JP4047313B2 - Surface acoustic wave filter - Google Patents

Description

  The present invention relates to a longitudinal mode type surface acoustic wave filter.

  In recent years, surface acoustic wave filters have been widely used in mobile communication devices. As the RF stage filter, a longitudinal mode type or ladder type surface acoustic wave filter is used. The demand for lower loss and higher attenuation of the surface acoustic wave filter has been increased with higher performance of communication devices such as mobile phone terminals.

  A conventional longitudinal mode type surface acoustic wave filter will be described below.

  FIG. 12 shows a configuration of a conventional longitudinal mode type surface acoustic wave filter. In FIG. 12, the surface acoustic wave filter includes first, second, and third IDT (interdigital transducer) electrodes 802, 803, and 804 and first and second reflector electrodes 805 and 806 on a piezoelectric substrate 801. It consists of. The upper electrode fingers of the second and third IDT electrodes 803 and 804 are respectively connected to the input terminal IN, and the lower electrode fingers of the second and third IDT electrodes 803 and 804 are respectively grounded. Yes. The lower electrode finger of the first IDT electrode 802 is connected to the output terminal OUT, and the upper electrode finger of the first IDT electrode 802 is grounded. Further, the center distance (hereinafter referred to as the pitch) indicated by P in FIG. 12 of the electrode fingers of the first, second, and third IDT electrodes 802, 803, and 804 has the same size. With the above configuration, a longitudinal mode type surface acoustic wave filter can be obtained.

  In the surface acoustic wave filter described above, the electrode fingers are arranged at the same pitch so that the sound speeds of the surface acoustic waves in the first, second, and third IDT electrodes 802, 803, and 804 are equal. However, from the viewpoint of bandwidth and impedance design, the first IDT electrode 802 and the second and third IDT electrodes 803 and 804 often have different numbers of electrode fingers. Usually, the number of electrode fingers of the first IDT electrode 802 is designed to be larger than the number of electrode fingers of the second and third IDT electrodes 803 and 804.

  For the purpose of realizing a low loss, a longitudinal mode type surface acoustic wave filter designed so that the pitch of each electrode finger of one IDT electrode is different as shown in FIG. 13 is also used. That is, FIG. 13 is a conventional longitudinal mode type surface acoustic wave filter, which is designed so that different electrode finger pitches are included in one IDT electrode.

  In FIG. 13, the surface acoustic wave filter includes first, second, and third IDT electrodes 1202, 1203, and 1204 and first and second reflector electrodes 1205 and 1206 on a piezoelectric substrate 1201. . The upper electrode fingers of the second and third IDT electrodes 1203 and 1204 are connected to the input terminal IN, and the lower electrode fingers of the second and third IDT electrodes 1203 and 1204 are grounded. Yes. The lower electrode finger of the first IDT electrode 1202 is connected to the output terminal OUT, and the upper electrode finger of the first IDT electrode 1202 is grounded.

  In FIG. 13, if the pitch of the region indicated by 1a of the first IDT electrode 1202 is P, P has a length of ½ wavelength. If the pitch of the region indicated by 1b is P ', P' is narrower than ½ wavelength. The pitch of the region indicated by 2a of the second IDT electrode 1203 is P, and P is a length of ½ wavelength. Further, the pitch of the region indicated by 2b is P ', and P' is narrower than ½ wavelength. Similarly, the pitch of the area | region shown by 3a of the 3rd IDT electrode 1204 is P, and P is the length of 1/2 wavelength. The pitch of the region indicated by 3b is P ', and P' has a length narrower than ½ wavelength.

  As described above, the first IDT electrode 1202, the second IDT electrode 1203, and the third IDT electrode 1204 have different electrode finger pitches in the same IDT electrode.

  Also in FIG. 13, the number of electrode fingers is often different between the first IDT electrode 1202 and the second and third IDT electrodes 1203 and 1204 from the viewpoint of bandwidth and impedance design. Usually, the number of electrode fingers of the first IDT electrode 1202 is designed to be larger than the number of electrode fingers of the second and third IDT electrodes 1203 and 1204.

  However, such a surface acoustic wave filter has a problem in that there is a limit in realizing a good filter characteristic having a wide band characteristic.

  In consideration of the above-described problems, an object of the present invention is to provide a surface acoustic wave filter having a wide band and a steep attenuation characteristic outside the band.

In order to solve the above-described problem, the first present invention includes a piezoelectric substrate,
Wherein arranged on a piezoelectric substrate, at least one input IDT electrode,
Wherein arranged on a piezoelectric substrate, and at least one output IDT electrodes,
A longitudinal mode surface acoustic wave filter in which the input IDT electrode and the output IDT electrode are disposed along one propagation path of the surface acoustic wave;
By comparing the number of electrode fingers constituting the input IDT electrode with the number of electrode fingers constituting the output IDT electrode, the metallization ratio of the IDT electrode having the larger number of electrode fingers is determined. An elastic surface that is larger than the metallization ratio of the IDT electrode with the smaller number, and the difference between the peak frequency of the radiation characteristic of the input IDT electrode and the peak frequency of the radiation characteristic of the output IDT electrode is less than 0.5% It is a wave filter.

The second aspect of the present invention is the surface acoustic wave filter according to the first aspect of the present invention including one input IDT electrode and two output IDT electrodes .

The third aspect of the present invention is the surface acoustic wave filter according to the first aspect of the present invention, comprising two input IDT electrodes and one output IDT electrode .

  As is apparent from the above description, the present invention can provide a surface acoustic wave filter having a further wide band and a steep attenuation characteristic outside the band.

  Embodiments of the present invention will be described below with reference to the drawings.

(First embodiment)
First, the first embodiment will be described. FIG. 1 shows a schematic diagram of a surface acoustic wave filter according to the present embodiment.

  In FIG. 1, the surface acoustic wave filter is composed of first, second, and third IDT electrodes 102, 103, and 104 and first and second reflector electrodes 105 and 106 on a piezoelectric substrate 101. .

  That is, the second IDT electrode 103 and the third IDT electrode 104 are arranged on both sides of the first IDT electrode 102, and is opposite to the side of the second IDT electrode 103 on which the first IDT electrode 102 is arranged. The reflector electrode 105 is disposed on the side, and the reflector electrode 106 is disposed on the opposite side of the third IDT electrode 104 from the side on which the first IDT electrode 102 is disposed. As described above, the first, second, and third IDT electrodes 102, 103, and 104 and the first and second reflector electrodes 105 and 106 are disposed along the direction in which the surface acoustic wave propagates.

  The upper electrode fingers of the second and third IDT electrodes 103 and 104 are connected to the input terminal IN, and the lower electrode fingers of the second and third IDT electrodes 103 and 104 are grounded. The lower electrode finger of the first IDT electrode 102 is connected to the output terminal OUT, and the upper electrode finger of the first IDT electrode 102 is grounded.

  The number of electrode fingers of the first IDT electrode 102 is larger than the number of electrode fingers of the second and third IDT electrodes 103 and 104, and the number of electrode fingers of the second IDT electrode 103 and the electrode of the third IDT electrode 104 The number of fingers is the same.

  Further, when the pitch of the first IDT electrode 102 is P1, and the pitch of the second and third IDT electrodes 103 and 104 is P2, there is a relationship of P1> P2.

  Further, the metallization ratio η indicating the ratio of the width of the electrode finger within one wavelength takes the same value for the first IDT electrode 102 and the second and third IDT electrodes 103 and 104.

  Here, the metallization ratio η is expressed by the following formula 1.

(Equation 1)
η = L / (L + S)
Here, L is the width of the electrode finger, and S is the interval from one electrode finger to the next electrode finger.

  Next, the operation of this embodiment will be described.

  FIG. 2 shows the relationship between the number of electrode fingers of the first IDT electrode 102, the metallization ratio η of the first IDT electrode 102, and the peak frequency of the radiation characteristic of the first IDT electrode 102. Here, the peak frequency of the radiation characteristic means a frequency at which the level of the radiation characteristic is maximized. That is, FIG. 2 shows that when the pitch is constant, the number of the electrode fingers of the first IDT electrode 102 and the metallization ratio η of the first IDT electrode 102 take a certain value. Is measured and plotted, and the peak frequency of the radiation characteristic is obtained.

  As described above, in FIG. 2, the electrode finger pitch is set to the same value even if the number of electrode fingers of the first IDT electrode and the metallization ratio η of the first IDT electrode 102 are changed.

  As apparent from FIG. 2, the peak frequency of the radiation characteristic of the first IDT electrode 102 increases as the number of electrode fingers of the first IDT electrode 102 increases. Further, the peak frequency of the radiation characteristic of the first IDT electrode 102 decreases as the metallization η of the first IDT electrode 102 increases. Thus, when the electrode film thickness of the first IDT electrode 102 is the same, the peak frequency of the radiation characteristic of the first IDT electrode 102 increases as the number of electrode fingers increases and the metallization η decreases. . The second and third IDT electrodes 103 and 104 have the same tendency as that seen with the first IDT electrode 102.

  Reference numeral 401 in FIG. 4 shows the radiation characteristic of the first IDT electrode 102. As is apparent from 401 in FIG. 4, the radiation characteristics of the first IDT electrode 102 are asymmetric with respect to the peak frequency due to the influence of the reflection characteristics.

  Further, reference numeral 402 in FIG. 4 shows the radiation characteristic of the second IDT electrode 103. The radiation characteristic of the second IDT electrode 103 is also asymmetric with respect to the peak frequency, similarly to the first IDT electrode 102, due to the influence of the reflection characteristic. Note that since the third IDT electrode 104 has the same number of electrode fingers as the second IDT electrode 103, the radiation characteristic of the third IDT electrode 104 is the same as that of the second IDT electrode 103. Accordingly, the radiation characteristic of the third IDT electrode 104 is also indicated by 402 in FIG. 4 as is the radiation characteristic of the second IDT electrode 103.

  On the other hand, as shown in FIG. 4, the inventor makes the peak frequency of the radiation characteristic 401 of the first IDT electrode 102 equal to the peak frequency of the radiation characteristic 402 of the second and third IDT electrodes 103 and 104. We discovered the fact that the surface acoustic wave filter has better characteristics when the surface acoustic wave filter is designed. That is, when the surface acoustic wave filter is designed so that the peak frequency of the radiation characteristic 401 of the first IDT electrode 102 is equal to the peak frequency of the radiation characteristic 402 of the second and third IDT electrodes 103 and 104, It has been discovered that the characteristics of a surface acoustic wave filter have a broader attenuation characteristic.

  As described above, the number of electrode fingers of the first IDT electrode 102 is larger than the number of electrode fingers of the second and third IDT electrodes 103 and 104. Therefore, as is clear from FIG. 2, when the pitch of the first IDT electrode 102 is the same as the pitch of the second and third IDT electrodes 103 and 104, the peak frequency of the radiation characteristic of the first IDT electrode 102 is obtained. Is higher than the peak frequency of the radiation characteristics of the second and third IDT electrodes 103 and 104.

  However, as is clear from FIG. 2, the peak frequency of the radiation characteristics of the first IDT electrode 102 is changed to the peak frequency of the radiation characteristics of the second and third IDT electrodes 103 and 104 by satisfying the relationship of P1> P2. Can be matched. Specifically, when the relationship of P1 = P2 is set, the peak frequency of the radiation characteristic is shifted by about 0.9%. However, by setting the relationship of P1> P2, it is about 0.5% to preferably 0.1%. It is possible to match the deviation of the peak frequency of the radiation characteristic. That is, among the IDT electrodes constituting the surface acoustic wave filter of FIG. 1, the pitch of the electrode finger having the larger number of electrode fingers of the IDT electrode is larger than the pitch of the electrode finger having the smaller number of electrode fingers. By adjusting in this way, the radiation characteristics of these IDT electrodes can be matched.

  With the above configuration, it is possible to realize a surface acoustic wave filter having a wide band and steep attenuation characteristics.

  In the present embodiment, the input terminal IN is described as being an unbalanced terminal, but the present invention is not limited to this, and a balanced terminal may be used.

  Furthermore, although the output terminal OUT has been described as an unbalanced type terminal in the present embodiment, the present invention is not limited to this and may be a balanced type terminal.

  Further, in the present embodiment, the second and third IDT electrodes 103 and 104 are connected to the input terminal IN, and the first IDT electrode 102 is connected to the output terminal OUT. Not limited to this, the second and third IDT electrodes 103 and 104 may be connected to the output terminal OUT, and the first IDT electrode 102 may be connected to the input terminal IN.

  Furthermore, in the present embodiment, the number of electrode fingers of the second IDT electrode and the third IDT electrode is the same, but if they are different, the radiation characteristics of the IDT electrodes are the same. You just have to adjust it.

(Second Embodiment)
Next, a second embodiment will be described.

  FIG. 3 shows a schematic diagram of the surface acoustic wave filter of the present embodiment.

  In FIG. 3, a first filter track 307 is formed on a piezoelectric substrate 301 by first, second, and third IDT electrodes 302, 303, and 304 and first and second reflector electrodes 305 and 306. The That is, the second IDT electrode 303 and the third IDT electrode 304 are disposed on both sides of the first IDT electrode 302, and the side of the second IDT electrode 303 on which the first IDT electrode 302 is disposed. A reflector electrode 305 is disposed on the opposite side, and a reflector electrode 306 is disposed on the opposite side of the third IDT electrode 304 from the side on which the first IDT electrode 302 is disposed.

  The fourth, fifth, and sixth IDT electrodes 308, 309, and 310 and the first and second reflector electrodes 311 and 312 constitute a second filter track 313. That is, the fifth IDT electrode 309 and the sixth IDT electrode 310 are arranged on both sides of the fourth IDT electrode 308, and the side of the fifth IDT electrode 309 on which the fourth IDT electrode 308 is arranged is A reflector electrode 311 is disposed on the opposite side, and a reflector electrode 312 is disposed on the opposite side of the sixth IDT electrode 310 from the side on which the fourth IDT electrode 308 is disposed.

  The upper electrode finger of the first IDT electrode 302 is connected to the input terminal IN, and the lower electrode finger of the second IDT electrode and the third IDT electrode 304 are the fifth IDT electrode 309 and the sixth IDT, respectively. It is connected to the electrode finger on the upper side of the electrode 310. The upper electrode finger of the fourth IDT electrode 308 is connected to one output terminal OUT1, and the lower electrode finger of the fourth IDT electrode 308 is connected to the other output terminal OUT2.

  The first IDT electrode 302 and the fourth IDT electrode 308 have the same number of electrode fingers, the second IDT electrode 303, the third IDT electrode 304, the fifth IDT electrode 309, and the sixth IDT electrode 308. The IDT electrodes 310 have the same number of electrode fingers.

  The number of electrode fingers of the first IDT electrode 302 and the fourth IDT electrode 308 is the second IDT electrode 303, the third IDT electrode 304, the fifth IDT electrode 309, and the sixth IDT electrode. The number of electrodes is greater than 310. Further, when the pitch of the first and fourth IDT electrodes 302 and 308 is P1, and the pitch of the second, third, fifth, and sixth IDT electrodes 303, 304, 309, and 310 is P2, the relationship of P1> P2 is satisfied. There is. The metallization ratio of each IDT electrode is the same value. Thus, a two-stage longitudinal mode type surface acoustic wave filter is formed.

  Next, the operation of this embodiment will be described.

  FIG. 8A shows the radiation characteristics of the first and second IDT electrodes 302 and 303. 1801 is the radiation characteristic of the first IDT electrode 302, and 1802 is the radiation characteristic of the second IDT electrode 303. As is clear from FIG. 8, the peak frequency of the radiation characteristic 1801 and the peak frequency of the radiation characteristic 1802 are the same. As described above, by setting the relationship of P1> P2 as in the first embodiment, the peak frequency fp of the radiation characteristic can be matched between the first IDT electrode 302 and the second IDT electrode 303. Similarly, by setting the relationship of P1> P2, the peak frequency fp of the radiation characteristic of the first IDT electrode 302 can be matched with the peak frequency fp of the radiation characteristic of the third IDT electrode 304. Further, by setting P1> P2, the peak frequency fp of the radiation characteristics of the fourth IDT electrode 308 can be matched with the peak frequency fp of the radiation characteristics of the fifth and sixth IDT electrodes 309 and 310. .

  FIG. 8B shows pass characteristics of the surface acoustic wave filter according to the present embodiment. Both 1803a and 1803b are pass characteristics of the surface acoustic wave filter of the present embodiment. 1803a shows the surface acoustic wave filter of the present embodiment in a wide gain range from about 0 dB to 90 dB, and 1803b shows the center portion of the pass characteristics of the surface acoustic wave filter of the present embodiment. Attention is paid to a narrow gain range of about 0 dB to 10 dB. fp is a peak frequency of the radiation characteristic of the IDT electrode, and is a pass characteristic of the surface acoustic wave filter when the peak frequency fp of the radiation characteristic of each IDT electrode is matched with the left side of the pass band, that is, the lowest frequency of the pass band. .

  On the other hand, FIG. 9A shows radiation characteristics of each IDT electrode of the conventional surface acoustic wave filter. In FIG. 9A, reference numeral 1901 denotes the radiation characteristics of the first IDT electrode 302 and the fourth IDT electrode 308. Reference numeral 1902 denotes radiation characteristics of the second IDT electrode 303, the third IDT electrode 304, the fifth IDT electrode 309, and the sixth IDT electrode 310. That is, the peak frequency fp1 of the radiation characteristics of the first IDT electrode 302 and the fourth IDT electrode 308 of the conventional surface acoustic wave filter, the second IDT electrode 303, the third IDT electrode 304, and the fifth IDT electrode 309. , And the peak frequency fp2 of the radiation characteristic of the sixth IDT electrode 310 does not match.

  FIG. 9B shows the pass characteristics of such a surface acoustic wave filter. Both 1903a and 1903b are pass characteristics of a conventional surface acoustic wave filter. 1903a illustrates a conventional surface acoustic wave filter in a wide gain range from about 0 dB to about 90 dB, and 1903b focuses on the central portion of the pass characteristics of the conventional surface acoustic wave filter from 0 dB. This is illustrated in a narrow gain range of about 10 dB.

  The pass characteristic 1803b shown in FIG. 8B has a wider band than the pass characteristic 1903b shown in FIG. That is, the loss at the end of the band is also improved.

  Thus, by making the peak frequency of the radiation characteristic of each IDT electrode coincide with each other, a surface acoustic wave filter having a wider band characteristic can be realized.

  As described above, according to the present embodiment, a surface acoustic wave filter having a wide band and a steep attenuation characteristic can be realized.

  In the present embodiment, the output terminal is a balanced type, but the effect of the present invention can be similarly obtained even if one of the upper and lower electrode fingers of the fourth IDT electrode is grounded to be an unbalanced type.

(Third embodiment)
Next, a third embodiment will be described.

  FIG. 6 shows a schematic diagram of a surface acoustic wave filter according to the present embodiment. In FIG. 6, the surface acoustic wave filter is configured by first, second, and third IDT electrodes 602, 603, and 604 and first and second reflector electrodes 605 and 606 on a piezoelectric substrate 601. .

  That is, the second IDT electrode 603 and the third IDT electrode 604 are arranged on both sides of the first IDT electrode 602, and is opposite to the side of the second IDT electrode 603 where the first IDT electrode 602 is arranged. A reflector electrode 605 is disposed on the side, and a reflector electrode 606 is disposed on the opposite side of the third IDT electrode 604 from the side on which the first IDT electrode 602 is disposed.

  The upper electrode fingers of the second and third IDT electrodes 603 and 604 are respectively connected to the input terminal IN, and the lower electrode fingers of the second and third IDT electrodes 603 and 604 are grounded. The lower electrode finger of the first IDT electrode 602 is connected to the output terminal OUT, and the upper electrode finger of the first IDT electrode 602 is grounded.

  The number of electrode fingers of the first IDT electrode 602 is larger than the number of electrode fingers of the second and third IDT electrodes 603 and 604, and the number of electrode fingers of the second IDT electrode 603 and the electrode of the third IDT electrode 604 The number of fingers is the same.

  Further, when the pitch of the first IDT electrode 602 is P1, and the pitch of the second and third IDT electrodes 603 and 604 is P2, there is a relationship of P1> P2.

  In the elastic surface filter of the present embodiment, the metallization ratio of the first IDT electrode 602 and the metallization ratios of the second and third IDT electrodes 603 and 604 have different values.

  Next, the operation of this embodiment will be described.

  FIG. 2 shows the relationship between the number of electrode fingers of the first IDT electrode 602 and the metallization ratio and the peak frequency of the radiation characteristic of the first IDT electrode 602. That is, FIG. 2 is a graph in which the peak frequency of the radiation characteristic of the first IDT electrode 602 is measured and plotted when the number of electrode fingers and the electrode finger pitch of the first IDT electrode 602 take certain values. .

  As apparent from FIG. 2, the peak frequency of the radiation characteristic of the first IDT electrode 602 increases as the number of electrode fingers of the first IDT electrode 602 increases. Further, as the metallization ratio of the first IDT electrode 602 increases, the peak frequency of the radiation characteristic of the first IDT electrode 602 decreases. Thus, when the electrode film thickness of the IDT electrode 602 is substantially the same, the peak frequency of the radiation characteristic of the first IDT electrode 602 increases as the number of electrode fingers increases and the metallization ratio decreases. The second and third IDT electrodes 603 and 604 have the same tendency as the tendency seen with the first IDT electrode 602.

  As described above, the number of electrode fingers of the first IDT electrode 602 is larger than the number of electrode fingers of the second and third IDT electrodes 603 and 604. Accordingly, as is apparent from FIG. 2, when the melaization ratio of the first IDT electrode 602 is the same as the metallization ratio of the second and third IDT electrodes 603 and 604, the radiation of the first IDT electrode 602 is obtained. The peak frequency of the characteristic is higher than the peak frequency of the radiation characteristic of the second and third IDT electrodes 603 and 604.

  However, as described above, the relationship of P1> P2 is satisfied, and the metallization ratio of the first IDT electrode 602 and the second and third IDT electrodes 603 and 604 are different from each other. By doing so, the peak frequency of the radiation characteristics of the first IDT electrode 602 can be matched with the peak frequency of the radiation characteristics of the second and third IDT electrodes 603 and 604.

  As described above, in this embodiment, the peak frequency of the radiation characteristics of the first IDT electrode 602 and the peak frequency of the radiation characteristics of the second and third IDT electrodes 603 and 604 are determined by the pitch of each IDT electrode and each IDT. It can be matched by adjusting the metallization ratio of the electrodes. By adjusting the metallization ratio of each IDT electrode, that is, by adjusting the excitation intensity and reflection amount of the surface acoustic wave of each IDT electrode, the degree of freedom in design is improved as compared with the first embodiment.

  In the present embodiment, the pitch is adjusted by making the relationship of P1> P2. However, the present invention is not limited to this, and the pitch may be made by the relationship of P1 = P2, and may be adjusted by the metallization ratio.

  With the above configuration, it is possible to realize a surface acoustic wave filter having a wide band and steep attenuation characteristics.

  In the present embodiment, the input terminal IN is described as being an unbalanced terminal, but the present invention is not limited to this, and a balanced terminal may be used.

  Furthermore, although the output terminal OUT has been described as an unbalanced type terminal in the present embodiment, the present invention is not limited to this and may be a balanced type terminal.

  Further, in the present embodiment, the second and third IDT electrodes 603 and 604 have been described as being connected to the input terminal IN, and the first IDT electrode 602 has been described as being connected to the output terminal OUT. Not limited to this, the second and third IDT electrodes 603 and 604 may be connected to the output terminal OUT, and the first IDT electrode 602 may be connected to the input terminal IN.

(Fourth embodiment)
Next, a fourth embodiment will be described.

  FIG. 7 shows a schematic diagram of the surface acoustic wave filter of the present embodiment.

  In FIG. 7, a first filter track 707 is formed on a piezoelectric substrate 701 by first, second, and third IDT electrodes 702, 703, and 704 and first and second reflector electrodes 705 and 706. The That is, the second IDT electrode 703 and the third IDT electrode 704 are arranged on both sides of the first IDT electrode 702, and the side of the second IDT electrode 703 on which the first IDT electrode 702 is arranged; A reflector electrode 705 is disposed on the opposite side, and a reflector electrode 706 is disposed on the opposite side of the third IDT electrode 704 from the side on which the first IDT electrode 702 is disposed.

  The fourth, fifth, and sixth IDT electrodes 708, 709, and 710 and the first and second reflector electrodes 711 and 712 form a second filter track 713. That is, the fifth IDT electrode 709 and the sixth IDT electrode 710 are arranged on both sides of the fourth IDT electrode 708. What is the side of the fifth IDT electrode 709 on which the fourth IDT electrode 708 is arranged? A reflector electrode 711 is disposed on the opposite side, and a reflector electrode 712 is disposed on the opposite side of the sixth IDT electrode 710 from the side on which the fourth IDT electrode 708 is disposed.

  The upper electrode fingers of the first IDT electrode 702 are connected to the input terminal IN, and the lower electrode fingers of the second IDT electrode and the third IDT electrode 704 are the fifth IDT electrode 709 and the sixth IDT, respectively. Connected to the upper electrode finger of the electrode 710. The upper electrode finger of the fourth IDT electrode 708 is connected to one output terminal OUT1, and the lower electrode finger of the fourth IDT electrode 708 is connected to the other output terminal OUT2.

  The first IDT electrode 702 and the fourth IDT electrode 708 have the same number of electrode fingers, and the second IDT electrode 703, the third IDT electrode 704, the fifth IDT electrode 709, and the sixth The IDT electrodes 710 have the same number of electrode fingers.

  The number of electrode fingers of the first IDT electrode 702 and the fourth IDT electrode 708 is the second IDT electrode 703, the third IDT electrode 704, the fifth IDT electrode 709, and the sixth IDT electrode. The number of electrode fingers is more than 710. Further, when the pitch of the first IDT electrode 702 is P11 and the pitch of the second and third IDT electrodes 703 and 704 is P12, the relation of P11> P12 is established. Further, when the pitch of the fourth IDT electrode 708 is P21 and the pitch of the fifth and sixth IDT electrodes 709 and 710 is P22, the relation of P21> P22 is established.

  In the first filter track 707, the metallization ratio η11 of the first IDT electrode 702 is expressed by the following formula 2.

(Equation 2)
η11 = L11 / (L11 + S11)
Here, L11 is the width of the electrode finger of the first IDT electrode 702, and S11 is the distance from the electrode finger having the first IDT electrode 702 to the next electrode finger.

  The metallization ratio η12 of the second and third IDT electrodes 703 and 704 is expressed by the following equation (3).

(Equation 3)
η12 = L12 / (L12 + S12)
Here, L12 is the width of the electrode fingers of the second and third IDT electrodes 703 and 704, and S12 is the distance from the electrode finger with the second and third IDT electrodes 703 and 704 to the next electrode finger. It is.

  On the other hand, in the second filter track 708, the metallization ratio η21 of the fourth IDT electrode 708 is expressed by the following equation (4).

(Equation 4)
η21 = L21 / (L21 + S21)
Here, L21 is the width of the electrode finger of the fourth IDT electrode 708, and S21 is the distance from the electrode finger having the fourth IDT electrode 708 to the next electrode finger.

  The metallization ratio η22 of the fifth and sixth IDT electrodes 709 and 710 is expressed by the following equation (5).

(Equation 5)
η22 = L22 / (L22 + S22)
Here, L22 is the width of the electrode fingers of the fifth and sixth IDT electrodes, and S22 is from the electrode finger having the metallization ratio η22 of the fifth and sixth electrode fingers 709 and 710 to the next electrode finger. Is the interval.

  In the present embodiment, η11 and η12 are different from each other, and η21 and η22 are different from each other.

  Thus, a two-stage longitudinal mode type surface acoustic wave filter is formed.

  Next, the operation of this embodiment will be described.

  In the surface acoustic wave filter of the present embodiment, as described in detail in the above embodiment, the relationship of P11> P12 is established, and η11 and η12 are adjusted to have different values. The peak frequency fp of the radiation characteristic is matched between the first IDT electrode 702 and the second and third IDT electrodes 703 and 704.

  Further, by adjusting P21> P22 and adjusting η21 and η22 to have different values, the peak frequency fp of the radiation characteristic is set to the fourth IDT electrode 708 and the fifth and sixth IDTs. The electrodes 709 and 710 are matched.

  Accordingly, as in the above embodiment, a surface acoustic wave filter having a wide band and steep attenuation characteristics can be realized.

  With the above configuration, it is possible to realize a surface acoustic wave filter having a wide band and steep attenuation characteristics.

  In this embodiment, the relationship of P11> P12 is set, and η11 and η12 are adjusted to be different values, and the relationship of P21> P22 is set, and η21 and η22 are set to different values. However, the present invention is not limited to this, and it is also possible to adjust only by the relationship of P11> P12 and P21> P22. It is also possible to adjust only by metallization as P11 = P12 and P21 = P22.

  In the present embodiment, the output terminal is a balanced type, but the effect of the present invention can be obtained in the same way even if either one of the upper and lower electrode fingers of the fourth IDT electrode 708 is grounded to be an unbalanced type. .

(Fifth embodiment)
Next, a fifth embodiment will be described.

  FIG. 10 shows a schematic diagram of a surface acoustic wave filter according to the present embodiment.

  In FIG. 10, the surface acoustic wave filter is configured by first, second, and third IDT electrodes 1002, 1003, and 1004 and first and second reflector electrodes 1005 and 1006 on a piezoelectric substrate 1001. .

  In other words, the second IDT electrode 1003 and the third IDT electrode 1004 are arranged on both sides of the first IDT electrode 1002, and the second IDT electrode 1003 is opposite to the side where the first IDT electrode 1002 is arranged. The reflector electrode 1005 is disposed on the side, and the reflector electrode 1006 is disposed on the opposite side of the third IDT electrode 1004 from the side on which the first IDT electrode 1002 is disposed. As described above, the first, second, and third IDT electrodes 1002, 1003, and 1004 and the first and second reflector electrodes 1005 and 1006 are arranged along the direction in which the surface acoustic wave propagates.

  The upper electrode fingers of the second and third IDT electrodes 1003 and 1004 are connected to the input terminal IN, and the lower electrode fingers of the second and third IDT electrodes 1003 and 1004 are grounded. The lower electrode finger of the first IDT electrode 1002 is connected to the output terminal OUT, and the upper electrode finger of the first IDT electrode 1002 is grounded.

  The number of electrode fingers of the first IDT electrode 1002 is larger than the number of electrode fingers of the second and third IDT electrodes 1003 and 1004, and the number of electrode fingers of the second IDT electrode 1003 and the electrode of the third IDT electrode 1004 The number of fingers is the same.

  Further, when the pitch of the region indicated by 1a of the first IDT electrode 1002 is P1, P is a length of ½ wavelength. If the pitch of the region indicated by 1b is P1 ', P' is narrower than ½ wavelength. The number of the regions 1a having the pitch P is larger than that of the regions 1b having the pitch P '. Therefore, in the first IDT electrode 1002, the region indicated by 1a is the main excitation region.

  When the pitch of the region indicated by 2a of the second IDT electrode 1003 is P2, P2 has a length of ½ wavelength. If the pitch of the region indicated by 2b is P2 ', P2' is narrower than ½ wavelength. The number of the regions 2a having the pitch P is larger than that of the regions 2b having the pitch P '. Therefore, in the second IDT electrode 1003, the region indicated by 2a is the main excitation region.

  Further, the pitch of the region indicated by 3a of the third IDT electrode 1004 is P2, and P is a length of 1/2 wavelength. The pitch of the region indicated by 3b is P2 ', and P2' has a length narrower than a half wavelength. The number of the regions 3a having the pitch P2 is larger than that of the regions 3b having the pitch P2 '. Therefore, in the third IDT electrode 1004, the region indicated by 3a is the main excitation region.

  As described above, each of the first IDT electrode 1002, the second IDT electrode 1003, and the third IDT electrode 1004 is the same IDT electrode and has different electrode finger pitches.

  Further, when the relationship between the pitch P1 and the pitch P2 satisfies P1> P2, an effect equivalent to that of the first embodiment can be obtained.

  When the relationship between the pitch P1 and the pitch P2 satisfies P1> P2, the relationship between the pitch P1 ′ and the pitch P2 ′ may satisfy P1 ′> P2 ′, and P1 ′ = P2 You don't mind being satisfied. In this case, discontinuity between adjacent electrode fingers can be reduced and deterioration of insertion loss can be suppressed when P1 '> P2' is satisfied, compared to when P1 '= P2' is satisfied.

  In the present embodiment, P1> P2 is described as being satisfied. In FIG. 10, P1 and P2 are adjusted so that the peak frequencies of the radiation characteristics of the 1a region, the 2a region, and the 3a region match. It doesn't matter. Further, the pitches P1, P1 ′, P2, and P2 ′ are adjusted so that the radiation characteristics of the first IDT electrode 1002, the second IDT electrode 1003, and the third IDT electrode 1004 are matched. It is desirable. In these cases, the pitches P2 and P2 'of the second and third IDT electrodes 1003 and 1004 are not necessarily the same.

  As described above, when the pitch of the electrode fingers of one IDT electrode is different, the above embodiments can be applied based on the pitch of the main excitation electrode in the main excitation region.

  With the above configuration, it is possible to realize a surface acoustic wave filter having a wide band and steep attenuation characteristics.

  In the present embodiment, the input terminal IN is described as being an unbalanced terminal, but the present invention is not limited to this, and a balanced terminal may be used.

  Furthermore, although the output terminal OUT has been described as an unbalanced type terminal in the present embodiment, the present invention is not limited to this and may be a balanced type terminal.

  Further, in the present embodiment, the second and third IDT electrodes 1003 and 1004 are connected to the input terminal IN, and the first IDT electrode 1002 is connected to the output terminal OUT. Not limited to this, the second and third IDT electrodes 1003 and 1004 may be connected to the output terminal OUT, and the first IDT electrode 1002 may be connected to the input terminal IN.

(Sixth embodiment)
Next, a sixth embodiment will be described.

  FIG. 11 shows a schematic diagram of a surface acoustic wave filter according to the present embodiment.

  In FIG. 11, the surface acoustic wave filter includes first, second, third, fourth, and fifth IDT electrodes 1102, 1103, 1104, 1105, and 1106 and first and second reflections on the piezoelectric substrate 101. And electrode electrodes 1107 and 1108.

  That is, the second IDT electrode 1103 and the third IDT electrode 1104 are arranged on both sides of the first IDT electrode 1102, and the fifth IDT electrode 1104 is opposite to the first IDT electrode 1102 side on the fifth side. IDT electrode 1106 is disposed, and the fourth IDT electrode 1105 is disposed on the opposite side of the second IDT electrode 1103 from the first IDT electrode 1102 side, and the fourth IDT electrode 1105 is disposed outside the fourth IDT electrode 1105. 1 reflector electrode 1107 is disposed, and the second reflector electrode 1108 is disposed outside the fifth IDT electrode 1106.

  Thus, the first, second, third, fourth, and fifth IDT electrodes 1102, 1103, 1104, 1105, 1106 and the first and second reflector electrodes 1107, 1108 are surface acoustic waves. Are arranged along the direction in which the light propagates.

  The lower electrode fingers of the second and third IDT electrodes 1103 and 1104 are connected to the output terminal OUT, and the upper electrode fingers of the second and third IDT electrodes 103 and 104 are grounded. Further, the upper electrode fingers of the first, fourth, and fifth IDT electrodes 1102, 1105, and 1106 are connected to the input terminal IN, and the first, fourth, and fifth IDT electrodes 1102, 1105, and 1106 are connected. The lower electrode finger is grounded.

  The number of electrode fingers of the first IDT electrode 1102 is larger than the number of electrode fingers of the second and third IDT electrodes 1103 and 1104, and the number of electrode fingers of the second IDT electrode 1103 and the electrode of the third IDT electrode 1104 The number of fingers is the same. In addition, the number of electrode fingers of the fourth and fifth IDT electrodes 1105 and 1106 is smaller than the number of the second IDT electrode 1103 and the third IDT electrode 1104, and the fourth IDT electrode 1105 and the fifth IDT electrode The number of electrode fingers 1106 is the same.

  Further, when the pitch of the first IDT electrode 1102 is P1, the pitch of the second and third IDT electrodes 1103 and 1104 is P2, and the pitch of the fourth and fifth IDT electrodes 1105 and 1106 is P3, P1> P2 > P3. That is, among the IDT electrodes constituting the surface acoustic wave filter of the present embodiment, the pitch of the electrode fingers having the larger number of electrode fingers of the IDT electrode is the pitch of the electrode finger having the smaller number of electrode fingers. There is a relationship of greater than.

  Further, the metallization ratio η indicating the ratio of the width of the electrode fingers within one wavelength is the same value for the first, second, third, fourth, and fifth IDT electrodes 1102, 1103, 1104, 1105, and 1106. I take the.

  Here, the metallization ratio η is expressed by Equation 1 described in the first embodiment.

  Next, the operation of this embodiment will be described.

  As described in the first embodiment, the peak frequency of the radiation characteristics of the first IDT electrode 1102 increases as the number of electrode fingers of the first IDT electrode 1102 increases. Further, as the metallization η of the first IDT electrode 1102 increases, the peak frequency of the radiation characteristic of the first IDT electrode 102 decreases. Thus, when the electrode film thickness of the first IDT electrode 1102 is the same, the peak frequency of the radiation characteristic of the first IDT electrode 1102 increases as the number of electrode fingers increases and the metallization η decreases. . The second, third, fourth, and fifth IDT electrodes 1103, 1104, 1105, and 1106 have the same tendency as that seen with the first IDT electrode 1102.

  Accordingly, as described above, the pitch of the first IDT electrode 1102 is P1, the pitch of the second and third IDT electrodes 1103 and 1104 is P2, and the pitch of the fourth and fifth IDT electrodes 1105 and 1106 is P3. Since the relationship of P1> P2> P3 holds, the peak frequencies of the radiation characteristics of the first, second, third, fourth, and fifth IDT electrodes 1102, 1103, 1104, 1105, and 1106 can be matched. I can do it.

  That is, since the peak frequencies of the radiation characteristics of the first, second, third, fourth, and fifth IDT electrodes 1102, 1103, 1104, 1105, and 1106 match, the characteristics of the surface acoustic wave filter of the present embodiment Has a broader attenuation characteristic.

  That is, with the above configuration, a surface acoustic wave filter having a wide band and steep attenuation characteristics can be realized.

  In the present embodiment, the input terminal IN is described as being an unbalanced terminal, but the present invention is not limited to this, and a balanced terminal may be used.

  Furthermore, although the output terminal OUT has been described as an unbalanced type terminal in the present embodiment, the present invention is not limited to this and may be a balanced type terminal.

  The relationship between the numbers of the first to fifth IDT electrodes is not limited to this, and is optimized according to the filter characteristics.

  Furthermore, in this embodiment, the second and third IDT electrodes 1103 and 1104 are connected to the output terminal OUT, and the first, fourth and fifth IDT electrodes 1102, 1105 and 1106 are connected to the input terminal IN. Although described as being connected, the present invention is not limited thereto, and the second and third IDT electrodes 1103 and 1104 are connected to the input terminal IN, and the first, fourth and fifth IDT electrodes 102, 1105 and 1106 are connected. May be connected to the output terminal OUT.

  In the present embodiment, the case of adjusting the pitch of the electrode fingers of each IDT electrode and the case of adjusting the pitch and metallization ratio of each IDT electrode have been described. The peak frequency of the radiation characteristic of the IDT electrode can be matched.

  That is, it has been found that the peak frequency of the radiation characteristics of the IDT electrode decreases as the film thickness of the IDT electrode increases. Therefore, by adjusting the film thickness of the first IDT electrode and the film thickness of the second and third IDT electrodes, the peak frequency of the radiation characteristic of each IDT electrode can be adjusted to be the same.

  It has also been found that the peak frequency of the radiation characteristics of the IDT electrode changes by changing the material of the IDT electrode. Therefore, by adjusting the material of the first IDT electrode and the material of the second and third IDT electrodes, the peak frequency of the radiation characteristic of each IDT electrode can be adjusted to be the same.

  It has also been found that the peak frequency of the radiation characteristics of the IDT electrode decreases as the metallization ratio of the IDT electrode increases. Therefore, the peak frequency of the radiation characteristic of each IDT electrode can be adjusted to be the same by making the metallization ratio of the first IDT electrode different from the metallization ratio of the second and third IDT electrodes. .

  Moreover, it can also adjust so that the peak frequency of the radiation | emission characteristic of each IDT electrode may correspond by combining the method demonstrated above arbitrarily.

  In the first to fourth embodiments, the number of electrode fingers of the second and third IDT electrodes is the same. However, the present invention is not limited to this, and the second and third IDT electrodes are not limited thereto. Even if the number of electrode fingers is not the same, if the electrode finger pitch is adjusted so that the peak frequency of the radiation characteristic is the same, the same effects as those of the first to fourth embodiments can be obtained. I can do it.

  Furthermore, a communication device using the surface acoustic wave filter of the present invention as a part of a transmission circuit or a reception circuit also belongs to the present invention. Examples of such communication devices include a mobile phone terminal, a base station of a mobile phone terminal, a car phone terminal, a PHS, and a radar device.

  Further, a surface acoustic wave filter manufacturing method for manufacturing a surface acoustic wave filter including a piezoelectric substrate, an input IDT electrode disposed on the piezoelectric substrate, and an output IDT electrode disposed on the piezoelectric substrate. In addition, a surface acoustic wave filter manufacturing method in which the peak frequency of the radiation characteristic of the input IDT electrode is substantially equal to the peak frequency of the radiation characteristic of the output IDT electrode also belongs to the present invention.

  Further, a surface acoustic wave filter for manufacturing a surface acoustic wave filter including a piezoelectric substrate, an input IDT electrode disposed on the piezoelectric substrate, and an output IDT electrode disposed on the piezoelectric substrate. A method of manufacturing a surface acoustic wave filter, wherein the pitch of electrode fingers of the input IDT electrode is different from the pitch of electrode fingers of the output IDT electrode, also belongs to the present invention.

  Further, the output IDT electrode of the present invention is the first IDT electrode of the surface acoustic wave filter described in FIGS. 1 and 6 in the present embodiment, or the first IDT electrode of the surface acoustic wave filter described in FIGS. The present invention is not limited to the fourth, fifth, and sixth IDT filters. Further, the input IDT electrode of the present invention includes the second and third IDT electrodes of the surface acoustic wave filter described in FIGS. 1 and 6 and the surface acoustic wave described in FIGS. The filter is not limited to the first, second and third IDT electrodes.

  Further, in the present embodiment, the case where the input IDT electrode and the output IDT electrode are composed of three IDT electrodes and the case where the input IDT electrode is composed of five IDT electrodes has been described. The input IDT electrode and the output IDT electrode may be composed of two IDT electrodes, four IDT electrodes, seven IDT electrodes, or more IDT electrodes.

  In the present embodiment, the number of electrode fingers of the second IDT electrode and the third IDT electrode is the same, and the number of electrode fingers of the fourth IDT electrode and the fifth IDT electrode is the same. Although they are the same, if they are different, they may be adjusted so that the radiation characteristics of the respective IDT electrodes match.

  The surface acoustic wave filter according to the present invention has an effect of having a steep attenuation characteristic in a wider band and out of the band, and is useful for a longitudinal mode type surface acoustic wave filter and the like.

1 is a configuration diagram of a surface acoustic wave filter according to a first embodiment of the present invention. Figure showing the relationship between the peak frequency of radiation characteristics and the number of electrode fingers Configuration diagram of a surface acoustic wave filter according to a second embodiment of the present invention Radiation characteristic diagram of IDT electrode in the first and third embodiments of the present invention Passage characteristic diagram of surface acoustic wave filter in first and third embodiments of the present invention Configuration diagram of a surface acoustic wave filter according to a third embodiment of the present invention Configuration diagram of a surface acoustic wave filter in a fourth embodiment of the present invention (A) Diagram of radiation characteristic of IDT electrode in second embodiment of the present invention (b) Passage characteristic diagram of surface acoustic wave filter in second embodiment of the present invention (A) Radiation characteristic diagram of IDT electrode in conventional surface acoustic wave filter whose IDT electrode radiation characteristic peak frequencies do not match (b) Passage characteristic diagram of surface acoustic wave filter of (a) Configuration diagram of a surface acoustic wave filter in a fifth embodiment of the present invention Configuration diagram of a surface acoustic wave filter according to a sixth embodiment of the present invention Configuration of conventional surface acoustic wave filter Configuration of conventional surface acoustic wave filter

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Piezoelectric substrate 102 1st IDT electrode 103 2nd IDT electrode 104 3rd IDT electrode 105 Reflector electrode 106 Reflector electrode 301 Piezoelectric substrate 302 1st IDT electrode 303 2nd IDT electrode 304 3rd IDT electrode 305 reflector electrode 306 reflector electrode 307 filter track 308 fourth IDT electrode 309 fifth IDT electrode 310 sixth IDT electrode 311 reflector electrode 312 reflector electrode 313 filter track 601 piezoelectric substrate 602 first IDT electrode 603 Second IDT electrode 604 Third IDT electrode 605 Reflector electrode 606 Reflector electrode 701 Piezoelectric substrate 702 First IDT electrode 703 Second IDT electrode 704 Third IDT electrode 705 Reflector electrode 706 Reflector electrode 707 Filter Track 708 4th IDT electrodes 709 a 5 IDT electrode 710 a 6 IDT electrode 711 reflector electrode 712 reflector electrode 713 filter track of

Claims (3)

A piezoelectric substrate;
Wherein arranged on a piezoelectric substrate, at least one input IDT electrode,
Wherein arranged on a piezoelectric substrate, and at least one output IDT electrodes,
A longitudinal mode surface acoustic wave filter in which the input IDT electrode and the output IDT electrode are disposed along one propagation path of the surface acoustic wave;
By comparing the number of electrode fingers constituting the input IDT electrode with the number of electrode fingers constituting the output IDT electrode, the metallization ratio of the IDT electrode having the larger number of electrode fingers is determined. An elastic surface that is larger than the metallization ratio of the IDT electrode with the smaller number, and the difference between the peak frequency of the radiation characteristic of the input IDT electrode and the peak frequency of the radiation characteristic of the output IDT electrode is less than 0.5% Wave filter. 2. The surface acoustic wave filter according to claim 1 , comprising one input IDT electrode and two output IDT electrodes . 2. The surface acoustic wave filter according to claim 1 , comprising two input IDT electrodes and one output IDT electrode .

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