JPH10256809A - Electronic tuning polar filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small sized electronic tuning polar filter that has a steep attenuation pole in the vicinity of a pass band and where the position of the attenuation pole is controlled electronically. SOLUTION: An auxiliary circuit 110 consisting of cascade connection of a variable phase shifter 102 whose phase shift amount is adjustable and a variable attenuator 103 whose attenuation is adjustable is connected to a band pass filter 101 via connection circuits 104, 105 respectively and the phase shift amount and the attenuation are controlled electrically by employing active elements for the variable phase shifter 102 and the variable attenuator 103. An attenuation pole of the title filter is caused at a frequency at which an amplitude of a signal from an input terminal 106 to an output terminal 107 via the band pass filter 101 is the same as an amplitude of a signal from the input terminal 106 to the output terminal 101 via the variable phase shifter 102 and the variable attenuator 103 and a phase of the former signal is opposite to a phase of the latter signal. Since the phase shift amount and the attenuation are controlled electrically, the frequency at which the attenuation pole is produced is easily adjusted. Moreover, circuit integration is possible for the variable phase shifter 102 and the variable attenuator 103 and then they are made small.

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 high frequency region such as a UHF band, a microwave band and a millimeter wave band, and more particularly to a high frequency filter suitable for a base station for mobile communication.

[0002]

2. Description of the Related Art A high-frequency filter used in a radio section of a mobile communication terminal is required to be small and lightweight. Similarly, the base station filter needs to be small and lightweight, but in order to amplify and transmit a plurality of transmission waves with a common amplifier or to receive a plurality of reception waves with good selectivity, adjacent channels must be used. It is more important to sharpen the attenuation characteristic near the pass band.

[0003] A conventional filter of this type will be described below. FIG. 6 is a circuit diagram showing an example of a conventional filter. This filter couples two resonators 11 and 12 with an inductance 13 and each has a capacitance of 1
This is a two-stage band-pass filter coupled to the input terminal 16 and the output terminal 17 via 4 and 15. By providing an auxiliary circuit 18 composed of a capacitor between the input terminal 16 and the output terminal 17 of this bandpass filter, a filter having attenuation poles on both sides of the passband can be configured. This auxiliary circuit 18
Conventionally, a passive element such as a lumped constant element such as a capacitor or an inductor or a distributed constant element such as a parallel coupling line is used. With such a configuration, this filter operates as a band-pass filter having an attenuation pole near a pass band in a high-frequency region.

[0004]

However, in the above-described conventional polar filter shown in FIG. 6, the frequency at which the attenuation pole is generated is uniquely determined by the auxiliary circuit, and can be set at any position without changing the auxiliary circuit. Since the attenuation pole cannot be changed, there is a problem that even in a system of the same frequency band, if the conditions such as the channel spacing are different, the design of the filter itself must be changed.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems, and provides an electronically tuned polarized filter having a small size, a steep attenuation pole near a pass band, and a position of the attenuation pole being electronically controllable. The purpose is to do so.

[0006]

In order to achieve the above object, the present invention relates to a variable phase shifter having an adjustable phase shift amount, a variable attenuator having an adjustable attenuation amount, a band pass filter, and two connections. An auxiliary circuit consisting of a cascade-connected variable phase shifter and variable attenuator is connected between the input and output of the band-pass filter via a connection circuit. The attenuator is configured by using an active element, thereby providing an electronically tuned polarized filter having a small size, a steep attenuation pole near a pass band, and the position of the attenuation pole being electronically controllable. be able to.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention according to claim 1 of the present invention provides a variable phase shifter having an adjustable phase shift amount, a variable attenuator having an adjustable attenuation amount, a band-pass filter, A connection circuit, wherein the cascade-connected variable phase shifter and variable attenuator constituting an auxiliary circuit are respectively connected between an input unit and an output unit of the band-pass filter via the connection circuit. An electronic tuned polar filter in which the variable phase shifter and the variable attenuator are configured using active elements,
This has the effect that the amount of change can be electronically controlled. Also, the auxiliary circuit in which the variable phase shifter and the variable attenuator are connected in cascade is mainly composed of active elements, and can be easily integrated into an IC, so that the entire filter can be downsized, and furthermore, it does not depend on the configuration of the bandpass filter. , A general-purpose IC can be configured.

[0008] The invention according to claims 2 to 4 of the present invention provides:
As a connection circuit for connecting the band-pass filter, a distributed coupling circuit such as a capacitance, an inductor, or a parallel coupling line using a strip line is used, and has the same effect as the first aspect of the present invention.

According to a fifth aspect of the present invention, in the first to fourth aspects, the band-pass filter is a resonator-coupling type filter such as a dielectric coaxial resonator or a strip line resonator. It has the same function as the first aspect of the present invention.

According to a sixth aspect of the present invention, in the first to fifth aspects, the variable attenuator comprises a PIN diode and a bias circuit for supplying a bias current to the PIN diode. Yes, this P
Since the resistance value of the PIN diode changes by changing the bias current flowing through the IN diode, there is an effect that the attenuation can be electronically controlled using this characteristic.

According to a seventh aspect of the present invention, in the first to fifth aspects, the variable attenuator comprises a dual gate FET and a bias circuit for determining a bias voltage of the dual gate FET. And
By changing the gate voltage of the dual-gate FET, the amount of attenuation of the signal passing through the dual-gate FET changes. Therefore, there is an effect that the attenuation can be electronically controlled using this characteristic.

According to an eighth aspect of the present invention, in the first to seventh aspects, the variable phase shifter comprises two balanced modulators, a 90-degree distributor, and an in-phase combiner. The input signal is divided into two signals having a phase difference of 90 degrees by the 90-degree distributor, and then the sine function and the cosine function of the desired phase shift amount are respectively formed by the balanced modulator. Proportional amplitude modulation,
Thereafter, the phase is electronically controllable by synthesizing by the in-phase synthesizer, whereby the amount of phase change can be continuously varied over 360 degrees or more, and a constant phase shift independent of frequency can be obtained.

The ninth aspect of the present invention is the first aspect of the present invention.
7. The variable phase shifter according to any one of claims 1 to 7, wherein the variable phase shifter includes a varactor diode, a circulator, and a bias circuit that applies a bias voltage to the varactor diode, and the varactor diode is added to a port from which an input signal to the circulator is output. By extracting a reflected wave from the varactor diode as an output signal from the remaining terminal of the circulator, the bias voltage can be controlled to change the capacitance of the varactor diode, thereby controlling the amount of phase shift electronically. .

According to a tenth aspect of the present invention, in the first to seventh aspects, the variable phase shifter includes two varactor diodes, a 90-degree hybrid circuit, and the second phase shifter.
A bias circuit that applies a bias voltage to two varactor diodes, wherein two adjacent isolation ports of the 90-degree hybrid circuit are used as an input terminal and an output terminal, and the varactor diode is added to the remaining two terminals. , The input signal from the input terminal is divided and connected to the varactor diode connected 2
And the reflected wave from the varactor diode is synthesized and output from the output terminal.The amount of phase shift is electronically controlled by controlling the bias voltage of the varactor diode by the bias circuit to change the capacitance. Has the effect of being able to.

According to an eleventh aspect of the present invention, in the first to tenth aspects, an auxiliary circuit in which a variable phase shifter and a variable attenuator are connected in series is connected to an input section of a band-pass filter. And an output unit, each of which is connected in parallel through a connection circuit, and has an effect of generating a plurality of attenuation poles near the passband by connecting the auxiliary circuits in parallel. .

According to a twelfth aspect of the present invention, in the first to eleventh aspects, the band-pass filter is constituted by three or more resonators, and the variable phase shifter and the variable attenuator are driven by the variable attenuator. A connected auxiliary circuit is connected to any two resonators constituting the band-pass filter via connection circuits, respectively. The attenuation pole can also be changed by changing the combination of the resonators connecting the auxiliary circuit. Has the effect of changing the position of.

The electronically tuned polarized filter of the present invention does not allow a large power signal to pass through the auxiliary circuit, and does not require power withstand characteristics for the active circuit. Therefore, it is particularly suitable as a filter for a base station.

An embodiment of the present invention will be described below with reference to FIGS. (Embodiment 1) FIG. 1 shows a first embodiment of the present invention. In FIG. 1, 101 is a band-pass filter,
102 is a variable phase shifter whose phase shift amount can be electronically controlled, 103 is a variable attenuator whose attenuation amount can be electronically controlled, 104 and 105 are an auxiliary circuit 110 composed of the variable phase shifter 102 and the variable attenuator 103, and a band pass. A connection circuit for connecting the filter 101,
106 is an input terminal, 107 is an output terminal, 108 and 109
Is a control terminal for controlling the amount of change of the variable phase shifter 102 and the variable attenuator 103, respectively.

The operation of the thus-configured electronically tuned polarized filter will be described below with reference to FIG. The signal input from the input terminal 106 passes through a first path passing through the band-pass filter 101 and a second path passing through the connection circuit 104, the variable phase shifter 102, the variable attenuator 103, and the connection circuit 105 in this order. The output terminal 107 is reached.
Here, at a frequency that satisfies the condition that the signal passing through the first path and the signal passing through the second path have the same amplitude and the phase is shifted by 180 degrees, the signals passing through the two paths are mutually different. Since they cancel each other out, they do not appear at the output terminal 107. That is, an attenuation pole occurs at this frequency. Since the phase shift amount and the variable attenuator 103 can be arbitrarily changed by the control terminals 108 and 109, the variable phase shifter 102 and the variable attenuator 103 can arbitrarily set a frequency that satisfies the condition for generating an attenuation pole. In other words, the generation position of the attenuation pole can be freely electronically controlled.

FIG. 2 shows an example of the variable attenuator 103. FIG. 2A shows an example of a circuit of the variable attenuator 103 using the PIN diode 201.
02, a bias circuit including a resistor and a capacitor is provided. 203 is an attenuator input terminal, and 204 is an attenuator output terminal. When the voltage of the control terminal 202 is increased, the DC bias current flowing through the PIN diode 201 increases, and the resistance value of the PIN diode 201 decreases.

FIG. 2B shows a dual gate FET 203.
This is an example of the variable attenuator 103 using the above. A bias circuit comprising a capacitor and a resistor is provided between the first gate and the attenuator input terminal 203, the drain terminal is connected to the attenuator output terminal 204, and the control terminal 202 is connected to the second gate. By changing the second gate voltage of the dual gate FET by the control terminal 202, the amount of attenuation changes. This circuit also has the advantage that the change in input impedance is small and the amount of reverse transmission can be reduced.

FIG. 3 shows an example of the variable phase shifter 102. FIG. 3A shows an armstrong type phase shifter using two balanced modulators 301 and 302. The 90 ° hybrid circuit 303 converts an input signal from a phase shifter input terminal 305 into a 90 ° phase difference. After splitting it into two signals,
The balance modulators 301 and 302 perform amplitude modulation in proportion to a sine function and a cosine function of a desired phase shift amount, respectively.
After that, by combining the signals in the in-phase hybrid circuit 304, a signal in which the amount of phase change continuously changes over 360 degrees can be obtained from the phase shifter output terminal 306, and a constant amount of phase shift independent of frequency can be obtained. Can be

FIG. 3B shows an example of the variable phase shifter 102 composed of a varactor diode and a circulator.
09, is reflected by the varactor diode 307, and the reflected wave is output to the phase shifter output terminal 306. The capacitance of the varactor diode 307 is set to the control terminal 3
The phase shift amount changes by changing with the voltage of 10.

FIG. 3C shows two varactor diodes 3.
11 and 12 show an example of the variable phase shifter 102 configured by the 90-degree hybrid circuit 313.
It is almost the same as (b). The input signal from the phase shifter input terminal 305 is distributed by the 90-degree hybrid circuit 313 and reaches two terminals to which the varactor diodes 311 and 312 are connected. And this varactor diode 3
The reflected waves from 11 and 312 are combined and output from the phase shifter output terminal 306. At that time, the capacitance of the varactor diodes 311 and 312 changes according to the voltage applied to the control terminal 310, and the phase shift amount can be changed.

In this embodiment, the connection circuit 1 shown in FIG.
04 and 105 are loosely coupled, and the amplitude condition of the generation of the attenuation pole is mainly satisfied by the variable attenuator, so that the variable phase shifter can be used even in a filter for handling a large power signal such as a base station for mobile communication. Since a large amount of power does not enter the variable attenuator 102 and the variable attenuator 103, the filter according to the present embodiment can be applied. Also,
The variable phase shifter 102 and the variable attenuator 103 are mainly composed of an active circuit and do not depend on the configuration of the band-pass filter, so that a general-purpose IC can be formed.

As described above, according to the first embodiment,
Cascaded variable phase shifter 1 constituting auxiliary circuit 110
02 and the variable attenuator 103 are connected to a connection circuit 104,
Since the variable phase shifter 102 and the variable attenuator 103 are connected using an active element while being connected between the input part and the output part of the band-pass filter 101 via 105, they have an attenuation pole near the pass band. In addition, an electronically tunable polarized filter capable of electronically controlling the frequency of the attenuation pole can be configured.

(Embodiment 2) FIG. 4 shows a second embodiment of the present invention, in which components having the same functions as those in FIG. 1 are denoted by the same reference numerals. 4 differs from FIG. 1 in that a plurality of auxiliary circuits 401 each including a variable phase shifter 102 and a variable attenuator 103 are connected in parallel between the input / output units of the bandpass filter 101.

The operation of the thus-configured electronically tuned polarized filter will be described below with reference to FIG. The basic operation is the same as in the first embodiment. In the present embodiment, a plurality of auxiliary circuits 401 each including a variable phase shifter 102 and a variable attenuator 103 are connected in parallel, and the phase shift amount and the attenuation amount are set independently of each other. By providing a plurality of second paths that pass through the auxiliary circuit 401 with respect to the first path that passes, a plurality of attenuation poles are generated. By generating a plurality of attenuation poles at appropriate frequency intervals, it is possible to obtain a broadband attenuation characteristic near the pass band.

As described above, according to the second embodiment,
A plurality of auxiliary circuits 410 in which the variable phase shifter 102 and the variable attenuator 103 are connected in series are provided. These auxiliary circuits 410 are connected between the input section and the output section of the bandpass filter 101 via connection circuits 104 and 105, respectively. Because it is configured by connecting multiple in parallel, it has a broadband attenuation pole near the passband,
In addition, an electronically tuned polar filter that can electronically control the frequency of the attenuation pole can be configured.

(Embodiment 3) FIG. 5 shows a third embodiment of the present invention, in which components having the same functions as those in FIG. 1 are denoted by the same reference numerals. 5 is different from FIG. 1 in that an auxiliary circuit 110 including a band-pass filter 101 including three resonators 501, 502, and 503 connected via capacitors, and a variable phase shifter 102 and a variable attenuator 103. Are connected to the two resonators 501 and 50 of the band-pass filter 101 via the connection circuits 104 and 105, respectively.
2.

The operation of the thus configured electronic tuned polar filter will be described below with reference to FIG. The basic operation is the same as in the first embodiment. In the present embodiment, an auxiliary circuit 11 including a variable phase shifter 102 and a variable attenuator 103 is provided between any two of the resonators 501, 502, and 503 constituting the band-pass filter 101.
0 is connected. The frequency at which the attenuation pole is generated also changes depending on how to select the resonator to be connected. That is, the position of the attenuation pole can be controlled by physical or electrical control, and the control range of the attenuation pole can be widened.

As described above, according to the third embodiment,
The band-pass filter 101 is divided into three resonators 501, 50
2, 503, and an auxiliary circuit 110 in which a variable phase shifter 102 and a variable attenuator 103 are connected in cascade.
02, via the connection circuits 104 and 105, respectively, it is possible to configure an electronically tuned polar filter having a broadband attenuation pole near the passband and capable of electronically controlling the frequency of the attenuation pole.

In the third embodiment, the example of the band-pass filter 101 in which the three resonators 501, 502, and 503 are capacitively coupled is shown, but it goes without saying that inductive coupling or distributed coupling may be used. Further, although an example in which only one auxiliary circuit 110 is connected has been described, a plurality of attenuation poles can be generated by connecting a plurality of auxiliary circuits. Further, an example in which there are three resonators has been described, but it goes without saying that four or more resonators may be used.

In all of the above-described embodiments, examples have been described in which a capacitor is used for a connection circuit. However, it goes without saying that a similar effect can be obtained by using an inductor or a distributed coupling circuit.

[0035]

As described above, according to the present invention, the auxiliary circuit composed of the cascade-connected variable phase shifter and variable attenuator is connected to the input section and the output section of the band-pass filter via the connection circuit. Since it is connected in between, it is possible to realize an electronically tuned polar filter having a steep attenuation pole near the pass band and electronically controlling the frequency at which the attenuation pole is generated. Further, since the variable phase shifter and the variable attenuator are mainly constituted by active elements, the auxiliary circuit can be integrated into an IC. Since this IC does not depend on the type and structure of the filter,
It can be manufactured as a general-purpose product. Furthermore, since large power does not flow through the auxiliary circuit portion, the present invention can also be applied to a filter that handles a large power signal, such as a base station for mobile communication.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an electronically tuned polar filter according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a circuit example of a variable attenuator used in the electronically tuned polarized filter according to the first embodiment of the present invention;

FIG. 3 is a circuit diagram showing a circuit example of a variable phase shifter used in the electronically tuned polarized filter according to the first embodiment of the present invention;

FIG. 4 is a block diagram showing an electronically tuned polar filter according to a second embodiment of the present invention.

FIG. 5 is a block diagram showing an electronically tuned polar filter according to a third embodiment of the present invention.

FIG. 6 is a block diagram showing a conventional polarized filter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 Band-pass filter 102 Variable phase shifter 103 Variable attenuator 104, 105 Connection circuit 106 Input terminal 107 Output terminal 108, 109 Control terminal 110, 410 Auxiliary circuit 501, 502, 503 Resonator

Claims (12)

[Claims] 1. A variable phase shifter having an adjustable phase shift amount, a variable attenuator having an adjustable attenuation amount, a band-pass filter,
The variable phase shifter and the variable attenuator, which are connected in series and form an auxiliary circuit, are connected between the input unit and the output unit of the band-pass filter via the connection circuit. In addition, an electronically tuned polar filter in which the variable phase shifter and the variable attenuator are configured using active elements. 2. The electronically tuned polar filter according to claim 1, wherein the connection circuit is a capacitive element. 3. The electronically tuned polarized filter according to claim 1, wherein the connection circuit is an inductor element. 4. The electronically tuned polar filter according to claim 1, wherein the connection circuit is a distributed coupling circuit. 5. The electronically tuned polarized filter according to claim 1, wherein the band-pass filter is a resonator coupling type filter. 6. A variable attenuator comprising a PIN diode and a bias circuit for supplying a bias current to the PIN diode, wherein the amount of attenuation can be electronically controlled by changing a current flowing through the PIN diode. An electronically tuned polarized filter according to any one of claims 1 to 5, characterized in that: 7. A variable attenuator comprising a dual gate FET and a bias circuit for determining a bias voltage of the dual gate FET, wherein an attenuation can be electronically controlled by changing a gate voltage of the dual gate FET. The electronically tuned polarized filter according to any one of claims 1 to 5, wherein: 8. A variable phase shifter comprising two balanced modulators and 90
An armstrong type phase shifter comprising a degree divider and an in-phase combiner.
After distributing the signals into two signals having a phase difference of 0 degree, the balanced modulator performs amplitude modulation in proportion to a sine function and a cosine function of a desired phase shift amount, and then combines the signals with the in-phase combiner. The electronically tuned polar filter according to any one of claims 1 to 7, wherein the amount of phase shift is electronically controllable. 9. A variable phase shifter comprising a varactor diode, a circulator, and a bias circuit for applying a bias voltage to the varactor diode, wherein the varactor diode is connected to a port from which a signal input to the circulator is output. 8. The electronically tuned polar filter according to claim 1, wherein the amount of phase shift can be electronically controlled by changing a bias voltage of the varactor diode. 10. A variable phase shifter includes two varactor diodes, a 90-degree hybrid circuit, and a bias circuit for applying a bias voltage to each of the varactor diodes, and a signal input to the 90-degree hybrid circuit is distributed and output. 8. The electronic tuning type according to claim 1, wherein the varactor diode is connected to two ports, and a phase shift amount can be electronically controlled by changing a bias voltage of the varactor diode. Polarized filter. 11. An auxiliary circuit in which a variable phase shifter and a variable attenuator are connected in cascade, and a plurality of auxiliary circuits are connected in parallel between an input section and an output section of the band-pass filter via respective connection circuits. The electronically tuned polarized filter according to any one of claims 1 to 10. 12. The band-pass filter is a filter formed by three or more resonators, and an auxiliary circuit in which a variable phase shifter and a variable attenuator are connected in series is an arbitrary circuit that forms the band-pass filter. The electronically tuned polarized filter according to any one of claims 1 to 11, wherein the two resonators are connected to each other via a connection circuit.