JP2003258666A - Receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate carrier sense errors caused by an image frequency signal. <P>SOLUTION: A modulation means 2 modulates a local signal source 1. A first mixer 5 mixes the output of the local signal source 1 with a receiving signal. A reverse modulation means 4 performs inverse modulation so as to cancel the modulation components of an output of the first mixer 5. A modulation component detecting means 8 detects the modulation components. A deciding means 10 decides whether a carrier is present, by using the output of the modulation component detecting means and the output of a carrier sensing means. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver mainly used in a wireless communication device such as a cordless remote controller, a pager, a cordless telephone, and a mobile telephone, and particularly to an image rejection mixer for omitting or simplifying a receiving filter. Regarding the receiver using.

[0002]

2. Description of the Related Art A conventional receiver will be described with reference to the drawings. FIG. 7 is a block diagram showing the configuration of a conventional receiver.

In FIG. 7, reference numeral 1 denotes a first local signal source, and 5
Is a first mixer, 7 is a calculation means, 9 is a carrier sense means, 10 is a determination means, 11 is a demodulation means, 12 is a channel selection filter, 13 is a frequency divider by 2, 14 is a reception amplifier, 1
Reference numeral 5 is an antenna, and 16 is a phase shifting means. The receiver of FIG. 7 has a single super-heterodyne system configuration, but employs an image rejection mixer in order to omit the reception filter directly below the antenna. The image rejection mixer prevents interference due to image frequency signals.

In the image rejection mixer, the received signal and the signal of the first local signal source 1, that is, the local signal are input to the pair of first mixers 5 and mixed with each other. Here, the received signal is divided into two and input to each pair of the first mixers 5. On the other hand, the frequency of the signal of the first local signal source 1 is divided into two by a frequency divider by two, and two signals having a relative phase difference of 90 ° are generated. The two signals are input to the pair of first mixers 5, respectively. By using a frequency divider by 2, the relative phase difference can be accurately set to 90 °.

Then, the respective outputs of the pair of the first mixers 5 are input to the phase shift means 16 to relatively change the phase by 90 °, and then input to the operation means 7 to add or subtract each other. To do. At this time, the signal having the desired frequency has the same phase and the signal having the image frequency has a phase opposite to each other, so that the image frequency can be suppressed. The image rejection mixer is configured as described above.

Next, the output of the calculation means 7 is input to the demodulation means 11 after removing unnecessary components by the channel selection filter 12. The demodulation means has a built-in circuit for outputting a voltage according to the level of the input signal, that is, a level detection circuit generally called an RSSI circuit. The carrier sense means 9 generates a signal when the output of the level detection circuit exceeds a preset level, that is, the carrier sense level. Then, the determination means 10 determines whether or not there is a desired carrier based on the output of the carrier sense means 9. When the determination means 10 determines that there is a desired carrier, the receiver enters the receiving operation and demodulates the received signal.

[0007]

However, in the above-mentioned conventional receiver, when a relatively large image frequency signal is input, the carrier sense means erroneously generates a signal and the determination means determines that the desired carrier is present. There is a case where a phenomenon of making a judgment, that is, an erroneous carrier sense occurs. This is a problem that occurs because the amount of suppression of the image frequency signal of the image rejection mixer is insufficient.

In a general image rejection mixer, the amount of suppression of an image frequency signal that can be stably realized is about 30 dB, which is smaller than the amount of suppression when a general receiving filter is used. This has been an obstacle to obtaining a highly reliable receiver.

[0009]

In order to solve the above conventional problems, a receiver of the present invention comprises a first local signal source, a modulation means, a mixer, an inverse modulation means, and a carrier sense means. A modulation component detection means and a determination means, wherein the modulation means modulates the local signal source, mixes an output of the local signal source and a received signal in the mixer, and the inverse modulation means outputs the output of the mixer. The output of the mixer is inversely modulated so as to cancel the modulation component, the modulation component detection means detects the modulation component included in the output of the inverse modulation means, and the output of the mixer or the output of the inverse modulation means is detected. The signal level is detected by the carrier sensing means, and the judging means judges the presence or absence of a carrier by using the output of the modulation component detecting means and the output of the carrier sensing means.

Since the modulation component is detected when the image frequency signal is received, it is possible to determine whether the received signal is the signal of the desired frequency or the image frequency signal, and the input of the image frequency signal is performed. Therefore, it is not possible to mistakenly determine that there is a carrier. As a result, an increase in current consumption due to an unnecessary receiving operation and a carrier sense due to carrier sense confirmation before transmission will not cause a transmission failure.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 comprises a first local signal source, a modulation means, a mixer, an inverse modulation means, a carrier sense means, a modulation component detection means, and a determination means. , The modulating means modulates the first local signal source,
The output of the first local signal source and the received signal are mixed by the mixer, and the inverse modulation means inversely modulates the output of the mixer so as to cancel the modulation component of the output of the mixer, and the modulation component detection means. Detects the modulation component contained in the output of the inverse modulation means, detects the signal level of the output of the mixer or the output of the inverse modulation means by the carrier sense means, and the determination means of the modulation component detection means. It is a receiver that determines the presence or absence of a carrier by using the output and the output of the carrier sensing means.

In the case of the signal of the desired frequency, the modulation is canceled by the inverse modulation, but in the case of the image frequency signal, the modulation component is detected without being canceled. Therefore, whether the received signal is the signal of the desired frequency or not It is possible to determine whether or not it is a frequency signal, and it is possible to prevent the erroneous determination of presence of a carrier due to the input of the image frequency signal.
As a result, an increase in current consumption due to an unnecessary receiving operation and a carrier sense due to carrier sense confirmation before transmission will not cause a transmission failure.

The invention according to claim 2 is characterized in that first and second mixers, first and second local signal sources, modulation means, inverse modulation means, carrier sense means, and modulation component detection means. And a reception signal and an output of the first local signal source modulated by the modulation means are mixed by the first mixer, and inversely modulated by the inverse modulation means so as to cancel the modulation. The output of the second local signal source and the output of the first mixer are mixed by the second mixer, and the modulation component detection means detects the modulation component included in the output of the second mixer. , A signal level of the output of the second mixer is detected by a carrier sensing means, and the judging means is a receiver for judging the presence or absence of a carrier by using the output of the modulation component detecting means and the output of the carrier sensing means. . Then, since the inverse modulation operation is performed by the second mixer,
It is easy to perform the inverse modulation in conjunction with the modulation of the first mixer and the first local signal source, and it can be configured with a simple circuit. In addition, the configuration can be simplified because it can be configured to also perform frequency conversion into the second intermediate frequency signal.

According to a third aspect of the present invention, there is provided a first local signal source, a modulation means, a mixer, a variable filter, a carrier sense means, a level fluctuation detection means, and a determination means, and the modulation means. Frequency-modulates the first local signal source, mixes the output of the local first part signal source and the received signal in the mixer, inputs the output of the mixer to the variable filter, and outputs the frequency of the variable filter. The characteristic or the pass characteristic is changed in synchronization with the modulation, the level fluctuation detecting means detects the level fluctuation of the output of the variable filter, and the signal level of the output of the mixer or the output of the variable filter is the carrier sense means. And the determination means is a receiver that determines the presence or absence of a carrier using the output of the level fluctuation detection means and the output of the carrier sense means. Since the variable filter is used, the second local frequency source and the second mixer are unnecessary. Further, it can be applied to a single super-heterodyne receiver.

The invention according to claim 4 is the receiver in which the variable filter is a channel selection filter. And
Since the channel selection filter is used as a variable filter, it is not necessary to additionally provide a variable filter, and the circuit scale can be reduced.

According to a fifth aspect of the present invention, there is provided a receiver for varying the center frequency of the variable filter so that the center frequency of the pass band of the variable filter becomes the same as the center frequency of the desired channel component of the mixer output. When a signal of a desired frequency is received, the modulation operation does not affect the demodulation operation by the demodulation means, so that stable demodulation operation can be performed at the same time while performing the carrier sensing operation.

According to a sixth aspect of the present invention, the variable filter has an insertion loss gradient in the frequency band including the desired channel component of the mixer output, and the desired channel component of the variable filter with respect to the modulation by the modulation means. It is a receiver that changes the insertion loss of the variable filter so that the output amplitude becomes constant. Then, since the frequency-modulated signal by the modulation means is input to the variable filter and converted into the amplitude-modulated signal, the modulation component can be detected by a simple circuit.

According to a seventh aspect of the present invention, the first local signal source, the modulation means, the mixer, the inverse modulation means, the channel selection filter, the carrier sense means, the reception level detection means, and the determination means. And the modulation means comprises the first
The local signal source is mixed, the output of the first local signal source and the received signal are mixed by the mixer, and the inverse modulation means reverses the output of the mixer so as to cancel the modulation component of the output of the mixer. Modulates and inputs the output of the inverse modulation means to the channel selection filter, the reception level detection means detects the output level of the channel selection filter, and the signal level of the output of the channel selection filter is detected by the carrier sense means. The determining means stops the output of the reception level detecting means and / or the output of the carrier sense means and the operation of the modulating means and the inverse modulating means when the modulating means and the inverse modulating means are operated. When the presence or absence of a carrier is determined by using the output of the reception level detection means and / or the output of the carrier sense means. It is a machine. Since the presence or absence of the image frequency signal can be determined only by the reception level detecting means and / or the carrier sensing means, the circuit can be simplified.

The invention according to claim 8 further comprises a first local signal source, a modulation means, a mixer, an inverse modulation means, a channel selection filter, and a demodulation means, wherein the modulation means is the first one. The local signal source is modulated, the output of the first local signal source and the received signal are mixed in the mixer, and the inverse modulation means inversely modulates the output of the mixer so as to cancel the modulation component of the output of the mixer. The output of the inverse modulation means is input to the demodulation means via the channel selection filter for demodulation. Then, the sensitivity suppression characteristic for the image frequency signal can be improved, and the image frequency signal cannot be demodulated so that the demodulation will not be erroneously performed.

According to a ninth aspect of the invention, the modulating means is a receiver for performing frequency modulation. The frequency modulation can be easily obtained by changing the oscillation frequency of the first local signal source, and the circuit can be simplified.

According to a tenth aspect of the present invention, the modulating means is a receiver for performing phase modulation. Further, the phase modulation can be configured by using a quadrature modulator, the modulation can be accurately performed, and therefore the reverse demodulation can also be accurately performed by the same configuration, so that the modulation component can be canceled with high accuracy.

[0022]

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

(Embodiment 1) FIG. 1 is a block diagram showing the configuration of a receiver according to Embodiment 1 of the present invention. Also, FIG.
FIG. 4 is an explanatory diagram illustrating a frequency relationship of signals processed by the receiver of the present invention. The receiver of this embodiment will be described with reference to FIGS.

In FIG. 1, 1 is a first local signal source and 2 is a local signal source.
Is a modulation means, 3 is a second local signal source, 4 is an inverse modulation means,
5 is a first mixer, 6 is a second mixer, 7 is a computing means,
8 is a modulation component detecting means, 9 is a carrier sense means, 10
Is a determination means, 11 is a demodulation means, 12 is a channel selection filter, 13 is a frequency divider by 2, 14 is a reception amplifier, and 15 is an antenna.

The receiver shown in FIG. 1 employs an image rejection mixer in order to omit the reception filter directly below the antenna, thereby preventing interference due to the input of the image frequency signal. Here, in the image rejection mixer, the received signal and the signal of the first local signal source 1, that is, the local signal are input to the pair of first mixers 5 and mixed. However, the received signal is divided into two and input to each pair of the first mixers 5. On the other hand, the first local signal source 1 is frequency-modulated by the modulator 2. Here, the modulation frequency of the modulation by the modulation means 2 is set to a frequency band different from the frequency band in which the modulation frequency component of the received signal, that is, the baseband frequency exists.

In this embodiment, the modulation frequency of the received signal is 1.
The modulation frequency of the modulation means 2 is set to 2.0 kHz, while it exists below 2 kHz. Then, the output signal of the first local signal source 1 is input to the frequency divider 13 to divide the frequency into ½ and generate two local signals having a relative phase difference of 90 °. . At this time, the output signal of the frequency divider 13 is frequency-modulated with a modulation frequency of 2.0 kHz. The two local signals are input to the pair of first mixers 5, respectively. Here, the frequency divider 13 is provided to accurately obtain the relative phase difference of 90 °. Then, the respective outputs of the pair of first mixers 5 are input to the pair of second mixers 6. Here, two local signals having a relative phase difference of 90 ° are input to the pair of second mixers 6 by dividing the signal of the second local signal source 3 by two, and the first local signal is input. It is mixed with the output signal of the mixer 5.

Here, the second local signal source 3 is subjected to characteristic modulation. That is, by the inverse modulation means 4, the second
The local signal source 3 is frequency-modulated. Here, the modulation frequency is the same as the modulation frequency of the first local signal source 1, and the frequency displacement is also set to be the same. However, since the frequency of the second local signal source 3 is several tenths of the frequency of the first local signal source 1, the ratio of the frequency displacement amount to the signal source frequency is the second frequency.
The local signal source 4 is larger. Further, the modulation phase of the frequency modulation is inverted between the first and second local signal sources. In this embodiment, the local signal is set to the Lower-Local frequency, which is a lower frequency than the received signal. Here, when the upper-local frequency is set, the modulation phases become the same phase. By performing the modulation by the modulation means 2 and the inverse modulation by the inverse modulation means 4, the modulation can be given only when the image frequency signal is input.

With respect to this, the frequency relationship of signals processed by the receiver of this embodiment will be described with reference to FIG.

As shown in FIG. 2, a desired signal ((a) in the figure) and an image signal ((c) in the figure) are included in the reception frequency band.
Exists. The local signal (first local signal) ((b) in the figure) has an intermediate frequency between the two signals. The desired signal, the image signal, and the first local signal are mixed by the first mixer, and frequency conversion is performed to a lower intermediate frequency of the first intermediate frequency. Here, if the first local signal is frequency-modulated by the modulating means and the frequency changes to the lower side at a certain moment (see the horizontal arrow in FIG. 2), among the first intermediate frequency signals, The component of the desired signal ((d) in the figure) changes to the higher frequency side. On the other hand, the component of the image signal ((e) in the figure) changes to the lower side. In this way, the behavior becomes different.

Next, the above first intermediate frequency signal is input to the second mixer and mixed with the second local signal. Here, the second local signal source is subjected to frequency modulation in which the modulation phase is inverted with the same modulation frequency and the same frequency displacement as the modulation of the first local signal source. That is, inverse modulation is performed so as to cancel the frequency modulation by the first mixer. Therefore, the output of the second mixer has no frequency change for the desired signal ((f) in the figure). On the other hand, the image signal ((g) in the figure) has twice the frequency displacement, and the frequency change is large. That is, when the image signal is input, the above modulation component remains, but when the desired signal is input, the modulation component is canceled and does not remain.

Next, as shown in FIG. 1, the second mixer 6
The outputs of the pairs are input to the calculation means 7. Here, the image frequency component is suppressed by performing addition or subtraction arithmetic processing so that the desired signal has the same phase and the image signal has the opposite phase. Then, the output of the calculation means 7 is input to the demodulation means 11 after the unnecessary components are removed by the channel selection filter 12. The demodulation means 11 has a built-in circuit for outputting a voltage according to the level of the input signal, that is, a level detection circuit generally called an RSSI circuit. The carrier sense means 9 generates a signal when the output of the level detection circuit exceeds a preset level, that is, the carrier sense level.
Here, the carrier sense level is -110 dBm in terms of antenna input level.

A modulation component detecting means 8 is also constructed. The modulation component detection means 8 detects a modulation component included in the output of the channel selection filter 12, that is, a frequency modulation component having a modulation frequency of 2 kHz. The modulation component detection means 8 is composed of a circuit for converting the component of the modulation frequency 2 kHz into a voltage change, a filter for extracting only the frequency component near 2 kHz and a smoothing circuit, and the frequency modulation component of 2 kHz is output to the output of the channel selection filter 12. When present, it outputs a DC voltage.

The output of the carrier sense means 9
Both outputs of the modulation component detection means 8 are input to the determination means 10. The determination means 10 is configured as a part of the function of the microcomputer. The determination means 10 determines the presence or absence of a carrier as follows.

First, when there is no carrier detection output from the carrier sensing means 9, the judging means 10 judges that there is no carrier on the desired channel. Next, the carrier sense means 9
When there is an output of carrier detection from, when the output voltage of the modulation component detecting means 8 is larger than a preset value,
It is determined that there is no carrier for the desired channel. in this case,
It is assumed that the image frequency signal is being input.

Further, when there is an output for carrier detection from the carrier sense means 9 and if the output voltage of the modulation component detection means 8 is smaller than a preset value, it is determined that there is a carrier for the desired channel.

As described above, since the presence or absence of the carrier of the desired channel is determined based on the information from the modulation component detecting means 8 in addition to the carrier sense means 9, it is erroneously determined that the carrier is present from the image frequency signal, There is no waste of battery power consumed by shifting to the receiving operation.

Further, there is a rule that a specific low power radio or the like executes a carrier sense operation for confirming whether or not there is a carrier in the used channel before transmission, and cannot shift to the transmission operation when there is a carrier. Even in this case, with the configuration of the present embodiment, it is possible to prevent the transmission from being disabled by erroneously determining that there is a carrier in the used channel due to the image frequency signal.

The modulation component detecting means 8 can be configured to detect by demodulating means 11 by filtering the demodulated analog output signal in the vicinity of the modulation frequency.

The value of the modulation frequency or frequency displacement by the modulation means 2 may be set to any value. For example, in this embodiment, 2 kHz, which is higher than the modulation frequency of the received signal, is set, but a small value such as 0.5 kHz can be selected.

The modulation component detecting means outputs the channel selection filter as shown in FIG. 2 ((h) (i) in the figure).
Is passed through a filter having a pass amplitude characteristic having a gradient with respect to frequency, frequency modulation is converted into amplitude fluctuation, and a configuration in which the signal with amplitude fluctuation is detected by envelope detection or the like can be used. . In this case, the desired signal is not amplitude-modulated, but the image signal is amplitude-modulated, so that it can be determined.

In this embodiment, frequency modulation is used for modulation and inverse modulation, but phase modulation may be used. In the phase modulation, since it is possible to perform accurate modulation using a quadrature modulator or the like, there is an advantage that accurate modulation and inverse modulation can be performed.

Further, although the first local signal source 1 and the second local signal source 3 are configured independently, the second signal source 3 may use a signal obtained by dividing the frequency of the first signal source 1. it can. Alternatively, a signal obtained by multiplying the second signal source by using a PLL circuit or the like may be used as the first local signal.

Further, as a structure for making the modulation shift amounts (frequency shift amounts) of the first and second local signal sources the same, another signal that is not modulated based on one modulated signal is used. The signal of the first or second local signal source can be obtained by mixing the signal with a mixer and performing frequency conversion. In particular, since the ratio of the frequency shift amount of the second local signal source to the signal frequency is significantly larger than that of the first local signal source, the configuration for obtaining the same frequency shift amount using the mixer is effective.

(Second Embodiment) FIG. 3 is a block diagram showing the configuration of a receiver according to a second embodiment of the present invention. In FIG.
16 is a phase shift means. Further, the same components as those in FIG. 1 are shown with the same numbers. The receiver of this embodiment will be described with reference to FIG.

The difference between this embodiment and the above-mentioned first embodiment lies in the position where the inverse modulation means is arranged. In the present embodiment, the second mixer arranged in the latter stage of the image rejection mixer including the first mixer 5, the phase shift means 16 and the calculation means 7.
The signal of the second local signal source 13 input to the mixer 6 is modulated by the inverse modulation means 4 so that the modulation by the modulation means 2 is inversely modulated. That is, it is not necessary to incorporate an inverse modulation mechanism in the image rejection mixer. Here, the phase shift means 16 is provided for relatively changing the phase of the first intermediate frequency signal, which is the output signal of the pair of the first mixer 5, by 90 °, and is respectively a low pass filter and a high pass filter. The property that the phase changes near the shoulder of the pass filter is used.

With the above-mentioned configuration, the second mixer 6 can be configured by one, the circuit scale can be reduced, and the inverse modulation operation can be performed more reliably than in the case of using a pair of mixers. There are advantages.

The present embodiment has a double superheterodyne system configuration.

(Third Embodiment) FIG. 4 is a block diagram showing the configuration of a receiver according to a third embodiment of the present invention. In FIG. 4, 17 is a frequency varying means, 18 is a level fluctuation detecting means, and 19 is a variable filter. Further, the same components as those in FIGS. 1 and 3 are designated by the same reference numerals.

The characteristics of this embodiment are the same as those of the first and second embodiments.
In contrast to the inverse modulation means used in, the variable filter 1
Frequency changing means 17 for changing the frequency characteristic of
In other words, the level fluctuation detecting means 18 is used instead of the modulation component detecting means.

Modulation is applied by mixing the signal of the first local signal source 1 modulated by the modulation means 2 and the received signal in the first mixer 5. When the modulation by the modulation means 2 is frequency modulation, the frequency of the first intermediate frequency signal which is the output of the first mixer 5 changes. The output of the first mixer 5 is input to the channel selection filter 12 via the phase shifter 15 and the calculator 7, and then the variable filter 19 is input.
Entered in. Here, the frequency changing means 17 changes the frequency characteristic of the variable filter so that the output level of the variable filter becomes constant with respect to the signal of the desired channel. The variable filter 19 has a characteristic in which the frequency characteristic of the passing amplitude has a gradient in the vicinity of the first intermediate frequency, and the modulation means 2
By shifting the frequency characteristic of the variable filter 19 in the frequency axis direction or in the passage amplitude axis direction in synchronization with the modulation of 1, the output level of the variable filter is controlled to be constant with respect to the desired channel signal.

At this time, when the received signal is the image frequency signal, the frequency change of the variable filter 19 and the frequency change of the first intermediate frequency signal are opposite to each other, so that the output level of the variable filter 19 changes. The level fluctuation detecting means 18 detects the change in the output level. Then, the level fluctuation detecting means 18 input to the judging means 10
When the output of is larger than a preset value, it is determined that there is no carrier. On the other hand, when the received signal is the desired channel signal, the output of the level fluctuation detecting means 18 becomes smaller than a preset value, so that the presence of carrier can be determined.

In this embodiment, there is no need for components such as the inverse modulation means for the inverse modulation operation, the second local signal source or the second mixer, and there is an advantage that the circuit can be simplified.

Further, there is an advantage that it can be applied to the configuration of the single super-heterodyne system.

In this embodiment, the variable filter 19 has a pass amplitude having a gradient with respect to the frequency, but a channel selection filter can be used. That is, the center frequency of the pass band of the channel selection filter can be changed in synchronization with the modulation. Then, the frequency varying means 17 controls so that the center frequency of the channel selection filter always matches the center frequency of the desired channel signal. As a result, when the received signal is the desired channel signal, the output level does not change, but when it is the image frequency signal, the frequency of the intermediate frequency signal changes outside the pass band of the channel selection filter, so the pass level is large. Change. By detecting the change in the passing level by the level fluctuation detecting means 18, it is possible to prevent erroneous carrier sense due to the image frequency signal.

Further, as the variable filter 19, it is possible to use one having a gradient in the pass amplitude characteristic within the pass band of the channel selection filter. In this case, the image frequency signal can be detected even when the frequency displacement amount by the modulation means 2 is relatively small.

(Fourth Embodiment) FIG. 5 is a block diagram showing the configuration of a receiver according to a fourth embodiment of the present invention.

FIG. 6 is an explanatory diagram for explaining the frequency relationship of signals processed by the receiver of the present invention. The receiver of this embodiment will be described with reference to FIGS.

In FIG. 5, 20 is a reception level detecting means. Further, the same components as those in FIG. 1 are shown with the same numbers.

The difference between the present embodiment and the first embodiment is that the reception levels in the two states when the modulation operation by the modulation means 1 and the inverse modulation operation by the inverse modulation means 4 are performed and when they are not performed, This is to prevent erroneous carrier sense due to the image frequency signal.

In this embodiment, the modulation means 2 and the inverse modulation means 3
It is possible to switch between two states, that is, a state in which is operated and a state in which it is not operated. Further, a reception level detecting means 20 for detecting the signal level of the output of the channel selection filter 12 is provided.

It is assumed that the signal level detected by the reception level detecting means 20 is at the first level when the modulating means 2 and the inverse modulating means 4 are not operating (state (A) in FIG. 6).

Next, when the modulating means 1 and the inverse modulating means 4 are operated, when the received signal is the desired channel signal, the detected level becomes a value substantially equal to the first level. On the other hand, the level detected when the signal is the image frequency signal has a value smaller than the first level. This is because the image frequency signal is largely frequency-modulated by the modulation and inverse modulation operations, and its spectrum spreads wider than the bandwidth of the channel selection filter 12. Then, a part or most of the signal component is attenuated by the channel selection filter 12, so that the detection level in the reception level detecting means 20 becomes small (FIG. 6).
Medium (B) state).

Therefore, even if the carrier sensing means 9 outputs a signal with carrier, the detection level by the reception level detecting means 20 with modulation is much lower than the preset width as compared with the case without modulation. If you do,
The determination means 10 determines that there is no carrier sense. As a result, it is possible to prevent erroneous determination of presence of a carrier by the image frequency signal.

As described above, by providing the two states, it is possible to reduce power consumption during standby reception. That is, the carrier sense operation is first performed without the operation of the modulation and the inverse modulation, and when the output of the carrier sense means 9 is performed, the operation of the modulation and the inverse modulation is performed to confirm whether the image frequency signal is detected. It can be performed. This allows most of the operating time to be performed without modulation and inverse modulation, thus reducing the power consumed by the modulation and inverse modulation operations.

Also, with the configuration of this embodiment, the sensitivity suppressing characteristic of the reception due to the input of the image frequency signal can be improved in the demodulation operation. In the demodulation operation by the demodulation means 11, by operating the modulation means 2 and the inverse modulation means 4, the image frequency signal can be frequency-modulated to spread the spectrum. Here, the frequency shift amount of the modulation of the modulation means 2 is set to be larger than the frequency band of the channel selection filter 12. Therefore, the image frequency signal subjected to the operations of the modulation by the modulation means 2 and the inverse modulation by the inverse modulation means 4 is spread in spectrum due to the frequency spread.

For example, if the frequency shift amount of modulation is set to 5 times the pass band of the channel selection filter 12, the spectrum of the image frequency component becomes 10 times the pass band of the channel selection filter after the operation of inverse modulation. Diffused. In this case, the level of the image frequency component passing through the channel selection filter 12 is reduced to 1/10. On the other hand, since the modulation of the desired channel signal is canceled by the inverse modulation, all the components pass through the channel selection filter 12. Therefore, the level ratio between the desired channel signal and the image frequency signal can be improved, and the sensitivity suppression characteristic is improved by 10 dB. That is, the feature is that the modulation is set to be larger than the band of the channel selection filter 12 and then most of the components of the image frequency signal are removed by the channel selection filter 12.

Furthermore, it is possible to prevent erroneous demodulation of the image frequency signal. That is, since the image frequency signal is largely modulated by the modulation means and the inverse modulation means in addition to the original modulation, the demodulation means 11 cannot demodulate the original modulation. This makes it possible to avoid erroneous demodulation.

[0068]

As is apparent from the above description, the receiver of the present invention has the following effects.

A first local signal source, a modulation means, a mixer, an inverse modulation means, a carrier sense means, a modulation component detection means, and a determination means are provided, and the modulation means is the first local signal source. And mixing the output of the first local signal source and the received signal in the mixer, the inverse modulation means inversely modulates the output of the mixer so as to cancel the modulation component of the output of the mixer, The modulation component detection means detects the modulation component included in the output of the inverse modulation means, the signal level of the output of the mixer or the output of the inverse modulation means is detected by the carrier sense means, and the determination means is the modulation The output of the component detection means and the output of the carrier sense means are used to determine the presence or absence of a carrier, whereby the modulation component is detected when the image frequency signal is received. , The received signal can be determined whether the image frequency signal or a signal of the desired frequency, there is an effect that does not perform the determination of Yes carrier accidentally by the input of the image frequency signal. Further, there is an effect that the consumption current is increased due to an unnecessary receiving operation, and that carrier sensing is performed by confirming the carrier sense before the transmission so that the transmission cannot be disabled.

[Brief description of drawings]

FIG. 1 is a block diagram of a receiver according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of frequency relationships of signals processed by a receiver according to the first embodiment of the present invention.

FIG. 3 is a block diagram of a receiver according to a second embodiment of the present invention.

FIG. 4 is a block diagram of a receiver in Embodiment 3 of the present invention.

FIG. 5 is a block diagram of a receiver in Embodiment 4 of the present invention.

FIG. 6 is an explanatory diagram of frequency relationships of signals processed by a receiver according to the fourth embodiment of the present invention.

FIG. 7 is a block diagram of a conventional receiver.

[Explanation of symbols]

1 First local signal source 2 Modulation means 3 Second local signal source 4 Inverse modulation means 5 First mixer 6 Second mixer 7 computing means 8 Modulation component detection means 9 Carrier sense means 10 Judgment means 11 Demodulation means 12 channel selection filter 13 2 frequency divider 14 Receiver amplifier 15 antenna 16 Phase shifting means 17 Frequency changing means 18 Level fluctuation detection means 19 Variable filter 20 Reception level detection means

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Claims (10)

[Claims] 1. A first local signal source, a modulation means, a mixer, an inverse modulation means, a carrier sense means, a modulation component detection means, and a determination means, wherein the modulation means includes the first local signal source.
The local signal source is mixed, the output of the first local signal source and the received signal are mixed by the mixer, and the inverse modulation means reverses the output of the mixer so as to cancel the modulation component of the output of the mixer. Modulation, the modulation component detection means detects the modulation component contained in the output of the inverse modulation means, the signal level of the output of the mixer or the output of the inverse modulation means is detected by the carrier sense means, the determination The means is a receiver for determining the presence or absence of a carrier by using the output of the modulation component detecting means and the output of the carrier sensing means. 2. A first and a second mixer, a first and a second local signal source, a modulation means, an inverse modulation means, a carrier sense means, a modulation component detection means, and a determination means, The received signal and the output of the first local signal source modulated by the modulating means are mixed by the first mixer, and the second local area is inversely modulated by the inverse modulating means so as to cancel the modulation. The output of the signal source and the output of the first mixer are mixed in the second mixer, and the modulation component detection means detects the modulation component included in the output of the second mixer,
A receiver for detecting the signal level of the output of the second mixer by a carrier sensing means, and the judging means for judging the presence or absence of a carrier by using the output of the modulation component detecting means and the output of the carrier sensing means. 3. A first local signal source, a modulating means, a mixer, a variable filter, a carrier sense means, a level fluctuation detecting means, and a judging means, wherein the modulating means comprises the first local signal. Frequency-modulating the source, mixing the output of the first local signal source and the received signal in the mixer, inputting the output of the mixer to the variable filter, and changing the frequency characteristic or pass characteristic of the variable filter to the modulation. The level fluctuation detection means detects the level fluctuation of the output of the variable filter, the signal level of the output of the mixer or the output of the variable filter is detected by the carrier sense means, and the determination means is changed in synchronization. A receiver for determining the presence or absence of a carrier by using the output of the level fluctuation detecting means and the output of the carrier sensing means. 4. The receiver according to claim 3, wherein the variable filter is a channel selection filter. 5. The receiver according to claim 3, wherein the center frequency of the variable filter is varied so that the center frequency of the pass band of the variable filter is the same as the center frequency of the desired channel component of the mixer output. 6. The variable filter has a slope in insertion loss in a frequency band including a desired channel component of a mixer output,
4. The receiver according to claim 3, wherein the insertion loss of the variable filter is varied so that the output amplitude of the desired channel component of the variable filter becomes constant with respect to the modulation by the modulation means. 7. A first local signal source, a modulation means, a mixer, an inverse modulation means, a channel selection filter, a carrier sense means, a reception level detection means, and a determination means, and the modulation means. The first local signal source is modulated, the output of the first local signal source and the received signal are mixed by the mixer, and the inverse modulation means of the mixer is configured to cancel the modulation component of the output of the mixer. The output is inversely modulated, the output of the inverse modulator is input to the channel selection filter, the reception level detector detects the output level of the channel selection filter, and the signal level of the output of the channel selection filter is the carrier sense. Detection means and the determination means outputs the reception level detection means and / or the carrier sensor when the modulation means and the inverse modulation means are operated. Receiver for determining the presence or absence of a carrier by using the output of the receiving means and the output of the receiving level detecting means and / or the output of the carrier sensing means when the operations of the modulating means and the inverse modulating means are stopped. 8. A first local signal source, a modulation means, a mixer, an inverse modulation means, a channel selection filter, and a demodulation means, wherein the modulation means modulates the first local signal source, The output of the first local signal source and the received signal are mixed by the mixer, and the inverse modulation means inversely modulates the output of the mixer so as to cancel the modulation component of the output of the mixer, and the inverse modulation means of the inverse modulation means. A receiver for performing demodulation by inputting an output to the demodulation means via the channel selection filter. 9. The receiver according to claim 1, wherein the modulation means performs frequency modulation. 10. The receiver according to claim 1, wherein the modulating means performs phase modulation.