JP2009044446A - Receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent interference between local oscillation signals during diversity reception. <P>SOLUTION: The receiver (1) is provided with two reception systems and executes the diversity reception. A first mixer (12) executes the frequency conversion of the reception signals of a first antenna (11) using a first local oscillation signal, and a second mixer (22) executes the frequency conversion of the reception signals of a second antenna (21) using a second local oscillation signal. A frequency difference is intentionally provided between the first and second local oscillation signals to prevent the interference between the local oscillation signals, correction of offsetting the frequency difference is executed in frequency offset correction parts (16, 26) and then diversity composition is executed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a receiving apparatus that receives a digital broadcast signal or the like.

  Diversity reception is often used for a receiver that is used in an environment where the received radio wave intensity of a radio signal constantly changes, such as a vehicle-mounted receiver (see, for example, Patent Document 1 below). A receiving apparatus that performs diversity reception includes a plurality of tuner units (reception systems), and a local oscillation circuit is provided for each tuner unit. When diversity reception is performed, each local oscillator circuit generates a local oscillation signal having the same frequency, so that each tuner section selects the same channel, and the output signals of each tuner section are diversity-synthesized. ing.

  The frequency of the local oscillation signal is stabilized by a PLL circuit provided for each local oscillation circuit. The PLL circuit operates on the basis of the input oscillation signal, and generally a crystal oscillator or the like is used to generate the oscillation signal input to the PLL circuit. When a plurality of tuner units are provided in the receiving apparatus, a local oscillation circuit, a PLL circuit, and a crystal oscillator are provided for each tuner unit, but the oscillation frequencies of the plurality of crystal oscillators completely match. There is no small difference in frequency between different oscillation frequencies. As a result, a minute frequency difference is generated between different local oscillation signals.

  On the other hand, there is a strong demand for downsizing the receiving device. When trying to reduce the size of the receiving apparatus, it is necessary to provide local oscillator circuits of a plurality of tuner units in the vicinity. In such a case, if the same channel is received by a plurality of tuner units (that is, if diversity reception is performed), local oscillation signals having a minute frequency difference interfere with each other, and reception demodulation characteristics deteriorate. (For example, refer to Patent Document 2 below).

  In the tuner described in Patent Document 3 below, a PLL circuit is provided for each of the two receiving systems, and a function for turning on / off the power of the PLL circuit is further provided. During diversity reception, the power of one PLL circuit is turned off, and the local oscillation signal corresponding to the other PLL circuit is shared by the two reception systems, thereby avoiding interference of the local oscillation signal. However, in the tuner described in Patent Document 3, the oscillation frequency determined by a single tank circuit is shared by the two reception systems, so that the two reception systems can always select only signals of the same frequency. That is, although two receiving systems are provided, it is not possible to select two channels having different frequency bands at the same time (selecting two broadcast programs corresponding to two channels at the same time). Can not).

JP 2003-179530 A JP 2003-347948 A JP 2007-74418 A

  Therefore, an object of the present invention is to provide a receiving apparatus capable of suppressing interference between local oscillation signals at the time of diversity reception.

  In order to achieve the above object, a receiving apparatus according to the present invention is a receiving apparatus that performs diversity reception using a plurality of antennas including a first antenna and a second antenna. A first mixing circuit that frequency-converts and outputs the received signal of the antenna, and a second mixing circuit that frequency-converts and outputs the received signal of the second antenna using a second local oscillation signal; And diversity reception is performed by differentiating the frequencies of the first and second local oscillation signals.

  As a result, it is possible to suppress interference between local oscillation signals during diversity reception.

  Specifically, for example, the receiving device includes a first filter that applies a band limitation to the output signal of the first mixing circuit, and a second filter that applies a band limitation to the output signal of the second mixing circuit. The first mixing circuit receives the output signal of the first mixing circuit through the first filter and the output signal of the second mixing circuit through the second filter, and the first and second local oscillations are received. A frequency correction circuit that corrects a frequency difference between output signals of each filter caused by a frequency difference between the signals, a diversity combining circuit that diversity-combines an output signal of each corrected filter given from the frequency correction circuit, and Is further provided.

  For example, the frequency correction circuit shifts the band of the output signal of at least one of the first and second filters according to the frequency difference between the first and second local oscillation signals. By doing so, the frequency difference between the output signals of each filter is corrected.

  More specifically, for example, the receiving device further includes a first local oscillation circuit that generates the first local oscillation signal and a second local oscillation circuit that generates the second local oscillation signal. And when the diversity reception is performed, the first and second local oscillation circuits are controlled so that a predetermined frequency difference is generated between the first and second local oscillation signals.

  Further, for example, a pass band in at least one of the first and second filters is variable, and according to a frequency difference between the first and second local oscillation signals, the pass band is Adjusted.

  As a result, it is possible to avoid signal component reduction due to the filter due to the different frequencies of the first and second local oscillation signals.

  According to the present invention, it is possible to suppress interference between local oscillation signals at the time of diversity reception.

  The significance or effect of the present invention will become more apparent from the following description of embodiments. However, the following embodiment is merely one embodiment of the present invention, and the meaning of the term of the present invention or each constituent element is not limited to that described in the following embodiment. .

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. In each of the drawings to be referred to, the same part is denoted by the same reference numeral, and redundant description regarding the same part is omitted in principle.

<< First Embodiment >>
First, a first embodiment of the present invention will be described. FIG. 1 is a configuration block diagram of a receiving device 1 according to the first embodiment.

  The receiving device 1 is provided with each part referred by the codes | symbols 11-16, 21-26, and 50-52. The receiving circuit 1 performs diversity reception using the antennas 11 and 21. The following description is mainly an operation description when performing diversity reception.

  The receiving circuit 1 includes two receiving systems, a first receiving system corresponding to the antenna 11 and a second receiving system corresponding to the antenna 21. The mixing circuit 12, the local oscillation circuit 13 and the filter circuit 14 form a tuner unit provided corresponding to the antenna 11, and the mixing circuit 22, the local oscillation circuit 23 and the filter circuit 24 are provided corresponding to the antenna 21. The formed tuner portion is formed.

  The RF signal processing unit 2 is formed by the parts referenced by reference numerals 12 to 14 and 22 to 24, and the baseband signal processing part 3 is formed by the parts referenced by reference numerals 15, 16, 25, 26 and 50. It is formed. Each part referred to by reference numerals 51 and 52 is realized by the microcomputer 4. Each part in the RF signal processing unit 2 is mounted, for example, on the same minute substrate.

  The receiving device 1 functions as a receiving device of a communication system used for terrestrial digital television broadcasting or terrestrial digital audio broadcasting. Assume that the receiving apparatus 1 receives a digital broadcast signal as a radio signal transmitted according to an OFDM (Orthogonal Frequency Division Multiplexing) transmission scheme. The same applies to the receiving apparatuses (1a, 1b) in other embodiments described later. In addition, for the sake of concrete description, the following description will be given on the assumption that the receiving apparatus 1 (and 1a and 1b) receives terrestrial digital broadcasting of ISDB-T (Integrated Services Digital Broadcasting-Terrestrial). .

  The OFDM transmission scheme is a scheme in which a large number of subcarriers orthogonal to each other are multiplexed and transmitted within one channel band. In a transmitter not shown, for each subcarrier, the subcarrier is modulated by a modulation scheme such as QAM (Quadrature Amplitude Modulation) according to the baseband signal to be transmitted, and the inverse fast Fourier transform is performed on the signal obtained by the modulation. An OFDM signal is generated by applying (IFFT; Inverse Fast Fourier Transform). The baseband signal includes a video signal and an audio signal to be transmitted. The generated OFDM signal is frequency-converted to a predetermined carrier band and then transmitted from the transmission device as a signal to be transmitted by digital broadcasting.

  Each of the antennas 11 and 21 receives the same digital broadcast signal transmitted by this digital broadcast. The digital broadcast signal includes OFDM signals for a plurality of channels.

  The local oscillation circuits 13 and 23 generate and output a first local oscillation signal and a second local oscillation signal, respectively. One PLL (Phase Locked Loop) circuit (not shown) is provided for each of the local oscillation circuits 13 and 23. A channel selection signal corresponding to a channel desired by the user is supplied from the oscillation frequency control unit 51 to each PLL circuit, and each PLL circuit is adapted to adapt to the frequency of the channel desired to be received according to this channel selection signal. Controls the frequency of each local oscillation signal. Hereinafter, a channel determined by a channel selection signal and desired to be received is referred to as a “channel selection channel”. The signal of any channel among the signals of a plurality of channels included in the reception signal of the antenna (11 or 21) is the signal of the channel selection channel.

  A reception signal of the antenna 11 is input to a first input terminal of a mixer (frequency mixing circuit) 12 through a band pass filter, a low noise amplifier (both not shown), and the like. The first local oscillation signal generated by the local oscillation circuit 13 is input to the second input terminal of the mixer 12. The mixer 12 performs frequency conversion of the received signal of the antenna 11 by frequency-mixing the input signal to the first input terminal and the input signal to the second input terminal of the mixer 12, and converts the frequency mixed signal obtained thereby. Output from the output terminal of the mixer 12.

  The filter circuit 14 generates and outputs a first IF signal by adding a band limitation to the frequency mixed signal from the mixer 12. That is, the first IF signal is selected and output from the frequency mixed signal by removing the high frequency component of the frequency mixed signal from the mixer 12.

  A reception signal of the antenna 21 is input to a first input terminal of a mixer (frequency mixing circuit) 22 through a bandpass filter, a low noise amplifier (both not shown), and the like. The second local oscillation signal generated by the local oscillation circuit 23 is input to the second input terminal of the mixer 22. The mixer 22 performs frequency conversion of the received signal of the antenna 21 by frequency-mixing the input signal to the first input terminal and the input signal to the second input terminal of the mixer 22, and converts the frequency mixed signal obtained thereby. Output from the output terminal of the mixer 22.

  The filter circuit 24 generates and outputs a second IF signal by adding a band limitation to the frequency mixed signal from the mixer 22. That is, the second IF signal is selected and output from the frequency mixed signal by removing the high frequency component of the frequency mixed signal from the mixer 22.

  In the case of performing diversity reception, the two tuner units select the same channel. For this reason, as described above, each local oscillation circuit is normally controlled so that the frequency of the local oscillation signal in each tuner unit is the same. However, if each local oscillation circuit is controlled in this way, reception demodulation characteristics are deteriorated due to interference between local oscillation signals. Therefore, in the receiving apparatus 1, when performing diversity reception, the frequencies of the first and second local oscillation signals generated by the local oscillation circuits 13 and 23 are intentionally different.

Now, assume that the frequencies of the first and second local oscillation signals when performing diversity reception are f _LO1 and f _LO2 (where f _LO1 > 0 [Hz] and f _LO2 > 0 [Hz]), respectively. In this case, interference between local oscillation signals is avoided by setting f _LO1 ≠ f _LO2 . Specifically, if the threshold value of the frequency difference at which interference is reduced to the extent that interference does not occur or is not a problem is set to α, f _LO1 and f _LO2 are set to satisfy at least the following expressions (1) and (2). To do. As can be seen from Equation (1), f _D represents the frequency difference between the first and second local oscillation signals.
f _D = f _LO1 -f _LO2 (1)
α ≦ | f _D | (2)

However, when trying to obtain good reception demodulation characteristics, it is not possible to select arbitrary f _LO1 and f _LO2 that satisfy the expressions (1) and (2). Hereinafter, the configuration and operation of the receiving apparatus 1 including the setting method of f _LO1 and f _LO2 will be described in detail.

Now, representing the center frequency of the selected channel before the frequency conversion in the mixer (12 or 22) at f _RF. Once the selected channel, f _RF is uniquely determined. In general, the center frequency of the IF signal obtained by frequency conversion of the received signal of the antenna is determined in advance in the specifications of the receiving apparatus or the communication system. Now, the predetermined center frequency of the IF signal corresponding to the center frequency f _RF of the selected channel is defined as f _IF , which is referred to as a reference frequency. The center frequencies of the first and second IF signals output from the filter circuits 14 and 24 are represented by f _IF1 and f _IF2, respectively.

In the first embodiment, it is assumed that the cutoff frequencies that define the passbands of the filter circuits 14 and 24 are fixed at the same frequency f _CA. Assume that f _IF1 = f _IF and f _LO1 > f _LO2 .

  FIGS. 2A and 2B show the output signals of the filter circuits 14 and 24 under this assumption on the frequency axis, respectively. 2A and 2B, the horizontal axis represents frequency, and the vertical axis represents signal power.

A broken line 62 in FIG. 2A represents the filter characteristic of the filter circuit 14, and a broken line 64 in FIG. 2B represents the filter characteristic of the filter circuit 24. Both filter characteristics are the same. A solid line 61 in FIG. 2A represents the output signal of the filter circuit 14, and the center frequency in the band of the output signal (first IF signal) of the filter circuit 14 is f _IF1 as described above. A solid line 63 in FIG. 2B represents the output signal of the filter circuit 24, and the center frequency in the band of the output signal (second IF signal) of the filter circuit 24 is f _IF2 as described above.

Since f _IF1 = f _IF is assumed and the above equation (1) is satisfied, the following equations (3) and (4) are established.
f _IF1 = f _IF = f _RF −f _LO1 (3)
f _IF2 = f _RF −f _LO2 = f _RF − (f _LO1 −f _D ) = f _IF1 + f _D (4)

That is, the center frequency f _IF2 of the output signal of the filter circuit 24 is larger than the center frequency f _IF1 of the output signal of the filter circuit 14 by f _D. On the other hand, in order to remove noise components other than signal components as much as possible, the pass band of the filter circuit is generally made as narrow as possible (that is, the cut-off frequency is made as low as possible). Therefore, when the filter characteristics of the filter circuit 14 are determined so that the output signal of the filter circuit 14 is as narrow as possible as shown in FIG. 2A, the signal components of the selected channel are shown in FIG. 2B. Is partially removed by the filter circuit 24. A hatched area 65 in FIG. 2B represents the removed signal component.

The center frequency related to the IF signal (in this example, f _IF2 ) means the center frequency of the IF signal when the removal of the signal component by the filter circuit (in this example, the filter circuit 24) is ignored. . It is also possible to determine the passband of each filter circuit so that signal components are not removed in the filter circuits 14 and 24.

When ISDB-T terrestrial digital broadcasting is operated in MODE 3, the number of subcarriers in the OFDM signal is 5617. If the number of subcarriers to be removed by filtering is somehow small among these 5617 subcarriers, reception is possible. The error correction function after carrier synthesis performed in the apparatus 1 provides a BER (bit error rate) characteristic that does not hinder viewing of digital terrestrial broadcasting. However, if the value of f _D is too large, it can not correct errors even using an error correction function is much subcarrier number to be removed, detrimental to the viewing of terrestrial digital broadcasting. The minimum receiver input level and jamming wave suppression level in Japanese terrestrial digital broadcasting are regulated by ARIB (Radio Industry Association), and it is necessary to prevent performance degradation so as to satisfy all of them.

That is, if the upper limit frequency difference between the first and second local oscillation signals that can satisfy the standard defined by ARIB is β, f _LO1 and f _LO2 are set so as to satisfy the following equation (5). Must be set. By setting f _LO1 and f _LO2 so as to satisfy Expression (5), it is possible to satisfy the ARIB standard while preventing interference between the local oscillation signals. Since the values of α and β depend on the shape of the board on which the RF signal processing unit 2 is mounted and the circuit wiring state, they are determined through experiments and the like at the design stage of the receiving apparatus 1. Of course, 0 <α <β holds.
α ≦ | f _LO1 −f _LO2 | ≦ β (5)

If the center frequency f _{RF of the} channel selection channel is determined, the reference frequency f _IF is determined, and f _LO1 is uniquely determined according to the equation (3). Therefore, f is satisfied so as to satisfy the equation (5) in relation to the determined f _{LO1. LO2} should be determined. Naturally, the specific values of f _LO1 and f _LO2 vary depending on which channel is selected. In addition to this, the values of α and / or β may differ depending on which channel the selected channel is. Therefore, in this case, the frequency difference f _D between f _LO1 and f _LO2 is also made different depending on which channel the selected channel is.

Actually, f _LO1 and f _LO2 satisfying Expression (5) are determined for each channel in the design stage of the receiving apparatus 1. That is, each of a plurality of channels in the received signal of the receiving apparatus 1 can be a channel selection channel, but specific numerical values of f _LO1 and f _LO2 satisfying the equation (5) are determined in advance for each channel. (At this point, the frequency difference f _{D for} each channel is also determined).

When the diversity reception is performed, the oscillation frequency control unit 51 causes the local oscillation circuits 13 and 23 to generate the first and second local oscillation signals having predetermined frequencies of f _LO1 and f _LO2. Each PLL circuit is controlled. The frequencies f _LO1 and f _{LO2 of} the first and second local oscillation signals actually generated and their frequency difference f _D are given to the PLL circuit according to which channel is selected (that is, to the PLL circuit). Depending on the channel selection signal). Note that it is also possible to design the receiving apparatus 1 so that the frequency difference f _D does not change regardless of which channel is selected.

  The operation of the baseband signal processing unit 3 in FIG. 1 will be described. Each IF signal from the filter circuits 14 and 24 is an analog signal. The A / D converters 15 and 25 convert the first IF signal from the filter circuit 14 and the second IF signal from the filter circuit 24 into digital signals, respectively, and the converted signals are frequency offset correction units 16. And 26.

The frequency offset correction units 16 and 26 form a frequency correction circuit 5. The frequency correction circuit 5 performs offset correction on the bands of the first and second IF signals converted into digital signals based on the offset correction signal from the offset correction control unit 52 in the microcomputer 4, thereby the center frequency. f _IF first and second IF signals are generated and output. The microcomputer 4, the formula (3) and is aware of the frequency difference f _D relationships and current (4), the offset correction signal is generated based on the perceptions.

As in the above example (see FIGS. 2A and 2B), only the f _IF2 of the center frequencies f _IF1 and f _IF2 of the first and second IF signals output from the filter circuits 14 and 24 is used. Consider a case where an offset of f _D [Hz] is given to the reference frequency f _IF .

In this case, if the center frequency of the second IF signal after the offset correction is f _IF2 ′, the frequency offset correction unit 26 satisfies the following expression (6) so that the center frequency (f _IF2 ) is offset corrected. That is, the frequency offset correction unit 26 shifts the band of the second IF signal from the filter circuit 24 to the lower frequency side by f _D, and the shifted second IF signal (that is, the center frequency is f _IF The second IF signal that has been offset-corrected so that
f _IF2 '= f _IF2 -f _D = f _IF1 = f _IF (6)

On the other hand, since no offset is given to the center frequency f _IF1 of the first IF signal with respect to the reference frequency f _IF , the frequency offset correction unit 16 does not perform offset correction. That is, when the center frequency of the output signal of the frequency offset correction unit 16 is f _IF1 ′, the following equation (7) is established. In the case of this example, the frequency offset correction unit 16 outputs the first IF signal output from the A / D converter 15 as it is (therefore, the frequency offset correction unit 16 is deleted from the receiving device 1). Is possible).
f _IF1 '= f _IF1 = f _IF (7)

  As described above, the offset correction is performed only for the system to which the frequency offset is given in the frequency conversion stage of the two receiving systems. The output signals on the frequency axis of the frequency offset correction units 16 and 26 are shown in FIGS. 3A and 3B, respectively.

  Thereafter, the diversity combining unit 50 combines the output signals of the frequency offset correction units 16 and 26. This synthesis is diversity synthesis. As this diversity combining method, any known diversity combining method can be used. For example, diversity combining is performed by applying a maximum ratio combining method in which the phases are combined for each subcarrier.

  The diversity combining unit 50 restores a baseband signal by performing predetermined signal processing including OFDM demodulation processing on the signal after diversity combining, and generates a data signal representing a video signal and an audio signal from the baseband signal. Output. This data signal is supplied to a display device or a speaker (not shown) connected to the receiving device 1 to perform video display or audio output.

  Further, although the configuration and operation related to diversity reception have been described, it is also possible for the receiving apparatus 1 to simultaneously select two channels having different frequency bands. When two channels having different frequency bands are selected, one channel is selected as a channel for the first receiving system corresponding to the antenna 11 and the other channel is selected for the second receiving system corresponding to the antenna 21. What is necessary is just to demodulate the signal of both channel selection channels separately, treating as a channel selection channel, and not performing diversity reception. In this case, the local oscillation circuit 13 generates a local oscillation signal for selecting one channel and supplies it to the mixer 12, and the local oscillation circuit 23 generates a local oscillation signal for selecting the other channel. To the mixer 22. The frequency difference between the two local oscillation signals at this time is equal to the frequency difference between one channel and the other channel. The output signal of the mixer 12 via the filter circuit 14 and the A / D converter 15 and the output signal of the mixer 22 via the filter circuit 24 and the A / D converter 25 are individually demodulated, Data signals for two channels are generated. From the data signals for the two channels, the video and audio for the two broadcast programs can be reproduced simultaneously.

  By configuring the receiving apparatus 1 as described above, it is possible to avoid interference between local oscillation signals when performing diversity reception, and it is possible to prevent deterioration of reception demodulation characteristics. Further, unlike the configuration of Patent Document 3, each receiving system can use an independent local oscillation signal, so that it is possible to select different channels in each receiving system.

  As described above, when the offset correction is performed based on the offset control signal from the offset correction control unit 52, the offset amount and the offset direction are automatically detected by the signal processing on the signals based on the reception signals of the antennas 11 and 21, Based on this detection result, offset correction in the frequency correction circuit 5 may be performed. In this case, the offset correction control unit 52 is not necessary. For example, since the OFDM signal contains a signal (pilot signal) known to the receiving apparatus 1, the frequency difference of the known signal is detected between the output signals of the A / D converters 15 and 25. To. Then, based on the detection result, the frequency correction circuit 5 may perform offset correction corresponding to the above equations (6) and (7).

Further, in the above example, among the center frequency f _IF1 and f _IF2 in the first and second IF signals, giving an offset to the reference frequency f _IF only f _IF2. Instead, an offset may be given only to f _IF1 , or an offset may be given to both f _IF1 and f _IF2 . When an offset is given to both f _IF1 and f _IF2 , first and second IF signals having a center frequency f _IF are generated by performing offset correction in both of the frequency offset correction units 16 and 26.

<< Second Embodiment >>
Next, a second embodiment of the present invention will be described. In the first embodiment described above, it is assumed that the cutoff frequencies that define the passbands of the filter circuits 14 and 24 are fixed at the same frequency f _CA. In the second embodiment, it is assumed that they are variable. Since the configuration block diagram of the receiving apparatus according to the second embodiment is the same as that of the receiving apparatus 1 of FIG. 1, overlapping illustration is omitted, and the receiving apparatus according to the second embodiment is also referred to by reference numeral 1. To do. The receiving apparatus 1 according to the second embodiment is the same as that of the first embodiment except that the passbands of the filter circuits 14 and 24 are variable, and unless there is a contradiction, the items ( (including definitions for frequency parameters such as f _LO1 , f _LO2 and f _D ) all apply to the second embodiment. Hereinafter, only the differences from the first embodiment will be described.

The receiving apparatus 1 is assumed to operate so that the above formulas (1) to (4) are satisfied. Further, f _LO1 > f _LO2 . FIGS. 4A and 4B show the output signals of the filter circuits 14 and 24 under this assumption on the frequency axis, respectively. 4A and 4B, the horizontal axis represents frequency, and the vertical axis represents signal power.

In FIG. 4A, the broken line 62 represents the filter characteristic of the filter circuit 14, and the cut-off frequency of the filter circuit 14 is f _CA. In FIG. 4A, the solid line 61 represents the output signal of the filter circuit 14, and the center frequency in the band of the output signal (first IF signal) of the filter circuit 14 is f _IF1 as described above. . 4A and FIG. 2A are the same drawing.

In FIG. 4B, the broken line 64a represents the filter characteristic of the filter circuit 24, and the cut-off frequency of the filter circuit 24 is f _CB . The filter circuit 24 adjusts its own cut-off frequency so that “f _CB = f _CA + f _D ” based on the frequency difference f _D between the first and second local oscillation signals. The frequency difference f _D can be specified from an offset correction signal of the offset correction control unit 52 or the like. In FIG. 4B, the solid line 63a represents the output signal of the filter circuit 24, and the center frequency in the band of the output signal (second IF signal) of the filter circuit 24 is f _IF2 as described above. .

Since the cut-off frequency of the filter circuit 24 is f _CB (= f _CA + f _D ), unlike the first embodiment, filtering of signal components by the filter circuit 24 is avoided, and deterioration of reception performance is prevented. .

As described above, the frequency difference f _D can vary depending on which channel is the selected channel. For this reason, the cutoff frequency (pass band) of the filter circuit 24 is dynamically changed according to which channel the selected channel is.

In the present embodiment, since filtering of the signal component by the filter circuit 24 is avoided, it is not necessary to consider the above equation (5) when determining f _LO1 and f _LO2 . However, since the adjustment width of the pass band of the filter circuit 24 is limited, the signal component may be filtered by the filter circuit 24 depending on the selected channel. The f _LO1 and f _LO2 for such a channel selection are selected so as to satisfy Equation (5).

In the above-described example, it is sufficient to adjust only the pass band of the filter circuit 24 among the filter circuits 14 and 24. Therefore, the pass band of the filter circuit 14 does not need to be variable. Conversely, fixing the pass band of the filter circuit 24, a variable pass band of the filter circuit 14, the pass band of the filter circuit 14 may be adjusted in accordance with the frequency difference f _D. Further, the pass bands of both the filter circuits 14 and 24 may be variable. When an offset with respect to the reference frequency f _IF is given to both f _IF1 and f _IF2 , the pass bands of both the filter circuits 14 and 24 may be adjusted according to the given offsets in order to avoid filtering of the signal component.

<< Third Embodiment >>
In the first and second embodiments, the receiving apparatus having two receiving systems has been described. However, the technical matters described in the first and second embodiments perform diversity reception using three or more receiving systems. It can be applied to any receiving device. The matters described in the first and second embodiments apply to this embodiment as long as there is no contradiction.

  As an example, in the third embodiment, a receiving device 1a having four receiving systems will be described. FIG. 5 is a configuration block diagram of a receiving device 1a according to the third embodiment. The receiving device 1a includes antennas 11, 11a, 21 and 21a, mixers 12, 12a, 22 and 22a, local oscillation circuits 13 and 23, filter circuits 14, 14a, 24 and 24a, and an A / D converter 15. 15a, 25 and 25a, frequency offset correction units 16, 16a, 26 and 26a, diversity combining unit 50a, oscillation frequency control unit 51, and offset correction control unit 52. The receiving circuit 1a performs diversity reception using the four antennas 11, 11a, 21 and 21a.

  The mixers 12, 12a, 22 and 22a, the local oscillation circuits 13 and 23, and the filter circuits 14, 14a, 24 and 24a form the RF signal processing unit 2a, and the A / D converters 15, 15a, 25 and 25a and the frequency The baseband signal processing unit 3a is formed by the offset correction units 16, 16a, 26 and 26a and the diversity combining unit 50a. The oscillation frequency control unit 51 and the offset correction control unit 52 are realized by the microcomputer 4a. Each part in the RF signal processing unit 2a is mounted on the same minute substrate, for example. The functions of the parts referred to by the same name in the receiving device 1a are the same.

  Each of the antennas 11, 11a, 21 and 21a receives the same digital broadcast signal. As described in the first embodiment, the local oscillation circuits 13 and 23 generate and output a first local oscillation signal and a second local oscillation signal under the control of the oscillation frequency control unit 51. When performing diversity reception, as described in the first embodiment, the frequencies of the first and second local oscillation signals are intentionally varied so as to satisfy the expressions (1) to (5). As described in the second embodiment, when the pass band of the filter circuit (14, 14a, 24 and 24a) is variable, it is not essential to satisfy the expression (5).

  The first local oscillation signal is supplied to the mixers 12 and 12a, and the second local oscillation signal is supplied to the mixers 22 and 22a. In the receiving device 1a, the first local oscillation signal is shared by the reception system corresponding to the antenna 11 and the reception system corresponding to the antenna 11a, and the second local oscillation signal is used for the reception system and the antenna 21a corresponding to the antenna 21. Shared by the receiving system corresponding to The offset control signal from the offset correction control unit 52 is given to the frequency offset correction units 16, 16a, 26 and 26a. The frequency offset correction units 16, 16a, 26 and 26a form a frequency correction circuit.

  The operations of the mixer 12, the filter circuit 14, the A / D converter 15, and the frequency offset correction unit 16 are the same as those described in the first or second embodiment. The mixer 12a, the filter circuit 14a, and the A / D The converter 15a and the frequency offset correction unit 16a operate in the same manner as the mixer 12, the filter circuit 14, the A / D converter 15, and the frequency offset correction unit 16, respectively.

  The operations of the mixer 22, the filter circuit 24, the A / D converter 25, and the frequency offset correction unit 26 are the same as those described in the first or second embodiment. The mixer 22a, the filter circuit 24a, and the A / D The converter 25a and the frequency offset correction unit 26a operate in the same manner as the mixer 22, the filter circuit 24, the A / D converter 25, and the frequency offset correction unit 26, respectively.

  The diversity combining unit 50a performs diversity combining of the output signals of the frequency offset correction units 16, 16a, 26, and 26a, similarly to the diversity combining unit 50 of FIG. The diversity combining unit 50a restores a baseband signal by performing predetermined signal processing including OFDM demodulation processing on the signal after diversity combining, and generates a data signal representing a video signal or an audio signal from the baseband signal. Output. This data signal is supplied to a display device and a speaker (not shown) connected to the receiving device 1a, and video display and audio output are performed.

  Further, instead of performing diversity reception, it is also possible to select two channels having different frequency bands at the same time in the receiving device 1a as in the receiving device 1 of FIG.

  The effect similar to that of the receiving apparatus 1 of FIG. 1 can be obtained by the receiving apparatus 1a. Of course, since the number of reception systems is increased as compared with the receiving apparatus 1, it is possible to improve reception demodulation performance by diversity reception.

<< Fourth Embodiment >>
An embodiment of another receiving apparatus having four receiving systems will be described. FIG. 6 is a configuration block diagram of a receiving device 1b according to the fourth embodiment. The matters described in the first and second embodiments apply to this embodiment as long as there is no contradiction.

  The receiving device 1b includes antennas 11, 21, 31 and 41, mixers 12, 22, 32 and 42, local oscillation circuits 13, 23, 33 and 43, filter circuits 14, 24, 34 and 44, A / D converters 15, 25, 35, and 45, frequency offset correction units 16, 26, 36, and 46, a diversity combining unit 50 b, an oscillation frequency control unit 51, and an offset correction control unit 52 are provided. The receiving circuit 1b performs diversity reception using the four antennas 11, 21, 31, and 41.

  The mixers 12, 22, 32 and 42, the local oscillation circuits 13, 23, 33 and 43 and the filter circuits 14, 24, 34 and 44 form an RF signal processing unit 2 b, and A / D converters 15, 25, 35. And 45, the frequency offset correction units 16, 26, 36 and 46, and the diversity combining unit 50b form a baseband signal processing unit 3b. The oscillation frequency control unit 51 and the offset correction control unit 52 are realized by the microcomputer 4b. Each part in the RF signal processing unit 2b is mounted on the same minute substrate, for example. The functions of the parts referred to by the same name in the receiving device 1b are the same.

The local oscillation circuits 13, 23, 33 and 43 generate and output first, second, third and fourth local oscillation signals, respectively. The frequencies of the first, second, third, and fourth local oscillation signals at the time of diversity reception are set to f _LO1 , f _LO2 , f _LO3, and f _LO4 (where f _LO1 > 0 [Hz]). F _LO2 > 0 [Hz], f _LO3 > 0 [Hz], f _LO4 > 0 [Hz]). One PLL (Phase Locked Loop) circuit (not shown) is provided for each of the local oscillation circuits 13, 23, 33 and 43. A channel selection signal corresponding to a channel desired by the user is supplied from the oscillation frequency control unit 51 to each PLL circuit, and each PLL circuit is adapted to adapt to the frequency of the channel desired to be received according to this channel selection signal. Controls the frequency of each local oscillation signal.

  The operations of the mixer 12, the filter circuit 14, the A / D converter 15 and the frequency offset correction unit 16, and the operations of the mixer 22, the filter circuit 24, the A / D converter 25 and the frequency offset correction unit 26 are as follows. The same as those described in the first or second embodiment. The operations of the mixer 32, the filter circuit 34, the A / D converter 35, and the frequency offset correction unit 36, and the operations of the mixer 42, the filter circuit 44, the A / D converter 45, and the frequency offset correction unit 46 are as follows. The operations are the same as those of the mixer 12, the filter circuit 14, the A / D converter 15, and the frequency offset correction unit 16.

  However, since the number of reception systems is four, the frequency of each local oscillation signal is set as follows.

That is, the following equation (8) is satisfied between any two frequencies f _LOi and f _{LOj out of} the frequencies f _LO1 , f _LO2 , f _LO3 and f _LO4 . Here, i and j are integers of 1 or more and 4 or less, respectively, and i ≠ j. Further, it is preferable to satisfy the expression (9) so that the ARIB standard can be satisfied.
α ≦ | f _LOi −f _LOj | (8)
| F _LOi −f _LOj | ≦ β (9)

As a specific example, f _LO1 , f _LO2 , f _LO3, and f _LO4 are _expressed by the following formulas (10) to (13) with reference to the reference frequency f _IF of the IF signal corresponding to the center frequency f _RF of the selected channel. The case where it is determined to satisfy is assumed.
f _RF -f _LO1 = f _IF -α / 2 (10)
f _RF -f _LO2 = f _IF + α / 2 (11)
f _RF -f _LO3 = f _IF -3α / 2 (12)
f _RF -f _LO4 = f _IF + 3α / 2 (13)

The output signals on the frequency axis of the filter circuits 14, 24, 34, and 44 when the expressions (10) to (13) are satisfied are shown in FIGS. 7 (a), 7 (b), 7 (c), and 7 (d), respectively. Shown in 7A, 7 </ b> B, 7 </ b> C, and 7 </ b> D, the horizontal axis represents frequency and the vertical axis represents signal power. F _IFA , f _IFB , f _IFC, and f _IFD shown in FIG. 7A and the like are the first, second, third, and fourth IFs output from the filter circuits 14, 24, 34, and 44, respectively. It represents the center frequency of the signal.

  The first, second, third, and fourth IF signals output from the filter circuits 14, 24, 34, and 44 are converted into digital signals, and then sent to the frequency offset correction units 16, 26, 36, and 46, respectively. Given. The frequency offset correction units 16, 26, 36, and 46 form a frequency correction circuit.

Based on the offset correction signal from the offset correction control unit 52, the frequency offset correction units 16, 26, 36, and 46 change the bands of the first, second, third, and fourth IF signals converted into digital signals. Offset correction is performed, thereby generating and outputting first, second, third, and fourth IF signals having a center frequency _fIF . The microcomputer 4b recognizes the relationship of the above formulas (10) to (13), and the offset correction signal is generated based on this recognition content. Specifically, for example, the frequency offset correction unit 16 shifts the band of the first IF signal from the filter circuit 14 to the high frequency side by α / 2 to thereby change the first IF signal having the center frequency f _IF . Generate. The same applies to the frequency offset correction units 26, 36 and 46.

  The diversity combining unit 50b performs diversity combining of the output signals of the frequency offset correction units 16, 26, 36, and 46, similar to the diversity combining unit 50 of FIG. The diversity combining unit 50b restores a baseband signal by performing predetermined signal processing including OFDM demodulation processing on the signal after diversity combining, and generates a data signal representing a video signal and an audio signal from the baseband signal. Output. This data signal is supplied to a display device and a speaker (not shown) connected to the receiving device 1b, and video display and audio output are performed.

  Further, instead of performing diversity reception, it is also possible to simultaneously select four channels having different frequency bands in the receiving device 1b as in the receiving device 1 of FIG.

  The effect similar to that of the receiving apparatus 1 of FIG. 1 can be obtained by the receiving apparatus 1b. Of course, since the number of reception systems is increased as compared with the receiving apparatus 1, it is possible to improve reception demodulation performance by diversity reception.

<< Fifth Embodiment >>
In the receiving apparatus according to the first to fourth embodiments, the high-frequency signal received by the antenna is temporarily converted into an intermediate frequency signal (IF signal), and offset correction or the like is performed at the stage of the intermediate frequency signal. Various methods exist as down-conversion methods for high-frequency signals, and the first to fourth receivers adopting a down-conversion method different from the down-conversion method in the receiving devices of the first to fourth embodiments. The technical matters described in the fourth embodiment are applicable.

For example, the operation of each part in the receiving apparatus 1 when the direct conversion method is adopted in the receiving apparatus 1 of FIG. 1 will be described. In this case, the mixers 12 and 22 perform quadrature detection by the direct conversion method by frequency-mixing the reception signals of the antennas 11 and 21 and the first and second local oscillation signals, respectively. At this time, the first local oscillation signal from the local oscillation circuit 13 is composed of two signals whose phases are different from each other by 90 degrees, and the second local oscillation signal from the local oscillation circuit 23 is also different from each other in phases by 90 degrees. Consists of two signals. When the center frequency of the channel selection channel is f _RF , the frequencies f _LO1 and f _LO2 of the first and second local oscillation signals are, for example, f _RF and (f _RF + f _D ), respectively. Also in this case, the above formulas (1) and (2) are satisfied, and preferably the formula (5) is also satisfied.

  By the quadrature detection, two baseband signals whose phases are different from each other by 90 degrees are output from the mixer 12. These two baseband signals are composed of an I (In-Phase) signal and a Q (Quadrature-Phase) signal. By the quadrature detection, two baseband signals whose phases are different from each other by 90 degrees are also output from the mixer 22. The filter circuit 14 applies band limitation to the two baseband signals from the mixer 12 to remove unnecessary wave components, and the filter circuit 24 applies band limitation to the two baseband signals from the mixer 22. To remove unwanted wave components.

Then, the frequency offset correction unit 26 shifts the bands of the two baseband signals given from the mixer 22 via the filter circuit 24 and the A / D converter 25 to the low frequency side by f _D , and after this shift 2 baseband signals are output. On the other hand, the frequency offset correction unit 16 outputs the two baseband signals given from the mixer 12 via the filter circuit 14 and the A / D converter 15 to the diversity combining unit 50 as they are. The diversity combining unit 50 performs diversity combining of the output signals of the frequency offset correction units 16 and 26, generates a data signal representing a video signal and an audio signal from the combined signal, and outputs the data signal.

<< Deformation, etc. >>
As modifications or annotations of the above-described embodiment, notes 1 to 3 are described below. The contents described in each comment can be arbitrarily combined as long as there is no contradiction.

[Note 1]
In each of the above-described embodiments, the receiving apparatus receives an OFDM signal, that is, a signal modulated according to the OFDM transmission scheme (OFDM modulated signal). However, the signal received by the receiving apparatus according to the present invention via the antenna is not limited to the OFDM signal. That is, the present invention can be applied to a receiving apparatus that receives any digitally modulated or analog modulated signal other than the OFDM signal.

[Note 2]
The receiving apparatus according to the present invention is used by being mounted on a vehicle such as an automobile, for example. This is because there is a strong demand for miniaturization of a receiving device for vehicles, and diversity reception functions particularly effectively.

[Note 3]
The receiving device (1, 1a or 1b) according to each embodiment can be realized by hardware or a combination of hardware and software.

1 is a configuration block diagram of a receiving device according to a first embodiment of the present invention. FIG. 2 is a diagram illustrating an output signal of each filter circuit of FIG. 1 on a frequency axis according to the first embodiment of the present invention. FIG. 2 is a diagram illustrating output signals of frequency offset correction units in FIG. 1 on a frequency axis according to the first embodiment of the present invention. FIG. 4 is a diagram illustrating an output signal of each filter circuit of FIG. 1 on a frequency axis according to the second embodiment of the present invention. FIG. 6 is a configuration block diagram of a receiving device according to a third embodiment of the present invention. FIG. 10 is a configuration block diagram of a receiving device according to a fourth embodiment of the present invention. FIG. 7 is a diagram illustrating an output signal of each filter circuit of FIG. 6 on a frequency axis according to the fourth embodiment of the present invention.

Explanation of symbols

1, 1a, 1b Receiver 2, 2a, 2b RF signal processing unit 3, 3a, 3b Baseband signal processing unit 4, 4a, 4b Microcomputer 5 Frequency correction circuit

Claims (5)

In a receiving apparatus that performs diversity reception using a plurality of antennas including a first antenna and a second antenna,
A first mixing circuit that frequency-converts and outputs a received signal of the first antenna using a first local oscillation signal;
A second mixing circuit that frequency-converts and outputs the received signal of the second antenna using a second local oscillation signal,
A receiving apparatus that performs diversity reception by changing the frequencies of the first and second local oscillation signals. A first filter for applying a band limitation to the output signal of the first mixing circuit;
A second filter for applying a band limitation to the output signal of the second mixing circuit;
The output signal of the first mixing circuit is received through the first filter and the output signal of the second mixing circuit is received through the second filter, and the first and second local oscillation signals are received. A frequency correction circuit for correcting the frequency difference between the output signals of each filter due to the frequency difference between,
The receiving apparatus according to claim 1, further comprising: a diversity combining circuit that diversity-combines the output signals of the corrected filters given from the frequency correction circuit. The frequency correction circuit shifts the band of the output signal of at least one of the first and second filters according to the frequency difference between the first and second local oscillation signals. The receiving apparatus according to claim 2, wherein a frequency difference between output signals of the filters is corrected. A first local oscillation circuit for generating the first local oscillation signal;
A second local oscillation circuit for generating the second local oscillation signal,
2. The first and second local oscillation circuits are controlled so that a predetermined frequency difference is generated between the first and second local oscillation signals when performing the diversity reception. Item 4. The receiving device according to any one of Items 3 to 4. The pass band in at least one of the first and second filters is variable,
The receiving apparatus according to claim 2 or 3, wherein the passband is adjusted according to a frequency difference between the first and second local oscillation signals.

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