JP4415258B2 - Receiving machine - Google Patents

Description

  The present invention relates to a receiver, and more particularly to a receiver that performs demodulation by a superheterodyne method.

  In the conventional radio communication device, the transmission frequency band and the reception frequency band are determined, and cannot be changed. Therefore, in a wireless communication device that defines two frequency bands, a transmitter that uses a high frequency band is a receiver that uses a high frequency band, and a transmitter that uses a low frequency band is a receiver that uses a low frequency band. You can only communicate with the machine. For this reason, in order to perform wireless communication, it is necessary to select a communication device that matches the frequency band between the transmission side and the reception side.

  In view of such circumstances, a wireless communication device as in Patent Document 1 has been proposed. A wireless communication device described in Patent Document 1 includes a band filter for receiving / transmitting a signal in a high frequency band and a band filter for receiving / transmitting a signal in a low frequency band, and transmits or receives a signal And a receiver that employs a superheterodyne system in which a bandpass filter to be used can be switched according to the frequency.

According to the wireless communication device having such a configuration, the frequency band of the other party (communication device) can be switched according to the frequency band of the signal to be transmitted or received, and the frequency band between the transmission side and the reception side can be changed as necessary. It is possible to match the signals of two frequency bands with one wireless communication device.
JP-A-6-132847

According to the wireless communication device described in Patent Literature 1, it is possible to certainly carry out communication in two frequency bands with one wireless communication device.
However, in recent years, there is a strong tendency for communication devices to be reduced in size and thickness, and this tendency is particularly strong for portable wireless communication devices. On the other hand, the wireless communication device described in Patent Document 1 has a larger number of parts than the conventional wireless communication device by the amount of the band filter corresponding to a plurality of frequency bands and its peripheral devices. This means that it becomes larger than the conventional wireless communication device, which is contrary to the market trend. Of course, it is certain that the volume of the wireless communication device is greatly reduced as compared with the case of having a plurality of conventional wireless communication devices, but it is not desired that the communication device itself be enlarged.

  An object of the present invention is to provide a receiver that can receive radio waves in a plurality of frequency bands with a single receiver and that is not different from the conventional one, or that is smaller and thinner than the conventional one.

  In a receiver employing the superheterodyne method, a received signal and a signal from a local oscillator are mixed to obtain an intermediate frequency signal, and a low frequency signal is demodulated based on the intermediate frequency signal. For this reason, if a signal of a plurality of frequency bands can be generated by a local oscillator, it is considered unnecessary to provide a plurality of band filters, and a small and thin receiver can be realized.

Therefore, the receiver according to the present invention, an antenna for receiving a signal transmitted as a radio wave, a local oscillator for outputting an oscillation signal, an intermediate frequency by mixing the signal received and the oscillation signal by the antenna A receiver comprising a mixer for converting the signal into a signal and a detector for demodulating the intermediate frequency signal into a low frequency signal, wherein the local oscillator comprises a pair of reflectors disposed on a piezoelectric substrate; comprising a SAW resonator having a pair of IDT composed of comb-like electrodes provided in parallel between a pair of reflectors, and an amplifier connected in parallel to a pair of IDT disposed on the SAW resonator, A pair of switching circuits provided between each of the pair of comb-like electrodes constituting the IDT of the pair of IDTs and the amplifier, and the switching circuit based on the input frequency selection signal Control unit that switches synchronously, connects one of the pair of comb-shaped electrodes to the input side or output side of the amplifier, and connects the other of the pair of comb-shaped electrodes to the output side or input side of the amplifier It is characterized by having.

  According to the receiver having the above configuration, the connection of the input / output signal to one IDT of the SAW resonator provided in the local oscillator is fixed, and the connection of the input / output signal to the other IDT can be switched by the switching circuit. Thus, a plurality of oscillation modes having different modes, for example, the S0 mode (in-phase) and the A0 mode (antiphase) can be realized by one SAW resonator. For this reason, it becomes possible to oscillate signals in two frequency bands from one local oscillator, and it is possible to obtain two received signal frequencies that can be converted to the same intermediate frequency. Therefore, the receiver can receive signals of a plurality of frequency bands, but can be small and thin.

  In addition, since it is possible to switch the frequency band with one SAW resonator, it is not necessary to tune the frequency accuracy or the frequency shift accuracy. For this reason, it becomes easy to adjust the frequency accuracy and the frequency shift accuracy, and both the frequency accuracy and the frequency shift accuracy can be kept good. In addition, by always oscillating any one of the pair of IDTs as an oscillating unit that performs oscillating as a reference, a reference oscillating unit can be provided in one oscillator. For this reason, even if the input / output signal is switched to the other IDT, the phase can be immediately matched to the oscillation of the one IDT, and the discontinuity of the output phase can be eliminated.

  Moreover, it is good also as a structure provided with the 2nd local oscillator connected to the said 2nd mixer and the said 2nd mixer between the said mixer and the said detector. With such a configuration, a double superheterodyne receiver can be obtained, and stable communication is possible even when the width of a reception frequency band in which a plurality of reception frequency settings are possible is wide. In addition, since the local oscillator provided in the preceding stage can oscillate signals in a plurality of frequency bands, the width of the reception frequency band can be expanded as compared with a conventional double superheterodyne receiver. Furthermore, compared with a conventional receiver having an equivalent function, it is possible to realize a reduction in size and thickness.

  In the receiver having the above-described configuration, the second local oscillator is arranged in parallel between the pair of reflectors disposed on the piezoelectric substrate and the pair of reflectors, similarly to the local oscillator provided in the preceding stage. A SAW resonator having a pair of IDTs formed of comb-like electrodes and an amplifier connected in parallel to the pair of IDTs arranged in the SAW resonator, and the IDT of one of the pair of IDTs A pair of switching circuits provided between each of the pair of comb-like electrodes constituting the amplifier and the amplifier, and the switching circuits are switched synchronously based on the input frequency selection signal, and the pair of comb teeth And a controller that connects one of the electrodes to the input or output side of the amplifier and connects the other of the pair of comb-shaped electrodes to the output or input side of the amplifier.

With the receiver having such a configuration, the combination of the local oscillator, the second local oscillator, and the frequency band of the oscillation signal has four patterns, and the width of the reception frequency band in which a plurality of reception frequencies can be set is further increased. It can be expanded and stable communication is also possible.
Further, the pair of IDT disposed on the SAW resonator, it is preferable to so configure the crossing width of the comb-shaped electrodes in the same.

  With the above configuration, it is possible to synchronize oscillations by mutual IDTs and improve frequency accuracy and frequency shift accuracy. This is because the IDT in the SAW resonator causes a slight change in the output frequency by changing its crossing width. For this reason, a desired frequency system can be realized by adjusting (controlling) the crossing width of the comb-like electrodes constituting the IDT.

  Hereinafter, embodiments of the receiver according to the present invention will be described with reference to the drawings. Note that the embodiments disclosed below are some embodiments according to the receiver of the present invention, and the present invention includes various forms as long as the main part is not changed.

  The receiver according to the first embodiment of the present invention uses a detector to demodulate the frequency difference (intermediate frequency) of each signal obtained by mixing the received signal from the antenna and the oscillation signal from the oscillator with a mixer. It is a receiver that employs a super heterodyne system.

With reference to FIG. 1, the structure of the receiver 100 which concerns on this embodiment is demonstrated.
The receiver 100 according to the present embodiment includes an antenna 52 for receiving a transmission signal transmitted as a radio wave, and an oscillator (local oscillator) that oscillates a signal in a frequency band different from the frequency band of the signal received by the antenna 52. 50), a signal received by the antenna 52 and a signal oscillated by the local oscillator 50 are mixed (mixed) 58, and a signal frequency-converted by the mixer 58 is demodulated. The detector 64 is the basic configuration. The receiver 100 including such basic components is configured such that a mixer 58 is disposed between the antenna 52 and the local oscillator 50, and a detector 64 is provided after the mixer 58.

  Between the antenna 52 and the mixer 58, a radio frequency filter (RF filter) 54 for obtaining a signal in a frequency band within a set range from a received high frequency signal, and the RF filter 54 A high-frequency amplifier (RF amplifier) 56 that amplifies the filtered high-frequency signal (received signal) is provided.

  As described above, the reception signal amplified by the RF amplifier 56 is mixed with the output signal from the local oscillator 50 by the mixer 58, converted into an intermediate frequency signal, and output to the detector 64 side. Here, the intermediate frequency is the output of the frequency difference between the frequency of the received signal and the frequency of the output signal from the local oscillator.

  Between the mixer 58 and the detector 64, an intermediate frequency filter (IF filter) 60 for removing signals other than the set frequency band from the intermediate frequency signal, and the IF filter 60 performs filtering. And an intermediate frequency amplifier (IF amplifier) 62 for amplifying the intermediate frequency signal.

  The detector 64 demodulates the intermediate frequency signal output from the IF amplifier 62 into a low frequency signal and outputs it to the output terminal 66. Note that a speaker (loudspeaker), an earphone, or the like can be connected to the output terminal 66 so that the signal can be recognized by human perception.

  Hereinafter, the configuration of the local oscillator 50 will be described with reference to FIG. The local oscillator 50 according to the present embodiment includes a SAW resonator 10, an inverting amplifier (hereinafter referred to as an inverter) 20 as an amplifier circuit that transmits a signal to the SAW resonator 10, and a power supply terminal connected to the inverter 20. The SAW resonator 10 is provided in a positive feedback circuit of the inverter 20.

  In the present embodiment, the SAW resonator 10 includes a piezoelectric substrate 12, a pair of reflectors 14 a and 14 b disposed on one main surface of the piezoelectric substrate 12, and the pair of reflectors 14, as shown in FIG. 3. (14a, 14b) is constituted by a conductive pattern forming a plurality of comb-like electrodes 18 (18a, 18b, 18c, 18d).

The piezoelectric substrate 12 is made of a piezoelectric single crystal such as quartz, lithium tantalate (LiTaO ₃ ), lithium tetraborate (Li ₂ B ₄ O ₇ ), lithium niobate (LiNbO ₃ ), or a ZnO thin film. What is necessary is just to comprise with the provided sapphire substrate etc.

  The conductive pattern for forming the reflector 14 and the comb-like electrode 18 disposed on the piezoelectric substrate 12 is formed by forming a thin film of conductive metal such as gold, copper, or aluminum by vapor deposition or sputtering, and etching (eg, photo The pattern may be formed by a lithography technique.

  The reflector 14 disposed on the piezoelectric substrate 12 of the SAW resonator 10 mounted on the local oscillator 50 of the present embodiment is a conductive pattern formed in a ladder shape, and surface acoustic waves are formed on the piezoelectric substrate 12. Ladder-shaped electrode portions 15 are arranged so as to be orthogonal to the propagation direction. A pair of reflectors 14 are disposed on the piezoelectric substrate 12. The arrangement of the pair of reflectors 14a and 14b on the piezoelectric substrate is made in a direction along the propagation direction of the surface acoustic wave.

  The comb-like electrode 18 constitutes one IDT (interdigital transducer) 16 by meshing two of the comb-like electrode on the signal input side and the comb-like electrode on the signal output side. .

  A pair of IDTs 16 are arranged in parallel on the piezoelectric substrate 12 between the reflectors 14a and 14b. Specifically, on the piezoelectric substrate 12, the direction in which the pair of reflectors 14 a and 14 b are arranged, and the direction along the propagation direction of the surface acoustic wave between the reflectors 14 a and 14 b is used as an axis. A pair of IDTs 16a and 16b are arranged line-symmetrically. When the IDT 16 is disposed, an insulating portion along the propagation direction of the surface acoustic wave is provided between the IDT 16a and the IDT 16b. By disposing the IDT as described above, the comb-shaped electrode portion of the comb-shaped electrode 18 is disposed so as to be orthogonal to the propagation direction of the surface acoustic wave.

  In the SAW resonator 10 configured as described above, the signals input to the comb-shaped electrodes 18a to 18c constituting the IDTs 16a and 16b and the signals to be output are reversed, so that the same is achieved between the IDT 16a and the IDT 16b. Oscillations in different modes such as phase and antiphase can be realized (S0 mode and A0 mode in this embodiment). For this reason, it is possible to produce vibrations in a plurality of frequency bands (two in this embodiment) by one SAW resonator 10. In addition, since the frequency band can be switched by one SAW resonator 10, it is not necessary to oscillate by tuning the frequency accuracy and frequency shift accuracy of the plurality of SAW resonators. For this reason, it becomes easy to adjust the frequency accuracy and the frequency shift accuracy, and both the frequency accuracy and the shift accuracy can be kept good.

  Further, by always oscillating any one IDT 16 of the pair of IDTs 16 (16a, 16b) as an oscillating unit that performs the reference oscillation, the reference oscillating unit is included in one SAW resonator 10. Will have. For this reason, even if the input / output signal of the other IDT 16 is switched, the phase can be immediately matched with one IDT 16 serving as the reference oscillation unit, and the output phase is not discontinuous.

In the present embodiment, the S0 mode and the A0 mode refer to vibration forms as shown in FIG. That is, the S0 mode is a line target mode that is a basic mode, and the A0 mode is a point-symmetric mode that is a higher-order mode.
The configuration of an oscillator mounting the SAW resonator having the above configuration is as follows (see FIG. 2).

  That is, the IDT 16a and the IDT 16b constituting the SAW resonator 10 are connected in parallel to the inverter 20, and a switching circuit (switching means) 22 is provided between the IDT 16b and the inverter 20. It is possible to reverse the input / output signal to the comb-like electrode 18 constituting the. The switching means 22 is connected to a control section 51 for switching the connection of the switching means 22a and 22b in synchronization by inputting a frequency selection signal for selecting the frequency band of the signal output from the mixer 58. The controller 51 is provided with a frequency selection signal input terminal 51a for inputting the frequency selection signal.

  Specifically, the configuration is as follows. When the comb-like electrode 18a of the IDT 16a is an input electrode and the comb-like electrode 18b is an output electrode, an input signal path 30 for inputting an input signal to the IDT 16a, which is an output signal from the inverter 20, is used as the comb-teeth. An output signal path 40 that is an input signal to the inverter 20 and outputs an output signal from the IDT 16a is connected to the comb-like electrode 18b.

  Further, the input signal path 30 and the output signal path 40 are branched to form an input signal path 30a and an output signal path 40a. In the input / output signal paths 30a and 40a, the switching means 22 (22a, 22a, 22) for enabling switching between α and β for selecting one of the two systems of the S0 mode signal transmission path and the A0 mode signal transmission path. 22b).

  The S0 mode signal transmission path and the A0 mode signal transmission path that can be switched by the switching means 22 are respectively connected to the IDT 16b. In the IDT 16b, the output-side and input-side signal paths are respectively connected to both the comb-like electrode 18c and the comb-like electrode 18d. That is, when the input side S0 mode signal transmission path (input signal path) 32 when α is selected is connected to the comb-shaped electrode 18c, the output side S0 mode signal transmission path (output signal path) 36 when α is selected is a comb tooth. To the electrode 18d. In this case, the input side A0 mode signal transmission path (input signal path) 34 when β is selected is connected to the comb-shaped electrode 18d, and the output side A0 mode signal transmission path (output signal path) 38 when β is selected is a comb tooth. Connected to the electrode 18c.

  With such a circuit configuration, it is possible to reverse the input / output of signals to / from the IDT 16b by switching between α and β by the switching means 22. Note that the switching means 22a and 22b perform switching between α and β in synchronization.

  In the receiver configured as described above, the IDT 16a to which the input / output signal paths 30 and 40 are connected switches between the comb-like electrode 18a to which signals are input and the comb-like electrode 18b to which signals are output. Since this is not done, there is no change in the phase of the surface acoustic wave.

  On the other hand, in the IDT 16b to which the input / output signal paths 30a and 40a are connected, the input / output path is switched by switching the α / β of the input / output path under the control of the switching means 22, and the comb on the input side and the comb on the output side. The phase of the surface acoustic wave that oscillates is reversed by 180 ° with respect to the toothed electrode.

  For this reason, when the switching means 22 is set to α, the comb-like electrode 18a and the comb-like electrode 18c serve as signal input electrodes, and the surface acoustic waves oscillated by the IDT 16a and the IDT 16b have the same phase. As an oscillation circuit, SO mode oscillation is performed. On the other hand, when the switching means 22 is set to β, the comb-teeth electrode 18a and the comb-teeth electrode 18d are electrodes on the signal input side, and surface acoustic waves oscillated by the IDT 16a and the IDT 16b are in opposite phases and oscillate. As a circuit, the A0 mode oscillation is produced.

  In this way, the SAW resonator having the above-described configuration controls the input / output of signals to the comb-shaped electrodes 18a to 18d, so that one SAW resonator has two modes (in-phase and anti-phase: S0 mode and A0). Mode) oscillation can be realized.

  In general, it is known that a set of comb-like electrodes constituting a SAW resonator causes a change in oscillation frequency by changing the crossing width. Therefore, in the SAW resonator 10 mounted on the local oscillator 50 having the above-described configuration, the cross width of each comb-like electrode 18 constituting the IDT 16 is adjusted (controlled) according to desired frequency accuracy. As a result, the frequency difference (frequency deviation) can be adjusted as shown in FIG. As can be seen from FIG. 5, the frequency difference can be adjusted to a practical level by setting the crossing width. Note that the crossing width of the comb-like electrode 18 between the IDT 16a and the IDT 16b is configured to be the same. Thereby, the oscillation of the mutual IDT can be tuned, and the oscillation in the S0 mode and the A0 mode is possible.

  In the local oscillator 50 configured as described above, when the signal transmission path is connected to the SAW resonator 10, the input / output signal paths 30 and 40 are connected to the IDT 16a, and the input / output signal paths 30a and 40a are connected to the IDT 16b. The input / output signal paths 30 and 40 may be connected to the IDT 16b, and the input / output signal paths 30a and 40a may be connected to the IDT 16a.

  Two receivers that can be converted to the same intermediate frequency by switching the frequency band of the signal output from the local oscillator as necessary (switching the channel) as in the receiver having the above configuration. The frequency of the signal can be obtained. That is, as shown in FIG. 6, even when a disturbance wave is applied to channel 1 that is a high frequency band, it is possible to switch to channel 2 that is a low frequency band. For this reason, it is possible to perform communication by selecting a frequency band with less interference wave for communication. Therefore, even with ASK (Amplitude Shift Keying) communication that is easily affected by interference waves, it is possible to perform good communication. ASK communication is suitable for long-time wireless communication because power consumption can be suppressed compared to FSK communication.

  Next, a second embodiment according to the receiver of the present invention will be described with reference to FIG. The receiver 100a of the present embodiment has the same basic configuration as the receiver 100 according to the first embodiment. However, the receiver 100 according to the first embodiment employs a single superheterodyne system, whereas the receiver 100a according to the present embodiment employs a double superheterodyne system. Accordingly, the same components as those in the first embodiment are denoted by the same reference numerals and detailed description thereof is omitted.

  The receiver 100a of the present embodiment is configured to generate an intermediate frequency signal once more on the output side of the IF amplifier (referred to as the first IF amplifier in this embodiment) 62. More specifically, a high frequency signal received from the antenna 52 and a high frequency signal oscillated from a local oscillator (referred to as a first local oscillator in this embodiment) 50 are mixed by a mixer (referred to as a first mixer in this embodiment) 58. The intermediate frequency signal obtained in this embodiment (referred to as the primary intermediate frequency signal in this embodiment) is further mixed with a high frequency signal to obtain a secondary intermediate frequency signal, which is demodulated.

As a specific configuration of the receiver 100a, a second mixer 72 is provided after the first IF amplifier 62, and the output terminal of the second local oscillator 70 is connected to the second mixer 72. The output signals from both sides are mixed to output a secondary intermediate frequency signal. Further, a second IF filter 74 for filtering the secondary intermediate frequency signal and a second IF amplifier 76 for amplifying the filtered secondary intermediate frequency signal are provided at the subsequent stage of the second mixer 72. The detector 64 is connected to the output side of the second IF amplifier 76.
Note that the second local oscillator 70 in the present embodiment may be a high-frequency oscillator using a general SAW resonator or the like.

  In the receiver 100a having such a configuration, image interference (reception) can be eliminated, and stable communication can be performed while receiving signals in a wider frequency band.

Next, a third embodiment according to the receiver of the present invention will be described.
The receiver according to the present embodiment is almost the same as the structure of the receiver 100a according to the second embodiment, and the configuration of the second local oscillator 70 is the same as the configuration of the first local oscillator 50. The point is different. Therefore, in the receiver of this embodiment, the second local oscillator 70 is provided with a control unit 71 similar to the first local oscillator 50 and a frequency selection signal input terminal 71a.

  In the receiver according to the present embodiment having such a feature, since the combinations of signals for obtaining the secondary intermediate frequency signal are four patterns, the generated secondary intermediate frequency signals are also in four frequency bands. It will be possible to obtain. Therefore, the number of frequency bands that can be selected to avoid interference waves in communication increases. For this reason, even if the reception frequency band is expanded, stable communication is possible.

It is a block diagram which shows schematic structure of the receiver which concerns on the 1st Embodiment of this invention. It is a figure which shows the structure of the local oscillator of the receiver of this invention. It is a figure which shows the SAW resonator used for the local oscillator of this invention. It is a figure which shows the oscillation mode of a SAW resonator. It is a figure which shows the change of the frequency difference at the time of changing the cross width of the comb-tooth shaped electrode of a SAW resonator. It is a figure which shows an example effective when switching a transmission radio wave. It is a block diagram which shows schematic structure of the receiver which concerns on the 2nd and 3rd Embodiment of this invention.

Explanation of symbols

  10 ... SAW resonator, 12 ... Piezoelectric substrate, 14 (14a, 14b) ... Reflector, 16 (16a, 16b) ... IDT, 18 (18a, 18b, 18c, 18d) ... ... Comb-like electrode, 20 ......... Inverter (inverted amplifier), 22 (22a, 22b) ......... Switching means, 42 ......... Power supply terminal, 50 ...... Local oscillator, 51 ... Control unit, 51a ......... Frequency selection signal input terminal, 52 ......... Antenna, 54 ... RF filter, 56 ... RF amplifier, 58 ... Mixer, 60 IF filter, 62 IF amplifier, 64 ……… Detector, 66 ……… Output terminal.

Claims (4)

An antenna that receives a signal transmitted as a radio wave ; a local oscillator that outputs an oscillation signal ; a mixer that mixes the signal received by the antenna and the oscillation signal to convert the signal to an intermediate frequency signal; A receiver comprising a detector for demodulating a frequency signal into a low frequency signal,
The local oscillator includes a SAW resonator having a pair of reflectors disposed on a piezoelectric substrate, and a pair of IDTs composed of comb-like electrodes provided in parallel between the pair of reflectors;
Comprising an amplifier connected in parallel to a pair of IDT disposed on the SAW resonator,
A pair of switching circuits provided between each of the pair of comb-like electrodes constituting the IDT of one of the pair of IDTs and the amplifier;
The switching circuit is switched synchronously based on the input frequency selection signal, one of the pair of comb electrodes is connected to the input side or the output side of the amplifier, and the other of the pair of comb electrodes is connected to the input side. A control unit connected to the output side or input side of the amplifier;
A receiver comprising:   The reception according to claim 1, wherein a second mixer and a second local oscillator connected to the second mixer are provided between the mixer and the detector. Machine. The second local oscillator includes a SAW resonator having a pair of reflectors disposed on a piezoelectric substrate, and a pair of IDTs composed of comb-like electrodes provided in parallel between the pair of reflectors;
An amplifier connected in parallel to a pair of IDTs disposed in the SAW resonator;
A pair of switching circuits provided between each of the pair of comb-like electrodes constituting the IDT of one of the pair of IDTs and the amplifier;
The switching circuit is switched synchronously based on the input frequency selection signal, one of the pair of comb electrodes is connected to the input side or the output side of the amplifier, and the other of the pair of comb electrodes is connected to the input side. A control unit connected to the output side or input side of the amplifier;
The receiver according to claim 2, comprising: The receiver according to any one of claims 1 to 3, wherein the pair of IDTs arranged in the SAW resonator have the same cross width of comb-like electrodes.

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