JP2935232B2 - Piezoelectric resonator for FM discriminator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezo-resonator for use in a quad launcher 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 quad launcher type FM discriminator. One of the FM intermediate frequency signals IF supplied via a not-shown limiting amplifier or the like is input to the multiplier 2 with the original phase, and the other is supplied via the phase shifter 4 at 90 ° ± θ °.
(Θ is 0 ≦ θ ≦ 90 in FM modulation) The phase is shifted and input to the multiplier 2. The multiplier 2 multiplies the original FM intermediate frequency signal IF by the phase-shifted signal and outputs a pulse signal having a width proportional to the phase difference between the two. This is averaged through a low-pass filter 10 and amplified by an amplifier 12 to obtain a demodulated signal DS.

The phase shifter 4 basically includes a capacitor 6
And a two-terminal type piezoelectric resonator 8 in an L-shape as shown in the figure. A resistor 9 is connected in parallel to the piezoelectric resonator 8 as necessary. The capacitor 6 functions to shift the phase of the input signal by 90 °, and the piezoelectric resonator 8 functions to change the frequency change between the resonance frequency and the anti-resonance frequency into the phase change. However, in an actual FM discriminator, the capacitor 6 is 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 thereto.

A conventional piezoelectric resonator 8 is as follows.
As shown in FIG. 3, a pair of vibration electrodes 82 and 83 facing each other across the piezoelectric substrate 81 is provided.
83 is connected to terminal electrodes 84 and 85, respectively.
The solid line in the figure indicates the front-side electrode, and the broken line indicates the back-side electrode. The vibrating electrode 83 on the back side is drawn larger than the vibrating electrode 82 on the front side for the sake of illustration, but they 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 (capacitance) of the capacitor 6 in the IC. Here, the state of matching is as follows:
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, when the capacitance C ₁ of the capacitor 6 is too large for the capacity C ₂ of the piezoelectric resonator 8,
The amplitude of the signal sent to the multiplier 2 becomes too large, and a band necessary for detection cannot be obtained.

As a countermeasure, 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, in addition to the fundamental vibration, a higher-order excitation occurs, causing a problem that the distortion factor is increased and the characteristics are deteriorated.

SUMMARY OF THE INVENTION Accordingly, it is a main object of the present invention to provide a piezoelectric resonator for an FM discriminator capable of realizing a large capacitance without deteriorating characteristics.

[0008]

In order to achieve the above object, a piezoelectric resonator for an FM discriminator according to the present invention has a plurality of pairs of vibrating electrodes opposed to each other with a piezoelectric substrate interposed therebetween. mutually almost the same said plurality
Make the resonance characteristics of the pair of vibrating electrodes almost equal to each other
And the vibration electrodes on the same surface side of the piezoelectric substrate are electrically connected in parallel to each other.

[0009]

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

[0010]

FIG. 1 is a plan view showing a piezoelectric resonator for an FM discriminator according to an embodiment of the present invention. This piezoelectric resonator 8a has two pairs of vibrating electrodes 82a, 83a and 82b, 83b opposed to each other with a piezoelectric substrate 81 interposed therebetween. Also, the vibration electrode 82 on the front side of the piezoelectric substrate 81
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 vibration electrodes 83a and 83b on the back side of the piezoelectric
They are connected in parallel to each other by a lead electrode 87 having a shape and connected to a common terminal electrode 85.

If the required capacitance is twice the normal value, two pairs of vibrating electrodes may be connected in parallel as in this example. If an n-fold capacitance value is required, n pairs of vibrating electrodes may be connected in parallel.

In any case, by connecting a plurality of pairs of vibrating electrodes in parallel, the area of each vibrating electrode does not increase until high-order excitation remarkably occurs, that is, without causing deterioration of characteristics. Capacitance can be realized.
As a result, a large internal capacitance (the capacitor 6 shown in FIG.
A piezoelectric resonator that is capacitively matched can also be realized for an FM discriminator having an IC configuration having a capacitance of (IC).

[0013]

As described above, according to the present invention, a plurality of pairs
Another vibration the dynamic electrode connected in parallel, and the area of each vibrating electrodes
And the resonance characteristics at multiple pairs of vibrating electrodes
Since they are substantially equal to each other , a large capacitance can be realized without increasing the area of each vibrating electrode until high-order excitation is significantly generated, that is, without deteriorating characteristics. As a result, it is possible to realize a piezoelectric resonator that is capacitively matched even for an FM discriminator having an IC configuration having a large internal capacitance.

[Brief description of the drawings]

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

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

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

[Explanation of symbols]

 Reference Signs List 2 multiplier 4 phase shifter 6 capacitor 8a piezoelectric resonator 81 piezoelectric substrate 82a, 82b, 83a, 83b vibrating electrode

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-107215 (JP, A) JP-A-62-261210 (JP, A) JP-A-63-2412 (JP, A)

Claims (1)

(57) [Claims] 1. A two-terminal type piezoelectric resonator used in a quad launcher type FM discriminator, comprising a plurality of pairs of vibrating electrodes opposed to each other with a piezoelectric substrate interposed therebetween, and an area of each vibrating electrode. The plurality of pairs of vibrations
A piezoelectric resonator for an FM discriminator , wherein resonance characteristics at electrode portions are substantially equal to each other , and vibration electrodes on the same surface side of the piezoelectric substrate are electrically connected in parallel to each other.