JPH10209723A - Low-pass filter with directional coupler and portable telephone set using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attenuate a desired frequency band and to decrease the number of components of a portable telephone set transmission system with the same line length as a conventional system by taking a monitor signal out by a directional coupler and removing an isolator, and connecting a stub line to a directional coupler main transmission line. SOLUTION: Stub lines 108 and 109 and stub lines 110 and 111 are connected respectively in parallel, to form the capacity of the low-pass filter with a directional coupler. The stub lines 108 to 111 serve as a series resonator, depending upon the characteristic impedance, termination conditions, and line length of the lines to form an attenuation electrode for frequency characteristics. Further, a main transmission line 105 operates as an inductance to form a low-pass filter, having two attenuation electrodes which have a passing band at a frequency of λ/4 wavelength. Then the stub lines are connected to both the ends of the main transmission line of a conventional directional coupler and their stub line characteristic impedance, terminating conditions, and line length are adjusted to give a low-pass filter function having an attenuation electrode for a desired frequency band.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-pass filter with a directional coupler suitable as a transmission system circuit of a mobile telephone for mobile communication, and a mobile telephone using the same.

[0002]

2. Description of the Related Art FIG. 5 shows a block diagram of a transmission system of a conventional portable telephone. A monitor signal is taken out from the power amplified by the power amplifier PA via the capacitor C for capacitive coupling,
When the low-pass filter LPF is connected via the isolator ISO and the mode switch SW is on the transmitting side, the system removes the second harmonic spurious oscillation and the third harmonic spurious oscillation and transmits the signal.

[0003]

However, in the above configuration, the number of stages of the low-pass filter LPF is increased in order to sufficiently attenuate the second-order and third-order spurious oscillations of the amplified system. In addition, the isolator ISO is connected for the purpose of preventing a reflected signal irrespective of the turned-on position of the mode switch SW, so that the price is increased.

SUMMARY OF THE INVENTION In view of the above problems, the present invention can attenuate high frequency bands, and especially attenuate second harmonic and third harmonic spurious oscillations of a system, and has a small and low-cost directional coupler. It is an object to provide a low-pass filter and a mobile phone.

[0005]

In order to achieve the above object, the present invention removes an isolator as a configuration for extracting a monitor signal with a directional coupler, and connects a stub line to a main transmission line of the directional coupler. Thus, the desired frequency band can be attenuated, and the number of components of the transmission system of the mobile phone can be reduced with the same line length as that of the conventional directional coupler.

[0006]

According to the first aspect of the present invention, at least one of the input and output ends of a main transmission line of a directional coupler is provided with a parallel connection body having a plurality of capacitors, at least one of which is a stub. It is a low-pass filter with a directional coupler, has the function of a low-pass filter having an attenuation pole in a desired frequency band in addition to the directional coupler, and the stub can be thinned by dividing the capacitance. It has the effect of being small.

According to a second aspect of the present invention, at least one stub is a low-pass filter with a directional coupler that performs series resonance so as to have a desired attenuation in a frequency band twice as high as a pass signal band frequency. This is a filter and has an effect of attenuating a frequency band twice as high as a pass signal band frequency.

According to a third aspect of the present invention, at least one stub is a low-pass filter with a directional coupler that performs series resonance so as to have a desired attenuation in a frequency band three times as high as a pass signal band frequency. It is a filter and has an effect of attenuating a frequency band three times as high as a pass signal band frequency.

According to a fourth aspect of the present invention, at least one stub is a stub that performs series resonance so as to have a desired attenuation in a frequency band twice as high as a pass signal band frequency, and at least one stub is provided. Is a low-pass filter with a directional coupler that resonates in series so as to provide a desired attenuation in a frequency band three times the pass signal band frequency. In particular, a frequency band twice and three times the pass signal band frequency is used. It has the effect of attenuating.

According to a fifth aspect of the present invention, at least one stub is connected in series so that a desired attenuation is obtained in a desired frequency band other than a frequency band twice or three times the pass signal band frequency. This is a low-pass filter with a directional coupler, which is a stub that resonates, and particularly has an effect of attenuating a desired frequency band other than a frequency band twice or three times the pass signal band frequency.

According to a sixth aspect of the present invention, at least one of the input and output ends of the main transmission line of the directional coupler is provided with a plurality of parallel connected bodies of at least one of which are stubs. A low-pass filter with a directional coupler provided with a single stub that performs series resonance so as to have a desired attenuation in a desired frequency band. Has an action.

According to a seventh aspect of the present invention, there is provided a low-pass filter with a directional coupler, wherein a stub, which is a parallel connection of a plurality of capacitors, is connected to the same side of the line. This has the effect of reducing the size of the low-pass filter.

[0013] The invention according to claim 8 of the present invention is a low-pass filter with a directional coupler, wherein a stub, which is a parallel connection of a plurality of capacitors, is connected to both sides of the line. This has the effect of reducing the size of the bandpass filter.

According to a ninth aspect of the present invention, there is provided a low-pass filter with a directional coupler having a stub mounted on a substrate, and has an effect of reducing the size of the low-pass filter with a directional coupler. .

According to a tenth aspect of the present invention, a parallel connection of a plurality of capacitors, at least one of which is a stub, is provided at one of input and output ends of a main transmission line of a directional coupler. This is a low-pass filter with a directional coupler using a chip component for the capacitance not depending on the stub, and has an effect of reducing the size of the low-pass filter with the directional coupler.

According to an eleventh aspect of the present invention, at least one of the input and output ends of the main transmission line of the directional coupler is provided with a plurality of parallel connected bodies each having at least one stub. Is a low-pass filter with a directional coupler in which a capacitance independent of the stub is mounted on a substrate, and has an effect of reducing the size of the low-pass filter with a directional coupler.

According to a twelfth aspect of the present invention, there is provided a portable telephone employing a low-pass filter with a directional coupler according to any one of the first to eleventh aspects in a transmission system circuit,
This has the effect of reducing the number of components from the conventional circuit and realizing a reduction in size and cost.

FIG. 1 shows an embodiment of the present invention.
This will be described with reference to FIG. (Embodiment 1) FIG. 1 shows a low-pass filter with a directional coupler used in a 900 MHz band according to Embodiment 1 of the present invention. In FIG.
A main transmission line 105 having terminals 1 and 102 and a sub transmission line 106 having terminals 103 and 104 at both ends are arranged in parallel with a dielectric substrate 107 having a lower surface as a shield electrode.

The main transmission line 105 and the sub transmission line 106 are electromagnetically coupled, and a directional coupler is formed with the terminal 104 terminated at 50 ohms. The dielectric substrate 107 is made of alumina, has a small relative dielectric constant, can increase the characteristic impedance of the transmission line, and can improve the characteristics of the directional coupler.

A stub line 108, a stub line 109, and a stub line 110 are connected to the terminals 101 and 102, respectively.
And the stub line 111 are connected. Various methods of forming these transmission lines and stub lines are possible, such as a screen printing method and an intaglio method for producing an integrated circuit board.

The operation of the low-pass filter with the directional coupler configured as described above will be described below.

The stub line 108 and the stub
The tab lines 109 are connected in parallel, and the stub lines 110 and
And the stub line 111 are connected in parallel,
Form the capacitance of the low pass filter with coupler. Stub line
Road 108, stub line 109, stub line 110,
Input impedance Z from the point of connection of the transmission line 111 _i
Is the characteristic impedance of the line_o, Phase constant β, line
Let the path length be l and the impedance at the end be Z_lWhen
And ignore the losses, Z_i= Z_o・ (Z_l+ JZ_otan
βl) / (Z_o+ JZ_itanβl).

Therefore, the stub line 108 and the stub line 1
09, the stub line 110 and the stub line 111 act as a series resonator depending on the characteristic impedance of the line, the termination condition, and the line length, and form an attenuation pole in the frequency characteristic. In addition, since the main transmission line 105 acts as an inductance, the present configuration sets the frequency at which the line length of the main transmission line 105 is λ / 4 wavelength to the pass band frequency (hereinafter, ω _o).
) As a low-pass filter having two attenuation poles.

As described above, according to the present embodiment, stub lines are connected to both ends of the main transmission line of the conventional directional coupler, and the characteristic impedance, termination condition, and line length of those stub lines are adjusted. By doing so, it is possible to provide a component having the function of a low-pass filter having an attenuation pole in a desired frequency band in addition to the directional coupler.

Although there are four stub lines in the present embodiment, the number of stub lines may be one to three. Also, five or more may be used, in which case there is an effect that the occupied area of the component can be reduced.

Further, the second harmonic frequency of at least the line length of the stub line in the present embodiment omega _o (hereinafter referred to as 2 [omega _o) may be the length which resonates at. In this case, there is an effect of suppressing the second harmonic spurious oscillation of the system.

Further, at least one line length the length which resonates at 2 [omega _o of the stub line of this embodiment, third harmonic frequency of the other of the at least one line length to omega _o (hereinafter,
3 ω _o ). In this case, there is an effect of suppressing the second harmonic spurious oscillation and the third harmonic spurious oscillation of the system.

Also, at least one line length of the stub line in the present embodiment may be a length that resonates at a desired frequency. In this case, the system has the effect of suppressing spurious oscillation at the desired frequency.

Although the operating frequency band in the present embodiment is a 900 MHz band, the same effect can be obtained by using the technique of the present invention for all high-frequency transmission frequencies.

Further, in this embodiment, the stub is connected to the same side of the line, but the same effect can be obtained by connecting the stub to the opposite side of the line.

(Embodiment 2) FIG. 2 shows a low-pass filter with a directional coupler used in a 900 MHz band according to Embodiment 2 of the present invention. Note that the low-pass filter with a directional coupler of the present embodiment shown in FIG. 2 has basically the same configuration as that of the first embodiment shown in FIG. And a detailed description is omitted.

The present embodiment has the same structure as that of the first embodiment except that at least one capacitor connected to the main transmission line is used as a stub line, and the chip capacitor 112 is used for the other capacitors.

The operation of the low-pass filter with the directional coupler configured as described above will be described below.

In the first embodiment, a low-pass filter having an attenuation pole is formed by operating a main transmission line as an inductance and connecting a stub line at both ends to operate as a series resonance. 9 on the board
13.4 to attenuate the second harmonic of 00 MHz
mm, the line length of the stub line becomes relatively long, and the shape of the low-pass filter with the directional coupler becomes large.

In this embodiment, a chip capacitor 112 is used as a capacitor connected to the main transmission line 105. A chip having a length of 1 mm can be used.

As described above, according to the present embodiment, at least one of the capacitors connected to the main transmission line is used as a stub line, and the chip capacitor is used for the other capacitors. A low-pass filter can be realized.

(Embodiment 3) FIG. 3 shows a low-pass filter with a directional coupler used in a 900 MHz band according to Embodiment 3 of the present invention. Note that the low-pass filter with a directional coupler of the present embodiment shown in FIG. 3 has basically the same configuration as that of the first embodiment shown in FIG. And a detailed description is omitted.

In this embodiment, the structure is the same as that of the first embodiment except that at least one of the capacitors connected to the main transmission line is a stub line, and the internal capacitor 113 is used for the other capacitors.

The operation of the low-pass filter with the directional coupler configured as described above will be described below.

In the first embodiment, a low-pass filter having an attenuation pole is formed by operating a main transmission line as an inductance and connecting a stub line to both ends thereof to operate as a series resonance. 9 on the substrate
13.4 to attenuate the second harmonic of 00 MHz
mm, the line length of the stub line becomes relatively long, and the shape of the low-pass filter with the directional coupler becomes large.

In the present embodiment, the internal capacitor 113 is used for the capacitance connected to the main transmission line 105. The length of the internal capacitor can be formed to be several mm or less.

As described above, according to this embodiment, at least one of the capacitors connected to the main transmission line is used as a stub line, and the other capacitors use internal capacitors, so that a small directional coupler is provided. A low-pass filter can be realized.

(Embodiment 4) FIG. 4 shows an output circuit of a transmission system of a mobile phone employing a low-pass filter with a directional coupler according to Embodiment 4 of the present invention. The low-pass filter with a directional coupler employed in the present embodiment may be the low-pass filter with a directional coupler shown in the first embodiment of the present invention.

In FIG. 4, terminal 101 is connected to power amplifier P
A, the terminal 102 is connected to the mode switch SW, the terminal 103 is used as a monitor terminal, and the terminal 104 is directly terminated with 50Ω.

The operation of the output circuit of the transmission system of the portable telephone configured as described above will be described.

The signal of the system is amplified by a power amplifier PA and transmitted from an antenna ANT via a low-pass filter with a directional coupler and a switch SW. At this time, the high frequency band of the system, especially the second harmonic spurious oscillation and the third harmonic spurious oscillation are attenuated by the low-pass filter with the directional coupler and are not transmitted to the antenna. Further, a monitor signal can be extracted by the directional coupler.

As described above, according to the present embodiment, by employing the low-pass filter with the directional coupler of the present invention, the number of components of the output circuit of the transmission system of the mobile phone can be reduced, and the size and the size can be reduced. Can be priced.

[0048]

As described above, according to the present invention, at least one capacitor is divided, and at least one of the capacitors is realized as a stub, thereby attenuating a desired frequency in addition to the directional coupler. It can also have the function of a filter. Further, since the stub can be thinned by dividing the capacitance, a small directional coupler with a low-pass filter function can be realized. Further, by employing the low-pass filter with the directional coupler of the present invention in a transmission system circuit of a mobile phone, the number of components can be reduced, and the size and the price can be reduced.

[Brief description of the drawings]

FIG. 1 is a perspective view of a low-pass filter with a directional coupler according to Embodiment 1 of the present invention.

FIG. 2 is a perspective view of a low-pass filter with a directional coupler according to Embodiment 2 of the present invention.

FIG. 3 is a perspective view of a low-pass filter with a directional coupler according to a third embodiment of the present invention.

FIG. 4 is a block diagram of a transmission system of a mobile phone employing a low-pass filter with a directional coupler according to a fourth embodiment of the present invention.

FIG. 5 is a block diagram of a transmission system of a conventional mobile phone.

[Explanation of symbols]

 101 to 104 Terminal 105 Main transmission line 106 Sub transmission line 107 Dielectric substrate 108 to 111 Stub line 112 Chip capacitance 113 Internal capacitor

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Naoki Yuda 1006 Kazuma Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (12)

[Claims] 1. A low-pass filter with a directional coupler, wherein at least one of input and output ends of a main transmission line of the directional coupler is provided with a parallel connection of a plurality of capacitors, at least one of which is a stub. filter. 2. The low-pass filter with a directional coupler according to claim 1, wherein at least one stub resonates in series so as to have a desired attenuation in a frequency band twice as high as the pass signal band frequency. filter. 3. The low-pass filter with a directional coupler according to claim 1, wherein at least one stub resonates in series so as to have a desired attenuation in a frequency band three times as high as the pass signal band frequency. filter. 4. At least one stub is a stub that resonates in series so as to have a desired attenuation in a frequency band twice as high as the pass signal band frequency, and at least one stub has a frequency three times as high as the pass signal band frequency. A series resonance is performed so that a desired attenuation is obtained in a band.
4. The low-pass filter with a directional coupler according to any one of 3. 5. The stub according to claim 1, wherein the at least one stub is a stub that performs series resonance so as to have a desired attenuation in a desired frequency band other than a frequency band twice or three times the pass signal band frequency. A low-pass filter with a directional coupler according to claim 1. 6. A parallel connection body having a plurality of capacitors, at least one of which is a stub, is provided at one of input and output ends of a main transmission line of a directional coupler, and a desired attenuation is provided in another desired frequency band. A low-pass filter provided with a directional coupler, wherein one stub that performs series resonance is provided such that: 7. A stub, which is a parallel connection of a plurality of capacitors, is connected to the same side of the line.
A low-pass filter with a directional coupler according to any one of the above. 8. The low-pass filter with a directional coupler according to claim 1, wherein stubs, which are a plurality of capacitors connected in parallel, are connected to both sides of the line. 9. The low-pass filter with a directional coupler according to claim 1, wherein a stub is provided inside the substrate. 10. A directional coupler having a plurality of parallel connection units having at least one stub at one of input and output ends of a main transmission line of a directional coupler, and a chip component connected to a capacitor independent of the other stub. A low-pass filter with a directional coupler, characterized by using: 11. A parallel connection body having a plurality of capacitors, at least one of which is a stub, is provided at one of input and output ends of a main transmission line of a directional coupler, and a capacitor which does not depend on the other stub is mounted on a substrate. A low-pass filter with a directional coupler. 12. A mobile phone, wherein the low-pass filter with a directional coupler according to claim 1 is used in a transmission system circuit.