JP2899210B2 - Variable frequency band filter - Google Patents

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 duplexer of a microwave radio communication device, and more particularly to a frequency band variable BEF (band rejection filter) having a variable pass band and stop band. Things.

[0002]

2. Description of the Related Art For example, as a frequency band variable filter used in a microwave radio communication device, there is a voltage control filter capable of making a center frequency of a pass band variable, and a band is variably set by a control voltage. it can. FIG. 1 shows an example of the configuration of the above-mentioned conventional frequency band variable filter, wherein 1 is an input terminal, 2 is an output terminal, and 3 and 4 are bias terminals for applying a control voltage. DR ₁ and DR ₂ are dielectric resonators, C ₁₄ and C ₁₅ are variable frequency width adjusting capacitors, X
_1, X ₂ are variable capacitance diodes, R _11, R ₁₂ is a bias voltage supply _{resistor, C 11, C 12, C} 13 is the coupling capacitor. The center frequency of the pass band of the bandpass filter having such a configuration is determined by the combined capacitance of the variable capacitance diodes X ₁ and X ₂ and the respective capacitances of the capacitors C ₁₄ and C ₁₅ ,
And the resonance frequency of the dielectric resonators DR ₁ and DR _2. The center frequency is made variable by changing the voltage applied to the bias terminals 3 and 4 to change the capacitance of the variable capacitance diodes X ₁ and X _2. be able to.

[0003]

However, the variable capacitance diode in the above-mentioned conventional circuit has low power durability and is non-linear because of the reverse voltage versus terminal capacitance characteristic called CV characteristic. There is a drawback that output linearity cannot be obtained. For this reason, a filter using a variable capacitance diode is mainly used only for a receiver handling a small amount of power, and is not used for a transmitter. In recent years, for miniaturization, there is a strong demand for a frequency band variable filter that can obtain a plurality of characteristics having different band frequencies with one filter, and the transmitter is no exception, and a method for realizing this is required. .

[0004] It is an object of the present invention to solve the above-mentioned problems of the prior art, to provide a frequency band variable filter having improved power durability and excellent input / output linearity.

[0005]

A frequency band variable filter according to a first aspect of the present invention has a low-pass type characteristic, and is connected between an input terminal and a ground terminal and has a first capacitor and a first capacitor. A first series resonance circuit comprising a distributed constant line and having a series resonance frequency as a first attenuation pole; a second capacitor connected between an output terminal and a ground terminal; and a second series resonance circuit comprising a second distributed constant line A second series resonance circuit having a frequency as a second attenuation pole; a coupling coil connected between an input terminal side of the first series resonance circuit and an output terminal side of the second series resonance circuit; , A first and a second coil connected in parallel with the first and second series resonance circuits, respectively, and a required high-frequency block is provided by the two attenuation poles.
The two series resonance circuits and the two coils provide a stopband characteristic, and a required low level is provided on the low frequency side of the high frequency stopband characteristic.
Low-pass type filter set to have bandpass characteristics
A first variable capacitance section connected between a connection point between the first capacitor and the first distributed constant line and ground, and formed of a series circuit of a third capacitor and a first switching diode. A second variable capacitance section which is connected between a connection point between the second capacitor and the second distributed constant line and the ground, and is formed of a series circuit of a fourth capacitor and a second switching diode; When the same positive bias voltage is applied to the anodes of both the first and second switching diodes to turn on the first and second switching diodes, the two attenuation pole frequencies become Lowered the high-pass stopband characteristics and the low-pass
Frequency characteristics while maintaining the relative spacing
And when the same negative bias voltage is applied to both the anodes to turn off the first and second switching diodes, the two attenuation pole frequencies rise to increase the high-frequency stop band characteristics. And the low-pass characteristic
Move to the higher frequency while maintaining the relative spacing.
It is characterized in that it is configured to be determined .

[0006] Before Symbol first and second distributed constant line may be a dielectric coaxial resonator.

[0007] Before Symbol first and second switching diodes can be realized even GaAs FET.

[0008] Before Symbol first and second switching diodes is composed of two switching diodes anode comrades are connected respectively, it may be configured such that the control voltage is applied to the connection point of the anode comrades.

As an application example of the first embodiment of the present invention, before <br/> SL one end to each of the third capacitor and the fourth capacitor and the connection point different from each capacitance value is connected in each It provided the other end and the fifth capacitor for variable band to <br/> Thus on / off between the ground switching diode and a sixth capacitor, a switching diode
Third and ON / OFF fourth capacitor due, by independently controlling the fifth and sixth capacitor on / off, both the passband and stopband simultaneously in a plurality of stages
It can be configured to be changeable .

A frequency band variable filter according to a second aspect of the present invention has a high-pass type characteristic, and is connected between an input terminal and a ground terminal from a first capacitor and a first distributed constant line. A first series resonance circuit having a series resonance frequency as a first attenuation pole; a second capacitor connected between an output terminal and a ground terminal; A coupling capacitor connected between an input terminal side of the first series resonance circuit and an output terminal side of the second series resonance circuit; And a third and a fourth capacitor connected in parallel with the second series resonance circuit, respectively, and a required low-frequency block by the two attenuation poles is provided.
The two series resonance circuits and the two capacitors provide a required high-frequency characteristic of the low-frequency stopband characteristic.
A high-pass filter set to have high-pass characteristics.
A first variable capacitance unit connected between a connection point between the first capacitor and the first distributed constant line and a ground, the first variable capacitance unit including a series circuit of a fifth capacitor and a first switching diode; , The second capacitor and the second
And a second variable capacitance section, which is connected between the connection point of the distributed constant line and the ground and is formed of a series circuit of a sixth capacitor and a second switching diode, is provided for the first and second switching diodes. Same for both anodes
When the first and second switching diodes are turned on by applying a positive bias voltage, the two attenuation pole frequencies are reduced, and the low-frequency stop band characteristic and the high-frequency band pass are reduced.
Low frequency while maintaining its relative spacing
When the same negative bias voltage is applied to both of the anodes to turn off the first and second switching diodes, the two attenuation pole frequencies increase and the low-frequency stop band is increased. Characteristics and the high-pass characteristics
Move to higher frequency while maintaining the relative spacing
It is configured to be set .

[0011] Before Symbol first and second distributed constant line may be a dielectric coaxial resonator.

[0012] Before Symbol first and second switching diodes may be gallium arsenide FET.

[0013] is configured in the previous SL first and second switching diodes two switching diodes anode comrades are connected respectively, it may be configured such that the control voltage to the connection point of the anode comrades are given.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction and operation of the present invention will be described. FIG.
FIG. 1 is a configuration diagram showing a first embodiment of the present invention. The attenuation characteristic is a low-pass notch filter characteristic as shown in FIG. That is, as clearly shown in FIG.
Both passband and stopband are specified according to control voltage
Will be satisfied. Z ₁ and Z ₂ are distributed constant lines having characteristic impedance. A coaxial resonator made of a high dielectric material may be used. C ₁ and C ₂ are coupling capacitors for determining the amount of stop band attenuation. C ₃ and C ₄ are capacitors for changing the two attenuation pole frequencies, respectively, and function to change the inductive reactance due to the distributed constant lines Z ₁ and Z ₂ . D ₁ and D ₂ are switching diodes. Control voltage V applied to bias terminal
_When a positive voltage is applied as _CTL , the current is limited by the resistors R ₁ and R _2, but the diodes D ₁ and D ₂ are turned on. As a result, the capacitors C ₃ and C ₄ are grounded via the diodes D ₁ and D ₂ , and the two attenuation pole frequencies are both reduced. Further, given a negative voltage as the control voltage V _CTL, diodes D _1, D ₂ is turned off, the capacitor C _3, C ₄ becomes open, two attenuation pole frequencies are both higher. At this time, the diodes D ₁ and D ₂ have a small capacitance, and the effect of changing the frequency by the capacitors C ₃ and C ₄ may not be sufficient. That time,
The choke coils L ₁ and L ₂ may be set so that the inductance value has an inductive reactance value that cancels out the reactance due to the capacitance. As described above, in this embodiment, the passband and the passband are controlled by one filter.
And the rejection band at the same time, two different frequency band characteristics can be obtained.

In this embodiment, when the diodes D ₁ and D ₂ are on, the maximum input power of the filter is determined by the heat generated by the series resistance of the diodes.
_1, when D ₂ is off, the control voltage V _CTL as the high frequency voltage diode does not turn on the condition to be applied across the diode is set. This value is determined by the reverse bias voltage of the diode. According to the configuration of the present invention described above, unlike the conventional circuit of FIG. 1, there is no restriction due to the nonlinearity of the CV characteristic of the variable capacitance diode, and thus the present invention handles an incomparably large power. be able to.

FIG. 4 shows an example in which FETs Q ₁ and Q ₂ are used as the switching elements of the first embodiment shown in FIG. FETQ
_1, Q ₂ does not require a current when the on like a diode, is excellent in low power consumption. Currently, GaA
When an s (gallium arsenide) FET is used, the resistance value when turned on at 1 GHz is 0.6Ω, and the capacitance when turned off is 1.1 p.
F, and having a performance similar to that of the high-frequency switching diode can be easily obtained. It is useful as a filter for terminals such as mobile phones that require low power consumption.

FIG. 5 expands on the first embodiment of FIG.
This is a circuit with improved power durability. In the example of FIG. 2, the linearity of the input power application is mostly determined by the reverse bias voltage value when the diode is off because the power consumption of the diode is small. To this further improve the control the voltage is not may be V _CTL set high, it is impossible to make unnecessarily high voltage is compact device. Therefore, connecting the diodes D _{1 to} D ₄ as shown in FIG. 5 has the same effect as providing twice the V _CTL with the same V _CTL . When the present embodiment is actually made, a three-terminal SMD (surface mount type) package diode in which the diodes D ₁ and D ₂ are connected as shown in the figure is commercially available, so that it can be easily realized.

FIG. 6 is a block diagram showing an application example of the first embodiment of the present invention, which is a circuit obtained by developing the first embodiment of FIG. 2 and changing the type of the variable band from 2 to 4. is there. By combining ON / OFF of the control voltages V _CTL1 and V _CTL2 , a filter capable of variably setting four frequency bands with one filter can be realized.

FIG. 7 is a characteristic illustration of the embodiment of FIG. 6,
(A) shows a transmission characteristic example, and (B) shows a reflection characteristic example. Figure is
As shown, in the transmission characteristic example (A), the stop band has four steps.
The reflection characteristic example (B) shows that
Shows that the passband with a small coefficient can be variably set in 4 steps
And the stopband and passband are simultaneously in four stages
This indicates that switching can be set. Distributed constant line Z
_{As 1} and Z ₂ , coaxial resonators having a relative dielectric constant of 90 are used, and the capacitance values of the capacitors are respectively C ₃ = 0.45 p
F, C ₇ = 0.8 pF, C ₄ = 0.45 pF, C ₈ =
0.85 pF, C ₁ , C ₂ = 2.5 pF, and the diodes D _{1 to} D 4 are band switching switching diodes (ON resistance = 0.5Ω, OFF capacitance = 1 pF). In this example, when all the diodes were on, the diode did not saturate even at a +35 dBm input at a forward current of 2 mA. When all the diodes were off, saturation started at +32 dBm at a reverse bias voltage of -20 V. Further, when a diode connection as shown in FIG. 5 is used, with the same reverse bias value,
Saturation started when the input was +40 dBm, and the effect was also confirmed in the circuit of FIG.

FIG. 8 is a block diagram showing a second embodiment of the present invention, in which the characteristics of a high-pass notch filter as shown in FIG. 3B are realized. That is, in FIG.
As specified, the passband and stopband correspond to the control voltage.
Both satisfy the predetermined standard . C ₂₂ is a coupling capacitor for connecting the two series resonant circuits, capacitor C _21, C _23, the first capacitor C ₁ of the series resonant circuit, C _3, a distributed constant line Z _1, and a second resonance The values of the capacitors C ₂ and C _{4 of the} circuit and the distributed constant line Z ₂ are selected so that anti-resonance occurs in a pass band that becomes inductive reactance. The operation is the same as that of the first embodiment in FIG. 2, and the modifications corresponding to FIGS. 4 to 6 are also the same.

[0021]

By implementing the present invention, the following effects can be obtained. (1) A variable filter excellent in power durability that cannot be obtained in the conventional example can be realized. (2) Therefore, it can be used as a filter for a transmitter that handles high power.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a conventional circuit configuration.

FIG. 2 is a configuration diagram showing a first embodiment of the present invention.

FIG. 3 is an explanatory diagram of a filter characteristic which is an object of the present invention.

FIG. 4 is a configuration diagram showing another example of the first embodiment of FIG. 2;

FIG. 5 is a configuration diagram showing another example of the first embodiment of FIG. 2;

FIG. 6 is a configuration diagram showing an application example of the first embodiment of the present invention.

FIG. 7 is a characteristic example diagram of FIG. 6;

FIG. 8 is a configuration diagram showing a second embodiment of the present invention.

[Explanation of symbols]

1 input terminal 2 output terminals 3 and 4 the bias terminal C _1, C ₂ resonance capacitor _{C 3, C 4, C 7} , C 8 band variable capacitors _{C 5, C 6, C 9} , C 10 capacitor L _1, L _{2, L 3, L 5,} L 6, L 7 coil L ₄ coupling coil Z _1, Z ₂ distributed constant lines _{D 1, D 2, D 3} , D 4 switching diode V _CTL control voltage R _1, R _2, R ₃ , R ₄ Control voltage supply resistors Q ₁ , Q ₂ FET C ₂₂ Coupling capacitors C ₂₁ , C ₂₃ Capacitors DR ₁ , DR ₂ Dielectric resonator X ₁ , X ₂ Variable capacitance diode C ₁₄ , C ₁₅ Frequency width adjusting capacitor C _11, C _12, C ₁₃ coupling capacitors

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Kazuo Murata 3-14-20 Higashinakano, Nakano-ku, Tokyo International Electric Co., Ltd. (56) References JP-A-2-16802 (JP, A) JP-A Heisei JP-A-4-148562 (JP, A) JP-A-60-27204 (JP, A) JP-A-3-34723 (JP, A) JP-A-4-249401 (JP, A) JP-A-63-90901 (JP, A) A) Japanese Utility Model No. 3-115420 (JP, U) Japanese Utility Model Application No. Sho 58-141618 (JP, U) US Pat. No. 5,227,748 (US, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01P 1 / 205 H03H 7/12

Claims (2)

(57) [Claims] A first series resonance circuit connected between an input terminal and a ground terminal, the first series resonance circuit including a first capacitor and a first distributed constant line, and having a series resonance frequency as a first attenuation pole; and an output terminal. A second series resonance circuit connected between the first series resonance circuit, the second series resonance circuit being connected between the first series resonance circuit and having a second capacitor and a second distributed constant line and having a series resonance frequency as a second attenuation pole. A coupling coil connected between a terminal side and an output terminal side of the second series resonance circuit; and a first and second series connection circuit connected in parallel with the first and second series resonance circuits, respectively.
And two coils are provided .
The two series resonance circuits and the two coils provide a high-frequency stopband characteristic on the low frequency side of the high-frequency stopband characteristic.
Low-pass type set to have essential low-pass characteristics
A filter, a first variable capacitance unit connected between a connection point between the first capacitor and the first distributed constant line and ground, and configured by a series circuit of a third capacitor and a first switching diode; A fourth capacitor connected between a connection point between the second capacitor and the second distributed constant line and a ground,
And a second variable capacitance section comprising a series circuit of switching diodes, wherein the same positive bias voltage is applied to both anodes of the first and second switching diodes to perform first and second switching. When the diode is turned on, the frequencies of the two attenuation poles decrease, and the frequency of the high-frequency stop band is reduced.
And the low-pass characteristics maintain their relative spacing.
When the same negative bias voltage is applied to both the anodes and the first and second switching diodes are turned off, the above-mentioned 2 is set.
One of the attenuation pole frequency up to the said high frequency stopband characteristics
Low passband characteristics and the frequency while maintaining the relative spacing
A low-pass type frequency band variable filter configured to be set to move to a higher one . 2. A first series resonance circuit connected between an input terminal and a ground terminal, the first series resonance circuit including a first capacitor and a first distributed constant line, and having a series resonance frequency as a first attenuation pole, and an output terminal. A second series resonance circuit connected between the first series resonance circuit, the second series resonance circuit being connected between the first series resonance circuit and having a second capacitor and a second distributed constant line and having a series resonance frequency as a second attenuation pole. A coupling capacitor connected between the terminal side and an output terminal side of the second series resonance circuit, and third and fourth capacitors connected in parallel with the first and second series resonance circuits, respectively. The two attenuation poles provide a required low-frequency stopband characteristic, and the two series resonance circuits and the two capacitors provide the low-frequency stopband characteristic.
Is set to have the required high-pass characteristics on the high-frequency side of
A high-pass filter, comprising a series connection of a fifth capacitor and a first switching diode connected between a connection point between the first capacitor and the first distributed constant line and a ground. A sixth capacitor connected between a capacitor, a connection point between the second capacitor and the second distributed constant line, and a ground;
And a second variable capacitance section comprising a series circuit of switching diodes, wherein the same positive bias voltage is applied to both anodes of the first and second switching diodes to perform first and second switching. When the diode is turned on, the frequencies of the two attenuation poles decrease, and the frequency of the low-frequency stop band is reduced.
And the high-pass characteristics maintain their relative spacing.
When the same negative bias voltage is applied to both the anodes and the first and second switching diodes are turned off, the above-mentioned 2 is set.
One of the attenuation pole the frequency up the low-frequency stop band characteristics
High passband characteristics and frequency while maintaining the relative spacing
A high- pass type frequency band variable filter configured to be set to move to a higher one .