CN100505525C - filter circuit - Google Patents

Abstract

The splitter (103) splits the input signal into split signals of two systems of equal amplitude and equal phase. Buffers (104, 105) suppress interference between distribution signals distributed to the two systems. A filter (106) performs frequency selection, allowing only allocated signals of a predetermined frequency band to pass. The differential amplifier (107) outputs the difference in amplitude component between the distribution signal frequency-selected by the filter (106) and the distribution signal not frequency-selected. This makes it possible to maintain attenuation characteristics or pass characteristics in the high frequency band.

Description

filter circuit

technical field

The present invention relates to a filter circuit and a radio device, especially a filter circuit and a radio device for high frequency bands such as those used in digital wireless communication systems.

Background technique

Some conventional filter circuits using an amplifier utilize the conductance and capacitance of the amplifier to achieve filter characteristics. According to this filter circuit, the non-inverting input terminal of the conductance amplifier constituting the front stage of the active filter is connected to the first input terminal through the first resistor, and connected to the ground point through the second resistor. In addition, the negative phase input terminal of the first conductance amplifier is connected to the second input terminal through the third resistor, and is connected to the external output terminal through the fourth resistor. Then, the resistance value ratio between the 1st resistor and the 2nd resistor is made equal to the resistance value ratio between the 3rd resistor and the 4th resistor, and a signal containing an in-phase signal component is applied to the 1st input terminal, another signal is applied to the 2nd input terminal. In this way, the traditional filter circuit adopts a multi-segment structure composed of capacitors and conductance amplifiers, so that sharp attenuation characteristics can be obtained.

However, conventional filter circuits and radio devices have only implemented filters with a low-pass structure. In order to realize a band-pass structure in the high frequency band, it is necessary to combine a low-pass structure and a high-pass structure. In addition, to obtain a sharp attenuation characteristic, multiple stages are required. structure, so there is a problem that circuit integration is difficult due to the increase in the number of capacitance and conductance amplifiers. On the other hand, reducing the attenuation of a desired frequency component in order to avoid circuit enlargement and reduce the number of stages of the filter circuit causes a problem that it is difficult to achieve a sharp attenuation characteristic or a pass characteristic in a high frequency band.

Contents of the invention

The object of the present invention is to provide a filtering circuit and a radio device for at least solving all or part of the above-mentioned problems in the prior art.

This object can be achieved by a filter circuit comprising: a reference signal source that generates a reference signal for adjusting the amount of phase rotation or amplitude attenuation; a splitter that splits the reference signal or input signal as a distribution of two systems a signal; a filter for frequency-selecting a first distribution signal distributed by the distributor to pass a predetermined frequency band; a correction circuit for providing a second distribution signal distributed by the distributor with a The phase rotation or amplitude attenuation in the frequency band of the filter is equal to the phase rotation or amplitude attenuation; the differential amplifier outputs the second distribution signal with the phase rotation or amplitude attenuation provided by the correction circuit and is obtained by the correction circuit. the difference in amplitude components between the first distribution signals for which the filter performs frequency selection; a switch that performs switching so that the reference signal is input to the splitter, and the input signal is input to the splitter when the correction circuit provides a phase rotation amount or an amplitude attenuation amount to the second split signal; and a comparator detecting the input to the difference in voltage between the first distribution signal and the second distribution signal of the differential amplifier, and the adjustment is performed so that the voltage difference is lower than a predetermined value.

This filter circuit and radio device can maintain attenuation characteristics and pass characteristics in a high frequency band by utilizing the in-phase cancellation effect of a differential amplifier.

The present invention also provides a filtering circuit, comprising: a reference signal source, which generates a reference signal for adjusting the amount of phase rotation; a splitter, which splits the reference signal or input signal into distribution signals of two systems; a filter, frequency selection of the first distribution signal distributed by the distributor to pass a predetermined frequency band; an adjustment circuit that provides a predetermined amount of phase rotation to the second distribution signal distributed by the distributor, and causes the The phase rotation amount provided by the two distribution signals is variable; a differential amplifier outputs the second distribution signal provided by the adjustment circuit with the phase rotation amount and the first frequency-selected frequency-selected signal by the filter. a difference in amplitude component between the distribution signals; a switch that performs switching so that the reference signal is input to the distributor when adjusting the amount of phase rotation to be provided by the adjustment circuit, and when the adjustment circuit is to The input signal is input to the divider when the second distribution signal provides the phase rotation amount; and a comparator detects a difference between the first distribution signal and the second distribution signal input to the differential amplifier. and performing the adjustment so that the voltage difference is lower than a predetermined value.

The present invention also provides a filter circuit including: a divider that divides an input signal into two systems of distribution signals; a filter that performs frequency selection on the first distribution signal distributed by the divider to pass through a predetermined frequency band; a differential amplifier that outputs the input signal as it is when the input signal is input, and when the second distribution signal distributed by the distributor and the first distribution signal frequency-selected by the filter are input , outputting the difference in amplitude component between the second distribution signal and the frequency-selected first distribution signal; a detection circuit, detecting a frequency component other than a desired frequency component; a switch, performing switching so that when the The input signal is input to the distributor when the detection circuit detects a frequency component other than the desired frequency component, and the input signal is input to the differential amplifier when only the desired frequency component is detected by the detection circuit.

Description of drawings

1 is a block diagram showing the structure of a filter circuit according to Embodiment 1 of the present invention;

FIG. 2 is a schematic diagram showing the relationship between signal power and frequency according to Embodiment 1 of the present invention;

3 is a schematic diagram showing the relationship between signal power and frequency according to Embodiment 1 of the present invention;

FIG. 4A is a schematic diagram showing the relationship between signal power and frequency according to Embodiment 1 of the present invention;

FIG. 4B is a schematic diagram showing the relationship between signal power and frequency according to Embodiment 1 of the present invention;

FIG. 4C is a schematic diagram showing the relationship between signal power and frequency according to Embodiment 1 of the present invention;

FIG. 5A is a schematic diagram showing the relationship between signal power and frequency according to Embodiment 1 of the present invention;

5B is a schematic diagram showing the relationship between signal power and frequency according to Embodiment 1 of the present invention;

FIG. 5C is a schematic diagram showing the relationship between signal power and frequency according to Embodiment 1 of the present invention;

6 is a schematic diagram showing the relationship between signal power and frequency according to Embodiment 1 of the present invention;

7 is a schematic diagram showing the relationship between signal power and frequency according to Embodiment 1 of the present invention;

8 is a block diagram showing the structure of a filter circuit according to Embodiment 2 of the present invention;

Fig. 9 is a block diagram showing the filter circuit structure according to Embodiment 3 of the present invention;

Fig. 10 is a block diagram showing the filter circuit structure according to Embodiment 4 of the present invention;

FIG. 11 is a block diagram showing the configuration of a radio apparatus according to Embodiment 5 of the present invention;

FIG. 12 is a block diagram showing the configuration of a radio apparatus according to Embodiment 6 of the present invention;

FIG. 13 is a block diagram showing the configuration of a radio apparatus according to Embodiment 7 of the present invention; and

Fig. 14 is a block diagram showing the configuration of a radio apparatus according to Embodiment 8 of the present invention.

Detailed ways

Embodiments of the present invention will be described below with reference to the accompanying drawings.

Example 1

FIG. 1 is a block diagram showing the configuration of a filter circuit 108 according to Embodiment 1 of the present invention.

Signal input 101 in FIG. 1 receives an input signal and sends it to splitter 103 . The signal output terminal 102 outputs the output signal from the differential amplifier 107 . Distributor 103 divides a signal of an arbitrary frequency band input from signal input terminal 101 into two systems of distribution signals of equal amplitude and equal phase, and outputs the distribution signals to buffer 104 and buffer 105 , respectively. The buffer 104 suppresses the interference between the divided signals input from the distributor 103 into two systems, and outputs the signal to the differential amplifier 107 . The buffer 105 suppresses interference between the distribution signals input from the distributor 103 and is divided into two systems, and outputs the signal to the filter 106 . The filter 106 performs frequency selection on the distribution signal input from the buffer 105 and outputs it to the differential amplifier 107 . The differential amplifier 107 outputs the difference in amplitude component between the distribution signal input from the buffer 104 to the non-inversion input terminal and the distribution signal input from the filter 106 to the inversion input terminal to the signal output terminal 102 .

The operation of the filter circuit 108 in the above configuration will be described below with reference to FIGS. 2 to 6. FIG.

First, the case where the attenuation characteristic of the filter 106 is a low-pass type, a high-pass type, or a band-pass type will be described.

Initially, as shown in FIG. 2 , the signal input terminal 101 is composed of frequency components f1 , f2 , and f3 with an input power of P1 . Then, the signal is divided into multiple parts of equal amplitude, power P2 (P1>P2) and amplitude halved by the distributor 103, and in the filter 106, the output of these signals as shown in Figure 3 One for frequency selection. As a result, when the filter 106 is of the low-pass type, an output signal whose power decreases in the order of f1, f2, f3 as shown in FIG. 4A is obtained. On the other hand, when the filter 106 is a high-pass type, an output signal whose power decreases in the order of f3, f2, and f1 is obtained as shown in FIG. 4B. In addition, when the filter 106 is a bandpass type, a signal having the highest power at f2 and the power of f1 and f3 being smaller than the power of f2 is obtained as shown in FIG. 4C. On the other hand, the other output of splitter 103 does not perform any frequency selection, so the signal in FIG. 3 is input to the non-inverting input of differential amplifier 107, while the signal in FIG. 4 is input to the inverting input. Due to the in-phase signal canceling action of the differential amplifier 107, an output signal of the difference in amplitude component between the divided signals divided by the divider 103 and input to the differential amplifier 107 as shown in FIG. 5 is obtained at the signal output terminal 102. That is to say, when the filter 106 adopts a low-pass filter, an output signal in which the amplitude component in the low domain is eliminated and the power decreases in the order of f3, f2, and f1 is obtained as shown in FIG. 5A. On the other hand, when the filter 106 adopts a high-pass filter, an output signal in which the high-range amplitude component is eliminated and the power of the amplitude component decreases in the order of f1, f2, and f3 is obtained as shown in FIG. 5B. In addition, when the filter 106 adopts a band-pass filter, an output signal in which the power of f2 is the minimum and the power of f1 and f3 is greater than the power of f2 is obtained as shown in FIG. 5C. As shown in FIG. 5, the output signal power of each frequency of the differential amplifier 107 becomes P3 obtained by multiplying the power of the received signal of each maximum frequency by the gain of the differential amplifier (if the gain is less than 0 [dB] then P2>P3, If the gain is equal to or greater than 0 [dB] then P2≦P3).

Next, a case where the attenuation characteristic of the filter 106 is a band-stop type will be described.

As shown in FIG. 2 , a signal composed of frequency components f1 , f2 , f3 having a power of P1 is input from a signal input terminal 101 . Then, the signal is divided into multiple parts of equal amplitude, power P2 (P1>P2) and amplitude halved by the distributor 103, and in the filter 106, the output of these signals as shown in Figure 3 One for frequency selection. As a result, an output signal in which the power of f2 is the lowest and the power of f1 and f3 is higher than that of f2 is obtained as shown in FIG. 6 . On the other hand, the other signal outputs of the divider 103 do not perform any frequency selection, so the signal in FIG. 3 is input to the non-inverting input of the differential amplifier 107, and the signal in FIG. 6 is input to the inverting input with the same phase end. Due to the in-phase signal canceling action of the differential amplifier 107, an output signal of the difference in amplitude component between the divided signals divided by the divider 103 and input to the differential amplifier 107 as shown in FIG. 7 is obtained at the signal output terminal 102. That is to say, as shown in FIG. 7 , an output signal in which the power of f2 is the largest and the power of f1 and f3 is smaller than the power of f2 is obtained. Here, the output signal power of the differential amplifier 107 shown in FIG. 7 becomes P3 obtained by multiplying the power of the received signal of f2 by the gain of the differential amplifier (P2>P3 if the gain is less than 0 [dB], and P3 if the gain is equal to or greater than 0 [dB] then P2≦P3).

Therefore, when the stop band of the filter 106 is set to the desired frequency band and the filter circuit 108 is used for the receiving part, the pass band of the filter 106 is set to the interference wave frequency band; In some cases, the passband of the filter 106 is set to an unnecessary frequency component band, so that only desired frequency components can be extracted.

The output signal from the signal output terminal 102 exists in the stopband of the filter 106, and even if some loss occurs when the received signal in the stopband is blocked, the loss has only a small influence on the received signal in the passband.

Therefore, according to the present embodiment 1, the input signal is divided into two systems, and the differential amplifier outputs the difference in the amplitude component between one divided signal frequency-selected by the filter and the other divided signal not frequency-selected, thereby enabling The attenuation characteristic or pass characteristic of the high frequency band is maintained. Furthermore, according to the present Embodiment 1, when the filter 106 employs a band-stop type filter that cuts out a predetermined frequency band, integration of a band-pass type structure having a sharp attenuation characteristic can be realized in a high frequency band. In addition, the present embodiment 1 has buffers 104 and 105 between the two output terminals of the divider 103 and subsequent circuits, and suppresses interference between the two output signals from the divider 103, thereby improving the stability of the attenuation characteristic sex.

According to Embodiment 1, the distribution signal that has not passed the filter is input to the inverting input terminal of the differential amplifier 107, and the distribution signal that has passed the filter is input to the non-inverting input terminal, but this embodiment is not limited thereto, and A method may be applied in which the polarity of the input terminal of the differential amplifier 107 is reversed, the distributed signal that has not passed the filter is input to the non-inverting input terminal, and the distributed signal that has passed the filter is input to the inverting input terminal.

Example 2

Fig. 8 is a block diagram showing the structure of a filter circuit 800 according to Embodiment 2 of the present invention.

The filter circuit 800 in this embodiment 2 corresponds to the filter circuit 108 in the embodiment 1 shown in FIG. 1, and the adjustment circuit 801 shown in FIG. 8, the comparator 802, the reference signal source 803 and the switch 804 are added. . In FIG. 8 , the same parts as those in FIG. 1 are assigned the same reference numerals, and description thereof will be omitted.

In FIG. 8, when the adjustment circuit 801 operates as a correction circuit, it performs phase rotation or amplitude attenuation by an amount equal to the phase rotation or amplitude attenuation performed by the filter 106 on the passband signal on the distribution signal input from the buffer 104. The amplitude is attenuated, and the resulting signal is output to the comparator 802 and the differential amplifier 107 . Furthermore, when the adjustment circuit 801 does not operate as a correction circuit, it performs a predetermined amount of phase rotation on the distribution signal input from the buffer 104, thereby making the frequency band of the output signal output from the differential amplifier 107 variable. That is, the adjustment circuit 801 sets the amount of phase rotation of the distribution signal input from the buffer 104 to a predetermined value so that the frequency band of the output signal output from the differential amplifier 107 is variable.

When the adjustment circuit 801 operates as a correction circuit, the comparator 802 detects the phase difference or the amplitude difference between the non-inverting input signals of the differential amplifier 107 during correction, and outputs the first control signal indicating the correction amount of the adjustment circuit 801 to The adjustment circuit 801 is used to adjust the correction amount of the adjustment circuit 801 and save the correction data after the correction is completed. On the other hand, when the adjustment circuit 801 does not operate as a correction circuit, the comparator 802 detects the phase difference between the non-inverting input signals of the differential amplifier 107 at the time of phase rotation amount adjustment, and will be used to set the phase rotation amount And the first control signal that makes the frequency band of the output signal output by the differential amplifier 107 a predetermined frequency band is output to the adjustment circuit 801, thereby adjusting the phase rotation amount set by the adjustment circuit 801, and saving the phase set after the adjustment of the phase rotation amount is completed. amount of rotation.

More specifically, the comparator 802 compares the midpoint of the transmission path connecting the adjustment circuit 801 and the non-inverting input of the differential amplifier 107 to The voltage (first voltage) of the (connected midpoint) is compared with the voltage (second voltage) of the midpoint (connected midpoint) of the transmission path connecting the filter 106 and the inverting input terminal of the differential amplifier 107, and the adjustment circuit 801 The amount of correction or phase rotation is adjusted so that the voltage difference is lower than a predetermined value. In addition, the comparator 802 controls switching of the switch 804 both in the case where the adjustment circuit 801 operates as a correction circuit and when the adjustment circuit 801 does not operate as a correction circuit. When the frequency of the input signal of the distributor 103 is high and exceeds the allowable comparison operation range of the comparator 802 , the comparator 802 internally provides a frequency division circuit to reduce the comparison frequency.

Here, "when correcting" refers to the adjustment stage where the phase rotation or amplitude attenuation is set to be equal to the amount of phase rotation or amplitude attenuation given by the filter 106 for the passband signal, and "when the correction is completed" refers to the completion of The stage of setting phase rotation or amplitude attenuation, "when the phase rotation amount is adjusted" refers to the adjustment stage of setting the phase rotation amount to obtain the output signal of the desired frequency band from the differential amplifier 107, "when the phase rotation amount adjustment is completed" refers to the completion This is the stage for setting the phase rotation amount. When the adjustment circuit 801 operates as a correction circuit, during correction, the comparator 802 repeatedly detects the phase difference or the amplitude difference each time the distribution signal is input from the adjustment circuit 801 and the filter 106, and adjusts the correction amount so that the detected phase The difference or amplitude difference is reduced to a predetermined value.

On the other hand, when the adjustment circuit 801 does not operate as a correction circuit, the comparator 802 repeatedly detects the phase difference every time the distribution signal is input from the adjustment circuit 801 and the filter 106, and adjusts the phase rotation amount. Rotate until the phase difference reaches a predetermined value, so that an output signal of a predetermined frequency band can be obtained. During calibration by the adjustment circuit 801 and phase rotation amount adjustment, the reference signal source 803 performs frequency sweep at a constant output level and outputs it to the distributor 103 . Based on the control of the comparator 802, when the correction is completed and the adjustment of the phase rotation amount is completed, the switch 804 is short-circuited between the signal input terminal 101 and the distributor 103; Short circuit between 803 and distributor 103.

Furthermore, the amplitude component output from the differential amplifier 107 is discarded at the time of correction and at the time of phase rotation amount adjustment, while the comparator 802 is put in a rest state and does not output any signal to the comparator at the time of correction and at the time of phase rotation amount adjustment.

Based on the research in the process of arriving at the present invention, it is known that when the phase error or the amplitude error of the in-phase input signals at the two input terminals of the differential amplifier 107 is equal to or higher than a predetermined value, the in-phase signal cancellation effect will be reduced, so to speak. Reducing the phase error and amplitude error described above is important in the sharp decay characteristic of circuit 800.

Therefore, a method and process capable of correcting the above-mentioned phase error and amplitude error with high precision will be described below.

Under ideal circumstances and when there are no differences among the components of the filter circuit 800 , the adjustment circuit 801 is set to provide the same amount of phase rotation and amplitude attenuation as that produced by the filter 106 .

When the filter circuit 800 is composed of discrete components, the adjustment circuit 801 can be adjusted for each component used in the filter 106, but when the components of the filter circuit 800 are formed on the same semiconductor substrate, it cannot be adjusted according to the components of each component. The difference in characteristics is adjusted individually, so in Embodiment 2, when the power of the filter circuit 800 is turned on, the switch 804 is first used to switch the input path of the signal to the distributor 103 to the side of the reference signal source 803, and the comparator 802 is used to compare the input path. The phase error and the amplitude error between the two signals to the differential amplifier 107 are monitored, and the adjustment circuit 801 is controlled so that the phase error and the amplitude error converge to a predetermined error range. In addition, when the power is turned on after the next time, a method of performing the correction operation again, or a method of saving the first control signal output to the correction circuit at the time of this correction in the comparator 802 and fixing the state of the adjustment circuit 801 may be employed. , and the adjustment circuit 801 is composed for the purpose of being able to deal with the above two situations.

Then, in the case of environmental changes such as temperature changes, the amount of phase rotation and amplitude attenuation generated in the filter 106 may change from the value when the power is turned on, so that the Moment improves correction accuracy by performing corrections similar to when the power is turned on. The rest of the operations are the same as those in Embodiment 1, so their related descriptions are omitted. In addition, each output signal is the same as that in FIG. 2 to FIG. 7 , so its related description is omitted.

Next, a description will be given of a case where the adjustment circuit 801 gives an amount of amplitude attenuation equal to that in the passband of the filter 106 and adjusts the amount of phase rotation.

As described above, when the amount of phase rotation given by the adjustment circuit 801 is equal to that in the passband of the filter 106, the frequency characteristics of the filter 106 and the filter circuit 800 are inverted. In addition, the cutoff frequency (3dB attenuation point) of the filter 106 is the same as that of the filter circuit 800 .

When the phase rotation amount given by the adjustment circuit 801 is different from the phase rotation amount at the same frequency in the passband of the filter 106, the in-phase cancellation effect of the differential amplifier 107 cannot be obtained even in the region within the passband of the filter 106. Then there is the stop band of the filter circuit 800 . Therefore, the cutoff frequency of the filter circuit 800 can be made variable.

As described above, in addition to the effects of the above-mentioned embodiment 1, this embodiment 2 uses the reference signal source 803 for correction, the adjustment circuit 801 and the comparator 802, and the in-phase input signals of the two input terminals of the differential amplifier 107 The phase error or amplitude error is suppressed to a value lower than a predetermined value, thereby realizing a very sharp attenuation characteristic. In addition, in Embodiment 2, when the calibration of the adjustment circuit 801 is performed, the reference signal source and the distributor are short-circuited, and the output frequency of the reference signal source is swept, so that higher-precision calibration can be realized.

When the adjustment circuit 801 does not operate as a correction circuit, the second embodiment only adjusts the amount of phase rotation, but the present invention is not limited thereto, and can also be applied in the following way: the adjustment circuit 801 adjusts the amount of amplitude attenuation and the amount of phase rotation. The distribution signal input from the buffer 104 gives phase rotation and amplitude attenuation equal to the phase rotation and amplitude attenuation given by the filter 106 to the signal of the pass band, and at the same time adjusts the frequency band of the output signal output from the differential amplifier 107 . In this case, the adjustment circuit for adjusting the frequency band of the output signal may be different from the correction circuit for giving the phase rotation amount and the amplitude attenuation amount, or these two circuits may be used as a common circuit.

Example 3

FIG. 9 is a structural block diagram of a filter circuit 900 according to Embodiment 3 of the present invention.

As shown in FIG. 9, the filtering circuit 900 according to the third embodiment corresponds to the filtering circuit 800 according to the second embodiment shown in FIG. Circuit 902 replaces adjustment circuit 801 . In FIG. 9, the same components as those in FIGS. 1 and 8 are denoted by the same reference numerals, and their related descriptions will be omitted.

In FIG. 9 , the filter 901 has a band-rejection structure composed of an inductor and a capacitor, and the stop band is variable by changing the inductance value or the capacitance value. That is, the filter 901 blocks passage of a part of frequency components within a predetermined communication frequency band, and allows passage of only predetermined frequency components. Next, the filter 901 outputs frequency components in the passband of the distribution signal input from the buffer 105 and in the passband other than the stopband to the differential amplifier 107 . When the adjustment circuit 902 operates as a correction circuit, the adjustment circuit 902 gives the output signal of the buffer 104 a phase rotation and an amplitude equal to the phase rotation and amplitude attenuation given by the filter 901 to the passband signal. Attenuation, and output to differential amplifier 107 and comparator 802. On the other hand, when the adjustment circuit 902 does not operate as a correction circuit, the adjustment circuit 902 gives a predetermined amount of phase rotation to the distribution signal input from the buffer 104, so that the frequency band of the output signal output from the differential amplifier 107 can be adjusted. Change. That is, the adjustment circuit 902 sets the amount of phase rotation to be given to the distribution signal input from the buffer 104 to a predetermined amount of phase rotation, thereby making it possible to make the frequency band of the output signal output from the differential amplifier 107 variable, as in This is the case where the frequency band of the allocated signal passing through the filter 106 is changed. The selector 903 controls the stop band of the filter 901 based on a band selection signal for selecting the band of the filter 901 input from a wave detection circuit (not shown), and outputs to the adjustment circuit 902 for generating The second control signal that controls the phase rotation amount and the amplitude attenuation amount of the adjustment circuit 902 according to the change of the phase rotation amount and the amplitude attenuation amount. In addition, the amplitude component of the output of the differential amplifier 107 is discarded at the time of correction, and the comparator 802 is set to an inactive state when the correction is completed, not outputting any signal to the comparator.

The operation of the filter circuit 900 configured as described above will be described below.

The frequency band selection signal is input to the selector 903 by manual selection by the user of the radio device to which the filter circuit 900 is applied or automatic selection based on the received electric field strength detected by the radio device and base station control channel information. The band variable signal is output to the filter 901 from the selector 903 receiving the band selection signal, and the stop band of the filter 901 is fixed.

When a band selection signal for selecting a band different from the previous one is received, the amount of phase rotation and the amount of amplitude attenuation in the pass band also change in the filter 901 due to a change in the stop band. When the adjustment circuit 902 gives a fixed amount of phase rotation and amplitude attenuation to the input signal, the filter circuit 900 cannot maintain the attenuation characteristic, so the adjustment circuit 902 preserves the passband of the filter 901 that changes as the band-variable signal changes. The input signal correction data corresponding to the phase rotation amount and the amplitude attenuation amount, or provide an individual circuit corresponding to each phase rotation amount and amplitude attenuation amount, based on the frequency band variable signal, the selector 903 changes the adjustment circuit 902 according to the second control signal state. After the above changes are completed, the phase error or amplitude error of the in-phase input signals at the two input terminals of the differential amplifier 107 is suppressed to be lower than a predetermined value through the same process as in the second embodiment. In addition, when the adjustment circuit 902 does not operate as a correction circuit, the adjustment circuit 902 gives a predetermined amount of phase rotation to the distribution signal input from the buffer 104, so that it can be changed from The frequency band of the output signal that the differential amplifier 107 outputs. The rest of the operations are the same as those in Embodiment 1 and Embodiment 2, so their related descriptions are omitted. In addition, each output signal is the same as that in FIG. 2 , FIG. 3 , FIG. 6 and FIG. 7 , and thus its related description is omitted.

As described above, in addition to the effects of Embodiments 1 and 2, the filter 901 of Embodiment 3 adopts a band-rejection structure, thereby enabling integration of a band-pass filter with a variable pass band. In addition, according to the third embodiment, while controlling the stop band of the filter 901, the phase rotation and amplitude attenuation of the adjustment circuit 902 are also controlled according to the stop band of the filter 901, so that the change of the desired frequency band can be handled flexibly, and the Sharper decay characteristics. In addition, in the third embodiment, the frequency band of the output signal output from the differential amplifier 107 can be changed by using the filter 901 and the adjustment circuit 902, so that an output signal of a desired frequency band can be obtained at high speed.

According to Embodiment 3, the frequency band selection signal is input from the outside of the filter circuit 900, but the present embodiment is not limited thereto, and may also be applied in the following manner: the function of generating the frequency band selection signal is integrated with the function of the filter circuit 900, A band selection signal generation section is provided, and a band selection signal is input to the selector 903 from the band selection signal generation section inside the filter circuit 900 .

Example 4

Fig. 10 is a block diagram showing the configuration of a filter circuit according to Embodiment 4 of the present invention.

As shown in FIG. 10, the filter circuit 1000 according to Embodiment 4 adds a detection circuit 1001, a switch 1002, a switch 1005 and a switch 1006 to the filter circuit 108 according to Embodiment 1 shown in FIG. 1, and uses a differential amplifier 1007 Instead of the original differential amplifier 107. In addition, in FIG. 10 , the same components as those in FIG. 1 are denoted by the same reference numerals, and their related descriptions are omitted.

In FIG. 10, a detection circuit 1001 detects an interference wave or an unnecessary frequency component outside a desired frequency band, and when an interference wave or an unnecessary frequency component is detected, the detection circuit 1001 changes a switch 1002 so that the signal input terminal 101 and the splitter 103; and when no interference wave or unnecessary frequency component is detected, the detection circuit 1001 changes the switch 1002 so that the signal input terminal 101 is connected to the non-inverting input terminal of the differential amplifier 1007. The switch 1002 includes a switch terminal 1003 and a switch terminal 1004, and is short-circuited between the signal input terminal 101 and the switch terminal 1003 or the switch terminal 1004 based on the detection result of the detection circuit 1001, so that when the signal input terminal 101 is connected to the non-inverting phase of the differential amplifier 1007 When the input terminal and the signal input terminal 101 are connected to the splitter 103, the paths are switched. The switch 1005 switches paths based on the detection result of the wave detection circuit 1001 when the buffer 104 is connected to the non-inverting input terminal of the differential amplifier 1007 and when the buffer 104 is not connected to any circuit. The switch 1006 switches paths based on the detection result of the wave detection circuit 1001 when the inverting input terminal of the differential amplifier 1007 is grounded and the inverting input terminal is connected to the filter 106 . The differential amplifier 1007 converts the difference in amplitude components between the distribution signal input from the buffer 104 to the non-inverting input terminal and the distribution signal input from the filter 106 to the inverting input terminal or the signal input terminal 101 to the non-inverting input terminal. The difference in the amplitude component between the input signal and the grounded inverting input terminal is output to the signal output terminal 102 . Furthermore, the differential amplifier 1007 changes the gain based on the detection result of the detection circuit 1001 . That is, the differential amplifier 1007 gives to the input distribution signal a gain that compensates for attenuation of the input signal that occurs when the distributor 103 distributes the input signal.

The operation of the filter circuit constructed as above will be described below.

When the detection circuit 1001 does not detect interference waves or unnecessary frequency components, the switch 1002 is short-circuited between the switch terminal 1003 and the signal input terminal 101, the switch 1005 disconnects the input terminal and the output terminal, and the switch 1006 is between the input terminal and the output terminal. Short circuit between them, ground the inverting input terminal of the differential amplifier 1007, and set the gain of the differential amplifier 1007 to G1 [dB]. On the other hand, when the detection circuit 1001 detects an interference wave or an unnecessary frequency component, the switch 1002 is short-circuited between the switch terminal 1004 and the signal input terminal 101, the switch 1005 is short-circuited between the input terminal and the output terminal, and the switch 1006 is disconnected. Open the input terminal and the output terminal, and set the gain of the differential amplifier 1007 to G2 (G2=G1+3)[dB] to compensate the attenuation of the filter 106, thereby suppressing the level change of the signal output terminal 102 when switching circuits. Other operations are the same as those in Embodiment 1, and their related descriptions will be omitted. In addition, the signals of each output terminal are the same as those in FIGS. 2 to 7 , so their related descriptions are omitted.

Therefore, in addition to the effect in Embodiment 1, this Embodiment 4 switches the switch 1002 so that the signal input terminal 101 is directly connected to the non-inverting input terminal of the differential amplifier 1007 when there are no disturbing waves and unnecessary frequency components. , thereby switching between operation/non-operation of the filter 106, preventing attenuation of a received signal of a desired frequency, thereby suppressing the gain of the differential amplifier 1007 and reducing current consumption. In addition, when the detection circuit 1001 detects a frequency component other than the desired frequency, the fourth embodiment switches the setting of the differential amplifier 1007 to a gain attenuated when compensating for signal distribution, so that the output level can be kept constant.

In this Embodiment 4, the distribution signal output from the buffer 104 is directly input to the non-inverting input terminal of the differential amplifier 1007, but the present invention is not limited thereto. A correction circuit is added between the non-inverting input terminal of the differential amplifier 104 and the differential amplifier 1007 to suppress the phase error or the amplitude error of the non-inverting input signal of the two input terminals of the differential amplifier 1007 to be lower than a predetermined value, or the filter 106 adopts a resistance With a variable band-stop filter, while adding a correction circuit to suppress the phase error or amplitude error of the in-phase input signal at the two input terminals of the differential amplifier 1007 to be lower than a predetermined value or to change the filter 106 in a variable manner Band selector. This allows the filter circuit to achieve a sharper attenuation characteristic. In addition, in Embodiment 4, the allocated signal frequency band passing through the filter 106 is fixed, but the present invention is not limited thereto, and may also be applied in the following manner: the filter 106 adopts a band-rejection structure, and as in Embodiment 3 A selector is provided as in the case of the case, and the frequency band to be blocked by the filter 106 is changed. In addition, when the detection circuit 1001 detects an interference wave or an unnecessary frequency component, the fourth embodiment increases the gain of the differential amplifier 1007 by 3 [dB]. However, this embodiment is not limited thereto, and the gain can also be set to any value.

Example 5

Fig. 11 is a block diagram showing the configuration of a radio apparatus 1100 according to Embodiment 5 of the present invention. A low noise amplifier 1101 , a filter circuit 1102 and a mixer 1103 constitute a high frequency section 1104 .

In FIG. 11 , a low noise amplifier 1101 amplifies a reception signal received by an antenna 1105 and outputs the amplified signal to a filter circuit 1102 . The filter circuit 1102 allows a desired frequency component of the received signal input from the low noise amplifier 1101 to pass, and outputs to the mixer 1103 . Here, for the filter circuit 1102, any one of the filter circuit 108 in FIG. 1, the filter circuit 800 in FIG. 8, the filter circuit 900 in FIG. 9, and the filter circuit 1000 in FIG. 10 can be suitably applied. The mixer 1103 converts the frequency of the received signal input from the filter circuit 1102 and outputs the received signal to the demodulator 1106 . Demodulator 1106 demodulates the received signal input from mixer 1103 to obtain received data.

The operation of the radio device 1100 constructed as shown above will be described below.

Interfering waves outside the desired frequency band or unnecessary frequency components present in the output of the low noise amplifier 1101 are attenuated by the filter 1102 to prevent saturation of the mixer 1103 . The operation of the filter circuit 1102 is the same as that described in any one of Embodiment 1 to Embodiment 4, and its related description will be omitted.

In addition to the effects of Embodiments 1 to 4, this Embodiment 5 uses the filter circuit 1102 to attenuate interference waves or unnecessary frequency components that exist in the low-noise amplifier 1101 outside the desired frequency band, preventing the mixer from The saturation of 1103 can suppress the deterioration of the sensitivity of the demodulator 1106. In addition, by adopting the same structure as any one of the filter circuits 108, 800, 900, 1000 in the filter circuit 1102, the present embodiment 5 makes it easier to form the high frequency part 1104 on the same semiconductor substrate, because all These filter circuits all have high integration and affinity, so that the radio device 1100 can be miniaturized and the number of components can be reduced.

In Embodiment 5, the filter circuit 1102 is arranged between the low-noise amplifier 1101 and the mixer 1103, but this embodiment is not limited thereto, and may also be adapted to the following method: the filter circuit 1102 is arranged in the high-frequency part 1104 It is placed at a position other than between the low noise amplifier 1101 and the mixer 1103, thereby enhancing the integration of the filter circuit in the high frequency band, and obtaining a sharp attenuation characteristic. In addition, in the fifth embodiment, the filter circuit 1102 is used in the high frequency part 1104, but the present invention is not limited thereto, and the filter circuit 1102 may be used in a low frequency part other than the high frequency part 1104 or the like.

Example 6

Fig. 12 is a block diagram showing the configuration of a radio apparatus 1200 according to Embodiment 6 of the present invention. The modulator 1201 , the filter circuit 1202 and the power amplifier 1203 constitute a high frequency section 1204 .

In FIG. 12 , modulator 1201 modulates a transmission signal input from baseband section 1206 and outputs the modulated signal to filter circuit 1202 . Filter circuit 1202 allows a desired frequency component of the transmission signal input from modulator 1201 to pass, and outputs the frequency component to power amplifier 1203 . Here, any one of the filter circuit 108 in FIG. 1 , the filter circuit 800 in FIG. 8 , the filter circuit 900 in FIG. 9 , and the filter circuit 1000 in FIG. 10 can be suitably used for the filter circuit 1202 . The power amplifier 1203 amplifies the transmission power of the transmission signal input from the filter circuit 1202 and transmits the transmission signal from the antenna 1205 . The baseband section 1206 processes transmission data to the baseband, generates a transmission signal, and outputs the generated transmission signal to the modulator 1201 .

The operation of radio device 1200 structured as above will be described below.

Unnecessary frequency components outside the desired frequency band present in the output of the modulator 1201 are attenuated in the filter circuit 1202 . The operation of the filter circuit 1202 is the same as that of Embodiment 1 to Embodiment 4, and its related description will be omitted.

As described above, in addition to the effects of Embodiments 1 to 4, this Embodiment 6 uses the filter circuit 1202 to attenuate unnecessary frequency components other than the desired frequency band present in the output of the modulator 1201, thereby suppressing the frequency components from the antenna. 1205 of unnecessary radiation. In addition, by adopting the filter circuit 1202 with the same structure as any one of the filter circuits 108, 800, 900, and 1000, Embodiment 6 makes it easier to form the high-frequency part 1204 on the same semiconductor substrate, because all these filter circuits The circuits all have a high degree of integration and affinity, so that miniaturization of the radio device 1200 and reduction in the number of parts can be achieved.

In Embodiment 6, the filter circuit 1202 is arranged between the modulator 1201 and the power amplifier 1203, but the present invention is not limited thereto, and may also be applied in the following manner: the filter circuit 1202 is located in the modulator 1201 in the high frequency part 1204 and power amplifier 1203 in order to enhance the integration of the filter circuit in the high frequency band and obtain a sharp attenuation characteristic. In addition, in the present embodiment 6, the filter circuit 1202 is used for the high frequency part 1204, but the present invention is not limited thereto, and the filter circuit 1202 may be used for a low frequency part other than the high frequency part 1204, etc.

Example 7

FIG.13 is a block diagram showing the configuration of a radio apparatus 1300 according to Embodiment 7 of the present invention.

A radio device 1300 according to this Embodiment 7 corresponds to the radio device 1100 according to Embodiment 5 shown in FIG. 11 , with a local oscillator 1301 and a filter circuit 1302 added, as shown in FIG. 13 . In FIG. 13 , the same components as those in FIG. 11 are assigned the same reference numerals, and their descriptions are omitted.

The low noise amplifier 1101 , the filter circuit 1102 , the mixer 1103 , the local oscillator 1301 and the filter circuit 1302 constitute a high frequency section 1303 .

In FIG. 13 , a local oscillator 1301 generates a signal of a predetermined frequency for frequency conversion, and outputs the signal to a filter circuit 1302 . The filter circuit 1302 allows a desired frequency component of a signal for frequency conversion input from the local oscillator 1301 to pass, and outputs the desired frequency component to the mixer 1103 . Here, any one of the filter circuit 108 in FIG. 1 , the filter circuit 800 in FIG. 8 , the filter circuit 900 in FIG. 9 , and the filter circuit 1000 in FIG. 10 can be suitably used for the filter circuit 1302 .

In the radio device 1300 configured as above, unnecessary frequency band components other than the desired frequency band present in the output of the local oscillator 1301 are attenuated in the filter circuit 1302 .

Therefore, in addition to the effects of Embodiments 1 to 4, this Embodiment 7 attenuates unnecessary frequency components other than the desired frequency components present in the output of the local oscillator 1301, thereby suppressing the generation of frequency components by the mixer 1103. intermodulation distortion, and suppresses the deterioration of the sensitivity of the demodulator 1106. In addition, by adopting the same structure as any one of the filter circuits 108, 800, 900, and 1000 for the filter circuit 1302, Embodiment 7 makes it easier to form the high-frequency portion 1303 on the same semiconductor substrate, because all these The filter circuits are all highly integrated and friendly, so that the radio device 1300 can be miniaturized and the number of components can be reduced.

In Embodiment 7, the filter circuit 1102 is placed between the low noise amplifier 1101 and the mixer 1103 in the high frequency part 1303, and the filter circuit 1302 is placed between the local oscillator 1301 and the mixer in the high frequency part 1303 1103, but the present invention is not limited thereto, and can also be applied in the following way: the filter circuit 1102 is placed in a position other than between the low noise amplifier 1101 and the mixer 1103 in the high frequency part 1303, or the filter circuit 1302 is placed in the The high frequency part 1303 is placed at a position other than between the local oscillator 1301 and the mixer 1103 to enhance the integration of the filter circuit in the high frequency band and obtain a sharp attenuation characteristic. In addition, in the seventh embodiment, the filter circuits 1102 and 1302 are used in the high frequency part 1303, but the present invention is not limited thereto, and the filter circuits 1102 and 1302 may be used in a low frequency part other than the high frequency part 1303, etc.

Example 8

Fig. 14 is a block diagram showing the configuration of a radio apparatus 1400 according to Embodiment 8 of the present invention. The divider 1403 , the 1/2 frequency divider 1404 , the differential amplifier 1405 , the even harmonic mixer 1406 , the even harmonic mixer 1407 , the filter circuit 1408 and the filter circuit 1409 constitute a frequency conversion circuit 1410 . Furthermore, quadrature demodulators 1411 a and 1411 b constitute receiver 1412 . Furthermore, quadrature modulators 1414 a and 1414 b constitute receiver 1415 . Here, the receiver 1412 is a direct conversion receiver using a radio frequency of 2.5×f0, and the receiver 1415 is a direct conversion receiver using a radio frequency f0.

In FIG. 14 , a local oscillator 1401 generates a frequency f0 and outputs it to a distributor 1402 . Divider 1402 divides the signal of frequency f0 input from local oscillator 1401 , and outputs the divided signal to divider 1403 and phase shifter 1413 . The divider 1403 divides the signal input from the divider 1402 and outputs the divided signal to the non-inverting input terminal of the 1/2 frequency divider 1404 and the differential amplifier 1405 . The 1/2 frequency divider 1404 divides the frequency of the signal input from the divider 1403 into 1/2 and outputs it to the even harmonic mixer 1406 and the even harmonic mixer 1407 . The inverting input terminal of the differential amplifier 1405 is grounded, and the differential amplifier 1405 outputs the divided signal input from the divider 1403 to the even harmonic mixers 1406 , 1407 . The even harmonic mixer 1406 mixes twice (2×f0) the output frequency of the differential amplifier 1405 and the output frequency (0.5×f0) of the 1/2 frequency divider 1404, and outputs the mixed frequency to the filter circuit 1408 . The even harmonic mixer 1407 mixes twice the output frequency (2×f0) of the differential amplifier 1405 and the output frequency (0.5×f0) of the 1/2 frequency divider 1404, and outputs the mixed frequency to the filter circuit 1409. Filter circuit 1408 allows a desired frequency component of the signal input from even harmonic mixer 1406 to pass, and outputs the desired frequency component to quadrature demodulator 1411a. Here, any one of the filter circuit 108 in FIG. 1 , the filter circuit 800 in FIG. 8 , the filter circuit 900 in FIG. 9 , and the filter circuit 1000 in FIG. 10 can be suitably used for the filter circuit 1408 . Filter circuit 1409 allows a desired frequency component of the signal input from even harmonic mixer 1407 to pass, and outputs the desired frequency component to quadrature demodulator 1411b. Here, any one of the filter circuit 108 in FIG. 1 , the filter circuit 800 in FIG. 8 , the filter circuit 900 in FIG. 9 , and the filter circuit 1000 in FIG. 10 can be suitably used for the filter circuit 1409 . The quadrature demodulator 1411a performs quadrature demodulation on the signal input from the filter circuit 1408, and obtains received data. The quadrature demodulator 1411b quadrature demodulates the signal input from the filter circuit 1409 to obtain received data. Phase shifter 1413 generates two waves having a phase difference of 90 degrees from the distribution signal input from distributor 1402, and outputs the two waves to quadrature demodulator 1414a and quadrature demodulator 1414b. Quadrature demodulator 1414a performs quadrature demodulation on the signal input from phase shifter 1413 to obtain received data. Quadrature demodulator 1414b performs quadrature demodulation on the signal input from phase shifter 1413 to obtain received data.

The operation of radio device 1400 structured as above will be described below.

At the output of the even harmonic mixers 1406, 1407, 2.5*f0 of the desired signal component and 1.5*f0 of the unwanted frequency component appear with equal amplitudes. By employing a low-pass property in the filter 106 constituting the filter circuit 108, 800 or 1000, only desired frequency components can be extracted.

When any frequency components other than the above-mentioned frequency components exist as unnecessary frequencies, the low-pass filter 901 of the filter 106 structure can be converted into a band-stop filter 901 to deal with it.

Here, for example, assuming that f0 is the 2GHz band, the output signal of the 5GHz band can be extracted from the frequency conversion circuit 1410, so by providing a local oscillator for the 2GHz band, a dual-band receiver suitable for the 2GHz band/5GHz band can be realized. The operations of the filter circuits 1408, 1409 are the same as those in Embodiment 1 to Embodiment 4, and their related descriptions are omitted.

Therefore, in addition to the effects of Embodiments 1 to 4, this Embodiment 8 can provide a radio device suitable for a dual-band system, reducing unnecessary frequencies due to local oscillation frequencies.

In Embodiment 8, the inverting input terminal of the differential amplifier 1405 is grounded, and the distribution signal is input to the non-inverting input terminal, but the present invention is not limited thereto, and may also be applied in the following manner: Inverting, grounding the non-inverting input, assigning the signal input to the inverting input. In addition, the eighth embodiment uses the differential amplifier 1405, but the present invention is not limited thereto, and the same effect can be obtained by using a divider instead of the differential amplifier 1405. In addition, the eighth embodiment applies the frequency conversion circuit 1410 to a direct conversion receiver, but the present invention is not limited thereto, and the same effect can be obtained by applying the frequency conversion circuit 1410 to a direct conversion transmitter.

As described above, the present invention can maintain the attenuation characteristic or the pass characteristic of the high frequency band using the in-phase cancellation effect of the differential amplifier.

This specification is based on Japanese Patent Application No. 2002-319745 filed on November 1, 2002 and Japanese Patent Application No. 2003-152532 filed on May 29, 2003, the entire contents of which are hereby incorporated by reference.

Industrial Applicability

The present invention is more suitable for application to high frequency band filter circuits and radio devices used in digital wireless communication systems and the like.

Claims (8)

1. A filter circuit, comprising: A reference signal source, which generates a reference signal for adjusting the amount of phase rotation or amplitude attenuation; a splitter for splitting said reference signal or input signal into split signals for two systems; a filter for frequency-selecting the first distribution signal distributed by the distributor to pass a predetermined frequency band; a correction circuit that provides, to the second distributed signal distributed by the distributor, an amount of phase rotation or amplitude attenuation equal to phase rotation or amplitude attenuation in a frequency band in which the first distributed signal passes through the filter; a differential amplifier outputting a difference in amplitude component between said second distribution signal to which a phase rotation amount or an amplitude attenuation amount is provided by said correction circuit and said first distribution signal frequency-selected by said filter; switch, performing switching so that the reference signal is input to the distributor when adjusting the phase rotation amount or the amplitude attenuation amount to be provided by the correction circuit, and when the correction circuit provides the second distribution signal inputting the input signal to the splitter by an amount of phase rotation or amplitude attenuation; and The comparator detects a difference in voltage between the first distribution signal and the second distribution signal input to the differential amplifier, and performs the adjustment so that the difference in voltage is lower than a predetermined value. 2. The filter circuit according to claim 1, further comprising: a first buffer suppressing, for the first assigned signal, interference generated between the first assigned signal and the second assigned signal; and a second buffer for suppressing said interference for said second assigned signal, wherein said filter is frequency selective to said first allocated signal with said interference suppressed by said first buffer; and The differential amplifier outputs a difference in amplitude component between the second distributed signal in which the interference is suppressed by the second buffer and the first distributed signal frequency-selected by the filter. 3. The filter circuit according to claim 1, wherein the comparator compares the first voltage with the second voltage, where the first voltage is on the transmission path connecting the correction circuit and the differential amplifier the voltage of the midpoint, the second voltage is the voltage of the midpoint on the transmission path connecting the filter and the differential amplifier, The correction circuit provides the phase rotation amount or the amplitude attenuation amount to the second distribution signal until the comparison result of the comparator is that the difference between the first voltage and the second voltage is lower than a predetermined value. 4. The filter circuit as claimed in claim 1 , wherein the filter is frequency-selective to the first distribution signal by preventing passage of the first distribution signal in a pass-prevention stopband, and The differential amplifier outputs a difference in amplitude components between the first distribution signal and the second distribution signal that have passed through the filter. 5. The filter circuit according to claim 1, wherein said filter prevents passage of said first distribution signal in a pass-prevention stop band, thereby performing frequency selection on said first distribution signal and making said variable stop band, and The correction circuit provides phase rotation and amplitude attenuation in frequency bands of the filter passing through the stopband change to the second allocated signal equal to the phase rotation and amplitude attenuation of the first allocated signal each time the stopband changes. The amount of phase rotation and amplitude attenuation of . 6. A filter circuit, comprising: a reference signal source, which generates a reference signal for adjusting the amount of phase rotation; a splitter for splitting said reference signal or input signal into split signals for two systems; a filter for frequency-selecting the first distribution signal distributed by the distributor to pass a predetermined frequency band; an adjustment circuit that provides a predetermined amount of phase rotation to the second distribution signal distributed by the distributor, and makes the amount of phase rotation provided to the second distribution signal variable; a differential amplifier outputting a difference in amplitude component between the second distribution signal provided with the phase rotation amount by the adjustment circuit and the first distribution signal frequency-selected by the filter; switch performing switching such that the reference signal is input to the splitter when the amount of phase rotation to be provided by the adjustment circuit is adjusted, and when the adjustment circuit is to provide the phase rotation to the second distribution signal inputting the input signal to the dispenser; and A comparator that detects a difference in voltage between the first distribution signal and the second distribution signal input to the differential amplifier, and performs the adjustment so that the difference in voltage is lower than a predetermined value. 7. A filter circuit, comprising: A splitter, which splits the input signal into split signals for two systems; a filter for frequency-selecting the first distribution signal distributed by the distributor to pass a predetermined frequency band; a differential amplifier that outputs the input signal as it is when the input signal is input, and when the second distribution signal distributed by the distributor and the first distribution signal frequency-selected by the filter are input , outputting a difference in amplitude component between the second allocated signal and the frequency-selected first allocated signal; a detection circuit for detecting frequency components other than desired frequency components; and a switch performing switching so that the input signal is input to the distributor when the detection circuit detects a frequency component other than the desired frequency component, and the input signal is input when only the desired frequency component is detected by the detection circuit. signal input to the differential amplifier. 8. The filter circuit according to claim 7, wherein when the detection circuit detects a frequency component other than the desired frequency, the differential amplifier outputs the difference between the amplitude components plus The gain by which the input signal is attenuated by distributing the input signal.

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