JPH08162894A - Surface acoustic wave filter - Google Patents

Abstract

PURPOSE: To improve the insertion loss of the surface acoustic wave filter by coupling other end of a boding wire to one of bonding pads. CONSTITUTION: One-side ends of bonding wires 26, 28, 30, 34, 35, 37, 39 are connected to nearly middle positions of positive electrodes 17, 20, 22, 24 and negative electrodes 18, 21, 23, 25 of transmitter side transducers 13, 15 of a 1st filter stage 11 and a 2nd filter stage 12 in the propagation direction of bus bars for the electrodes, the other side ends of the bonding wires 26, 28, 30, 34, 35, 37, 39 are connected to bonding pads 27, 29, 31, 33, 36, 38, 40. An electric resistance when an output signal is extracted is reduced by connecting the bonding pads 27, 29, 31, 33, 36, 38, 40 in this way to improve the insertion loss.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave filter device, and more particularly to a surface acoustic wave filter device with improved insertion loss.

[0002]

2. Description of the Related Art A surface acoustic wave filter device for extracting a signal in a specific frequency band by forming an interdigital transmitter and receiver on a piezoelectric substrate has been put into practical use. In this surface acoustic wave filter device, a unidirectional converter is used as the transmitter-side converter and the receiver-side converter in order to minimize the insertion loss. The surface acoustic wave filter device using the unidirectional converter has a relatively small insertion loss and is highly useful because the phase characteristic and the frequency characteristic can be controlled appropriately. However,
The side lobe characteristic is insufficient, and it is strongly demanded to further improve the out-of-band attenuation characteristic.

As a method of improving the out-of-band attenuation characteristic, a method of forming several filter stages on a piezoelectric substrate and continuously connecting these filter stages can be considered. For example, if two surface acoustic wave filter devices are constructed by continuously connecting two filter stages, the obtained attenuation characteristic is a characteristic obtained by multiplying the attenuation characteristics of the two filter stages, so that the out-of-band attenuation characteristic is obtained. Can be greatly improved. As such a surface acoustic wave filter device, there is a surface acoustic wave filter device described in Japanese Patent Application No. 5-72059 proposed by the present applicant. In this surface acoustic wave filter device, a transmitter-side converter and a receiver-side converter are provided on a single piezoelectric substrate.
The filter stages are formed parallel to one another and interconnect the positive electrode of the receiving converter of the first filter stage and the positive electrode of the transmitting converter of the second filter stage.

[0004]

The above-described two-stage continuous type surface acoustic wave filter device has an advantage that the out-of-band attenuation characteristic can be greatly improved. However, since the insertion loss also has a characteristic obtained by multiplying the insertion losses of the two filter stages, the insertion loss is somewhat deteriorated. Therefore, if the insertion loss of such a two-stage continuous surface acoustic wave filter device is further reduced, it is possible to realize a surface acoustic wave filter device having a small insertion loss and significantly improved out-of-band characteristics.

An object of the present invention is to provide a surface acoustic wave filter device in which the advantages of the two-stage cascade type surface acoustic wave filter device can be effectively utilized and the insertion loss is further improved.

[0006]

A surface acoustic wave filter device according to the present invention includes a piezoelectric substrate, an interdigital transmitter and an interdigital receiver, which are formed on the piezoelectric substrate. A first and a second filter stage each having a converter; and a package containing the piezoelectric substrate and having a plurality of bonding pads, wherein each of the transmitter-side converter and the receiver-side converter has a plurality of electrodes. A positive electrode and a negative electrode each having a finger and a bus bar for electrically connecting these electrode fingers are provided, and one end of the bonding wire is located at a substantially central position when viewed in the propagation direction of the surface acoustic wave of the bus bar of the positive electrode and the negative electrode. And the other ends of these bonding wires are connected to one of the bonding pads.

As a result of various experiments and analyzes by the inventor of the two-stage continuous filter device, it was found that the electric resistance of the electrode bus bar greatly affects the insertion loss. For example, consider the case where each transmitter-side transducer and receiver-side transducer comprises a positive electrode and a negative electrode, each having ten electrode fingers and a busbar electrically connecting these electrode fingers (FIG. 6). Here, when an electric signal is supplied to each electrode finger via the bus bar of the electrode of the converter, and the surface acoustic wave excited by the converter is picked up by each electrode finger of the bus bar of the electrode of the converter and converted into an electric signal. The electrical resistance of the bus bar when converted and the output signal is taken out through the bus bar is calculated.

The electrical resistance R _A when one end of the bonding wire is connected to a substantially central position (point A) when viewed in the propagation direction of the surface acoustic wave of the bus bar is the total length of the bus bar in the surface acoustic wave propagation direction. l, the cross-sectional area of the busbar is S, and the resistivity of the busbar is ρ,

[Equation 2] Becomes

The bus bar when one end of the bonding wire is connected to a position (point B) which is displaced by three electrode fingers in the opposite direction from the substantially central position (point A) as viewed in the propagation direction of the surface acoustic wave of the bus bar. The electrical resistance R _B of

(Equation 3) Becomes Further, the electric resistance R _C of the bus bar when one end of the bonding wire is coupled to almost the end portion (point C) when viewed in the propagation direction of the surface acoustic wave of the bus bar is:

[Equation 4] Becomes From the above calculation,

## EQU00005 ## R _A <R _B <R _C , and the electrical resistance of the bus bar is better when one end of the bonding wire is connected to the center position of the bus bar when viewed in the propagation direction of the surface acoustic wave of the bus bar. It can be seen that the size is smaller than that in the case of being connected to the end of the bus bar.

As described above, when the electric signal is supplied to each electrode finger through the bus bar of the electrode of the converter and the surface acoustic wave excited by the converter is picked up by each electrode finger of the bus bar of the electrode of the converter. The electrical resistance when the output signal is extracted via the bus bar after being converted into an electric signal is the one when one end of the bonding wire is connected to the center position of the bus bar when viewed in the propagation direction of the surface acoustic wave of the bus bar. However, it is smaller than when it is connected to the end of the bus bar. Therefore, the insertion loss is improved when one end of the bonding wire is connected to the central position of the bus bar when viewed in the propagation direction of the surface acoustic wave, compared to when the bonding wire is connected to the end of the bus bar.

Further, in the embodiment of the surface acoustic wave filter device according to the present invention, the film thickness of the bus bar of the positive electrode and the negative electrode of the transmitter side converter and the receiver side converter is made thicker than the film thickness of the electrode finger. It is characterized by having done.

In this example, the resistance value of the bus bar of each of the positive and negative electrodes of the four transducers is reduced to suppress the attenuation of the signal to be filtered and the filtered signal as it passes through the bus bar. That is, the electric signal to be converted by the electrode finger or the converted electric signal is input to the bus bar from the electrode finger, passes through the bus bar, and is supplied to the external circuit. On the other hand, the bus bar is composed of a conductor pattern formed on the piezoelectric substrate together with the electrode fingers in the process of forming the electrode fingers. However, the optimum film thickness of the electrode fingers is determined by the center frequency of the designed filter device, for example, 240
In the case of a filter device of MHz, the thickness is set to about 0.15 μm, and the film thickness is set thinner as the center frequency becomes higher. In the conventional surface acoustic wave filter device, the thickness of the bus bar is set to be the same as the thickness of the electrode fingers due to manufacturing requirements, so that the bus bar itself has a non-negligible electrical resistance component. The components attenuate the converted and converted signals. Therefore, by increasing the film thickness of the bus bar to reduce the electric resistance of the bus bar, that is, by further increasing the film thickness of the bus bar, the insertion loss as the filter device can be significantly improved.

Further, in another embodiment of the surface acoustic wave filter device according to the present invention, each of the transmitting side transducers is periodically formed at a pitch of λ when λ is the propagation wavelength of the basic surface acoustic wave. A positive electrode having a plurality of electrode fingers and a plurality of electrode fingers that are periodically formed at a pitch of λ, and each electrode finger has a center distance of λ / 2 with the electrode finger of the positive electrode. Positioned negative electrode, and a plurality of electrode fingers arranged between the positive electrode and the negative electrode, each electrode finger is an intermediate position between the adjacent positive electrode electrode finger and the negative electrode electrode finger. From the surface acoustic wave propagating direction to the opposite direction to the floating electrode, each of the receiving side transducers, when λ is the propagation wavelength of the basic surface acoustic wave, the pitch of λ A positive electrode having a plurality of electrode fingers that are periodically formed in the same manner and periodically formed at a pitch of λ A negative electrode having a plurality of electrode fingers, each electrode finger being positioned with a center distance of λ / 2 with the electrode finger of the positive electrode, and a plurality of electrodes arranged between the positive electrode and the negative electrode. A floating electrode that has fingers and each electrode finger is displaced from the intermediate position between the adjacent positive electrode electrode finger and negative electrode electrode finger in the same direction as the surface acoustic wave propagation direction; It is characterized by including.

In the case of using the transmitter-side converter and the receiver-side converter composed of such a unidirectional converter, the floating electrode is placed between the electrode finger of the positive electrode and the electrode finger of the negative electrode which are adjacent to each other. The insertion loss is reduced by greatly deviating from the intermediate position of 1 to further enhance the one-way propagation based on the asymmetric structure.

Another embodiment of the surface acoustic wave filter device according to the present invention is the propagation direction of the surface acoustic wave of the positive electrode and the negative electrode of each of the transmitter and receiver transducers and the floating electrode. The width d at

## EQU6 ## The displacement amount of the floating electrode is set to λ / 1 by setting 1.0 × λ / 12 ≦ d <1.5 × λ / 12.
It is characterized in that it is set to 2.

If the displacement amount of the floating electrode is set to λ / 8, the unidirectionality based on the asymmetric structure cannot be sufficiently achieved because the displacement amount of the floating electrode is small.
For this purpose, the width of the electrode finger is set to λ / 12, and the floating electrode is moved from the intermediate position between the adjacent positive electrode electrode finger and negative electrode electrode finger to the same or opposite direction to the surface acoustic wave propagation direction. λ
Deviation by / 12.

Next, as a result of various experiments and analyzes conducted by the present inventor, it is extremely effective to positively utilize the mechanical perturbation effect by the electrode fingers of the transducer in order to reduce the insertion loss. I found something. In order to utilize the mechanical perturbation effect, it is effective to set the width of the surface of the electrode finger in the propagation direction of the surface acoustic wave to be large. According to the experimental results described later, the insertion loss decreases as the width of the electrode finger increases. It was confirmed. On the other hand, it was also confirmed that the GDT deteriorates as the width of the electrode finger increases. Therefore, the lower limit of the width of the electrode finger is limited by the insertion loss, and the upper limit is regulated by the GDT characteristic. Further, according to the experimental results, it was found that the user usage standard can be satisfied for both the insertion loss and the GDT by setting the width d of the electrode finger in the above range.

Another embodiment of the surface acoustic wave filter device according to the present invention is characterized in that the piezoelectric substrate is a quartz substrate and the floating electrode is a short-circuit type floating electrode.

Since the quartz substrate has a small frequency fluctuation with respect to temperature change, when the quartz substrate is used as the piezoelectric substrate, the change of the passing frequency band due to the temperature change can be maintained within a minute range. However, since the crystal has a small electromechanical coupling coefficient, it cannot be put to practical use from the viewpoint of insertion loss if the existing converter is formed as it is.
As a result of the inventor's detailed examination of the insertion loss in the quartz substrate, it was found that the sign of the reflection coefficient of the floating electrode strongly influences the insertion loss. For a crystal substrate,
The reflection coefficient of the short circuit type floating electrode is larger than that of the open type floating electrode. Therefore, it is preferable to use a short circuit type floating electrode as the floating electrode. With this configuration, the insertion loss can be suppressed to an extremely small range even if a crystal substrate having a small electromechanical coupling coefficient is used, and as a result, a surface acoustic wave filter device having excellent temperature characteristics and low loss is realized. be able to.

Another embodiment of the surface acoustic wave filter device according to the present invention is characterized in that the surface acoustic wave is propagated when the transmitter-side converter and the receiver-side converter have λ as the propagation wavelength of the fundamental surface acoustic wave. The electrode fingers having widths λ / 8 and 3λ / 8 in the direction are set to electrode fingers with a center-to-center distance of 3λ / 8.
It is characterized by having at least one electrode having electrode fingers which are periodically formed at the pitch.

As described above, the electrode finger having a width of λ / 8 in the propagation direction of the surface acoustic wave and the electrode finger having a width of 3λ / 8 in the propagation direction of the surface acoustic wave are combined to form one direction. The surface acoustic wave incident on the sex converter is reflected by the mismatch of acoustic impedance at the edge of each electrode finger, but the phase of the composite vector is the exact opposite of the phase of the electrical reflected wave. The reflected wave can be made zero, and the reflected wave can be eliminated without sacrificing the insertion loss.

The surface acoustic wave filter device according to the present invention comprises:
A piezoelectric substrate, first and second filter stages formed on the piezoelectric substrate, each having an interdigital transmission side converter and an interdigital type reception side converter, and the piezoelectric substrate are housed. And a package having a plurality of bonding pads, wherein each of the transmitter-side converter and the receiver-side converter has a positive electrode and a negative electrode respectively having a plurality of electrode fingers and a bus bar electrically connecting these electrode fingers. Each of the positive and negative electrode bus bars has one end of a bonding wire connected to the center of the bus bar as viewed in the propagation direction of the surface acoustic wave, and the other end of the bonding wire connected to one of the bonding pads. Then, the positive electrode bus bar of the receiving side converter of the first filter stage and the negative electrode bus bar of the transmitting side converter of the second filter stage are pressed. Electrically connected by the connection conductor pattern formed on sex substrate, couples the one end of the bonding wire substantially intermediate position of the connecting conductor pattern,
The other end of the bonding wire is connected to one of the bonding pads.

Although it is necessary to connect an inductance between the first filter stage and the second filter stage to cancel the capacitance component of each converter, the signal input side and signal It has been found that the inductance cannot function sufficiently effectively unless the output side and the output side are balanced. In particular, there is a difference in resistance component, capacitance component and reactance component between the connection line from the inductance connection point to the reception side converter of the first filter stage and the connection line to the transmission side converter of the second filter stage. If so, the insertion loss will decrease by several dB. Based on the above reason, in the surface acoustic wave filter device according to the present invention, one end of the bonding wire is coupled to the bus bar of the positive electrode and the negative electrode at a substantially central position as viewed in the propagation direction of the surface acoustic wave. The other end is coupled to one of the bonding pads, and the bus bar of the positive electrode of the receiving converter of the first filter stage and the bus bar of the negative electrode of the transmitting converter of the second filter stage are connected. Electrical connection is made by the connecting conductor pattern formed on the piezoelectric substrate, and one end of the bonding wire is connected to the connecting conductor pattern at approximately the center position in the propagation direction of the surface acoustic wave, and the other end of the bonding wire is connected. To one of the bonding pads. Therefore, according to the present invention, when the output signal is taken out, the electrical resistance becomes smaller, the insertion loss is improved, and the electrical characteristics of the connection line from the connection point of the inductance to each converter are made equal to each other. Therefore, the input side and the output side can be electrically balanced with respect to the connection point of the inductance, and as a result, the insertion loss can be further reduced.

Further, since the positive electrode of the receiving side converter of the first filter stage and the positive electrode of the transmitting side converter of the second filter stage are connected by the conductor pattern formed on the piezoelectric substrate, It can be formed together with the electrode structure of the converter in the step of forming the converter.

Another embodiment of the surface acoustic wave filter device according to the present invention is characterized in that the conductor pattern is thicker than the electrode fingers.

In this example, the film thickness of the connecting conductor pattern on the substrate for connecting the first filter stage and the second filter stage is made thick so that its resistance value is negligible.
By increasing the thickness of the conductor pattern and decreasing the resistance value, the attenuation of the signal filtered by the first filter stage can be greatly reduced. If the bus bar has the same film thickness as the conductor pattern for connecting the filter stage, the manufacturing process is further simplified.

[0027]

FIG. 1 is a circuit diagram showing a filter circuit having a surface acoustic wave filter device according to the present invention. The signal input terminal 1 to which the signal to be filtered is input is connected to the first inductor 2 and the surface acoustic wave filter device 3. The surface acoustic wave filter device 3 is a two-stage continuous-coupling filter device having a first filter stage 3a and a second filter stage 3b. The input signal is filtered by the first filter stage 3a, and the filtered signal is output. Further filtering is carried out in the second filter stage 3b. Between the first filter stage 3a and the second filter stage 3b,
The second inductor 4 for canceling the capacitance component is connected. The third inductor 5 and the signal output terminal 6 are connected to the output section of the surface acoustic wave filter device 3, and the filtered signal is taken out from this signal output terminal.

FIG. 2 is a diagrammatic plan view showing the structure of an example of the surface acoustic wave filter device shown in FIG. A rectangular crystal substrate 10 is used as the piezoelectric substrate, and the first and second filter stages 11 and 12 are formed on the crystal substrate 10. The first filter stage 11 includes a first transmitter-side converter 13 and a first transmitter-side converter 13.
, The second filter stage 12 comprises a second transmitter converter 15 and a second receiver converter 16. The transmitting side converters 13 and 15 are both unidirectional converters having the same structure, and the receiving side converters 14 and 16 are both unidirectional converters having the same structure. The first transmitter-side converter 13 includes a positive electrode 17 and a negative electrode 18,
The floating electrode 19 is arranged between the positive electrode 17 and the negative electrode 18 between the electrode fingers. The widths of the electrode fingers of the positive electrode 17, the negative electrode 18, and the floating electrode 19 are λ / 12, respectively.
Set to. Here, λ is the wavelength of the basic surface acoustic wave. The electrode fingers of the positive electrode 17 and the negative electrode 18 are respectively λ
And the center distance between the electrode finger of the positive electrode 17 and the electrode finger of the adjacent negative electrode 18 is set to λ / 2. Further, the electrode fingers of the floating electrodes 19 are the positive electrodes 17 adjacent to each other.
Further, the unidirectionality is enhanced by arranging the negative electrode 18 so as to deviate by, for example, λ / 12 from an intermediate position between the negative electrode 18 and the electrode finger to the upstream side in the propagation direction of the surface acoustic wave.

Similarly, the first receiving side converter 14 also has a positive electrode 20 and a negative electrode 21, and a floating electrode arranged between the electrode fingers of the positive electrode 20 and the negative electrode 21. Further, the second transmitter-side converter 15 also has a positive electrode 22 and a negative electrode 23, and a floating electrode arranged between the electrode fingers of the positive electrode 22 and the negative electrode 23. Further, the second reception side converter 16 also similarly has a positive electrode 24 and a negative electrode 25, and a floating electrode arranged between the electrode fingers of the positive electrode 24 and the negative electrode 25. In this case, the floating electrode is deviated by λ / 12 downstream in the surface acoustic wave propagation direction. The number of pairs of electrodes of each converter is set to be the same, and the input side and the output side of the first filter stage 11 and the second filter stage 12 are balanced so as to be equal to each other when viewed from the midpoint.
However, the number of pairs of electrodes may be changed according to the characteristics.

In the transmitter-side converters 13 and 15 and the receiver-side converters 14 and 16, the propagation direction of the surface acoustic wave in the first filter stage 11 and the propagation direction of the second filter stage 12 are parallel to each other and are in the same direction. So that Further, the first filter stage 11 and the second filter stage 12 are arranged in parallel in the direction orthogonal to the propagation direction of the surface acoustic wave. Further, in the first transmitter-side converter 13, the bus bar 17a of the positive electrode 17 is the quartz substrate 10
The positive electrode and the negative electrode in the first receiving side converter 14 are reversed so as to directly face one end edge of the first electrode. Further, in the second transmitter converter 15, the bus bar of the negative electrode 23 directly faces the opposite edge of the crystal substrate 10, and in the second receiver converter 16, the positive electrode 20 and the negative electrode 21. Reverse the placement of.

One end of the bonding wire 26 is connected to the bus bar 17a of the positive electrode 17 of the first transmission side converter 13 at a substantially central position as viewed in the propagation direction of the surface acoustic wave, and the other end of the bonding wire 26 is It is coupled to the bonding pad 27 connected to the signal input terminal 1 and the inductor 2. On the other hand, the negative electrode 1 of the first transmitter-side converter 13
One end of the bonding wire 28 is bonded to the bus bar 18 a of FIG. 8 at a substantially central position as viewed in the surface acoustic wave propagation direction, and the other end of the bonding wire 28 is bonded to the bonding pad 29.

Similarly, one end of the bonding wire 30 is coupled to the positive electrode 20 of the first receiving side transducer 14 at a substantially central position as viewed in the propagation direction of the surface acoustic wave of the bus bar, and the other end of the bonding wire 30 is joined. The bonding pad 31
Bind to. On the other hand, one end of the bonding wire 32 is coupled to the negative electrode 21 of the first receiving-side converter 14 at a substantially central position as viewed in the propagation direction of the surface acoustic wave of the bus bar.
The other end of the bonding wire 32 is coupled to the bonding pad 33 to which the inductor 4 is connected.

One end of the bonding wire 34 is connected to the positive electrode 22 of the second transmitting side converter 15 at a substantially central position of the bus bar of the positive electrode 22 when viewed in the propagation direction of the surface acoustic wave, and the other end of the bonding wire 34 is connected to the inductor. 4 is connected to the connected bonding pad 33. On the other hand, the bonding wire 3 is formed at the substantially central position of the negative electrode 23 of the second transmitter-side converter 15 when viewed in the propagation direction of the surface acoustic wave of the bus bar.
One end of the bonding wire 35 is bonded, and the other end of the bonding wire 35 is bonded to the bonding pad 36.

Similarly, one end of the bonding wire 37 is coupled to the bus bar of the positive electrode 24 of the second receiving side converter 16 at a substantially central position as viewed in the propagation direction of the surface acoustic wave, and the other end of the bonding wire 37 is connected. Are bonded to the bonding pad 38 connected to the inductor 5 and the signal output terminal 6. On the other hand, one end of the bonding wire 39 is coupled to the negative electrode 25 of the second receiving side transducer 16 at a substantially central position as viewed in the propagation direction of the surface acoustic wave of the bus bar, and the other end of the bonding wire 39 is connected. Bonding pad 40
Bind to.

The electrical signal to be filtered is supplied to each electrode finger from the input terminal 1 via the bus bar of the positive electrode 17 of the first transmitter side converter 13. The surface acoustic wave excited by the first transmitter 13 is picked up by each electrode finger of the first receiver 14 and converted into an electric signal. This electric signal is supplied to the second transmitter transducer 15 via the bonding wires 30 and 34, and the surface acoustic wave excited by the second transmitter transducer 15 is supplied to each of the second receiver transducers 16. It is picked up by an electrode finger, converted into an electric signal, and taken out from the signal output terminal 6 via the bus bar of the positive electrode 23. Therefore, the signal to be filtered is filtered twice by two continuously connected filter stages and output via the eight busbars.

According to this embodiment, the bonding pads are connected with the intermediate position of the bus bar of each electrode as a connection point. Therefore, when an electric signal is supplied to each electrode finger via the bus bar of the electrode of the converter and conversion is performed. The surface acoustic wave excited by the transducer is picked up by each electrode finger of the bus bar of the transducer electrode and converted into an electric signal, and the electric resistance when the output signal is taken out through the bus bar becomes small, resulting in insertion loss. Be improved.

Next, setting of the width of the electrode finger of each transducer in the propagation direction of the surface acoustic wave will be described. In the case of the two-stage cascade connection type surface acoustic wave filter device, the out-of-band attenuation also increases, but the insertion loss also increases. For this reason, it is preferable to configure each converter so that the insertion loss does not increase. In order to reduce the insertion loss, the width of the electrode finger can be increased to positively utilize the mechanical perturbation effect. For this reason, a surface acoustic wave filter device having a center frequency of 240 MHz and different electrode finger widths was prototyped, and the relationship between the electrode finger width and the insertion loss was obtained.

FIG. 3 is a graph showing the relationship between the width of the electrode finger and the insertion loss. In FIG. 3, the horizontal axis represents the width of the electrode finger, and the vertical axis represents the insertion loss. In the experiment, 350 pairs of converters were formed on the quartz substrate to make a two-stage cascade connection. Five electrode finger widths were prototyped on the basis of λ / 12. As is clear from FIG. 3, the insertion loss decreases as the width of the electrode finger increases. On the other hand, in the two-stage cascade connection type surface acoustic wave filter device, since the out-of-band attenuation is large and one stage of the amplifier can cover up to 10 dB, the user use standard of the insertion loss is specified to be 10 dB or less. To meet this user criteria, the electrode finger width is

(7) It is necessary to satisfy the condition of d ≧ 1.0 × λ / 12.

On the other hand, as the width d of the electrode finger increases, G
DT may be deteriorated. Therefore, the width d of the electrode finger
Experiments were also conducted on the relationship between GDT and GDT. The results of this experiment are shown in FIG. The GDT increases linearly with the width of the electrode finger. On the other hand, GDT user usage standard 0.5
It is specified in μsec or less. Therefore, the width d of the electrode finger
The upper limit of is regulated by GDT and is set to less than 1.5 × λ / 12. From these insertion loss and GDT user usage standards, the electrode finger width d is

It is desirable to satisfy 1.0 × λ / 12 ≦ d <1.5 × λ / 12.

In this example, the bus bar of each electrode is thicker than the electrode finger of each electrode. Thereby, the film thickness of the bus bar is increased to reduce the electric resistance of the bus bar, so that the insertion loss of the filter device can be significantly improved.

FIG. 5 is a diagrammatic plan view showing the configuration of a modification of the surface acoustic wave filter device shown in FIG. Also in this example, a rectangular crystal substrate 50 is used as the piezoelectric substrate, and the first and second filter stages 51 and 52 are formed on the crystal substrate 50. The first filter stage 51 comprises the first transmitter side converter 5
3 and a first receiver converter 54, the second filter stage 52 comprises a second transmitter converter 55 and a second receiver converter 56. These four converters 53 to 56 are all unidirectional converters having the same structure. The first transmitting-side converter 53 has a set of electrode fingers in which electrode fingers having widths λ / 8 and 3λ / 8 are arranged with a center-to-center distance of 3λ / 8.
And a negative electrode 58 in which electrode fingers having a width of λ / 8 are periodically formed in a pitch of λ. Further, the center-to-center distance between the electrode finger of the positive electrode 57 and the electrode finger of the adjacent negative electrode 58 is 3λ / 4.
Set to.

The first receiving-side converter 54 has a positive electrode 59 in which electrode fingers having a width of λ / 8 are periodically formed at a pitch of λ, and a width of the electrode fingers is λ / 8. A set of electrode fingers in which 3λ / 8 electrode fingers are arranged with a center-to-center distance of 3λ / 8 is composed of a negative electrode 60 which is periodically formed at a pitch of λ. In this case as well, the center-to-center distance between the electrode finger of the positive electrode 59 and the electrode finger of the adjacent negative electrode 60 is similarly set to 3λ / 4. Further, the second transmitter side converter 55 also has electrode finger widths of λ / 8 and 3λ /, similarly to the second transmitter side converter 53.
A positive electrode 61 in which a set of electrode fingers in which eight electrode fingers are arranged with a center-to-center distance of 3λ / 8 are periodically formed at a pitch of λ;
An electrode finger having a width of λ / 8 is composed of a negative electrode 62 which is periodically formed at a pitch of λ. Further, the center-to-center distance between the electrode finger of the positive electrode 61 and the electrode finger of the adjacent negative electrode 62 is set to 3λ / 4. Furthermore, the second receiving side converter 5
Similarly to the first receiving-side converter 54, the electrode 6 has a width of the electrode finger of λ.
Positive electrode 6 in which electrode fingers of / 8 are periodically formed at a pitch of λ
3 and an electrode finger with a width of λ / 8 and 3λ / 8 is 3λ
A set of electrode fingers arranged with a center-to-center distance of / 8 and the negative electrode 64 formed periodically at a pitch of λ. Also in this case, similarly, the negative electrode 64 adjacent to the electrode finger of the positive electrode 63 is
The center-to-center distance between the electrode finger and the electrode finger is set to 3λ / 4. The number of pairs of electrodes of each converter is set to be the same, and the input side and the output side are balanced so as to be equal to each other when viewed from the midpoint of the first filter stage 51 and the second filter stage 52.

In the transmitter side converters 53 and 55 and the receiver side converters 54 and 56, the propagation direction of the surface acoustic wave in the first filter stage 51 and the propagation direction of the second filter stage 52 are parallel to each other and in the same direction. So that Further, the first filter stage 51 and the second filter stage 52 are arranged in parallel in the direction orthogonal to the propagation direction of the surface acoustic wave. Further, in the first transmitting-side converter 53, the bus bar of the positive electrode 57 is arranged so as to directly face one edge of the crystal substrate 50. In addition, in the second transmitter-side converter 55, the bus bar of the negative electrode 60 is the quartz substrate 5.
It is arranged so as to directly face the opposite edge of 0.

In this example, the conductor pattern 65 is formed on the crystal substrate 50, and the positive electrode 59 of the first receiving side converter 54 is formed.
And the negative electrode 61 of the second transmitter-side converter 55 are interconnected.

One end of the bonding wire 66 is connected to the positive electrode 57 of the first transmitting side converter 53 at a substantially central position as viewed in the propagation direction of the surface acoustic wave of the bus bar, and the other end of the bonding wire 66 is connected to a signal. It is coupled to the bonding pad 67 connected to the input terminal 1 and the inductor 2. On the other hand, one end of the bonding wire 68 is coupled to the negative electrode 58 of the first transmitting-side converter 53 at a substantially central position as viewed in the propagation direction of the surface acoustic wave of the bus bar, and the other end of the bonding wire 68 is connected. Bond to the bonding pad 69.

Similarly, one end of the bonding wire 70 is coupled to the negative electrode 60 of the first receiving-side converter 64 at a substantially central position of the bus bar in the propagation direction of the surface acoustic wave, and the other end of the bonding wire 70 is joined. The bonding pad 71
Bind to.

One end of the bonding wire 72 is coupled to a substantially central position of the conductor pattern 65 when viewed in the surface acoustic wave propagation direction, and the other end of the bonding wire 72 is connected to the bonding pad 73 to which the inductor 4 is connected. .

One end of the bonding wire 74 is coupled to the positive electrode 62 of the second transmitting side converter 55 at a substantially central position of the bus bar of the positive electrode 62 in the propagation direction of the surface acoustic wave, and the other end of the bonding wire 74 is bonded to the bonding pad. Bind to 75.

Similarly, one end of the bonding wire 76 is coupled to the positive electrode 63 of the second receiving side converter 56 at a substantially central position as viewed in the propagation direction of the surface acoustic wave of the bus bar, and the other end of the bonding wire 76 is connected. To the bonding pad 77 to which the inductor 5 and the signal output terminal 6 are connected. On the other hand, one end of the bonding wire 78 is coupled to the negative electrode 64 of the second receiving side converter 56 at a substantially central position as viewed in the propagation direction of the surface acoustic wave of the bus bar, and the other end of the bonding wire 78 is connected. Bonding pad 79
Bind to.

The electric signal to be filtered is supplied from the input terminal 1 to each electrode finger through the bus bar of the positive electrode 57 of the first transmitter side converter 53. The elastic wave excited by the first transmitting-side converter 53 is picked up by each electrode finger of the first receiving-side converter 54 and converted into an electric signal.
This electric signal is supplied to the second transmitting-side converter 55 through the conductor pattern 65, and the surface acoustic wave excited by the second transmitting-side converter 55 is the electrode finger of the second receiving-side converter 56. Is picked up by and converted into an electric signal,
It is taken out from the signal output terminal 6 via the bus bar of the positive electrode 63. Therefore, the signal to be filtered is filtered twice by two continuously connected filter stages and output via the eight busbars.

According to this embodiment, the bonding pads are connected with the intermediate position of the bus bar of each electrode as a connection point. Therefore, when an electric signal is supplied to each electrode finger via the bus bar of the electrode of the converter and conversion is performed. The elastic wave excited by the converter is picked up by each electrode finger of the bus bar of the converter electrode and converted into an electric signal, and the electrical resistance when the output signal is taken out through the bus bar is reduced, and the insertion loss is improved. To be done.

Further, in this example, the bus bar of the positive electrode 59 of the receiving side converter 54 of the first filter stage 51 and the bus bar of the negative electrode 61 of the transmitting side converter 55 of the second filter stage 52 are connected to the quartz substrate. Electrical connection is made by the conductor pattern 65 formed on the conductor 50, and the bonding wire 7 is formed at a substantially central position of the conductor pattern 65 in the propagation direction of the surface acoustic wave.
Since one end of 2 is connected and the other end of the bonding wire 72 is connected to the bonding pad 73, the electrical characteristics of the connection line from the connection point of the inductor 4 to each converter can be made equal to each other, The input side and the output side can be electrically balanced with respect to the connection point of the inductor 4, and as a result, the insertion loss can be further reduced.

In this example, the bus bar of each electrode is thicker than the electrode finger of each electrode. Thereby, the film thickness of the bus bar is increased to reduce the electric resistance of the bus bar, so that the insertion loss of the filter device can be significantly improved.

Further, in this example, the film thickness of the conductor pattern 65 is made thicker than the film thickness of the electrode finger of each electrode. As a result, the resistance value of the conductor pattern 65 is small, and therefore the attenuation of the signal filtered by the first filter stage 51 can be greatly reduced.

The present invention is not limited to the above-mentioned embodiments, but various modifications and changes can be made. For example,
Either the transmitting side converter or the receiving side converter may be a bidirectional converter. First filter stage and second
It is also possible to apply a sound absorbing material to the other filter stage so that surface acoustic waves excited in one filter stage do not enter the other filter stage. Further, a grounded guard electrode may be disposed between the first filter stage and the second filter stage to prevent electromagnetic coupling between the first filter stage and the second filter stage. it can. Furthermore, a shield electrode may be arranged between the transmitter-side converter and the receiver-side converter to prevent electromagnetic coupling between the transmitter-side converter and the receiver-side converter.

Further, as the piezoelectric substrate material, not only the quartz substrate but also other substrate materials such as LiNbO ₃ and LiTaO ₃ can be used.

[0057]

As described above, according to the surface acoustic wave filter device of the present invention, the surface acoustic waves of the positive electrode and negative electrode bus bars of the transducers on the transmitting side and the transducers on the receiving side are viewed in the propagation direction. Since one end of the bonding wire is connected to the central position and the other end of the bonding wire is connected to one of the bonding pads, an electric signal is supplied to each electrode finger via the bus bar of the electrode of the converter. The elastic wave excited by the transducer and picked up by each electrode finger of the bus bar of the electrode of the transducer is converted into an electric signal, and the electric resistance becomes small when the output signal is taken out through the bus bar. , Insertion loss is improved.

In particular, the connecting conductor pattern in which the positive electrode bus bar of the receiving side converter of the first filter stage and the negative electrode bus bar of the transmitting side converter of the second filter stage are formed on the piezoelectric substrate. By electrically connecting the bonding conductor pattern with one end of the bonding wire at substantially the center of the connection conductor pattern in the propagation direction of the surface acoustic wave, and the other end of the bonding wire with one of the bonding pads. In this case, since the electrical characteristics of the connection line from the inductance connection point to each converter can be made equal to each other, the input side and the output side must be electrically balanced based on the inductance connection point. As a result, the insertion loss can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a filter circuit including a surface acoustic wave filter device according to the present invention.

FIG. 2 is a diagrammatic plan view showing the configuration of an example of the surface acoustic wave filter device shown in FIG.

FIG. 3 is a graph showing a relationship between an electrode finger width and insertion loss.

FIG. 4 is a graph showing the relationship between the width of an electrode finger and GDT.

5 is a diagrammatic plan view showing the configuration of a modified example of the surface acoustic wave filter device shown in FIG. 1. FIG.

FIG. 6 is a diagram for explaining a relationship between a connection position of a bonding wire and an electric resistance of a bus bar.

[Explanation of symbols]

10, 50 Quartz substrate, 11, 12, 51, 52 Filter stage, 13, 15, 53, 55 Transmitter side converter, 14,
16, 54, 56 receiver side converter, 17, 20, 22,
24, 57, 59, 61, 63 Positive electrode, 18, 21,
23, 25, 58, 60, 62, 64 Negative electrode, 19
Floating electrode, 26, 28, 30, 32, 34, 35, 3
7, 39, 66, 68, 70, 72, 74, 76, 78
Bonding wire, 27, 29, 31, 33, 3
6,38,40,67,69,71,73,75,7
7,79 Bonding pad, 65 Conductor pattern

Claims (15)

[Claims] 1. A first and second piezoelectric substrate, and an interdigital transmitter-side converter and an interdigital receiver-side converter formed on the piezoelectric substrate, respectively.
And a package containing the piezoelectric substrate and having a plurality of bonding pads, wherein each transmitter-side converter and receiver-side converter electrically connects a plurality of electrode fingers and these electrode fingers. A positive electrode and a negative electrode, each having a bus bar, and one end of the bonding wire is coupled to the positive electrode and the negative electrode at a substantially central position in the propagation direction of the surface acoustic wave of the bus bar. Is coupled to one of the bonding pads. 2. The elastic surface according to claim 1, wherein the film thickness of the bus bar of the positive electrode and the negative electrode of the transmitter-side converter and the receiver-side converter is larger than the film thickness of the electrode fingers. Wave filter device. 3. The transmission side converter and the reception side converter are all unidirectional converters.
The surface acoustic wave filter device described. 4. Each of the transmitter transducers has a positive electrode having a plurality of electrode fingers periodically formed at a pitch of λ, where λ is the propagation wavelength of the fundamental surface acoustic wave, and λ Between a negative electrode having a plurality of electrode fingers periodically formed at a pitch, each electrode finger being positioned with a center distance of λ / 2 from the electrode finger of the positive electrode, and between the positive electrode and the negative electrode. Has a plurality of electrode fingers arranged in each, and each electrode finger is displaced from the intermediate position between the adjacent positive electrode electrode finger and negative electrode electrode finger in the direction opposite to the surface acoustic wave propagation direction. And a floating electrode positioned in the above, each receiving side transducer, when λ is the propagation wavelength of the fundamental surface acoustic wave, a positive electrode having a plurality of electrode fingers periodically formed at a pitch of λ and , Similarly, it has a plurality of electrode fingers periodically formed with a pitch of λ, and each electrode finger and the electrode finger of the positive electrode are λ 2 has a negative electrode respectively positioned with a center-to-center distance and a plurality of electrode fingers arranged between the positive electrode and the negative electrode, and each electrode finger is an electrode finger of an adjacent positive electrode and an electrode of a negative electrode. 4. The surface acoustic wave filter device according to claim 3, further comprising: a floating electrode which is displaced from an intermediate position between the finger and the finger in the same direction as the propagation direction of the surface acoustic wave. 5. The width d in the propagation direction of the surface acoustic wave of each electrode finger of the positive electrode and the negative electrode and the floating electrode of the transmitter-side converter and the receiver-side converter is given by: 1.0 × λ / 12 ≦ d <1.5 × λ / 12, and the displacement amount of the floating electrode is set to λ / 1.
5. The surface acoustic wave filter device according to claim 4, wherein the surface acoustic wave filter device is 2. 6. The surface acoustic wave filter device according to claim 4, wherein the piezoelectric substrate is a quartz substrate, and the floating electrode is a short-circuit type floating electrode. 7. The transmitter-side converter and the receiver-side converter are λ
Is the propagation wavelength of the fundamental acoustic wave, the electrode fingers whose widths in the propagation direction of the surface acoustic wave are λ / 8 and 3λ / 8 are 3λ.
4. The surface acoustic wave filter device according to claim 3, further comprising at least one electrode having electrode fingers in which a set of electrode fingers positioned with a center distance of / 8 is periodically formed at a pitch of λ. 8. A first and second piezoelectric substrate, and an interdigital transmission side converter and an interdigital type reception side converter formed on the piezoelectric substrate, respectively.
And a package containing the piezoelectric substrate and having a plurality of bonding pads, wherein each transmitter-side converter and receiver-side converter electrically connects a plurality of electrode fingers and these electrode fingers. A positive electrode and a negative electrode, each having a bus bar, and one end of the bonding wire is coupled to the positive electrode and the negative electrode at a substantially central position in the propagation direction of the surface acoustic wave of the bus bar. Is coupled to one of the bonding pads, and the positive electrode busbar of the receiving transducer of the first filter stage and the negative electrode busbar of the transmitting transducer of the second filter stage are piezoelectrically coupled. Electrically connected by the connecting conductor pattern formed on the flexible substrate, and one end of the bonding wire is connected to the intermediate position of the connecting conductor pattern. SAW filter device characterized by the other end of the down loading wire bonded to one of the bonding pads. 9. The film thickness of the bus bar of the positive electrode and the negative electrode of the transmitter side converter and the receiver side converter is made thicker than the film thickness of the electrode fingers. Surface acoustic wave filter device. 10. The film thickness of the conductor pattern is made thicker than the film thickness of the electrode fingers.
The surface acoustic wave filter device described. 11. The surface acoustic wave filter device according to claim 8, wherein all of the transmitter-side converter and the receiver-side converter are unidirectional converters. 12. Each of the transmitter transducers has a positive electrode having a plurality of electrode fingers periodically formed at a pitch of λ, where λ is a propagation wavelength of a fundamental surface acoustic wave, and similarly, Between a negative electrode having a plurality of electrode fingers periodically formed at a pitch, each electrode finger being positioned with a center distance of λ / 2 from the electrode finger of the positive electrode, and between the positive electrode and the negative electrode. Has a plurality of electrode fingers arranged in each, and each electrode finger is displaced from the intermediate position between the adjacent positive electrode electrode finger and negative electrode electrode finger in the direction opposite to the surface acoustic wave propagation direction. And a floating electrode positioned in the above, each receiving side transducer, when λ is the propagation wavelength of the fundamental surface acoustic wave, a positive electrode having a plurality of electrode fingers periodically formed at a pitch of λ and , Similarly having a plurality of electrode fingers periodically formed at a pitch of λ, each electrode finger being the electrode finger of the positive electrode Has a negative electrode positioned at a center distance of / 2 and a plurality of electrode fingers arranged between the positive electrode and the negative electrode, and each electrode finger has an electrode finger of an adjacent positive electrode and a negative electrode. The surface acoustic wave filter device according to claim 11, further comprising: a floating electrode that is displaced from an intermediate position between the electrode fingers and in the same direction as the surface acoustic wave propagation direction. 13. The displacement amount of the floating electrode is defined as the width in the propagation direction of surface acoustic waves of the floating electrode and the electrode fingers of the positive electrode and the negative electrode of the transmitting side converter and the receiving side converter. 13. The surface acoustic wave filter device according to claim 12, wherein is λ / 12. 14. The surface acoustic wave filter device according to claim 12, wherein the piezoelectric substrate is a quartz substrate, and the floating electrode is a short-circuit type floating electrode. 15. The transmitter-side converter and the receiver-side converter,
When λ is the propagation wavelength of the fundamental acoustic wave, three electrode fingers having widths λ / 8 and 3λ / 8 in the propagation direction of the surface acoustic wave are used.
The surface acoustic wave filter device according to claim 11, further comprising at least one electrode having electrode fingers in which a set of electrode fingers positioned with a center-to-center distance of λ / 8 is periodically formed at a pitch of λ.