JP2007194897A - Surface acoustic wave filter and electronic apparatus using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress deterioration in filter characteristic in a second frequency band of a second filter section when an input portion of a first filter section, an input portion of the second filter section, and an output side of an antenna are connected not through a switch. <P>SOLUTION: A surface acoustic wave filter is a ladder type surface acoustic wave filter including the first filter section 19 which passes a signal in a first frequency band and the second filter section 20 which is connected to the first filter section 19 in parallel and passes a signal in the second frequency band adjacent to the high-frequency side of the first frequency band. The first filter section 19 has a first resonator connected to an input portion 26, a second resonator connected to the first resonator, and a third resonator which has one end connected between the first resonator and second resonator and the other end grounded. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a surface acoustic wave filter and an electronic device using the same.

  Hereinafter, a conventional surface acoustic wave filter will be described with reference to FIG. In FIG. 4, the receiving device 1 includes a switch 3 that is connected in series to the output side of the antenna 2 and switches a signal in the first frequency band and a signal in the second frequency band. The receiving device 1 is connected to the first output 4 of the switch 3 and is connected to the first filter unit 5 that passes the signal of the first frequency band, and the second output 6 of the switch 3, and the second frequency. It has the 2nd filter part 7 which lets the signal of a band pass. Further, the receiving device 1 includes a high frequency IC 10 connected to the output unit 8 of the first filter unit 5 and the output unit 9 of the second filter unit 7.

  Note that the receiving device 1 has a channel switching control unit (not shown), and when the first frequency band is selected, the channel switching control unit switches the switch 3 to the first filter unit 5 side to the high frequency IC 10. A signal in the first frequency band is received. When the second frequency band is selected, the channel switching control unit switches the switch 3 to the second filter unit 7 side and causes the high frequency IC 10 to receive a signal in the second frequency band.

  Next, the conventional 1st filter part 5 is demonstrated using FIG. In FIG. 5, the first filter unit 5 includes a resonator 13 that is connected to the input unit 11 and whose other is short-circuited, and a resonator 14 and a resonator 15 that are electromagnetically coupled to the resonator 13 in a high frequency manner. One of the resonators 14 and one of the resonators 15 are short-circuited, and the other of them is connected to the output unit 8 of the first filter unit 5. Such a conventional surface acoustic wave filter is referred to as a DMS (Double Mode SAW) filter. The second filter unit 7 has the same configuration as the first filter unit 5.

As prior art document information related to the invention of this application, for example, Patent Document 1 is known.
JP 2004-166258 A

  In the conventional receiving apparatus 1, since the switching switch 3 exists between the antenna 2 and the first filter unit 5 and the second filter unit 7, a decrease (loss) in the received signal level occurs in the switch 3. 1 reception performance deteriorates. In addition, since the switch 3 is present, the area of the receiving device 1 is increased. Therefore, when the input unit 11 of the first filter unit 5 and the input unit 12 of the second filter unit 7 and the output side of the antenna 2 are connected without going through the switch 3, the second filter unit 7 in the second frequency band. There was a problem that the filter characteristics deteriorated. This is because the first filter unit 5 is a DMS filter, so that the impedance is not sufficiently high in the second frequency band adjacent to the high frequency side of the first frequency band that is the signal pass band. That is, in principle, the DMS filter obtains an attenuation amount by reducing the impedance on the high frequency side of the signal pass band.

  Therefore, the present invention solves such a problem. When the input unit of the first filter unit and the input unit of the second filter unit and the output side of the antenna are connected without a switch, the second filter The purpose is to suppress the deterioration of the filter characteristics in the second frequency band of the part.

  In order to achieve the above object, a surface acoustic wave filter according to the present invention includes a first filter unit that allows a signal in a first frequency band to pass therethrough, and is connected in parallel to the first filter unit and has the first frequency band. And a second filter unit that passes a signal in a second frequency band adjacent to the high frequency side. The first filter unit includes an input unit, a first resonator connected to the input unit, a second resonator connected to the first resonator, the first resonator, and the second resonator. A ladder-type surface acoustic wave filter having a third resonator having one end connected to the resonator and the other end connected to the ground.

  With the above configuration, since the first filter unit is a ladder-type surface acoustic wave filter, the impedance of the first filter unit in the second frequency band adjacent to the high frequency side of the first frequency band, which is the signal pass band of the first filter unit, is set. Can be high enough. As a result, even if the input unit of the first filter unit, the input unit of the second filter unit, and the output side of the antenna are connected without a switch, the filter characteristics in the second frequency band of the second filter unit are degraded. Can be suppressed.

(Embodiment 1)
Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1, 2, and 3.

  In FIG. 1, the receiving device 16 includes a first filter unit 19 connected to the output side 18 of the antenna 17, and a second filter unit 20 connected to the output side 18 of the antenna 17 in parallel with the first filter unit 19. Have Further, the receiving device 16 has a first frequency band receiving terminal 22 connected to the output side 21 of the first filter unit 19 and a second frequency band receiving terminal 24 connected to the output side 23 of the second filter unit 20. A high frequency IC 25 is included.

  The antenna 17 is, for example, an antenna for a VHF (Very High Frequency) band, and receives a band from about 90 MHz to about 220 MHz.

  The first filter unit 19 is composed of, for example, a ladder-type surface acoustic wave filter, and allows a signal in the VHF band 7 channel, which is the first frequency band, among signals from the antenna 17 to pass therethrough. That is, the first filter unit 19 attenuates signals other than the VHF band 7 channel which is the first frequency band, and in particular attenuates the signals of the 8 channel and 6 channel which are related to the upper and lower adjacent disturbances of the VHF band 7 channel.

  The second filter unit 20 is formed of, for example, a surface acoustic wave filter, and allows a signal of the VHF 8 channel, which is the second frequency band adjacent to the high frequency side of the first frequency band, to pass through the signal from the antenna 17. That is, the second filter unit 20 attenuates signals other than the VHF band 8 channel, which is the second frequency band, and particularly attenuates the signals of the 9 channel and the 7 channel, which are in the relationship of upper and lower adjacent disturbances in the VHF band 8 channel.

  Next, the 1st filter part 19 which is a ladder type surface acoustic wave filter is demonstrated. In FIG. 2, the first filter unit 19 includes a first resonator 28 connected in series to the input unit 26, a second resonator 29 connected in series to the first resonator 28, and a first resonator 28. Between the second resonator 29, a third resonator 30 is connected to the shunt to ground.

  Next, an equivalent circuit of the first filter unit 19 will be described with reference to FIGS. The first resonator 28 is represented by an equivalent circuit 31 in the vicinity of a frequency band including a series resonance frequency band and a parallel resonance frequency band described later. The equivalent circuit 31 includes a series inductor 32 connected in series to the input unit 26, a series capacitor 33 connected in series to the series inductor 32, and a parallel capacitor 34 connected in parallel to the series inductor 32 and the series capacitor 33. It consists of. The second resonator 29 and the third resonator 30 can also be represented by an equivalent circuit similar to the first resonator 28. As shown in FIG. 3, the second resonator 29 is represented by an equivalent circuit 35. The third resonator 30 is represented by an equivalent circuit 36.

  The equivalent circuit 31 has a unique series resonance frequency band determined by the series inductor 32 and the series capacitor 33 and a unique parallel resonance frequency band determined by the series inductor 32, the series capacitor 33, and the parallel capacitor 34. The parallel resonance frequency band is a frequency band higher than the series resonance frequency band. Since the equivalent circuits 31 and 35 are connected in series, the series resonance frequency band f1 of the equivalent circuits 31 and 35 becomes the signal pass band of the first filter unit 19, and the parallel resonance frequency band f2 of the equivalent circuits 31 and 35 is This is the signal stop band of the first filter unit 19. In addition, since the equivalent circuit 36 is connected in parallel, the series resonance frequency band f3 of the equivalent circuit 36 becomes a signal blocking band of the first filter unit 19, and the parallel resonance frequency band f4 of the equivalent circuit 36 is of the first filter unit 19. This is the signal passband. That is, by setting the series resonance frequency band f1 of the equivalent circuits 31 and 35 connected in series and the parallel resonance frequency band f4 of the equivalent circuit 36 connected in parallel to substantially the same frequency band, this frequency band f1 (= f4). Is the first frequency band which is the signal pass band of the first filter unit 19. The series resonance frequency band f1 of the equivalent circuits 31 and 35 (= the parallel resonance frequency band f4 of the equivalent circuit 36), the parallel resonance frequency band f2 of the equivalent circuits 31 and 35, and the series resonance frequency band f3 of the equivalent circuit 36. The magnitude is f3 <f1 <f2.

  With the above configuration, since the first resonator 28 connected in series to the input unit 26 exists, the first filter unit 19 is a first resonator having a frequency band higher than the series resonance frequency band f1 of the first resonator 28. The impedance becomes sufficiently high in the 28 parallel resonance frequency bands f2. By setting the parallel resonance frequency band f2 of the first resonator 28 as a second frequency band that is a signal pass band of the second filter unit 20, the input unit 26 of the first filter unit 19 and the input of the second filter unit 20 are used. Even if the unit 27 and the output side 18 of the antenna 17 are connected without a switch, the deterioration of the filter characteristics in the second frequency band of the second filter unit 20 can be suppressed.

  Further, when the second filter unit 20 is a surface acoustic wave filter, a high attenuation is obtained in the first frequency band of the second filter unit 20. That is, since the reflection coefficient in the first frequency band of the second filter 20 is sufficiently large, the first frequency of the second filter unit 20 is connected to the input unit 27 of the second filter unit 20 by grounding the reactance element 37 to the shunt. The impedance in the band can be made sufficiently large. As a result, even if the input unit 26 of the first filter unit 19, the input unit 27 of the second filter unit 20, and the output side 18 of the antenna 17 are connected without a switch, the first frequency band of the first filter unit It is possible to suppress the deterioration of the filter characteristics.

  With the above configuration, the high frequency IC 25 receives a signal in the first frequency band from the first filter unit 19 without passing through a switch that causes a loss of the received signal, and receives a signal in the second frequency band higher than the first frequency band. Received from the second filter unit 20. As a result, the reception performance of the high frequency front end unit 16 can be improved. In addition, since no switch is arranged, the area of the receiving device 16 can be reduced.

  In FIG. 1 of the present embodiment, the first filter unit 19 and the second filter unit 20 are described as separate filters, but the first filter unit 19 and the second filter unit 20 may be integrated filters. . Thereby, the area of the high frequency front end part 16 can be reduced in size.

  In the above configuration, when the input impedance in the second frequency band of the first filter unit 19 is inductive, the input impedance in the second frequency band of the second filter unit 20 is capacitive, and the first filter unit The 19 input units 26 may be connected to the input unit 27 of the second filter unit 20. That is, since the input impedance in the second frequency band of the first filter unit is inductive, it is equivalent to connecting the other of the inductors, one of which is grounded, between the antenna 17 and the second filter unit 20. Become. Thereby, as a result of the capacitive reactance component in the second frequency band of the second filter unit 20 becoming smaller, matching is achieved and insertion loss can be reduced. Further, when the input impedance in the second frequency band of the first filter unit 19 is capacitive, the input impedance of the second filter unit 20 in the second frequency band is set to be inductive, and the input unit of the first filter unit 19 26 and the input unit 27 of the second filter unit 20 may be connected. Thereby, the inductive reactance component in the 2nd frequency band of the 2nd filter part 20 becomes small, and insertion loss can be reduced. The same applies to the impedance of the first filter unit 19 and the impedance of the second filter unit 20 in the first frequency band.

  Note that the amount of the second frequency band signal flowing into the first filter unit 19 is dominated by the reactance component rather than the resistance component of the first filter unit 19 in the second frequency band, particularly in the high frequency band. Therefore, it is desirable to set the absolute value of the reactance component in the second frequency band of the first filter unit 19 high. In particular, by setting the absolute value of the reactance component in the second frequency band of the first filter unit 19 to be higher than the value obtained by multiplying the characteristic impedance (for example, 50 ohms) by 2, the second value of the second filter unit 20 is set. Loss in the frequency band can be suppressed to 1 dB or less.

  In the surface acoustic wave filter of the present invention, the input unit of the first filter unit and the input unit of the second filter unit, which are ladder type surface acoustic wave filters, and the output side of the antenna are connected without a switch. The reception performance of the high-frequency front end unit can be improved, and can be used for electronic devices such as televisions and portable terminals mounted in automobiles.

The block diagram of the high frequency front end part in Embodiment 1 of the present invention The circuit diagram of the 1st filter part in Embodiment 1 of the present invention. FIG. 3 is an equivalent circuit diagram of the first filter unit in the first embodiment of the present invention. Block diagram of a conventional high-frequency front end Circuit diagram of a conventional surface acoustic wave filter

Explanation of symbols

16 High Frequency Front End 17 Antenna 19 First Filter Part 20 Second Filter Part 25 High Frequency IC
28 1st resonator 29 2nd resonator 30 3rd resonator

Claims (9)

A first filter section for passing a signal in the first frequency band, and a second filter section connected in parallel to the first filter section and passing a signal in a second frequency band adjacent to the high frequency side of the first frequency band. The first filter unit includes an input unit, a first resonator connected to the input unit, a second resonator connected to the first resonator, and the first resonator. A surface acoustic wave filter having a third resonator grounded to a shunt between the second resonator and the second resonator. 2. The surface acoustic wave filter according to claim 1, wherein when the input impedance of the first filter unit in the first frequency band is capacitive, the input impedance of the second filter unit in the first frequency band is inductive. 3. . 2. The surface acoustic wave filter according to claim 1, wherein when the input impedance of the first filter unit in the first frequency band is inductive, the input impedance of the second filter unit in the first frequency band is capacitive. 3. . 2. The surface acoustic wave filter according to claim 1, wherein when the input impedance of the second filter unit in the second frequency band is capacitive, the input impedance of the first filter unit in the second frequency band is inductive. 3. . 2. The surface acoustic wave filter according to claim 1, wherein when the input impedance of the second filter unit in the second frequency band is inductive, the input impedance of the first filter unit in the second frequency band is capacitive. 3. . The surface acoustic wave filter according to claim 1, wherein the first filter portion and the second filter portion are formed in the same casing. 2. The surface acoustic wave filter according to claim 1, wherein an absolute value of an imaginary part of an input impedance in the second frequency band of the first filter unit is equal to or greater than a value obtained by multiplying a characteristic impedance by two. An antenna, a first filter connected to the output side of the antenna and passing a signal in a first frequency band; and an output side of the antenna connected in parallel to the first filter unit and the first filter A second filter unit that passes a signal of a second frequency band adjacent to a high frequency side of the frequency band, and a high frequency IC connected to an output side of the first filter unit and the second filter unit, One filter unit includes an input unit, a first resonator connected to the input unit, a second resonator connected to the first resonator, and the first resonator and the second resonator. An electronic device having a third resonator connected to a shunt between and a ground. The electronic device according to claim 8, further comprising a reactance element grounded to a shunt between an output side of the antenna and an input unit of the second filter unit.

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