JPH09172340A - Branching filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a branching filter which can securely execute impedance matching with few reception elements in spite of the impedance characteristic of a band pass filter to be used and which is easily manufactured. SOLUTION: The branching filter 11 is provided with an input. terminal 12 connected to a transmission system. First and second band pass filters F1 and F2 are connected to the input terminal 12 in parallel. Transmission lines DL1 and DL2 whose characteristic impedance is different. from that of the transmission system are connected between the first, and second band pass filters F1 and F2 and the input terminal 12. The characteristic impedance of the transmission lines DL1 and DL2 are selected in such a way that impedance in the pass bands of the band pass filters F1 and F2. to which the transmission lines are connected is matched with the impedance of the transmission system, a phase beyond the pass bands us rotated and impedance is manacle high.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a duplexer in which two bandpass filters are connected in parallel, and more particularly to a duplexer having an improved matching circuit for matching the impedance of each bandpass filter.

[0002]

2. Description of the Related Art A duplexer is a device that separates two types of signals from a common transmission system by utilizing the difference in carrier frequencies.
In particular, in recent years, the use of a duplexer as an antenna duplexer for separating transmission / reception signals in mobile communication has been increasing.

The basic structure and characteristics of a conventional duplexer will be described with reference to FIGS. 1 and 2. In the duplexer 1 shown in FIG. 1, the first band-pass filter F1 and the second band-pass filter F2 are connected to the input terminal 2, and the first and second band-pass filters F1 and F2 are parallel to each other. It is connected. The attenuation frequency characteristics of the first and second bandpass filters F1 and F2 are as shown in FIG.

In FIG. 2, the characteristic curves indicated by F1 and F2 are the first and second band-pass filters F, respectively.
1 shows the characteristics of F2. That is, the first band-pass filter F1 has the frequency band f1 as the pass band, and the second band-pass filter F2 has the frequency band f2 as the pass band. Therefore, the passband of the first bandpass filter F1 is the attenuation band of the second bandpass filter F2, while the passband of the second bandpass filter F2 is the attenuation band of the first bandpass filter F1.

In order for the demultiplexer 1 to exhibit good characteristics, the bandpass filters F1 and F2 must be matched to appropriate impedances. In this case, the appropriate impedance means the bandpass filters F1,
The impedance when looking at F2 is matched with the impedance of the transmission system in the pass band of the filter, and the impedance becomes very high in the frequency region corresponding to the pass band of the other filters F ₂ and F _1. I say the condition.

Taking the duplexer shown in FIG. 1 as an example, the impedance seen from the point A is matched in the frequency domain f1 in the first band-pass filter F1, and the impedance is seen in the frequency domain f2.
It is necessary to satisfy a condition that the impedance is high and that the second band-pass filter F2 has a high impedance in the frequency region f1 and impedance matching is achieved in the frequency region f2.

However, such a condition is not always satisfied in a general duplexer in which the first and second bandpass filters F1 and F2 having different pass bands are connected in parallel. Normally, a circuit for phase rotation for rotating the phase outside the pass band was usually inserted between the filters F1 and F2 and the connection point A.

To rotate the phase of the filter, a method of inserting a transmission line between the filter and the input / output terminal is generally used. The transmission line rotates the phase of the filter in the positive direction, and its rotation angle is determined by the length of the transmission line. In this case, by making the characteristic impedance of the transmission line equal to the impedance of the transmission system, it is possible to rotate only the phase without changing the impedance matching state in the pass band of the filter.

FIG. 3 is a circuit diagram showing an example of a demultiplexer using the above transmission line. Between the connection point A and the first and second band-pass filters F1 and F2, the transmission lines DL1 and DL2 having a characteristic impedance equal to the impedance of the transmission system.
Are connected respectively.

By selecting the lengths of the transmission lines DL1 and DL2, as shown in FIGS. 4A and 4B, only the phase can be rotated without changing the matching state of the pass band. That is, in FIG. 4A, in the first bandpass filter F1, the left side of the arrow is a Smith chart showing the phase rotation before connecting the transmission line DL1, and the right side of the arrow connects the transmission line DL1. It is a Smith chart which shows the subsequent phase rotation. By connecting the transmission line DL1, it can be seen that the phase in the frequency region f2, which is the attenuation region, can be rotated without significantly changing the impedance in the frequency region f1. Similarly, in the second band-pass filter F2 as well, by connecting the transmission line DL2 from the state shown on the left side of the arrow in FIG. 4B, the phase in the frequency domain f2 is positively changed without significantly changing the impedance. It can be seen that the impedance is increased in the frequency region f1 which is the attenuation region by rotating the motor in the direction.

If the band-pass filter is not impedance-matched with the outside by itself, first, the reactance element is used to achieve impedance junction in the pass band, and then the phase outside the pass band is rotated by the transmission line. The method has been adopted. FIG. 5 shows a conventional duplexer having such a configuration.

In the duplexer 5 shown in FIG. 5, a reactance element composed of an inductance L1 and an electrostatic capacitance C1 is connected between the connection point A and the bandpass filter F1 in addition to the transmission line DL1. Similarly, between the connection point A and the second bandpass filter F2, in addition to the transmission line DL2, a reactance element including an inductance L2 and a capacitance C2 is connected. 6 (a) and 6 (b)
6A and 6B are Smith charts for explaining an impedance matching method of the first and second bandpass filters F1 and F2 in the duplexer 5 shown in FIG. 5, respectively.

As is apparent from FIG. 6A, the first bandpass filter F1 to which the transmission line DL1 and the reactance element are not connected has the characteristics shown in the Smith chart shown on the leftmost side. Therefore, it is understood that the impedance is not matched with the impedance Zs of the transmission system in the frequency region f1 which is the pass band. Therefore,
By connecting the reactance element including the inductance L1 and the electrostatic capacitance C1, impedance matching in the pass band can be achieved as shown in the Smith chart at the center of FIG. 6A. Further, by connecting the transmission line DL1 having the same characteristic impedance value as the transmission system, as shown in the Smith chart on the right side of FIG. 6A,
The phase is rotated, and the impedance in the frequency domain f2, that is, the pass band of the second band pass filter F2 is made very large.

Similarly, in the second bandpass filter F2 as well, according to the characteristic of the filter itself shown on the leftmost side of FIG. 6B, the impedance in the frequency region f2, which is the passband, is matched with the impedance Zs of the transmission system. Absent. On the other hand, as shown in the center of FIG. 6B, by connecting a reactance element composed of an inductance L2 and an electrostatic capacitance C2, impedance matching in the frequency domain f2 is achieved, and further the characteristic impedance is transmitted. By connecting the transmission line DL2 which is the same as the above, the phase is rotated, and as shown in the rightmost characteristic of FIG.
That is, the impedance in the attenuation band of the second bandpass filter F2 is made very high.

Further, as disclosed in Japanese Patent Laid-Open No. 5-16837, depending on the impedance of the bandpass filter used, the reactance element such as the inductance or the capacitance alone is used to form the passband of the other bandpass filter. It may be possible to increase the impedance in the region.

[0016]

As described above, in the conventional duplexer, the first and second bandpass filters having different pass bands are connected in parallel, and the pass band of each filter is connected to the transmission system. Impedance matching is achieved, and impedance is increased in the attenuation band, which is the pass band of the other band filter, to realize the characteristics as a duplexer.

However, as in the demultiplexer shown in FIG. 3, the above effect can be obtained by connecting only the transmission lines DL1 and DL2 to the filter. Only when F1 and F2 are impedance-matched within the pass band. That is, when the band-pass filters F1 and F2 are not impedance-matched within the pass band, the reactance elements such as the inductance L1 and the capacitors C1 and C2 must be connected as described above.

Although a method of performing phase rotation only by an LC circuit has been proposed, in this case, the impedance characteristic before coupling of the bandpass filters F1 and F2 is limited, and therefore, it can be used also. There is a problem that the bandpass filter is limited.

Of the various methods described above, the method of rotating the phase using a transmission line after achieving impedance matching in the pass band of the band filter, that is, the configuration of the demultiplexer 5 shown in FIG. It has the advantages that the number of filters is small and the circuit configuration is easy to understand. However, two reactance elements and transmission lines must be connected to each of the bandpass filters F1 and F2, and up to six circuit elements are required only on the side of the connection point A, The circuit becomes complicated and the work of adjusting each element is inevitable.

Therefore, an object of the present invention is to separate two types of signals with high accuracy regardless of the impedance characteristics of the bandpass filter used, that is, the impedance characteristics of the bandpass filter to be used are not so limited. It is to provide a demultiplexer capable of performing.

[0021]

According to a broad aspect of the present invention, an input terminal or an output terminal connected to a transmission system and the input terminal or the output terminal are connected in parallel with each other. A transmission line connected between the first and second bandpass filters having different passbands, the input terminal or the output terminal, and at least one of the first and second bandpass filters; The characteristic impedance of the transmission line is selected so that the impedance in the pass band of the at least one band filter is matched with the impedance of the transmission system, and the phase outside the pass band is rotated, and the characteristic impedance of the transmission system is A duplexer is provided that is different from the impedance.

In the duplexer of the present invention, a transmission line is connected between the input terminal or the output terminal of the duplexer and at least one of the first and second bandpass filters, and the transmission line is connected. The characteristic impedance of the line is different from the impedance of the transmission system, but as described above,
It is selected to match the impedance in the passband of the at least one bandpass filter to the impedance of the transmission system and rotate the phase outside the passband. Therefore, as is clear from the description of the embodiments below, the phase rotates in the positive direction on the Smith chart, so that the impedance outside the pass band, particularly in the pass band of the other band filter, is increased. Not only that, the phase rotation is performed so as to match the impedance in the pass band with the impedance of the transmission system, so that the impedance of the filter seen from the connection point in the pass band is also effectively matched with the impedance of the transmission system. .

Therefore, by connecting the transmission line having the characteristic impedance selected as described above so as to be different from the impedance of the transmission system, not only the high impedance outside the pass band due to the rotation of the phase but also the passage can be obtained. Impedance matching within the band can also be achieved.

In a particular aspect of the present invention, a reactance element is further connected between a connection point of the transmission line and at least one of the first and second bandpass filters and the reference potential. This reactance element is configured to match the impedance of the at least one band filter as viewed from the input terminal or output terminal side with the impedance of the transmission system. Therefore, by further including the reactance element, The impedance can be easily matched with the impedance of the transmission system.

According to another specific aspect of the present invention, the transmission line has a relatively low characteristic impedance with a first transmission line connected in series with each other and having a relatively high characteristic impedance. A second transmission line.
In this case, the first transmission line is connected to the input terminal or output terminal side, and the second transmission line is connected to the at least one filter side. According to such a configuration, as is clear from the description of the third embodiment described later, not only can the phase be rotated to the high impedance side in the pass band of the band filter on the other side, but the reflection coefficient can be increased. Therefore, the deterioration of the insertion loss can be effectively suppressed.

According to still another specific aspect of the present invention, the first and second bandpass filters are surface acoustic wave filters, the transmission line is built in the multilayer substrate, and the transmission line is provided on the multilayer substrate. The surface acoustic wave filter is fixed. Similarly, when a transmission line and a reactance element are used,
The second bandpass filter is a surface acoustic wave filter,
The transmission line and the reactance element are built in the multilayer substrate, and in this case also, the surface acoustic wave filter is fixed on the multilayer substrate.

As described above, when the transmission line or the transmission line and the reactance element are built in the multi-layer substrate, the impedance matching circuit portion according to the present invention can be formed in the multi-layer substrate. The duplexer of the present invention can be provided as an integrated component packaged using a substrate.

In particular, the matching circuit of the duplexer according to the present invention comprises the above-mentioned transmission line or the transmission line and the reactance element. The transmission line is provided with a line electrode in the central layer in the multilayer substrate. By forming the ground electrodes above and below it, that is, as a triplate line, it can be easily constructed in the multilayer substrate.
Similarly, a capacitive element as a reactance element can be easily manufactured by forming electrodes above and below the layers in the multilayer substrate. Therefore, if a multilayer substrate provided with the transmission line or the transmission line and the reactance element as described above is prepared, only by mounting the surface acoustic wave filter on the multilayer substrate, the demultiplexer of the present invention can be processed as one component. The container can be easily configured.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment FIG. 7 is a circuit diagram showing a duplexer according to a first embodiment of the present invention. In the demultiplexer 11, the first and second pass bands are different.
The second bandpass filters F1 and F2 are connected to the input terminal 12. However, the first and second bandpass filters F1,
Transmission lines DL1 and D are provided between F2 and the input terminal 12.
L2 are respectively connected.

In the present embodiment, the impedance of the transmission system to which the duplexer is connected is 50Ω. The band-pass filters F1 and F2 are each composed of a surface acoustic wave filter, and each of them has the attenuation amount frequency characteristic shown in FIG. In FIG. 8, the bandpass filters F1,
The attenuation-frequency characteristics of F2 are represented by the curves indicated by the arrows of F1 and F2, respectively.

FIG. 9 shows the reflection characteristics of the bandpass filters F1 and F2 alone as seen from the input terminals 13 and 14. FIG.
As is clear from (a), in the bandpass filter F1, the impedance seen from the connection point side in the frequency region f1 which is the pass band is deviated to the higher impedance side than the impedance of the transmission system. On the contrary, in the bandpass filter F2, the impedance is shifted to the side lower than the impedance of the transmission system in the frequency region f2 that is the passband. Further, at the frequencies corresponding to the pass bands of the band filters F ₂ , F ₁ of the other side of the band filters F ₁ , F ₂ , respectively,
The phase is capacitively located. Therefore, in order to move the phase to the high impedance side in the frequency region corresponding to the pass band of the other band filter, it is understood that the transmission line is connected and the phase is rotated by about 270 ° in the positive direction.

However, the characteristic impedance is 50
When a transmission line of Ω is connected, the impedance in the pass band shifts to the low impedance side. Therefore,
In the present embodiment, the characteristic impedance of the transmission lines DL1 and DL2 is made different from the impedance Zs of the transmission system = 50Ω, impedance matching in the pass band and phase rotation in the pass band of the other band filter are performed simultaneously, and good demultiplexing is performed. It has realized the characteristics of vessels.

That is, in this embodiment, the transmission line DL1 is a transmission line having a characteristic impedance of 45Ω, and the transmission line DL2 is a characteristic impedance of 55.
A transmission line of Ω is used, and thereby a duplexer having the attenuation frequency characteristic shown in FIG. 10 and the reflection characteristic shown in FIG. 11 is configured. As is clear from FIG.
It can be seen that this duplexer matches the impedance of the transmission system in the pass band. Further, phase rotation is performed due to the difference in the characteristic impedance, and high impedance is realized in the stop band outside the pass band of the band-pass filters F1 and F2. That is, good demultiplexer characteristics are realized. The reason for this will be described with reference to FIGS.

FIG. 12 is a Smith chart for explaining phase rotation due to transmission lines having different characteristic impedances, and FIG. 13 is a diagram showing a circuit configuration for explaining phase rotation shown in FIG. As shown in FIG. 13, a circuit in which the transmission line DL is connected to the bandpass filter F is assumed. Here, the impedance of the transmission system, that is, the measurement system is Zs, and the characteristic impedance of the transmission line DL is Z ₀ .

In this case, the impedance of the bandpass filter F viewed from the point A in FIG. 13 rotates in phase as indicated by arrows B to D in FIG. 12 by changing the impedance value Z0 of the transmission line.

Arrow B in FIG. 12 indicates that the impedance of the transmission line DL is lower than the impedance of the transmission system (Z
0 <Zs) and the impedance Z of the Smith chart
It rotates on the circumference centered on the point on the side of lower impedance than the point of s. Similarly, arrow C and arrow D
Indicates that the impedance of the transmission line DL is Z0 = Zs, Z0
The phase rotation when> Zs is shown. In these cases, in the Smith chart, the phase rotates on a circle centered on Zs (in the case of arrow C) or rotates on a circle centered on a point on the side of higher impedance than Zs. This is the case (in the case of arrow D).

As described above, it is understood that the center position of phase rotation can be changed by changing the characteristic impedance of the transmission line DL. Therefore, it can be seen that by using the transmission line having an appropriate characteristic impedance, the phase rotation and the pass band matching can be achieved at the same time.

In this embodiment, the characteristic impedances of the transmission lines DL1 and DL2 are selected according to the above method. That is, in the present embodiment, the characteristic impedance of the transmission line DL1 connected to the bandpass filter F1 whose pass band is shifted toward the low impedance side is selected to be lower than the impedance Zs of the transmission system. Therefore, FIG.
The transmission line DL1 is added to the bandpass filter F1 whose reflection characteristic is shown in the Smith chart shown on the left side of (b).
It can be seen that, when is connected to rotate the phase, the phase rotates around a point on the lower impedance side than the impedance Zs of the transmission system, and is matched with the impedance Zs in the pass band. In this case, it can be seen that the impedance becomes high in the frequency region f2 which is the pass band of the band filter F2 of the other party.

By connecting the transmission line DL2 to the bandpass filter F2, the phase rotation of the bandpass filter F2 having the reflection characteristic shown on the left side of FIG. 14B is higher than the impedance Zs of the transmission system. It turns out that the frequency region f2 that is the pass band is matched with the impedance Zs by rotating around the impedance side, while the impedance becomes high in the frequency region f1 that is the pass band of the partner band filter F1.

That is, in the duplexer of the present embodiment, the bandpass filter F whose pass band is shifted to the low impedance side.
By connecting the transmission line DL1 having a low characteristic impedance to 1 to rotate the phase around the lower impedance side than the impedance Zs of the transmission system, the frequency range f1 which is the pass band of the band pass filter F1 having a low pass band is It is matched to the impedance Zs of the transmission system, and the other side bandpass filter F2 is generated by phase rotation.
The frequency region f2, which is the pass band of, has a high impedance.

On the contrary, in the bandpass filter F2 whose pass band is shifted to the high impedance side, by connecting the transmission line DL2 having a higher impedance than the impedance Zs of the transmission system, an impedance higher than the impedance Zs of the transmission system is obtained. The phase is rotated as a center, the impedance in the frequency region f2 which is the pass band of the band pass filter F2 is matched with the impedance Zs of the transmission system, and the impedance is phase rotated in the frequency region f1 corresponding to the pass band of the partner band filter F1. To increase the impedance. Therefore, it is possible to obtain the duplexer 11 that can exhibit the excellent characteristics shown in FIGS. 10 and 11.

Second Embodiment FIG. 15 is a circuit diagram showing a duplexer according to the second embodiment of the present invention. In the demultiplexer 21, bandpass filters F1 and F2 having different pass bands are connected to the input terminal 22 in parallel with each other. In addition, the impedance Zs of the transmission line is 5
It is set to 0Ω.

The first and second bandpass filters F1 and F2
FIG. 16 shows the attenuation frequency characteristic as a simple substance of FIG. 16 and the reflection characteristics are shown in FIGS. 17 (a) and 17 (b), respectively. FIG.
As is clear from 6, the pass band of the first band filter F1 is in the frequency domain f1 and the second band filter F2 is
Is in the frequency domain f2.

Further, as is clear from FIGS. 17A and 17B, in the present embodiment, the impedance in the pass band of the first band pass filter F1 is shifted to the side lower than the impedance Zs of the transmission system. . However, the band-pass filter F2 is impedance-matched in the frequency region f2 that is the pass band.

In the present embodiment, the bandpass filters F1,
Transmission lines DL1 and DL2 are connected between the input terminal 22 and a connection point on the side of the input terminals 22 and 23 of F2. The transmission line DL1 has a characteristic impedance of 40Ω.
And a capacitance C2 of 4 pF is added. As described above, the bandpass filter F2 is almost impedance-matched in the pass band, and therefore, the transmission line DL2 is a transmission line having a characteristic impedance of 50Ω.

Since the second band-pass filter F2 is impedance-matched in the pass band, it can be seen that it is only necessary to rotate the phase in the frequency domain f1 to the high impedance side. Therefore, as described above, as the transmission line DL2, a transmission line having a characteristic impedance of 50Ω, that is, a characteristic impedance equal to the impedance of the transmission system is used.

On the other hand, the bandpass filter F1 requires both impedance matching and phase rotation. In this case, as is apparent from FIG. 17A, only by adjusting the characteristic impedance of the transmission line DL1, impedance matching in the pass band and high impedance in the frequency region of the other pass band due to phase rotation cannot be realized. . That is, it is not possible to construct a duplexer having good characteristics only by using a transmission line whose characteristic impedance is different from that of the transmission line. Therefore, in the present embodiment, a reactance element is further connected, and thereby a duplexer corresponding to a bandpass filter having various input / output impedances can be configured.

A reactance element composed of an inductance L1 and a capacitance C1 is connected to the output side of the bandpass filter F1. Thereby, impedance matching on the output side is realized.

An impedance matching method in the duplexer of the second embodiment will be described with reference to FIGS. 20 (a) and 20 (b). FIG. 20A is a Smith chart for explaining the impedance matching method in the bandpass filter F1. First, the leftmost Smith chart in FIG. 20A shows the characteristics of the bandpass filter F1 as a single unit. When the transmission line is inserted, the impedance rotates clockwise as shown in the central Smith chart, but at a certain angle of rotation, a point Y0 intersecting the admittance circle y passing through the center of the Smith chart occurs. Then, the parallel reactance element (the capacitor C2 in the present embodiment) moves the impedance along the admittance circle.

Therefore, if the impedance of the pass band is rotated by the transmission line until it coincides with the point Y0 and a reactance element of an appropriate value is inserted in parallel to move to the impedance Zs of the transmission system. It can be seen that impedance matching can be achieved in the pass band. In this case, the phase outside the pass band also rotates, but when the characteristic impedance of the transmission line DL1 is equal to the impedance Zs of the transmission system, the length of the transmission line (that is, the phase rotation angle) and the value of the parallel capacitance are It is uniquely determined and the phase outside the pass band cannot be adjusted.

On the other hand, in the present embodiment, the characteristic impedance of the transmission line DL1 is different from the impedance Zs of the transmission system, and the phase outside the pass band is adjusted thereby. FIGS. 20A and 20B are diagrams for comparing the amount of phase rotation due to the difference in characteristic impedance of the transmission line. When the transmission line DL1 having a high characteristic impedance is used, as shown in FIG.
Impedance matching in the pass band can be achieved even if both the rotation angle and parallel capacitance of the transmission line are small.
The rotation angle of the phase outside the pass band is also small. Therefore, when a large phase rotation angle is required, a transmission line having a low characteristic impedance is used as shown in FIG. 20A, and a transmission line having a low characteristic impedance is used when the phase rotation angle is small. , It is possible to simultaneously perform impedance matching and phase adjustment within the pass band.

In the above method, two matching elements of the transmission line and the reactance element are required for each band filter, but the parallel capacitance to be connected to each band filter F1, F2 is combined into one element. be able to. Therefore, FIG.
Since it suffices to add the capacitance C2 shown in (3), the matching circuit elements required on the input terminal 22 side of the bandpass filters F1 and F2 are three elements of the transmission lines DL1 and DL2 and the capacitance C2.

As described above, in the second embodiment,
Since impedance matching is achieved by the transmission lines DL1 and DL2 and the capacitor C2, a duplexer having excellent characteristics having the attenuation frequency characteristic shown in FIG. 18 and the reflection characteristic shown in FIG. 19 can be configured.

Third Embodiment FIG. 21 is a circuit diagram for explaining a duplexer according to the third embodiment of the present invention. In the demultiplexer 31, the first and second bandpass filters F1 and F2 having different passbands are connected to the input terminal 32, and the bandpass filters F1 and F2 are connected.
Are connected in parallel with each other.

The band-pass filters F1 and F2 are surface acoustic wave filters, and the impedance of the transmission system to which the demultiplexer is connected is Zs = 50Ω. The bandpass filters F1 and F
The attenuation frequency characteristic of the single unit of No. 2 is as shown in FIG. 22, and its reflection characteristic is as shown in FIGS. 23 (a) and 23 (b).

As is apparent from FIG. 22, the pass band of the first band filter F1 is in the frequency domain f1 and the pass band of the second band filter F2 is in the frequency domain f2.
Further, in the frequency region f1 which is the pass band of the first band pass filter F1, impedance matching is not achieved in the first band pass filter F1 and the second band pass filter F2.
In, the impedance is almost matched in the frequency region f2 which is the pass band.

Referring to FIG. 21, the first band-pass filter F1 requiring impedance matching is
The transmission lines DL1 and DL2 are connected in series with the input terminal 32. These two transmission lines DL1 and DL2
Has a characteristic impedance of the transmission line DL1 on the side of the bandpass filter F1 of 40Ω and a characteristic impedance of the transmission line DL2 of the input terminal 32 side of 60Ω. Further, as the parallel capacitance C2, a capacitance of 6 pF is inserted between the transmission line DL2 and the input terminal 32. On the other hand, the second band-pass filter F2, which does not need impedance matching,
A transmission line DL3 having a characteristic impedance equal to the impedance of the transmission line is connected.

A reactance element having an inductance L1 = 10 nH and a parallel capacitance C1 = 8 pF is connected to the output side of the demultiplexer. Therefore, the demultiplexer 31 of the third embodiment is substantially the same as the demultiplexer 21 of the second embodiment except that the transmission line connected to the first bandpass filter is different. Have a configuration.

As described in the second embodiment, by using one transmission line and one reactance element,
An impedance matching circuit of the duplexer can be constructed. However, as in the present embodiment, by adding one more transmission line connected to the bandpass filter that requires impedance matching, the insertion loss can be effectively reduced, and the demultiplexing with more excellent characteristics can be performed. Can be configured.

Generally, the insertion loss of the duplexer is larger than the insertion loss of the bandpass filter alone. The cause of this is not only the loss of the matching element and the mismatch loss, but also the deterioration of the loss that occurs due to the low reflectance of the other-side band filter in the passband frequency region.

As shown in FIG. 24 (b), the transmission lines DL1 and DL2 are provided between the bandpass filter F1 and the input terminal 32.
The reflection characteristics in the case where is connected are as shown in FIG. In this case, when the reflection coefficient of the other side, that is, the second band-pass filter F2 is decreased, it is measured how much the insertion loss in the pass band of the first band-pass filter F1 changes, and the result shown in FIG. was gotten.

As is apparent from FIG. 25, the loss increases as the reflection coefficient of the other band filter decreases. Therefore, in order to reduce the insertion loss, not only the phase is rotated to the high impedance side in the pass band of the partner side band filter, but also the reflection coefficient of the filter itself, that is, the first band pass filter F1 is made as large as possible. That is, it can be seen that it is necessary to bring the impedance curve closer to the outer peripheral portion in the Smith chart. This can be easily realized by combining two types of transmission lines having different characteristic impedances.

That is, to explain with reference to the Smith chart of FIG. 24 (a), in the phase rotation by the transmission line, the characteristic impedance has a low characteristic impedance in the C region of the Smith chart (that is, the lower half region). When used, the phase rotates on a circle (y1) centered on the low impedance side of the Smith chart, and when a transmission line with high characteristic impedance is used, it rotates on a circle y2 centered on the high impedance side. become.

Therefore, in the C region of impedance (the lower half region of the Smith chart), the phase is L on the circumference y1 and L
In the sex area (the upper half area of the Smith chart), the circumference is y2.
If it is configured to rotate upward, the phase is always rotated so as to approach the outer peripheral portion of the Smith chart.

Therefore, in the duplexer of the third embodiment, the transmission line DL1 having a relatively low characteristic impedance is connected to the bandpass filter F1 side, and the transmission line DL2 having a relatively high characteristic impedance is connected to the input terminal 32 side. However, the insertion loss is reduced.

FIG. 26 shows the attenuation frequency characteristic of the duplexer of the third embodiment, and FIG. 27 shows the reflection characteristic thereof. As is clear from FIG. 27, also in the duplexer of the third embodiment, impedance matching is achieved in the passbands of the first and second bandpass filters F1 and F2, and the passage of the other side is caused by the phase rotation. Impedance is increased by phase rotation in the frequency region of the band. Further, the combination of the transmission lines DL1 and DL2 can suppress the deterioration of the insertion loss.

Fourth Embodiment FIG. 28 is a sectional view for explaining a duplexer according to a fourth embodiment of the present invention. The description of the first to third embodiments has been given centering on the impedance matching circuit of the duplexer of the present invention. Specifically, the duplexer of the present invention is, for example, the fourth embodiment shown in FIG. It can be configured like the duplexer according to the embodiment.

In the duplexer 41 shown in FIG. 28, first and second bandpass filters 43, 4 made of surface acoustic wave filters are provided on a laminated ceramic substrate 42 made of dielectric ceramics.
4 is fixed. A packaging material 45 is fixed on the laminated ceramic substrate 42, and the packaging material 45 has a shape capable of forming a space for accommodating the band-pass filters 43 and 44 therein.

Transmission lines 46 and 47 are formed in the laminated ceramic substrate 42. The transmission lines 46 and 47 are
Each is electrically connected to electrodes 48 and 49 formed on the upper surface of the ceramic multilayer substrate 42. Electrodes 48,4
9 is electrically connected to the bandpass filters 43 and 44 by bonding wires 50 and 51. Transmission line 46,
The other end of 47 is led out to the side surface of the ceramic multilayer substrate and electrically connected to the external electrodes 52 and 53 formed on the side surface.

On the other hand, the electrodes connected to the other potential of the bandpass filters 43 and 44 are electrically connected to the electrode pads 56 and 57 by the bonding wires 54 and 55.
The electrode pads 56 and 57 are drawn out from positions not shown.

Further, ground electrodes 58 and 59 are formed on the upper and lower sides of the transmission lines 46 and 47, thereby forming a triplate line together with the transmission lines 46 and 47.

As described above, in the duplexer of the present invention, the reactance element is formed by forming the transmission line in the ceramic multi-layer substrate and further forming the ground electrode as described above if necessary. Can also be integrally configured. That is, since the transmission line for impedance matching or the transmission line and the reactance element can be integrated by using the ceramic multilayer substrate, it is necessary to connect the matching element after manufacturing the ceramic multilayer substrate and to adjust the matching element after manufacturing. Not. Therefore, the duplexer of the present invention can be constructed with a small number of elements.

[0073]

According to the broad aspect of the present invention, the transmission line is connected between at least one of the first and second bandpass filters and the input terminal or the output terminal, and the transmission line Since the characteristic impedance is selected to match the impedance in the pass band of the bandpass filter with the impedance of the transmission system while rotating the phase outside the pass band, the impedance matching of the duplexer can be ensured, Moreover, since the impedance matching circuit can be configured only by the transmission line,
Impedance matching can be achieved with a small number of elements regardless of the impedance characteristics of the bandpass filter.

Further, in a specific aspect of the present invention, a reactance element is further provided in addition to the above transmission line,
As a result, the impedance of the bandpass filter is effectively matched with the impedance of the transmission system, so that it is possible to configure a duplexer that can exhibit good characteristics by using filter elements having various impedance characteristics.

Further, the first and second transmission lines are provided as the transmission lines, and the first transmission line is connected to the input terminal or output terminal side and the second transmission line is connected to the at least one filter side. Then, the insertion loss of the duplexer can be effectively reduced by the combination of the first and second transmission lines, and the duplexer with more excellent characteristics can be provided.

Further, in the case of the structure in which the transmission line or the transmission line and the reactance element are built in the multilayer substrate and the surface acoustic wave filters constituting the first and second bandpass filters are fixed on the multilayer substrate, The duplexer including the impedance matching circuit can be easily provided as a single component. That is, since the impedance matching circuit is also configured at the stage of manufacturing the multilayer substrate, it becomes possible to omit the complicated work of connecting the impedance matching circuit element to the surface acoustic wave filter and the complicated adjustment work of each element. , The productivity of the duplexer can be significantly increased.

[Brief description of the drawings]

FIG. 1 is a diagram showing a basic circuit configuration of a known duplexer.

FIG. 2 is a diagram showing an example of attenuation-frequency characteristics of a conventional duplexer.

FIG. 3 is a circuit diagram showing another example of a conventional duplexer.

4A and 4B are transmission lines D shown in FIG.
9 is a Smith chart for explaining phase rotation by L1 and DL2.

FIG. 5 is a diagram showing a circuit configuration of a conventional duplexer formed by coupling a transmission line and a reactance element.

6A and 6B are diagrams for explaining an impedance matching method for the first and second bandpass filters F1 and F2 having the circuit configuration shown in FIG. 5;

FIG. 7 is a diagram showing a circuit configuration of a duplexer according to the first embodiment of the present invention.

FIG. 8 is a diagram showing the first and second bandpass filters F1, shown in FIG.
The figure which shows the amount of attenuation-frequency characteristic as a simple substance of F2.

9 (a) and (b) are first and second parts shown in FIG.
FIG. 6 is a diagram showing the reflection characteristics of the bandpass filters F1 and F2 as a single unit.

10 is a diagram showing an attenuation-frequency characteristic of the duplexer shown in FIG.

11 is a diagram showing the reflection characteristic of the duplexer shown in FIG.

FIG. 12 is a diagram for explaining phase rotation due to transmission lines having different characteristic impedances in the first embodiment.

FIG. 13 is a circuit diagram for explaining phase rotation due to transmission lines having different characteristic impedances.

14A and 14B are diagrams for explaining phase rotation by the first and second bandpass filters F1 and F2.

FIG. 15 is a diagram showing a circuit configuration of a duplexer according to a second embodiment.

FIG. 16 is a diagram showing an attenuation-frequency characteristic of the second duplexer.

17 (a) and (b) are the first and second views, respectively.
FIG. 6 is a diagram showing the reflection characteristics of the bandpass filters F1 and F2 of FIG.

FIG. 18 is a diagram showing attenuation-frequency characteristics of the duplexer of the second embodiment.

FIG. 19 is a diagram showing reflection characteristics of the duplexer of the second embodiment as a whole.

20A and 20B are diagrams illustrating an impedance matching method using transmission lines having different characteristic impedances according to the second embodiment.

FIG. 21 is a diagram for explaining phase rotation when using two different types of transmission lines in the third embodiment.

FIG. 22 is a first and a second used in the third embodiment.
FIG. 6 is a diagram showing the attenuation-frequency characteristics of the bandpass filter alone.

23 (a) and 23 (b) are diagrams showing reflection characteristics of the first and second bandpass filters used in the third embodiment.

24 (a) and 24 (b) are diagrams showing a configuration in which two transmission lines are connected between a bandpass filter and an input terminal and a reflection characteristic thereof.

FIG. 25 is a diagram showing the relationship between the reflection coefficient of the partner side band filter and the insertion loss of the duplexer.

FIG. 26 is a diagram showing attenuation-frequency characteristics of the duplexer according to the third embodiment.

FIG. 27 is a diagram showing reflection characteristics of the duplexer of the third embodiment.

FIG. 28 is a sectional view for explaining the structure of the duplexer according to the fourth embodiment.

[Explanation of symbols]

F1 ... 1st bandpass filter F2 ... 2nd bandpass filter DL1 ... Transmission line DL2 ... Transmission line 21 ... Demultiplexer 22 ... Input terminal 31 ... Demultiplexer DL3 ... Transmission line C2 ... Parallel capacitance 41 ... Demultiplexer 42 ... Multilayer ceramic multilayer substrate 43, 44 ... Surface acoustic wave filter as first and second bandpass filter 45 ... Package material 46, 47 ... Transmission line

Claims (5)

[Claims] 1. An input terminal or an output terminal connected to a transmission system, and first and second band-pass filters having different pass bands, which are connected to the input terminal or the output terminal and are connected in parallel with each other. A transmission line connected between the input terminal or the output terminal and at least one band filter of the first and second band filters, and transmitting impedance in a pass band of the at least one band filter. Match the impedance of the system,
A duplexer in which the characteristic impedance of the transmission line is selected so as to rotate the phase outside the pass band, and the characteristic impedance is different from the impedance of the transmission system. 2. A connection point between the transmission line and at least one band filter of the first and second band filters and a reference potential, and from the input terminal or output terminal side. The duplexer according to claim 1, further comprising a reactance element for matching the impedance of the at least one band-pass filter seen with the impedance of the transmission system. 3. The transmission line includes a first transmission line that is connected in series with each other and has a relatively high characteristic impedance, and a second transmission line that has a relatively low characteristic impedance. 3. The duplexer according to claim 1, wherein one transmission line is connected to the input terminal or output terminal side, and the second transmission line is connected to the at least one filter side. 4. The first and second bandpass filters are surface acoustic wave filters, further comprising a multilayer substrate having the transmission line built-in, and the surface acoustic wave filter being fixed on the multilayer substrate. ,
The duplexer according to claim 1. 5. The first and second bandpass filters are surface acoustic wave filters, further comprising a multi-layer substrate having the transmission line and a reactance element built-in, and the surface acoustic wave filter being fixed on the multi-layer substrate. The duplexer according to claim 2, which is provided.