JPS5840911A - Surface acoustic wave filter device - Google Patents

Abstract

PURPOSE:To prevent the occurrence of an undesired reflected wave for a surface acoustic wave filter element for multichannel, by short-circuiting both terminals of an unused input transducer. CONSTITUTION:A surface acoustic wave filter device is provided with two input transducers 321 and 322 which are formed interdigitally on a piezoelectric substrate 31 with different frequency bands, an output transducer 33 which is formed interdigitally at a place close to the transducers 321 and 322, and a sound absorber layer 34 provided near the substrate 31. A common terminal 32a of both transducers 321 and 322 is grounded and at the same time connected to the 1st changeover switch 36. Other terminals 32b and 32c are connected to the contacts 36b and 36c of the switch 36, and these contacts serve as the contact of the 2nd changeover switch 37 of an electric signal generator 35. As a result, a reflected wave 38c sent from the transducer 322 is extremely reduced regardless of the presence of a reflected wave 38b given from the transducer 33.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface acoustic wave filter device, and particularly relates to a surface acoustic wave filter device in which input and output transducers are provided on one piezoelectric plate, and one of the input and output transducers is separated into a plurality of pieces. The present invention relates to a surface acoustic wave filter device in which a so-called multi-channel surface acoustic wave filter element can be effectively switched by a switch circuit.

The surface acoustic wave filter element usually has L1 as shown in FIG.
A piezoelectric substrate (1) made of 'l''aO, LiNb0., crystal, ceramics, etc., and a human quadrature transducer (2) formed in an interdigital shape for converting electrical signals into surface acoustic waves. Input quadrant transducer (
2) is formed into an interdigital type that converts surface acoustic waves into electrical signals, and is arranged at a predetermined distance from the output transducer (3) and the solder substrate (1) in the direction of propagation of the surface acoustic waves. A sound absorbing layer (4) is provided near the end.

The surface acoustic wave filter element having the above-described structure is used, for example, as an intermediate frequency filter element in an intermediate frequency amplification circuit of a television receiver. By the way, in French television broadcasting, for example, the frequency difference between the audio carrier and the video carrier is different between VHF broadcasting and UHF broadcasting, and this frequency difference is, for example, 11.1 in VHF broadcasting.
5 MHz, and 6.5 MHz for UHF broadcasting. The intermediate frequency filter element of the ninth TV station must use a surface acoustic wave filter element with different bandpass characteristics for vHP broadcasting and UHP broadcasting, so input and output A surface acoustic wave filter am is used in which a so-called multi-channel surface acoustic wave filter element in which either one of the inducers is separated into a plurality of pieces can be switched by a switch circuit.

Next, this surface acoustic wave filter l! ! An example of l will be explained with reference to FIGS. 2 and 3.

That is, the surface acoustic wave filter element is made of LiTa0. , Li
Nb0. .

Two input transducers (121) (12m) with different frequency bands are formed on a piezoelectric substrate man made of crystal, ceramics, etc. in an interdigital type for converting electric signals into surface acoustic waves, and this input transducer (121) (12m) Quadrature transducer (12r) (12t) K is an interdigital shaped output quadrature transducer disposed at a predetermined distance that converts surface acoustic waves into electrical signals. It is equipped with a sound absorbing material layer a4 provided near the end of the inlet quadrangle transducer (12,) (
The 12 common terminal (12a) is connected to the power supply (+B) K, and the other terminal (12b) (12C) of the input quadrature transducer (12+1 (12t)) is connected to the electric signal generator αS through a series resistor (Rg). fixing part of the mechanical switch (16
A), solid line arrow (17a), and dotted line arrow (17b) show that the contacts (16b) and (16c) are connected respectively. Both terminals (13a) and (13b) of the output transducer I are connected to the load W resistor (R/), forming a surface acoustic wave filter device ai.

In such a surface acoustic wave filter device, the switch is connected as shown by the solid arrow, and the input quadrature transducer (12
, ) and combine them, and connect the 6-person cutler □-nonsducer (121) and output transducer (II).
K: When a surface acoustic wave filter element is constructed, acoustic waves (18a) formed by surface waves are generated, but in this case, the terminals (12a) (12,
c) If you open the space between the
, )K reflected wave (18b) K ! re-reflection [(18
c) is inputted to the output transducer αIVC, which has the disadvantage of deteriorating the characteristics as a surface acoustic wave filter device.

Figure 3 shows this as an equivalent circuit, and the same reference numerals as in Figure 2 indicate the same parts, and no special explanation will be given. , ), the electrical signal from this signal source is acoustically converted by the input transducer (12,) and generated as an acoustic signal (18M) as a mechanical signal, which is converted by the output transducer I. Load (Z/) K
A signal voltage (v3) is generated. At this time, load (Z/) K
Due to the generated signal voltage (Vs), the output transducer (1311) is re-excited and the reflected wave (18bl) (18b
, ) occurs. This reflected wave (18b,
, ) is received at the load (Z, ) and similarly reexcited,
A reflected wave (18c,) (18c, 1 is generated and received by the load (2/) of the output transducer a.
cho) and becomes an unnecessary signal with a delay difference from the main signal.

Currently, this reflected wave is suppressed by a surface acoustic wave filter element as shown in Fig. 1, even with a moderate mismatch between each transducer 12) + 3) and its load. In the case of a multi-channel surface acoustic wave filter element as shown in Fig.
There was a drawback that the reflected waves (18c,) of 12 snow) were added.

The present invention has been made in view of the various drawbacks of the conventional art as described above.141.Surface acoustic wave filter device for multi-channel surface acoustic wave filter elements can be effectively switched by a switch circuit! is intended to provide.

First, the origin of the present invention will be explained using the equivalent circuit shown in Fig. 4. That is, the transducer @ is expressed by radiation conductance (Ga) and capacitive reactance (Xa). This transducer (to) K load (2/ ) is connected, this transducer (2) receives an input sound signal (28al
The power of the reflected wave (28b) and the reflected wave (28b) are expressed as (P) (Pt
), then the following relationship holds true between the power (P, )(P, >).

As can be seen from this equation, the reflected wave (28b) becomes O when 1'=ONL and Y/=.

However, when yz=o, that is, one terminal (22a) (22b) of the transducer t-open, it is normal high #! In the l-wave tnaiv, it is very difficult to make the rounded reflected wave (28b) of the floating instance zero. On the other hand, Y/=casting, that is, both terminals of transdue t'W (2
2a) (22b) t-Shorting is relatively easy.

Next, an embodiment of the surface acoustic wave filter device of the present invention based on the above-mentioned principle will be described with reference to FIG. , crystal, +5
Two input quadrature transducers (32,) (32,) with different frequency bands are formed in a rounded interdigital shape that converts electrical signals into surface acoustic waves on a piezoelectric substrate (of) consisting of a snare etc. and the input quadrature transducer (32,) (321) K, the output quadrature transducer (to) formed in an interdigital type that converts surface acoustic waves into electrical signals and arranged at a predetermined distance, and the piezoelectric substrate 0
A common terminal (32a) of an input quadrature transducer (32,) (32t) of a surface acoustic wave filter element made of an absorbent layer trout provided near the end in the surface acoustic wave propagation direction of #9.
After I is grounded, the fixed part of the changeover switch (3)
6a) and the man quadrature transducer (32i) (
The other terminals (32b) (32c) of the first changeover switch (32g) are connected to the contact (36b) (36c) to which the movable part (3at) of the first changeover switch (to) is connected.
) (36C) Fi electrical signal generator C1! HC! ! The series resistor (TLg) connected to the fixed part (37a) is connected to the movable part 11 (371) of the second changeover switch (2) connected to the fixed part (37a).
) also serves as the contact point to which it is connected. The movable parts (36,) (371) of these first changeover switch (to) and II2 changeover switch (b) are connected to each other (arrow (3g)
, ) (38 It is designed to operate in two directions, and the first changeover switch (to) and the second changeover switch @
can be easily made using a double-pole, double-throw switch. t+ Both terminals of the output transducer (to) (33al
A load resistor (R/) is connected to the connection (33b), forming a surface acoustic wave filter device.

By adopting the structure as in the embodiment described above, the input transducer is connected to the output transducer (to) by a switch circuit consisting of the first changeover switch (to) and the @2 changeover switch (b). Both terminals (36,
g) (36c) is short-circuited to the movable part (361) K. That is, the electric signal generation 111as using the input power source
The terminal is terminated with an impedance sufficiently smaller than the impedance of the series resistor (fLg), so even if there is a reflected wave from the output transducer (38b), there is no reflection from the input transducer (32t). wave(
38c) Id is extremely small, so the characteristics Fi as a surface acoustic wave filter device are extremely good.

Next, another embodiment of the surface acoustic wave filter device of the present invention will be described with reference to FIG. In the figure, the same surface acoustic wave filter element as in the previous embodiment is used, so the same reference numerals are given and no special explanation will be given.

That is, this embodiment uses a semiconductor switch instead of a mechanical switch, has nine input transducers (321
The common terminal of 1 (32) is grounded, and the other terminal (32b) is connected to a diode (Di) (Dt
)(D, is connected to the anode of the diode bridge consisting of 3 (D4), and the terminal (:12c) is connected to the cathode of the diode bridge through the capacitor (C), and the diodes (D, ) and (D,) are The connection part is connected to the input power source (10B) via a resistor (Rt), is further grounded via a resistor (to), and is connected to a signal terminal (4eVC) via a capacitor 411<c. Maku diode (D Rito)
The connection part of R4) is connected to the input power supply (10B) through a resistor (R3), is grounded through a switch (SW), and is further grounded through a capacitor (C,). There is.

In such a circuit, when the switch (SW) is closed, the diode (D, )CD+) is closed and the diode (Dt
) (oa) is open, and both terminals (32a) (32b) of the input transducer (32) are connected to the capacitor (C8) die #.
-) (D,) capacitance (C) is terminated in a series circuit, and when the switch (8W) is opened, the diode (D) (R3) is closed and the diode CD, 1 (R4) is open and input. Quadrant transducer (321) #I capacitance (C8) Diode (D) It is terminated with a series circuit of D capacitance (CI).

That is, by opening and closing the switch (8W), the input quadrature transducer (3zt) (3
2*) is terminated and short-circuited. The effect in this case is the same as that of the previous embodiment.O As described above, according to the present invention, the surface acoustic wave filter element,
In particular, it is possible to use a multi-channel surface acoustic wave filter element extremely effectively, and the frequency characteristics when using a surface acoustic wave filter element are also extremely good.

In the embodiment, the input transducer was separated into multiple pieces, but the output transducer was separated into multiple pieces.
The same applies to

[Brief explanation of the drawing]

111 is a plan view showing the basic form of a surface acoustic wave filter element, FIG. 2 is a plan view showing an example of a conventional surface acoustic wave filter device, FIG. 3 is an equivalent circuit diagram of FIG. An equivalent circuit diagram showing the basic form of the surface acoustic wave filter device of the invention, FIG. 5 is a plan view showing one embodiment of the surface acoustic wave filter device of the invention, and FIG. It is a top view showing an example of. 1.11.31...Piezoelectric substrate 2.121.12y, 22,321.321...Input transducer 3.13.33...Output transducer 18a, 28a, 38a...Music signal 18b
,18c,18b,,18b,,18c1.18c,,
28b, 38b, 38c...Reflected wave agent Patent attorney Inoue - Male Figure 1

Claims (1)

[Scope of Claims] 11) Input and output transducers each formed in an interdigital type are provided oppositely on the four pressure substrates, and either one of these human power and output transducers is separated into a plurality of pieces. and a switch circuit that selectively couples any one terminal of the plurality of separated transducers to an input power source or an output power source. Surface wave filter! I
I! In the surface acoustic wave 7, the terminal of the A transducer to which the switch circuit is connected is terminated with an impedance sufficiently lj smaller than the impedance of the input power source or the output power source. Iruta! i+! iit. (2) The surface acoustic wave filter device according to claim 1, wherein the plurality of separated transducers are input quadrature transducers. (31) The surface acoustic wave filter device according to claim 1, wherein the transducer separated into a plurality of pieces is an output transducer.