams of the polarized multimode filter according to the present invention, and FIGS. 14 and 15 are equivalent circuits of the polarized multimode filter according to the present invention. FIG. 7 is a structural diagram and a characteristic diagram of another example of a mode filter. Explanation of symbols, 1...Signal input terminal, 2-4...
... Common return line of filter, 3 ... Signal output terminal, 5 ... Signal input electrode, 6 ... Energy confinement electrode, 7 ... signal output electrode,
8... Common electric terminal, 9... Common return terminal of filter.

Claims (1)

[Claims] 1. At least one set of three pairs of electrodes including an energy trapping electrode formed on one piezoelectric crystal plate,
A member that commonly connects one set of electrodes on one surface of the crystal plate, an input terminal and an output terminal that are connected to the electrodes on the other surface of the crystal plate, and a common input/output terminal with the member. An energy trapping type polarized multimode filter characterized by realizing an attenuation pole on a finite frequency axis by utilizing the feedback effect of an electric signal by using a capacitor or inductor connected between the filters.