JP2014216746A - Disturbing wave attenuation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable disturbing wave attenuation in consideration of a situation where a desired wave and a disturbing wave, whose frequencies are close to each other, are received.SOLUTION: A distributor 7 unequally distributes a radio wave received by an antenna 2, outputs a slightly attenuated signal to a first route 5, and outputs a significantly attenuated signal to a second route 6. The signal inputted into the second route is amplified by a first amplifier 9 and is converted by a phase inverter 10 into a signal whose phase is delayed by 180°. The signal, whose phase is delayed by 180°, is synthesized by a synthesizer 11 with the signal inputted into the first route 5. When a desired wave is small and a disturbing wave is large, the desired wave is buried in a noise floor due to a branch loss of the distributor 7 and only the disturbing wave is delayed in phase by 180° in the second route 6, so only the disturbing wave is attenuated at the time of the synthesizing. The signal after the synthesizing is amplified by a second amplifier 12 and is inputted into a reception circuit 4.

Description

  The present invention relates to an interference wave attenuating circuit capable of attenuating a received interference wave.

  2. Description of the Related Art Conventionally, when a radio wave receiver receives a desired signal (Desired Signal), an interfering wave attenuation circuit capable of attenuating an interfering wave (Undesired Signal) from the received radio wave is well known (see, for example, Patent Document 1). . Further, as an interference wave attenuating circuit, a technique for reducing the interference wave by band limitation such as a SAW (Surface Acoustic Wave) filter is known. In this case, for example, if the frequencies of the desired wave and the interference wave are separated by a predetermined amount, the interference wave can be reduced, and the D / U ratio (signal-to-noise ratio) is improved.

JP 2002-76978 A

  However, if the frequencies of the desired wave and the jamming wave are too close, there is a limit to the attenuation of the jamming wave by the filter, and there is a problem that the D / U ratio cannot be improved. In particular, when the desired wave is handled as a weak signal, the amplifier of the radio wave receiver may be saturated by the jamming wave in an environment where very strong signals transmitted and received by amateur radio etc. are mixed as the jamming wave. There was sex. Therefore, there is a need to attenuate the interference wave in order to improve the D / U ratio even when the frequencies of the desired wave and the interference wave are close and the interference wave is strong.

  An object of the present invention is to provide an interference wave attenuating circuit capable of attenuating an interference wave based on receiving a desired wave and an interference wave having similar frequencies.

  The jamming wave attenuating circuit for solving the above problems is a jamming wave attenuating circuit capable of attenuating a jamming wave of a strong signal received by an antenna. A phase converter that changes the phase of the signal greatly attenuated by the distributor at the time of branching; and a combiner that combines the signal attenuated by the distributor at the time of branching and the signal whose phase has been changed. It was.

  According to this configuration, the received radio wave is divided unevenly by the distributor, and thus is branched into a signal whose reception level is slightly attenuated and a signal whose reception level is greatly attenuated. The phase of the signal whose reception level is greatly attenuated by the distributor is changed by the phase converter. The signal whose phase is changed is combined with a signal whose reception level is slightly attenuated by a combiner. For example, if a signal whose phase is inverted by 180 ° is combined, the signal component is canceled. Here, for example, a communication environment is assumed in which the desired wave and the jamming wave are close in frequency, the desired wave is received as a weak signal, and the strong wave is received as a jamming wave. When a strong signal jamming wave is received, even if the reception level is greatly attenuated by the distributor, a signal of a certain level remains, so that the jamming wave output after passing through the combiner is greatly attenuated. . On the other hand, when the desired signal of the weak signal is received, if the reception level is greatly attenuated by the distributor, the signal is buried in the noise floor or only a low level signal remains. The reception level does not attenuate so much. Therefore, when the frequencies of the desired wave and the jamming wave are close and the jamming wave is strong, only the jamming wave can be greatly attenuated.

  In the interference wave attenuating circuit, it is preferable that an amplifier for amplifying the signal is provided in a path through which the signal greatly attenuated by the distributor at the time of branching is input. According to this configuration, the signal whose phase is inverted by the phase converter, that is, the signal that cancels the interference wave at the time of synthesis can be amplified by the amplifier, so that the interference wave can be greatly attenuated. .

  The interference wave attenuation circuit preferably includes a received signal strength measuring unit that measures the received signal strength of the received radio wave, and an amplifier control unit that controls on / off of the amplifier based on the received signal strength. According to this configuration, for example, the path from the distributor to the phase converter → synthesizer is validated only when the received signal strength of the received interference wave is large. Therefore, since the phase inversion path can be made effective only when necessary, it is possible to suppress the power consumed by the jamming wave attenuating circuit as compared with the constant activation.

  In the interference wave attenuating circuit, a threshold value for switching on / off the amplifier is set to a value different from an on threshold value when the amplifier is turned on and an off threshold value when the amplifier is turned off. It is preferable that the threshold is set higher than the off threshold. According to this configuration, the threshold value for switching on / off the amplifier is set with hysteresis, so that a situation in which the amplifier is repeatedly turned on / off in the vicinity of the threshold value does not occur.

  In the interference wave attenuating circuit, it is preferable that the distributor and the combiner are passive circuits, and a saturation level of reception due to the interference wave is larger than a saturation level of the reception circuit. According to this configuration, if the distributor and the synthesizer are passive circuits such as Wilkinson synthesizers, for example, the reception saturation range can be increased, so that the operation according to the above-described theory is ensured. Is advantageous.

  According to the present invention, it is possible to attenuate a jamming wave based on receiving a desired wave and a jamming wave having similar frequencies.

The circuit diagram of the disturbance wave attenuation circuit of one Embodiment. (A)-(c) is a reception level comparison figure which shows the intensity | strength relationship of the jamming wave and the desired wave in each point on a circuit. Explanatory drawing which shows the operation | movement content of an interference wave attenuation circuit. FIG. 6 is a magnitude relationship diagram of an ON threshold value and an OFF threshold value set with hysteresis. (A)-(c) is a reception level comparison figure which shows the intensity | strength relationship of the jamming wave and the desired wave in each point on a circuit. The reception level comparison figure which shows the intensity relationship of an interference wave and a desired wave. The circuit block diagram of the divider | distributor or synthesizer of another example. The change waveform figure of the input-output level of a passive circuit.

Hereinafter, an embodiment of an interference wave attenuation circuit will be described with reference to FIGS.
As shown in FIG. 1, for example, a terminal such as a smart portable device of a vehicle is provided with a radio wave receiving device 1 capable of receiving UHF (Ultra High Frequency) radio waves transmitted from a transmission antenna of the vehicle. The radio wave receiving device 1 includes an antenna 2 capable of receiving UHF radio waves, a received signal processing circuit 3 that applies a process for attenuating interference waves to a signal received by the antenna 2, and demodulation to a signal that has passed through the received signal processing circuit 3. And a receiving circuit 4 for performing the various processes described above. The UHF radio wave transmitted from the vehicle includes, for example, a request signal that requests a smart portable device to return an ID code.

  The received signal processing circuit 3 includes a distributor 7 that distributes the signal received by the antenna 2 to the two paths 5 and 6, a filter 8 that filters a signal input to the first path 5, and a second path. A first amplifier 9 for amplifying the signal input to 6 and a phase inverter 10 for inverting the phase of the signal amplified by the first amplifier 9 by, for example, 180 ° are provided. The distributor 7 is set to a distribution ratio such that the level of the signal input to the second path 6 is sufficiently smaller than the level of the signal input to the first path 5. The reception signal processing circuit 3 is provided with a synthesizer 11 that synthesizes the signal that has passed through the filter 8 and the signal whose phase is inverted by 180 ° by the phase inverter 10. The phase inverter 10 is an example of a phase converter.

  The receiving circuit 4 includes a second amplifier 12 that amplifies the combined signal that has passed through the combiner 11, a received signal strength measuring unit 13 that measures a received signal strength indicator (RSSI) of the received radio wave, and a reception thereof. An amplifier controller 14 that controls on / off of the first amplifier 9 based on the signal intensity is provided. The received signal strength measurement unit 13 measures the received signal strength of the signal that has passed through the received signal processing circuit 3 in the signal received by the antenna 2. For example, the amplifier controller 14 turns on the first amplifier 9 when the received signal strength of the received radio wave is high, and turns off the second amplifier 12 when the received signal strength of the received radio wave is low.

Next, the operation of the interference wave attenuation circuit will be described with reference to FIGS.
[Operation when the level of jamming waves is high]
FIG. 2A shows the reception levels of the interference wave and the desired wave at the “point A” of the reception signal processing circuit 3 when the interference wave level is high. In the figure, the reception level of the interference wave at “point A” is “Xu1”, and the reception level of the desired wave is “Xd1”. Although the interference wave and the desired wave have very close frequencies (for example, tens to hundreds of kHz), there is a large difference (for example, tens of dB) in the reception level. The reception levels Xu1 and Xd1 are received signal strengths based on the noise floor.

  As shown in FIG. 3, the signal received by the antenna 2 is unequally distributed by the distributor 7 and output to the first path 5 and the second path 6, respectively. For example, when the distribution ratio is “first path 5: second path 6 = 9: 1”, the reception level of the signal input to the first path 5 is hardly attenuated (for example, attenuation of about 0.46 dB). In addition, the reception level of the signal input to the second path 6 is greatly attenuated (for example, about 10 dB). Only a predetermined frequency of the signal input to the first path 5 is passed through the filter 8 and is output to the synthesizer 11.

  The reception signal strength measurement unit 13 measures the reception signal strength of a signal input via the synthesizer 11 and the second amplifier 12 when receiving radio waves. Here, since reception of an interference wave having a high reception level is assumed, the reception signal strength measurement unit 13 measures a high reception signal strength. When the amplifier control unit 14 confirms that the received signal strength is equal to or higher than the on threshold value K1, the amplifier control unit 14 turns on the second amplifier 12. That is, when the radio signal is received, the second path 6 is effectively switched if the received signal strength is equal to or higher than the ON threshold value K1.

  The signal input to the second path 6 is amplified by the second amplifier 12 and output to the phase inverter 10. The phase of the signal input to the phase inverter 10 is inverted by 180 ° by the phase inverter 10 and output to the synthesizer 11. As a result, the phase of the signal input to the second path 6 is delayed by 180 ° with respect to the phase of the signal input to the first path 5. Therefore, the signal input to the first path 5 and the signal that has passed through the phase inverter 10 are signals having positive and negative amplitudes.

  FIG. 2B shows the reception levels of the interference wave and the desired wave at the “point B” of the reception signal processing circuit 3. In the figure, the amount of attenuation on the second path 6 side of the distributor 7 is “Y”, and the reception level of the disturbing wave input to the second path 6 after attenuation is “Xu2”. The interference wave input to the second path 6 is attenuated by Y [dB] by the distributor 7 and becomes Xu2 (= Xu1−Y). When Y> Xd1, the desired wave input to the second path 6 is buried in the noise floor after being attenuated by Y [dB] by the distributor 7. As a result, only the interference wave passes through the second path 6.

  As shown in FIG. 3, the signal passing through the first path 5 and the signal whose phase is inverted by 180 ° by the phase inverter 10 are combined into one signal by the combiner 11. The interference wave input to the first path 5 is synthesized by the combiner 11 in the second path 6 whose phase is inverted by 180 °, so that the amplitude is attenuated accordingly. That is, the interference wave received by the antenna 2 is attenuated. On the other hand, the desired wave input to the first path 5 passes through the combiner 11 as it is because there is no target to be combined in the combiner 11.

  FIG. 2C shows the reception levels of the interference wave and the desired wave at “point C” of the reception signal processing circuit 3. As can be seen from the figure, at the point C, a signal having a reception level of “Xu1−Xu2”, that is, a signal having a reception level of “Y” remains. On the other hand, the desired wave is a signal having a reception level of “Xd1” as acquired at the point C. That is, although the interference wave is attenuated, the desired wave is not attenuated and the value at the time of reception remains as it is. Therefore, since the desired wave is not attenuated but only the interference wave is attenuated, the D / U ratio of the received radio wave is improved.

Incidentally, when the branching loss of the distributor 7 is “R1”, the combining loss of the combiner 11 is “R3”, the gain of the second amplifier 12 is “G”, and the attenuation of the phase inverter 10 is “R2”, the received signal The level “Xc” of “C point” of the processing circuit 3 is expressed by the following equation (α). It is assumed that the reception level Xc is sufficiently higher than the branch loss R1, and at least the level of the interference wave of the signal passing through the second path 6 is higher than the noise floor.
Xc = −R1 + G−R2−R3 (α)
As shown in FIG. 4, the amplifier control unit 14 switches the first amplifier 9 off when the antenna 2 stops receiving radio waves and the received signal strength is equal to or less than the off threshold value K2. As a result, the operation of the circuit group of the second path 6 can be stopped after the end of radio wave reception, so that the power consumed by the reception signal processing circuit 3 can be kept small. The on / off threshold value of the first amplifier 9 is set to hysteresis so that the first amplifier 9 does not always repeat on / off in the vicinity of the threshold value. That is, the on threshold value K1 is set higher than the off threshold value K2, and when the first amplifier 9 is turned on, it is not immediately turned off due to a slight change in the received signal strength.

[Operation when Y <Xd1]
As shown in FIGS. 5A to 5C, when Y <Xd1, even if the desired wave of the second path 6 is attenuated by the distributor 7, it is not buried in the noise floor (FIG. 5B). reference). However, when the signal of the first path 5 and the signal of the second path 6 are combined by the combiner 11, only the reception level is “Y” for both the interference wave and the desired wave, Although the reception level is slightly lowered, an improvement in the D / U ratio can be expected (see FIG. 5C).

[Operation when the level of interference is low]
As shown in FIG. 6, when the level of the interference wave is small, the reception level of the desired wave is higher than that of the interference wave at “point A” of the reception signal processing circuit 3. Here, since a desired wave having a low reception level is mainly received, the reception signal strength measurement unit 13 measures a low reception signal strength. The amplifier control unit 14 turns off the second amplifier 12 because it confirms that the received signal strength does not exceed the ON threshold value K1. That is, when the desired wave is received in an environment where the level of the interference wave is small, the second path 6 is maintained invalid, and the radio wave reception is executed only by the first path 5.

  The received radio wave of the antenna 2 is distributed by the distributor 7, but only the first path 5 is enabled, so only the signal input to the first path 5 is output to the subsequent stage. The signal input to the first path 5 is input to the receiving circuit 4 after passing through the filter 8, the synthesizer 11, and the second amplifier 12. At this time, the signal input to the receiving circuit 4 is originally received as a signal having a higher desired wave level than the disturbing wave, that is, a signal having a good D / U ratio, and can be acquired without any problem. is there.

According to the configuration of the present embodiment, the following effects can be obtained.
(1) When the radio wave receiving apparatus 1 receives a strong signal jamming wave, a jamming wave whose reception level is greatly attenuated by the unequal distribution of the distributor 7 is input to the second path 6, but it is originally high. Since the strong interference wave is attenuated, the interference wave having a certain level passes through the second path 6. For this reason, the synthesizer 11 synthesizes the interference wave that is slightly attenuated in the reception level and passes through the first path 5 and the interference wave whose phase is inverted by 180 ° by the phase inverter 10 in the second path 6. Then, the interfering wave is greatly attenuated and output from the combiner 11. On the other hand, when the radio wave receiving apparatus 1 receives a desired wave of a weak signal, the desired wave whose reception level is greatly attenuated by the unequal distribution of the distributor 7 is input to the second path 6. Therefore, the desired wave is buried in the noise floor, for example, or the reception level is significantly lowered. For this reason, the combiner 11 combines the desired wave passing through the first path 5 with the reception level attenuated only slightly and the disturbing wave whose phase is inverted by 180 ° in the second path 6 by the phase inverter 10. However, the desired wave is output from the synthesizer 11 without being attenuated. Therefore, when the frequencies of the desired wave and the jamming wave are close and the jamming wave is strong, only the jamming wave can be greatly attenuated. Therefore, the D / U ratio (signal noise ratio) of the radio wave receiver 1 can be improved.

  (2) In the second path 6, the first amplifier 9 is provided before the phase inverter 10. Therefore, when the interference wave is received, a signal for canceling the interference wave input from the first path 5 at the time of signal synthesis by the combiner 11 can be amplified by the first amplifier 9. It is advantageous to greatly attenuate the wave.

  (3) The received signal strength of the received radio wave is measured, and on / off of the first amplifier 9 is controlled based on the received signal strength. For this reason, when the interference wave reception level is high, the first amplifier 9 is turned on and the second path 6 is enabled. When the interference wave or desired wave reception level is low, the first amplifier 9 is turned off and the second path 6 is turned on. The path 6 becomes invalid. Therefore, since it is not necessary to always start the 1st amplifier 9, the power consumption concerning the electromagnetic wave receiver 1 (received signal processing circuit 3) can be restrained small.

  (4) The ON / OFF threshold value of the first amplifier 9 is set by hysteresis by setting the ON threshold value K1 higher than the OFF threshold value K2. Therefore, the first amplifier 9 does not always repeat on / off near the threshold value.

  (5) The ON threshold value K1 of the first amplifier 9 is set to a value having a higher reception level than the desired wave that is assumed to be received. Therefore, since the first amplifier 9 can be turned on only when a strong signal jamming wave is received, the first amplifier 9 can be switched on at a true timing when it is desired to attenuate the jamming wave.

Note that the embodiment is not limited to the configuration described so far, and may be modified as follows.
As shown in FIG. 7, the distributor 7 or the combiner 11 may be constructed from a passive circuit made up of the illustrated Wilkinson combiner. The passive circuit is not limited to the Wilkinson combiner, and can be changed to various configurations such as a circuit in which one resistor is connected to the middle point of two resistors connected in series.

  FIG. 8 shows the waveform change of the input / output levels of the passive circuit and the active circuit. Note that the active circuit is a circuit in which the circuit illustrated in FIG. 7 is replaced with a transistor structure. As shown in FIG. 8, it can be seen that the saturation level P1 of the passive circuit is higher than the saturation level (P1 dBm) of the active circuit, and is higher than the point P2 in FIG. 8 (P1> P2 is established). That is, the reception saturation level due to the interference wave is larger than the saturation level of the reception circuit 4. Therefore, if the distributor 7 and the synthesizer 11 are configured by passive circuits, it is advantageous to ensure an operation based on the theory of this example described in the embodiment because a large saturation region, that is, saturation is difficult. Become. Incidentally, the active circuit has the advantage of preventing the reflected wave from one output end from being reflected to the input end or the other output end, but has the disadvantage of lowering the saturation level as shown in FIG. .

A circuit (element) in which the first amplifier 9 and the phase inverter 10 are integrated may be used.
The ratio of unequal distribution is not limited to 9: 1 and can be changed to various combinations.
The number of paths branched from the distributor 7 is not limited to two, and may be three or more, for example.

The phase amount of the phase inverter 10 may be changed to a value other than 180 °.
The on / off threshold value of the first amplifier 9 may be a single value.
As the filter 8, various filters such as a low-pass filter and a band-pass filter can be used.

The frequency of the radio wave received by the radio wave receiver 1 can be changed to a frequency other than UHF.
The received signal processing circuit 3 may be integrated into the receiving circuit 4.

The radio wave receiving device 1 is applicable not only for vehicles but also to other devices and devices.
Next, technical ideas that can be grasped from the above-described embodiment and other examples will be described below together with their effects.

  (A) In the interference wave attenuating circuit, an ON threshold value when the amplifier is switched from OFF to ON is set to a value having a higher reception level than a desired wave assumed to be received. According to this configuration, the interference wave attenuating circuit can be operated only when a high level interference wave is received, which is advantageous in suppressing the power consumed by the interference wave attenuating circuit.

  DESCRIPTION OF SYMBOLS 2 ... Antenna, 4 ... Reception circuit, 5 ... 1st path | route, 6 ... 2nd path | route, 7 ... Divider, 9 ... 1st amplifier, 10 ... Phase inverter as a phase converter, 11 ... Synthesizer, 13 ... Received signal strength measurement unit, 14... Amplifier control unit, K1... ON threshold, K2... OFF threshold, P1, P2.

Claims (5)

In the interference wave attenuation circuit that can attenuate the interference signal of the strong signal received by the antenna,
A distributor that divides the received radio waves unequally and branches them into multiple paths;
A phase converter that changes the phase of the signal greatly attenuated by the distributor at the time of branching;
An interference wave attenuating circuit comprising: a synthesizer that synthesizes the signal attenuated by the distributor at the time of branching and the signal whose phase has been changed. 2. The interference wave attenuating circuit according to claim 1, wherein an amplifier for amplifying the signal is provided in a path through which the signal greatly attenuated by the distributor at the time of branching is input. A received signal strength measuring unit for measuring the received signal strength of the received radio wave;
The interference wave attenuation circuit according to claim 2, further comprising: an amplifier control unit that controls on / off of the amplifier based on the received signal strength. The threshold value for switching on / off of the amplifier is set to a value different from the on threshold value when turning on the amplifier and the off threshold value when turning off the amplifier, and the on threshold value is set higher than the off threshold value. 4. The interference wave attenuating circuit according to claim 3, wherein the interference wave attenuating circuit is provided. The distributor and the combiner are composed of passive circuits,
The interference wave attenuation circuit according to any one of claims 1 to 4, wherein a saturation level of reception by the interference wave is larger than a saturation level of the reception circuit.