JP2000114814A - Frequency variable filter, antenna sharing device and communication equipment device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the degree of freedom for design and to provide satisfactory filter characteristics. SOLUTION: At one terminal of resonators 2 and 3-6, the cathodes of PIN diodes D1, D2 and D4-D6 as switching elements are respectively electrically connected. The anodes of PIN diodes D1 and D3-D6 are respectively grounded through variable band capacitors C3, C4 and C7-C9. Further, stray capacitance Cs1-Cs5 are respectively electrically connected to the variable band capacitors C3-C9. The stray capacitance Cs1 and Cs3-Cs5 are electrostatic capacity generated between a soldering land for anodes of PIN diodes D1 and D4-D6 and a ground conductor. The stray capacitance Cs2 is an electrostatic capacity generated between a soldering land for the cathode of the PIN diode D3 and the ground conductor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable frequency filter used in a microwave band, an antenna duplexer, and a communication device.

[0002]

2. Description of the Related Art Conventionally, there has been known a variable frequency filter in which a switching element such as a PIN diode is connected to a resonator via a capacitor or the like and the voltage is controlled to change the resonance frequency. FIG. 9 is an electric circuit diagram showing a conventional variable frequency filter 151. The variable frequency filter 151 includes input / output terminals 154 and 155
Are two-stage coupled resonant circuits. Resonator 1
The series resonance circuit of the resonance capacitor 52 and the resonance capacitor C53 is electrically connected to the series resonance circuit of the resonator 153 and the resonance capacitor C54 via the coupling coil L51. Further, capacitors C55 and C56 are electrically connected in parallel to these two series resonance circuits, respectively.

An anode of a PIN diode D51 as a switching element is connected to an intermediate connection point between the resonator 152 and the resonance capacitor C53 via a band variable capacitor C51. The cathode of the PIN diode D51 is grounded, and the PIN diode D51 is electrically connected to the resonator in parallel. On the other hand, resonator 1
A PIN diode D is connected to an intermediate connection point between the resonance diode C53 and the resonance capacitor C54 through a band variable capacitor C52.
52 is electrically connected to the resonator 153 in parallel. The anode of the PIN diode D52 is electrically connected to the band variable capacitor C52, and the cathode is grounded.

A voltage control terminal CONT1 is connected to a control voltage supply resistor R51, a capacitor C57 and a choke coil L.
52, an electrical connection between the anode of the PIN diode D51 and the intermediate connection point between the band variable capacitor C51 and the control voltage supply resistor R51 and the capacitor C51.
It is electrically connected to an intermediate connection point between the anode of the PIN diode D52 and the band variable capacitor C52 via the choke coil L53 and the anode 57.

When a positive voltage is applied as a control voltage to the voltage control terminal CONT1, the PIN diodes D51, D52
Is turned on. Therefore, the band variable capacitor C5
1 and C52 are grounded via PIN diodes D51 and D52, respectively. Band-variable capacitors C51 and C52 are respectively connected in parallel to the resonators 152 and 153, and the frequency-variable filter 151 has a first pass frequency.

When a negative voltage is applied to the voltage control terminal CONT1 as a control voltage, the PIN diodes D51 and D52
Is turned off and a high impedance capacitive PIN
It becomes a diode. The resonator 152 is electrically connected in parallel to a series circuit including a band variable capacitor C51 and a capacitive PIN diode D51. Similarly, the resonator 153 includes a band variable capacitor C52 and a capacitive PI
A series circuit including an N diode D52 is electrically connected in parallel. Thus, the variable frequency filter 151
Obtains a second pass frequency. Since the capacitive PIN diodes D51 and D52 have high impedance, the capacitance value is small, and the capacitive variable diodes C51 and C52 and the capacitive P
The capacitance of each series circuit including the IN diodes D51 and D52 is almost the same as that of the capacitive PIN diodes D51 and D52.
52 becomes dominant. Therefore, the second pass frequency is higher than the first pass frequency.

[0007]

In the variable frequency filter 151 having the above-described structure, the elements for shifting the pass frequency are only the band variable capacitors C51 and C52. However, this band variable capacitor C5
1, C52 often uses chip capacitors,
For this reason, there is a case where there is no capacitor having the optimum capacitance value for the shift amount, and the degree of freedom in designing the frequency variable filter 151 is small. In particular, when the shift amount of the pass frequency is small, the band variable capacitors C51 and C52
Is also extremely small, and it has been difficult to obtain a chip capacitor having such a small capacitance. Further, when the shift amount of the pass frequency is small, there is a problem that the tolerance of the capacitance of the chip capacitor cannot be ignored, and the characteristics of the frequency variable filter 151 tend to vary.

Further, it is necessary to form a through hole and a wiring pattern for electrically connecting the cathodes of the PIN diodes D51 and D52 to the ground, which hinders downsizing of the frequency variable filter 151. Was.

SUMMARY OF THE INVENTION An object of the present invention is to provide a small frequency variable filter, antenna duplexer, and communication device that have a large degree of freedom in design and provide excellent filter characteristics.

[0010]

To achieve the above object, a variable frequency filter according to the present invention comprises a voltage control terminal, at least one resonator, and a control voltage supplied to the voltage control terminal. A PIN diode that is turned on / off, a cathode of the PIN diode is electrically connected to one end of the resonator, and an anode of the PIN diode is grounded via a capacitance. Here, the capacitance uses a capacitance of a capacitor element or a stray capacitance formed between a solder land of the PIN diode provided on a circuit board and a ground conductor. As the resonator, a dielectric resonator is used.

With the above configuration, when a positive voltage is applied to the voltage control terminal, the PIN diode is turned on, and in addition to the capacitance of the conventional capacitor element, the PIN diode is connected between the soldering land of the PIN diode and the ground conductor. The passing frequency also shifts due to the formed stray capacitance.

Further, the antenna duplexer and the communication device according to the present invention are provided with the variable frequency filter having the above-mentioned characteristics, so that the degree of freedom of design is increased and excellent filter characteristics are obtained.

[0013]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of a variable frequency filter, an antenna duplexer and a communication device according to the present invention. In each embodiment, the same reference numerals are given to the same parts and the same components.

[First Embodiment, FIGS. 1 to 6] FIG. 1 shows an antenna duplexer 1, and FIG.
FIG. 3 is a perspective view of the antenna duplexer 1 on which components are mounted. In the antenna duplexer 1, the transmitting circuit 25 is electrically connected between the transmitting terminal Tx and the antenna terminal ANT, and the receiving circuit 26 is electrically connected between the receiving terminal Rx and the antenna terminal ANT.

The transmitting side circuit 25 has a variable frequency band rejection filter circuit 27 and a phase circuit 29. The band rejection filter circuit 27 is a circuit in which resonance circuits are coupled in two stages. The resonator 2 electrically connected to the transmission terminal Tx via the resonance capacitor C1 and the phase circuit 29 via the resonance capacitor C2. And a resonator 3 electrically connected to the The resonance capacitors C1 and C2 are capacitors that determine the magnitude of the stopband attenuation. The series resonance circuit of the resonator 2 and the resonance capacitor C1 is electrically connected to the series resonance circuit of the resonator 3 and the resonance capacitor C2 via the coupling coil L1. Further, a capacitor C is electrically connected in parallel to these two series resonance circuits.
5, C6 are connected.

A PIN diode D serving as a switching element is provided at an intermediate connection point between the resonator 2 and the resonance capacitor C1.
One cathode is electrically connected. The anode of the PIN diode D1 is grounded via the band variable capacitor C3. Further, a stray capacitance Cs1 is connected between an intermediate connection point between the PIN diode D1 and the band variable capacitor C3 and the ground. On the other hand, resonator 3
Two series-connected PIN diodes D2 and D3 are electrically connected to an intermediate connection point between the resonance capacitor C2 and the resonance capacitor C2. The cathode and the anode of the PIN diode D2 are electrically connected to the resonator 3 and the anode of the PIN diode D3, respectively, and the cathode of the PIN diode D3 is grounded via the band variable capacitor C4.
Further, a stray capacitance C is provided between an intermediate connection point between the PIN diode D3 and the band variable capacitor C4 and the ground.
s2 is connected. Band variable capacitors C3 and C4
Are capacitors for changing the two attenuation pole frequencies of the attenuation characteristics of the frequency variable band rejection filter circuit 27, respectively. Also, PIN diodes D2 and D3 are ON
In this case, a choke coil L4 is connected between the PIN diode D3 and the band variable capacitor C4 in order to allow a direct current to flow.

The voltage control terminal CONT1 is connected to a control voltage supply resistor R1, a capacitor C22 and a choke coil L2.
, And electrically connected to an intermediate connection point between the anode of the PIN diode D1 and the band variable capacitor C3, and via the control voltage supply resistor R1 and the capacitor C22 and the choke coil L3.
Are electrically connected to the intermediate connection point of the anode.

The phase circuit 29 includes the band rejection filter circuit 2
7, a coil L20 electrically connected between the antenna terminal ANT, a capacitor C15 electrically connected between the ground and the antenna terminal ANT, a band-pass filter circuit 28 (described later) of the receiving circuit 26, and an antenna terminal. This is a T-shaped circuit composed of a coil L21 electrically connected between ANT.

On the other hand, the receiving side circuit 26 has a variable frequency band-pass filter circuit 28 and a phase circuit 29. In the case of the receiving circuit 26 of the first embodiment, the phase circuit 2
9 is shared with the transmission side circuit 25,
Needless to say, the receiving side circuit 26 may have an independent phase circuit.

The band-pass filter circuit 28 is formed by coupling resonance circuits in three stages. The band-pass filter circuit 28 receives a signal via the resonator 4 electrically connected to the phase circuit 29 via the resonance coil L9 and a signal via the resonance coil L10. A resonator 6 electrically connected to the terminal Rx, and coupling capacitors C11 and C
And a resonator 5 which is electrically connected via C12, C13 and C14.

The cathode of a PIN diode D4 is electrically connected to an intermediate connection point between the resonator 4 and the resonance coil L9. The anode of the PIN diode D4 is grounded via the band variable capacitor C7. A stray capacitance Cs3 is connected between an intermediate connection point between the PIN diode D4 and the band variable capacitor C7 and the ground. One end of the resonator 5 is electrically connected to a cathode of a PIN diode D5. The anode of the PIN diode D5 is grounded via the band variable capacitor C8. A stray capacitance C is provided between an intermediate connection point between the PIN diode D5 and the band variable capacitor C8 and the ground.
s4 is connected. A cathode of a PIN diode D6 is electrically connected to an intermediate connection point between the resonator 6 and the resonance coil L10. The anode of the PIN diode D6 is grounded via the band variable capacitor C9.
A stray capacitance Cs5 is connected between an intermediate connection point between the PIN diode D6 and the band variable capacitor C9 and the ground.

The voltage control terminal CONT2 is connected to a control voltage supply resistor R2, a capacitor C23 and a choke coil L6.
, And is electrically connected to an intermediate connection point between the anode of the PIN diode D4 and the band variable capacitor C7 through the control voltage supply resistor R2 and the capacitor C23 and the choke coil L7 and the anode of the PIN diode D5 and the band variable capacitor. Electrically connected to the intermediate connection point of the capacitor C8,
Furthermore, a control voltage supply resistor R2 and a capacitor C23
And an intermediate connection point between the anode of the PIN diode D6 and the band variable capacitor C9 via the choke coil L8.

Here, the stray capacitances Cs1 to Cs5 will be described in detail. As shown in FIG. 3, on the surface of the circuit board 40, a large number of circuit patterns, a large-area ground pattern 41a that occupies approximately half the area of the upper surface, and small-area ground patterns 41b, 41c, and 41d are formed. Have been. A ground pattern 41e is formed on substantially the entire back surface of the circuit board 40. The ground patterns 41 a to 41 d formed on the front surface of the circuit board 40 and the ground pattern 41 e formed on the back surface are electrically connected through a plurality of through holes 47.

The stray capacitance Cs1 is calculated based on the circuit pattern 42 (in other words, the soldering land 42 for the anode of the PIN diode D1) indicated by oblique lines among a number of circuit patterns formed on the surface of the circuit board 40. And the ground pattern 41e formed on the back surface of. The stray capacitance Cs2 is the circuit pattern 4
3 (the cathode solder land 43 of the PIN diode D3) and the ground pattern 41e. The stray capacitance Cs3 is the circuit pattern 44
(Soldering land 4 for anode of PIN diode D4
4) and the ground pattern 41e. The stray capacitance Cs5 is determined by the circuit pattern 46 (P
Soldering land 46 for anode of IN diode D6)
And the ground pattern 41e. In addition, even in the case of the conventional antenna duplexer, PI
An N diode solder land is formed on the circuit board. However, since the cathode of the PIN diode is grounded to the ground, even if the PIN diode is turned on, the stray capacitance generated between the solder land of the PIN diode and the ground hardly affects the frequency shift. .

As the resonators 2 to 6, for example, as shown in FIG. 4, a λ / 4 dielectric resonator is used. FIG. 4 shows the resonator 2 as a representative example. Dielectric resonator 2
Reference numeral 6 denotes a cylindrical dielectric 21 formed of a high dielectric constant material such as TiO ₂ -based ceramic, an outer conductor 22 provided on the outer peripheral surface of the cylindrical dielectric 21, and an inner periphery of the cylindrical dielectric 21. And an inner conductor 23 provided on the surface. The outer conductor 22 is
One open end face 21a (hereinafter, referred to as open end face 21a) of the dielectric 21 is electrically opened (separated) from the inner conductor 23 and the other open end face 21b (hereinafter, short-circuit end face 2).
1b), the inner conductor 23 is electrically short-circuited (conductive).
Have been. The dielectric resonator 2 includes a band variable capacitor C3 and a PIN diode D on the open end face 21a.
One series circuit is electrically connected with the cathode of the PIN diode D1 connected to the inner conductor 23 and one end of the band variable capacitor C3 is grounded, and the outer conductor 22 is grounded.

Next, the operation and effect of the antenna duplexer 1 having the above configuration will be described. This antenna duplexer 1
Outputs a transmission signal that has entered the transmission terminal Tx from the transmission circuit system to the antenna terminal ANT via the transmission side circuit 25, and outputs a reception signal entered from the antenna terminal ANT to the reception terminal Rx via the reception side circuit 26. Output to the receiving circuit system.

The trapping frequency of the variable frequency band rejection filter circuit 27 of the transmission side circuit 25 is determined by the following: a resonance system composed of the band variable capacitor C3, the stray capacitance Cs1, the resonance capacitor C1, and the resonator 2, It is determined by the respective resonance frequencies of the resonance system constituted by the capacitor C4, the stray capacitance Cs2, the capacitor C2 for resonance, and the resonator 3. When a positive voltage is applied as a control voltage to the voltage control terminal CONT1, the PIN diode D1,
D2 and D3 are turned on. Therefore, as shown in FIG. 5, the resonator 2 is electrically connected to the band variable capacitor C3 and the stray capacitance Cs1 in parallel. FIG.
In the equation, Rd is the forward resistance of the PIN diode D1. Similarly, the resonator 3 includes a band variable capacitor C
4 and the stray capacitance Cs2 are electrically connected in parallel. As a result, the two attenuation pole frequencies are both low, and the pass band of the transmission side circuit 25 is low.

Then, the band variable capacitors C3 and C4
The amount of shift of the trap frequency of the band rejection filter circuit 27 can be set optimally with the floating capacitances Cs1 and Cs2. That is, if it is not possible to sufficiently narrow and secure the optimum capacitance value only by changing the band variable capacitors C3 and C4, the PIN diodes D1 and D3
The pattern area of the soldering lands 42, 43 is changed to finely adjust the capacitance values of the stray capacitances Cs1, Cs2 to obtain the optimum capacitance value. Specifically, the optimum capacitance value is 1.65 pF
, A standard product 1.5 pF chip capacitor is used as the band variable capacitors C3 and C4.
The necessary optimum capacitance value can be obtained by combining with the stray capacitances Cs1 and Cs2 of 5 pF.

Conversely, when a negative voltage is applied to the voltage control terminal CONT1 as a control voltage, the PIN diode D1,
D2 and D3 are turned off. Instead of applying a negative voltage, the control circuit that supplies the control voltage to the voltage control terminal CONT1 has a high impedance of 100 KΩ or more, and the control voltage is reduced to 0 V by preventing the voltage from being applied to the voltage control terminal CONT1. Thus, the PIN diodes D1 to D3 may be turned off.

As a result, as shown in FIG. 6, the PIN diodes D1, D2 and D3 become high impedance capacitive diodes. In FIG. 6, Cd is the capacitance of the PIN diode D1. Band variable capacitor C3
A parallel circuit including the stray capacitance Cs1 is connected in series to the capacitance Cd of the PIN diode D1. Further, this series-parallel circuit is connected to the resonator 2 in parallel. Similarly, the band variable capacitor C4 and the stray capacitance C
The parallel circuit composed of s2 includes PIN diodes D2 and D3.
And the series-parallel circuit is connected to the resonator 3 in parallel. As a result, the two attenuation pole frequencies are both increased, and the transmission side circuit 2
The passband of 5 becomes higher. Thus, the transmission side circuit 2
5 can have two different passband characteristics by turning on and off the PIN diodes D1 to D3 by voltage control.

On the other hand, the passing frequency of the variable frequency band-pass filter circuit 28 of the receiving side circuit 26 is determined by the resonance system including the band variable capacitor C7, the stray capacitance Cs3, the resonance coil L9, and the resonator 4. Band variable capacitor C
8, a stray capacitance Cs 4 and a resonator 5, and a resonance frequency of a resonance system including a band variable capacitor C 9, a stray capacitance Cs 5, a resonance coil L 10 and a resonator 6. . Then, when a positive voltage is applied as a control voltage to the voltage control terminal CONT2,
PIN diodes D4, D5 and D6 are turned on.
Therefore, the band variable capacitor C7 and the stray capacitance Cs3 are electrically connected in parallel to the resonator 4, the band variable capacitor C8 and the stray capacitance Cs4 are electrically connected in parallel to the resonator 5, and the band variable capacitor C9 and stray capacitance Cs5
Are electrically connected to the resonator 6 in parallel. As a result, the passing frequency becomes lower.

Conversely, when a negative voltage is applied to the voltage control terminal CONT2, the PIN diodes D4, D5 and D6 become O
The state becomes the FF state and becomes a capacitive PIN diode. Since the capacitive PIN diodes D4 to D6 have high impedance, their capacitance values are small. Therefore, the band variable capacitor C7
The capacitance of the series-parallel circuit including the stray capacitance Cs3 and the capacitive PIN diode D4 is almost dominated by the capacitance of the capacitive PIN diode D4. Similarly, the capacitance of the series-parallel circuit including the band variable capacitor C8, the stray capacitance Cs4, and the capacitive PIN diode D5 is almost dominated by the capacitance of the capacitive diode D5. Further, the capacitance of the series-parallel circuit including the band variable capacitor C9, the stray capacitance Cs5, and the capacitive PIN diode D6 is also almost dominated by the capacitance of the capacitive diode D6. As a result, the pass frequency increases. Thus, the receiving side circuit 2
6 can have two different passband characteristics by turning on and off the PIN diodes D4 to D6 by voltage control.

Also, PIN diodes D1, D2, D
4, D5, and D6 are connected to the resonators 2, 3, 4,
It can be DC-grounded via 5,6. Therefore, it is not necessary to form a dedicated through hole or a wiring pattern for electrically connecting the cathodes of the PIN diodes D1, D2, D4, D5, and D6 to the ground on the circuit board 40. Becomes possible.

Further, the antenna duplexer 1 of the first embodiment
In the transmission side circuit 25, two PIN diodes D2 and D3 are connected in series only to the resonator 3 electrically connected to the antenna terminal ANT closest to the antenna terminal ANT.
The voltage control terminal CONT1 is connected to the anode of D3 to divide the high frequency voltage. Thereby, the intermodulation distortion wave F3 of the transmission wave F1 and the intrusion wave F2 entering from the antenna terminal ANT can be suppressed efficiently. The intermodulation distortion wave F3 of the transmission wave F1 and the intrusion wave F2 invading from the antenna terminal ANT is the voltage connected to the resonator 3 closest to the antenna terminal ANT among the plurality of resonators 2 and 3 of the transmission side circuit 25. This is because suppressing the nonlinear distortion of the controllable impedance element is most effective.

[Second Embodiment, FIG. 7] FIG. 7 shows a configuration of an antenna duplexer 61 according to a second embodiment. The antenna duplexer 61 is the same as the antenna duplexer 1 of the first embodiment, except that the band variable capacitors C3, C4, C
It is the same as that in which 7, C8 and C9 are omitted. When the amount of frequency shift is small, the optimum capacitance value may be small (for example, about 0.2 pF).
A desired frequency shift amount can be obtained only with s1 to Cs5.

[Third Embodiment, FIG. 8] In the third embodiment,
A mobile phone will be described as an example of a communication device according to the present invention. FIG. 8 is an electric circuit block diagram of the RF portion of the mobile phone 120. 8, reference numeral 122 denotes an antenna element, 123 denotes a duplexer, 131 denotes a transmission-side isolator, 132 denotes a transmission-side amplifier, 133 denotes a transmission-side interstage bandpass filter, 134 denotes a transmission-side mixer, 135 denotes a reception-side amplifier, and 136 denotes a reception-side amplifier. Bandpass filter for inter-stage on the receiving side,
137 is a reception side mixer, 138 is a voltage controlled oscillator (VC
O) 139 is a local band-pass filter.

Here, as the duplexer 123, the duplexers 1 and 61 of the first and second embodiments can be used. By mounting these duplexers 1 and 61, it is possible to realize a small-sized mobile phone having a large degree of freedom in design and excellent frequency characteristics. Further, the band-pass filter 13 between the transmission side and the reception side
3, 136 and the local bandpass filter 139
For example, the variable frequency band-pass filter circuit 28 shown in FIG. 1 can be used.

[Other Embodiments] The variable frequency filter, the antenna duplexer and the communication device according to the present invention are not limited to the above-described embodiments, but may be variously modified within the scope of the invention. it can. In particular, the resonator may be a microstrip line resonator other than a dielectric resonator, or may be an LC resonance circuit combining an inductor element and a capacitor element. Although the above embodiment has been described with respect to the antenna duplexer, for example, the frequency variable type band rejection filter circuit 27 and the frequency variable type band pass filter circuit 28 constituting the antenna duplexer 1 shown in FIG. May be separately manufactured and commercialized as a variable frequency filter.

[0039]

As apparent from the above description, according to the present invention, the cathode of the PIN diode is electrically connected to one end of the resonator, and the anode of the PIN diode is grounded via the capacitance. In addition to the conventional capacitance of the capacitor element, PIN
The passing frequency can also be shifted by the stray capacitance formed between the soldering land of the diode and the ground conductor. Therefore, by changing the pattern area of the solder land of the PIN diode, the amount of frequency shift can be finely adjusted, and the optimum capacitance value can be narrowed to improve the filter characteristics. Further, the degree of freedom in designing the frequency variable filter can be increased.

Further, when the frequency shift amount is small, the desired frequency shift amount can be obtained only by the stray capacitance formed between the soldering land of the PIN diode and the ground conductor. Can be reduced. Further, since the cathode side of the PIN diode can be DC-grounded via the resonator, the PIN
There is no need to provide a dedicated through hole or a wiring pattern for electrically connecting the cathode of the diode to the ground on the circuit board, which leads to a reduction in the size of the device.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram showing a first embodiment of an antenna duplexer according to the present invention.

FIG. 2 is a perspective view showing a mounting structure of the duplexer shown in FIG. 1;

FIG. 3 is a plan view showing a circuit board used in the antenna duplexer shown in FIG. 2;

FIG. 4 is a sectional view showing an example of a resonator used in the antenna duplexer shown in FIG. 1;

FIG. 5 is an operation explanatory diagram of the antenna duplexer shown in FIG. 1;

FIG. 6 is an operation explanatory diagram of the antenna duplexer shown in FIG. 1;

FIG. 7 is an electric circuit diagram showing a second embodiment of the antenna duplexer according to the present invention.

FIG. 8 is a block diagram showing an embodiment of a communication device according to the present invention.

FIG. 9 is an electric circuit diagram showing a conventional frequency variable filter.

[Explanation of symbols]

 1, 61 antenna duplexer 2, 3, 4, 5, 6 resonator 25 transmission circuit 26 reception circuit 27 frequency variable band rejection filter circuit 28 frequency variable band pass filter circuit 41a to 41e ... Ground patterns 42 to 46... PIN diode solder lands C3, C4, C7, C8, C9... Band variable capacitors Cs1 to Cs5. Terminals CONT1, CONT2: Voltage control terminal 120: Mobile phone 123: Duplexer 133, 136, 139: Band-pass filter

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5J006 HA03 HA15 HA32 HA34 JA01 JA02 KA02 KA11 KA12 KA13 KA24 LA11 LA13 LA21 MA07 MA09 NA05 NB08 5J098 AA04 AA11 AA14 AA16 AB05 AB32 AC02 AC18 AC20 AD25 AD29 CA05 CA06 CB02 CB02

Claims (6)

[Claims] 1. A voltage control terminal, at least one resonator, and a PIN diode which is turned on / off by a control voltage supplied to the voltage control terminal, wherein a cathode of the PIN diode is provided at one end of the resonator. A variable frequency filter electrically connected, wherein an anode of the PIN diode is grounded via a capacitance. 2. The variable frequency filter according to claim 1, wherein said capacitance is formed by a capacitor element. 3. The frequency variable according to claim 1, wherein the capacitance is a stray capacitance formed between a solder land of the PIN diode provided on a circuit board and a ground conductor. Type filter. 4. The variable frequency filter according to claim 1, wherein said resonator is a dielectric resonator. 5. An antenna duplexer comprising at least one of the variable frequency filters according to claim 1. Description: 6. A communication device comprising at least one of the frequency variable filter according to claim 1 and the antenna duplexer according to claim 5.