JPS58131810A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To reduce the number of descrete components, by providing a capacitor forming electrode on a board and forming capacitors in using a capacitance between the electrode and a metallic base on which the board is mounted. CONSTITUTION:A surface acoustic wave exciting inter-digital electrode 12 is provided on a piezoelectric board 11 on which a surface acoustic wave is propagated. Grading reflectors 13, 14 comprising by arranging strips having a wavelength being 1/4 of that of the surface acoustic wave are provided to both sides of the electrode 12 to form a surface acoustic wave resonator. The capacitor forming electrodes 16, 17 formed incorporatedly with the electrode 12 are provided on the board 11. The electrodes 16, 17 are connected to heady leads 20, 21 fixed to the metallic base 15 via insulators 18, 19 like glass with aluminum wires 22, 23. Capacitors C1, C2 are formed between the heady leads 20, 21 and an earth lead 24.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a surface acoustic wave device suitable for use in an excavator.

[Technical background of the invention and its problems]

As shown in FIG. 1, a surface acoustic wave resonator generally consists of a piezoelectric substrate 1 for propagating surface acoustic waves, interdigital electrodes 2 for excitation of surface acoustic waves, and a large number of strips arranged at face angles in the direction of surface acoustic wave propagation. It is constructed by forming grating reflectors 3 and 4 in which gratings are arranged periodically. Such an elastic optical surface resonator is exactly the same as a crystal oscillator when expressed as a frost-like equivalent circuit, and can be expressed as shown in FIGS. 2(a) and 2(b). Therefore, an oscillator using a surface acoustic wave resonator can also be configured in the same way as a crystal oscillator.

FIG. 3 shows the most commonly used Colpitts oscillator. This can be expressed as shown in FIG. 4 if the resonator 5 and the circuit 6 other than the resonator are considered separately.

The impedance zL (=-RL + jXL) on the side of the circuit 6 can be expressed as in equation (1) if the transistor pace expansion is 9 and the resistor and collector capacitance are omitted.

When oscillation is in a steady state, the following equation holds between the impedance of the resonator 5 and the impedance of the circuit 6.
8=l-RLI (RL is a positive number)...
・(3) In the case of a Colpitts type oscillator, the resonator 5 resonates -
Since it acts as an inductive reactance, that is, an inductance L at a frequency between antiresonance, in this case, XL on the circuit 6 side has a capacitance as shown in equation (1), which is important in the design of the oscillator. In this case, the oscillation frequency is approximately the series resonance frequency of L and CL, as shown in equation (2).

However, conventionally, in order to obtain the necessary load capacity CL,
There was a problem in that discrete capacitors CB and Cc had to be added.

[Purpose of the invention]

An object of the present invention is to provide a surface acoustic wave device that can be realized without using a capacitor as a discrete cable when configuring a Colpitts oscillator, for example.

[Summary of the invention]

In the present invention, a surface acoustic wave resonator is connected to a surface acoustic wave excitation interdigital electrode on a substrate that propagates hexagonal acoustic waves. .

-;゛→ A forming electrode is provided, and a capacitor is formed by utilizing the capacitance between this electrode and the metal base on which the substrate is placed and fixed.

〔Effect of the invention〕

According to the present invention, the capacitor formed as described above can be used as a load capacitor or the like in a Colpitts oscillator, so the number of discrete elements is reduced. In this case, since the electrodes for forming the capacitor can be provided at the same time during the manufacturing process of the surface acoustic wave resonator,
The manufacturing cost of the entire device can be reduced.

[Embodiments of the invention]

FIG. 5 shows a surface acoustic wave device according to an embodiment of the present invention, which is an example applied to a surface acoustic wave resonator used in a carrier wave oscillator for a domestic second channel in an RF converter for a VTR. In the figure, reference numeral 11 denotes a piezoelectric substrate for propagating surface acoustic waves, for example a 1iTa05 substrate, on which an interdigital electrode 12 for excitation of surface acoustic waves made of a thin aluminum film of 1.3 μm in thickness, for example, is provided. By providing grating reflectors 13 and 14, each consisting of 200 strips with a line width of 90 μm, which is 1/4 of the surface acoustic wave wavelength, arranged at 1/2 wavelength intervals on both sides, a so-called one-terminal pair is provided. A type of surface acoustic wave resonator is constructed.

The substrate 11 is mounted and fixed on a metal base 15 which also serves as a package.

Further, on the substrate 11, a capacitor forming electrode 1 is formed integrally with the excitation interdigital electrode 12.
6.17 is provided.

These electrodes 16, 17 are connected by aluminum wires 22, 23 to henody leads 20, 21 fixed to the metal base 15 via an insulator 18, 19 such as glass. 24 is a ground lead that is in direct contact with the metal base 15.0 The electrical equivalent circuit of the surface acoustic wave device shown in FIG. 5 is as shown in FIG.
4, a capacitor C1°6-C2 is formed between the two. Note that 25 represents a surface acoustic wave resonator.

FIG. 7 shows an example in which a Colpitts oscillator is constructed using the surface acoustic wave device 25' of FIG. 5, and includes a DC bias circuit. Disc IJ-to capacitors CB and Cc in Figure 3
Capacitor CI+C2 to surface acoustic wave resonator 25 instead of O
is added, so it becomes a common emitter type Colpitts oscillator. In this case, by changing the value of CI+c2, that is, the size and shape of the electrode 16.17, according to the values of the emitter capacitance and collector capacitance of the transistor Q,
Of course, it is possible to obtain optimal oscillation conditions.

FIG. 8 shows another embodiment of the present invention, in which an interdigital electrode with a period length different from that of the interdigital electrode 12 for excitation of surface acoustic waves is used as an electrode for forming a capacitor. Electrodes 26, 27 are provided and one end of each is connected to the metal substrate 15 by aluminum wires 28, 29 to form a capacitor CI as in the embodiment of FIG.

C2 is added. In this case as well, the oscillator can be configured as shown in FIG.

It should be noted that the present invention can be implemented with various other modifications. For example, a so-called multi-pair resonator configured without a grating reflector as a surface acoustic wave resonator and consisting only of interdigital electrodes for surface acoustic wave excitation is configured. However, you can add a capacitor in the same way.

[Brief explanation of the drawing]

Figure 1 is a perspective view of a conventional surface acoustic wave resonator, Figure 2 is its electrical equivalent circuit diagram, Figure 3 is a basic configuration diagram of a Colpitts oscillator, and Figure 4 is its two-terminal equivalent circuit. 5 is a perspective view of a surface acoustic wave device according to an embodiment of the present invention, FIG. 6 is an electrical equivalent circuit diagram thereof, and FIG. 7 is a Colpitts oscillator using the entire surface acoustic wave device of the present invention. FIG. 8 is a perspective view of a surface acoustic wave device according to another embodiment of the present invention. 1 No... Piezoelectric substrate, 12... Surface acoustic wave resonator interdigital electrode, 13.14... Grating reflector, 15... Metal base, 16.17... Electrode for capacitor formation, 2o , 21... Hella Bereed, 2
4... Earth lead, 25... Surface acoustic wave resonator,
25...Surface acoustic wave device, 26.27...Interpisotal electrode for capacitor formation, C1, C2...Capacitor as load capacitance. Applicant's agent Patent attorney Takehiko Suzue 9-4S

Claims (3)

[Claims] (1) The substrate of a surface acoustic wave resonator consists of a substrate that propagates surface acoustic waves, and an intermediate isotal electrode for a surface acoustic wave device that is provided on this substrate and converts an electric signal into a surface acoustic wave. In a surface acoustic wave device mounted and fixed on a metal base, a capacitor forming electrode connected to the interpinotal electrode is provided on the base;
A surface acoustic wave device characterized in that a capacitor connected to the resonator is formed by a capacitance between the L pole and the metal base. (2) The surface acoustic wave device according to claim 1, wherein the elastic surface resonator is a Colpitts oscillator, and the capacitor is used as a load capacitor in the oscillator. (3) A patent characterized in that the capacitor forming electrode is formed by an interdigital electrode having a period length different from that of the surface acoustic wave excitation interdigital electrode, and one end of this interdigital electrode is connected to a metal base. A surface acoustic wave device according to claim 1 or 2.