JP2007336340A - Fsk transceiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an FSK transceiver with a miniaturized circuit scale. <P>SOLUTION: The FSK transceiver 10 is provided with an antenna 19, a transmission part 20 connected to the antenna 19, a reception part 30 connected to the antenna 19, a plurality of SAW elements 14 that excite SAWs mutually having different frequencies, a first switch part 12 that selects either of the transmission part 20 and the reception part 30 so as to connect it with a plurality of the SAW elements 14, and a second switch part 22 that selects any one of a plurality of the SAW elements 14 when a plurality of the SAW elements 14 are connected to the transmission part 20. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to frequency shift keying (FSK) transceivers.

  A transceiver 100 (FSK transceiver) 100 that uses the FSK communication system includes a transmission unit 110 and a reception unit 120, as shown in FIG. The transmission unit 110 includes an oscillator 111, an amplifier 112, a filter 113, and a transmission antenna 114. The oscillator 111 includes a surface acoustic wave (SAW) element 115 and an oscillation circuit 116 that resonates the element and outputs a signal. The oscillation circuit 116 includes a variable capacitance diode 117 and an expansion coil 118 in order to shift the frequency in response to binary “0” and “1” signals input from the signal input terminal 119. When the binary signal is input to the oscillator 111, the oscillator 111 causes the SAW element 115 to resonate and outputs a signal having a frequency f0 corresponding to the “0” signal and a signal having a frequency f1 corresponding to the “1” signal. The signal output from the oscillator 111 is transmitted from the transmission antenna 114 through the amplifier 112 and the filter 113.

  The receiving unit 120 includes a receiving antenna 121, a high frequency (RF) filter 122, a low noise amplifier (LNA 123), a mixer 124, a local oscillator 126, an intermediate frequency (IF) filter 127, an IF amplifier 128, and a frequency-voltage (FV). A converter 129 and a comparator 130 are provided. Then, the signal transmitted from the FSK transmitter as the other party is input to the mixer 124 through the receiving antenna 121, the RF filter 122 and the LNA 123. The mixer 124 also receives a signal from the local oscillator 126, down-converts the signal input from the LNA 123, and outputs it. The down-converted signal is input to the FV converter 129 through the IF filter 127 and the IF amplifier 128. The FV converter 129 replaces the frequency change of the input signal with a voltage change and outputs the voltage change to the comparator 130. The comparator 130 compares the signal input from the FV converter 129 with the input reference voltage Vref and outputs binary “0” and “1” signals. Patent Document 1 discloses such a transmitter / receiver.

Patent Document 2 discloses a modulator and a transmitter. The transmitter disclosed in Patent Document 2 includes an oscillation circuit connected to each of a plurality of SAW elements having different resonance frequencies, and a switching circuit that selects any one of these oscillation circuits according to a digital modulation signal. And.
Japanese Patent Laid-Open No. 11-196139 (FIG. 15) Japanese Patent No. 2925158

In the FSK transceiver described above, the transmitter is provided with an oscillator, and the receiver is provided with a local oscillator. For this reason, since an oscillator is required for each of the transmission unit and the reception unit, the circuit scale of the transmission unit and the reception unit is increased, and the FSK transceiver cannot be reduced in size. In addition, since the oscillator requires a variable capacitance diode and an extension coil for modulation, the number of parts increases. For this reason, the FSK transceiver cannot be reduced in size.
An object of the present invention is to provide a miniaturized FSK transceiver.

  The FSK transceiver according to the present invention includes a plurality of SAW elements that excite SAWs having different frequencies, a transmission unit using the FSK communication method, a reception unit using the FSK communication method, and any of the transmission unit and the reception unit. It is characterized by comprising a first switch unit that selects one of them and connects to a plurality of SAW elements. The oscillation unit includes an oscillation circuit and an amplifier. As a result, the transmitting unit and the receiving unit can share the SAW element, so that it is not necessary to provide a local oscillator for each of the transmitting unit and the receiving unit, and the circuit scale of the FSK transceiver can be reduced. The transmission unit performs transmission using a signal obtained by resonating the SAW element piece. For this reason, the transmission unit does not need to include a variable capacitance diode and an extension coil for modulation, and thus the number of parts of the transmission unit can be reduced. Therefore, the FSK transceiver can be downsized.

  An FSK transceiver according to the present invention includes an antenna, a transmission unit connected to the antenna, a reception unit connected to the antenna, a plurality of SAW elements that excite SAWs having different frequencies, a transmission unit, and a reception unit. A first switch unit that selects any one of the units and connects to a plurality of SAW elements; and a second switch that selects any one of the plurality of SAW elements when a plurality of SAW elements are connected to the transmission unit. And a switch part. As a result, the transmitting unit and the receiving unit can share the SAW element, so that it is not necessary to provide a local oscillator for each of the transmitting unit and the receiving unit, and the circuit scale of the FSK transceiver can be reduced. Further, the transmission unit obtains signals having different frequencies by selecting the SAW element piece by the second switch unit. Therefore, FSK modulation can be performed by switching the switch unit. And since the transmission part does not need to be provided with a variable capacitance diode and an extension coil for modulation, the number of parts of the transmission part can be reduced. Therefore, the FSK transceiver can be downsized.

  The antenna described above is connected to a third switch unit that selects one of the transmission unit and the reception unit. The third switch unit is configured to be switched in conjunction with the first switch unit. As a result, the antenna can be shared by the transmission unit and the reception unit, so that the FSK transceiver can be downsized.

  In addition, the receiving unit described above includes a detection circuit in the subsequent stage of the SAW element connected to the receiving unit by switching the first switch unit, and the detection circuit is formed by connecting a limiter, a frequency discriminator, and a comparator in series. It is characterized by. As a result, a direct detection type receiver can be configured. In addition, the receiving unit does not require a conventionally used down-conversion component, and the circuit scale and the number of components can be reduced. Therefore, the FSK transceiver can be downsized.

  The plurality of SAW elements described above are characterized in that two sets of IDTs for resonating at different frequencies are provided on one piezoelectric substrate. Thereby, a SAW element can be reduced in size. Therefore, the FSK transceiver equipped with this SAW element can be further downsized.

  The best embodiment of the FSK transceiver according to the present invention will be described below. FIG. 1 is a block diagram of an FSK transceiver. The FSK transceiver 10 includes a transmission unit 20 using the FSK communication method, a reception unit 30 using the FSK communication method, and a first switch unit 12 (12a, 12b provided in common with the transmission unit 20 and the reception unit 30. , 12c, 12d), and a plurality of SAW elements 14 (14a, 14b) provided in common to the transmission unit 20 and the reception unit 30.

  Specifically, each SAW element 14 has a configuration in which an interdigital electrode (IDT), a reflector, and the like are provided on a piezoelectric substrate, and each SAW having a different frequency is excited on the piezoelectric substrate. That is, the FSK transceiver 10 includes a SAW element 14a that resonates at a frequency f0 and a SAW element 14b that resonates at a frequency f1. The SAW element 14 may be provided with two sets of the IDT and the reflector on one piezoelectric substrate, or may be provided with the IDT and the reflector on each of the two piezoelectric substrates.

  The first switch unit 12 is provided at both ends of each SAW element 14. The first switch unit 12 is connected to the transmission unit 20 and the reception unit 30, and the SAW element 14 is connected to the transmission unit 20 or the SAW element 14 is connected to the reception unit 30 by switching the switch. . In the first switch unit 12, all switches are switched in conjunction with each other according to the input switching signal.

  The transmission unit 20 includes a second switch unit 22, an oscillation circuit 24, an amplifier 26, and a ground unit 28 in addition to the SAW element 14 and the first switch unit 12 shared with the reception unit 30. The second switch unit 22 is connected to the first switch units 12 a and 12 b provided at one end of the SAW element 14. The second switch unit 22 selects one of the plurality of SAW elements 14 according to the input modulation signal when the transmission unit 20 is selected by the first switch unit 12. . An oscillation circuit 24 that resonates the SAW element 14 is connected to the second switch unit 22. An amplifier 26 is connected to the oscillation circuit 24. The grounding unit 28 is connected to the first switch units 12 c and 12 d provided at the other end of the SAW element 14.

  The receiving unit 30 includes a low noise amplifier (LNA) 32 and a detection circuit 34 in addition to the SAW element 14 and the first switch unit 12 shared with the transmitting unit 20. The LNA 32 is connected to the first switch portions 12 a and 12 b provided at one end of the SAW element 14. In addition, the detection circuit 34 is connected to first switch portions 12 c and 12 d provided at the other end of the SAW element 14.

  The detection circuit 34 includes a plurality of limiters 36 (36a, 36b), a frequency discriminator 40, and a comparator 38. The limiter 36 is provided for each SAW element 14. That is, one limiter 36a is connected to the SAW element 14a that resonates at the frequency f0 via the first switch unit 12d. The other limiter 36b is connected to the SAW element 14b that resonates at the frequency f1 via the first switch unit 12c. The frequency discriminator 40 is connected to each limiter 36 and includes a circuit composed of a diode 42, a resistor 44 and a capacitor 46. Further, the comparator 38 is connected to the frequency discriminator 40, and receives a signal output from each SAW element 14 via the first switch unit 12, the limiter 36 and the frequency discriminator 40.

  Such a transmitting unit 20 and receiving unit 30 are connected to the third switch unit 16. That is, the third switch unit 16 is connected to the amplifier 26 provided in the transmission unit 20 and the LNA 32 provided in the reception unit 30. The third switch unit 16 is connected to the antenna 19 through the filter 18. And the 3rd switch part 16 switches in response to the 1st switch part 12 with the input switching signal.

  Next, the operation of the FSK transceiver 10 will be described. First, the operation of the transmission unit 20 will be described. When the FSK transceiver 10 transmits a signal, the first switch unit 12 and the third switch unit 16 select the transmission unit 20 according to the input switching signal. As a result, the antenna 19, the filter 18, and the SAW element 14 are connected to the transmission unit 20. Then, “0” and “1” signals are input to the second switch unit 22 as modulation signals. The second switch unit 22 selects one of the plurality of SAW elements 14 depending on the difference between “0” and “1” of the modulation signal. For example, when a “0” signal is input as the modulation signal, the second switch unit 22 selects the SAW element 14a that resonates at the frequency f0. Further, when a signal “1” is input as the modulation signal, the second switch unit 22 selects the SAW element 14b that resonates at the frequency f1.

  The oscillation circuit 24 resonates the SAW element 14 selected by switching the second switch unit 22 and outputs a signal corresponding to the resonance frequency of each SAW element 14. For example, when the SAW element 14a that resonates at the frequency f0 and the oscillation circuit 24 are connected, a signal of the frequency f0 is output from the oscillation circuit 24. When the SAW element 14b that resonates at the frequency f1 and the oscillation circuit 24 are connected, the signal at the frequency f1 is output from the oscillation circuit 24. The amplifier 26 amplifies the signal output from the oscillation circuit 24, and the filter 18 filters the signal output from the amplifier 26. The modulated signal is transmitted from the antenna 19.

  Next, the operation of the receiving unit 30 will be described. When the FSK transceiver 10 receives a signal, the first switch unit 12 and the third switch unit 16 select the receiving unit 30 according to the input switching signal. As a result, the antenna 19, the filter 18, and the SAW element 14 are connected to the receiving unit 30. The transmitted signal is input to the filter 18 via the antenna 19. The filter 18 filters the input signal and outputs it. This signal is input to the receiving unit 30 via the third switch unit 16. In the receiving unit 30, first, a signal is input to the LNA 32. The LNA 32 amplifies the input signal and outputs it. The signal is divided in the middle and then input to each SAW element 14 via the first switch parts 12a and 12b. Each SAW element 14 filters the input signal and outputs it. For example, in the SAW element 14a that resonates at the frequency f0, when a signal is input, it is filtered and only the signal at the frequency f0 is passed. Further, in the SAW element 14b that resonates at the frequency f1, when a signal is input, it is filtered and only the signal at the frequency f1 passes.

  The signal filtered by the SAW element 14 is input to the detection circuit 34 via the first switch units 12c and 12d. The detection circuit 34 inputs a signal from only one of the SAW element 14a that resonates at the frequency f0 and the SAW element 14b that resonates at the frequency f1, and does not simultaneously input signals from the SAW elements 14a and 14b. .

  In the detection circuit 34, first, a signal is input to the limiter 36. The limiter 36 limits the amplitude of the input signal and outputs it. The frequency discriminator 40 performs envelope detection on the signal input from the limiter 36 and outputs the detected signal to the comparator 38. The comparator 38 inputs a signal output from the SAW element 14a that resonates at the frequency f0 and detected, or a signal output from the SAW element 14b that resonates at the frequency f1 and detected, and outputs “0” and “1”. Output the demodulated signal.

  The transmission unit 20 and the reception unit 30 of the FSK transceiver 10 share the SAW element 14. Further, since the transmitter 20 obtains the modulation frequency with the SAW element 14 and uses it for signal transmission as it is, the variable capacitance diode or expansion coil for modulation used in the conventional oscillator is used. This is unnecessary, and the circuit scale and the number of parts of the transmission unit 20 can be reduced. Further, since the receiving unit 30 is a direct detection system, conventionally used down-conversion parts are not required, and the circuit scale and the number of parts of the receiving unit 30 can be reduced. The transmitter 20 and the receiver 30 share the filter 18 and the antenna 19. From the above, the FSK transceiver 10 can be downsized.

  Further, if two sets of IDTs and the like are provided on one piezoelectric substrate, the SAW element 14 can be reduced in size. Further, the FSK transceiver 10 can be formed as an integrated circuit (IC) chip except for the SAW element 14. That is, the antenna 19, the filter 18, the third switch unit 16, the amplifier 26, the oscillation circuit 24, the second switch unit 22, the LNA 32, the first switch unit 12, and the detection circuit 34 can be formed as an IC chip. From the above, the FSK transceiver 10 can be downsized. Since the SAW element 14 and the above-described IC chip can be mounted in one package, the FSK transceiver 10 can be further downsized.

It is a block diagram of a FSK transceiver. It is a schematic block diagram of the FSK transceiver which concerns on a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ......... FSK transmitter / receiver, 12 ......... 1st switch part, 14 ......... SAW element, 16 ......... 3rd switch part, 19 ......... Antenna, 20 ......... Sending part, 22 ......... Second switch section, 30... Receiving section, 34 ... Detection circuit, 40 ... Frequency discriminator.

Claims (5)

A plurality of SAW elements that excite SAWs having different frequencies;
A transmitter using the FSK communication method;
A receiver using the FSK communication method;
A first switch that selects one of the transmitter and the receiver and connects to the plurality of SAW elements;
An FSK transceiver characterized by comprising: An antenna,
A transmitter connected to the antenna;
A receiver connected to the antenna;
A plurality of SAW elements that excite SAWs having different frequencies;
A first switch that selects one of the transmitter and the receiver and connects to the plurality of SAW elements;
A second switch unit that selects one of the plurality of SAW elements when the plurality of SAW elements are connected to the transmission unit;
An FSK transceiver characterized by comprising:   The FSK transceiver according to claim 2, wherein a third switch unit that selects one of the transmission unit and the reception unit is connected to the antenna.   4. The FSK transceiver according to claim 1, wherein the reception unit includes a detection circuit at a subsequent stage of the SAW element connected by switching of the first switch unit. 5.   5. The FSK transceiver according to claim 1, wherein each of the plurality of SAW elements includes two sets of IDTs for resonating different frequencies on one piezoelectric substrate.

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