JP3514624B2 - Digital broadcast receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] The present invention relates to digital broadcast reception.
In particular, when a seek is instructed,
Tune in order to the frequency of digital broadcasting and receive
Seek to stop seeking when a digital broadcast is found
The present invention relates to a digital broadcast receiver having a function of locking. [0002] 2. Description of the Related Art In Europe, DAB (Digital Audio
-Diobroadcasting; Digital Audio Broa
digital audio broadcasting called dcasting)
Has been This DAB uses a multi-carrier modulation method.
OFDM (Orthogonal Frequency Division Multiplexing Modulation)
thogonal Frequency Division Multiplex)
In this method, transmission symbols are
Ghost resistance
Reception is enabled. Each DAB carrier is DQPS
It is K-modulated. In DAB, band II (87-108 MHz band), band II
Band III (175 to 250 MHz band), L band (1.452 to 1.49)
Band 2) is used, and band II and band 2
III has a transmission frame period of 96 ms and a carrier interval of 1 kHz.
Transmission mode 1 (multi-path strong, SFN; single frequency
Network is used) (Transmission mode 1 is
Limited to use in bands II and III). L band
Transmission mode with a frame period of 24 ms and a carrier interval of 4 kHz
2 (strong against movement), frame period 24ms, carrier interval 8k
Hz transmission mode 3 (satellite broadcasting, etc.), frame period 48m
s, a transmission mode 4 with a carrier interval of 2 kHz is used. [0004] In the upper part of FIG.
3 shows a format of a transmission frame signal. First 1.29
7ms NULL symbol and 1.246ms phase reference symbol
Synchronization signal consisting of (PRS: Phase Reference Symbol)
Followed by 7 OFDM symbols of 1.246 ms each.
Five are included. For transmission symbols other than NULL symbols,
Bol, the guard interval is 0.246 ms from the beginning,
The remaining 1 ms is a valid symbol. [0005] S = the first transmission symbol is AFC (automatic
PRS used to perform frequency adjustment)
A predetermined specific code (CAZAC code; Cons)
tantAmplitude Zero Auto Correlation Code
) Is differentially modulated between adjacent carriers. S = 2-4
The third transmission symbol is used by the receiver to select the desired program.
F that transmits necessary information and auxiliary information for programs
IC (Fast Information Channel)
 ), S = 5-76th transmission symbol is voice or data
M that multiplexes and transmits the sub-channels of
SC (MainServiceChannel). Usually, sub-chan
One channel corresponds to one program, and the subchannel is in MSC
The structure information indicating how multiplexing is performed in FI
C, and the program desired by the user with reference to the FIC
Can be extracted. Transmission mode
Mode 2 is obtained by reducing each symbol period of FIG. 3 to 1/4.
In transmission mode 3, each symbol period in FIG.
And the number of OFDM symbols is increased.
In the transmission mode 4, each symbol period in FIG.
It is. FIG. 4 is a block diagram of a DAB receiver with a seek function.
It is. For example, band I caught by antenna 1
Reception of DAB broadcast signal by I, band III, L band
The signal is sent to the front end 2 and bands II and III are R
The signal is input to the terminal a of the F changeover switch 3. L band
Received signal is band-limited by BPF4 and AGC
The row input from the PLL circuit 7 by the mixer 6 through the width unit 5
Cull oscillation signal L₀Mixed with band III
Numbers are converted. The PLL circuit 7 includes a reference oscillator 13 described later.
F of the reference oscillation signal input from₁For f₁・
(N₀/ M₀) Times frequency L₀Is output. n₀, M
₀Is a fixed value. The output of the mixer 6 is an RF switching switch.
The signal is output to the terminal b of switch 3. The output of mixer 6 is
The envelope detection circuit 9 detects the envelope and detects the AGC voltage.
Output to the GC amplifier 5. AGC amplifier 5 is an AGC
Decrease or increase the gain as the pressure increases or decreases,
Regardless of the level of the antenna input level, the output of the mixer 6
The level should be almost constant. The output of the RF switch 3 is an AGC
RF amplification by RF amplifier circuit 10 that can change gain by pressure
After that, the signal was input from the PLL circuit 12 by the mixer 11.
First local oscillation signal L₁And the center frequency is f
_IF1To the first intermediate frequency signal. PLL circuit 12
Is the frequency f of the reference oscillation signal input from the reference oscillator 13
₁For f₁・ (N₁/ M₁) Times frequency L₁Out
Power. m₁Is a fixed value but n₁Is the microcomputer described later
Variablely set by the configured system controller
Then, the tuning frequency is varied in, for example, 16 kHz steps. Base
The quasi-oscillator 6 is a VCXO and controls for automatic frequency adjustment.
The oscillation frequency is varied according to the voltage. 1st intermediate frequency signal
Is 1. Due to the SAW filter (surface acoustic wave filter) 14.
Bandwidth limited to 536 MHz passband. The output of the SAW filter 14 is AGC amplified.
Input from the PLL circuit 17 by the mixer 16 through the mixer 15
Second local oscillation signal L_TwoAnd the center frequency is mixed
f_IF2(<F_IF1) Is converted into a second intermediate frequency signal.
The PLL circuit 17 receives the reference oscillation input from the reference oscillator 13.
Signal frequency f₁For f₁・ (N_Two/ M_Two) Double lap
L of wave number_TwoIs output. n_Two, M_TwoAre fixed values
is there. The second intermediate frequency signal is an anti-aliasing filter
18 limits the band to a pass bandwidth of 1.536 MHz. Output from anti-aliasing filter 18
The second intermediate frequency signal is enveloped by an envelope detection circuit 19.
The signal is detected and converted to an AGC voltage by the RF amplifier circuit 10 and the AGC
The signal is output to the amplifier 15 (see FIG. 3A). RF amplification times
The path 10 and the AGC circuit 15 are connected to the
The antenna input level by decreasing or increasing
Second intermediate frequency signal of almost constant level regardless of the size of the bell
Is obtained. The output of the envelope detection circuit 19 is
Null detection circuit 2 for detecting NULL symbols
Input to 0. In the NULL detection circuit 20, NULL
After the symbol portion is shaped (see FIG. 3B)
Fall time length Td was measured and specified by DAB
Matches NULL symbol length in any transmission mode
At the time of the rising edge, NULL symbol
The signal ND (see FIG. 3C) is a timing synchronization circuit.
21, output to the system controller and the like. Also,
A transmission mode detection signal TM is also output (see d in FIG. 3).
In FIG. 3D, since Td = 1.297 ms, the transmission mode
When transmission mode 1 is output as the code detection signal TM
Is shown). The timing synchronizing circuit 21 is usually described later.
PRS input from the FFT circuit (valid symbol period)
Input the carrier-specific components of (between) and measure the power by carrier
From the cepstrum calculated by IFFT processing
Detects frame synchronization and outputs a synchronization detection signal
Output to the timing signal generation circuit to generate various timing signals.
Let it run. However, immediately after starting reception of a certain ensemble
Thereafter, the null synth input from the null detection circuit 20 is set.
Detects frame synchronization using the vol detection signal ND
Outputs a detection signal. The output of the anti-aliasing filter 18 is
After A / D conversion by the A / D converter 30, I / Q demodulation
The I / Q component is demodulated in the circuit 31 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
Is subjected to FFT processing, and OFDM variable
N harmonics (in the case of transmission mode 1, n = 153
6. In the case of transmission mode 2, n = 384 lines, transmission mode 3
, N = 192 lines, and in the case of transmission mode 4, n = 76
Carrier component (carrier) for 8 carriers
Separately, complex number data representing the amplitude and phase of the carrier are extracted.
Will be issued. The FFT circuit 32 follows a predetermined timing signal.
The component for each carrier in the effective symbol period of the PRS part is
Output to the frequency error detection circuit 33. Frequency error detection times
In the path 33, the component for each carrier in the PRS portion is
After differential demodulation and decoding (PRS part
Is fixed-modulated between carriers), a predetermined
Calculate the correlation function between the reference code and the graph of the correlation function.
FIG. 7). Then, from this correlation function, the tuning frequency
And the frequency error of the DAB broadcast signal frequency
Put out. The frequency error detection circuit 33 is a system control
Frequency error data while AFC is turned on by the
Is output to the integration circuit 34 (while the AFC is off).
Outputs data indicating that the frequency error is zero.
). The integration data in the integration circuit 34 is converted by a D / A converter 35
After the D / A conversion, the reference oscillator 13
It is output as a control voltage for adjustment. Reference oscillator 13
The oscillation frequency is varied according to the control voltage,
Frequency f₁In the direction to cancel the frequency error.
You. The FFT circuit 32 includes S = 2 to 76 in FIG.
Key after FFT for transmission symbol (effective symbol period)
Carrier-specific components (carrier-by-carrier amplitude and phase
Is output to the channel decoder 36.
You. In the channel decoder 36, the frequency
And DQPSK symbol demapping, FIC / MS
C separation is performed, and three effective symbols of FIC
After being divided into four equal parts, error detection / correction (Viterbi recovery
No. 12) and 12 FIBs (high
FastInformation Block) and FI
Called G (Fast Information Group)
To the system controller in the form of packet data
Is forced. On the other hand, the effective symbol of MSC is 18 symbol
4 CIFs (Common Interleaved
 Frame). Each CIF has multiple sub-channels
Channel (Sub Channel), usually one sub-channel
File corresponds to one program. When the user presses a program selection key on the operation panel 40,
When a desired program is selected, the system controller 3
7 performs a predetermined program selection control, and refers to FIC information.
Outputs sub-channel designation information corresponding to the desired program
Then, the channel decoder 36 selects a sequence from among the four CIFs.
The sub-channel specified by the stem controller 37
After demultiplexing, time deinterleaving and error detection
Output / correction (Viterbi decoding), descrambling and DA
DAB decoded by decoding B audio frame data
Output audio frame data to MPEG decoder 38
Power. The MPEG decoder 38 is a DAB audio frame.
Decode the frame data and audio for 2 channels
Output data. This audio data is converted to D / A
Converter 39 converts the analog audio signal into an analog audio signal.
Is output. The operation panel 40 is also provided with a seek key.
ing. The memory 41 stores a plurality of ensembles.
Transmission frequency data is stored. System control
When the seek key is pressed on the operation panel 40,
When a command is given, ensemble seek control is performed.
U. Hereinafter, the seek operation will be described with reference to the flowchart shown in FIG.
The control process will be described. When a seek command is given, the system
The controller 37 controls the frequency error detection circuit 33 with A
Give FC off command and output data indicating zero frequency error.
Force to fix the oscillation frequency of the reference oscillator 13
(Step S1 in FIG. 5). Then, referring to the memory 41, the first
Read the broadcast frequency data of Samburu, Band II, II
If I, switch the RF switch 3 to the a side,
In the case of the L band, switch the RF switch 3 to the b side.
Change. And correspond to the frequency of the first ensemble.
N₁Is set in the PLL circuit 12, and the first ensemble
(Step S2). Next, the NULL detection time
Null symbol detection signal ND is input from path 20
Is checked (step S3). At this reception frequency
When the ensemble is caught, the NULL symbol part
The output of the envelope detection circuit 19 drops in minutes. NULL detection
The circuit 20 shapes the output of the envelope detection circuit 19,
Outputs NULL symbol detection signal ND at rising edge
I do. The system controller 32 detects a NULL symbol.
When the output signal is input, YES is determined in step S3.
Then, it is determined that there is a DAB broadcast signal at the current reception frequency.
An AFC ON command is given to the wave number error detection circuit 28,
The control process ends (step S4). The system controller 38 is a NULL thin
When the vol detection signal is input, YES is determined in step S3.
Judgment, there is a DAB broadcast signal at this reception frequency
AFC ON command is given to the frequency error detection circuit 33 to
The work control process ends (step S4). The output of the front end 2 is an I / Q demodulation circuit
After I / Q demodulation at 31, FFT circuit 32
Processing is performed. The component of each carrier in the PRS part is the frequency
The difference between the carriers is demodulated by the error detection circuit 33 and the
Between the decoded code and a predetermined reference code.
Is calculated. Figure shows an example of a graph of the correlation function
7 (the horizontal axis in FIG. 7 is the frequency, and the vertical axis is the correlation value). this
From the correlation function, the frequency between the tuning frequency and the frequency of the DAB broadcast signal is calculated.
The wave number error is detected by calculation. Now, the reception antenna viewed from the first intermediate frequency signal
The center of the spectrum distribution of the bull is as shown by the solid line A in FIG.
And the regular center frequency f_IF1Shift to higher frequency
(The dashed-dotted line B in FIG.
The graph of the attenuation function) and the correlation function are as shown in FIG. frequency
The AFC ON command is given to the number error detection circuit 33.
Indicates the frequency error detected by calculation from the correlation function.
Output frequency error data. The frequency error data is the product
After being integrated by the dividing circuit 34, the D / A converter 35
The signal is A-converted and output to the reference oscillator 13. The reference oscillator 13 oscillates according to the control voltage.
The wave number is varied and the local oscillation signal L₀Departs from the first local
Shake signal L₁, The second local oscillation signal L_TwoFrequency
Variable in the direction to cancel the wave number error. As a result, the first
Received ensemble spectrum as seen from the intermediate frequency signal
The cloth shifts to a lower frequency (see arrow C in FIG. 6).
8) Finally, as shown in A ′ of FIG.
It falls within 14 passbands. This allows the channel
Coder 36 can recover FIC and MSC information without error
You. When the user selects a desired program on the operation panel 40,
The system controller 37 supplies the channel decoder 36 with
Instruct the DAB audio frame data of the desired program
Output to the MPEG decoder 38. This allows
Listen to programs. If NO in step S3,
There is no ensemble that can be received at this tuning frequency.
The system controller 37 refers to the memory 41
The next ensemble broadcast frequency data exists
Check (step S5), if not, seek
After the control process, if there is, the corresponding frequency division ratio data
Ta n₁Is set in the PLL circuit 12, and a new ensemble is set.
After tuning in, the same processing as described above is repeated (step
Step S6). [0021] SUMMARY OF THE INVENTION However, the conventional
DAB receiver with seek function receives bands II and III.
When transmitting, the RF switch 3 is switched to the a side.
However, the isolation between the terminals b and c is 50d
It is about B. According to the DAB standard, the minimum is -90 dBm
Must be able to receive the antenna input of
Because the GC is applied, the RF switch 3
Isolation is not enough. That is, the figure
As shown in A of 9 (1), in an ensemble of L band
Then, the frequency converted to band III by the mixer 6 is received.
The signal is reduced by 50 dB with the RF switch 3
(See B in FIG. 9B), the RF amplifier circuit 10, the AG
The signal is again amplified by the C amplifier 15 (C in FIG. 9 (3)).
reference). Therefore, the ensemble of bands II and III
During seek, at a certain tuning frequency, bands II and III
Has no receivable ensemble, but some L band
The received signal frequency-converted by the ensemble mixer 6 is
Upon entering the pass band of the SAW filter 14, the receiver
Incorrect frequency pull-in for L-band ensemble
Ensemble of Bands II and III
There was a problem that it was not possible to seek correctly. The present invention is
In view of the problems of the prior art described above,
To provide a digital broadcasting receiver that can perform the work correctly
Is its purpose. [0023] According to the first aspect of the present invention,
Digital broadcast receivers consist of OFDM modulated waves
Digital broadcast signals are received and high band digital
The broadcast signal is frequency-converted to a lower band, and
Of the high band signal and the original low band signal
Of the broadcast signal and the received signal by the switching means (3)
High frequency amplification, frequency conversion and band
Automatic gain adjuster with variable reception frequency for limiting output
Receiving means (2) having an
Extraction means (31, 32) for extracting rear component, extraction
Program desired by the user from carrier-specific components extracted by means
Program information demodulation means (36, 38) for demodulating information;
Detects wave number error and adjusts frequency to cancel frequency error
Automatic frequency adjusting means (33A, 34, 35, 1
3, 7, 12, 17) digital broadcast reception
Machine stores frequency information of multiple digital broadcasts
Storage means (41) and a NULL symbol from the received signal.
NULL detecting means (20) for detecting the presence or absence of
Transmission mode detecting means (2) for detecting a transmission mode from a signal.
0) and when the seek is instructed, the receiving means is stored in the storing means.
Tune to the frequency of each digital broadcast stored in the
At a certain reception frequency, and
When the LL symbol is detected, the transmission mode is further detected.
The transmission mode detected by the
Matches the transmission mode allowed in the digital broadcasting band
Stop seek if they match, automatic frequency adjustment
Adjustment means to adjust the frequency, and if they do not match, seek
And seek control means (37A) for continuing.
Features. According to the first aspect of the present invention, during the seek,
When a NULL symbol is detected at the reception frequency,
The transmission mode detected by the transmission mode detection means is
Mode permitted in the digital broadcast band to be monitored
Judge whether it matches, stop seeking only when it matches,
The frequency adjusting means performs frequency adjustment. During the seek
When a NULL symbol is detected at the receiving frequency
Detected if digital broadcast targeted for networking was received
Transmission mode is allowed in the digital broadcast band to be sought.
Matches the allowed transmission mode. So during the seek
When a NULL symbol is detected at the receiving frequency
The transmission mode detected by the transmission mode detection means
Modes allowed in digital broadcasts to be sought
Judge whether it matches and stop seeking only when it matches
This ensures that digital broadcasts targeted for seeking can be
You. The automatic frequency adjusting means includes, for example, an extracting means
Decode the PRS carrier component extracted in (32)
Frequency from the correlation function calculated with the predetermined reference code.
Detect the number error and cancel the detected frequency error
Frequency adjustment may be performed. [0026] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, referring to FIG.
One embodiment will be described. FIG. 1 shows a seek according to the present invention.
FIG. 5 is a block diagram of a DAB receiver with a function, the same as FIG.
The components are denoted by the same reference numerals. Microcomputer configuration
The system controller 37A uses the operation panel 40 to
When the seek key is pressed and a seek instruction is given,
Control process, and program selection operation with program selection key
Then, predetermined program selection control is performed. Among them, sea
In the seek control processing, a NULL thin
In addition to the detection of a bol, the ensemble
Transmission mode and transmission detected by the NULL detection circuit 20.
The condition is that it matches the transmission mode. Other structures
The components are configured exactly the same as in FIG. Next, the embodiment described above with reference to FIG.
Will be described. Figure 2 shows the system controller
9 is a flowchart illustrating a seek control process of the roller 37A.
is there. Note that the memory 41 has band II, band II
Broadcast frequencies of 10 ensembles in I and L bands
Numerical data is stored in the memory channels CH1 to CH10.
It is assumed that The user presses a seek key on the operation panel 40.
When a seek is instructed, the system controller 37A
An AFC off command is given to the frequency error detection circuit 33A.
To output data indicating zero frequency error, and
The oscillation frequency of the device 13 is fixed (step S1 in FIG. 2).
1). Then, referring to the memory 41, the memory channel
Broadcasting cycle of the first ensemble stored in channel CH1
Read the wave number data and apply to bands II and III
Switches the RF changeover switch 3 to the a side,
In the case of, switch the RF switch 3 to the b side,
N corresponding to the broadcast frequency data of the ensemble₁To
Set to PLL circuit 12 and tune to first ensemble
(Step S12). Next, the NULL detection circuit 20
Check if the NULL symbol detection signal ND is input from
(Step S13). If NO, receive this time
It is unlikely that an ensemble was received on the frequency
Is not the last memory channel yet
The ensemble stored in the next memory channel CH2
Read out the broadcast frequency data of the
If it is, switch RF switch 3 to a side
For the L band, set the RF switch 3 to the b side.
Switching and also for ensemble broadcast frequency data.
Respond to n₁Is set in the PLL circuit 12, and the second answer
(Steps S14 and S15). It is a DAB broadcast signal at the current reception frequency
When the ensemble is caught, the front end 2
Is output as a second intermediate frequency signal. And NUL
The output of the envelope detection circuit 19 drops at the L symbol portion.
The NULL detection circuit 20 detects the output of the envelope detection circuit 19
Shape, measure the fall time length Td, and
NULL symbol length of any of the specified transmission modes
If they match, a NULL symbol is detected at the rising edge.
Output signal ND, and a transmission mode corresponding to Td.
Is output (see FIG. 3).
See). Timing using the NULL symbol detection signal ND
The synchronization circuit 21 detects frame synchronization and outputs a synchronization detection signal.
And a timing signal generation circuit (not shown)
Generates and outputs an imaging signal. The system controller 37A is a NULL system.
When the symbol detection signal ND is input, in step S13
It is determined as YES. However, look at the output of front end 2.
Ensemble received by Bands II and III
It is not clear whether it is due to the L band. After step S13, the system control
37A is a transmission mode detection signal from the NULL detection circuit 20.
Enter the number TM, and the ensemble
Mode II and III, the transmission mode is set to 1
Therefore, if the radio waves reach a long distance,
In order to secure the length of the guard interval,
Mode 1), transmission mode detection signal
Check whether the transmission mode indicated by TM matches 1
(Step S16). If not 1, some L band
Because the ensemble was frequency converted to Band III,
It is determined that only a NULL symbol has been detected, and
Proceed to step S14. The ensemble for this seek is a band
II and III, and the transmission mode indicated by the transmission mode detection signal TM.
When the code is 1, this reception ensemble is
Since the ensemble is likely to be
An AFC ON command is given to the error detection circuit 33A,
Start a timer for measuring a fixed time (step S
17, S18). On the other hand, in the determination of step S16,
And the ensemble for this seek is the L band
When the transmission mode is 2, 3, 4 is allowed,
The transmission mode indicated by the transmission mode detection signal TM is band L
Check if it matches any of 2, 3, or 4
Click. If they do not match, certain addresses in bands II and III
Ensemble leaks to the output side of RF changeover switch 4
Judging that only a NULL symbol has been detected,
Proceed to step S14. Ensemble for this seek
Is the L band and the transmission mode detection signal TM indicates
When the transmission mode is 2, 3, or 4,
The reception ensemble can be an ensemble to be sought.
High performance, the AFC
And a timer that counts a certain amount of time.
Start (steps S17, S18). The output of the front end 2 is an I / Q demodulation circuit
After I / Q demodulation at 31, FFT circuit 32
Processing is performed. Frequency error detection in response to AFC ON command
The circuit 33A carries the PRS portion from the FFT circuit 32.
(A) Each time a component is input, differential demodulation between carriers is performed and decoded.
And calculate a correlation function between the signal and a predetermined known reference code.
You. Then, the frequency error is calculated from the obtained correlation function.
And outputs the detected frequency error data to the integration circuit 34.
Output. This frequency error data is integrated by the integration circuit 34.
After that, it is D / A converted by the D / A converter 35 and
It is output to the reference oscillator 13 as a control voltage for adjusting the wave number.
You. The reference oscillator 13 generates an oscillation frequency f according to the control voltage.₁
And the local oscillation signal L₀, The first local oscillation signal
No. L₁, The second local oscillation signal L_TwoThe frequency of the
Variable in a direction to cancel the error. Originally, when viewed with the first intermediate frequency signal,
The center frequency of the ensemble
Center frequency f_IF1Away from the AFC frequency
If pulling in is not possible, even if the time has elapsed since AFC was turned on
The frequency error is not reduced, and the ensemble is received normally
It will not be possible. In addition, detection of the NULL symbol this time
The output is not due to the ensemble,
TV broadcast signal other than DAB broadcast signal due to aging phenomenon etc.
Only a dip on the time axis occurred,
If the maximum value of the correlation function is equal to or greater than the reference value Sc
Frequency error is small even if the time elapses after AFC is turned on.
Does not go away. The system controller 37A has a timer
After finishing the time measurement,
Frequency error data is input from the number error detection circuit 33A,
Check whether the convergence is below a certain value (Step S1)
9, S20). If NO, the mobile reception
The TV broadcasting signal has a dip on the time axis due to the
Is detected as a NULL symbol by mistake
NUL of transmission mode 1 for some reason, such as
Judge that only L symbol is detected, and detect frequency error
After giving the AFC off command to the circuit 33A (step
Step S21), the process proceeds to step S14, and the next memory channel
Synchronized with the ensemble stored in channel 3
Is performed. This results in unnecessary frequency pull-in operation.
And seek can be made faster and more accurate.
Become. Conversely, Y is determined in step S20.
If it is ES, the program of the ensemble targeted for seek is normal
Finish the seek because you can listen to it. FFT circuit 32
From the carrier component of each symbol input from
The decoder 36 restores FIC and MSC information. You
When the user selects a desired program on the operation panel 40, the system
The controller 37A instructs the channel decoder 36.
The DAB audio frame data of the desired program to MPE
Output to the G decoder 38. This allows the desired program to be
You can listen. According to the above-described embodiment, during the seek,
When a NULL symbol is detected at a certain reception frequency,
If the target ensemble is band II or III, transmit
Since the mode is 1, it is detected by the NULL detection circuit 20.
AFC is turned on only when the transmission mode matches 1.
When the frequency error within the fixed time converges below a certain
By stopping the seek, you can receive the seek target correctly,
Also, if the ensemble to be sought is the L band, transmission
The mode can be only 2, 3 or 4, so NULL detection
The transmission mode detected by the circuit 20 is permitted in the L band.
AFC is turned on only when the transmission mode matches the
Seek when frequency error within time converges below a certain level
By stopping, the seek target can be correctly received. In each of the above-described embodiments and modifications,
Is intended for DAB broadcasting in Europe.
However, the present invention is not limited to this.
Digital terrestrial TV broadcasting, digital satellite broadcasting, etc.
The same applies to broadcasting and communication for other purposes.
it can. [0041] According to the present invention, a certain reception cycle is performed during a seek.
When a NULL symbol is detected by the wave number, the transmission mode
The transmission mode detected by the data detection means is the data to be sought.
One of the transmission modes permitted in the digital broadcast transmission mode
Stopping the seek only when you
Digital broadcasting can be received correctly.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a DAB receiver with a seek function according to one embodiment of the present invention. FIG. 2 is a flowchart showing a seek control process by the system controller of FIG. 1; FIG. 3 is an explanatory diagram illustrating a configuration of a DAB transmission frame signal and an operation of detecting a NULL symbol. FIG. 4 is a block diagram of a conventional DAB receiver with a seek function. FIG. 5 is a flowchart showing a seek control process by the system controller of FIG. 4; FIG. 6 is a diagram showing a frequency spectrum of an ensemble viewed from a first intermediate frequency signal. FIG. 7 is a diagram illustrating the operation of the frequency error detection circuit. FIG. 8 is a diagram illustrating a frequency spectrum of an ensemble viewed from a first intermediate frequency signal. FIG. 9 is a diagram showing a frequency spectrum of an L-band ensemble. [Description of Signs] 1 Antenna 2 Front End 5, 15 AGC Amplifier 6, 11, 16
Mixers 7, 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 33A Frequency error detection circuit 34 Integration circuit 35 D / A Converter 36 Channel decoder 37A System controller 38 MPEG decoder 40 Operation panel 41 Memory

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H04J 11/00

Claims (1)

(57) [Claim 1] A digital broadcast signal composed of an OFDM modulated wave is received, a digital broadcast signal in a high band is frequency-converted to a low band, and the frequency-converted high band is transmitted. After selectively switching between the reception signal of the band and the reception signal of the digital broadcasting signal of the original low band by the switching means, the reception frequency to output after high-frequency amplification, frequency conversion and band limitation is variable and automatic gain Receiving means having an adjusting function; extracting means for extracting a component for each carrier from the output of the receiving means; program information demodulating means for demodulating program information desired by the user from the component for each carrier extracted by the extracting means; Frequency adjustment means for detecting and adjusting the frequency so as to cancel the frequency error. Means for storing information, and NUL for detecting the presence or absence of a NULL symbol from a received signal.
L detection means, transmission mode detection means for detecting a transmission mode from a received signal, and when a seek is instructed, the reception means is sequentially tuned to the frequency of each digital broadcast stored in the storage means,
When a NULL symbol is detected by the NULL detection means at a certain reception frequency, it is further determined whether or not the transmission mode detected by the transmission mode detection means matches the transmission mode permitted in the digital broadcast band to be searched this time. A digital broadcast receiver comprising: a seek control unit that stops seeking when the values match, causes the automatic frequency adjusting unit to adjust the frequency, and continues seeking if the values do not match.