JP2007067772A - Filter circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-cost filter circuit which is small and integrated, and by which disturbance signals of arbitrary frequencies can be eliminated. <P>SOLUTION: The filter circuit is provided with a 90° phase shifter 5 to which desired signals and disturbance signals are inputted; a first phase shifter 1 which has phase shift amounts different between the desired signal frequency, and the disturbance signal frequency and to which one output a1 of the 90° phase shifter 5 is inputted; a second phase shifter 2 to which the other output b1 of the 90° phase shifter 5 is inputted; and a synthesizer 6 to which an output cl of the first phase shifter 1 and an output d1 of the second phase shifter are inputted, and which synthesizes the two outputs. The first phase shifter 1 and the second phase shifter 2 perform phase shifting processing by different phase shift amounts between the desired signal frequency and the disturbance signal frequency. The synthesizer 6, to which the output c1 of the first phase shifter 1 and the output d1 of the second phase shifter 2 are inputted and which synthesizes the outputs, offsets and eliminates the disturbance signals and allows only the desired signals to pass through. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a filter circuit, and more particularly to a filter circuit that removes an interference signal from a desired signal in a high-frequency circuit.

  Conventionally, as a circuit that allows a desired signal to pass through and removes an unnecessary / interfering signal, a filter used in a high-frequency circuit includes a filter circuit such as an LC filter composed of an inductor and a capacitor, a SAW filter, and a ceramic filter. Among these filters, the LC filter is inexpensive and easy to use, but has a problem that it is difficult to reduce the size because it is difficult to integrate the inductor. In addition, the SAW filter and the ceramic filter have excellent characteristics, but there are a problem that it is difficult to reduce the size and a cost.

As a conventional filter circuit that allows a desired signal to pass through and removes an unnecessary / interfering signal, there is, for example, one described in Patent Document 1. The filter circuit will be described with reference to FIG. The filter circuit shown in FIG. 8 includes first and second reception antennas 20a and 20b that are spaced from each other in the direction of arrival of the desired wave, and a variable phase shifter 21 to which the reception signals of the first reception antenna 20a are input. A first synthesizer 22 that synthesizes the output of the variable phase shifter 21 and the received signal of the second receiving antenna 20b, and a signal obtained by branching the output of the variable phase shifter 21 by the branch circuit 29 is 180 degrees. The phase shifter 24, two notch filters 25, 26 for removing the desired wave component from the signal branched by the branch circuit 28 from the reception output of the second receiving antenna 20b and the output of the 180 ° phase shifter 24, both A second synthesizer 23 for synthesizing the outputs of the notch filters 25 and 26, and an interference wave level detector for controlling the phase shift amount of the variable phase shifter 21 so that the output level of the second synthesizer 23 is always the maximum. With 27 It is a configuration.
JP 59-2443 A

  The filter circuit described in Patent Document 1 removes an interference wave by detecting the interference wave component by cutting a desired wave having a known frequency and performing phase control of the received signal so that the interference wave detection level is minimized. It is what makes it possible. However, the circuit described above requires a circuit for detecting the interference wave component by cutting the desired wave, and its circuit configuration is large and complicated. Further, the notch filter for cutting the desired wave of the above circuit is usually composed of an LC filter in the frequency band of TV radio waves, and there is a problem that it is difficult to miniaturize and integrate.

  In the filter circuit described in Patent Document 1, it is assumed that the phase shift amount of the variable phase shifter is the same for the desired wave and the interference wave. In general, it is difficult to construct a variable phase shifter that realizes an arbitrary amount of phase shift at an arbitrary frequency.

Another conventional technique for passing a desired signal and removing unnecessary / interfering signals is a filter technique described in Patent Document 2, for example. FIG. 9 shows a configuration diagram of a synthesis filter for removing noise components other than the specific frequency in the technology. An all-pass filter 30a and an all-pass filter 30b are cascaded, and a synthesis filter is configured by providing an adder 31 that adds the input of the first-stage filter 30a and the output of the second-stage filter 30b. By setting the two-stage all-pass filter 30b so that the frequency component to be removed is phase-shifted by 180 degrees, the first-stage input and the second-stage output are out of phase with each other with respect to the frequency component to be removed. Will be canceled. FIG. 10 shows a specific configuration of the all-pass filters 30a and 30b. It comprises resistors 32a, 32b, 32c, a capacitor 34, and a differential amplifier 35.
JP 2002-164597 A (paragraphs [0019] to [0021], FIGS. 3 to 6)

  In the description of Patent Document 2, the frequency to be removed (hereinafter referred to as “fundamental wave”) 1 f is shifted by 180 degrees by a two-stage all-pass filter, and the phase shift amount is 0 degree in the frequency range lower than the fundamental wave 1 f. It is described that the phase shift amount is 360 degrees in the frequency range higher than the wave 1f. In that case, it is necessary to realize a phase shift amount of 360 degrees for 2f of the second harmonic wave with respect to the phase shift amount of 180 degrees of the fundamental wave 1f. However, in order to construct an all-pass filter having such a phase shift amount, the Q value of the filter needs to be very large. However, when a filter having a large Q value is used, the phase shift of the fundamental wave 1f greatly changes from 180 degrees due to variations in the value of the resistor 32a and the value of the capacitor 34 relating to the phase characteristics. Therefore, even if the phase shift amount is set to 180 degrees at the frequency of the fundamental wave 1f, the phase shift amount becomes 0 degrees or 360 degrees depending on the element variation of the resistor 32a and the capacitor 34, and the fundamental wave 1f is removed. It may be impossible to do so.

  Further, in the above filter technique, when the frequency component to be removed is high with respect to the desired frequency (fourth harmonic wave 4f component in the example of the present invention), in order to set the phase shift amount of the desired frequency 3f to be extracted to 0 degree. It is necessary to further increase the Q value of the all-pass filter as compared with the above-described all-pass filter that shifts 1f by 180 degrees and 2f by 360 degrees. There is a possibility that the amount of phase shift will greatly change from 180 degrees and 4f will not be canceled. Furthermore, the amount of phase shift of 3f may also deviate from 0 degrees and attenuate to the desired component.

  As described above, the above synthesis filter has a problem that it is difficult to stably remove an interference wave having an arbitrary frequency.

Also, there is a circuit called an image removal mixer that can remove a specific interference signal and is suitable for integration. FIG. 11 shows a Hartley image removal mixer. The Hartley-type image removal mixer includes mixers 40a and 40b, 90-degree phase shifters 41 and 42, and an adder 43. The desired signal is cos (ωRF) t, and the image interference signal is cos (ωIM) t. The desired signal and the image interference signal input to the mixer 40a are frequency-converted into the following signals by the local signal cos (ω0) t.
(1/2) * cos (ω0−ωRF) t + (1/2) * cos (ωIM−ω0) t
... (1)
On the other hand, the desired signal and the image interference signal input to the mixer 40b are converted to the following frequencies by the local signal sin (ω0) that has passed through the 90-degree phase shifter 41.
(1/2) * sin (ω0−ωRF) t− (1/2) * sin (ωIM−ω0) t
... (2)
Next, the output signal (2) of the mixer 40b is converted into the following signals by passing through the 90-degree phase shifter 42.
(1/2) * cos (ω0−ωRF) t− (1/2) * cos (ωIM−ω0) t
... (3)
Next, the output signal represented by the expression (1) of the mixer 40a and the output signal represented by the expression (3) of the 90-degree phase shifter 42 are combined by the adder 43, thereby canceling the image signal component. Thus, it is possible to extract only the desired signal component.

  As described above, since the image removal mixer can remove the image interference signal, it is often used in the heterodyne reception circuit. However, the image removal mixer has a problem in that it cannot remove interference waves of any frequency other than the image frequency.

Patent Documents 3 to 5 are examples of the receiving circuit using the image removal mixer as described above. Each of these receiving circuits removes an image interference signal using an image removal mixer.
Japanese Patent Laid-Open No. 11-355168 Japanese Patent Laid-Open No. 2001-45080 JP 2001-177425 A

  As described above, it is difficult to miniaturize and integrate the conventional LC filter circuit. Also, conventional SAW filters and ceramic filters are difficult to miniaturize and integrate, and are expensive.

  In addition, the conventional technique for passing a desired signal and removing unnecessary / interfering signals requires a circuit for detecting a disturbing wave component by cutting the desired wave, and the circuit configuration becomes large and complicated. . In addition, a notch filter for cutting a desired wave is usually composed of an LC filter in the frequency band of TV radio waves, and it is difficult to reduce the size and integration. In addition, it is assumed that the phase shift amount of the variable phase shifter is the same for the desired wave and the interference wave, but it is difficult to construct a variable phase shifter that realizes an arbitrary phase shift amount at an arbitrary frequency. is there.

  In addition, it is difficult to stably remove an interfering wave having an arbitrary frequency with the conventional technique that passes a desired signal and removes an unnecessary / interfering signal. In addition, a conventional image removal mixer suitable for integration cannot remove interference waves having frequencies other than the image interference frequency.

  An object of the present invention is to solve the above-mentioned problems and to provide a small and integrated low-cost filter circuit capable of removing an interference signal having an arbitrary frequency.

  In order to achieve the above object, the filter circuit according to the present invention has a 90-degree phase shifter to which a desired signal and an interference signal are input, and has different phase shift amounts for the desired signal frequency and the interference signal frequency. A first phase shifter to which one output of the 90-degree phase shifter is input, a second phase shifter to which the other output of the 90-degree phase shifter is input, and the first phase shifter And an output of the second phase shifter are input, and a synthesizer is provided for synthesizing the outputs.

  According to this filter circuit, the first phase shifter to which one output of the 90-degree phase shifter is input and the second phase shifter to which the other output of the 90-degree phase shifter is input are desired. A synthesizer that performs phase shift processing with different phase shift amounts for the signal frequency and the interference signal frequency, receives the output of the first phase shifter and the output of the second phase shifter, and combines the outputs. In this case, the interference signal is canceled and removed, and only the desired signal can be passed.

  In the above filter circuit, the first phase shifter rotates -90 degrees phase at the desired signal frequency, rotates -135 degrees phase at the interference signal frequency, and the second phase shifter rotates -90 degrees phase at the desired signal frequency. It can rotate and phase rotate -225 degrees at the jamming signal frequency.

  In the filter circuit, the first phase shifter rotates -270 degrees phase at the desired signal frequency and rotates -135 degrees phase at the disturbing signal frequency, and the second phase shifter rotates -270 degrees phase at the desired signal frequency. It can rotate and phase rotate -225 degrees at the jamming signal frequency.

  In the filter circuit, the 90-degree phase shifter can be an RC-CR circuit or a 90-degree hybrid. In the filter circuit, the first phase shifter and the second phase shifter can be allpass filters, and in the filter circuit, the synthesizer can be configured by a resistor network. it can.

  As described above, the filter circuit according to the present invention has a 90-degree phase shifter to which a desired signal and an interference signal are input, and has a phase shift amount different between the desired signal frequency and the interference signal frequency. A first phase shifter to which one output of the phase shifter is input, a second phase shifter to which the other output of the 90 ° phase shifter is input, and an output of the first phase shifter And the second phase shifter input and a synthesizer for synthesizing the two outputs, a filter circuit that allows a desired signal to pass and removes an interference signal is realized. The

  Also, the first phase shifter rotates by -90 degrees at the desired signal frequency and rotates by -135 degrees at the interference signal frequency, and the second phase shifter rotates by -90 degrees at the desired signal frequency and interferes by the interference signal frequency. Then, by rotating the phase by -225 degrees, a filter circuit capable of passing a desired signal and removing an interference signal is realized.

  Further, the first phase shifter rotates -270 degrees phase at the desired signal frequency and rotates -135 degrees phase at the interference signal frequency, and the second phase shifter rotates -270 degrees phase at the desired signal frequency. Then, by rotating the phase by -225 degrees, a filter circuit capable of passing a desired signal and removing an interference signal is realized.

  In addition, since the 90-degree phase shifter is an RC-CR circuit, a 90-degree phase shifter that is small and can be integrated and is low-cost is realized. Moreover, a 90 degree phase shifter with a small size and low cost is realized by making the 90 degree phase shifter into a 90 degree hybrid. In addition, by using the first phase shifter and the second phase shifter as an all-pass filter, a phase shifter that is small and can be integrated and is low-cost is realized. Furthermore, a compact and low-cost synthesizer can be realized by configuring the synthesizer with a resistor network.

  Hereinafter, embodiments of a filter circuit according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the filter circuit according to the first embodiment of the present invention. This filter circuit includes a 90-degree phase shifter 5, a first phase shifter 1 and a second phase shifter 2 having different phase shift amounts at a desired signal frequency and an interference signal frequency, and a combiner 6. Has been. The input of the first phase shifter 1 is connected to one output of the 90 degree phase shifter 5, the input of the second phase shifter 2 is connected to the other output of the 90 degree phase shifter 5, and the second The output of the phase shifter 1 and the output of the second phase shifter 2 are input to the synthesizer 6.

  The desired wave signal input to the 90 phase shifter 5 is cos (ωRF) t, and the interference signal is cos (ωUD) t. Further, the first phase shifter 1 rotates θ1 with respect to the desired signal frequency and φ1 phase rotation with respect to the interference signal frequency, and the second phase shifter 2 has θ2 with respect to the desired signal frequency and the interference signal frequency. Is assumed to be rotated by φ2 phase. That is, the phase shift amount is generally different between the desired signal frequency and the interference signal frequency even in the same phase shifter, and the phase shift amount can be different if the phase shifter is different.

The signals a1 and b1 output from the 90 degree phase shifter 5 are as follows.
a1: cos (ωRF) t + cos (ωUD) t (4)
b1: sin (ωRF) t + sin (ωUD) t (5)
The signal a1 expressed by the equation (4) output from the 90-degree phase shifter 5 is rotated by a phase of θ1 by the first phase shifter 1, and the interference signal is rotated by a phase of φ1 and the following signal It becomes.
c1: cos {(ωRF) t + θ1} + cos {(ωUD) t + φ1} (6)
The signal b1 represented by the equation (5) output from the 90-degree phase shifter 5 is rotated by a phase of θ2 by the second phase shifter 2, and the interference signal is rotated by a phase of φ2 and the following signal It becomes.
d1: sin {(ωRF) t + θ2} + sin {(ωUD) t + φ2} (7)
The signal c1 represented by the equation (6) output from the first phase shifter 1 and the signal d1 represented by the equation (7) output from the second phase shifter 2 are Is converted into a signal.
e1: cos {(ωRF) t + θ1} + cos {(ωUD) t + φ1}
+ Sin {(ωRF) t + θ2} + sin {(ωUD) t + φ2}
= Cos (ωRF) t * cosθ1-sin (ωRF) t * sinθ1
+ Cos (ωUD) t * cosφ1-sin (ωUD) t * sinφ1
+ Sin (ωRF) t * cos θ2 + cos (ωRF) t * sin θ2
+ Sin (ωUD) t * cosφ2 + cos (ωUD) t * sinφ2
= Cos (ωRF) t * (cos θ1 + sin θ2)
+ Sin (ωRF) t * (− sin θ1 + cos θ2)
+ Cos (ωUD) t * (cosφ1 + sinφ2)
+ Sin (ωUD) t * (− sinφ1 + cosφ2) (8)

Here, the following conditions are considered.
cos θ1 + sin θ2 ≠ 0 or −sin θ1 + cos θ2 ≠ 0
... (9)
cosφ1 + sinφ2 = 0 and −sinφ1 + cosφ2 = 0
... (10)
By selecting θ1, θ2, φ1, and φ2 that satisfy the conditions of Expressions (9) and (10), it is possible to leave the desired signal frequency component and remove the interference signal frequency component. Therefore, a filter circuit capable of passing a desired signal and removing an interference signal is realized by the above circuit configuration.

  FIG. 2 is a graph showing the frequency-phase characteristics of the first phase shifter 1 and the second phase shifter 2 used in the second embodiment of the filter circuit according to the present invention. The first phase shifter 1 rotates -90 degrees phase at the desired signal frequency and rotates -135 degrees phase at the interference signal frequency, and the second phase shifter 2 rotates -90 degrees phase at the desired signal frequency. The frequency rotates -225 degrees. Other configurations are the same as those of the filter circuit according to the first embodiment of the present invention.

The desired wave signal input to the 90 phase shifter 5 is cos (ωRF) t, and the interference signal is cos (ωUD) t. Here, it is assumed that the interference signal frequency ωUD is higher than the desired signal frequency ωRF. The signals output from the 90-degree phase shifter 5 are as follows.
a1: cos (ωRF) t + cos (ωUD) t (11)
b1: sin (ωRF) t + sin (ωUD) t (12)

The signal a1 represented by the equation (11) output from the 90-degree phase shifter 5 is rotated by −90 degrees (θ1) phase for the desired signal by the first phase shifter 1, and − The signal is rotated as follows by 135 degrees (φ1) phase rotation.
c1: cos {(ωRF) t−π / 2} + cos {(ωUD) t−3π / 4}
... (13)
Further, the signal b1 represented by the equation (12) output from the 90-degree phase shifter 5 is rotated by −90 degrees (θ2) phase with respect to the desired signal by the second phase shifter 2, and the interference signal is transmitted. Is -225 degrees (φ2) phase rotated to give the following signal.
d1: sin {(ωRF) t−π / 2} + sin {(ωUD) t−5π / 4}
(14)
The signal c1 expressed by the equation (13) output from the first phase shifter 1 and the signal d1 expressed by the equation (14) output from the second phase shifter 2 are expressed by the synthesizer 6 as follows. Is converted into a signal.
e1: cos {(ωRF) t−π / 2} + cos {(ωUD) t−3π / 4}
+ Sin {(ωRF) t−π / 2} + sin {(ωUD) t−5π / 4}
= Sin (ωRF) t
+ Cos (ωUD) t * cos (−3π / 4) −sin (ωUD) t * sin (−3π / 4)
-Cos (ωRF) t
+ Sin (ωUD) t * cos (−5π / 4) + cos (ωUD) t * sin (−5π / 4)
= Sin (ωRF) t
-1 / √2cos (ωUD) t + 1 / √2sin (ωUD) t
-Cos (ωRF) t
-1 / √2 sin (ωUD) t + 1 / √2cos (ωUD) t
= Sin (ωRF) t-cos (ωRF) t (15)

  From equation (15), it is understood that the interference frequency component ωUD is canceled and only the desired frequency component ωRF is output to the output of the synthesizer 6. Therefore, the first phase shifter 1 and the second phase shifter 2 having the above characteristics realize a filter circuit that can pass a desired signal and remove an interference signal.

  FIG. 3 is a graph showing frequency-phase characteristics of the first phase shifter 1 and the second phase shifter 2 according to the third embodiment of the filter circuit according to the present invention. The first phase shifter 1 rotates -270 degrees phase at the desired signal frequency and rotates -135 degrees phase at the interference signal frequency, and the second phase shifter 2 rotates -270 degrees phase at the desired signal frequency. The frequency rotates -225 degrees. Other configurations are the same as those of the filter circuit according to the first embodiment of the present invention.

The desired wave signal input to the 90 phase shifter 5 is cos (ωRF) t, and the interference signal is cos (ωUD) t. Here, it is assumed that the interference signal frequency ωUD is lower than the desired signal frequency ωRF. The signals output from the 90-degree phase shifter 5 are as follows.
a2: cos (ωRF) t + cos (ωUD) t (16)
b2: sin (ωRF) t + sin (ωUD) t (17)

The signal a2 represented by the equation (16) output from the 90-degree phase shifter 5 is phase-rotated by −270 degrees (θ1) with respect to the desired signal by the first phase shifter 1, and the interference signal is −135. The following signal is obtained by rotating the phase by degrees (φ1).
c2: cos {(ωRF) t-3π / 2} + cos {(ωUD) t-3π / 4}
... (18)
Further, the signal b2 represented by the equation (17) output from the 90-degree phase shifter 5 is rotated by -270 degrees (θ2) in phase with the desired signal by the second phase shifter 2, and the interference signal is − 225 degrees (φ2) phase rotation results in the following signal.
d2: sin {(ωRF) t-3π / 2} + sin {(ωUD) t-5π / 4}
... (19)
The signal (18) output from the first phase shifter 1 and the signal (19) output from the second phase shifter 2 are converted into the following signals by the combiner 6.
e2: cos {(ωRF) t-3π / 2} + cos {(ωUD) t-3π / 4}
+ Sin {(ωRF) t-3π / 2} + sin {(ωUD) t-5π / 4}
= -Sin (ωRF) t
+ Cos (ωUD) t * cos (−3π / 4) −sin (ωUD) t * sin (−3π / 4)
-Cos (ωRF) t
+ Sin (ωUD) t * cos (−5π / 4) + cos (ωUD) t * sin (−5π / 4)
= -Sin (ωRF) t
-1 / √2cos (ωUD) t + 1 / √2sin (ωUD) t
-Cos (ωRF) t
-1 / √2sin (ωUD) t + 1 / √2cos (ωUD) t
= -Sin (ωRF) t-cos (ωRF) t (20)

  It can be seen from equation (20) that the interference frequency component ωUD is canceled and only the desired frequency component ωRF is output to the output of the synthesizer 6. Therefore, the first phase shifter 1 and the second phase shifter 2 having the above characteristics realize a filter circuit that can pass a desired signal and remove an interference signal.

FIG. 4 is a block diagram showing an example of an RC-CR circuit that realizes the 90-degree phase shifter 5 used in the filter circuit according to the present invention. It consists of resistors 10a and 10b and capacitors 11a and 11b. The phase shifts of the outputs Vout1 and Vout2 with respect to the signal having the input frequency ω are as follows.
π / 2-tan ⁻¹ (RCω) (21)
−tan ⁻¹ (RCω) (22)
From this, it can be seen that the phase difference between Vout1 and Vout2 is 90 degrees regardless of the frequency. As described above, by using the RC-CR circuit for the 90-degree phase shifter 5, the 90-degree phase shifter 5 that is small and can be integrated and is low-cost is realized.

FIG. 5 is a configuration diagram showing a basic example of a 90-degree hybrid that realizes the 90-degree phase shifter 5 used in the filter circuit according to the present invention. It comprises a resistor 10c and transmission lines 12a, 12b, 12c, and 12d. Here, the lengths of the transmission lines 12a, 12b, 12c, and 12d are all λ / 4. The resistance value of the resistor 10c is R, and the characteristic impedances of the transmission lines 12a, 12b, 12c, and 12d are R, R / √2, R / √2, and R.
The signal input from the terminal 1 is output to the terminal 4 through the path 1-2-4 and the path 1-3-4. At this time, since the two path lengths are the same λ / 2, a signal half of the input power whose phase shift is 180 degrees with respect to the terminal 1 is output to the terminal 4.
The signal input from the terminal 1 is output to the terminal 2 through the path 1-2 and the path 1-3-4. Since the signal of the path 1-3-3-4-2 is greatly attenuated, the signal of the path 1-2 is almost output to the terminal 2. Therefore, a signal that is half of the input power with a phase shift of λ / 4, that is, 90 degrees, is output to the terminal 2.
Here, since the phase difference between the terminal 2 and the terminal 4 is 90 degrees, the 90-degree phase shifter 5 is realized by adopting the configuration of FIG. As described above, by using the 90-degree hybrid for the 90-degree phase shifter 5, a small and low-cost 90-degree phase shifter 5 is realized.

  FIG. 6 is a block diagram showing a basic example of an all-pass filter that realizes the first phase shifter 1 and the second phase shifter 2 used in the filter circuit according to the present invention. Resistors 10d, 10e, 10f, and 10g, capacitors 11c and 11d, and a differential amplifier 9 are included. With the configuration shown in FIG. 6, a second-order all-pass filter is formed, the gain is constant, and only the phase with respect to the frequency can be changed. By changing the values of the resistors 10d, 10e, 10f, and 10g and the capacitors 11c and 11d, it is possible to adjust the desired phase at the desired signal frequency and the interference signal frequency. As described above, by using an all-pass filter for the first phase shifter 1 and the second phase shifter 2, the first phase shifter 1 and the second phase shifter can be miniaturized and integrated and are low-cost. Phaser 2 is realized.

  FIG. 7 is a block diagram showing a basic example of a resistor network for realizing the combiner 6 used in the filter circuit according to the present invention. The resistor network includes resistors 10h, 10i, and 10j. When the input / output impedance is R, the resistors 10h, 10i, and 10j are set to R / 3, R / 3, and R / 3, thereby realizing a compact and low-cost combiner 6.

1 is a block diagram of a filter circuit according to a first embodiment of the present invention. The figure which shows the frequency-phase characteristic of the 1st phase shifter used for the 2nd Example of the filter circuit by this invention and a 2nd phase shifter. The figure which shows the frequency-phase characteristic of the 1st phase shifter and 2nd phase shifter which are used for the 3rd Example of the filter circuit by this invention. The block diagram which shows an example of the RC-CR circuit which implement | achieves the 90 degree | times phase shifter used for the filter circuit by this invention. The block diagram which shows the basic example of the 90 degree hybrid which implement | achieves the 90 degree phase shifter used for the filter circuit by this invention. The block diagram which shows the basic example of the all-pass filter which implement | achieves the 1st phase shifter and 2nd phase shifter which are used for the filter circuit by this invention. The block diagram which shows the basic example of the resistive network which implement | achieves the combiner | synthesizer used for the filter circuit by this invention. The block diagram which shows the structure of the interference wave removal apparatus by a prior art. The block diagram which shows the structure of the synthetic | combination filter for extracting and removing the specific frequency component used by a prior art. The block diagram of the all pass filter used by a prior art. The block diagram which shows an example of the conventional Hartley type image removal mixer.

Explanation of symbols

1 ... Phase shifter 1
2 ... Phase shifter 2
5, 41, 42 ... 90 degree phase shifters 6, 22, 23 ... Synthesizers 9, 35 ... Differential amplifiers 10a, 10b, 10c, 10d, 10e, 10f, 10g, 10h, 10i, 10j, 32a, 32b, 32c ... resistors 11a, 11b, 11c, 11d, 34 ... capacitors 12a, 12b, 12c, 12d ... transmission lines 20a, 20b ... antenna 21 ... variable phase shifter 24 ... 180 degree phase shifter 25, 26 ... notch filter 27 ... Interference wave level detectors 28, 29 ... branch circuits 30a, 30b ... all-pass filters 31, 43 ... adders 40a, 40b ... mixers

Claims (7)

  A 90-degree phase shifter to which a desired signal and an interference signal are input, a phase shift amount different between the desired signal frequency and the interference signal frequency, and one output of the 90-degree phase shifter is input. A first phase shifter and a second phase shifter to which the other output of the 90-degree phase shifter is input; and an output of the first phase shifter and an output of the second phase shifter are input. A filter circuit comprising a synthesizer for synthesizing both outputs.   The first phase shifter rotates -90 degrees phase at the desired signal frequency and rotates -135 degrees phase at the interference signal frequency, and the second phase shifter rotates -90 degrees phase at the desired signal frequency. 2. A filter circuit according to claim 1, comprising a phase rotation of -225 degrees at the interference signal frequency.   The first phase shifter rotates -270 degrees phase at the desired signal frequency and rotates -135 degrees phase at the jamming signal frequency, and the second phase shifter rotates -270 degrees phase at the desired signal frequency. 2. A filter circuit according to claim 1, comprising a phase rotation of -225 degrees at the interference signal frequency.   4. The filter circuit according to claim 1, wherein the 90-degree phase shifter is an RC-CR circuit.   The filter circuit according to claim 1, wherein the 90-degree phase shifter is a 90-degree hybrid.   The filter circuit according to any one of claims 1 to 3, wherein the first phase shifter and the second phase shifter are all-pass filters.   The filter circuit according to any one of claims 1 to 3, wherein the synthesizer includes a resistor network.