JP2006129201A - Radio receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio receiver that prevents the increase of a circuit scale due to an increase in types of frequency bandwidth corresponding to a radio communication system. <P>SOLUTION: This radio receiver is a radio receiver that corresponds to a plurality of radio signals with different frequency bandwidth and is provided with: a receiving circuit 24 for receiving a radio signal and outputting the received signal; a mixer 33 and a mixer 34 for converting the received signal into a baseband signal in frequency by multiplying the received signal by a local oscillation signal; a control circuit 23 for outputting a band switching signal representing the frequency bandwidth of the received signal; and an active filter 35 and an active filter 36 for attenuating components outside the band of a baseband band signal having frequency bandwidth represented by the band switching signal among frequency components of the baseband signal. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a wireless reception device, and more particularly, to a wireless reception device corresponding to a plurality of wireless signals having different frequency bandwidths.

  In recent years, wireless communication systems such as PHS (Personal Handy Phone System) have been required to support high-speed data communication compared to voice communication. For this reason, PHS has been proposed to support signals with a frequency bandwidth of 900 kHz in addition to signals with a conventional frequency bandwidth of 300 kHz. A PHS that transmits and receives radio signals of both frequency bandwidths is particularly called advanced PHS.

  Generally, in a wireless reception device in a wireless communication system, unnecessary waves outside a predetermined frequency band are removed by a filter. Here, in order to cope with the advanced PHS, it is necessary to arrange a filter that passes a signal having a frequency bandwidth of 900 kHz. However, when this filter is arranged, when a radio signal with a frequency bandwidth of 300 kHz is received, a signal in a frequency region outside the 300 kHz band of the radio signal and within the 900 kHz band, that is, a radio signal of an adjacent channel, etc. The interference wave cannot be removed by a filter.

  Here, in the IF (Intermediate Frequency) circuit described in Patent Document 1, a configuration for switching between a wideband reception filter and a narrowband reception filter has been proposed. Further, in the multi-band mobile radio apparatus described in Patent Document 2, a configuration is proposed in which radio signals having different frequency bands are received by adjusting the local oscillation frequency so that the frequencies of the signals output from the mixer are the same. . In the FM receiver described in Patent Document 3, a configuration is proposed in which two types of IF frequency band filters corresponding to the bandwidths of the two systems are switched by a switching signal.

With such a configuration, it is possible to provide a wireless reception device that supports a plurality of wireless signals having different frequency bandwidths.
JP-A-6-303161 Japanese Patent Laid-Open No. 9-275357 Japanese Patent Laid-Open No. 9-83385

  By the way, the IF circuit described in Patent Document 1, the multi-band mobile wireless device described in Patent Document 2, and the FM receiver described in Patent Document 3 include a mixer according to the type of the frequency bandwidth of the radio signal supported by the wireless communication system. There is a configuration in which a plurality of receiving circuits such as filters are arranged, and there is a problem that the circuit scale increases as the types of frequency bandwidths corresponding to the wireless communication system increase.

  Therefore, an object of the present invention is to provide a radio receiving apparatus capable of preventing an increase in circuit scale due to an increase in the types of frequency bandwidths corresponding to the radio communication system.

  In order to solve the above-described problem, a radio reception apparatus according to the present invention is a radio reception apparatus corresponding to a plurality of radio signals having different frequency bandwidths, and a reception unit that receives a radio signal and outputs a reception signal; A mixer that multiplies the received signal and the local oscillation signal to convert the frequency of the received signal into a baseband signal, a control unit that outputs a band switching signal representing the frequency bandwidth of the received signal, and a frequency component of the baseband signal And a low-pass filter for attenuating a component outside the band of the baseband signal having the frequency bandwidth represented by the band switching signal.

  Preferably, the low-pass filter includes a transconductance amplifier, a capacitor, and a variable current source. The transconductance amplifier has an input connected to the baseband signal, an output connected to the capacitor, and the variable current source includes the transconductance. The variable current source is connected to the amplifier and changes the current value based on the band switching signal, and the transconductance amplifier changes the conductance according to the current value of the variable current source.

  Preferably, the wireless receiver further includes an analog-digital converter that converts the baseband signal into a digital signal, and the low-pass filter is a component outside the band of each signal in the baseband having each frequency bandwidth of the wireless signal. A tap coefficient representing the amplitude at each sampling point of each impulse response waveform having the characteristic of attenuating the frequency is stored for each frequency bandwidth of the radio signal, and the tap coefficient corresponding to the frequency bandwidth represented by the band switching signal A shift register that sequentially delays the digital signal in the sampling period and holds the number of tap coefficients, a multiplier that multiplies the digital signal held in the shift register and the tap coefficient, and a multiplication result. And an adder for adding.

  Preferably, the wireless reception device further includes a plurality of bandpass filters for attenuating components outside the band of the reception signal having each frequency bandwidth of the wireless signal, and a band corresponding to the frequency bandwidth represented by the band switching signal. A first switch that outputs a received signal received from the received signal to the pass filter; a second switch that outputs an attenuated signal received from the bandpass filter corresponding to the frequency bandwidth represented by the band switching signal; And an RSSI detector that detects the power of the attenuated signal received from the switch 2 and converts the detected power into a voltage and outputs the voltage.

  ADVANTAGE OF THE INVENTION According to this invention, the increase in the circuit scale by the increase in the kind of frequency bandwidth corresponding to a radio | wireless communications system can be prevented.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same reference numerals indicate the same or corresponding parts.

<First Embodiment>
FIG. 1 is a functional block diagram of a radio reception apparatus according to the first embodiment of the present invention. The radio reception apparatus according to the present embodiment employs a superheterodyne method in which a radio signal is once converted into an IF signal and then converted into a baseband signal.

  Referring to the figure, this wireless receiver includes an antenna 1, a switch 2, a receiving circuit 3, a transmitting circuit 4, a mixer 5, a switch 6, a band pass filter 7 to a band pass filter 12, Mixer 13 to mixer 16, switch 17, mixer 18 to mixer 19, shift circuit 20, A / D converter 21, A / D converter 22, and control circuit 23 are included.

  The bandpass filter 7 to the bandpass filter 9 and the mixer 13 to the mixer 14 constitute an IF signal circuit having a bandwidth of 300 kHz.

  The bandpass filter 10 to the bandpass filter 12 and the mixer 15 to the mixer 16 constitute an IF signal circuit having a bandwidth of 900 kHz.

  The switch 2 outputs a 1.9 GHz band radio signal received via the antenna 1 to the receiving circuit 3.

  The receiving circuit 3 outputs the radio signal received from the switch 2 to the mixer 5.

  The control circuit 23 generates and outputs a band switching signal representing the frequency bandwidth of the received radio signal.

  The transmission circuit 4 outputs a 1.9 GHz band radio signal to the switch 2.

  The switch 2 transmits a 1.9 GHz band radio signal via the antenna 1.

  The mixer 5 multiplies the radio signal received from the receiving circuit 3 and the local oscillation signal RFLO, thereby frequency-converting the radio signal into an IF signal having a center frequency of 250 MHz, and outputs the IF signal to the switch 6.

  Switch 6 switches the output destination of the IF signal received from mixer 5 based on the band switching signal received from control circuit 23. That is, when the band switching signal represents the frequency bandwidth 300 kHz, an IF signal is output to the bandpass filter 7, and when the band switching signal represents the frequency bandwidth 900 kHz, the IF signal is output to the bandpass filter 10.

  The bandpass filter 7 attenuates a signal in a frequency region outside the 300 kHz width band having a center frequency of 250 MHz among the IF signals received from the switch 6 and outputs the attenuated signal to the mixer 13.

  The mixer 13 multiplies the IF signal received from the bandpass filter 7 by the local oscillation signal IFLO1, thereby frequency-converting the IF signal received from the bandpass filter 7 into an IF signal having a center frequency of 10 MHz. Output to.

  The band-pass filter 8 attenuates the signal in the frequency region outside the 300 kHz width band having a center frequency of 10 MHz among the IF signal received from the mixer 13 and outputs the attenuated signal to the mixer 14.

  The mixer 14 multiplies the IF signal received from the bandpass filter 8 by the local oscillation signal IFLO2, thereby frequency-converting the IF signal received from the bandpass filter 8 into an IF signal having a center frequency of 1.2 MHz. Output to the filter 9.

  The bandpass filter 9 attenuates the signal in the frequency region outside the 300 kHz width band having 1.2 MHz as the center frequency among the IF signals received from the mixer 14 and outputs the attenuated signal to the switch 17.

  On the other hand, the band pass filter 10 attenuates the signal in the frequency region outside the 900 kHz width band having the center frequency of 250 MHz among the IF signals received from the switch 6 and outputs the attenuated signal to the mixer 15.

  The mixer 15 multiplies the IF signal received from the bandpass filter 10 and the local oscillation signal IFLO1 to frequency-convert the IF signal received from the bandpass filter 10 into an IF signal having a center frequency of 10 MHz. Output to.

  The band pass filter 11 attenuates the signal in the frequency region outside the 900 kHz width band having 10 MHz as the center frequency among the IF signals received from the mixer 15 and outputs the attenuated signal to the mixer 16.

  The mixer 16 multiplies the IF signal received from the bandpass filter 11 and the local oscillation signal IFLO2 to frequency-convert the IF signal received from the bandpass filter 11 into an IF signal having a center frequency of 1.2 MHz. Output to the filter 12.

  The band pass filter 12 attenuates the signal in the frequency region outside the 900 kHz width band having 1.2 MHz as the center frequency among the IF signals received from the mixer 16 and outputs the attenuated signal to the switch 17.

  Switch 17 outputs the IF signal received from bandpass filter 9 to mixer 18 and mixer 19 when the band switching signal received from control circuit 23 represents a frequency bandwidth of 300 kHz, and the band switching signal has a frequency bandwidth of 900 kHz. , The IF signal received from the bandpass filter 12 is output to the mixer 18 and the mixer 19.

  Shift circuit 20 shifts the phase of local oscillation signal BBLO by π / 2 and outputs the result.

  The mixer 18 multiplies the IF signal received from the switch 17 by the local oscillation signal received from the shift circuit 20, thereby converting the IF signal received from the switch 17 to a baseband signal and outputting the baseband signal.

  The mixer 19 multiplies the IF signal received from the switch 17 by the local oscillation signal BBLO, thereby frequency-converting the IF signal received from the switch 17 into a baseband signal and outputting the baseband signal.

  The A / D converter 21 converts the baseband signal received from the mixer 18 into a digital signal and outputs it as an I signal.

  The A / D converter 22 converts the baseband signal received from the mixer 19 into a digital signal and outputs it as a Q signal.

  As described above, in the radio reception apparatus according to the present embodiment, it is possible to sufficiently remove interference waves outside the frequency bands of the radio signal having a frequency bandwidth of 300 kHz and the radio signal having a frequency bandwidth of 900 kHz.

<Second Embodiment>
FIG. 2 is a functional block diagram of a radio reception apparatus according to the second embodiment of the present invention. The radio reception apparatus according to the present embodiment employs a direct conversion method that frequency-converts radio signals directly into baseband signals.

  Referring to the figure, this radio receiving apparatus includes antenna 1, switch 2, receiving circuit 24, transmitting circuit 4, mixer 33, mixer 34, active filter 35, active filter 36, and A. / D converter 21, A / D converter 22, control circuit 23, and shift circuit 39 are included.

  The reception circuit 24 includes a band pass filter 31 and an amplifier 32.

  The band pass filter 31 attenuates a signal in a frequency region outside the 900 kHz width band having a center frequency of 1.9 GHz from the radio signal received from the switch 2 and outputs the attenuated signal to the amplifier 32.

  The amplifier 32 amplifies the radio signal received from the band pass filter 31 and outputs the amplified signal to the mixer 33 and the mixer 34.

  Shift circuit 39 shifts the phase of local oscillation signal DRFLO by π / 2 and outputs the result.

  The mixer 33 multiplies the radio signal received from the amplifier 32 by the local oscillation signal received from the shift circuit 39, thereby frequency-converting the radio signal into a baseband signal and outputs the baseband signal to the active filter 35.

  The mixer 34 multiplies the radio signal received from the amplifier 32 by the local oscillation signal DRFLO, thereby frequency-converting the radio signal into a baseband signal and outputs the baseband signal to the active filter 36.

  The active filter 35 has a function as a low-pass filter. Active filter 35 selects a cutoff frequency for attenuating a component outside the band of the baseband signal having the frequency bandwidth represented by the band switching signal received from control circuit 23, and attenuates the baseband signal received from mixer 33. That is, when the band switching signal represents a frequency bandwidth of 300 kHz, the active filter 35 selects a cutoff frequency that attenuates a signal in a frequency region greater than 300 kHz from the baseband signal received from the mixer 33, and the band switching signal Represents a frequency bandwidth of 900 kHz, a cutoff frequency that attenuates a signal in a frequency region greater than 900 kHz among the baseband signals received from the mixer 33 is selected.

  Here, the cutoff frequency is a frequency that a signal has when the signal after passing through the filter is attenuated by 3 dB with respect to the signal before passing through the filter. Therefore, as described above, in the active filter 35, a signal in a frequency region of 300 kHz or less is not attenuated, and in order to attenuate a signal in a frequency region above 300 kHz, the cutoff frequency needs to be made larger than 300 kHz. The exact value of the cutoff frequency in this case needs to be determined according to the frequency characteristics of the active filter 35.

  Similarly to active filter 35, active filter 36 selects a cutoff frequency for attenuating a component outside the band of the baseband signal having the frequency bandwidth represented by the band switching signal received from control circuit 23, and received from mixer 34. Attenuate the baseband signal.

  The A / D converter 21 converts the baseband signal received from the active filter 35 into a digital signal and outputs it as an I signal.

  The A / D converter 22 converts the baseband signal received from the active filter 36 into a digital signal and outputs it as a Q signal.

  Other configurations and operations are the same as those in the first embodiment.

  FIG. 3 is a diagram illustrating a configuration of a Gm-C filter, which is an example in which the active filter 35 and the active filter 36 are embodied.

  Referring to FIG. 6, this Gm-C filter includes a transconductance amplifier 71, a capacitor 72, and a variable current source 73.

  One of the variable current sources 73 is connected to the transconductance amplifier 71, and the other is connected to the ground potential.

  The variable current source 73 changes the current value based on the band switching signal received from the control circuit 23.

  The transconductance amplifier 71 is an amplifier whose output signal is a current while the input signal is a voltage.

  When the current value of the variable current source 73 changes, the conductance amplifier 71 changes its conductance Gm.

  By connecting a capacitor 72 to the output of the transconductance amplifier 71, these constitute a low-pass filter. The cut-off frequency fc of the Gm-C filter is expressed as follows when the capacitance of the capacitor 72 is C.

fc = Gm / (2π × C) (A1)
From equation (A1), the cutoff frequency fc of the Gm-C filter can be changed by changing the conductance Gm, that is, changing the current value of the variable current source 73 based on the band switching signal. Therefore, the frequency component to be attenuated can be changed when the band switching signal represents the frequency bandwidth of 300 kHz and when the band switching signal represents the frequency bandwidth of 900 kHz.

  By the way, the IF circuit described in Patent Document 1, the multi-band mobile wireless device described in Patent Document 2, and the FM receiver described in Patent Document 3 include a mixer according to the type of the frequency bandwidth of the radio signal supported by the wireless communication system. There is a configuration in which a plurality of receiving circuits such as filters are arranged, and there is a problem that the circuit scale increases as the types of frequency bandwidths corresponding to the wireless communication system increase.

  However, in the radio reception apparatus according to the present embodiment, active filter 35 and active filter 36 attenuate components outside the band of the baseband signal having the frequency bandwidth represented by the band switching signal. Therefore, in the radio reception apparatus according to the present embodiment, it is not necessary to add another active filter in addition to the active filter 35 and the active filter 36 even when the types of frequency bandwidths corresponding to the radio communication system are increased. An increase in scale can be prevented.

  Here, an amplifier such as a transconductance amplifier generally used in an active filter has a frequency characteristic in which the gain decreases as the frequency of the input signal increases. For this reason, when an active filter having equivalent performance is arranged in a circuit for a signal in a higher frequency band, a desired wave that is a signal in a frequency band that is originally desired to pass through may be attenuated.

  Therefore, in the radio receiving apparatus according to the present embodiment, the active filter 71 is arranged in the baseband signal circuit, so that the desired gain due to the gain reduction of the amplifier can be obtained as compared with the case where the active filter is arranged in the IF signal circuit. Wave attenuation can be prevented and the selectivity of the desired wave can be increased. Further, by disposing a filter having a high desired wave selectivity in the baseband signal circuit, the number of filters disposed in the radio signal and IF signal circuits can be reduced, and the production cost can be reduced. In addition, since it is less necessary to select filter components that do not attenuate the desired wave in the radio frequency band and the IF band, the range of component selection is widened, and the production cost can be reduced.

<Third Embodiment>
FIG. 4 is a functional block diagram of a radio reception apparatus according to the third embodiment of the present invention. As in the second embodiment, the radio reception apparatus according to the present embodiment employs a direct conversion method in which a radio signal is directly converted into a baseband signal.

  Referring to the figure, this radio reception apparatus is different from the radio reception apparatus according to the second embodiment shown in FIG. 2 in that a digital filter 41 and a digital filter 42 are used instead of the active filter 35 and the active filter 36. Including.

  The output of the mixer 33 is connected to the A / D converter 21. The output of the A / D converter 21 is connected to the digital filter 41. The output of the mixer 34 is connected to the A / D converter 22. The output of the A / D converter 22 is connected to the digital filter 42.

  The digital filter 41 has a function as a low-pass filter. Digital filter 41 selects a cutoff frequency for attenuating a component outside the band of the baseband signal having the frequency bandwidth represented by the band switching signal received from control circuit 23, and attenuates the digital signal received from A / D converter 21. And output as an I signal. That is, when the band switching signal represents a frequency bandwidth of 300 kHz, the digital filter 41 selects a cut-off frequency that attenuates a signal in a frequency region greater than 300 kHz among the digital signals received from the A / D converter 21, and When the switching signal represents a frequency bandwidth of 900 kHz, a cutoff frequency that attenuates a signal in a frequency region greater than 900 kHz among the digital signals received from the A / D converter 21 is selected.

  Similarly to the digital filter 41, the digital filter 42 selects a cutoff frequency that attenuates a component outside the band of the baseband signal having the frequency bandwidth represented by the band switching signal received from the control circuit 23, and the A / D converter 22. The digital signal received from is attenuated and output as a Q signal.

  Other configurations and operations are the same as those in the second embodiment.

  FIG. 5 is a diagram illustrating a configuration of an example of a digital filter that embodies the digital filter 41 and the digital filter 42.

  Referring to the figure, the digital filter includes a shift register including cascaded eight stages of delay elements D1 to D8, nine multipliers M0 to M8, and an adder A for adding the multiplication results. And a memory circuit R1.

  The shift register holds the input signal by sequentially delaying it by the sampling period. Then, the first stage input and the output of each stage of the shift register become nine tap outputs.

  Nine tap coefficients h0 to h8 each representing 16 kinds of values in one sampling period and representing the amplitude at a point at which a predetermined impulse response waveform is sampled at nine locations are stored in the storage circuit R1. Here, the predetermined impulse response waveform is an impulse response having characteristics of each low-pass filter that attenuates a component outside the band of the baseband signal having a frequency bandwidth of 300 kHz and a component outside the band of the baseband signal having a frequency bandwidth of 900 kHz. This is a waveform, and two types of tap coefficients h0 to h8 corresponding to these impulse response waveforms are stored in the storage circuit R1.

  The storage circuit R1 outputs nine tap coefficients h0 to h8 corresponding to the frequency bandwidth of 300 kHz or 900 kHz to the multipliers M0 to M8 based on the frequency bandwidth represented by the band switching signal received from the control circuit 23. To do.

  Multipliers M0 to M8 multiply 9 tap outputs and 9 tap coefficients h0 to h8 for each sampling period, and output the multiplication results to adder A.

  Adder A adds the multiplication results received from multipliers M0 to M8, and outputs the addition result of the current sampling period.

Then, in the next sampling period, the input signal held in the eight delay elements D1 to D8 is output to the next delay element, and in that state, the nine tap outputs and the nine taps as described above. Multiplication with a coefficient and addition of multiplication results are performed.

  By repeatedly holding the input signal in the shift register, multiplying the tap output by the tap coefficient, and adding the multiplication results at the sampling period, a digital filter output corresponding to the characteristics of a predetermined low-pass filter can be obtained.

  As described above, in the radio receiving apparatus according to the present embodiment, the frequency component to be attenuated can be changed when the band switching signal represents the frequency bandwidth 300 kHz and when the band switching signal represents the frequency bandwidth 900 kHz. it can.

  By the way, the IF circuit described in Patent Document 1, the multi-band mobile wireless device described in Patent Document 2, and the FM receiver described in Patent Document 3 include a mixer according to the type of the frequency bandwidth of the radio signal supported by the wireless communication system. There is a configuration in which a plurality of receiving circuits such as filters are arranged, and there is a problem that the circuit scale increases as the types of frequency bandwidths corresponding to the wireless communication system increase.

  However, in the radio reception apparatus according to the present embodiment, digital filter 41 and digital filter 42 attenuate components outside the band of the baseband signal having the frequency bandwidth represented by the band switching signal received from control circuit 23. Therefore, in the radio receiving apparatus according to the present embodiment, it is not necessary to add another digital filter in addition to the digital filter 41 and the digital filter 42 even when the types of frequency bandwidths corresponding to the radio communication system are increased. An increase in scale can be prevented.

<Fourth embodiment>
FIG. 6 is a functional block diagram of a radio reception apparatus according to the fourth embodiment of the present invention. The radio reception apparatus according to the present embodiment employs a superheterodyne method in which a radio signal is once converted into an IF signal and then converted into a baseband signal.

  Referring to the figure, this radio receiving apparatus includes antenna 1, switch 2, receiving circuit 59, transmitting circuit 4, mixer 56, mixer 57, active filter 35, active filter 36, and A. / D converter 21, A / D converter 22, control circuit 23, and shift circuit 58 are included.

  The reception circuit 59 includes an amplifier 51, a mixer 52, a SAW (Surface Acoustic Wave) filter 53, a mixer 54, and an amplifier 55.

  The amplifier 51 amplifies the radio signal received from the switch 2 and outputs it to the mixer 52.

  The mixer 52 multiplies the radio signal received from the amplifier 51 by the local oscillation signal RFLO, thereby frequency-converting the radio signal into an IF signal having a center frequency of 250 MHz, and outputs the IF signal to the SAW filter 53.

  The SAW filter 53 attenuates a signal in a frequency region outside the 900 kHz width band having a center frequency of 250 MHz among the radio signals received from the mixer 52 and outputs the attenuated signal to the mixer 54.

  The mixer 54 multiplies the IF signal received from the SAW filter 53 and the local oscillation signal IFLO3 to frequency-convert the IF signal received from the SAW filter 53 into an IF signal having a center frequency of 1.2 MHz, and an amplifier 55 Output to.

  Amplifier 55 amplifies the IF signal received from mixer 54 and outputs the amplified signal to mixer 56 and mixer 57.

  Shift circuit 58 shifts the phase of local oscillation signal IFLO4 by π / 2 and outputs the result.

  The mixer 56 multiplies the IF signal received from the amplifier 55 by the local oscillation signal received from the shift circuit 58, thereby frequency-converting the IF signal into a baseband signal and outputs the baseband signal to the active filter 35.

  The mixer 34 multiplies the IF signal received from the amplifier 55 by the local oscillation signal IFLO4, thereby frequency-converting the IF signal into a baseband signal and outputting the baseband signal to the active filter 36.

  Other configurations and operations are the same as those in the second embodiment.

  As described above, in the radio reception apparatus according to the present embodiment, the radio signal is once converted into an IF signal, the interference wave is removed by the SAW filter 53, and the amplifier 55 amplifies the IF signal. The second embodiment and the third embodiment adopting the direct conversion method by converting the frequency to a baseband signal and removing the interference wave contained in the baseband signal in the active filter 35 and the active filter 36. Compared with, the interference wave can be further removed and the selectivity of the desired wave can be enhanced.

<Fifth embodiment>
FIG. 7 is a functional block diagram of a radio reception apparatus according to the fifth embodiment of the present invention. As in the fourth embodiment, the radio receiving apparatus according to the present embodiment employs a superheterodyne method that once converts a radio signal to an IF signal and then converts the IF signal to a baseband signal. Yes.

  Referring to FIG. 6, this wireless reception device is different from the wireless reception device according to the fourth embodiment shown in FIG. 6 in that digital filter 41 and digital filter 42 are used instead of active filter 35 and active filter 36. Including.

  The configurations and operations of the digital filter 41 and the digital filter 42 are the same as those in the third embodiment.

  The configuration and operation other than the digital filter 41 and the digital filter 42 are the same as those in the fourth embodiment.

  As described above, in the radio reception apparatus according to the present embodiment, the radio signal is once converted into an IF signal, the interference wave is removed by the SAW filter 53, and the amplifier 55 amplifies the IF signal. The second embodiment and the third embodiment adopting the direct conversion method by converting the frequency into a baseband signal and removing the interference wave contained in the baseband signal in the digital filter 41 and the digital filter 42. Compared with, the interference wave can be further removed and the selectivity of the desired wave can be enhanced.

<Sixth Embodiment>
FIG. 8 is a functional block diagram of a radio reception apparatus according to the sixth embodiment of the present invention. As in the fifth embodiment, the radio receiving apparatus according to the present embodiment employs a superheterodyne system that once converts a radio signal to an IF signal and then converts the IF signal to a baseband signal. Yes.

  Referring to FIG. 7, this wireless reception device further includes a switch 61, a bandpass filter 62, a bandpass filter 63, and a wireless reception device according to the fifth embodiment shown in FIG. A switch 64 and an RSSI (Received Signal Strength Indicator) detection circuit 65 are included.

  Switch 61 outputs the IF signal received from bandpass filter 53 to bandpass filter 62 when the band switching signal received from control circuit 23 represents a frequency bandwidth of 300 kHz, and the band switching signal has a frequency bandwidth of 900 kHz. When represented, the IF signal received from the bandpass filter 53 is output to the bandpass filter 63.

  The band-pass filter 62 attenuates the signal in the frequency region outside the 300 kHz width band having a center frequency of 250 MHz among the IF signals received from the switch 61 and outputs the attenuated signal to the switch 64.

  The band pass filter 63 attenuates the signal in the frequency region outside the 900 kHz width band having the center frequency of 250 MHz among the IF signals received from the switch 61 and outputs the attenuated signal to the switch 64.

  Switch 64 outputs the IF signal received from bandpass filter 62 to RSSI detection circuit 65 when the band switching signal received from control circuit 23 represents a frequency bandwidth of 300 kHz, and the band switching signal has a frequency bandwidth of 900 kHz. In the case of representation, the IF signal received from the band pass filter 63 is output to the RSSI detection circuit 65.

  The RSSI detection circuit 65 detects the power of the IF signal received from the switch 64, converts the detected power into a voltage, and outputs the voltage as an RSSI signal. Here, the RSSI signal is a signal used for performing various controls such as AGC (Auto Gain Control) and measurement of the communication environment based on the power of the received signal.

  Other configurations and operations are the same as those of the fifth embodiment.

  As described above, in the radio reception apparatus according to the present embodiment, the interference wave removal according to the frequency bandwidth is performed not only for the main signal but also for the RSSI signal in addition to the fifth embodiment. Thus, it is possible to further remove the interference wave and detect the power of the received signal accurately.

[Modification]
The present invention is not limited to the above embodiment, and includes, for example, the following modifications.

[Modification 1]
In the radio receiving apparatus according to the embodiment of the present invention, an active filter or a digital filter is used as a low-pass filter arranged in a circuit for baseband signals, but the present invention is not limited to this. Any other type of filter can be used as long as it can change the cutoff frequency based on the band switching signal.

[Modification 2]
In the radio reception apparatus according to the sixth embodiment of the present invention, a configuration in which a signal in a frequency region outside the frequency band represented by the band switching signal among the IF signal having a center frequency of 250 MHz received from the bandpass filter 53 is attenuated. However, the present invention is not limited to this. Switch 61 outputs the 1.2 MHz IF signal received from amplifier 55 to bandpass filter 62 or bandpass filter 63 based on the frequency bandwidth represented by the band switching signal. The band-pass filter 62 or the band-pass filter 63 is configured to attenuate the signal in the frequency region outside the 300 kHz or 900 kHz band having a center frequency of 1.2 MHz among the IF signal received from the switch 61. Can do.

[Modification 3]
In the radio reception apparatus according to the sixth embodiment of the present invention, the bandpass filter 62 and the bandpass filter 63 are arranged in the IF signal circuit, but the present invention is not limited to this. A mixer and an active filter are arranged after the SAW filter 53. The mixer frequency-converts the IF signal received from the SAW filter 53 into a baseband signal. The active filter selects a cutoff frequency for attenuating a component outside the band of the baseband signal having the frequency bandwidth represented by the band switching signal received from the control circuit 23, and attenuates the baseband signal received from the SAW filter 53. The RSSI detection circuit 65 detects the power of the baseband signal received from the active filter, converts the detected power into a voltage, and outputs the voltage as an RSSI signal.

  With such a configuration, compared with the case where an active filter is arranged in the IF signal circuit, the attenuation of the desired wave due to the gain reduction of the amplifier is prevented, and the selectivity of the desired wave is increased, so that the accurate power of the received signal can be obtained. Can be detected.

[Modification 4]
In the radio reception apparatus according to the sixth embodiment of the present invention, the bandpass filter 62 and the bandpass filter 63 are arranged in the IF signal circuit, but the present invention is not limited to this. A mixer, an A / D converter, and a digital filter are arranged after the SAW filter 53. The mixer frequency-converts the IF signal received from the SAW filter 53 into a baseband signal. The A / D converter converts the baseband signal received from the mixer into a digital signal. The digital filter selects a cutoff frequency for attenuating a component outside the band of the baseband signal having the frequency bandwidth represented by the band switching signal received from the control circuit 23, and attenuates the digital signal received from the A / D converter. The RSSI detection circuit 65 detects the power of the digital signal received from the digital filter, converts the detected power into a voltage, and outputs it as an RSSI signal.

  With such a configuration, it is possible to further remove the interference wave and detect the power of the received signal accurately.

[Modification 5]
The mixer in the wireless reception apparatus according to the embodiment of the present invention is configured to perform frequency conversion to a signal having a center frequency of 250 MHz, 10 MHz, or 1.2 MHz, but is not limited thereto. The mixer may be configured to perform frequency conversion to a signal having a frequency other than the above as a center frequency and finally frequency conversion to a baseband signal.

  Moreover, although the radio | wireless receiver which concerns on embodiment of this invention was set as the structure corresponding to frequency bandwidth 300kHz and 900kHz, it is not limited to this. By changing the frequency characteristics of the active filter or the digital filter, other frequency bandwidths can be easily accommodated. For example, in the Gm-C filter which is an example of the active filter shown in FIG. 3, the variable current source 73 receives the band switching signal representing the frequency bandwidth other than the frequency bandwidths 300 kHz and 900 kHz from the control circuit 23 and the variable current source 73 By changing the value and the transconductance amplifier 71 changing the conductance Gm, the cut-off frequency fc can be changed to cope with other frequency bandwidths. In the example of the digital filter shown in FIG. 5, tap coefficients h0 to h8 corresponding to other frequency bandwidths are further stored in the storage circuit R1. Then, upon receiving a band switching signal representing a frequency bandwidth other than the frequency bandwidths 300 kHz and 900 kHz from the control circuit 23, the memory circuit R1 outputs tap coefficients h0 to h8 corresponding to the other frequency bandwidths. , Other frequency bandwidths can be accommodated.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a functional block diagram of the radio | wireless receiver which concerns on the 1st Embodiment of this invention. It is a functional block diagram of the radio | wireless receiver which concerns on the 2nd Embodiment of this invention. It is a figure which shows the structure of the Gm-C filter which is an example of an active filter. It is a functional block diagram of the radio | wireless receiver which concerns on the 3rd Embodiment of this invention. It is a figure which shows an example of a digital filter. It is a functional block diagram of the radio | wireless receiver which concerns on the 4th Embodiment of this invention. It is a functional block diagram of the radio | wireless receiver which concerns on the 5th Embodiment of this invention. It is a functional block diagram of the radio | wireless receiver which concerns on the 6th Embodiment of this invention.

Explanation of symbols

  1 antenna, 2, 6, 17, 61, 64 switch, 3, 24, 59 reception circuit, 4 transmission circuit, 5, 13-16, 18, 19, 33, 34, 52, 54, 56, 57 mixer, 7 -12, 31, 62, 63 Band pass filter, 35, 36 active filter, 20, 39, 58 shift circuit, 21, 22 A / D converter, 23 control circuit, 32, 51, 55 amplifier, 71 transconductance amplifier, 72 capacitors, 73 variable current sources, 41, 42 digital filters, D1-D8 delay elements, M0-M8 multipliers, A adders, R1 storage circuits, 53 SAW filters, 65 RSSI detection circuits.

Claims (4)

A wireless reception device corresponding to a plurality of wireless signals having different frequency bandwidths,
A receiver that receives the wireless signal and outputs a received signal;
A mixer that frequency-converts the received signal into a baseband signal by multiplying the received signal and the local oscillation signal;
A control unit for outputting a band switching signal representing the frequency bandwidth of the received signal;
A radio receiving apparatus comprising: a low-pass filter that attenuates a component outside a band of a baseband signal having a frequency bandwidth represented by the band switching signal among frequency components of the baseband signal. The low-pass filter includes a transconductance amplifier, a capacitor, and a variable current source,
The transconductance amplifier has an input connected to the baseband signal, an output connected to the capacitor,
The variable current source is connected to the transconductance amplifier,
The variable current source changes a current value based on the band switching signal,
The radio receiving apparatus according to claim 1, wherein the transconductance amplifier changes conductance according to a current value of the variable current source. The wireless receiving device further includes:
An analog-digital converter that converts the baseband signal into a digital signal;
The low-pass filter is
A tap coefficient representing the amplitude at the point where each impulse response waveform having a characteristic of attenuating a component outside the band of each signal in the baseband having each frequency bandwidth of the radio signal is sampled at a plurality of locations is represented by the tap signal of the radio signal. A storage unit that stores each frequency bandwidth and outputs the tap coefficient corresponding to the frequency bandwidth represented by the band switching signal;
A shift register that sequentially delays the digital signal in the sampling period and holds the number of tap coefficients;
A multiplier for multiplying the digital signal held in the shift register by the tap coefficient;
The radio reception apparatus according to claim 1, further comprising: an addition unit that adds the multiplication results. The wireless receiving device further includes:
A plurality of bandpass filters for attenuating each component outside the band of the received signal having each frequency bandwidth of the radio signal;
A first switch for outputting a reception signal received from the reception unit to the bandpass filter corresponding to the frequency bandwidth represented by the band switching signal;
A second switch for outputting the attenuated signal received from the bandpass filter corresponding to the frequency bandwidth represented by the band switching signal;
The radio reception apparatus according to claim 1, further comprising: an RSSI detection unit that detects the power of the attenuated signal received from the second switch, converts the detected power into a voltage, and outputs the voltage.

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