JPH10294634A - Filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a miniaturized filter which can deal with the high frequency signals of plural comparatively proximate frequency bands. SOLUTION: A filter F1 is composed of transmission lines L11-L13 of inductance elements, PIN diode PD and capacitor C11 and between the node of transmission lines L11 and L12 and the ground, an LC resonance circuit composed of the transmission line L13, PIN diode PD and capacitor C11 is connected. Then, a band pass filter is constituted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter used in a mobile communication device, for example, a portable telephone corresponding to a plurality of frequency bands.

[0002]

2. Description of the Related Art Conventionally, when two communication frequency bands are relatively close to each other, an antenna of a mobile communication device for each frequency band is commonly used. FIG. 8 is a block diagram showing a configuration in which an antenna of a conventional mobile communication device for a different frequency band is shared. In FIG. 8, 50 is an antenna, 51 is a switch composed of a coaxial switch or a PIN diode, 52 is a duplexer on the transmission (Tx) side,
53 indicates a duplexer on the receiving (Rx) side. The antenna 50 is connected to the first terminal 52a of the duplexer 52 via the switch 51, and the second and third terminals 52b,
52c includes low-pass filters LPF1 and LPF, respectively.
High-power amplifier P on the Tx side in the 900 MHz band via F2
A1 is connected to a 1.8-GHz band Tx-side high-output amplifier PA2. Similarly, the first of the duplexers 53
Of the antenna 50 via the switch 51
Is connected to the second and third terminals 53b and 53c via band-pass filters BPF1 and BPF2, respectively.
Low noise amplifiers LNA1 and 1.8 on the Rx side in the 00 MHz band
The low-noise amplifier LNA1 on the Rx side in the GHz band is connected. Then, by switching the switch 51 and connecting the antenna 50 to the duplexer 52 or the duplexer 53, transmission and reception can be performed in two frequency bands of the 900 MHz band and the 1.8 GHz band.

[0003]

However, in a configuration in which a conventional antenna is shared, a duplexer on the transmitting side and a receiving side is connected to one antenna via a switch, and the duplexers are connected to these duplexers via a band-pass filter. However, since a high-output amplifier on the transmitting side and a low-noise amplifier on the receiving side in a plurality of frequency bands are connected, there is a problem that the number of components increases. As a result, there has been a problem that it is difficult to reduce the size of a mobile communication device on which these are mounted.

The present invention has been made to solve such a problem, and an object of the present invention is to provide a small-sized filter that can handle high-frequency signals in a plurality of frequency bands relatively close to each other.

[0005]

In order to solve the above-mentioned problems, a filter according to the present invention includes an LC resonance circuit including at least one inductance element and at least one capacitance element.
Alternatively, a frequency band is controlled by using a diode for at least one of the capacitance elements and controlling a voltage applied to the diode.

In addition, the multi-layer substrate is formed by laminating a plurality of dielectric layers provided with the inductance element or the capacitance element on at least one surface, and the diode mounted on the multi-layer substrate. It is characterized by.

According to the filter of the present invention, by controlling the voltage applied to the diode forming the inductance element or the capacitance element, the inductance value of the inductance element forming the LC resonance circuit is controlled.
Alternatively, since the capacitance value of the capacitance element is controlled, one filter can handle a plurality of frequency bands.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a first example of a filter according to the present invention.
FIG. 3 shows a circuit diagram of the embodiment of FIG. The filter F1 includes transmission lines L11 to L13 which are inductance elements, a pin diode PD, and a capacitor C which is a capacitance element.
11, a transmission line L13, a pin diode PD,
The capacitor C11 is a band-pass filter forming an LC resonance circuit.

When the pin diode PD of the filter F1 in FIG. 1 is on, the pin diode PD becomes a coil LL and a resistor R as shown in the equivalent circuit of FIG. , A coil LL of the pin diode PD and a capacitor C11. On the other hand, the pin diode P of the filter F1 in FIG.
When D is off, as shown in the equivalent circuit of FIG.
Since the pin diode PD becomes the capacitor CC, it becomes an LC resonance circuit including the transmission line L13, the capacitor CC of the pin diode PD, and the capacitor C11.

With the above configuration, the pin diode PD
Is turned on and off, the resonance frequency of the filter F1 can be changed.

FIG. 3 shows the pass characteristics of the filter F1 of FIG. In FIG. 3, the solid line indicates the pin diode P.
When D is turned on, the broken line indicates the case where the pin diode PD is turned off. From this figure, it can also be seen that turning the pin diode PD on or off sets the frequency band of the high-frequency signal passing through to 900 MHz or 1.8 GHz and turning on the high-frequency signal of another adjacent frequency band, for example, the pin diode PD. In this case, a high frequency signal of 1.8 GHz is used.
It is clear that the high frequency signal of 0 MHz is not passed.

FIG. 4 is a perspective view of the filter F1 shown in FIG. The filter F1 includes a multilayer substrate 2 including transmission lines L11 to L13 and a capacitor C11 (not shown). The pin diode PD is mounted on the front surface, which is one main surface of the multilayer substrate 2, and external terminals Ta to Tc are provided from the front surface to the side surface and the back surface.

An example of the manufacturing process of the filter F1 (FIG. 2) having the above configuration will be described. First, strip electrodes forming the transmission lines L11 to L13 and capacitor electrodes forming the capacitor C11 are printed at desired positions on a ceramic sheet obtained by kneading a ceramic material and extending into a sheet shape by screen printing or the like, and punching or the like. To form a through hole. Next, these ceramic sheets are laminated so that the through holes coincide with each other, and pressed to obtain a multilayer substrate 2 including the transmission lines L11 to L13 and the capacitor C11.

Next, the multi-layer substrate 2 is semi-baked, and external terminals Ta to Tc extend from the front surface to the side surface and the back surface of the multi-layer substrate 2.
Is printed by screen printing or the like and then completely baked.
Next, the pin diode PD is mounted on the surface of the multilayer substrate 2, and the filter F1 is completed.

As described above, in the filter of the first embodiment, by changing the applied voltage of the pin diode and turning on and off the pin diode, the resonance frequency of the LC resonance circuit including the transmission line, the pin diode and the capacitor is changed. Can be changed. Therefore, it is possible to change the frequency band of the high-frequency signal passing through the filter, which is a pass band filter, and not to pass the high-frequency signal of another adjacent frequency band. Therefore, one filter has a different frequency band. It can respond to two high frequency signals.

Further, as shown in FIG. 4, when the filter is constituted by a multilayer substrate, the inductance element and the capacitance element constituting the filter can be built in the multilayer substrate, so that the size of the filter can be reduced.

FIG. 5 shows a circuit diagram of a second embodiment of the filter according to the present invention. The filter F2 is composed of transmission lines L21 to L23, which are inductance elements, and a varicap diode BD, and the transmission line L23 and the varicap diode BD are bandpass filters forming an LC resonance circuit.

With the above configuration, the resonance frequency of the filter F2 can be changed by changing the capacitance value of the varicap diode BD.

FIG. 6 shows the pass characteristics of the filter F2 of FIG. In FIG. 6, the solid line shows the case where the capacitance value is 1 pF, and the broken line shows the case where the capacitance value is 5 pF. From this figure, it can be seen that by changing the capacitance value of the varicap diode DB from 1 pF to 5 pF, the frequency band of the passing high-frequency signal is changed from 1.8 GHz to 900 MHz, and the high-frequency signal of another adjacent frequency band, for example, the capacitance is changed. In the case of a value of 1 pF, a high frequency signal of 900 MHz, a capacitance value of 5
It is clear that the 1.8 GHz high frequency signal is not passed in the case of pF.

As described above, in the filter according to the second embodiment, the voltage applied to the varicap diode is continuously changed, and the capacitance value of the varicap diode is continuously changed. Can be continuously changed. Therefore, it is possible to continuously change the frequency band of the high-frequency signal passing through the filter, which is a pass band filter, and not to pass the high-frequency signal of another adjacent frequency band. It can correspond to three or more high-frequency signals having a band.

Here, the filters of the above-described first and second embodiments are connected to two frequency bands relatively close to each other, for example, 9
GSM (Global
System for Mobile communications) and 1.8GHz
DCS (Dynamic Cell Syst.)
FIG. 7 shows an example in which one antenna is shared with the em) 1800.

The antenna 11 is connected to a first terminal 12a of a switch 12 composed of a coaxial switch or a PIN diode. One terminal of a filter F1 (F2) that can handle a plurality of frequency bands with one is connected to a switch. Twelve second and third terminals 12b and 12c are connected to the transmission terminal and the reception terminal, respectively. A low-pass filter LPF is connected to the other terminal of the filter F1 (F2).
, The transmission (Tx) side high-power amplifier PA shared by the 900 MHz band GSM and the 1.8 GHz band DCS 1800 or the 900 MHz band GSM and the 1.8 GHz band GSM through the band pass filter BPF. DC
The low-noise amplifier LNA on the reception (Rx) side shared by S1800 is connected.

With the above-described configuration, the switches (Fx) F1 and Fx on the transmission (Tx) side can switch the switch 12 to support two frequency bands with one antenna 11.
2 or two different frequency ranges, eg 900 MH, for connection to the receiving (Rx) side filters F1, F2.
High frequency signals of z-band GSM and 1.8 GHz-band DCS 1800 can be distributed and combined. That is,
Transmission and reception are possible in two frequency bands.

Therefore, an antenna, a high-output amplifier on the transmitting side, and a low-noise amplifier on the receiving side can be shared between GSM in the 900 MHz band and DCS1800 in the 1.8 GHz band, which are two frequency bands relatively close to each other. .

In the above-described embodiment, the case where the filter is a band-pass filter has been described. However, if the filter is constituted by an LC resonance circuit, such as a low-pass filter, a high-pass filter, a band rejection filter, etc. It is within the scope of the invention.

Also, a case has been described where both the receiving filter and the transmitting filter constituting the high-frequency component are band-pass filters. However, the low-pass filter and the high-pass filter, the band-pass filter and the band-stop filter, The same effect can be obtained with a combination of a rejection filter and a band rejection filter.

[0027]

According to the filter of the first aspect, the resonance voltage of the LC resonance circuit is controlled by controlling the voltage applied to the diode constituting the inductance element or the capacitance element and controlling the inductance value or the capacitance value of the diode. The frequency can be controlled. Therefore, since it is possible to control the frequency band of the high-frequency signal passing through the filter and not to pass the high-frequency signal of another adjacent frequency band, a plurality of high-frequency signals having different frequency bands can be controlled by one filter. Can be handled.

Further, by using this filter for a mobile communication device of a plurality of frequency bands relatively close to each other, it is possible to share an antenna, a high-output amplifier on the transmission side and a low-noise amplifier on the reception side.

According to the filter of the second aspect, since the filter is constituted by the multilayer substrate, the inductance element and the capacitance element constituting the filter can be built in the multilayer substrate. Therefore, the size of the filter can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a first embodiment of a filter according to the present invention.

2A and 2B are an equivalent circuit diagram when a pin diode of the filter of FIG. 1 is turned on, and FIG. 2B is an equivalent circuit diagram when a pin diode is turned off.

FIG. 3 is a diagram illustrating a frequency characteristic of the filter of FIG. 1;

FIG. 4 is a perspective view of the filter of FIG. 1;

FIG. 5 is a circuit diagram of a second embodiment of the filter according to the present invention.

FIG. 6 is a diagram illustrating frequency characteristics of the filter of FIG. 5;

FIG. 7 is a block diagram showing a configuration in which each mobile communication device in a different frequency band shares an antenna using the filter of FIG. 1 or FIG. 5;

FIG. 8 is a block diagram showing a conventional configuration in which an antenna is shared by mobile communication devices of different frequency bands.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 High frequency component 2 Multilayer board BD, PD Diode C11 Capacitance element F1, F2 Filter (band-pass filter) L11-L13, L21-L23 Inductance element

Claims (2)

[Claims] An LC comprising at least one inductance element and at least one capacitance element
A resonance circuit, and using a diode for at least one of the inductance element or the capacitance element;
A filter for controlling a frequency band by controlling a voltage applied to the diode. 2. A multi-layer substrate comprising a plurality of dielectric layers provided with the inductance element or the capacitance element on at least one surface, and the diode mounted on the multi-layer substrate. The filter according to claim 1, wherein: