JP2002374142A - Surface acoustic wave filter and communication equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface acoustic wave filter, in which balance between balance signal terminals 210 and 211 is improved, and to provide communication equipment which uses the filter. SOLUTION: Three interdigital electrode parts 204, 205, 206 are installed to obtain balance-unbalance converting function. The balanced signal terminals 210, 211 are connected with the interdigital electrode part 205. Duty of electrode fingers 219, 220 in a part where two interdigital electrode parts out of the interdigital electrode parts 204, 205, 206 are adjacent to each other is made different from the duties of other electrode fingers.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave filter, and more particularly to a surface acoustic wave filter having a balance-unbalance conversion function and a communication device having the same.

[0002]

2. Description of the Related Art Heretofore, there has been remarkable technical progress in recent years in reducing the size and weight of communication devices such as mobile phones. As means for achieving this, not only the number of constituent components has been reduced and the size has been reduced, but also the development of components having a plurality of combined functions has been advanced. Against this background, a surface acoustic wave filter used in the RF stage of a mobile phone having a balance-unbalance conversion function, that is, a so-called balun function, has been actively researched in recent years. fo
r Mobile communications).

In a balun, when a balanced line such as a parallel two-wire feeder and an unbalanced line such as a coaxial cable are directly connected, an unbalanced current flows and the feeder itself (feeder) operates as an antenna. It is a circuit that blocks unbalanced current and matches balanced and unbalanced lines because it is undesirable.

Several patents relating to a surface acoustic wave filter having such a balance-unbalance conversion function have been filed. A configuration as shown in FIG. 23 is widely known as a surface acoustic wave filter having a balanced-unbalanced conversion function in which input impedance and output impedance are substantially equal.

In the surface acoustic wave filter shown in FIG. 23, a comb-shaped electrode portion (inter-digital transducer, hereinafter referred to as IDT) 101 is provided on a piezoelectric substrate 100, and left and right of the IDT 101. (Positions along the propagation direction of the surface acoustic wave)
03 is arranged.

Further, in the surface acoustic wave filter, reflectors 104 and 105 for reflecting the surface acoustic wave and improving the conversion efficiency are arranged so as to sandwich these IDTs 101, 102 and 103 from the left and right. Have been. Further, each balanced signal terminal 106, 107 connected to the IDT 101, and each IDT
An unbalanced signal terminal 108 connected to 102 and 103 is provided.

Such a surface acoustic wave filter has a 3ID
It is called a T-type longitudinally coupled resonator type surface acoustic wave filter, and has a balance-unbalance conversion function by conversion using surface acoustic waves between the IDTs 101, 102, and 103.

[0008]

However, the above conventional surface acoustic wave filter has a problem that the degree of balance between balanced signal terminals is deteriorated. That is, in the surface acoustic wave filter having the balanced-unbalanced conversion function, the amplitude characteristics are equal and the phase is 180 in the transmission characteristics in the pass band between the unbalanced signal terminal and the balanced signal terminal. Degrees are required, and are called amplitude balance and phase balance between balanced signal terminals, respectively.

The amplitude balance and the phase balance are determined by the balance
Consider a surface acoustic wave filter having an unbalanced conversion function as a three-port device. For example, when an unbalanced input terminal is a first port, and a balanced output terminal is a second port and a third port, respectively, the degree of amplitude balance = [ A], A = [20 log
(S21)]-[20 log (S31)], phase balance = [B-180], and B = [ＢS21-∠S31]. Note that S21 indicates a transfer coefficient from the first port to the second port, S31 indicates a transfer coefficient from the first port to the third port, and [] in each of the above equations indicates an absolute value. belongs to.

The degree of balance between such balanced signal terminals is ideally such that the amplitude balance is 0 dB and the phase balance is 0 degrees within the pass band of the surface acoustic wave filter.

However, the conventional configuration shown in FIG. 23 has a problem that the degree of balance between the balanced signal terminals is deteriorated. There are several possible reasons. One of the reasons is the distance between the electrode finger connected to the balanced signal terminal 106 and the signal electrode finger of the IDT 102 (10 in FIG. 23).
9) and the distance between the electrode finger connected to the balanced signal terminal 107 and the signal electrode finger of the IDT 103 (11 in FIG. 23).
0) differs by 0.5 times the wavelength determined by the pitch of the electrode fingers.

As a result, each of the balanced signal terminals 106, 10
7 have different total capacitances of the electrode fingers connected thereto, and have different conversion efficiencies between electric signals and surface acoustic waves. As a result, the degree of balance has been deteriorated.

Therefore, the balanced signal terminal 107 shown in FIG. 23 is connected to the ground as shown in FIG. 24, and the amplitude characteristic with respect to the frequency output from the balanced signal terminal 106 is connected to the balanced signal terminal 106 shown in FIG. The amplitude characteristic output from the balanced signal terminal 107 is measured by connecting to the ground, and the resulting difference in the amplitude characteristic is shown in FIG. 2
The two amplitude characteristics are greatly different from each other, and this difference leads to deterioration of the degree of balance.

An object of the present invention is to correct the above-mentioned difference between the balanced signal terminals, which is one of the causes of the deterioration of the balance between the balanced signal terminals, so that the balance between the balanced signal terminals is good. An object of the present invention is to provide a surface acoustic wave filter having a balance conversion function.

[0015]

In order to solve the above-mentioned problems, a surface acoustic wave filter according to the present invention includes an elastic surface acoustic wave (IDT) including a plurality of comb-shaped electrodes provided with electrode fingers on a piezoelectric substrate. In a surface acoustic wave filter having a plurality of balanced signal input terminals or balanced signal output terminals connected to the IDT and having a plurality of pieces along the propagation direction of the surface acoustic wave,
The duty of at least some of the electrode fingers of the DT (hereinafter referred to as
duty) is different from the duty of the other electrode fingers.

According to the above configuration, the ID including the plurality of opposed comb-shaped electrodes provided with the electrode fingers on the piezoelectric substrate.
T having a plurality of T along the propagation direction of the surface acoustic wave,
By having a balanced signal input terminal or a balanced signal output terminal connected to T, a conversion function between a balanced signal and an unbalanced signal can be exhibited together with a filter function.

Further, in the above configuration, the duty of at least a part of the electrode fingers of each IDT is changed to the duty of the other electrode fingers.
y, so that the total capacitance of the electrode fingers connected to each of the balanced signal terminals and the conversion efficiency between electric signals and surface acoustic waves can be adjusted, and between balanced signal input terminals or balanced signal output terminals The degree of equilibrium between them can be improved.

In the surface acoustic wave filter, two IDs
At least one duty of each electrode finger at a position where T is adjacent to each other may be different from the duty of another electrode finger. According to the above configuration, the effect of adjusting the degree of balance can be increased.

In the above-mentioned surface acoustic wave filter, the duty of an electrode finger located near a position where the two IDTs are adjacent to each other may be different from the duty of another electrode finger. According to the above configuration, the effect of adjusting the degree of balance can be increased.

In the above-mentioned surface acoustic wave filter, the duty of at most several electrode fingers of one of the interdigital electrodes of at least one IDT may be different from the duty of other electrode fingers. According to the above configuration, the effect of adjusting the degree of balance can be increased.

In the above-mentioned surface acoustic wave filter, the electrode fingers at the positions where two IDTs are adjacent may be thinned and weighted. According to the above configuration, the two IDTs are weighted by thinning out the electrode fingers at adjacent positions.
The degree of freedom in adjusting the degree of balance can be improved.

In the above surface acoustic wave filter, each IDT
May be set to a longitudinally coupled resonator type. According to the above configuration, a conversion function between a balanced signal and an unbalanced signal can be more reliably exerted.

In the above surface acoustic wave filter, it is desirable that at least one surface acoustic wave resonator is connected in series, in parallel, or in both. According to the above configuration, by connecting at least one or more surface acoustic wave resonators in series and / or in parallel, the attenuation outside the connection pass band can be increased.

[0024] A communication device according to the present invention includes the surface acoustic wave filter described above.
According to the above configuration, the filter function and the excellent balanced signal
By having a surface acoustic wave filter having a function of converting between unbalanced signals, downsizing can be achieved by combining functions, and transmission characteristics can be improved by an excellent conversion function.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to FIGS.

FIG. 1 shows the configuration of the first embodiment of the present invention. In the following embodiments, PCS receiving filters will be described as examples. In the first embodiment, 40
Piezoelectric substrate 2 made of ± 5 ° YcutX propagation LiTaO ₃
A longitudinally coupled resonator type surface acoustic wave filter 201 and a surface acoustic wave resonator 202 and a surface acoustic wave resonator 203 connected in series to the longitudinally coupled resonator type surface acoustic wave filter 201 are formed by photolithography or the like. Formed by the aluminum (Al) electrode.

Vertically coupled resonator type surface acoustic wave filter 20
1. Surface acoustic wave resonator 202 and surface acoustic wave resonator 2
Numeral 03 is composed of an IDT and a reflector, respectively.

The IDT has a band-shaped base end (bus bar),
A comb-shaped electrode having a plurality of mutually parallel electrode fingers extending in a direction orthogonal to one side of the base end;
The comb-shaped electrodes are provided in such a manner that the side portions of the electrode fingers of the respective comb-shaped electrodes face each other so as to face each other.

In such an IDT, the length and width of each electrode finger, the distance between adjacent electrode fingers, and the intersection width indicating the intricate face-to-face length between the electrode fingers are set, respectively. The signal conversion characteristics and the pass band can be set.

The reflector has a function of reflecting the surface acoustic wave propagating thereon and returning it to the direction in which it propagated. That is, the reflector extends from a pair of band-shaped base ends (bus bars) and one side of the base ends in a direction perpendicular to the longitudinal direction of the base ends, and And a plurality of mutually parallel electrode fingers are provided on the piezoelectric substrate.

The reflector is excited by the propagating surface acoustic wave, cancels the traveling surface acoustic wave by the surface acoustic wave generated by the excitation electric signal, and propagates the surface acoustic wave. It is set to generate a new surface acoustic wave in the direction opposite to the direction. Therefore, the reflector is configured to pseudo-reflect the propagating surface acoustic wave.

Longitudinally coupled resonator type surface acoustic wave filter 201
Is configured such that each IDT 205 is sandwiched from the left and right.
DTs 204 and 206 are formed, and reflectors 207 and 208 are formed on both sides thereof. As can be seen from FIG. 1, the pitch of several electrode fingers (narrow pitch electrode fingers) between the IDT 204 and the IDT 205 and between the IDT 205 and the IDT 206 is made smaller than other portions of the IDT. (Places 213 and 214 in FIG. 1).

Terminals 210 and 211 are balanced signal terminals, and terminal 209 is an unbalanced signal terminal. The surface acoustic wave resonator 202 and the surface acoustic wave resonator 203 are connected to the unbalanced signal terminal 209 and each IDT 20 via a signal line 212.
4, 206 are connected in series. Incidentally, FIG. 1 shows a small number of electrode fingers to simplify the drawing. The ground line 221 is connected to the signal line 212.
This is a shield pattern for reducing the capacitance entering in a bridge between the balance signal terminal 210 and the balance signal terminal 210.

The surface acoustic wave resonator 202 is an IDT
202a, and each reflector 202b disposed so as to sandwich it from both sides (along the propagation direction of the surface acoustic wave);
202c. The aforementioned surface acoustic wave resonator 20
Reference numeral 3 has an IDT 203a and reflectors 203b and 203c arranged so as to sandwich the IDT 203a from both sides.

The feature of the first embodiment is that the IDT
That is, the duty of each electrode finger 219, 220 at a position adjacent to each IDT 204, 206 in 205 is set to be smaller than the duty of the other electrode fingers.

Vertically coupled resonator type surface acoustic wave filter 201
The detailed design of is that if the wavelength determined by the pitch of the narrow pitch electrode fingers is λI ₂ (at 213 and 214 in FIG. 1) and the wavelength determined by the pitch of the other electrode fingers is λI ₁ , the intersection width W: 60 .6λI ₁ IDTs (in the order of 204, 205, 206): 29
(4) / (4) 45 (4) / (4) 29 (the number in parentheses is the number of electrode fingers with a reduced pitch) IDT wavelength λI ₁ : 2.06 μm, λI ₂ : 1.88 μm Reflector wavelength λR: 2 .07 μm Number of reflectors: 100 IDT-IDT interval: 0.50 λI ₂ Interval between portions between electrode fingers of wavelengths λI ₁ and λI ₂ (215, 216, 217, 218 in FIG. 1): 0.25λI
₁ + 0.25λI ₂ IDT-reflector interval: 0.47λR duty: 0.60 (both IDT and reflector) Electrode film thickness: 0.080λI ₁ The detailed design of the surface acoustic wave resonator 202 is shown below. Intersection width W: 49.1λ Number of IDTs: 401 Wavelength λ (both IDT and reflector): 2.04 μm Number of reflectors: 30 IDT-reflector interval: 0.50λ duty: 0.60 (both IDT and reflector) Electrode film Thickness: 0.080λ The detailed design of the surface acoustic wave resonator 203 is shown below. Intersection width W: 40.6λ Number of IDTs: 241 Wavelength λ (both IDT and reflector): 1.97 μm Number of reflectors: 30 IDT-reflector interval: 0.50λ duty: 0.60 (both IDT and reflector) Electrode film Thickness: 0.084λ The above “interval” refers to the distance between two electrode fingers adjacent to each other.
It is the distance between centers in the width direction. In addition, the duty of each of the electrode fingers 219 and 220, which is a feature point in the first embodiment, is set to 0.40.

The operation and effect of such a surface acoustic wave filter will be described below. First, FIG. 2 shows the amplitude balance between balanced signal terminals with respect to frequency in the configuration of the first embodiment, and FIG. 3 shows a graph of the degree of phase balance. As a comparison, each ID in the IDT 205 shown in FIG.
The amplitude balance and the phase balance in the configuration of the conventional example having the IDT 205a in which the duty of the electrode finger adjacent to T204 and 206 is not changed are also shown in FIG. 2 and FIG. 3, respectively. The frequency range of the pass band in the PCS receiving filter is 1930 MHz to 1990 MHz.

The configuration of the prior art shown in FIG. 4 is different from the first embodiment in that each IDT 204, 206 in the IDT 205 is different from the first embodiment.
The configuration is exactly the same, except that the duty of the electrode finger adjacent to is not changed. In FIG. 4, the description of each of the reflectors 202b, 202c, 203b, and 203c is omitted in order to simplify the description of each of the surface acoustic wave resonators 202 and 203. The same applies to the following drawings.

The maximum amplitude balance in this range is 2.3 dB in the conventional example, while it is 2.0 dB in the first embodiment, which is an improvement of about 0.3 dB. Next, the phase balance is 7.0 degrees at the maximum in the conventional example, but is 6.0 degrees at the maximum in the first embodiment, which is an improvement of about 1.0 degree.

This corresponds to each IDT2 in the IDT205.
By making the duty of the electrode finger adjacent to the electrode fingers 04 and 206 smaller than the duty of the other electrode fingers, the total capacity of the electrode fingers connected to the balanced signal terminal 210 and the balanced signal terminal 211 and the electric signal This is the effect of correcting the conversion efficiency of the surface acoustic wave.

The difference in the total capacitance and the like of the electrode fingers is particularly
Since one IDT is large at each electrode finger in the vicinity of a place (facing area) adjacent to each other, as in the first embodiment, each IDT is located in the vicinity of the place (preferably adjacent to the place). At least one dut in the electrode finger
The largest effect can be obtained by adjusting y.

In order to further obtain the effect, as shown in FIG. 5, the two IDTs are close to each other where they are adjacent to each other.
The duty of at most several (plurality, 10% or less of the number of IDTs, more preferably 5% or less (decimal point is rounded up)) electrode duty is reduced, for example, to small (like IDT205b).
Adjust it.

Next, as another modified example of the first embodiment of the present invention, as shown in FIG. 6, the IDTs 204 and I shown in FIG.
The duty of the electrode fingers (the electrode fingers 301 and 302 in FIG. 6) adjacent to the IDT 205 in the DT 206 is
IDT 204a smaller than the duty of other electrode fingers
FIG. 7 shows a graph of the amplitude balance between the balanced signal terminals with respect to the frequency, and FIG. 8 shows a graph of the phase balance when the IDT 206a and the IDT 206a are provided. In this case, IDT 205
Is the IDT 205a described above.
It is also possible to leave 5 as it is.

At this time, the duty between the electrode finger 301 and the electrode finger 302 is 0.40. As a comparison, FIG.
7 and 8 also show the amplitude balance and the phase balance in the conventional configuration of FIG. 7 and 8, in the frequency range of the pass band of the PCS receiving filter, the configuration of FIG. 6 improves the amplitude balance by about 0.3 dB and the phase balance by about 1.5 degrees with respect to the conventional example. ing.

As described above, the effect of the present invention can be obtained by adjusting the duty of at least one of the electrode fingers of the IDTs 204a and 206a connected to the unbalanced signal terminal as shown in FIG. Of course, in addition to this, IDT2
The effect of the present invention can be obtained even if the duty is adjusted for 05a.

As described above, in the first embodiment, in the surface acoustic wave filter having the balance-unbalance conversion function, the two IDTs have the duplication of the electrode finger at the adjacent position.
By adjusting ty, a surface acoustic wave filter in which the degree of balance between balanced signal terminals is improved as compared with the conventional surface acoustic wave filter can be obtained.

In the first embodiment, the three IDTs 204, 205, and 20 of the longitudinally coupled resonator type surface acoustic wave filter are used.
Although the total number of the IDTs 205 at the center among the six IDTs is an odd number, the effect of the present invention can be obtained even if the number of the IDTs 205 is an even number as shown in FIG.

In the first embodiment, a longitudinally coupled resonator type surface acoustic wave filter has a configuration in which two surface acoustic wave resonators are connected in series to one longitudinally coupled resonator type surface acoustic wave filter having three IDTs. Although a configuration in which a balanced signal is obtained from the central IDT has been described, the present invention is not limited to this configuration, and a similar effect can be obtained in a surface acoustic wave filter having any configuration of balanced signal terminals.

For example, surface acoustic wave resonators 202 and 203
Is not connected, in the case of a longitudinally coupled resonator type surface acoustic wave filter having two or three or more IDTs, or in the case where surface acoustic wave resonators are connected in parallel, an unbalanced signal as shown in FIG. IDT of longitudinally coupled resonator type surface acoustic wave filter
The same effect can be obtained even when input (output) is performed from the opposite sides of the above, or when the longitudinally coupled resonator type surface acoustic wave filters are cascaded in two stages as shown in FIG. In the case of FIG. 10, for example, instead of the IDT 206 shown in FIG. 1, for example, the IDT 206 b
Is provided.

A surface acoustic wave filter according to a second embodiment of the present invention will be described below with reference to FIG.
In the first embodiment, each ID in the IDT 205
Dut of only electrode fingers adjacent to T204, 206
Although y is set to 0.40, in the second embodiment, FIG.
Is connected to the balanced signal terminal 210,
The IDT 205 shown in FIG. 1 has an IDT 205d in which all electrode fingers have a duty of 0.40, instead of the IDT 205. All other configurations are the same as those of the first embodiment.

FIG. 13 is a graph showing the amplitude balance between the balanced signal terminals with respect to the frequency in the configuration of the second embodiment, and FIG. 14 is a graph showing the phase balance. For comparison, the amplitude balance and the phase balance in the configuration of the conventional example shown in FIG. 4 are also shown.

The maximum amplitude balance in the frequency range of the pass band of the PCS receiving filter is 2.3 dB in the conventional example, whereas it is 1.6 dB in the second embodiment, which is about 0.7 dB. The balance has improved. However, the phase balance is 7.0 degrees in the conventional example, but is 7.5 degrees in the second embodiment, which is about 0.5 degrees, which is a deterioration of the phase balance.

As shown in FIG. 12, when all the duty of each electrode finger of the IDT 205d connected to the balanced signal terminal 210 is adjusted, the amplitude balance can be further improved, but the phase balance is worsened. Would. However, FIG.
By adjusting the required number of electrodes without adjusting all the electrode fingers as in 2, or by making the adjustment amounts of duty different for each electrode finger, the amplitude balance can be adjusted without deteriorating the phase balance. It is possible to improve.

In the second embodiment, among the three IDTs of the longitudinally coupled resonator type surface acoustic wave filter, the total number of the central IDTs is an odd number. However, as shown in FIG. Even if there is, the effect of the present invention can be obtained similarly.

FIG. 16 shows a third embodiment of the present invention.
This will be described below based on The third embodiment of FIG.
As shown in FIG. 6, the IDT 204 and the IDT 20 shown in FIG.
The electrode fingers 401 of the IDT 205 at the places where
IDT205f with reduced duty of IDT205
It has in place of.

Further, the IDT 205 and the IDT 205 shown in FIG.
In an area adjacent to the IDT 206, the IDT 206 is formed by thinning out the electrode fingers 402 of the IDT 206.
c is provided instead of the IDT 206.

The thinning weighting is a method for controlling the cross width of the IDT. For example, in the case of the IDT 206c, one of the comb-shaped electrode fingers is omitted (that is, the cross width is reduced to zero).

The operation of such a configuration will be described. When thinning-out weighting is applied to a portion where two IDTs are adjacent to each other, the same as adjusting the duty, the electrode fingers of the balanced signal terminals 210 and 211 are adjusted. Total capacity can be corrected. That is, by further applying the thinning-out weighting to the duty adjustment according to the present invention, the degree of freedom in adjusting the degree of balance can be further improved.

In the surface acoustic wave filters according to the first to third embodiments, the piezoelectric substrate 200 made of 40 ± 5 ° YcutX propagating LiTaO ₃ is used, but as can be seen from the principle of obtaining the effect. However, the present invention is not limited to the piezoelectric substrate 200, and the 64 ° to 72 ° YcutX propagation Li
A similar effect can be obtained with a piezoelectric substrate such as NbO ₃ or 41 ° YcutX-propagating LiNbO ₃ .

In the first to third embodiments, the present invention has been described with a configuration in which the input impedance and the output impedance are substantially equal. However, as can be understood from the principle of the present invention, the input impedance and the output impedance are different. However, the effects of the present invention can be obtained even in configurations different from each other.

For example, as shown in FIG. 17, two longitudinally coupled resonator type surface acoustic wave filters 41 whose phases are different by 180 degrees
1 and 412 are connected in parallel. As shown in FIG. 18, an unbalanced signal terminal 209 is connected to the central IDT 502, and the IDTs 502 and 503 sandwich the IDT 502 from the left and right, respectively, and are 180 ° out of phase with each other. The effect of the present invention can be obtained even in a configuration in which the signal terminals 210 and 211 are connected.

Further, as shown in FIG.
The center IDT 632 sandwiched from the left and right by the IDTs 631 and 633 connected to the terminal 09 is divided into two in the propagation direction of the surface acoustic wave, and the balanced signal terminals 210 and
A configuration in which two IDTs 211 are connected, as shown in FIG.
701, 703, 704, 705 along the propagation direction of the surface acoustic wave, and the IDTs 701, 703, 70
5 is connected to the unbalanced signal terminal 209, and the IDTs 702 and 7 are connected.
The effect of the present invention can also be obtained with a configuration in which balanced signal terminals 210 and 211 are connected to each of the components 04.

Further, as shown in FIG.
01, 802, and 803 along the surface acoustic wave propagation direction, the unbalanced signal terminal 209 is connected to the IDTs 801 and 803, and the IDT 802 is divided into two in the cross width direction, and the balanced signal terminals 210 and 211 are respectively connected. The effect of the present invention can be obtained even in a connected configuration.

Next, a communication device according to a fourth embodiment of the present invention will be described with reference to FIG. As shown in FIG.
The communication device 600 includes a receiver (Rx
Side), antenna 601, antenna common part / RFT
op filter 602, amplifier 603, Rx interstage filter 604, mixer 605, 1st IF filter 606, mixer 607, 2nd IF filter 608, 1st + 2n
d Local synthesizer 611, TCXO (temperatur
e compensated crystal oscillator (temperature compensated crystal oscillator) 612, divider 613, local filter 6
14 is provided.

The Rx interstage filter 604 to the mixer 605
As shown in FIG. 22, it is preferable to transmit each balanced signal in order to secure balance.

The communication device 600 is used as a transceiver side (Tx side) that performs transmission.
And the above-mentioned common antenna / RFTop filter 602
, A Tx IF filter 621, a mixer 622, a Tx inter-stage filter 623, an amplifier 624, a coupler 625, an isolator 626, and an APC (automatic power supply).
er control (automatic output control) 627.

As the Rx interstage filter 604, the surface acoustic wave filters described in the first to third embodiments of the present invention can be suitably used.

The surface acoustic wave filter according to the present invention has an unbalanced-balanced conversion function as well as a filter function.
It has excellent characteristics that the amplitude characteristics and phase characteristics between the balanced signals are closer to ideal.

Therefore, the communication apparatus of the present invention having the above-mentioned surface acoustic wave filter can reduce the number of components and size by using the above-mentioned surface acoustic wave filter having a complex function. -Transmission characteristics can be improved by an excellent conversion function between unbalanced signals.

[0070]

As described above, the surface acoustic wave filter of the present invention has a plurality of IDTs on a piezoelectric substrate along the propagation direction of surface acoustic waves, and has a balanced signal input terminal or a balanced signal input / output terminal. In the surface acoustic wave filter having
The configuration is such that the duty of at least some of the electrode fingers of the DT is different from the duty of other electrode fingers.

Therefore, in the above configuration, the duty of at least a part of the electrode fingers of each IDT is changed to the duty of the other electrode fingers.
, It is possible to improve the degree of balance between the balanced signal terminals.

As described above, the communication device of the present invention has the above-described surface acoustic wave filter.

Therefore, the above configuration has a filter function and
Since the surface acoustic wave filter has an excellent function of converting between a balanced signal and an unbalanced signal, the size of the filter can be reduced by combining the functions, and the transmission characteristics can be improved by the excellent conversion function.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a surface acoustic wave filter according to a first embodiment of the present invention.

FIG. 2 is a graph showing a difference in amplitude balance between the first embodiment and a conventional example.

FIG. 3 is a graph showing a difference in the degree of phase balance between the first embodiment and the conventional example.

FIG. 4 is a schematic configuration diagram showing a conventional surface acoustic wave filter for comparison with the surface acoustic wave filter according to each embodiment of the present invention.

FIG. 5 is a schematic configuration diagram showing a modification of the first embodiment.

FIG. 6 is a schematic configuration diagram showing another modified example of the first embodiment.

7 is a graph showing a difference in amplitude balance between the surface acoustic wave filter shown in FIG. 6 and a conventional example.

8 is a graph showing a difference in the degree of phase balance between the surface acoustic wave filter shown in FIG. 6 and a conventional example.

FIG. 9 is a schematic configuration diagram showing still another modified example of the first embodiment.

FIG. 10 is a schematic configuration diagram showing still another modified example of the first embodiment.

FIG. 11 is a schematic configuration diagram showing still another modified example of the first embodiment.

FIG. 12 is a schematic configuration diagram of a surface acoustic wave filter according to a second embodiment of the present invention.

FIG. 13 is a graph showing a difference in amplitude balance between the second embodiment and the conventional example.

FIG. 14 is a graph showing a difference in the degree of phase balance between the second embodiment and the conventional example.

FIG. 15 is a schematic configuration diagram showing a modification of the second embodiment.

FIG. 16 is a schematic configuration diagram of a surface acoustic wave filter according to a third embodiment of the present invention.

FIG. 17 is a schematic configuration diagram of a surface acoustic wave filter according to the present invention in which input impedance and output impedance are different.

FIG. 18 is a schematic configuration diagram of a modified example of the surface acoustic wave filter.

FIG. 19 is a schematic configuration diagram of another modified example of the surface acoustic wave filter.

FIG. 20 is a schematic configuration diagram of still another modified example of the surface acoustic wave filter.

FIG. 21 is a schematic configuration diagram of still another modified example of the surface acoustic wave filter.

FIG. 22 is a main block diagram of a communication device according to a fourth embodiment of the present invention.

FIG. 23 is a schematic configuration diagram showing a conventional surface acoustic wave filter having a balance-unbalance conversion function.

FIG. 24 is a schematic configuration diagram of a surface acoustic wave filter in FIG. 23 in which one of the balanced signal terminals is connected to ground.

FIG. 25 is a schematic configuration diagram of a surface acoustic wave filter in which the other of the balanced signal terminals is connected to the ground in FIG.

FIG. 26 is a graph showing a difference between frequency-amplitude characteristics in each of the surface acoustic wave filters of FIGS. 24 and 25.

[Description of Signs] 204 IDT (comb-shaped electrode section) 205 IDT (comb-shaped electrode section) 206 IDT (comb-shaped electrode section) 210 Balanced signal terminal 211 Balanced signal terminal 219 Electrode finger 220 Electrode finger

Claims (8)

[Claims] 1. A comb-shaped electrode portion comprising a plurality of comb-shaped electrode portions on a piezoelectric substrate, the plurality of comb-shaped electrode portions including a plurality of opposing comb-shaped electrodes provided with electrode fingers, along the propagation direction of the surface acoustic wave. In the surface acoustic wave filter having a balanced signal input terminal or a balanced signal output terminal connected to, the duty of at least a part of the electrode fingers of each of the comb-shaped electrode portions is different from the duty of other electrode fingers. A surface acoustic wave filter. 2. The surface acoustic wave filter according to claim 1, wherein at least one duty of each electrode finger at a position where the two comb-shaped electrode portions are adjacent to each other is different from the duty of another electrode finger. A surface acoustic wave filter characterized by the above-mentioned. 3. The surface acoustic wave filter according to claim 1, wherein the duty of an electrode finger located near a position where two comb-shaped electrode portions are adjacent to each other is made different from the duty of another electrode finger. A surface acoustic wave filter. 4. The surface acoustic wave filter according to claim 1, wherein at least one of the interdigital electrodes of at least one of the interdigital electrodes has a duty of at least several electrode fingers and a duty of other electrode fingers. A surface acoustic wave filter characterized by being different from the above. 5. The surface acoustic wave filter according to claim 1, wherein the electrode fingers at positions where two comb-shaped electrode portions are adjacent to each other are thinned and weighted. 6. The surface acoustic wave filter according to claim 1, wherein each of the comb-shaped electrode portions is set to a longitudinally coupled resonator type. 7. A surface acoustic wave filter according to claim 1, wherein at least one surface acoustic wave resonator is connected in series, in parallel, or both. Surface wave filter. 8. A communication device comprising the surface acoustic wave filter according to claim 1.