JPH05122002A - Leaky saw resonator - Google Patents

Abstract

PURPOSE:To obtain a leaky SAW resonator for voltage control oscillator which does not generate ripple in a frequency variable area by arranging an inter- digital transducer electrode, inclining it by only a specific angle for the X-axis of a 64-degree cut LiNbO3 substrate. CONSTITUTION:An inter-digital transducer electrode 2 for exciting a leaky SAW is arranged on a 64-degree Y cut LiNbO3 substrate 1 whose coupling factor is large by inclining the electrode 2 by 3 deg. to 8 deg. for a X-axis which is a leaky SAW propagation direction. By this, a spurious on a lower band side than a resonance point almost extinguishes. This reason is considered that a resonator Q lowers to some degrees by slightly being shifted by the propagation direction of the leaky SAW and the propagation direction of the energy. But as the lowering of the Q is no more than about 10%, the value is endurable one practically when this resonator is used for a voltage control oscillator. In future, the resonator is applicable to ones which are used in wide- band multi-channel communication equipments of which the necessity is increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a SAW resonator, and more particularly to a leaky SAW resonator having a small capacitance ratio used in a voltage controlled oscillator (VCO) having a wide frequency variable width.

[0002]

2. Description of the Related Art Conventionally, V in the high frequency range of VHF
A SAW resonator using a piezoelectric material having a wide frequency variable width and a large coupling coefficient is required as a CO oscillator. The inventors of the present application have proposed a 64-degree Y-cut X-propagation LiNbO ₃ substrate which has a coupling coefficient of 11% and was discovered by Shibayama et al. Focusing on the SAW resonator used, various parameters of the electrode necessary for the SAW resonator for VCO were found experimentally.

However, the above-described prototype made by the inventors of the present application, for example, is in the frequency variable region in the case of the 86 MHz resonator, despite the fact that the value of the electrode parameter is changed minutely. There is a defect that the spurious generated at every 1 MHz cannot be removed, and when the voltage applied to the VCO varicap is changed, the frequency jumps at the position of the spurious.

[0004]

SUMMARY OF THE INVENTION The present invention is a conventional SCO for VCO as described above.
It was designed to eliminate defects in the AW resonator,
Leaky S for VCO with no ripple in the variable frequency range
It is intended to provide an AW resonator.

[0005]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention adopts a configuration in which an IDT is arranged at a predetermined angle with respect to the X axis of a 64 ° Y-cut LiNbO ₃ substrate.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on the embodiments shown in the drawings. Prior to the description of the embodiments, a leaky SAW resonator, which has been studied by the inventors of the present invention in order to facilitate understanding of the present invention, will be briefly described. Figure 2
(A) is a plan view showing a configuration of a leaky SAW resonator, in which an IDT electrode 2 having an appropriate logarithm is provided along a surface X axis of a 64 ° Y-cut X-propagation LiNbO ₃ substrate 1. Since the leaky SAW resonator has an extremely large coupling coefficient of the substrate, it generally does not require a reflector and has a logarithm of the number 1
A characteristic is that a sufficient Q can be obtained as a resonator used for a VCO even if the number of pairs is relatively small as 0 pairs.

However, the resonance characteristics of the resonator having the electrode arrangement as shown in FIG. 7A are lower than the resonance point f _s which is the frequency variable range of the VCO as shown in FIG. At this time, many spurious products due to the reflection of leaky SAW from the end face of the substrate 1 were generated, and these spurious products could not be sufficiently suppressed even if the end face of the substrate 1 was obliquely cut or the IDT electrode 2 was weighted. As described above. In order to solve this problem, the leaky S according to the present invention
As shown in FIG. 1A, the AW resonator has the IDT electrode 2 inclined by a predetermined angle α with respect to the X axis of the substrate 1. In the resonance characteristics is referred to as 5.2 ° to the predetermined inclination angle α is in spurious low frequency side of the resonance point f _a is as shown in FIG. (B) it disappeared almost completely. It is considered that the reason for this is that the Q of the resonator was somewhat lowered due to a slight deviation between the propagation direction of the leaky SAW and the direction of the energy transfer plate, but the Q reduction was 10%.
Since it is only inside and outside, it is a sufficient value for using this resonator in a VCO.

Generally, in an oscillator circuit, C / N
Needs approximately 75 dB or more, but in order to do so, the group delay time deviation needs to be 10 nsec or less, and it is considered that frequency jump does not occur in such a state. Therefore, this is the leaky SAW resonance of the present invention. As a result of examining the non-defective product rate by experiments, the tilt ratio α of the IDT with respect to the substrate X-axis was variously changed as the specifications of the child.
The results shown in are obtained. From this, the value of α is 3 ° to 8
It turned out that it can withstand practical use if it is °.

[0009]

Since the present invention is configured as described above, it is possible to reduce the spurious in the frequency variable region of a leaky SAW resonator having an extremely wide frequency range without requiring a special manufacturing process. Therefore, it has a remarkable effect when applied to a VCO used for a communication device of a wideband other channel, which is particularly needed in the future.

[0010]

[Brief description of drawings]

FIG. 1A and FIG. 1B are diagrams showing a configuration of an embodiment of a leaky SAW resonator according to the present invention and a resonance characteristic thereof, respectively.

2 (a) and 2 (b) are related leaky S of the related art, respectively.
The figure which shows the structure of one Example of an AW resonator, and its resonance characteristic.

FIG. 3 shows the I in the leaky SAW resonator according to the present invention.
The figure which shows the relationship between the inclination angle (alpha) with respect to the board | substrate X-axis, and a non-defective rate.

[Explanation of symbols] 1 ... 64 degree Y-cut LiNbO ₃ substrate 2 ... IDT electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshitaka Izu 2-1-1 Otani, Samukawa-cho, Takaza-gun, Kanagawa Toyo Communication Equipment Co., Ltd.

Claims (3)

[Claims] 1. A 64-degree Y-cut LiNb having a large coupling coefficient.
An interdigital transducer (IDT) electrode for exciting a leaky SAW on the O ₃ substrate is leaky SA.
A leaky SAW resonator, wherein the leaky SAW resonator is arranged so as to be inclined by a predetermined angle α with respect to an X axis which is a W propagation direction. 2. The leaky SAW resonator according to claim 1, wherein the tilt angle α of the IDT electrode with respect to the X axis is 3 ° to 8 °. 3. The leaky SAW resonator according to claim 1, wherein the IDT electrode is given a required weighting.