JPH05160666A - Piezoelectric resonator for fm discriminator - Google Patents

Abstract

PURPOSE:To provide a piezoelectric resonator for FM discriminator which realizes a large electrostatic capacity without degrading the characteristic. CONSTITUTION:A piezoelectric resonator 8a is provided with two pairs of oscillating electrodes 82a, 83a, 82b, and 83b which face each other respectively with a piezoelectric substrate 81 between them. Oscillating electrodes 82a and 82b on the front face of the piezoelectric substrate 81 are connected in parallel by a Y-shaped leading-out electrode 86 and are connected to a common terminal electrode 84. Oscillating electrodes 83a and 83b on the rear face of the piezoelectric substrate 81 are connected in parallel by a Y-shaped leading-out electrode 87 and are connected to a common terminal electrode 85.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric resonator used in a quadrature type FM discriminator for demodulating an FM signal of, for example, a television or an FM radio.

[0002]

2. Description of the Related Art FIG. 2 is a circuit diagram showing an example of a quadrature type FM discriminator. The FM intermediate frequency signal IF given through a not-shown limiting amplifier or the like is input to the multiplier 2 in one phase as it is, and the other is 90 ° ± θ ° via the phase shifter 4.
(Θ is an FM modulation amount 0 ≦ θ ≦ 90) The phase is shifted and input to the multiplier 2. The multiplier 2 multiplies the original FM intermediate frequency signal IF and the phase-shifted signal and outputs a pulse signal having a width proportional to the phase difference between the two. The demodulated signal DS is obtained by averaging this through the low-pass filter 10 and amplifying it by the amplifier 12.

This phase shifter 4 basically comprises a capacitor 6
And a two-terminal type piezoelectric resonator 8 are connected in an L shape as shown in the figure. A resistor 9 is connected in parallel to the piezoelectric resonator 8 if necessary. The capacitor 6 has a function of shifting the phase of the input signal by 90 °, and the piezoelectric resonator 8 has a function of changing a frequency change amount to a phase change amount between the resonance frequency and the anti-resonance frequency. However, in the actual FM discriminator, the capacitor 6, the multiplier 2, the low-pass filter 1
0, an amplifier 12 and the like are incorporated in one IC, and the piezoelectric resonator 8 is externally attached to this.

The conventional piezoelectric resonator 8 as described above is
As shown in FIG. 3, it has a pair of vibrating electrodes 82 and 83 facing each other with the piezoelectric substrate 81 interposed therebetween.
83 is connected to the terminal electrodes 84 and 85, respectively.
In the figure, the solid line shows the front side electrode, and the broken line shows the back side electrode. The backside vibrating electrode 83 is drawn larger than the frontside vibrating electrode 82 for the sake of illustration, but both are actually the same size (the same applies to FIG. 1 described later).

[0005]

One of the characteristics required of the piezoelectric resonator 8 is that it has a capacitance value that matches the capacitance (electrostatic capacitance) of the capacitor 6 in the IC. The matching state here means
The amplitude of the signal sent to the multiplier 2 via the piezoelectric resonator 8 is an appropriate value (generally about 150 to 400 mV)
Say that. However, if the capacitance C _{1 of the} capacitor 6 is too large with respect to the capacitance C _{2 of the} piezoelectric resonator 8,
The amplitude of the signal sent to the multiplier 2 becomes too large, and the band required for detection cannot be obtained.

As a countermeasure against this, the capacity of the piezoelectric resonator 8 may be increased, and for that purpose, the area of the vibrating electrodes 82 and 83 shown in FIG. 3 is increased. However,
As the area of the vibrating electrodes 82 and 83 is increased, higher-order excitation is generated in addition to the fundamental vibration, and the distortion rate is increased, which causes a problem that the characteristics are deteriorated.

Therefore, the main object of the present invention is to provide a piezoelectric resonator for an FM discriminator capable of realizing a large capacitance without deteriorating the characteristics.

[0008]

In order to achieve the above object, a piezoelectric resonator for an FM discriminator of the present invention has a plurality of pairs of vibrating electrodes facing each other with a piezoelectric substrate interposed therebetween, and the piezoelectric substrate has the same piezoelectric electrode. The vibrating electrodes on the surface side are electrically connected in parallel to each other.

[0009]

According to the above structure, since the plurality of pairs of vibrating electrodes on the same surface side are electrically connected in parallel to each other, the area of each vibrating electrode is increased until high-order excitation remarkably occurs. A large capacitance can be realized without doing so.

[0010]

1 is a plan view showing a piezoelectric resonator for an FM discriminator according to an embodiment of the present invention. The piezoelectric resonator 8a has two pairs of vibrating electrodes 82a, 83a and 82b, 83b facing each other with the piezoelectric substrate 81 interposed therebetween. In addition, the vibrating electrode 82 on the front surface side of the piezoelectric substrate 81
The a and 82b are connected in parallel to each other by a Y-shaped extraction electrode 86 and connected to a common terminal electrode 84. Similarly, the vibrating electrodes 83a and 83b on the back surface side of the piezoelectric substrate 81 are set to Y
Shaped lead-out electrodes 87 are connected in parallel to each other and connected to a common terminal electrode 85.

When the required electrostatic capacitance is twice as large as usual, two pairs of vibrating electrodes may be connected in parallel as in this example. Further, when a capacitance value of n times is required, n pairs of vibrating electrodes may be connected in parallel. If n is not an integer,
It is possible to deal with this by connecting vibrating electrodes of different sizes in parallel.

In any case, by connecting a plurality of pairs of vibrating electrodes in parallel, the area of each vibrating electrode is not increased until high-order excitation is significantly generated, that is, the characteristics are not deteriorated. Capacitance can be realized.
As a result, a large internal capacitance (capacitor 6 shown in FIG.
It is possible to realize a piezo-resonator that is electrostatically matched even for an FM discriminator having an IC configuration having a capacitance of 1).

[0013]

As described above, according to the present invention, since a plurality of pairs of vibrating electrodes are connected in parallel, the area of each vibrating electrode is not increased until high-order excitation is remarkably generated.
That is, a large capacitance can be realized without deteriorating the characteristics. As a result, I with a large internal capacitance
It is possible to realize a piezo-resonator that is electrostatically matched even for an FM discriminator having a C configuration.

[Brief description of drawings]

FIG. 1 is a plan view showing a piezoelectric resonator for an FM discriminator according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing an example of a quadrature type FM discriminator.

FIG. 3 is a plan view showing an example of a conventional piezoelectric resonator for FM discriminator.

[Explanation of symbols]

 2 Multiplier 4 Phase shifter 6 Capacitor 8a Piezoelectric resonator 81 Piezoelectric substrate 82a, 82b, 83a, 83b Vibration electrode

Claims (1)

[Claims] 1. A two-terminal type piezoelectric resonator used in a quadrature type FM discriminator, which has a plurality of pairs of vibrating electrodes facing each other with a piezoelectric substrate interposed therebetween, and has the same piezoelectric substrate. A piezoelectric resonator for an FM discriminator, characterized in that vibrating electrodes on the surface side are electrically connected in parallel to each other.