JP2002135144A - Receiving set - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small and low-cost receiving set which has superior image disturbance-proof characteristics. SOLUTION: This receiving set provides a local signal source 5, which outputs a frequency which is ((2n-1)/4) times (where n: a natural number) a channel frequency interval, as high as or as low as a desired channel frequency of a receiving signal; a mixer 4, which inputs the receiving signal and the output of the local signal source, converts to an intermediate frequency signal and outputs it; a channel selecting filter 6, which inputs the intermediate frequency signal and passes only the desired channel components; and a decoder circuit 7 which inputs the output of the channel selecting filter 6 and decodes it. Thus, since the image frequency signal components can be made small, this receiving set enables obtaining superior image disturbance-proof characteristics, even if the amount of attenuation of the filter for elimination of the image components is small.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a receiver mainly used for a wireless communication device such as a cordless remote controller, a pager, a cordless telephone, and a portable telephone.

[0002]

2. Description of the Related Art A conventional receiver will be described with reference to the drawings. FIG. 8 is a block diagram showing a configuration of a conventional receiver.

In FIG. 8, 1 is an antenna, 3 is a high frequency amplifier, 6 is a channel selection filter, 7 is a demodulation circuit, 8
Is a demodulated data output terminal, 21 is a high frequency filter, 22 is an intermediate frequency filter, 23 is a first local signal source, 24 is a second local signal, 25 is a first mixer, and 26 is a second mixer. The receiver shown in FIG. 8 shows a configuration of a double superheterodyne system. The received signal input to the antenna is input to a high frequency filter to remove unnecessary frequency components. Here, in particular, the image frequency component at the time of frequency conversion by the first mixer is removed to ensure the image interference resistance.

[0004] Next, the output of the high frequency filter 21 is amplified by the high frequency amplifier 3. The output of the high-frequency amplifier 3 and the output of the first local signal source 23 are mixed by a first mixer 25 and converted into a first intermediate frequency signal. The first intermediate frequency signal is input to the intermediate frequency filter 22, where the image frequency component at the time of frequency conversion by the second mixer 26 is removed. Intermediate frequency filter 2
2 and the output of the second local signal source 24 are mixed by a second mixer 26 and converted into a second intermediate frequency signal. The second intermediate frequency signal is input to the channel selection filter 6, and unnecessary components other than the desired channel component are removed. The output of the channel selection filter 6 is a demodulation circuit 7
And the demodulated output is output from the demodulated data output terminal 8.

[0005]

However, the conventional receiver requires the use of a plurality of filters for removing image frequency components, and has a problem that it is difficult to reduce the size of the receiver. In addition, there is a problem that the cost of a filter or the like is high.

As another configuration, the number of filters can be reduced by the single superheterodyne method, but a filter for removing image frequency needs to have a steep attenuation characteristic, and it is difficult to reduce the size and cost of the filter. . Further, in the direct conversion method, since the intermediate frequency component is around 0 Hz, there is a problem that it is difficult to secure a dynamic range, and an auxiliary circuit needs to be added, so that downsizing and cost reduction cannot be realized.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned conventional problems, a receiver according to the present invention uses a channel frequency interval ((2n-1) / 4) from a desired channel frequency of a received signal.
A local signal source that outputs a frequency that is higher or lower by a factor (where n is a natural number), a mixer that receives the received signal and the output of the local signal source, converts the signal into an intermediate frequency signal, and outputs the intermediate frequency signal. It has a channel selection filter that inputs and passes only desired channel components, and a demodulation circuit that receives the output of the channel selection filter and performs demodulation. Since the signal component of the image frequency can be reduced, good image disturbance resistance can be obtained even if the amount of attenuation of the filter for removing the image component is small.

[0008]

According to the first aspect of the present invention, the channel frequency interval ((2)
a local signal source that outputs a frequency higher or lower by n-1) / 4) times (where n is a natural number), and a mixer that inputs the received signal and the output of the local signal source, converts the signal into an intermediate frequency signal, and outputs the intermediate frequency signal And a channel selection filter that receives the intermediate frequency signal and passes only the desired channel component, and a demodulation circuit that receives the output of the channel selection filter and performs demodulation. Since the signal component of the image frequency can be reduced, good image disturbance resistance can be obtained even if the amount of attenuation of the filter for removing the image component is small.

According to a second aspect of the present invention, the channel frequency interval ((2n-1)) is more than the desired channel frequency of the received signal.
/ 4) a local signal source that outputs a frequency higher or lower by a factor of n (where n is a natural number), and an image rejector that receives the output of the received signal and the local signal source, suppresses image frequency components, and outputs an intermediate frequency signal. A mixer for inputting the intermediate frequency signal and passing only the desired channel component; and a demodulation circuit for inputting the output of the channel selection filter and performing demodulation. Since the image frequency component can be further reduced, a high image interference resistance can be obtained even if a filter for removing the image component is omitted.

According to a third aspect of the present invention, there is provided a local signal source for outputting a frequency higher or lower by three-fourths of a channel frequency interval than a desired channel frequency of a received signal, and an output of the received signal and the output of the local signal source. A mixer that inputs and converts the signal into an intermediate frequency signal and outputs the signal; a channel selection filter that receives the intermediate frequency signal and passes only the desired channel component; and a demodulation circuit that receives and demodulates the output of the channel selection filter. Things. Since the frequency of the intermediate frequency signal can be reduced and does not include a frequency component near DC, it is easy to configure the channel selection filter with a transistor or the like and incorporate it in the semiconductor integrated circuit, thereby reducing the size and cost. Can be realized.

According to a fourth aspect of the present invention, there is provided a local signal source for outputting a frequency higher or lower by three-fourths of a channel frequency interval than a desired channel frequency of a received signal, and an output of the received signal and the output of the local signal source. An image rejection mixer that inputs and suppresses image frequency components and outputs an intermediate frequency signal, a channel selection filter that receives the intermediate frequency signal and passes only desired channel components, and receives an output of the channel selection filter and performs demodulation. And a demodulation circuit for performing the demodulation. Since the frequency of the intermediate frequency signal can be reduced and does not include a frequency component near DC, it is easy to configure the channel selection filter with a transistor or the like and incorporate it in the semiconductor integrated circuit, thereby reducing the size and cost. Can be realized.

According to a fifth aspect of the present invention, reception is performed by switching the frequency of a local signal source between a frequency higher and lower by a predetermined frequency than a desired channel frequency of a received signal. In addition, the frequency of occurrence of image disturbance can be reduced, and communication reliability can be improved.

[0013]

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

(First Embodiment) FIG. 1 is a block diagram showing a configuration of a receiver according to a first embodiment of the present invention.

FIG. 2 is a graph showing a frequency spectrum of a received signal input to the mixer.

FIG. 3 is a graph showing the frequency spectrum of the intermediate frequency signal input to the channel selection filter.

The receiver of this embodiment will be described with reference to FIGS. 1, 2 and 3.

In FIG. 1, 1 is an antenna, 2 is a high frequency filter, 3 is a high frequency amplifier, 4 is a mixer, 5 is a local signal source, 6 is a channel selection filter, 7 is a demodulation circuit, and 8 is a demodulated data output terminal. .

The received signal input to the antenna is input to the high frequency filter 2. Here, the high-frequency filter 2 is provided to remove unnecessary frequency components, but has a relatively simple configuration, and the amount of attenuation of the image frequency components of the mixer described later is the same as that of the high-frequency filter 21 described in the conventional example. Can be smaller. In the conventional receiver, a SAW filter or the like is used to secure the amount of out-of-band attenuation. In this embodiment, a small and low-cost CR filter is used. That is, since the amount of attenuation of the image frequency component required for the high-frequency filter 2 is small, it is possible to realize the high-frequency filter 2 in a small size and at low cost.

The output of the high frequency filter 2 is a high frequency amplifier 3
, And is input to the mixer 4 and mixed with the output of the local signal source 5. Here, the frequency of the local signal source 5 is set to a frequency lower than the desired channel frequency of the received high-frequency signal by ((2n-1) / 4) times (where n is a natural number) the channel frequency interval. By selecting the local signal frequency as described above, the image frequency of the mixer 4 can be set to a frequency band in which the signal components between channels are relatively small.

FIG. 2 shows the frequency spectrum of the received signal when the local signal source frequency is set to a frequency corresponding to the case where n = 2 in the above relational expression. The frequency of the local signal source is set to a frequency that is lower than the desired channel frequency by three quarters of the channel frequency interval. In this case, the image frequency is the middle frequency between the lower adjacent channel frequency and the lower next adjacent channel frequency. In this frequency band, the signal components of the adjacent channel and the next adjacent channel are small.

As an example, a 400 MHz band specific low power radio band in Japan will be described. In the specific low power radio band, the channel frequency interval is 12.5 KHz. The typical occupied bandwidth of the transmission signal is 5.5 KHz, and the bandwidth of a relatively small signal component between channels is 7.0 KHz.
The bandwidth of the channel selection filter 6 on the receiving side is 8.
It is 0 KHz. Therefore, by selecting the band between the channels as the image frequency, most of the signal components of the adjacent and next adjacent channels that interfere can be attenuated by the channel selection filter 6, so that the image interference can be prevented. However, if the bandwidth of the channel selection filter 6 is slightly larger than the bandwidth of the relatively small signal component, the adjacent and next adjacent channel components cannot be completely removed. By giving the insufficient amount of attenuation to the characteristics of the high-frequency filter 2, the anti-interference characteristics can be improved. Further, by setting the band of the channel selection filter 6 to a relatively narrow band such as 6 KHz, it is possible to improve the anti-interference characteristics.

The intermediate frequency signal output from the mixer 4 is input to the channel selection filter 6. FIG. 3 shows a frequency spectrum of the intermediate frequency signal. On both sides of the desired channel component, there is a lower adjacent channel component and a lower next adjacent channel component of frequency aliasing. Then, the component other than the desired channel component is attenuated by the channel selection filter 6, thereby obtaining the anti-interference characteristic.

The output of the channel selection filter 6 is input to a demodulation circuit 7, where a demodulation operation is performed, and demodulation data is output from a demodulation data output terminal 8.

In this embodiment, the case where n = 2 has been described, but n may be an arbitrary natural number. Further, although the local signal frequency is selected to be lower than the desired channel frequency by a certain frequency, the same effect can be obtained by selecting the local signal frequency to be higher than the desired channel frequency by a certain frequency.

As described above, by setting the local signal source frequency so that the image frequency becomes a frequency in the middle of the channel interval, it is not necessary to attenuate the image frequency component by the high frequency filter or the intermediate frequency filter as in the related art. , Or the required deduction amount can be reduced. Therefore, the filter can be simplified, and the size and cost of the device can be reduced.

In particular, when n = 2, the desired channel component of the intermediate frequency signal has a relatively low frequency, which is advantageous for forming a channel selection filter on a semiconductor integrated circuit. This makes it possible to realize a channel selection filter whose characteristics are stable at a low current. Furthermore, since the desired channel component of the intermediate frequency signal does not include a component near DC, it is possible to adopt a configuration in which DC is separated by inserting a capacitor or the like between the stages of the multi-stage active filter. Thereby, the influence of the DC drift of the circuit can be suppressed, and the dynamic range can be widened. Since there is no need to pass a DC component, the capacitance of the capacitor between the stages may be relatively small, and it is possible to use a capacitor on a semiconductor integrated circuit. As a result, the size and cost of the device can be reduced.

When n = 1, since there is no other channel component such as an adjacent channel at a frequency lower than the desired channel component of the intermediate frequency signal, there is an advantage that the channel selection filter can be constituted by a low-pass filter. Also in this case, the configuration is suitable for a semiconductor integrated circuit of the channel selection filter.

When n is increased, the image frequency becomes a frequency separated from the desired channel frequency.
In this case, there is a feature that the high frequency filter is easily provided with a characteristic of attenuating the image frequency component. Of the required attenuation amounts of the channel frequency components above and below the image frequency, the shortage of the channel selection filter can be compensated for by the high frequency filter, so that there is an advantage that the image interference resistance can be improved.

(Embodiment 2) FIG. 4 is a block diagram showing a configuration of a receiver according to Embodiment 2 of the present invention. FIG. 5 is a block diagram showing a configuration of an image rejection mixer which is a component of the present invention. FIG. 6 is a graph showing the frequency spectrum of the intermediate frequency signal input to the channel selection filter.

In FIG. 4, reference numeral 10 denotes an image rejection mixer. The same components as those in FIG. 1 are denoted by the same reference numerals.

In FIG. 5, reference numeral 11 denotes a reception signal input terminal;
12 is a mixer, 13 is a +90 degree phase shifter, 14 is a +45 degree phase shifter, 15 is a -45 degree phase shifter, 16 is an adder, 17 is an intermediate frequency signal output terminal, and 18 is a local signal input terminal. .

The receiver of this embodiment will be described with reference to FIGS.

The difference between this embodiment and the first embodiment is that the image rejection filter is used to improve the image interference resistance.

First, the operation of the image rejection mixer shown in FIG. 5 will be described. The reception signal input to the reception signal input terminal 11 is branched and input to the two mixers 12. The local signal input to the local signal input terminal 18 is branched and input to the two mixers 12. In the following, the phase near the image frequency signal is considered.

The local signals input to the two mixers 12 are orthogonal to each other because the + 90-degree phase shifter 13 is inserted in one path. The received signal and the local signal are mixed by the two mixers 12, respectively, and the converted signal is output. One of the converted signals is input to the adder 16 via the +45 degree phase shifter 14. The other is -45
The signal is input to the adder 16 via the phase shifter 15.
The signal obtained by adding the two signals is an intermediate frequency signal output terminal 1
7 is output. In the image rejection mixer 10 having the above configuration, the local signals orthogonal to each other are input to the two mixers 12, and the output signals of the two mixers 12 are also orthogonal to each other. And the +45 degree phase shifter 1
The relative phase difference is further increased by 90 by the 4 and -45 degree phase shifter 15.
The degree has been increased. Here, the image frequency component is 2
Since the outputs of the two mixers have phases opposite to each other, the adder 16
They are canceled by each other.

FIG. 6 shows the frequency spectrum of the intermediate frequency signal. In this embodiment, n = 2. As shown in FIG. 6, the levels of the lower adjacent channel frequency component and the lower next adjacent channel frequency component are attenuated by the effect of the image rejection mixer 10. Here, when the image rejection mixer 10 is configured on a semiconductor integrated circuit, a typical image suppression amount is about 30.
dB. Also, setting the image frequency between channels has the effect of reducing the level by about 30 dB. Therefore, a total of about 60 dB of image disturbance resistance can be obtained.

As described above, by using the image rejection mixer 10, the lower adjacent and next adjacent channel frequency components passing through the channel selection filter 6 can be greatly reduced, and a good anti-jamming wave characteristic can be obtained. can get.

Third Embodiment FIG. 7 is a graph showing a frequency spectrum of an intermediate frequency signal input to a channel selection filter of a receiver according to a third embodiment of the present invention. The configuration of the receiver of this embodiment is the same as that of the first embodiment or the second embodiment.

The feature of this embodiment is that the local signal frequency is switched according to the communication conditions. That is, the frequency of the local signal source is ((2n-1) / 4) times ((2n-1) / 4) times lower than the desired channel frequency to be received by a channel frequency interval ((2n-1) / 4) (where n is a natural number). (n: natural number). The local signal source is constituted by a PLL frequency synthesizer, and the frequency is switched by changing the frequency division number of the frequency divider. FIG. 7 shows a case where n = 2. In FIG. 7, as an example of the communication state, a transmission signal of a relatively large level exists in the lower adjacent channel and the lower next adjacent channel. This shows a state where the transmission signal of the upper adjacent channel or the upper next adjacent channel does not exist or the level is low. Here, when the local signal frequency is set lower than the desired channel, there is a relatively high possibility of image disturbance. On the other hand, if it is set to a higher side than the desired channel, the possibility of image disturbance is reduced. If sensitivity cannot be obtained while monitoring the error rate of demodulated data, reception can be continued by switching the local signal source frequency as described above. When the local signal source frequency is switched, the polarity of the demodulated data output must also be switched at the same time.

The method described in the present embodiment is particularly effective when the mixer is a normal mixer other than the image rejection mixer as in the first embodiment. When a normal mixer is used, the image interference resistance tends to be slightly insufficient, and can be compensated for by performing control as in the present embodiment.

Incidentally, even when the image rejection mixer is used as in the second embodiment, the configuration of the present embodiment enables more stable reception.

[0043]

As is apparent from the above description, the following effects can be obtained according to the receiver of the present invention.

A local signal source for outputting a frequency higher or lower by ((2n-1) / 4) times (where n is a natural number) times a channel frequency interval than a desired channel frequency of a received signal; the received signal and the local signal; A mixer that receives the output of the source and converts it to an intermediate frequency signal and outputs the signal; a channel selection filter that receives the intermediate frequency signal and passes only the desired channel component; and a demodulation that receives and demodulates the output of the channel selection filter. Since the circuit is provided and the signal component of the image frequency can be reduced, there is an effect that even if the amount of attenuation of the filter for removing the image component is small, good image disturbance resistance can be obtained.

A local signal source for outputting a frequency higher or lower by ((2n-1) / 4) times (where n is a natural number) times the channel frequency interval than the desired channel frequency of the received signal; An image rejection mixer that receives an output of a local signal source, suppresses image frequency components and outputs an intermediate frequency signal, a channel selection filter that receives the intermediate frequency signal and passes only desired channel components, and a channel selection filter. Since a demodulation circuit for inputting and demodulating the output is provided and the image frequency component can be further attenuated, there is an effect that a high image interference resistance can be obtained even if a filter for removing the image component is omitted.

Further, a local signal source for outputting a frequency higher or lower by three-fourths of a channel frequency interval than a desired channel frequency of a received signal, an output of the received signal and the output of the local signal source, and an image frequency component are inputted. An image rejection mixer that suppresses and outputs an intermediate frequency signal;
A channel selection filter that receives the intermediate frequency signal and passes only the desired channel component, and a demodulation circuit that receives an output of the channel selection filter and performs demodulation;
Since the frequency of the intermediate frequency signal can be reduced and does not include a frequency component near DC, it is easy to configure the channel selection filter with a transistor or the like and incorporate it in a semiconductor integrated circuit, and to achieve a reduction in size and cost. This has the effect.

Further, since the frequency of the local signal source is switched between a higher frequency and a lower frequency by a predetermined frequency from the desired channel frequency of the received signal and reception is performed, the frequency of occurrence of image interference can be reduced. .

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating a frequency spectrum of a received signal according to the first embodiment of the present invention.

FIG. 3 is a diagram illustrating a frequency spectrum of an intermediate frequency signal according to the first embodiment of the present invention.

FIG. 4 is a block diagram of a receiver according to a second embodiment of the present invention.

FIG. 5 is a block diagram of an image rejection mixer according to a second embodiment of the present invention.

FIG. 6 is a diagram illustrating a frequency spectrum of an intermediate frequency signal according to a second embodiment of the present invention.

FIG. 7 is a diagram illustrating a frequency spectrum of an intermediate frequency signal according to a third embodiment of the present invention.

FIG. 8 is a block diagram of a conventional receiver.

[Explanation of symbols]

 2 High frequency filter 4 Mixer 5 Local signal source 6 Channel selection filter 7 Demodulation circuit 8 Demodulation data output terminal 10 Image rejection mixer

Claims (5)

[Claims] 1. A local signal source for outputting a frequency higher or lower by ((2n-1) / 4) times (where n is a natural number) times a channel frequency interval than a desired channel frequency of a received signal; A mixer that receives the output of the local signal source, converts the output to an intermediate frequency signal, and outputs the input signal; a channel selection filter that receives the intermediate frequency signal and passes only the desired channel component; and inputs and demodulates the output of the channel selection filter. Receiver with demodulation circuit to perform. 2. A local signal source for outputting a frequency higher or lower by ((2n-1) / 4) times (where n is a natural number) times a channel frequency interval than a desired channel frequency of a received signal; An image rejection mixer that receives an output of a local signal source, suppresses image frequency components and outputs an intermediate frequency signal, a channel selection filter that receives the intermediate frequency signal and passes only desired channel components, and a channel selection filter. A receiver equipped with a demodulation circuit that receives an output and performs demodulation. 3. A local signal source that outputs a frequency higher or lower by three-fourths of a channel frequency interval than a desired channel frequency of a received signal, and an output of the received signal and the output of the local signal source, which is input to an intermediate frequency signal. A receiver comprising: a mixer that converts and outputs a signal; a channel selection filter that receives the intermediate frequency signal and passes only a desired channel component; and a demodulation circuit that receives an output of the channel selection filter and performs demodulation. 4. A local signal source for outputting a frequency higher or lower by three-fourths of a channel frequency interval than a desired channel frequency of a received signal, an output of the received signal and an output of the local signal source, and an image frequency component is input. An image rejection mixer that suppresses and outputs an intermediate frequency signal, a channel selection filter that receives the intermediate frequency signal and passes only a desired channel component, and a demodulation circuit that receives an output of the channel selection filter and performs demodulation. Receiving machine. 5. The receiver according to claim 1, wherein the reception is performed by switching the frequency of the local signal source to a frequency higher or lower by a predetermined frequency than a desired channel frequency of the received signal.