JPH09181504A - Dielectric filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a filter which is capable of changing a band pass characteristics. SOLUTION: The signal line of a high frequency signal is serially connected with coupling capacitors C11, C12, C21 and C22. On the side of the outputs of the coupling capacitors (C11, C12), (C21 and C22), the signal line is connected with dielectric resonators X11 and X21 in parallel. This filter is provided with switch circuits S11 to S22 changing the values of the coupling capacitors (C11, C12), (C21 and C22). By the coupled capacitors (C11, C12), (C21 and C22) and the dielectric resonators X11 and X21, a band pass characteristics is obtained in the signal line. By the switch circuits S11 to S22, the coupling capacitors (C11, C12), (C21 and C22) are changed and the band pass characteristics is changed.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a dielectric filter.

[0002]

2. Description of the Related Art In a cellular type mobile phone, when transmitting and receiving at the same time by using an up-channel radio wave and a down-channel radio wave, an antenna duplexer splits the transmission wave and the reception wave. It is carried out.

That is, FIG. 4 shows an outline of a signal system of such a mobile phone, in which a voice signal from the transmitter 1 is supplied to a baseband processing circuit 2 to provide data for band limitation and control. The signal processing for transmission such as addition of is executed. Then, the processed voice signal is supplied to the transmission circuit 3 to be an uplink channel transmission signal, and this signal is supplied to the transmission / reception antenna 5 through the bandpass filter 4T and transmitted to the base station (not shown). It

Further, a downlink channel transmission signal from a base station is received by an antenna 5, and the received signal is supplied to a receiving circuit 6 through a bandpass filter 4R to extract a voice signal and control data. Be done. Then, the extracted signal is supplied to the baseband circuit 2 and the original audio signal is extracted even if the signal processing complementary to that at the time of transmission is executed, and the audio signal is supplied to the handset 7.

Further, at this time, the system control microcomputer 8 controls the channels and transmission / reception of the transmission circuit 3 and the reception circuit 6, and the control data transmitted / received to / from the base station is the microcomputer. 8 and the baseband circuit 2 are accessed.

In this case, the bandpass filter 4
T and 4R compose the antenna duplexer 4 described above, and as is clear from the above, the bandpass filter 4T uses all upstream channels as pass bands, and the bandpass filter 4R has all downstream channels. Is the pass band.

Since the bandpass filters 4T and 4R are required to have the above-mentioned frequency characteristics, the bandpass filters 4T and 4R are generally constituted by dielectric filters.

That is, for example, as shown in FIG. 5, in a signal line of a high frequency signal (transmission signal or reception signal),
The coupling capacitors C1 and C2 are connected in series, and the 1/4 wavelength dielectric resonators X1 and X2 having a high dielectric constant are connected in parallel to form a bandpass characteristic dielectric filter 40. The transmission band pass filter 4T is configured by connecting the dielectric filters 40 in series over, for example, five stages, and the receiving band pass filter 4R is configured by connecting the dielectric filters 40 in series over, for example, three stages. To be done.

[0009]

By the way, the frequency bands used for portable telephones are roughly classified into the 1.8 GHz band, which is used in Europe. 1.9 GHz band ..... Used in the United States. It can be classified into two.

Therefore, in order to improve convenience, it is required that one mobile phone can be used in both the term frequency band and the term frequency band.

However, the frequency is different between the term frequency band and the term frequency band. Therefore, when the mobile phone can be used in both the frequency band of the term and the frequency band of the term, for example, as shown in FIG.
An antenna duplexer 41 that operates in the frequency band of the term is provided, and an antenna duplexer 42 that operates in the frequency band of the term
Is provided.

Then, these antenna duplexers 41 and 42
, The switch circuits 91 to 9 depending on the case
It will be switched by 3 and used. The switching of the switch circuits 91 to 93 can be performed by a control signal from the microcomputer 8.

However, in this case, the number of the dielectric filters 40 having a relatively large volume is doubled among the components used in the mobile phone, which hinders downsizing of the mobile phone. turn into. Also, the cost will increase.

The present invention is intended to solve such a problem.

[0015]

According to the present invention, first and second coupling capacitors are connected in series to a signal line of a high frequency signal, and the signal is output at the output side of the first and second coupling capacitors. First and second dielectric resonators are connected in parallel to the line, and changing means for changing the values of the first and second coupling capacitors are provided, the first and second coupling capacitors, and First
The bandpass characteristic is obtained in the signal line by the second dielectric resonator, and the bandpass characteristic is changed by changing the values of the first and second coupling capacitors by the changing means. This is a dielectric filter.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION In the dielectric filter 40 shown in FIG. 5, even if the resonators X1 and X2 are constant, if the values of the coupling capacitors C1 and C2 are changed, the band pass characteristic, that is, the pass band is changed. Is known to change.

In view of such a point, the present invention constructs a dielectric filter of an antenna duplexer which can be used both in the case of the term and in the case of the term.

That is, FIG. 1 shows one embodiment of the present invention, in which the input terminal T11 is connected to the movable contact of the switch circuit S11, and between the fixed contact and the fixed contact of the switch circuit S12. , And coupling capacitors C11 and C12 are connected. Further, the 1/4 wavelength dielectric resonator X11 is connected in parallel between the movable contact of the switch circuit S12 and the ground, and the movable contact of the switch circuit S12 is connected to the movable contact of the switch circuit S21. .

Further, a fixed contact of the switch circuit S21,
Coupling capacitors C21 and C22 are connected between the fixed contact of the switch circuit S22, the movable contact of the switch circuit S22 is connected to the output terminal T21, and this terminal T21,
A 1/4 wavelength dielectric resonator X21 is connected in parallel with the ground.

Thus, the dielectric filter 40 is constructed. Further, when it is used in the antenna duplexer 4 in FIG. 4, the dielectric filter 40 includes the bandpass filters 4T, which are the required number of stages (orders) as described above.
It is provided at 4R. Then, the switch circuits S11, S12,
S21 and S22 correspond to the frequency band used for the call and are shown in FIG.
The microcomputer 8 in FIG.

In such a configuration, the switch circuit S
When 11 to S22 are connected as shown in the figure, the filter 40 includes capacitors C11 and C21, a resonator X11,
The bandpass characteristic is determined by X21 and acts as the antenna duplexer 4 corresponding to the above-mentioned items, for example.

However, when the switch circuits S11 to S22 are connected in the state opposite to that shown in the figure, the filter 40
Has a bandpass characteristic determined by the capacitors C12 and C22 and the resonators X11 and X21, and acts as the antenna duplexer 4 corresponding to the above-mentioned item, for example.

Thus, according to this dielectric filter 40, bandpass characteristics can be selectively obtained for two frequency bands. Moreover, in that case, since the dielectric resonators X11 and X21 having a relatively large volume are common to the two frequency bands, the size can be reduced as a whole. Also, the cost can be reduced.

In the circuit shown in FIG. 2, in the dielectric filter 40 of FIG. 1, the switch circuits S11 to S22 are composed of transistors, and further, bandpass characteristics are selectively obtained for a plurality of N bands. This is the case.

The resistors R10 to R12 form a voltage line for the DC bias voltage and have a sufficiently large value as compared with the impedance of the signal line.

Therefore, when the switch circuit S10 is connected to the first contact as shown in the figure, the bias voltage V11 causes the transistors Q111, Q121, Q211,
Q221 is forward biased and is on, but the other transistors (Q112, Q122, Q212, Q222) to (Q11N,
Q12N, Q21N, Q22N) are off due to no bias. Therefore, capacitors C11, C21 and resonator X
It is possible to obtain the bandpass characteristics determined by 11 and X12.

Similarly, when the switch circuit S10 is switched to the ith contact (i is any of 1 to N), the transistors (Q111, Q121, Q211 and Q221) are switched.
Of (Q11N, Q12N, Q21N, Q22N), the transistor (Q11i, Q12i, Q21i, Q22i) connected to the i-th contact of the switch circuit S10 is turned on, and the capacitor C1i connected to this transistor is turned on. , C2i and resonator X1
The bandpass characteristics determined by 1 and X12 can be obtained.

Therefore, by switching the switch circuit S10, it is possible to switch to a plurality of band pass characteristics.

In the circuit shown in FIG. 3, variable capacitance diodes D11 and D12 are connected as coupling capacitors. The resistors R11, R12, R21, and R22 serve as voltage lines when supplying the control voltage to the variable capacitance diodes D11 and D21. The capacitors C31 and C32 are for cutting direct current.

In this circuit, bandpass characteristics are obtained by the capacitances of the variable capacitance diodes D11, D21 and the resonators X11, X21, and at that time, the variable capacitance diodes D11, D21 are controlled by the control voltages V11, V21. Since the capacitance of the signal changes, the bandpass characteristic can be changed by changing the voltages V11 and V21. Also, its characteristics can be changed continuously.

In the above description, the terms and the cases of terms are mainly described, but the present invention is also applied to portable telephones of other frequency bands, for example, portable telephones for both analog and digital cellular systems in the United States. can do. Also, in the above,
The switch circuits S11 and S12 may be switch circuits including FETs and diodes.

[0032]

According to the present invention, bandpass characteristics can be selectively obtained for a plurality of frequency bands. Moreover, in that case, since the dielectric resonator having a relatively large volume is common to a plurality of frequency bands, the size can be reduced as a whole. Also, the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a connection diagram illustrating one embodiment of the present invention.

FIG. 2 is a connection diagram illustrating one embodiment of the present invention.

FIG. 3 is a connection diagram illustrating one embodiment of the present invention.

FIG. 4 is a system diagram for explaining a mobile phone.

FIG. 5 is a connection diagram for explaining a dielectric filter.

FIG. 6 is a system diagram for explaining a mobile phone.

[Explanation of symbols]

 C11-C22 coupling capacitor S11-S22 switch circuit T11 input terminal T21 output terminal X11, X21 dielectric resonator

Claims (3)

[Claims] 1. A first and a second coupling capacitors are connected in series to a signal line of a high frequency signal, and the first and second coupling capacitors are connected to the signal line at the output side of the first and the second coupling capacitors. Dielectric resonators are connected in parallel, change means for changing the values of the first and second coupling capacitors are provided, the first and second coupling capacitors, and the first and second dielectric resonances. A dielectric filter configured to obtain a bandpass characteristic on the signal line by means of a child, and to change the bandpass characteristic by changing the values of the first and second coupling capacitors by the changing means. 2. The dielectric filter according to claim 1, wherein a plurality of the first and second coupling capacitors are provided, and the plurality of first and second coupling capacitors are switched by a switch means. Thus, the dielectric filter having the above-mentioned changing means. 3. The dielectric filter according to claim 1, wherein the first and second coupling capacitors are respectively composed of variable capacitance diodes, and the control voltage supplied to these variable capacitance diodes is changed. , A dielectric filter in which the changing means is configured.