JP2004350333A - Polarized saw filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To sufficiently enlarge an attenuation based on a change of a formed attenuation pole not only in a high frequency side attenuation band but also in a low frequency side attenuation band in spite of a miniaturized configuration. <P>SOLUTION: The polarized SAW filter using a passband ladder type SAW filter using a SAW resonator, has a serial arm SAW resonator and a second parallel arm SAW resonator, a two-terminal-pair circuit is serially connected to the passband ladder type SAW filter, the two-terminal-pair circuit is composed of three inductors provided between the passband ladder type SAW filter which is provided on the surface of a piezoelectric substrate, and a common terminal disposed in the area surrounding the passband ladder type SAW filter on the surface side of the piezoelectric substrate, and the common terminal is provided on the side of a package closest to the other terminals of first and second parallel arm SAW resonators. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a polar SAW filter, and is suitably applied to, for example, a transmission or reception filter used in a small mobile communication device such as a mobile phone.

  Documents describing this type of polarized SAW filter include the following Patent Documents 1 and 2 and Non-Patent Document 1.

  2. Description of the Related Art In recent years, small and lightweight mobile communication device terminals such as mobile phones have been rapidly developed. Along with this, there has been a demand for smaller and higher-performance components to be used, and there has been a demand for the development of RF components (high-frequency components) based on surface acoustic wave (SAW) elements.

  FIG. 2 shows a basic circuit configuration of the ladder-type SAW filter described in Non-Patent Document 1.

  Since the ladder-type SAW filter of FIG. 2 is a device that greatly contributes to downsizing of the RF unit, its practical use is strongly demanded. An RF device such as a SAW duplexer using the ladder-type SAW filter has already been developed and partly put to practical use.

  FIG. 3 shows the characteristics (attenuation characteristics (1) and Return Loss characteristics (2)) of the 800 (MHz) band ladder type SAW filter of FIG. The filter characteristics in FIG. 3 correspond to the case where the cross length of the serial arm resonator is 100 μm and the logarithm is 100, and the cross length of the parallel arm resonator is 70 μm and the logarithm is 70.

  FIG. 4 also shows the characteristics of the series arm resonator and the parallel arm resonator of FIG. 3 (that is, the imaginary part characteristic of the series arm resonator is jx, the imaginary part characteristic of the parallel arm resonator is jb, The real part characteristic indicates rs, and the imaginary part characteristic of the parallel arm resonator indicates rp).

  The attenuation pole in the high-frequency side attenuation band of the pass band (around 863 MHz to around 911 MHz) shown in FIG. 3 is determined by the infinite point (that is, about 42 dB) frequency (that is, around 919 MHz) of the series arm resonator circuit. It can be seen from a comparison between FIG. 4 and FIG. 3 that the parallel arm resonator circuit generates the attenuation pole in the lower attenuation band at zero frequency (that is, near 855 MHz).

  FIG. 3 also shows the real part of the circuit of each SAW resonator when Q = 500.

  As can be seen from the characteristics of FIG. 3, the attenuation pole of the ladder type SAW filter of FIG. 2 has one attenuation band in the lower attenuation band of the pass band and one attenuation pole in the higher attenuation band. It is known that the characteristics of the attenuation band and the characteristics of the high-frequency side attenuation band have substantially the same characteristics.

  However, with the rapid increase in demand for mobile communication device terminals, the transmission band and the mobile communication system using the 800 (MHz) band frequency band and the mobile communication system using the 2 (GHz) band frequency band are both increased. The reception band is set wide, and the interval between the transmission band and the reception band is set narrow.

  As an example, when the transmission band is 824 to 849 MHz and the reception band is 869 to 894 MHz as in the CDMA (code division multiple access) system in the United States, the reception band is in the higher attenuation band of the transmission band. Position, the attenuation in the lower attenuation band of the transmission band does not have to be so large, but if the attenuation in the higher attenuation band is not large enough, the mobile communication equipment terminal transmits. There is a high possibility that the radio wave leaks into its own reception band and deteriorates the reception quality.

  Looking at FIG. 3 from this point of view (considering the characteristic curve shifted to the left (low frequency side) on FIG. 3), in the filter characteristic of FIG. 3, the attenuation amount is high, and the high frequency side attenuation band is equal to the low frequency side attenuation band. Since they are the same and approximately -10 dB, the magnitude of the attenuation on the high frequency side is not always sufficient.

  On the other hand, for example, in Patent Document 1 (or Patent Document 2), a filter characteristic as shown in FIG. 5 can be obtained by using a SAW filter having a structure shown in FIG. The SAW filter of FIG. 6 has a ladder-type SAW filter CP1 of FIG. 2 and one L (inductor LX) two-port pair circuit CP2, and is configured by connecting these two two-port pair circuits CP1 and CP2 in series. This is a polarized SAW filter LA.

  In FIG. 5, mark # 1 indicates a point with a frequency of 818 MHz and attenuation of -3.0609 dB, mark # 2 indicates a point with a frequency of 843 MHz and attenuation of -2.9886 dB, and mark # 3 indicates a point of frequency 863 MHz and attenuation- A mark of 43.794 dB is shown, and a mark # 4 indicates a point of a frequency of 888 MHz and an attenuation of −38.099 dB.

As is apparent from FIG. 5, if the SAW filter having the filter characteristic of FIG. 5 is applied to the transmission band of the CDMA system in the United States, the attenuation in the high-frequency attenuation band is sufficiently large, so that the leakage to the reception band is caused. And good communication quality can be obtained for both transmission and reception.
JP-A-10-93382 JP-A-10-163808 Low loss bandpass filter using SAW resonator: Sato, Igata, Miyashita, Matsuda, Nishihara: IEICE Transactions A, Vol. J76-A, No. 2, pp 245-252, 1993.

  However, even with the filter characteristics shown in FIG. 5, the attenuation in the lower attenuation band cannot be said to be sufficiently large. Therefore, in the above-described example of the CDMA system in the United States, when the SAW filter of Patent Document 1 is applied as a receiving filter. However, the filter characteristics are not always sufficient, and the reception quality may be degraded.

  That is, in the example of the CDMA system described above, when a filter having no good characteristics such as the SAW filter of Patent Document 1 is used as a transmission filter, the leakage from the transmission side of the terminal of the own mobile communication device is performed. If the effects of interference cannot be sufficiently reduced by the receiving filter, and there is an effect of interference waves arriving from wireless communication devices other than the mobile communication device terminal, this can be sufficiently reduced by the receiving filter. It cannot be reduced.

  Note that, depending on the system, contrary to the above-described U.S. CDMA system, the transmission band may be set to have a higher frequency than the reception band. In such a case, the transmission filter and the reception filter may be used. It is necessary to replace the filter for use.

  Regardless of whether the filter is a transmission filter or a reception filter, focusing on the operation principle of the polarized SAW filter in Patent Documents 1 and 2, the problem to be solved by the present invention is as follows. Can be expressed.

  In the conventional polarized SAW filters described in Patent Documents 1 and 2, etc., an attenuation pole is formed within a finite frequency by one L two-port pair circuit. The amount decreases in the lower attenuation band of the pass band, and increases in the upper attenuation band of the pass band. Therefore, there is a high possibility that even if the required standard of the high attenuation amount in the high-side attenuation band of the passband can be satisfied, the required standard in the low-side attenuation band of the passband cannot be satisfied.

  If the L value of the inductance LX in FIG. 6 is set to be extremely large, it is considered that the attenuation of the high-frequency side attenuation band can be sufficiently increased. It is difficult to realize.

  When the interval between the attenuation band and the pass band (for example, the interval between the transmission frequency band and the reception frequency band for the same mobile communication terminal) is, for example, about 20 (MHz) as described above, it is steep. It requires a good filter characteristic.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and in a polarized SAW filter, an attenuation pole is formed in a lower attenuation band and a higher attenuation band of a pass band to eliminate the above problems, and It is an object of the present invention to provide a polarized SAW filter having steep characteristics in a lower attenuation band and a higher attenuation band of a band.

  According to a first aspect of the present invention, there is provided a polarized SAW filter using a band-pass ladder type SAW filter using a SAW resonator, wherein the band-pass ladder type SAW filter has an input terminal and an output terminal. A serial arm SAW resonator connected to the terminal, a first parallel arm SAW resonator having one end connected to the input terminal, and a second parallel arm SAW resonator having one end connected to the output terminal. A two-terminal pair circuit is connected in series to the band-pass appearance type SAW filter. The two-terminal pair circuit includes the band-pass ladder-type SAW filter provided on a surface of a piezoelectric substrate, and the piezoelectric substrate. And three common inductors disposed between the common terminal and a common terminal disposed in a region surrounding the band-pass ladder-type SAW filter. The series arm SAW resonator and the first and second Parallel arms Each of the AW resonators is disposed on the piezoelectric substrate, and the first parallel arm SAW resonator and the second parallel arm SAW resonator are disposed so that the other ends thereof face each other. Each of the SAW resonators constituting the bandpass ladder-type SAW filter is provided so as to be surrounded by a rectangular package, and the common terminal is connected to the first and second parallel arms SAW in the package. The resonator is provided on a side closest to the other end of the resonator.

  According to a second aspect of the present invention, in the polarized SAW filter using a band-pass ladder-type SAW filter using a SAW resonator, the band-pass ladder-type SAW filter is provided between an input terminal and an output terminal. A first and a second series arm SAW resonator connected in series; a first end connected to the input terminal, and a second end connected to a terminal electrically mirrored to the common terminal via an inductor. One parallel arm SAW resonator, a second parallel arm SAW resonator having one end connected between the first and second series arm SAW resonators, and a third parallel arm SAW resonator having one end connected to the output terminal. And a two-port pair circuit is connected in series to the band-pass ladder type SAW filter, and the two-port pair circuit is connected to each of the second and third parallel-arm SAW resonators. The two-terminal pair circuit is connected to the end of the piezoelectric substrate. And three inductors provided between the band-pass ladder-type SAW filter provided on the surface of the piezoelectric substrate and a common terminal disposed in a region surrounding the band-pass ladder-type SAW filter. The serial arm SAW resonator and the second and third parallel arm SAW resonators are both disposed on the piezoelectric substrate, and the second parallel arm SAW resonator and the third parallel arm SAW resonator are arranged on the piezoelectric substrate. The arm SAW resonators are arranged in such a manner that the other ends thereof face each other, and each of the SAW resonators constituting the bandpass ladder type SAW filter is provided so as to be surrounded by a rectangular package, The common terminal is provided on a side of the package closest to the other end of the second and third parallel arm SAW resonators.

  As described above, according to the present invention, since a plurality of attenuation poles are formed in each of the high-side attenuation band and the low-side attenuation band of the pass band of the polarized SAW filter, the configuration is reduced in size. However, the amount of attenuation due to the change in the formed attenuation pole can be made sufficiently large not only in the high-frequency band but also in the low-frequency band.

(A) Embodiment Hereinafter, an embodiment of a polarized SAW filter according to the present invention will be described.

  In general, if a large number of SAW resonators are used in a SAW filter, the filter has a sufficiently large amount of attenuation in both the low-side attenuation band and the high-side attenuation band of the pass band, and has a steep, ideal filter characteristic. It is possible to obtain a good filter characteristic close to such an ideal filter characteristic by using a SAW filter as small as possible using as few SAW resonators as possible. is important.

  SAW filters are mainly used from the viewpoint of miniaturization, such as portable terminal devices for mobile communication using a frequency band of 800 (MHz) band and portable terminal devices for mobile communication using a frequency band of 2 (GHz) band. It is being widely used as an RF filter.

(A-1) Configuration of First Embodiment FIG. 1 shows a circuit diagram of a SAW (Surface Acoustic Wave) filter 10 of the present embodiment. The SAW filter 10 functions as, for example, a reception filter of a mobile phone in the above-described U.S. CDMA system. Of course, if necessary, it can be used as a transmission filter.

  In FIG. 1, the SAW filter 10 includes input terminals IN and GND1, output terminals OUT and GND2, three SAW resonators SR1, PR1, PR2, three inductances L1 to L3, and six connection points P1 to P1. P6.

  The SAW resonator SR1 is a series arm SAW resonator disposed between the input terminal IN and the output terminal OUT and provided in a series arm having connection points P3 and P4.

  Further, the SAW resonator PR1 (110) is a parallel arm SAW resonator provided in a parallel arm having the connection point P3 and the connection point P1, and similarly, the SAW resonator PR2 (111) includes the SAW resonator PR2 (111). This is a parallel arm SAW resonator provided in a parallel arm having a connection point P4 and a connection point P2.

  The inductance L2 (131) is connected between the connection points P1 and P2.

  Further, connection points P5 and P6 are provided between the input terminal GND1 and the output terminal GND2, and an inductance L1 (130) is connected between the connection point P1 and the connection point P5. The inductance L3 (132) is connected between the connection points P6.

  That is, the polarized SAW filter 10 is configured such that the components P1, P2, P5, P6, L1 to L3, GND1, GND2 are supplied to the two-terminal pair circuit 30 having the components IN, P3, P4, SR1, PR1, PR2. Are connected in series.

  Note that L1 to L3 are also used as values indicating the L value of each inductance as necessary.

  FIG. 11 shows an implementation example corresponding to the circuit diagram of FIG. FIG. 11 shows a SAW filter package 10A realized by the same fine processing technology as a normal IC (semiconductor integrated circuit).

  In FIG. 11, the SAW filter package 10A has pads 12 and 16 formed on the package 11, and a piezoelectric substrate 21.

  SAW resonators 100, 110, and 111 are connected to electrodes 14A and 14B of, for example, tungsten, which are provided on the piezoelectric substrate 21 and form a “π” shape, respectively.

The SAW resonator 100 includes two grating reflectors 100A and 100C, and an interdigital electrode (interdigital converter: IDT) 100B disposed therebetween.

  The interdigital electrode 100B constituting the interdigital electrode 100B is electrically connected to the electrode 14A, and the other interdigital electrode 100B constituting the interdigital electrode 100B is electrically connected to the electrode 14B. It is connected to the.

  The structure of the resonator other than the SAW resonator 100 is the same, and the SAW resonator 110 includes two grating reflectors 110A and 110C and an interdigital electrode 110B disposed therebetween, and the SAW resonator 111 Includes two grating reflectors 111A and 111C and an interdigital electrode 111B disposed therebetween.

  The interdigital electrode 110B constituting the interdigital electrode 110B is electrically connected to the electrode 14A, and the other interdigital electrode 110B constituting the interdigital electrode 110B is electrically connected to the pad P22 (the pad P22). (Corresponding to P1).

  Similarly, the interdigital electrode 111B constituting the interdigital electrode 111B is electrically connected to the pad 23 (corresponding to P2), and another interdigital electrode 111BB constituting the interdigital electrode 111B. Are electrically connected to the electrode 14B.

  However, in this embodiment, the intersection length and logarithm of each of the SAW resonators SR1, PR1, PR2 are as shown in FIG.

  That is, the cross length of the series arm resonator SR1 is 55 μm and the logarithm is 100, the cross length of the parallel arm resonator PR1 is 66 μm and the logarithm is 66, and the cross length of the parallel arm resonator PR2 is 66 μm and the logarithm is 66. It is a book.

  The pad 12 and the electrode 14A in FIG. 11 are connected by a bonding wire 13 having a sufficiently small inductance, and the pad 16 and the electrode 14B are connected by a bonding wire 15 having a sufficiently small inductance. The bonding wires 17 (corresponding to L1), 18 (corresponding to L2) and 19 (corresponding to L3) each have a desired L value.

  In the present embodiment, it is assumed that the L value of each of the bonding wires 17 to 19 is the same value (for example, 0.1 nH).

  Compared with the conventional SAW filter shown in FIG. 6 at the circuit diagram level, the SAW filter 10 of the present embodiment is different in the structure of the two-port pair circuit 31.

  Hereinafter, the operation of the present embodiment having the above configuration will be described.

(A-2) Operation of the First Embodiment FIG. 12 shows a bisecting circuit diagram of the polarized SAW filter 10 of the present embodiment.

  FIG. 13 is a lattice equivalent circuit diagram for explaining the operation of the polarized SAW filter 10.

  The ladder-type SAW filter 10 shown in FIG. 1 has a two-stage π-type configuration including three SAW resonators (SR1 (100), PR1 (110), and PR2 (111)). In contrast, a two-terminal pair circuit 31 composed of three Ls (L1 (130), L2 (131), L3 (132)) is connected in series.

  Here, in order to evaluate the operation of the polar SAW filter 10 of FIG. 1 and obtain the relationship between the attenuation pole frequency and the L value of the polar SAW filter 10, the bisecting circuit of FIG. 12 is used.

  The input impedance of the circuit when the terminals (OUT (1), OUT (2), E) of the bisector of the bisecting circuit in FIG. 12 are opened is ZF, and the terminal of the bisector (OUT (1) , OUT (2), E), the input impedance of the circuit at the time of short circuit is ZS, and ZF and ZS are given by equations (1) and (2).

ZF = Z (PR1 (110)) + jωL1 (130) (1)
ZS = 1 / ((1 / Z (SR1 (100))) + 1 / (1 / Z (PR1 (110)) + jω (1 / (1 / L1 (130) + 1 / L21 (131)))) (2)
Here, Z (PR1 (110)) is the impedance of the parallel arm resonator 110 in FIG. 12, and the L value of L21 (131) is half of L2 (131), that is, L21 (131) = L2 (131) / 2. Also, ω is ω = 2.0 * π * f where f is the frequency, and Z (SR1 (100)) is １ ／ of the impedance of the series arm resonator 100 in FIG.

  Normally, the characteristics of the circuit of FIG. 12 are evaluated based on the characteristics of the lattice circuit of FIG. That is, as the operation transmission coefficient (characteristic SF of the circuit of FIG. 12) of the lattice circuit of FIG. 13, the values (ZF, ZS) of Expressions (1) and (2) are substituted into the following Expression (3). It is required by that.

SF = (1 + ZF) (1 + ZS) / (ZF-ZS) (3)
Therefore, the attenuation characteristic α (ω) is given by Expression (4).

α (ω) = 20 * LOG (ABS (SF)) (4)
Here, ABS (SF) represents an absolute value in parentheses, and * represents multiplication.

  That is, the attenuation pole frequency is formed in the attenuation band by L or the attenuation increases by L when either of the following conditions (5A) or (5B) is satisfied.

ZF = ZS (5A)
ZS = ∞ (5B)
A feature of the present embodiment is that L (L1 or L21) is included in ZF and ZS in Expressions (1) and (2). That is, when L is included in ZF and ZS, the condition (5A) is satisfied to form an attenuation pole frequency in the attenuation band, or the condition (5B) is satisfied and the attenuation pole frequency is formed in the attenuation band. This is the case where the attenuation increases due to the formation. This point will be described using an equivalent LC circuit of a SAW resonator as shown in FIG.

  Using the equivalent LC circuit of FIG. 14, equations (1) and (2) are given by equations (6) and (7).

ZF = (S ＾ 2 + ω1 ＾ 2 + S ＾ 2 * L11 * Cf * (S ＾ 2 + ω2 ＾ 2)) / (S * Cf * (S ＾ 2 + ω2 ＾ 2)) (6)
ZS = (S ＾ 2 + ω3 ＾ 2 + S ＾ 2 * L22 * Cs * (S ＾ 2 + ω4 ＾ 2)) / (S * Cs * (S ＾ 2 + ω4 ＾ 2)) (7)
Here, L11 = L1 (130), 1 / L22 = 1 / L1 (130) + 1 / L21 (131), Cf = capacity of parallel arm, Cs = capacity of serial arm, ω1 = zero point of parallel arm (that is, impedance Ω2 = extreme point of the parallel arm (that is, the point where the impedance becomes maximum or minimum), ω3 = zero point of the serial arm, and ω4 = pole point of the serial arm.

  That is, the frequency at which an attenuation pole is provided using Expressions (6) and (7) and the condition (5A) that is a condition for forming the attenuation pole is obtained from the following Expression (8).

Cf * (S ＾ 2 + ω2 ＾ 2) * (S ＾ 2 + ω1 ＾ 2 + S ＾ 2 * L11 * Cf * (S ＾ 2 + ω2 ＾ 2)) = (S ＾ 2 + ω3 ＾ 2 + S ＾ 2 * L22 * Cs * (S ＾ 2 + ω4 ＾) 2)) * Cs * (S ＾ 2 + ω4 ＾ 2)) (8)
＾ 2 means the square of the immediately preceding numerical value.

  Here, a feature of the present embodiment is that L11 and L22 are included in Expression (8). In particular, due to the presence of L22, the attenuation pole frequency obtained from Expression (8) becomes the lower attenuation band of the pass band.

  Next, the present embodiment will be compared with the conventional SAW filter LA shown in FIG. The ZF and ZS for the SAW filter LA are given by Expressions (9) and (10).

ZF = Z (PR1 (110)) + jωL11 (130) (9)
ZS = 1 / ((1 / Z (SR1 (100))) + 1 / (1 / Z (PR1 (110))) (10)
Here, Z (PR1 (110)) is the impedance of the parallel arm resonator 110 shown in FIG. 6, L11 (130) = 2.0 * L1 (130), and ω is ω = 2. It is given by 0 * π * f, and Z (SR1 (100)) is an impedance value corresponding to の of the series arm resonator 110 in FIG.

  As is clear from the comparison of the corresponding equations, a major difference between the SAW filter 10 of the present embodiment and the SAW filter LA of FIG. 6 lies in whether or not L is included in ZS.

  In this case, the pole frequency corresponding to the equation (8) is obtained from the following equation (11).

Cf * (S ＾ 2 + ω2 ＾ 2) * (S ＾ 2 + ω1 ＾ 2 + S ＾ 2 * L11 * Cf * (S ＾ 2 + ω2 ＾ 2)) = Cs * (S ＾ 2 + ω3 ＾ 2) * (S ＾ 2 + ω4 ＾ 2)) … (11)
Using the condition ZF = ZS for the formation of the attenuation pole ((5A)), the frequency at which the attenuation pole is given is obtained from the above equation (8) in the case of the present embodiment, and in the case of the conventional SAW filter LA shown in FIG. It is obtained from the equation (11).

  Comparing the two expressions, expression (8) includes L11 and L22, whereas expression (11) includes only L11. For this reason, in the conventional SAW filter LA, an attenuation pole is formed in the high-frequency attenuation band of the pass band.

  On the other hand, FIG. 15 is a characteristic simulation result using the L values of the three inductances L1 to L3 in the two-terminal pair circuit 31 as parameters in the polarized SAW filter 10 of the present embodiment. Here, the characteristic curve of L = 0 in FIG. 15 corresponds to the filter characteristic of the conventional two-stage π-type ladder-type SAW filter shown in FIG.

  FIG. 15 shows the following (1) to (3) as compared with the conventional two-stage π-type ladder type SAW filter shown in FIG.

  (1) The L1 (130), L2 (131), and L3 (132) provide the (low-band) attenuation poles LP21 to LP21 in the low-band attenuation band and the high-band attenuation band of the pass band (about 860 MHz to about 900 MHz). LP41, LP22 to LP42 and (high frequency) attenuation poles HP21 to HP41, HP22 to HP42 are formed.

  Among them, the low-frequency attenuation poles LP21 and LP22 correspond to the case of L = 0.1 nH, the low-frequency attenuation poles LP31 and LP32 correspond to the case of L = 0.2 nH, and the low-frequency attenuation poles LP41 and LP42 have the L = 0.1 nH. This corresponds to the case of 0.4 nH. Similarly, the high-frequency attenuation poles HP21 and HP22 correspond to the case of L = 0.1 nH, the high-frequency attenuation poles HP31 and HP32 correspond to the case of L = 0.2 nH, and the high-frequency attenuation poles HP41 and HP42 have the L = 0.1 nH. = 0.4 nH.

  (2) Further, as shown in FIG. 8, these attenuation poles cause a 30 dB attenuation width indicating a width of a frequency band in which the attenuation amount is equal to or more than 30 (dB) to be, for example, L = 0.2 ( In the case of nH), it is 54.5 (MHz) in the lower attenuation band and 36.5 (MHz) in the higher attenuation band. On the other hand, the conventional ladder-type SAW filter shown in FIG. 2 has 43.5 (MHz) in the lower band attenuation band and 35.0 (MHz) in the higher band attenuation band. This embodiment is wider by 11.5 (MHz) in the lower band attenuation band and 1.5 (MHz) in the higher band attenuation band, and compared with the conventional ladder type SAW filter, High attenuation characteristics can be obtained.

  As is clear from FIG. 15, the 30 dB attenuation width in the present embodiment tends to increase as the L value of L1 to L3 increases.

  (3) Furthermore, as is clear from FIG. 15, the slope between the pass band and the attenuation band does not change even if the L value of L1 to L3 changes, and is sufficiently steep.

  At the actual product level, the filter characteristics required for a SAW filter are determined in consideration of the relationship with an amplifier and a modulator incorporated in the mobile communication device terminal and the like together with the SAW filter. According to the polarized SAW filter of the embodiment, it is possible to cope with such considerations.

(A-3) Effects of the First Embodiment According to the present embodiment, two attenuation poles are formed in the high-frequency attenuation band and the low-frequency attenuation band of the passband by the two-port pair circuit (31). However, the amount of attenuation due to the change in the formed attenuation pole is sufficiently large not only in the high-frequency band but also in the low-frequency band.

  As a result, the possibility of satisfying the requirement of the high attenuation amount in the higher attenuation band of the pass band and the requirement of the lower attenuation band of the pass band is increased.

  Moreover, in the present embodiment, such a filter characteristic can be realized by using a miniaturized SAW filter that uses a sufficiently small inductance of an L value.

  Further, as described above, the filter characteristic of the present embodiment is a sufficiently steep characteristic.

  Considering these points, for example, in the above-described example of the CDMA system in the United States, when the polarized SAW filter of the present embodiment is applied as a receiving filter, sufficiently good filter characteristics can be obtained. The reception quality is improved.

  Of course, as described above, the polarized SAW filter of the present embodiment has excellent characteristics even when used as a transmission filter.

(B) Second Embodiment In the following, only differences between the present embodiment and the first embodiment will be described.

(B-2) Configuration and Operation of Second Embodiment FIG. 16 shows a circuit diagram of a SAW filter 40 of the present embodiment. The SAW filter 40 is a filter corresponding to the SAW filter 10.

  In FIG. 16, the functions of the respective units denoted by the same reference numerals as those in FIG. 1 correspond to FIG. 1.

  Therefore, the SAW filter 40 has a configuration in which a series arm resonator SR2, a parallel arm resonator PR3, an inductance L4, and connection points P7 and P8 are added to the SAW filter 10.

  Here, the series arm resonator SR2 is the same SAW resonator as the series arm resonator SR1, and the parallel arm resonator PR3 is the same SAW resonator as the parallel arm resonator PR1 or PR2. The inductance L4 is the same as the inductance L1 to L3.

  That is, the polarized SAW filter 40 includes a two-port pair circuit forming a 4-stage π-type ladder-type SAW filter and three Ls (L1 (120), L2 (121), L3 (122)). It is configured by connecting two terminal pair circuits in series.

  Also, in FIG. 17 showing the mounting example 40A corresponding to the circuit diagram in FIG. 16, the functions of the respective units denoted by the same reference numerals as in FIG. 11 are the same as those in FIG.

  That is, the mounting example 40A of FIG. 17 is different from the mounting example 10A of FIG. 11 in that the series arm resonator SR2 (101), the parallel arm resonator PR3 (112), the inductance L4 (42), and the pads 41 and 43. Is added.

  Again, the bonding wire 42 functions as the inductance L4.

  In the layout, the electrode connected to the pad 12 by the bonding wire 13 is not the electrode 14A but the electrode 14C.

  In the SAW filter 40 of the present embodiment, as shown in FIG. 9, the cross length and logarithm of each SAW resonator are selected.

  FIG. 18 shows a characteristic simulation result using L as a parameter using the intersection length and logarithm of FIG. FIG. 10 shows changes in the attenuation pole and the 30 (dB) attenuation width in the lower attenuation band and the higher attenuation band due to the change in L.

  As is clear from FIGS. 10 and 18, an attenuation pole is formed by the L values of L1 to L4 in the lower attenuation band and the higher attenuation band of the pass band. ), The attenuation poles in the lower attenuation band are 851.5 MHz (this corresponds to point LP81 in FIG. 18) and 841.0 MHz (this corresponds to point LP82 in FIG. 18).

  Since the number of attenuation poles becomes two in this manner, when the 30 dB attenuation width is L = 0.5 (nH), the attenuation band is 20.0 (MHz) in the lower band attenuation band and 12 in the higher band attenuation band. 0.0 (MHz), which is 7 (MHz) wider in the lower band attenuation band and 2 (MHz) wider in the higher band attenuation band as compared with the conventional ladder type SAW filter.

  That is, it can be seen that the attenuation characteristics in the low-frequency attenuation band and the high-frequency attenuation band are greatly improved, and the standard is satisfied.

  Further, in the filter characteristics of FIG. 18, the slopes of the pass band and the attenuation band do not change even when the L values of L1 to L4 change, and are sufficiently steep.

(B-2) Effects of the Second Embodiment As described above, according to the present embodiment, it is possible to obtain effects substantially equivalent to those of the first embodiment.

  In addition, in the present embodiment, the attenuation characteristics of the lower attenuation band and the higher attenuation band of the pass band can be controlled relatively freely.

(C) Other Embodiments In the above-described first and second embodiments, for the sake of simplicity, many specific numerical values are shown. However, these are merely examples, and application of the present invention is not limited. The range is not limited by these numbers.

  Therefore, the above-described L value can be changed to various values, but the present invention can be realized by a small L value.

  Regardless of the first and second embodiments, it goes without saying that a T-type two-port pair circuit may be used as the two-port pair circuit instead of the π-type two-port pair circuit.

  Further, the implementation example of FIG. 17 of the second embodiment can be replaced with the implementation example of FIG. 19 as an example.

  In the mounting example of FIG. 19, the electrode pattern 50 is used as an inductance instead of the bonding wire 17 (L2).

  In the mounting example of FIG. 19, an example is shown in which a part of the plurality of inductances present in the two-terminal pair circuit is configured by the electrode pattern. Naturally, it may be constituted by a pattern.

  As described above, the inductor of the two-terminal pair circuit of the present invention is suitable for realization by a multilayer substrate package.

FIG. 2 is a circuit diagram of a polarized SAW filter according to the first embodiment. It is a circuit diagram of the conventional ladder type SAW filter. FIG. 4 is an explanatory diagram of an operation of a SAW filter. FIG. 4 is an explanatory diagram of an operation of a SAW filter. FIG. 4 is an explanatory diagram of an operation of a SAW filter. It is a circuit diagram of the conventional polarized SAW filter. FIG. 3 is an operation explanatory diagram of the polarized SAW filter according to the first embodiment. FIG. 3 is an operation explanatory diagram of the polarized SAW filter according to the first embodiment. FIG. 9 is an explanatory diagram of an operation of the polarized SAW filter according to the second embodiment. FIG. 9 is an explanatory diagram of an operation of the polarized SAW filter according to the second embodiment. FIG. 2 is a schematic diagram illustrating a mounting example of a polarized SAW filter according to the first embodiment. FIG. 3 is an operation explanatory diagram of the polarized SAW filter according to the first embodiment. FIG. 3 is an operation explanatory diagram of the polarized SAW filter according to the first embodiment. FIG. 3 is an operation explanatory diagram of the polarized SAW filter according to the first embodiment. FIG. 3 is an operation explanatory diagram of the polarized SAW filter according to the first embodiment. FIG. 9 is a circuit diagram of a polarized SAW filter according to a second embodiment. It is a schematic diagram showing the example of mounting of the polar type SAW filter concerning a 2nd embodiment. FIG. 9 is an explanatory diagram of an operation of the polarized SAW filter according to the second embodiment. It is the schematic which shows another example of implementation of the polar SAW filter concerning 2nd Embodiment.

Explanation of reference numerals

  10, 40: Polarized SAW filter, 13, 15, 17 to 19: Bonding wire, 21: Piezoelectric substrate, 30, 31: Two-terminal pair circuit, 100, 110, 111: SAW resonator, L1 to L4 Inductance, LP21 to LP41, LP22 to LP42, HP21 to HP41, HP22 to HP42 ... attenuation pole.

Claims (7)

In a polarized SAW filter using a band-pass ladder type SAW filter using a SAW resonator,
The band-pass ladder type SAW filter includes a series arm SAW resonator connected to an input terminal and an output terminal, a first parallel arm SAW resonator having one end connected to the input terminal, and one end connected to the output terminal. And a second parallel arm SAW resonator connected to
A two-terminal pair circuit is connected in series to the bandpass appearance type SAW fill,
The two-port pair circuit includes a band-pass ladder-type SAW filter provided on a surface of a piezoelectric substrate, and a common terminal disposed on a surface side of the piezoelectric substrate and surrounding the band-pass ladder-type SAW filter. Composed of three inductors provided between
The series arm SAW resonator and the first and second parallel arm SAW resonators are both disposed on the piezoelectric substrate, and the first parallel arm SAW resonator and the second parallel arm SAW The resonator is arranged in a direction in which the other end sides face each other,
Each of the SAW resonators constituting the band-pass ladder type SAW filter is provided so as to be surrounded by a rectangular package, and the common terminal is connected to the first and second parallel arm SAW resonators in the package. A polar SAW filter provided on the side closest to the other end. In a polarized SAW filter using a band-pass ladder type SAW filter using a SAW resonator,
The band-pass ladder type SAW filter includes first and second series arm SAW resonators connected in series between an input terminal and an output terminal, one end connected to the input terminal, and the other end connected to an inductor. A first parallel arm SAW resonator connected to a terminal electrically mirrored to the common terminal via a common terminal, and a second parallel arm SAW resonator having one end connected between the first and second series arm SAW resonators. And a third parallel arm SAW resonator having one end connected to the output terminal.
A two-port pair circuit is connected in series to the bandpass ladder type SAW filter,
The two-port pair circuit is connected to the other end of each of the second and third parallel arm SAW resonators, and the two-port pair circuit includes the band-pass ladder type SAW filter provided on a surface of a piezoelectric substrate; On the front surface side of the piezoelectric substrate, three inductors are provided between a common terminal disposed in a region surrounding the bandpass ladder type SAW filter,
The series arm SAW resonator and the second and third parallel arm SAW resonators are both disposed on the piezoelectric substrate, and the second parallel arm SAW resonator and the third parallel arm SAW The resonator is disposed in a direction in which the other end sides face each other,
Each of the SAW resonators constituting the band-pass ladder type SAW filter is provided so as to be surrounded by a rectangular package, and the common terminal is provided in the second and third parallel arm SAW resonators in the package. And a polar SAW filter provided on the side closest to the other end.   3. The polarized SAW filter according to claim 1, wherein the two-port pair circuit is a π-type two-port pair circuit.   The polarized SAW filter according to any one of claims 1 to 3, wherein each of the three inductors is configured using a bonding wire or configured using an electrode pattern.   The polarized SAW filter according to any one of claims 1 to 3, wherein a part of the three inductors is formed using an electrode pattern, and the remaining part is formed using a bonding wire.   The common terminal is arranged on a side of the package closest to the other end of the second and third parallel arm SAW resonators, at an intermediate position between the second and third parallel arm SAW resonators. The polarized SAW filter according to any one of claims 1 to 5, wherein:   An interdigital electrode forming the second and third parallel arm SAW resonators in a direction perpendicular to a side closest to the other end of the second and third parallel arm SAW resonators in the package; The polar SAW filter according to any one of claims 1 to 6, further comprising: arranging a plurality of grating reflectors; and arranging comb-shaped electrodes constituting the interdigital electrode.

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