JP2005218026A - Receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a small receiver that can receive two different frequency bands and requires only low power consumption. <P>SOLUTION: This receiver for receiving a first frequency band has a free frequency selecting means for selecting a free frequency of the first frequency band and is added with a second frequency conversion circuit 4 for converting a received signal of a second frequency into the free frequency selected by the free frequency selecting means to receive it. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a circuit configuration of a receiver that receives signals of two or more frequency bands.

  In recent years, there has been a movement to digitize wireless communication for the purpose of advanced use of radio waves and efficient use of frequencies. As for broadcasting, digital satellite broadcasting has already been put into practical use, and terrestrial digital television broadcasting has started in some areas.

  Japanese terrestrial digital television broadcasts have started in the UHF television broadcast frequency band (hereinafter referred to as UHF) rather than the VHF television broadcast frequency band (hereinafter referred to as VHF) in which conventional analog television broadcasts are mainly performed. On the other hand, digital audio broadcasting using 7 channels in the VHF band has been started as a practical test broadcast.

  Thus, although it is at the stage of starting to rise, digital broadcasting is being performed in each frequency band of VHF and UHF. Since these broadcasts are not transmitted according to independent standards like conventional analog television broadcast and FM audio broadcast, both television and audio broadcast are transmitted by ISDB-T (Terrestrial Integrated Services Digital Broadcasting) system. It is also possible to receive with the same receiver, although there are some differences such as different frequencies.

  As means for receiving terrestrial digital broadcasting performed by both VHF and UHF, it is conceivable that the high frequency tuner circuit has the same configuration as a conventional tuner circuit for VHF and UHF television broadcasting. Patent Document 1 shows a configuration for receiving each band of VHF and UHF by independently providing two VHF receiver circuits and two UHF receiver circuits.

In addition, as shown in Patent Document 2, a method of receiving a signal by converting the frequency of the VHF band into the UHF band has also been proposed.
JP 2000-32361 A (page 8, FIG. 4) JP-A-7-336613 (page 9, FIG. 5)

  The configuration of the receiver shown in Patent Document 1 is a circuit system that requires a VHF receiver circuit and a UHF receiver circuit independently of each other, so that it is not suitable for downsizing the receiver and the price is high. There are challenges.

  The configuration of the receiver shown in Patent Document 2 is a frequency conversion circuit that converts a VHF reception signal for UHF reception, and a method for reducing the size of the device by adding such a circuit to the UHF receiver. Is also possible. However, there is a problem that reception quality deteriorates due to interference if other signals are present at a corresponding frequency in the UHF band when the VHF band signal is converted into the UHF band. When receiving with the receiver installed at a fixed position, there is no problem just by manually setting the frequency with no signal once. However, when receiving while moving, it may be converted depending on the area moved. There is a case where broadcasting is performed at a later frequency. In such a case, there is a problem that interference is caused and reception cannot be performed normally.

  Therefore, the present invention has been made in view of the unsolved problems of the above-described conventional example, and in the circuit system to which the frequency conversion circuit that can reduce the circuit configuration of the receiver is added, the frequency conversion by the frequency conversion circuit is performed. Another object of the present invention is to realize a receiver that obtains good reception characteristics without causing interference.

  In order to solve the above-described problem, a receiver according to a first aspect of the present invention includes a receiving circuit that receives a signal in a first frequency band, and a vacant frequency selection unit that selects a vacant frequency in the first frequency band A frequency conversion circuit that converts a signal in a second frequency band different from the first frequency band into a free frequency in the first frequency band selected by the selection unit and supplies the converted signal to the reception circuit; It is a feature.

  First, a reception target signal in the second frequency band is a reception signal, a frequency in which the reception signal exists is a reception frequency, and a reception signal after being converted to the first frequency band is a converted reception signal and a frequency of the converted reception signal Is defined as the conversion target frequency.

  In the first aspect of the invention, in a receiver that performs reception processing after frequency conversion of a received signal to a conversion target frequency, the reception signal is converted to a uniquely defined conversion target frequency in the first frequency band. Instead, the idle frequency selection means selects an idle frequency where no other signal exists in the first frequency, and performs frequency conversion using the frequency as a conversion target frequency. As a result, good reception performance can be obtained without causing interference between the converted received signal and the signal present at the conversion target frequency.

  A receiver according to a second invention is the receiver according to the first invention, wherein the vacant frequency selecting means is configured such that the first frequency band is higher than the signal frequency of the second frequency band. When a frequency obtained by multiplying the signal frequency of the second frequency band by an integer of 2 or more overlaps with the first frequency band, it is determined that the frequency is not a free frequency.

  In the second aspect of the invention, the harmonics generated when the received signal in the second frequency band is frequency-converted by the mixer are avoided from overlapping with the conversion target frequency. As a result, interference interference due to harmonics of the received signal can be prevented.

  A receiver according to a third invention is the receiver according to the first or second invention, wherein after the signal of the second frequency band is converted to the first frequency band, the reception quality of the signal is increased. A reception quality detecting means for detecting; and a free frequency changing means for selecting another free frequency by the free frequency selecting means when the reception quality detected by the reception quality detecting means is low. It is said.

  In the third aspect of the invention, the determination as to whether the conversion target frequency is empty is performed based on the reception quality of the converted reception signal. When the reception quality of the converted reception signal is deteriorated compared to the predetermined good reception quality, the free frequency changing unit causes the free frequency selection unit to select another conversion target frequency that does not deteriorate the reception quality. Thus, a receiver with stable reception quality can be provided.

  A receiver according to a fourth invention is the receiver according to any one of the first to third inventions, wherein the first frequency band is a frequency band of UHF television broadcasting, and the second frequency The band signal is a terrestrial digital broadcast transmitted in seven channels in the VHF television broadcast frequency band.

  According to the fourth aspect of the invention, the circuit is simplified by converting the VHF band terrestrial digital broadcast signal, which is scheduled to be broadcast only on 7 channels for the time being, to the UHF band where many broadcasts are scheduled. A digital broadcast receiver is provided. In particular, by detecting a vacant frequency in the UHF band, in which the reception status is likely to change compared to the VHF band in mobile reception, and performing frequency conversion on the frequency and receiving it, the stable reception status can be reduced in size and with low power consumption. Can be realized with a machine.

  An embodiment of the present invention will be described.

  First, the first embodiment will be described. The configuration of the receiver according to the present embodiment is shown using the block diagram of FIG.

  In FIG. 1, reference numeral 1 denotes a reception antenna. A reception signal received by the reception antenna 1 is supplied to a frequency band changeover switch 2. The frequency band changeover switch 2 is a switch for selecting a desired reception frequency band. When the user selects reception of the first frequency band of the UHF band, for example, the received signal is supplied to the first frequency conversion circuit 3. Then, it is down-converted by the first frequency conversion circuit 3 and supplied to an intermediate frequency (hereinafter referred to as IF) circuit 5 for amplification. The output signal of the IF circuit 5 is supplied to the demodulator 6 and demodulated. On the other hand, when reception of a second frequency band lower than the first frequency band, for example, the VHF band is selected by the user, the received signal is supplied to the second frequency conversion circuit 4, and the second frequency conversion circuit 4 Then, after up-conversion to the first frequency band, the signal is input to the first frequency conversion circuit 3 and thereafter received. Further, the output of the IF circuit 5 is supplied to the electric field strength detection circuit 9, the state of the signal is detected, and the detection result is output to the control unit 7. Reference numeral 8 denotes an operation unit.

  Here, the antenna 1 is for receiving a target signal, and can be housed in the same housing as the receiving circuit depending on the form of the receiver, or can be connected to the receiving circuit by a cable that is located away from the receiving circuit. Sometimes it is done.

  The movable contact c of the frequency band change switch 2 is connected to the antenna 1, the normally closed contact a of the frequency band change switch 2 is connected to the first frequency conversion circuit 3, and the normally open contact b of the frequency band change switch 2 is the second frequency conversion. It is connected to the circuit 4.

  The first frequency conversion circuit 3 includes a first band-pass filter 31 that selects a first frequency band, a first high-frequency amplifier circuit 32 that amplifies a received signal, a first mixer 33, and a first local oscillation circuit 34-1. And a first PLL circuit 35-1. The first local oscillation circuit 34-1 and the first PLL circuit 35-1 generate a first local oscillation signal, which is supplied to the first mixer 33. In the first mixer 33, the received signal is converted into an IF signal and supplied to the IF circuit 5.

  The second frequency conversion circuit 4 includes a second band-pass filter 41 that selects a second frequency band, a second high-frequency amplifier circuit 42 that amplifies a received signal, a second mixer 43, and a second local oscillation circuit 34-2. And a second PLL circuit 35-2. The second local oscillation circuit 34-2 and the second PLL circuit 35-2 generate a second local oscillation signal, which is supplied to the second mixer 43. The second mixer 43 up-converts the received signal into a converted received signal corresponding to the first frequency band and supplies it to the first frequency conversion circuit 3.

  The IF circuit 5 includes an IF band pass filter 51 and an IF amplifier 52. The IF signal output from the first frequency conversion circuit 3 is amplified to a desired amplitude by the IF amplifying circuit 52 after the desired signal is selected by the IF bandpass filter 51 and output. In this embodiment, the IF amplifier circuit 52 uses a variable gain amplifier that controls the gain according to the electric field strength of the received signal.

  The control unit 7 is connected to an operation unit 8 where a user performs a channel selection operation or the like, and by this operation, a reception frequency is set for the PLL circuits 35-1 and 35-2 of the receiver. When the channel selection operation is performed from the operation unit 8 to the first frequency band, the control unit 7 switches the movable contact of the frequency band changeover switch 2 to the a side, and the frequency division ratio of the first PLL circuit 35-1 will be described later. Set the frequency corresponding to the received signal in the procedure. On the other hand, when a channel selection operation is performed from the operation unit 8 to the second frequency band, the control unit 7 switches the movable contact of the frequency band changeover switch 2 to the b side and sets the frequency division ratio of the second PLL circuit 35-2. The frequency is set so that the received signal becomes the converted received signal in the procedure described later. The control unit 7 is generally realized by a microcomputer, a storage element, an interface circuit, etc. (not shown) in addition to the operation unit 8. The operation unit 8 may be provided with a display circuit for confirming the status of the receiver.

  The IF signal output from the IF circuit 5 is input to the demodulator 6. The demodulator 6 performs processing for extracting desired information from the received signal according to a predetermined procedure.

  The output of the IF circuit 5 is connected to the electric field intensity detection circuit 9, and the detection result is determined by the control unit 7, and the unused frequency detection means is realized by controlling the PLL circuits 35-1 and 35-2. ing.

  Next, the operation of the first embodiment will be described.

  In FIG. 1, the signal received by the antenna 1 is input to the frequency band changeover switch 2. The frequency band changeover switch 2 selects and connects the received signal input from the antenna to the first frequency conversion circuit 3 or the second frequency conversion circuit 4 by the operation of the operation unit 8 connected to the control unit 7 by the user. To do.

  When the user performs an operation of selecting the first frequency band, the frequency band changeover switch 2 inputs the received signal to the first frequency conversion circuit 3. The received signal input to the first frequency conversion circuit 3 is selected by the first band-pass filter 31 to a band including a channel desired to be received, and then amplified by the first high-frequency amplifier circuit 32 to be first mixed. Is input to the device 33. The received signal input to the first mixer 33 is converted into an IF signal that is the difference from the first local oscillation signal. The first local oscillation signal is generated in the first local oscillation circuit 34-1. The oscillation frequency is controlled by the control circuit 7 such that the frequency division ratio of the first PLL circuit 35-1 is set to be the sum of the reception frequency and the IF frequency.

  Next, when the user performs an operation of selecting the second frequency band, the frequency band selector switch 2 inputs the received signal to the second frequency conversion circuit 4. The received signal input to the second frequency conversion circuit 4 is selected by the second band-pass filter 41 into a band including a channel desired to be received, then amplified by the second high-frequency amplifier circuit 42, and second mixed. Is input to the device 43. The reception signal input to the second mixer 43 is converted into a frequency that is a difference from the second local oscillation signal. The second local oscillation signal is generated in the second local oscillation circuit 34-2. The oscillation frequency is controlled by the control circuit 7 by setting the frequency division ratio of the second PLL circuit 35-2 so as to be the sum of the reception frequency and the conversion target frequency.

  As described above, the received signal in the second band is once up-converted to the first frequency band by the second frequency conversion circuit 4, and then converted to the IF frequency by the first frequency conversion circuit 3, and then the demodulator 6 is demodulated.

  Further, details of the first embodiment will be described. The received signal in the first frequency band is converted to an IF frequency by the first frequency conversion circuit 3 and demodulated by the demodulator 6. On the other hand, the received signal in the second frequency band is converted into the frequency to be converted in the first frequency band by the second frequency conversion circuit 4, then converted to the IF frequency, and demodulated by the demodulator 6. .

  Here, in the embodiment of the present invention, a receiver for receiving terrestrial digital broadcasting will be described as an example. First, the signal frequency relationship between terrestrial television broadcasting and terrestrial digital broadcasting is shown in FIG. The horizontal axis in FIG. 2 represents the frequency, and the symbol shown as #n represents the number of channels (n). The broadcast wave has a band of about 6 MHz, but is described at the center frequency for convenience. Digital terrestrial broadcasting is currently planned to use 7 channels (# 7) in the VHF band and 13 channels (# 13) to 62 channels (# 62) in the UHF band. In addition, in the future, terrestrial analog television broadcasting will be completely abolished and unified with UHF band terrestrial digital television broadcasting, and thereafter the VHF band will be used for terrestrial digital audio broadcasting.

  In the receiver of the present invention, UHF is handled as the first frequency band and VHF is handled as the second frequency band. In the embodiment of the present invention, a dedicated circuit for VHF band reception is not provided, but the second frequency conversion circuit 4 is added to the UHF band reception circuit. This is due to the following reason.

  VHF terrestrial digital broadcasting is a practical test broadcast using 7 channels, which is the gap between the current terrestrial television broadcasts, and there is a possibility that a VHF band reception circuit will not be provided when commercializing terrestrial digital broadcast receivers. is there. In that case, a UHF band dedicated receiver and a UHF band VHF band can be obtained by adding a frequency conversion circuit for receiving the VHF band to the UHF band receiving circuit instead of mounting a UHF band and VHF band independent receiving circuit. In the two types of receivers, the common receiver, since many parts of the circuit board and parts can be shared, development can be made more efficient and a price reduction effect can be expected.

  Furthermore, since the first local oscillation circuit 34-1 and the second local oscillation circuit 34-2 are oscillation circuits that use the same frequency band, the same circuits and components can be used. In addition, since the high-frequency oscillator circuit has a high degree of design difficulty and it is necessary to ensure sufficient reliability and the like, it is possible to reduce the design man-hour by making this part common.

  Next, the selection of the frequency to be converted will be described in the case where the receiver shown in the first embodiment of the present invention is used and the broadcast is received in the area A having the frequency arrangement shown in FIG. In the area A, terrestrial digital broadcasting is transmitted from 20 channels to 28 channels in the first frequency band (UHF band).

  In this situation, when receiving radio waves in the second frequency band (VHF band) 7 channel, the user first designates the reception frequency 7 channel in the second frequency band from the operation unit 8.

  When the reception frequency 7 channel is designated in this way, the control unit 7 executes a free frequency selection process shown in FIG. In this idle frequency selection process, first, in step 1, the frequency division ratio of the first PLL circuit 35-1 of the first frequency conversion circuit 3 is set so as to receive the lowest frequency in the first frequency band, and the process proceeds to step 2. To do.

  In step 2, the received electric field intensity is read from the electric field intensity detection circuit 9, and the process proceeds to step 3.

  In step 3, the control unit 7 compares the electric field intensity detection information read from the electric field intensity detection circuit 9 with a predetermined free frequency electric field intensity threshold value. It is determined that there is, and the process proceeds to step 4.

  If the electric field strength detection information is smaller than the vacant frequency electric field strength threshold, the process proceeds to step 5.

  In step 4, the value of the channel is recorded in the used channel list prepared in the storage area in the control unit 7, and the process proceeds to step 5.

  In step 5, the frequency division ratio of the first PLL circuit 35-1 is increased by one channel and the process proceeds to step 6.

  In step 6, it is determined whether or not the channel set in step 5 is included in the first frequency band. If it is in the first frequency band, the process returns to step 2, and all the channels in the first frequency band are returned. The detection of the electric field strength is repeated for the channel, and a used channel list is created.

  On the other hand, if it is determined in step 6 that the frequency band is outside the first frequency band, creation of the channel list in use in the area is completed, and the process proceeds to step 7.

  In step 7, it is determined whether the lowest channel in the used channel list created in the above step is the lowest frequency of the first frequency band. If it is not the lowest frequency, a usable channel under the channel is determined. It moves to step 8.

  In step 8, an empty channel one lower than the lowest used channel is selected, and the process proceeds to step 9.

  Here, the channel lower than the lowest used channel is selected by selecting the empty channel closest to the used channel, so that the signal in the first frequency band is received from the signal in the second frequency band. This is because the switching time when switching between can be shortened.

  In step 9, the reception process is started and the free frequency selection process is ended.

  If it is determined in step 7 that the lowest channel in the used channel list is the lowest frequency in the first frequency band, the process proceeds to step 10.

  In step 10, it is determined whether the highest channel in the used channel list created in the above step is the highest frequency in the first frequency band. If it is not the highest frequency, a usable channel on the channel is determined. Is determined to exist, and the process proceeds to step 11.

  In step 11, an empty channel that is one higher than the highest used channel is selected, and the process proceeds to step 9.

  If it is determined in step 10 that the highest channel in the used channel list is the highest frequency in the first frequency band, the process proceeds to step 12.

  In step 12, a channel with a gap is extracted from the channel list, and the process proceeds to step 9.

  As described above, the processing of FIG. 3 corresponds to the vacant frequency selection means.

  In the free frequency selection process, a used channel list is created because it is assumed that the number of used channels is smaller than the number of free channels, and thus the storage area used for the channel list can be reduced. Therefore, when the number of used channels is larger than the number of empty channels, an empty channel list may be created.

  Here, when channel display is performed on the receiver, it may be displayed as 7 channels that are actual reception frequencies instead of 19 channels that are conversion target frequencies. In this case, since the program table provided by a newspaper or the like matches the channel display of the receiver, the user can select the reception channel without being aware of the frequency conversion.

  As another example of the embodiment of the vacant frequency selection means described above, the storage area of the control unit 7 can receive the frequency broadcasted in the second frequency band for each region in the country as a receivable channel. You may register in advance. In that case, when the user inputs the current position of the receiver, a list of used channels in the area is prepared. Based on the used channel list, by performing Step 7 and the subsequent steps in FIG. 3, it is possible to select a free frequency without performing a channel search.

  When the receiver is installed and used at a certain place such as a home, the selection of the empty channel by the empty frequency selection means is almost unnecessary to be changed after it is first selected. However, when it is used as a portable or in-vehicle receiver, the channel to be used is different for each area moved, and it is necessary to select a free frequency again according to the channel.

  For example, in the above reception example, when reception starts in the A area having the frequency arrangement shown in FIG. 2, and then moves to the B area shown in FIG. Since this is not done, these 19 channels are selected by the free frequency selection means.

  Next, when moving to area B, since broadcasting is performed on 19 channels in area B, if the received electric field strength of the 19-channel broadcast signal is strong, 19-channel converted from the 19-channel broadcast signal and 7-channel signal Interference is caused by the converted received signal. In such a case, the user can select a conversion target frequency in which interference does not occur by newly operating the vacant frequency selection means in the B region.

  In the embodiment of the present invention, one antenna is selectively connected using the frequency band changeover switch so as to be shared in the first and second frequency bands. However, in each of the first and second frequency bands, A dedicated antenna may be used.

  Next, a second embodiment of the present invention will be described. In the first embodiment, the configuration in which the received signal in the second frequency band is upconverted to the conversion target frequency by the second frequency conversion circuit 4 and then received in the first frequency band is shown. In the second mixer 43 of the second frequency conversion circuit 4, a signal of the sum and difference of the received signal and the second local oscillation frequency is generated. However, since the second mixer 43 is composed of a semiconductor element that operates nonlinearly, there is a problem that harmonics of the input signal are generated.

  The problem of this harmonic will be described with reference to FIG. 2 used in the first embodiment. Similarly to the first embodiment of the present invention, when the VHF band 7 channel (# 7) is up-converted to the UHF band in the second frequency conversion circuit 4, a waveform that is an integral multiple of 2 or more of the 7 channel (191 MHz), that is, a harmonic. A wave is generated. Among the generated harmonics, the triple harmonic is 573 MHz and falls between channel 29 (# 29) and channel 30 (# 30). Actually, the 7th channel has a band of ± 3 MHz, so that the third harmonic becomes a band of 564 to 582 MHz. This overlaps channels 28 to 31 in the UHF band, and when the channel between them is a conversion target frequency, the converted reception signal is disturbed by the harmonics of the reception signal generated in the second frequency conversion circuit 4. .

  Therefore, in the second embodiment, in order to avoid interference due to the harmonics of the reception signal in this way, whether or not the harmonics of the reception signal in the second frequency band overlap with the first frequency band is determined. It is determined and an appropriate conversion target frequency is selected.

Next, the operation of the second embodiment will be described. First, by operating the user operation section 8, by selecting a channel of the received signal of the second frequency band, the control unit 7 calculates a center frequency f ₂ corresponding to the channel. Next, when the idle frequency selection unit selects a channel to be converted in the first frequency band, the control unit 7 obtains the center frequency f ₁ corresponding to the channel. Next, the control unit 7 calculates the following equation (1) based on a predetermined bandwidth B of the received signal.

| (F ₂ ± B) × n−f ₁ | ≦ B ... (1)
|| on the left side of Equation (1) represents an absolute value, and n is increased from 2 to 3 and 4 in order, and calculation is performed, so that a received signal in band ± B at frequency f ₂ in the second frequency band It is possible to determine whether or not the nth-order harmonics interfere with the range of the band ± B at the frequency f ₁ in the first frequency band. Here, when Expression (1) is satisfied, interference due to the harmonics of the received signal may occur, so f ₁ is excluded from the conversion target frequency. That is, it can be considered that the frequency is not a free frequency described in the first embodiment of the present invention, and the frequency can be excluded from the conversion target frequency to prevent the reception quality from deteriorating.

  Next, a third embodiment of the present invention will be described with reference to FIG. The third embodiment includes a reception quality detection circuit 10 that detects the reception quality of a received signal based on the data output from the demodulator 6 of the receiver exemplified in the first or second embodiment of the present invention. The detection result can be determined by the control unit 7.

  In the first or second embodiment, the selection of the vacant frequency in the first frequency band is performed based on whether or not a signal exists in the conversion target frequency in the first frequency band, and reception of the converted reception signal is performed. Quality was not considered. For example, even when there is no signal at the conversion target frequency, an image interference signal or an out-of-band unnecessary wave that is generated when the received signal is converted by the second frequency conversion circuit 4 is transmitted to the first frequency conversion circuit 3. In some cases, the quality of the converted received signal is deteriorated by frequency conversion again. When the receiver is used in a mobile manner, the reception quality may be deteriorated due to interference generated at the destination without the user's knowledge.

  In such a case, by checking the reception quality of the converted reception signal as the circuit configuration shown in the third embodiment, it is possible to appropriately operate the vacant frequency selection unit.

  Next, the operation of the third embodiment will be described. As exemplified in the first or second embodiment of the present invention, when the received signal of the second frequency band is frequency-converted to the first frequency band and received, the data output from the demodulator 6 of the receiver The reception quality detection circuit 10 detects the reception quality. When the control unit 7 compares the reception quality information of the reception quality detection circuit 10 with a predetermined reception quality threshold value and determines that the reception quality is deteriorated below the threshold value, the vacant frequency changing means In addition, the reception quality deterioration notification is performed, and another frequency to be converted with good reception quality can be automatically selected using the vacant frequency selection means.

  For detection of reception quality, a signal-to-noise ratio and a distortion rate can be used for receiving an analog signal, and a bit error rate and a packet error rate can be used for receiving a digital signal.

  Next, a fourth embodiment of the present invention will be described with reference to FIG. In the first to third embodiments of the present invention, a receiver for receiving a signal of the first frequency band is shown as an example of a structure for receiving the signal of the second frequency band after frequency conversion. It was explained that it is suitable for receiving digital broadcasting. The fourth embodiment shows the configuration of a receiver that is particularly suitable for reception of terrestrial digital broadcasting. In the configuration of the first to third embodiments, the decoding / drawing unit 11 is included in the output of the demodulation unit 6, A display unit 12 and a speaker 13 are added.

  The operation of the fourth embodiment will be described. The terrestrial digital broadcast signal transmitted through the VHF channel 7 is input from the antenna 1 to the second frequency conversion circuit 4 via the frequency band changeover switch 2. The 7-channel signal input to the second frequency conversion circuit 4 is up-converted to the UHF band and input to the first frequency conversion circuit 3. The signal input to the first frequency conversion circuit 3 is down-converted to an IF frequency, amplified by the IF circuit 5, and then output to the demodulator 6. The IF signal input to the demodulating unit 6 is digitally demodulated and output to the decoding / drawing unit 11 as a received data string. The data string input to the decoding / drawing unit 11 is decoded into image information and audio information. The decoded image information is further drawn on a moving image and output to the display unit 12. The decoded audio information is output to the speaker 13.

  On the other hand, the terrestrial digital broadcast signal transmitted in the UHF band is input to the first frequency conversion circuit 3 from the antenna 1 through the wave number band changeover switch 2, and thereafter is demodulated and decoded in accordance with the VHF band signal reception procedure. Is done.

  As described above, each embodiment of the present invention is suitable for receiving terrestrial digital broadcast waves in the VHF band and the UHF band, and can reduce the size and power consumption of the receiver. It is particularly suitable for digital broadcast receivers. In addition, since problems that may occur during mobile reception can be solved, it is suitable for mobile receivers and portable receivers.

It is a block diagram which shows an example of the receiver in 1st Embodiment. It is frequency frequency explanatory drawing of terrestrial digital broadcasting. It is a flowchart which shows an example of the idle frequency selection means in 1st Embodiment. It is a block diagram which shows an example of the receiver in 3rd Embodiment. It is a block diagram which shows an example of the receiver in 4th Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Antenna 2 Frequency band changeover switch 3 1st frequency conversion circuit 4 2nd frequency conversion circuit 5 IF circuit 6 Demodulation part 7 Control part 8 Operation part 9 Electric field strength detection circuit 10 Reception quality detection circuit

Claims (4)

  A receiving circuit for receiving a signal in a first frequency band; empty frequency selecting means for selecting an empty frequency in the first frequency band; and a signal in a second frequency band different from the first frequency band, A receiver comprising a frequency conversion circuit for converting to a free frequency of the first frequency band selected by the selection means and supplying the frequency to the reception circuit.   The vacant frequency selecting means is configured such that the first frequency band is higher than the signal frequency of the second frequency band, and the frequency obtained by multiplying the signal frequency of the second frequency band by an integer of 2 or more is the first frequency band. The receiver according to claim 1, wherein when the frequency band overlaps, it is determined that the frequency is not a free frequency.   After the signal of the second frequency band is converted to the first frequency band, the reception quality detection means for detecting the reception quality of the signal, and the reception quality detected by the reception quality detection means is deteriorated The receiver according to claim 1, further comprising: empty frequency changing means for selecting another empty frequency by the empty frequency selecting means.   The first frequency band is a UHF television broadcast frequency band, and the second frequency band signal is a terrestrial digital broadcast transmitted in seven channels in a VHF television broadcast frequency band. The receiver according to any one of claims 1 to 3.

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