JP3394186B2 - Digital broadcast receiver - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital broadcast receiver, and more particularly to a digital broadcast receiver capable of receiving digital broadcast over a plurality of bands in a DAB receiver or the like.

[0002]

2. Description of the Related Art In Europe, DAB (Digital Audio Broadcasting; Digital Audio Broa.
Digital audio broadcasting called dcasting) has been put to practical use. In this DAB, OFDM (Orthogonal Frequency Division Multiplexing Modulation; Or
A modulation method called thogonal Frequency Division Multiplex) is used, and the transmission symbol is composed of a guard interval and an effective symbol, which enables strong reception in multipath. Each DAB carrier is DQP
It is SK modulated.

In DAB, band II (87 to 108 MHz band), band III (175 to 250 MHz band), L band (1.452 to 1.49)
3 GHz band (2 GHz band) is used, and band II and
In III, transmission mode 1 with a transmission frame period of 96 ms and carrier spacing of 1 kHz (strong in multipath, SFN; suitable for single frequency network) is used (transmission mode 1 is limited to use in bands II and III). Exist). In L band, frame mode 24ms, carrier interval 4kHz transmission mode 2 (strong against movement), frame period 24ms, carrier interval 8k
Hz transmission mode 3 (satellite broadcasting, etc.), frame cycle 48m
Transmission mode 4 with a carrier spacing of 2 kHz is used.

The format of the transmission frame signal in the DAB transmission mode 1 is shown on the upper side of FIG. First 1.29
There is a synchronization signal consisting of a 7ms null symbol and a 1.246ms phase reference symbol (PRS), followed by 1.246ms OFDM symbols each.
Five are included. Except for the NULL symbol, it is a transmission symbol, 0.246ms is the guard interval, and the remaining 1
ms is a valid symbol.

The S = 1st transmission symbol is a PRS used for performing AFC (automatic frequency adjustment) and the like, and a predetermined specific code (CAZAC code; Cons).
tantAmplitude Zero Auto Correlation code) is differentially modulated between adjacent carriers. S = 2-4
The th transmission symbol is an F that transmits information necessary for the receiver to select a desired program and auxiliary information for the program.
IC (Fast Information Channel)
l), S = 5th to 76th transmission symbols are Ms that are transmitted by multiplexing subchannels of voice and data.
SC (Main Service Channel). Normally, one subchannel corresponds to one program, and the subchannel is MSC.
The structural information indicating how the data is multiplexed in
It is included in the IC, and it is possible to extract the subchannel related to the program desired by the user by referring to the FIC. Transmission mode 2 is one in which each symbol period in FIG. 9 is set to 1/4, and transmission mode 3 is one in which each symbol period in FIG. 9 is set to 1/8 and the number of OFDM symbols is increased. In transmission mode 4, each symbol period in FIG. 9 is halved.

FIG. 10 is a block diagram of a DAB receiver with a seek function. For example, the band caught by antenna 1
The received signals of the DAB broadcast signals in the II, band III and L bands are sent to the front end 2 and the bands II and III are R
It is input to the a terminal of the F changeover switch 3. The reception signal of the L band is band-limited by the BPF 4, and then is mixed with the local oscillation signal L ₀ input from the PLL circuit 7 by the mixer 6 through the AGC amplifier 5 and frequency-converted to the band III band. The PLL circuit 7 includes a reference oscillator 13 described later.
The frequency f ₁ · (n ₀ / m ₀ ) of the reference oscillation signal input from
Output L _{0 of} double frequency. n ₀ and m ₀ are fixed values. The output of the mixer 6 is output to the b-side terminal of the RF changeover switch 3. The output of the mixer 6 is the envelope detection circuit 9
Then, the envelope detection is performed, and it is output to the AGC amplifier 5 as an AGC voltage. The AGC amplifier 5 reduces or increases the gain according to the increase or decrease of the AGC voltage so that the output of the mixer 6 becomes a substantially constant level regardless of the magnitude of the antenna input level.

The output of the RF changeover switch 3 is the AGC electric power.
High frequency amplification with the RF amplifier circuit 10 whose gain can be changed by pressure
And then input from the PLL circuit 12 in the mixer 11.
First local oscillation signal L₁Mixed with the center frequency f
_IF1Of the first intermediate frequency signal. PLL circuit 12
Is the frequency f of the reference oscillation signal input from the reference oscillator 13.
₁On the other hand, f₁・ (N₁/ M₁) Double frequency L₁Output
It m₁Is a fixed value, but n₁Is the microcomputer configuration described below.
By being variably set by the system controller,
The tuning frequency is changed in 16 kHz steps, for example. Reference oscillation
The device 13 is a VCXO, which is a control voltage for automatic frequency adjustment.
The oscillation frequency is changed according to. The first intermediate frequency signal is S
1.536M by AW filter (surface acoustic wave filter) 14
Band-limited to the passband width of Hz.

The output of the SAW filter 14 is mixed with the second local oscillation signal L ₂ input from the PLL circuit 17 in the mixer 16 through the AGC amplifier 15, and the second frequency of which the center frequency is f _IF2 (<f _IF1 ). Converted to an intermediate frequency signal. P
The LL circuit 17 outputs L ₂ having a frequency f ₁ · (n ₂ / m ₂ ) times the frequency f ₁ of the reference oscillation signal input from the reference oscillator 13. Both n ₂ and m ₂ are fixed values. The second intermediate frequency signal is band-limited by the anti-aliasing filter 18 to a pass band width of 1.536 MHz.

The second intermediate frequency signal output from the anti-aliasing filter 18 is envelope-detected by the envelope detection circuit 19, and the RF amplification circuit 10 and the AGC are used as the AGC voltage.
It is output to the amplifier 15 (see a in FIG. 9). The RF amplifier circuit 10 and the AGC circuit 15 reduce or increase the gain according to the increase and decrease of the AGC voltage so that the second intermediate frequency signal of a substantially constant level can be obtained regardless of the magnitude of the antenna input level. . The output of the envelope detection circuit 19 is
A NULL detection circuit 2 for detecting a NULL symbol
Input to 0. In the NULL detection circuit 20,
After the symbol part is waveform-shaped (see b in FIG. 9),
When the fall time length Td is measured and coincides with the NULL symbol length of any of the transmission modes defined by DAB, the NULL symbol detection signal ND (see c in FIG. 9) is output at the timing of the rising edge. , System controller, etc. Also,
The transmission mode detection signal TM is also output (see d in FIG. 9).
Note that in FIG. 9 d, Td = 1.297 ms, so the transmission mode 1 is output as the transmission mode detection signal TM).

The timing synchronization circuit 21 receives the carrier-specific component of the PRS portion (effective symbol period) normally input from the FFT circuit described later, calculates the carrier-specific power, and then performs IFFT processing to obtain the frame from the cepstrum. Synchronization is detected and a synchronization detection signal is output to a timing signal generation circuit (not shown) to generate various timing signals. However, immediately after the reception of a certain ensemble is started, frame synchronization is detected using the NULL symbol detection signal ND input from the NULL detection circuit 20, and a synchronization detection signal is output.

The output of the anti-aliasing filter 18 is
I / Q demodulation after A / D conversion by A / D converter 30
The circuit 31 demodulates the I / Q components, and the transmission shown in FIG.
The frame signal is restored. And the demodulated I / Q
FFT circuit 32 composed of a dedicated processor for components
FFT processing is performed in the
N harmonics (in the case of transmission mode 1, n = 153
6, in the case of transmission mode 2, n = 384, transmission mode 3
In case of, n = 192 lines, in transmission mode 4, n = 76
Component by carrier (carrier)
Another complex number data) is extracted. The FFT circuit 32 is
Valid symbol of PRS part according to a fixed timing signal
Outputs the carrier-specific component of the period to the frequency error detection circuit 33
To do. In the frequency error detection circuit 33, the PRS part
After differentially demodulating the rear component by inter-carrier differential demodulation (P
In the RS part, a fixed code on the transmitter side is
Is adjusted), and the correlation function with a predetermined reference code is calculated.
(See FIG. 13 for the graph of the correlation function). And this
Of the tuning frequency and the frequency of the DAB broadcast signal from the correlation function of
The frequency error is detected by calculation. Frequency error detection circuit
In 33, AFC is turned on by the system controller
Outputs frequency error data to integrating circuit 34 during
(While the AFC is off, the frequency error must be zero.
And output data indicating). The integration data in the integration circuit 34
After the data is D / A converted by the D / A converter 35, the reference
It is output to the oscillator 13 as a control voltage for automatic frequency adjustment.
Be done. The reference oscillator 13 changes the oscillation frequency according to the control voltage.
Variable, the frequency f of the reference oscillation signal ₁The frequency error
Change in the direction to erase.

The FFT circuit 32 outputs a component for each carrier (complex number data for each carrier) after FFT for each transmission symbol (effective symbol period) of S = 2 to 76 in FIG. 9 to the channel decoder 36. In the channel decoder 36, DQPSK symbol demapping and FIC / MSC separation are performed, and after three effective symbols of FIC are divided into four equal parts, error detection / correction (Viterbi decoding),
After descrambling, it becomes 12 FIBs (Fast Information Blocks).
It is output to the system controller in the form of data called (Fast Information Group).
On the other hand, the effective symbols of the MSC are divided into 18 symbols and reconstructed into 4 CIFs (Common Interleaved Frames). Each CIF has multiple subchannels (Sub
Channel), and usually one sub-channel corresponds to one program.

When the user selects a desired program with the program selection key on the operation panel 40, the system controller 3
7 performs predetermined program selection control, outputs subchannel designation information corresponding to a desired program by referring to FIC information, and a channel decoder 36 designates a subchannel designated by the system controller 37 from four CIFs. After demultiplexing, time deinterleave, error detection / correction (Viterbi decoding) and descrambling are performed to DA
Decoded B audio frame data and decrypted DAB
The audio frame data is output to the MPEG decoder 38. The MPEG decoder 38 decodes DAB audio frame data and outputs audio data for two channels. This audio data is D / A converted by the D / A converter 39 and output as an analog audio signal.

The operation panel 40 is also provided with a seek key. The memory 41 also stores broadcast frequency data for a plurality of ensembles. When the seek key is pressed on the operation panel 40 and a seek command is given, the system controller 37 performs seek control of the ensemble. The seek control process will be described below with reference to the flowchart shown in FIG. When the seek command is given, the system controller 37 gives an AFC off command to the frequency error detection circuit 33 to output data showing a frequency error of zero and fix the oscillation frequency of the reference oscillator 13 (step S1 in FIG. 11). ).

Then, the broadcasting frequency data of the first ensemble is read out by referring to the memory 41, and the band II, II
If it is I, switch the RF selector switch 3 to the a side,
If it is the L band, the RF switch 3 is switched to the b side. Then, n ₁ corresponding to the frequency of the first ensemble is set in the PLL circuit 12 and tuned to the first ensemble (step S2). Next, it is checked whether the NULL symbol detection signal ND is input from the NULL detection circuit 20 (step S3). When the ensemble is caught at the current reception frequency, the output of the envelope detection circuit 19 drops at the NULL symbol portion. The NULL detection circuit 20 waveform-shapes the output of the envelope detection circuit 19 and outputs the NULL symbol detection signal ND at the rising edge. When the NULL symbol detection signal ND is input, the system controller 32 determines YES in step S3, issues a DAB broadcast signal at the current reception frequency, gives an AFC on command to the frequency error detection circuit 28, and performs seek control processing. Finish (step S4).

When the NULL symbol detection signal ND is input to the system controller 38, YE is detected in step S3.
When it is determined to be S, it is determined that there is a DAB broadcast signal at the current reception frequency, an AFC on command is given to the frequency error detection circuit 33, and the seek control process ends (step S4).

The output of the front end 2 is I / Q demodulated by an I / Q demodulation circuit 31, and then FFT circuit 32 performs an FFT.
Is processed. The carrier-specific component of the PRS portion is subjected to inter-carrier differential demodulation and decoded by the frequency error detection circuit 33, and then the correlation function between the decoded code and a predetermined reference code is calculated. An example of the graph of the correlation function is shown in FIG. 13 (the horizontal axis in FIG. 13 is frequency, and the vertical axis is correlation value).
From this correlation function, the frequency error between the tuning frequency and the frequency of the DAB broadcast signal is detected by calculation.

Now, when the center of the spectrum distribution of the received ensemble seen with the first intermediate frequency signal is deviated to a higher frequency than the normal center frequency f _IF1 as shown by the solid line A in FIG. 12 (in FIG. 12). The dashed-dotted line B is the attenuation characteristic of the SAW filter 14), and the graph of the correlation function is as shown in FIG. When the AFC ON command is given, the frequency error detection circuit 33 outputs frequency error data indicating the frequency error detected by calculation from the correlation function. The frequency error data is integrated by the integrating circuit 34, and then the D / A converter 3
It is D / A converted in 5 and output to the reference oscillator 13.

The reference oscillator 13 oscillates according to the control voltage.
Variable the wave number, local oscillation signal L ₀, 1st local departure
Swing signal L₁, The second local oscillation signal L₂Frequency of
Variable to cancel the numerical error. As a result, the first
Spectral distribution of received ensemble as seen by inter-frequency signal
Shifts to the lower frequency (see arrow C in Fig. 12).
Finally, as shown in A ′ of FIG.
It falls within the pass band of the filter 14. This allows the channel
The decoder 36 can restore the FIC and MSC information without error.
Wear. The user selects a desired program on the operation panel 40
And the system controller 37 is the channel decoder 3
Instruct 6 to select the DAB audio frame data of the desired program.
Data to the MPEG decoder 38. This allows
You can listen to the desired program.

If NO in step S3,
Since there is no ensemble that can be received at the tuning frequency this time, the system controller 37 refers to the memory 41 to check whether broadcasting frequency data for the next ensemble exists (step S5), and if not, ends the seek control process. , If present, PL corresponding n ₁
After setting to the L circuit 12 and tuning to the new ensemble, the same processing as described above is repeated (step S6).

[0021]

However, in the conventional DAB receiver with a seek function described above, when receiving the bands II and III, the RF changeover switch 3 is changed over to the side a, but between the terminals b and c. Isolation of 50d
It is about B. The DAB standard is a minimum of -90 dBm
Must be able to receive the antenna input of
Since the GC is applied, the isolation of the RF changeover switch 3 is not sufficient.

That is, while the RF selector switch 3 is switched to the a side and the ensemble B of a DAB broadcast of band III caught by the antenna 1 is being received, the ensemble A of a DAB broadcast of a weak electric field in the L band is an antenna. 1
When the frequency spectrum seen at the output side of the BPF 4 is as shown by A _{0 in} FIG.
Since it is amplified to a large level by the C amplifier 5,
(2) Reference A ₁ in), the RF changeover switch 3 -50
Even if attenuated by dB, it still remains at a relatively large level when viewed from the output side of the RF changeover switch 3 (FIG. 15).
(See A _{2 in} (3)). Therefore, even if the received electric field strength of the ensemble B which is the original receiving target is relatively high,
If the frequency spectrum of the ensemble B and the frequency spectrum of the ensemble A when viewed from the output side of the changeover switch 3 overlap (see B ₀ and A _{2 in} FIG. 15 (3)), the ensemble B is disturbed and received. The condition deteriorates or, in the worst case, reception becomes impossible.

When the ensemble A of the band III is tuned to the broadcasting frequency of the ensemble B but B cannot be received and the ensemble A having a weak electric field is caught in the L band, the ensemble A is -50 dB by the RF changeover switch 3. After being attenuated only, it is again amplified by the RF amplifier circuit 10 and the AGC amplifier 15 (see A _{3 in} FIG. 15 (4)). Therefore, at the seek time of the ensemble of band III, at a certain tuning frequency, there is no ensemble that can be received in band III, but the received signal whose frequency is converted by the mixer 6 of the ensemble A of the L band is the pass band of the SAW filter 14. Upon entering, the receiver is the ensemble A of the L band.
However, the frequency pull-in operation is mistakenly performed, and the ensemble of Band III cannot be correctly sought.

On the contrary, the RF selector switch 3 is switched to the b side, the certain ensemble A of the L band caught by the antenna 1 is received, and the frequency spectrum seen at the output side of the AGC amplifier 5 is shown in FIG. ) A ₀ , the antenna 1 catches an ensemble B of a certain strong electric field in band III, and the frequency spectrum seen at the input side of the RF changeover switch 3 is B ₀ in FIG. 16 (2). At this time, even if it is attenuated by -50 dB by the RF changeover switch 3, it still remains at a relatively large level when viewed from the output side of the RF changeover switch 3 (B in FIG. 16 (3)).
See ₁ ). Therefore, when the frequency spectrum of the ensemble A and the frequency spectrum of the ensemble B when viewed from the output side of the RF changeover switch 3 overlap (see FIG. 1).
6 (3) A ₁ and B ₁ ), the ensemble A is disturbed and the reception condition deteriorates.

When the ensemble A of the L band is tuned to the broadcasting frequency of the ensemble A, but the A cannot be received and the ensemble B of a band III having a strong electric field is caught, the ensemble B is -50 dB by the RF changeover switch 3. After being attenuated only, it is amplified again by the RF amplifier circuit 10 and the AGC amplifier 15. Therefore, when seeking the ensemble of the L band, there is no ensemble that can be received in the L band at a certain tuning frequency, but when the received signal of the ensemble B of the band III enters the pass band of the SAW filter 14, the receiver is concerned. The frequency pull-in operation is mistakenly performed on the ensemble B of the band III, and the ensemble of the L band cannot be correctly sought. The present invention has been made in view of the above problems of the prior art, and an object thereof is to provide a digital broadcast receiver capable of correctly receiving a digital broadcast signal of a desired band.

[0026]

In the digital broadcast receiver according to claim 1 of the present invention, a high frequency band digital broadcast signal caught by an antenna (1) and a first local oscillation signal whose oscillation frequency is variable are generated. A first frequency conversion means (6) for mixing the first local oscillation signals generated by the means (7, 13) and converting to a low frequency, and a low frequency band digital broadcast signal caught by the antenna (1). And a switching means (3) for switching and outputting the output of the first frequency converting means (6), and an output of the switching means (3) and a second local oscillation signal generating means (12, 13) whose oscillation frequency is variable. Receiving means (2A) including a second frequency converting means (11) for mixing the generated second local oscillation signal and converting it into an intermediate frequency signal, the receiving frequency being variable and having an automatic gain adjusting function.
And a program information demodulating means (31, 32, 36, 38) for demodulating user-desired program information from the output of the receiving means, and a switching means (3) for switching the high band digital when receiving the high band. Switch to the broadcast signal input system, first
By controlling the oscillation frequency of the local oscillation signal generation means (7) and the oscillation frequency of the second local oscillation signal generation means (12), the high frequency is controlled by the first frequency conversion means (6) and the second frequency conversion means (11). Convert a digital broadcast signal of a desired broadcast frequency of a range band into an intermediate frequency signal of a predetermined frequency. At this time,
The oscillation frequency of the first local oscillation signal generating means (7, 13) is the frequency at which the digital broadcasting signal of the desired broadcasting frequency in the high band is distant from the low band when viewed at the output point of the first frequency converting means (6). On the other hand, when receiving in the low band, the switching means (3) is switched to the input system of the digital broadcast signal in the low band, and the second local oscillation signal generating means (12, 13) By controlling the oscillation frequency, the second frequency conversion means (11) converts the digital broadcast signal of the desired broadcast frequency in the low frequency band into the intermediate frequency signal of the predetermined frequency. At this time, the first local oscillation signal generation means ( The high frequency band is converted into a frequency away from the signal band of the digital broadcast signal of the desired broadcast frequency in the low frequency band by the first frequency conversion means (6) by controlling the oscillating frequency of 7, 7). Tuning control means as a (37)
It is characterized by having and.

According to the first aspect of the present invention, when the high band is received, the switching means is switched to the input system of the digital broadcast signal of the high band, and the oscillation frequency of the first local oscillation signal generating means and the second local oscillation signal generating means are set. The oscillation frequency of the local oscillation signal generating means is controlled so that the first frequency converting means and the second frequency converting means convert the digital broadcasting signal of the desired broadcasting frequency in the high frequency band into the intermediate frequency signal of the predetermined frequency. At this time, the oscillation frequency of the first local oscillation signal generating means is set so that the digital broadcasting signal of the desired broadcasting frequency in the high frequency band is converted to a frequency apart from the low frequency band when viewed at the output point of the first frequency conversion means. On the other hand, when receiving in the low band, the switching means is switched to the input system of the digital broadcast signal in the low band, and the oscillation frequency of the second local oscillation signal generating means is controlled. The two frequency conversion means converts the digital broadcast signal of a desired low frequency band broadcasting frequency into an intermediate frequency signal of a predetermined frequency. At this time, by controlling the oscillation frequency of the first local oscillation signal generation means, the high frequency band The first frequency conversion means converts the frequency of the digital broadcast signal of the desired broadcast frequency in the low band to a frequency apart from the signal band.

Thus, when the receiving means is tuned to a certain digital broadcasting frequency of one of the high band and the low band, even if the digital broadcasting signal of the other band is caught by the antenna, Since the interference component is located at a frequency position far from the received signal band of the desired broadcast frequency seen at the output of the two frequency conversion means, if the digital broadcast of the desired broadcast frequency is received, it can be received correctly without interference. Further, even if the digital broadcast of the desired broadcast frequency is not received, the digital broadcast signal of the other band will not be erroneously received.

According to another aspect of the digital broadcast receiver of the present invention, the high frequency band digital broadcast signal caught by the antenna and the first local oscillation signal generating means generate the first broadcasting signal.
First frequency conversion means for mixing local oscillation signals and converting to a low frequency, switching means for switching and outputting the low frequency band digital broadcast signal caught by the antenna and the output of the first frequency conversion means, and switching means And a second frequency conversion means for mixing the second local oscillation signal generated by the second local oscillation signal generation means and converting it into an intermediate frequency signal, the reception frequency being variable and having an automatic gain adjustment function. Means, a program information demodulating means for demodulating program information desired by the user from the output of the receiving means, and a switching means for receiving the high frequency band, the switching means is switched to the input system of the digital broadcasting signal of the high frequency band, and the second local part By controlling the oscillation frequency of the oscillation signal generation means, the first frequency conversion means and the second frequency conversion means perform digital broadcast transmission of a desired broadcast frequency in the high frequency band. Is converted into an intermediate frequency signal of a predetermined frequency, and when the low band is received, the switching means is switched to the input system of the digital broadcast signal of the low band to control the oscillation frequency of the second local oscillation signal generating means. And a tuning control means for converting the digital broadcast signal of a desired broadcast frequency in the low frequency band into an intermediate frequency signal of a predetermined frequency by the second frequency conversion means, and the oscillation frequency of the first local oscillation signal generation means is It is characterized in that the digital broadcasting signal of a desired broadcasting frequency in the high frequency band is converted into a frequency apart from the low frequency band when viewed from the output point of the first frequency conversion means.

Also by this, when the receiving means is tuned to a certain digital broadcasting frequency of one of the high band and the low band, even if the digital broadcasting signal of the other band is caught by the antenna, With respect to the reception signal band of the desired broadcast frequency seen at the output of the switching means, the interference component comes to a frequency position distant, so that if the digital broadcast of the desired broadcast frequency is received, it can be correctly received without interference, and Even if the digital broadcast of the desired broadcast frequency is not received, the digital broadcast signal of the other band is not received by mistake.

In the digital broadcasting receiver according to claim 3 of the present invention, the high frequency band digital broadcasting signal caught by the antenna (1) and the first local oscillation signal generating means (7, 13) whose oscillation frequency is variable. The first frequency conversion means (6) that mixes the first local oscillation signal generated in (1) and converts it into an intermediate frequency signal, and the low frequency band digital broadcast signal caught by the antenna (1) and the oscillation frequency are variable. A second frequency conversion means (11) for mixing the second local oscillation signals generated by the second local oscillation signal generation means (12, 13) and converting the mixture into an intermediate frequency signal; and a first frequency conversion means (6). The receiving means (2B), which includes an output and a switching means (3B) for switching between the output of the second frequency conversion means (11) and outputting the variable reception frequency and having an automatic gain adjusting function, and the receiving means (2B). Program information demodulating means (31,32,36,38) for demodulating the user desired program information from the force,
When receiving the high band, the switching means (3B) is switched to the input system of the digital broadcast signal of the high band,
By controlling the oscillation frequency of the first local oscillation signal generating means (7, 13), the first frequency converting means (6) converts the digital broadcasting signal of the desired broadcasting frequency in the high frequency band into the intermediate frequency signal of the predetermined frequency. At this time, the oscillation frequency of the second local oscillation signal generating means (12, 13) is controlled to convert the low band to a frequency apart from the predetermined intermediate frequency signal band by the second frequency converting means (11). Thus, when receiving the low frequency band, the switching means (3B) is switched to the input system of the low frequency band digital broadcast signal, the oscillation frequency of the second local oscillation signal is controlled, and the second frequency conversion means ( According to 11), the digital broadcast signal of the desired broadcast frequency in the low frequency band is converted into the intermediate frequency signal of the predetermined frequency, and at this time, the first local oscillation signal generating means (7, 13)
Tuning control means (37B) for controlling the oscillation frequency of the high frequency band so that the high frequency band is converted to a frequency away from the predetermined intermediate frequency signal band by the first frequency conversion means (6),
It is characterized by having.

According to the invention of claim 3, when the receiving means is tuned to a certain digital broadcasting frequency of one of the high band and the low band, the digital broadcasting signal of the other band is transmitted by the antenna. Even if it is caught, the interference component comes to a frequency position far from the reception signal band of the desired broadcast frequency as seen from the output of the switching means, so if the digital broadcast of the desired broadcast frequency is received, it will be correct without interference. Even if the digital broadcast of the other band can be received and the digital broadcast of the desired broadcast frequency is not received, the digital broadcast signal of the other band is not received by mistake.

[0033]

BEST MODE FOR CARRYING OUT THE INVENTION Next, a first embodiment of the present invention will be described with reference to FIG. 1 is a block diagram of a DAB receiver with a seek function according to the present invention, and the same components as those in FIG. 10 are designated by the same reference numerals. The PLL circuit 7A of the front end 2A outputs L ₀ having a frequency f ₁ · (n ₀ / m ₀ ) times the frequency f ₁ of the reference oscillation signal input from the reference oscillator 13. m ₀ is a fixed value, but n ₀
Is variably set by the system controller 37A, so that the L band can be down-converted by the mixer 6 to an arbitrary frequency F within a certain frequency range.

System controller 37 of microcomputer configuration
When the seek key is pressed on the operation panel 40 and a seek instruction is given, A executes a predetermined seek control process, and when a program selection operation is performed by the program selection key, a predetermined program selection control is performed. When the seek target is an ensemble of DAB broadcasting of the L band which is the high band, the frequency F down-converted by the mixer 6 to the PLL circuit 7A is around 50 MHz apart from the bands II and III which are the low bands. By setting n ₀ and varying n ₁ set in the PLL circuit 12, the center frequency of the first intermediate frequency signal of the L band ensemble output from the mixer 11 is f _IF1
So that As a result, even if the antenna 1 catches the ensemble of DAB broadcasting of bands II and III that interferes with reception of the L band, the interference component output from the mixer 11 is the first intermediate frequency signal of the L band ensemble. It comes to a frequency position away from the signal band and is blocked by the SAW filter 14.

Band II whose seek target is a low band,
In the case of the DAB broadcasting ensemble of III, the PLL circuit 7
In contrast to A, the down conversion frequency F in the mixer 6 is, for example, 320 MHz apart from the low frequency bands II and III.
Set n ₀ in the vicinity and set n ₁ in the PLL circuit 12.
By changing the, the band I output from the mixer 11
The center frequency of the first intermediate frequency signal of the ensemble of I and III is set to _fIF1 . This allows the antenna 1
DAB in the L band that interferes with reception of bands II and III
Even if the broadcast ensemble is caught, the interference component output from the mixer 11 comes to a frequency position away from the signal band of the first intermediate frequency signal of the ensemble of bands II and III, and is blocked by the SAW filter 14. . The other components are constructed in exactly the same way as in FIG.

Next, the seek operation in the above embodiment will be described with reference to FIG. FIG. 2 is a flowchart showing the seek control processing of the system controller 37A. The memory 41 is previously stored in the band II and the band II.
Broadcast frequency data of ten ensembles in the I and L bands are stored in the memory channels CH1 to CH10.

When the user presses the seek key on the operation panel 40 to instruct a seek, the system controller 37A gives an AFC off command to the frequency error detection circuit 33 to output data showing a frequency error of zero, and the reference oscillator 13 outputs the data. Fix the oscillation frequency (step S1 in FIG. 2)
1). Next, referring to the memory 41, the memory channel C
When the broadcasting frequency data of the ensemble A of the first DAB broadcast stored in H1 is read and, for example, when it corresponds to the L band of 1.455 GHz, the mixer 6 sets the center frequency of the ensemble A of 1.455 GHz to the PLL circuit 7A. F = 50MHz
Of Set n ₀ be converted to a frequency, a frequency component after conversion is to come to a position away from the band II, III (see A ₁ of A _0, (2) in FIG. 3 (1)). Further, n _{1 at} which the center frequency of the first intermediate frequency signal of the ensemble A output from the mixer 11 is set to f _IF1 is set in the PLL circuit 12 (steps S12 to S14. A _{2 in} FIG. 3C). reference). Then, the RF switch 3 is switched to the b side (step S15).

The ensemble A of the L band is caught by the antenna 1, and the frequency spectrum is shown in FIG. 3 (1).
When it is like A ₀ of F, it is F = 50MHz by the mixer 6.
The frequency spectrum is down-converted to
It becomes like A _{1 in} (2), and is further down-converted by the mixer 11, so that the frequency spectrum becomes like A _{2 in} FIG. 3 (3).

At this time, if the broadcasting frequency of band III is 22
When the ensemble B of a strong electric field at ₀ MHz is caught by the antenna 1 and the frequency spectrum is as shown in B ₀ of FIG. 3 (1), the RF changeover switch 3 makes -50d.
The interference component due to the ensemble B attenuated by B moves to a position 170 MHz away from the center frequency f _IF1 of the intermediate frequency signal of the ensemble A in the mixer 11 and therefore does not overlap with the ensemble A (B in FIG. 3 (3)). ₂ ), and is removed by the SAW filter 14.

The system controller 37A executes step S
After 15, it is checked whether the NULL symbol detection signal ND is input from the NULL detection circuit 20 (step S16). When viewed from the output side of the SAW filter 14, only the frequency spectrum of the ensemble A is shown (see FIG.
(See A _{3 in} (4)), the mixer 16 converts the signal to the second intermediate frequency signal and outputs the second intermediate frequency signal, and the output of the envelope detection circuit 19 drops at the NULL symbol portion. The NULL detection circuit 20 shapes the output of the envelope detection circuit 19 and measures the fall time length Td. When it matches the NULL symbol length of one of the transmission modes defined by DAB, the NULL symbol is detected at the rising edge. The detection signal ND is output (see FIG. 9). The timing synchronization circuit 21 detects frame synchronization using the NULL symbol detection signal ND and outputs a synchronization detection signal, and a timing signal generation circuit (not shown) generates and outputs various timing signals.

When the NULL symbol detection signal ND is input, the system controller 37A determines YES in step S16, and since the L band ensemble to be sought is correctly received, the AFC ON command is sent to the frequency error detection circuit 33. Then, the seek control is finished (step S17). The output of the front end 2A is I / Q demodulated by the I / Q demodulation circuit 31, and then FFT is performed by the FFT circuit 32.
Is processed. Whenever the frequency error detection circuit 33 receives the AFC ON command, it carries out the differential demodulation between carriers and decodes it every time the component for each carrier of the PRS portion is inputted from the FFT circuit 32, and the correlation with a predetermined known reference code. Calculate the function. Then, the frequency error is calculated and detected from the obtained correlation function, and the detected frequency error data is output to the integrating circuit 34. The frequency error data is integrated by the integrating circuit 34, D / A converted by the D / A converter 35, and output to the reference oscillator 13 as a control voltage for automatic frequency adjustment. The reference oscillator 13 generates an oscillation frequency f ₁ according to the control voltage.
By changing the frequency of the local oscillation signal L ₀ , the first local oscillation signal L ₁ , and the second local oscillation signal L _{2 in} the direction of canceling the frequency error.

The channel decoder 36 restores FIC and MSC information from the carrier-specific components of each symbol input from the FFT circuit 32. When the user selects a desired program on the operation panel 40, the system controller 37A instructs the channel decoder 36 to output the DAB audio frame data of the desired program to the MPEG decoder 38. Thereby, the desired program can be listened to.

In contrast to this, when the first ensemble A is not sought when the seek is made, even if the DAB broadcasting ensemble of bands II and III is caught by the antenna 1, the mixer is used as described above. 11
When viewed from the output side of the SAW filter 14, the SAW filter 14 comes at a position at least 20 MHz away from the center frequency f _IF1 of the intermediate frequency signal of the ensemble A (see B _{2 in} FIG. 3C).
Will be removed. Therefore, the reception signal of any ensemble is not output from the front end 2A, and the reception signal is NULL.
The detection circuit 20 does not output the NULL symbol detection signal ND. At this time, the system controller 37A determines NO in step S16, and does not proceed to step S17. Therefore, the frequency is not accidentally pulled in the ensembles of bands II and III.

When the result in step S16 is NO, i is incremented to 2 and it is checked whether the broadcast channel data of the next ensemble is stored in the memory channel CHi of the memory 41 (steps S18 and S1).
9). If YES, the broadcast frequency data of the second ensemble C is read out. For example, when it corresponds to 230 MHz band III, the center frequency of the first intermediate frequency signal of the ensemble C output from the mixer 11 to the PLL circuit 12. _{n 0} There set n ₁ serving as f _IF1, to a PLL circuit 7A, the oscillation frequency of the local oscillation signal L ₀ becomes 1.152GHz
Is set (steps S13 and S20). And RF
The changeover switch 3 is changed over to the side a (step S2).
1). The frequency of 1.452 GHz, which is the lower limit of the L band, is converted by the mixer 6 to 300 MHz, which is higher than the upper limit of the band III.

Ensemble C of Band III is Antenna 1
It was caught in and the frequency spectrum is shown in Fig. 4.
When it is like C _{0 in} (1), it is down-converted to the first intermediate frequency f _IF1 by the mixer 11, and the frequency spectrum becomes like C _{2 in} FIG. 4 (3).

At this time, if the broadcasting frequency of the L band is 1.45.
When the 2 GHz ensemble D is caught by the antenna 1 and the frequency spectrum seen on the output side of the AGC amplifier 5 is as D _{0 in} FIG. 4 (1), the center frequency of the ensemble D is changed by the mixer 6. It is down-converted to a frequency F = 300 MHz apart from the bands II and III (for frequency spectrum, see D _{1 in} FIG. 4 (2)). The interference component due to the ensemble D, which is attenuated by -50 dB by the RF changeover switch 3, moves to a position 70 MHz away from the center frequency f _IF1 of the intermediate frequency signal of the ensemble C in the mixer 11 and does not overlap with the ensemble C ( Figure 4
(See D _{2 in} (3)), and is removed by the SAW filter 14.

The system controller 37A executes step S
After 15, it is checked whether the NULL symbol detection signal ND is input from the NULL detection circuit 20 (step S16). When viewed from the output side of the SAW filter 14, only the frequency spectrum of the ensemble C becomes (see FIG.
(See C _{3 in} (4)), converted into the second intermediate frequency signal by the mixer 16 and output, and the NULL detection circuit 20 outputs NULL.
The L symbol detection signal ND is output. When the NULL symbol detection signal ND is input, the system controller 37A determines YES in step S16, and correctly receives the ensemble of band III to be sought, so the frequency error detection circuit 33 is given an AFC ON command to seek. The control ends (step S17).

On the other hand, if the second ensemble C cannot be caught when seeking the second ensemble C, even if an ensemble in the L band happens to be caught by the antenna 1, the output side of the mixer 6 will operate as described above. SAW, because it comes at a distance of at least 70 MHz or more from the center frequency f _IF1 of the ensemble C seen (see D _{2 in} FIG. 4 (3)).
It is removed by the filter 14. Therefore, the reception signal of any ensemble is not output from the front end 2A, and the NULL detection circuit 20 does not output the NULL symbol detection signal ND. At this time, the system controller 3
7A determines NO in step S16, and executes step S17
I can't go to. Therefore, the frequency is not accidentally pulled in the L-band ensemble. When NO is obtained in step S16, the process proceeds to step S18, and the same process is performed for the ensembles of the memory channel CH3 and the subsequent channels of the memory 41.

According to the above-described embodiment, the front end 2A has one of the L band, which is the high band, and one of the L bands (or the bands II and III), which are the low bands II and III. When the DAB broadcast ensemble on the other band II, III (or L band) is caught by the antenna 1 when tuned to the DAB broadcast ensemble, the DAB broadcast of the desired frequency seen by the output of the mixer 11 is obtained. Since the interference component is located at a frequency position far away from the reception signal band of, if the DAB broadcast of the desired frequency is received, it can be correctly received without interference, and the DAB broadcast of the desired frequency is not received. However, the DAB broadcast signal of the undesired band is not received by mistake.

In the above embodiment, the PLL circuit 7A makes n ₀ variable, and steps S14 and S2 in FIG.
At 0, the system controller 37A with respect to the PLL circuit 7A has a n ₀ is variably set, the n _0, and fixed so that the oscillation frequency of the local oscillation signal L ₀ is for example 1.152GHz, band L is mixed Band II, II in vessel 6
Even if it is converted to a frequency near 320 MHz apart from I, the same effect as in the above-described embodiment can be obtained.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 5 shows a seek function D according to the present invention.
It is a block diagram of an AB receiver, and the same components as those in FIG. 1 are denoted by the same reference numerals. Of the front end 2B, the output of the L-band AGC amplifier 5 is the mixer 6
Then, it is mixed with the local oscillation signal L ₀ input from the PLL circuit 7B and converted into a first intermediate frequency signal having a center frequency of f _IF1 . The PLL circuit 7B responds to the frequency f ₁ of the reference oscillation signal input from the reference oscillator 13 by f ₁ · (n ₀ / m ₀ ).
Output L _{0 of} double frequency. m ₀ is a fixed value, but n
₀ is 1 by the system controller 37B with a microcomputer configuration
The tuning frequency for the L band is varied in 16 kHz steps, for example, by variably setting the 6 kHz step.

On the output side of the antenna 1, there is provided an RF amplifier circuit 10 for performing RF amplification of an ensemble of DAB broadcasts of bands II and III. This RF amplifier circuit 10 is an AG
The gain varies depending on the C voltage. A mixer 11 is provided on the output side of the RF amplifier circuit 10, and a PLL circuit 12 is provided.
It is mixed with the first local oscillation signal L ₁ input from and is converted into the first intermediate frequency signal whose center frequency is f _IF1 . P
The LL circuit 12 outputs L ₁ having a frequency f ₁ · (n ₁ / m ₁ ) times the frequency f ₁ of the reference oscillation signal input from the reference oscillator 13. Although m ₁ is a fixed value, n ₁ is variably set by the system controller of the microcomputer configuration, so that the tuning frequency can be changed in 16 kHz steps, for example. The output sides of the mixers 6 and 11 are connected to the SAW filter 14 via the changeover switch 3B.

The system controller 37B is an operation panel.
The seek key is pressed at 40 to give a seek instruction.
And a predetermined seek control process are executed, and the program selection key
When a program selection operation is performed, predetermined program selection control is performed.
Seek for L-band DAB broadcasting, which is the high band
In the case of an ensemble, the mixer 6 is added to the PLL circuit 7B.
First intermediate frequency of L-band ensemble output from
The center frequency of the signal is f _IF1While PL
Lower limit frequency 87MHz of band II is mixed with L circuit 12.
The center frequency f of the first intermediate frequency signal_IF1From
If you go up about 20MHz n₁To set.

When the seek target is an ensemble of bands II and III which is a low band, the center frequency of the first intermediate frequency signal of the ensemble of bands II and III output from the mixer 11 is input to the PLL circuit 12. Is set to f _IF1 while the lower limit frequency 1.452 GHz of the L band is set to the PLL circuit 7B by the mixer 6 such that n ₀ is separated from the center frequency f _IF1 of the first intermediate frequency signal by about 20 MHz, for example. . The other components are the same as those in FIG.

Next, the seek operation in the above embodiment will be described with reference to FIG. FIG. 6 is a flowchart showing the seek control processing of the system controller 37B. The memory 41 is previously stored in the band II and the band II.
Broadcast frequency data of ten ensembles in the I and L bands are stored in the memory channels CH1 to CH10.

When the user presses the seek key on the operation panel 40 to instruct a seek, the system controller 37B gives an AFC off command to the frequency error detection circuit 33 to output the data showing the frequency error zero, and the reference oscillator 13 outputs. Fix the oscillation frequency (step S3 in FIG. 6)
1). Next, referring to the memory 41, the memory channel C
When the broadcasting frequency data of the ensemble A of the first DAB broadcast stored in H1 is read and, for example, it corresponds to the L band of 1.455 GHz, the mixer circuit 6 sets the center frequency of the ensemble A of 1.455 GHz to the PLL circuit 7B. set n ₀ be converted to f _IF1, whereas, with respect to the PLL circuit 12 sets n ₁ that the lower limit frequency of the band II is converted to f _IF1 + 20 MHz (step S32 to S34). Then, the changeover switch 3B is changed over to the b side (step S3).
5).

The L band ensemble A is caught by the antenna 1, and the frequency spectrum is shown in FIG. 7 (1).
When was as A _0, the frequency spectrum is down-converted to f _IF1 by the mixer 6 is as A ₁ in FIG. 7 (2). At this time, if the ensemble B of the broadcasting frequency 220 MHz of band III is caught by the antenna 1 and the frequency spectrum is as shown by B _{0 in} FIG. 7 (1), the mixer 11 uses the first ensemble A signal. Since it moves to a position 153 MHz away from the center frequency f _IF1 of the intermediate frequency signal, it does not overlap with the signal band of the ensemble A (see B _{1 in} FIG. 7 (2)), and even if it leaks to the subsequent stage from the changeover switch 3B, the SAW filter Removed at 14.

The system controller 37B executes step S
After 35, it is checked whether the NULL symbol detection signal ND is input from the NULL detection circuit 20 (step S36). When viewed from the output side of the SAW filter 14, only the frequency spectrum of the ensemble A becomes, and the mixer 1
6 is converted into the second intermediate frequency signal and output,
The detection circuit 20 outputs the NULL symbol detection signal ND.

When the NULL symbol detection signal ND is input, the system controller 37B determines YES in step S36, and since the L band ensemble to be sought is correctly received, the AFC ON command is sent to the frequency error detection circuit 33. Then, the seek control is finished (step S37). The output of the front end 2B is I / Q demodulated by the I / Q demodulation circuit 31, and then FFT circuit 32 performs FFT.
Is processed. Whenever the frequency error detection circuit 33 receives the AFC ON command, it carries out the differential demodulation between carriers and decodes it every time the component for each carrier of the PRS portion is inputted from the FFT circuit 32, and the correlation with a predetermined known reference code. Calculate the function. Then, the frequency error is calculated and detected from the obtained correlation function, and the detected frequency error data is output to the integrating circuit 34. The frequency error data is integrated by the integrating circuit 34, D / A converted by the D / A converter 35, and output to the reference oscillator 13 as a control voltage for automatic frequency adjustment. The reference oscillator 13 generates an oscillation frequency f ₁ according to the control voltage.
By changing the frequency of the local oscillation signal L ₀ , the first local oscillation signal L ₁ , and the second local oscillation signal L _{2 in} the direction of canceling the frequency error.

The channel decoder 36 restores the FIC and MSC information from the carrier-specific component of each symbol input from the FFT circuit 32. When the user selects a desired program on the operation panel 40, the system controller 37B instructs the channel decoder 36 to output the DAB audio frame data of the desired program to the MPEG decoder 38. Thereby, the desired program can be listened to.

In contrast to this, when the first ensemble A is sought and cannot be caught, even if a certain ensemble of bands II and III is caught by the antenna 1, the output of the mixer 11 is as described above. Seen on the side, the SAW filter 14 removes the intermediate frequency signal of the ensemble A because it comes at a position at least 20 MHz away from the center frequency f _IF1 . Therefore, the front end 2
No received signal of the ensemble is output from B, and the NULL detection circuit 20 does not output the NULL symbol detection signal ND. At this time, the system controller 3
7B determines NO in step S36, and determines in step S37.
I can't go to. Therefore, the frequency is not accidentally pulled in the ensembles of bands II and III.

When the result in step S36 is NO, i is incremented to 2 and it is checked whether the broadcast channel data of the next ensemble is stored in the memory channel CHi of the memory 41 (steps S38, S3).
9). If YES, the broadcast frequency data of the second ensemble C is read out. For example, when it corresponds to the band III of 230 MHz, the center frequency of the ensemble C output from the mixer 11 to the PLL circuit 12 becomes f _IF1 n ₁ is set, and n ₀ with which the lower limit frequency of the L band is converted to f _IF1 +20 MHz is set to the PLL circuit 7B (steps S33 and S40). Then, change the switch 3B to a
To the side (step S41).

Ensemble C of Band III is Antenna 1
It was caught in and the frequency spectrum is shown in Fig.8.
When it is like C _{0 in} (1), it is down-converted to the first intermediate frequency f _IF1 by the mixer 11, and the frequency spectrum becomes like C _{1 in} FIG. 8 (2).

At this time, if the broadcasting frequency of the L band is 1.45.
When the 5 GHz ensemble D is caught by the antenna 1 and the frequency spectrum is as shown by D _{0 in} FIG. 8 (1), the mixer 6 shifts the center frequency of the ensemble D to a position more than f _IF1 +20 MHz away. , C does not overlap with the signal band of C (see D _{1 in} FIG. 8 (2)).
Even if the changeover switch 3B leaks to the subsequent stage, it is removed by the SAW filter 14.

The system controller 37B executes step S
After 35, it is checked whether the NULL symbol detection signal ND is input from the NULL detection circuit 20 (step S36). When viewed from the output side of the SAW filter 14, only the frequency spectrum of the ensemble C becomes, and the mixer 1
6 is converted into the second intermediate frequency signal and output,
The detection circuit 20 outputs the NULL symbol detection signal ND. When the NULL symbol detection signal ND is input, the system controller 37B determines YES in step S36, and correctly receives the ensemble of band III that is the seek target.
Gives an ON command and ends seek control (step S3).
7).

In contrast to this, when the second ensemble C is not sought when the seek is performed, even if a certain L-band ensemble is caught by the antenna 1, the output side of the mixer 6 is output as described above. At least 20 MHz from the center frequency f _IF1 of the ensemble C when viewed
Since it comes to a place far away (see D _{1 in} Fig. 8 (2)), S
It is removed by the AW filter 14. Therefore, the reception signal of any ensemble is not output from the front end 2B, and the NULL detection circuit 20 does not output the NULL symbol detection signal ND. At this time, the system controller 37B determines NO in step S36, and the system controller 37B determines NO in step S36.
I can't go to 37. Therefore, the frequency is not accidentally pulled in the L-band ensemble. When NO is obtained in the step S36, the process proceeds to a step S38, and the same processing is performed for the ensembles of the memory channel CH3 and thereafter of the memory 41.

According to the above-described embodiment, the front end 2B has one of the L band (or the band II and III) which is the high band and the band II and III which is the low band. When the DAB broadcast ensemble on the other band II, III (or L band) is caught by the antenna 1 when tuned to the DAB broadcast ensemble, the desired DAB seen from the output of the selector switch 3B.
Since the interference component is located at a frequency position far from the received signal band of the broadcast, if the desired DAB broadcast is received, it can be correctly received without interference, and the DA of the desired broadcast frequency is received.
DA of undesired band even if B broadcast is not received
There is no mistaken reception of the B broadcast signal.

In each of the above-described embodiments and modifications, the DAB broadcasting carried out in Europe has been described, but the present invention is not limited to this, and digital terrestrial TV broadcasting is carried out. The present invention can be similarly applied to broadcasting, communication, etc. for other purposes such as digital satellite broadcasting.

[0069]

According to the present invention, when the receiving means is tuned to a certain digital broadcasting frequency of one of the high band and the low band, the digital broadcasting signal of the other band is caught by the antenna. However, since the interference component is located at a frequency position far from the reception signal band of the desired broadcast frequency, if the digital broadcast of the desired broadcast frequency is received, it can be correctly received without interference, and the desired broadcast Even if the digital broadcast of the frequency is not received, the digital broadcast signal of the other band is not erroneously received.

[Brief description of drawings]

FIG. 1 is a block diagram of a DAB receiver with a seek function according to a first embodiment of the present invention.

FIG. 2 is a flowchart showing seek control processing by the system controller of FIG.

FIG. 3 is a diagram showing an operation of the DAB receiver with a seek function of FIG.

4 is a diagram showing an operation of the DAB receiver with a seek function of FIG. 1. FIG.

FIG. 5 is a block diagram of a DAB receiver with a seek function according to a second embodiment of the present invention.

FIG. 6 is a flowchart showing seek control processing by the system controller of FIG.

7 is a diagram showing an operation of the DAB receiver with a seek function of FIG.

FIG. 8 is a diagram showing an operation of the DAB receiver with a seek function of FIG.

FIG. 9 is an explanatory diagram illustrating a configuration of a DAB transmission frame signal and a NULL symbol detection operation.

FIG. 10 is a block diagram of a conventional DAB receiver with a seek function.

11 is a flowchart showing seek control processing by the system controller of FIG.

FIG. 12 is a diagram showing a frequency spectrum of an ensemble viewed from a first intermediate frequency signal.

FIG. 13 is a diagram showing the operation of the frequency error detection circuit.

FIG. 14 is a diagram showing a frequency spectrum of an ensemble viewed from a first intermediate frequency signal.

15 is a diagram showing the operation of the DAB receiver with a seek function of FIG.

16 is a diagram showing an operation of the DAB receiver with a seek function of FIG.

[Explanation of symbols]

1 antenna 2A, 2B front end 3 RF selector switch 3B selector switch 5, 15 AGC amplifier 6, 11, 16
Mixers 7A, 7B, 12, 17 PLL circuit 13 Reference oscillator 14 SAW filter 18 Anti-aliasing filter 19 Envelope detection circuit 20 NULL detection circuit 31 I / Q demodulation circuit 32 FFT circuit 33 Frequency error detection circuit 34 Integration circuit 35 D / A converter 36 channel decoder 37A, 37B
System controller 38 MPEG decoder 40 Operation panel 41 Memory

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H04B 1/26 H04B 1/16 H04J 4/00-15/00 H04B 1/10-1/14

Claims (3)

(57) [Claims] 1. A first frequency conversion means for mixing a high frequency band digital broadcast signal caught by an antenna and a first local oscillation signal generated by a first local oscillation signal generation means, and converting to a low frequency. Switching means for switching and outputting the low frequency band digital broadcast signal caught by the antenna and the output of the first frequency converting means, the output of the switching means and the second local oscillation signal generating means
Receiving means including a second frequency converting means for mixing a local oscillation signal and converting it into an intermediate frequency signal, having a variable receiving frequency and having an automatic gain adjusting function, and demodulating program information desired by the user from the output of the receiving means. When receiving the program information demodulation means and the high frequency band, the switching means is switched to the input system of the digital broadcast signal of the high frequency band, and the oscillation frequency of the first local oscillation signal generating means and the second local oscillation signal generating means. The first frequency conversion means and the second frequency conversion means are controlled by controlling the oscillation frequency.
The frequency converting means converts the digital broadcasting signal of a desired broadcasting frequency in the high frequency band into an intermediate frequency signal of a predetermined frequency. At this time, the oscillation frequency of the first local oscillation signal generating means is the output of the first frequency converting means. In view of the point, the digital broadcasting signal of the desired broadcasting frequency in the high frequency band is converted into a frequency away from the low frequency band, while at the time of receiving the low frequency band, the switching means is set to the low frequency band digital signal. Switching to the input system of the broadcast signal, controlling the oscillation frequency of the second local oscillation signal generating means, and converting the digital broadcast signal of the desired broadcast frequency in the low band to the intermediate frequency signal of the predetermined frequency by the second frequency converting means. Let ’s say
The high frequency band is controlled so that the oscillation frequency of the first local oscillation signal generation means is controlled so that the first frequency conversion means converts the frequency to a frequency apart from the signal band of the digital broadcast signal of the desired broadcast frequency of the low frequency band. A digital broadcasting receiver, characterized by comprising: 2. A first frequency conversion means for mixing a high frequency band digital broadcast signal caught by an antenna and a first local oscillation signal generated by a first local oscillation signal generation means and converting the mixture to a low frequency. Switching means for switching and outputting the low frequency band digital broadcast signal caught by the antenna and the output of the first frequency converting means, the output of the switching means and the second local oscillation signal generating means
Receiving means including a second frequency converting means for mixing a local oscillation signal and converting it into an intermediate frequency signal, having a variable receiving frequency and having an automatic gain adjusting function, and demodulating program information desired by the user from the output of the receiving means. When receiving the program information demodulating means and the high frequency band, the switching means is switched to the input system of the digital broadcasting signal of the high frequency band, and the oscillation frequency of the second local oscillation signal generating means is controlled to control the first frequency converting means. And the second frequency conversion means for converting the digital broadcast signal of the desired broadcast frequency in the high frequency band into an intermediate frequency signal of a predetermined frequency, while the switching means is used for changing the low frequency band when receiving the low frequency band. Switching to the input system of the digital broadcasting signal, controlling the oscillation frequency of the second local oscillation signal generating means, and the desired broadcasting frequency of the low band by the second frequency converting means. Tuning control means for converting the digital broadcast signal into an intermediate frequency signal of a predetermined frequency, and the oscillation frequency of the first local oscillation signal generating means is a desired broadcast in a high band when viewed at the output point of the first frequency converting means. A digital broadcasting receiver characterized in that a frequency digital broadcasting signal is converted to a frequency apart from a low frequency band. 3. A high frequency band digital broadcast signal caught by an antenna and a first local oscillation signal generated by a first local oscillation signal generating means having a variable oscillation frequency are mixed,
The first frequency conversion means for converting into an intermediate frequency signal, the low frequency band digital broadcast signal caught by the antenna, and the second local oscillation signal generated by the second local oscillation signal generating means having a variable oscillation frequency are mixed. A second frequency conversion means for converting to an intermediate frequency signal, and a switching means for switching between the output of the first frequency conversion means and the output of the second frequency conversion means, and outputting the variable frequency with an automatic gain adjustment function. Receiving means included therein, program information demodulating means for demodulating the program information desired by the user from the output of the receiving means, and when the high frequency band is received, the switching means is switched to the input system of the digital broadcasting signal of the high frequency band, By controlling the oscillation frequency of the one local oscillation signal generating means, the first frequency converting means converts the digital broadcasting signal of the desired broadcasting frequency in the high frequency band to a predetermined frequency. It was converted during frequency signal,
At this time, the oscillation frequency of the second local oscillation signal generating means is controlled so that the low frequency band is converted by the second frequency converting means into a frequency apart from the predetermined intermediate frequency signal band,
When receiving the low frequency band, the switching means is switched to the input system of the low frequency band digital broadcast signal, the oscillation frequency of the second local oscillation signal is controlled, and the second frequency conversion means controls the desired frequency of the low frequency band. Converting a digital broadcasting signal of a broadcasting frequency into an intermediate frequency signal of a predetermined frequency, at this time,
Tuning control means for controlling the oscillation frequency of the first local oscillation signal generating means so that the high frequency band is converted by the first frequency converting means into a frequency away from the predetermined intermediate frequency signal band. A digital broadcasting receiver characterized by.