JPS6230413A - Surface acoustic wave resonator device - Google Patents

Abstract

PURPOSE:To oscillate easily two prescribed frequency levels by providing the titled device with the characteristics of two vertical resonance modes having respective peaks in different frequency levels of which amplitude levels are almost equal to each other and having different phase characteristics. CONSTITUTION:Exciting electrodes 6a-6d and a grading reflection electrodes 7a, 7b are formed on a piezo-electric substrate 5. The electrodes 6a-6d have respective peaks in different frequency levels and are arranged on the substrate 5 with an interval corresponding to a transmission line length L forming the characteristics of two vertical resonance modes having almost equal peak amplitude levels and different phase characteristics. One electrodes 6a, 6b are used as input electrodes and the other electrodes 6c, 6d are used as output electrodes to generate a standing wave between the electrodes 7a, 7b. Consequently, the circuit can be provided with a filter function of a narrow band having sharp peaks in two prescribed frequency levels on passing frequency characteristics and prescribed two frequency levels can be oscillated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a surface acoustic wave resonator device used as an oscillation element in a local oscillation circuit of a CATV converter, for example.

[Technical Background of the Invention] In recent years, CATV (cable television), which was developed as a measure against difficult viewing, is becoming widely popular as a new media with regional characteristics and uniqueness.

In general, CATV is a method in which image and audio signals propagated by a wired cable are received on an empty channel of a TV device via a CATV converter.The CATV converter uses a mixer circuit in the tuner section to convert the input signal into a first signal. After the frequency signal of the local oscillator circuit is added, an intermediate frequency signal is selected, and then, in order to convert this intermediate frequency signal into a frequency signal of a predetermined frequency corresponding to an empty channel of the TV device, a frequency signal corresponding to that channel is selected. There is a need for a second local oscillator circuit that oscillates.

In such a CATV system, for example, in the United States, a system is adopted in which a channel signal shifted by 1 to 2 MHz from the normal TV channel frequency is propagated through the cable in order to prevent beat disturbances. Therefore, a system transmitting with a normal channel signal and
It is also necessary to change the frequency of the second local oscillation circuit of the 0ATV converter with the system transmitting this shifted channel signal.

On the other hand, in recent years, with the development of surface acoustic wave oscillators capable of direct high-frequency oscillation, surface acoustic wave resonator devices are being adopted as oscillation elements in excavation circuits in place of crystal oscillators that require a multiplier circuit.

FIG. 5 is an enlarged top view showing the surface acoustic wave resonator device used in the second local oscillation circuit described above.

As shown in the figure, this surface acoustic wave resonator device has excitation electrodes 2a to 2d formed by combining two pairs of comb-shaped electrodes arranged on a piezoelectric substrate 1 at intervals of a predetermined propagation path distance.
and a pair of grating reflective electrodes 3a and 3b arranged on the piezoelectric substrate 1 with excitation electrodes 2a to 2d in between.

Then, by using one of the excitation electrodes 2a and 2b as an input electrode and the other excitation electrode 2C12d as an output electrode, and generating a standing wave between the grating reflection electrodes 3a and 3b, the passing frequency characteristics can be improved, for example as shown in FIG. As shown in
It has the function of a narrow band filter with a sharp peak at a certain predetermined frequency.

When this surface acoustic wave resonator device is used as a local oscillation circuit, as shown in FIG. This is done by oscillating it.

Conventionally, the design of such a surface acoustic wave resonator device has been to make the grating reflective electrodes 3a and 3b have high reflectance of the reflection frequency characteristic in a predetermined frequency band, and to generate a surface acoustic wave of a predetermined frequency in that frequency band. to form a resonant mode of
A high Q resonance peak is generated, but due to the difference in the distribution of standing waves in the surface acoustic wave propagation direction, there are resonance modes on both sides of the surface acoustic wave resonance mode of the predetermined frequency. Occur. These resonance modes are collectively called longitudinal resonance modes, among which the resonance mode with a high Q resonance peak is called the main longitudinal resonance mode, and the resonance modes on both sides thereof are called sub-longitudinal resonance modes.

Furthermore, the sub-longitudinal resonance mode is generally reduced by narrowing the reflection frequency band of the grating reflection electrodes 3a and 3b, as shown in FIG. There was a level difference between the two.

[Problems with the background art] However, in the local excavation circuit using the above-mentioned surface acoustic wave resonator device, it is common to oscillate near the main longitudinal resonance mode, and it is difficult to capture images when the resonance point deviates from this point. and the oscillation stops, or even if it oscillates,
Stability may deteriorate.

Also, if the oscillation point shifts from the resonance point of the main longitudinal resonance mode to the sub-longitudinal resonance mode, oscillation can be caused depending on the gain of the amplifier 4, but in that case, the oscillation output level will be lower than that of the oscillation in the main resonance mode. may become very low, or it may become difficult to oscillate.

Therefore, in the conventional surface acoustic wave resonator device, a specific one
Since oscillation can only occur at one frequency, when the frequency signal of a local oscillation circuit such as the above-mentioned CATV converter requires two frequencies, a surface acoustic wave resonator device corresponding to each frequency is used. I had to.

[Objective of the Invention] The present invention has been made in response to the above-mentioned circumstances, and is designed to provide two longitudinal resonance modes having peaks at different frequencies, the amplitude levels of these peaks being approximately the same, and having different phase characteristics. It is an object of the present invention to provide a surface acoustic wave resonator device that can easily oscillate at two predetermined frequencies by imparting characteristics.

[Summary of the Invention] That is, the surface acoustic wave resonator device of the present invention has a substrate for propagating surface acoustic waves, peaks at different frequencies on this substrate, and an amplitude level difference of the peaks in a 50Ω system. an excitation electrode formed by combining a pair of comb-shaped electrodes arranged at an interval of a propagation path distance that provides characteristics of two longitudinal resonance modes having different phase characteristics and within 5 dB, and the substrate. By comprising a pair of grating reflective electrodes disposed above with the excitation electrode sandwiched therebetween, it is possible to easily oscillate at two predetermined frequencies.

[Embodiments of the Invention] Hereinafter, details of embodiments of the present invention will be described based on the drawings.

Fig. 1 is an enlarged top view showing a surface acoustic wave resonator device according to an embodiment of the present invention, Fig. 2 is a chart showing the relationship between frequency and amplitude level in a 50Ω system of this device, and Fig. 3 is a vertical view. A chart showing the difference in amplitude levels between the main resonance mode and the vertical sub-resonance mode and the relationship between those frequency differences and the propagation path distance. Figure 4 shows the elastic surface when a surface acoustic wave resonator device is used in an oscillation circuit. 2 is a chart showing the relationship between insertion loss and oscillation output level of a wave resonator device.

As shown in FIG. 1, this surface acoustic wave resonator device has a piezoelectric substrate 5 and peaks at different frequencies on the piezoelectric substrate 5, and the amplitude levels of these peaks are approximately the same and have different phase characteristics. Excitation electrodes 6a to 6d formed by combining a pair of comb-shaped electrodes arranged at an interval equal to the propagation path distance that is the characteristic of two longitudinal resonance modes, and excitation electrodes 6a to 6d on the piezoelectric substrate 5. It consists of a pair of grating reflective electrodes 7a and 7b arranged with 6d in between.

Then, one of the excitation electrodes 6a and 6b is used as an input electrode, the other excitation electrode 6C16d is used as an output electrode, and a standing wave is generated between the grating reflection electrodes 7a and 7b. It has the function of a narrow band filter with a sharp peak in frequency.

When this surface acoustic wave resonator device is used in an oscillation circuit, it consists of an amplifier and a positive feedback circuit using a matching circuit such as an LC. This is performed by oscillating at a predetermined frequency near the peak frequency of the surface acoustic wave resonator device.

For example, a 600 MHz band surface acoustic wave resonator device is constructed by forming an excitation electrode and a grating reflecting electrode on a piezoelectric substrate using an 8β material, and changing the propagation path distance around 6λ (λ = surface wave wavelength). At this time, the amplitude level difference between the longitudinal main resonance mode and the longitudinal sub-resonance mode and their frequency difference show changes as shown in FIG.

In the figure, the area where the level difference between the peaks of two longitudinal resonance modes is within 5 dB and the amplitude level of the remaining longitudinal resonance modes is 10 dB or more higher than the amplitude level of the remaining longitudinal resonance modes is indicated by A in the figure.
is within the range of Within this range, the frequency difference between these resonance modes can be set to 1 to 3 M)Iz.

Therefore, in order to set the frequency difference between the peaks of the two longitudinal resonance modes of this surface acoustic wave resonator device to, for example, 2M1h, the propagation path distance should be set to 6.46λ, and the level difference should be set to about 1.3 dB. be able to.

Also, for example, the difference between the insertion loss of a surface acoustic wave resonator device and the oscillation output level when the gain of the amplifier is about 15 dB in a resonant circuit in the 600 MHz band is based on the insertion loss as shown in Figure 4. If it becomes larger than about 5 dB from the value,
The oscillation output drops rapidly and oscillation stops at about 10 dB.

Therefore, as long as the level difference between the two longitudinal resonance modes is within about 5 dB, there is no practical problem.
The z-band surface acoustic wave resonator device can be fully used in two types of frequency oscillation circuits.

Although the propagation path distance in the above-mentioned embodiment was set to 6.46λ, the present invention is not limited to this, and the optimum value can be determined depending on the number of excitation electrodes, the film thickness at A° C., the material of the substrate, etc. The values may be set accordingly.

[Effects of the Invention] As explained above, according to the surface acoustic wave resonator device of the present invention, the surface acoustic wave resonator device has peaks at different frequencies, the amplitude level difference of these peaks in a 50Ω system is within 5 dB, and the surface acoustic wave resonator device has different phases. By arranging the excitation electrodes at propagation path distances that provide the characteristics of two longitudinal resonance modes, oscillation at two different frequencies can be easily performed.

[Brief explanation of drawings]

FIG. 1 is an enlarged top view showing a surface acoustic wave resonator device according to an embodiment of the present invention, FIG. 2 is a diagram showing the relationship between frequency and amplitude level of this device, and FIG. 3 is a diagram showing the longitudinal main resonance. A chart showing the difference in amplitude level between the mode and the longitudinal subresonant mode and the relationship between the frequency difference and the propagation path distance. Figure 4 shows the surface acoustic wave resonance when a surface acoustic wave resonator device is used in the oscillation circuit. 5 to 7 are graphs showing the relationship between the insertion loss of the child device and the oscillation output level, and are diagrams for explaining conventional examples. 5...Piezoelectric substrate 6a to 6d...Excitation electrode

Claims (5)

[Claims] (1) A substrate that propagates surface acoustic waves, and two longitudinal resonance modes on this substrate that have peaks at different frequencies, have an amplitude level difference of within 5 dB in a 50Ω system, and have different phase characteristics. an excitation electrode formed by combining a pair of comb-shaped electrodes arranged at an interval of a propagation path distance having a characteristic of A surface acoustic wave resonator device consisting of. (2) The difference in phase characteristics of the two longitudinal resonance modes is approximately 1
The surface acoustic wave resonator device according to claim 1, wherein the angle is 80°. (3) The difference between the peak frequencies of the two longitudinal resonance modes is
The surface acoustic wave resonator device according to claim 1 or 2, wherein the frequency is within 3 MHz. (4) The surface acoustic wave according to any one of claims 1 to 3, wherein the amplitude levels of the peaks of the two longitudinal resonance modes are 10 dB or more higher than the amplitude levels of other peaks. Resonator device. (5) The surface acoustic wave resonator device according to any one of claims 1 to 4, which is a surface acoustic wave resonator device for a local oscillation circuit of a CATV converter.