JP2000349668A - Digital broadcast receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a digital broadcast receiver by controlling a demodulation carrier frequency so that a difference between a frequency of an intermediate frequency signal received by a demodulator and the demodulation carrier frequency is a prescribed value thereby limiting the synchronization time within a prescribed time and conducting high-speed channel selection and searching. SOLUTION: Difference frequency value detectors 9, 13 in the digital broadcast receiver R measure a difference frequency (ΔF1st) between an intermediate frequency (F(sif)) and a demodulation carrier frequency (F(Sca)). Reception control sections 13, 7 correct the demodulation carrier frequency (FSca) so that the measured difference frequency (Δ) is within a 1st difference frequency region where a rate of change in a synchronization time with respect to the difference frequency between the intermediate frequency and the demodulated carrier frequency is small. The synchronization time (Ts) can be limited within a prescribed time by demodulating the intermediate frequency (F(Sif)) with the corrected demodulation carrier frequency (FSca).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency of an intermediate frequency signal input to a QPSK demodulator and a carrier for demodulation in a channel selection operation of a digital broadcast receiving apparatus in which broadcast contents are time division (TDM) and QPSK modulated. A digital broadcast receiving apparatus capable of controlling a frequency of a demodulation carrier signal so that a difference from a signal frequency becomes a predetermined value, thereby suppressing a QPSK synchronization time within a predetermined time, and selecting and searching at high speed. About.

[0002]

2. Description of the Related Art FIG. 7 shows a difference between an intermediate frequency generally input to a QPSK demodulator and a carrier frequency for demodulation.
This shows the relationship with the QPSK synchronization time. In the figure, the horizontal axis represents a QPSK modulated signal S, which is an input intermediate frequency signal.
if frequency F (Sif) and demodulation carrier signal Sca
Frequency value Δf [KHz] from the frequency F (Sca)
Represents That is, the difference frequency value Δf = F (Sif) −F
(Sca). The vertical axis represents the QPSK synchronization time Ts (ms) at each value of the difference frequency value Δf shown on the horizontal axis.
Represents

As shown in FIG. 1, the rate of change of the QPSK synchronization time Ts in the QPSK demodulator is extremely high at a certain point of the difference between the frequency of the input intermediate frequency signal and the frequency of the demodulation carrier signal. different. In this example, the difference frequency value Δf is the minimum value (F (Sif) = F (Sca))
At this time, the QPSK synchronization time Ts also becomes the minimum value (zero). When the difference frequency value Δf is positive (F (Sif)> F (Sc
In the region a)), as represented by the straight line Lp, the QPSK synchronization time Ts gradually changes according to the difference frequency value Δf.

However, when the difference frequency value Δf is negative (F (Si
f) In the region where <F (Sca)), the straight line Ln
As shown in the equation, QPSK according to the difference frequency value Δf
The synchronization time Ts changes rapidly. Straight line Lp and straight line L
As shown by n, the QPSK synchronization time Ts increases in proportion to the absolute value of the difference frequency value Δf. If the inclinations of the straight line Lp and the straight line Ln with respect to the horizontal axis Δf are α and β, respectively, then α <β. Thus, the difference frequency value Δf, which is the boundary point at which the rate of increase of the QPSK synchronization time Ts with respect to the difference frequency value Δf changes abruptly, is called the boundary difference frequency Fdb. Note that this boundary difference frequency Fdb
Is normally zero, as shown in FIG.

[0005]

SUMMARY OF THE INVENTION A QPSK modulated signal Si
Since there is a relationship as shown in FIG. 7 between the difference frequency value Δf between f and the demodulation carrier signal Sca and the QPSK synchronization time Ts, the difference frequency value Δf is theoretically the boundary difference frequency The digital broadcast receiving apparatus may be configured to match Fdb. However, in an actual digital broadcast receiving apparatus, the manufacturing accuracy and quality of its components and the assembling accuracy and quality of a digital broadcast receiving apparatus assembled using those components cannot be kept completely constant. Furthermore, the frequency of a signal generated or processed inside the digital broadcast receiving apparatus varies due to a change over time or a change in temperature in a unit of a component or an assembled digital broadcast receiving apparatus. Therefore, the boundary difference frequency Fdb also fluctuates to both the positive and negative sides with the passage of time.

Therefore, even if the demodulation carrier signal Sca can be set for the QPSK modulated signal Sif such that the difference frequency value Δf matches the boundary difference frequency Fdb, the boundary difference frequency Fdb and the difference frequency Value △ f
And fluctuate relatively. That is, the boundary difference frequency Fdb
Is considered to be immobile, the difference frequency value Δf can be regarded as jitter on both the positive and negative sides of the boundary difference frequency Fdb.

When the difference frequency value Δf is located in the negative side region, as shown by a straight line Ln in FIG.
SK synchronization takes a very long time. On the other hand, the difference frequency value △
When f is located in the positive side region, as shown by the straight line Lp, it takes more time than in the case where it is located at the boundary difference frequency Fdb, but it is permissible compared with the case where it is located in the negative side region. Synchronization can be achieved in about a time. Note that both the straight lines Ln and Lp represent the characteristics of the frequency difference and the QPSK synchronization time in the digital broadcast receiving device. In this sense, the straight lines Ln and Lp can be called a characteristic straight line frequency difference-synchronization time characteristic straight line.

Ideally, the demodulation carrier signal Sca should be set so that the difference frequency value Δf is always located on the boundary difference frequency Fdb. However, as described above, it is practically impossible to keep the variation in physical accuracy and quality of each component part within a desired allowable range. Therefore, if the difference frequency value △ f is set on or near the boundary difference frequency Fdb in order to reduce the QPSK synchronization time Ts, the set difference frequency value に f can be rapidly shifted to both the positive and negative sides of the boundary difference frequency Fdb. Because of the jitter, the QPSK synchronization time is not stabilized, and the synchronization time at the time of the channel selection operation becomes longer. At the time of search, a sufficient waiting time is required because the QPSK synchronization time is not stable.

In FIG. 7, the slope of the frequency difference-synchronization time characteristic line in the positive region with the boundary difference frequency Fdb as a boundary, as typically shown by the frequency difference-synchronization time characteristic lines Lp and Ln. Is smaller than the slope in the negative region. However, the same problem occurs when the slope of the frequency difference-synchronization time characteristic straight line in the negative region is small. Therefore, in the present invention, even if the difference frequency value Δf is jittered, the slope of the frequency difference-synchronization time characteristic straight line is on the small side and the QPSK synchronization time Ts falls within a region as close to zero as possible. Controlling. When the slope of the frequency difference-synchronization time characteristic line in the positive region and the negative region is the same, the problem caused by the radical change in characteristics due to the jitter does not occur. That is, if the difference frequency value Δf is set as far as possible on the boundary difference frequency Fdb,
This is because even if the difference frequency value Δf is jittered, the QPSK synchronization time Ts becomes the minimum value on average.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and a minimum difference frequency value with respect to a boundary difference frequency can be minimized by appropriately setting a difference frequency value with respect to each variation of a digital receiver. It is an object of the present invention to provide a digital broadcast receiving method and apparatus for performing high-speed channel selection and search operations in QPSK synchronization time.

[0011]

Means for Solving the Problems and Effects of the Invention The first invention relates to demodulation of a digital broadcast wave, wherein a change rate of a synchronization time with respect to a difference frequency value between an intermediate frequency and a demodulated carrier frequency is a first value. A first differential frequency domain;
A digital broadcast receiving apparatus having a second difference frequency region in which a rate of change is a second value larger than the first value,
A difference frequency value detecting unit configured to measure a difference frequency value between the intermediate frequency value and the demodulated carrier frequency to generate difference frequency information; and, based on the difference frequency information, the difference frequency value is within a first difference frequency region. A demodulation carrier frequency correction unit that corrects a demodulation carrier frequency, wherein the demodulation carrier frequency correction unit uses a specified frequency predetermined as an intermediate frequency according to the digital broadcast wave as a demodulation carrier frequency. First to set demodulation carrier frequency
And a difference detection for obtaining a difference frequency between a difference frequency value between the intermediate frequency and the first demodulation carrier frequency and a target difference frequency predetermined as a correction target value, based on the difference frequency information. And a second demodulation carrier frequency setting unit for setting a second demodulation carrier frequency, which sets a value obtained by adding a difference frequency to a specified frequency as a demodulation carrier frequency, and It is characterized in that the synchronization time at the time of demodulation is suppressed within a predetermined time.

As described above, in the first aspect, by setting the difference frequency value in the difference frequency region where the synchronization time is short, the synchronization time can be suppressed within a predetermined time. In addition, the speed of the search operation can be increased. Further, even if the characteristic of the difference frequency value of the digital broadcast receiving apparatus is not accurately known, first, the difference between the frequency difference value when demodulated at the first demodulation carrier frequency, which is the specified frequency, and the target difference frequency is determined by the specified frequency. By performing demodulation at the generated second demodulation carrier frequency in addition to the above, the difference frequency value can be set so as to be near the boundary between the first frequency domain and the second frequency domain.

According to a second aspect of the present invention, in the first aspect, the difference frequency value between the corrected demodulation carrier frequency and the intermediate frequency is within the second difference frequency domain even once within a first predetermined number of consecutive times. In the case of, further comprising a first demodulation carrier frequency correction control unit that controls the demodulation carrier frequency correction unit so that the corrected demodulation carrier frequency is changed by a predetermined frequency and further corrected. I do.

As described above, in the second invention, the differential frequency value is measured for the first predetermined number of times, and if it is in the second frequency region having poor characteristics even once, the demodulated carrier frequency is changed by the predetermined frequency. By shifting the resulting difference frequency value to the first frequency domain side,
The difference frequency value is changed to the second
Frequency domain.

According to a third aspect, in the second aspect, the first aspect is the first aspect.
The demodulation carrier frequency correction control unit of the first embodiment, after the demodulation carrier frequency correction unit corrects the demodulation carrier frequency by the second predetermined number of times, the difference frequency value between the corrected demodulation carrier frequency and the intermediate frequency is the first continuous frequency. If even one of the predetermined number of times is within the second difference frequency region, it is determined that correction is impossible, and further correction is not performed.

As described above, in the third aspect, even after the demodulation carrier frequency is corrected for the second predetermined number of times, the difference frequency value again enters the second frequency region due to the frequency fluctuation of the clock. This prevents unnecessary correction of the demodulated carrier frequency.

According to a fourth aspect, in the first aspect, the difference frequency value between the corrected demodulation carrier frequency and the intermediate frequency is within the first difference frequency region for a first predetermined number of times. A second demodulation carrier frequency correction control unit for controlling the demodulation carrier frequency correction unit so as to generate corrected demodulation carrier frequency information indicating the corrected demodulation carrier frequency and not to perform further correction of the demodulation carrier frequency. Prepare.

As described above, according to the fourth aspect, if the difference frequency value when demodulated at the specific corrected demodulation carrier frequency is within the first difference frequency region for the first predetermined number of consecutive times, It is determined that there is no possibility that the differential frequency value falls in the second differential frequency region due to the clock frequency fluctuation, and the demodulation carrier frequency is set so that the differential frequency value is at an appropriate position in the first frequency region. By doing so, the synchronization time can be reduced.

In a fifth aspect based on the fourth aspect, the apparatus further comprises a non-volatile memory unit for storing the corrected demodulated carrier frequency information.

As described above, in the fifth aspect, by storing the appropriate demodulated carrier frequency information in the non-volatile memory, the appropriate demodulated carrier frequency information can be stored as needed without performing the processing according to the first to fifth aspects. A suitable demodulation carrier frequency can be determined.

In a sixth aspect based on the fifth aspect, at the time of startup, the first demodulated carrier frequency setting section sets the demodulated carrier frequency based on the corrected demodulated carrier frequency information stored in the nonvolatile memory section. decide.

As described above, the sixth invention has the same effects as the fifth invention.

According to a seventh aspect based on the first aspect, the target difference frequency value is set such that the difference frequency value Δf is equal to the first difference frequency region and zero for the broadcast receiving apparatus from the manufacturing process capability and the accuracy of the product. Is a difference frequency value estimated to be close to

As described above, in the seventh aspect, since the target difference frequency value is a value estimated based on the manufacturing process capability of the digital broadcast receiver, the target difference frequency value is the value of the boundary between the first and second frequency domains. The vicinity of the optimal difference frequency value can be roughly set. Furthermore, since the optimum difference frequency value is searched based on the roughly set difference frequency value,
A demodulated carrier frequency that determines the optimum difference frequency value effectively and reliably can be obtained.

An eighth invention relates to demodulation of a digital broadcast wave, wherein a change rate of a synchronization time with respect to a difference frequency value between an intermediate frequency value and a demodulated carrier frequency is a first value which is a first value.
And a second frequency region having a change rate larger than the first value.
A digital broadcast receiving method having a second differential frequency domain that is the value of the differential frequency value between the intermediate frequency value and the demodulated carrier frequency, a differential frequency value detecting step of generating differential frequency information, A demodulation carrier frequency correction step of correcting the demodulation carrier frequency so that the difference frequency value falls within the first difference frequency region based on the difference frequency information. The synchronization time is kept within a predetermined time.

As described above, in the eighth aspect, by setting the difference frequency value to the shorter side of the synchronization time,
Synchronization time can be kept within a predetermined time, and as a result,
The tuning operation and the search operation can be speeded up.

In a ninth aspect based on the eighth aspect, in the demodulation carrier frequency correcting step, the first demodulation carrier frequency is set to a predetermined frequency determined as an intermediate frequency according to the digital broadcast wave as a demodulation carrier signal. A first demodulation carrier frequency setting step to be set, and a difference frequency between a difference frequency value between the intermediate frequency and the first demodulation carrier frequency and a target difference frequency predetermined as a correction target value based on the difference frequency information. And a second demodulation carrier frequency setting step of setting a second demodulation carrier frequency using a value obtained by adding the difference frequency to the specified frequency as a demodulation carrier frequency.

As described above, according to the ninth aspect, even if the characteristics of the differential frequency value of the digital broadcast receiving apparatus are not accurately known, the frequency at the time of demodulation with the first demodulated carrier frequency which is the specified frequency is first used. By demodulating with a second demodulation carrier frequency generated by adding the difference from the difference value target difference frequency to the specified frequency, the difference frequency value is near the boundary between the first frequency region and the second frequency region. Can be set to

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing a receiving apparatus according to the present invention, reference will be made to FIGS. 5 and 6 to describe a difference frequency value generated according to individual variations of a digital broadcasting receiving apparatus according to the present invention. The basic concept of a method of setting a difference frequency value while avoiding jitter at the difference frequency will be described.

As described above, the set difference frequency value △
In order to avoid the jitter due to the relative fluctuation between f and the boundary difference frequency Fdb, in the example shown in FIG. 7, the boundary difference frequency Fd when the difference frequency value Δf is jittered to the positive side
From b, it is the minimum value (resolution) of the difference frequency value △ f △
What is necessary is just to set to the difference frequency value Di separated to the positive side by f (min). Note that the ideal difference frequency value Di is expressed by the following equation (1).
Can be represented by Di = Fdb (max) + Δf (min) (1) Fdb (max) is the maximum boundary difference frequency Fdb which is the boundary difference frequency Fdb when jittering to the positive side. At this time, the difference frequency value Δf never enters the difference frequency region represented by the straight line Ln on the negative side of the boundary difference frequency Fdb, and the QPSK synchronization time Ts is stabilized. This difference frequency value Di is defined as an ideal difference frequency value Di.

Referring to FIG. 6, a method of setting the ideal difference frequency value Di will be described. In FIG.
i indicates an ideal difference frequency value Di in the digital broadcast receiving apparatus. However, the ideal difference frequency value Di differs in each digital broadcast receiving apparatus, and varies with time and temperature change even in the same digital broadcast receiving apparatus. Hence,
The ideal difference frequency value Di cannot be accurately known in advance for each digital broadcast receiving apparatus. Therefore, instead of the ideal difference frequency value Di, the ideal difference frequency value Di of the digital broadcast receiving apparatus is estimated from the design specifications and the manufacturing process capability, and the estimated value is obtained as the estimated ideal difference frequency value Drp.

In the negative region shown on the left side of the boundary difference frequency Fdb in the figure, the QPSK synchronization time Ts rapidly increases according to the difference frequency value Δf.
It is not allowed to set the estimated ideal difference frequency value Drp such that the difference frequency value Δf is located in this region. In this sense, this negative region is defined as a non-permissible region NAR.

The ideal boundary difference frequency Fdbi differs depending on each digital broadcast receiving apparatus, and varies even with the same digital broadcast receiving apparatus due to factors such as aging. Since it is impossible to accurately estimate such a variation, the estimated ideal difference frequency value Drp is set to be larger than the ideal difference frequency value Di for safety. The dashed-dotted line Lrp indicates a set boundary frequency Fdbrp that is a difference frequency value Δf that is separated from the boundary difference frequency Fdb that fluctuates to the positive and negative sides by the estimated ideal difference frequency value Drp set in view of safety as described above. In this case, the difference between the estimated ideal difference frequency value Drp and the ideal difference frequency value Di is an excessive difference frequency value D that is unnecessarily shifted for safety.
ep.

Q corresponding to the excess difference frequency value Dep
The PSK synchronization time Ts (Dep) is the time that QPSK synchronization is wastefully used because the inherent performance of the digital broadcast receiving apparatus cannot be fully utilized.

In the present invention, in order to reduce such useless QPSK synchronization time, the estimated ideal difference frequency value Drp
Instead, a guaranteed ideal difference frequency value Dr is obtained. The guaranteed ideal difference frequency Dr value is closest to the boundary difference frequency Fdb based on the accuracy and quality of each component of the receiving device R and the manufacturing process capability of the receiving device R including the assembling accuracy and quality of the receiving device R. The difference frequency value Δf is set. Then, a demodulation carrier signal Sca having a frequency corresponding to the guaranteed ideal difference frequency value Dr is generated. The difference frequency value Δf corresponding to the guaranteed ideal difference frequency value Dr is called a corrected boundary frequency Fdbr. The demodulated carrier signal S
The QPSK modulation signal Sif is demodulated by ca, and it is determined whether the actual difference frequency value Δf at that time is as set by the guaranteed ideal difference frequency value Dr, and the appropriate demodulation carrier frequency of the demodulation carrier signal Sca is determined. Determine Fsca.

FIG. 5 illustrates a method for determining the demodulation carrier frequency Fsca according to the embodiment of the present invention.
Note that, in this figure, the portion between the boundary difference frequency Fdb and the set boundary frequency Fdbrp shown in FIGS. 7 and 6 is enlarged and displayed. Further, the ideal boundary difference frequency Fdbi and the corrected boundary frequency Fdbr are indicated by straight lines Li and Lr, respectively.

As described above, the vertical axis Ts and the respective difference frequency values Δf
Fluctuates relatively. For ease of understanding, the following description will be made on the assumption that the value of the difference frequency value Δf varies with respect to the vertical axis Ts.

Now, based on the frequency of the digital broadcast wave Srf 'assigned to the broadcast channel that the user wants to listen to, the specified frequency F of the QPSK modulated signal Sif specified in advance for the digital broadcast receiving apparatus.
modulates the QPSK modulation signal Sif with the demodulation carrier signal Sca having a th
Frequency average difference frequency △ F1s between the frequency F (sif) of the demodulation signal and the frequency F (sca) of the demodulation carrier signal Sca
First, t is determined. The average difference frequency △ F1st represents the current frequency error of the digital broadcast receiving device. Note that FIG. 3 illustrates a more severe condition in which the average difference frequency ΔF1st is in the non-permissible region NAR. However, it can be understood from the following description that the same applies to the case where it is on the positive side of the boundary difference frequency Fdb.

Therefore, the difference value (デ ィ ジ タ ル) from the target difference frequency value △ Ftar, which is estimated in advance to the digital broadcast receiving apparatus, assuming that the difference frequency value 以上 f is not less than zero and is close to the ideal boundary difference frequency Fdbi as much as possible. Ftar-average difference frequency {F1st) is obtained, and the QPSK modulated signal S
The carrier frequency F for demodulation is set such that the frequency difference value Δf with respect to the target difference frequency value ΔFtar becomes the target difference frequency value ΔFtar.
The carrier signal Sca is generated by correcting the sca. Then, the difference frequency value when the QPSK modulation signal Sif is again QPSK-demodulated with the corrected carrier signal Sca, △
If f is sufficiently stable (outside the non-permissible region NAR), the target difference frequency value ΔFta, which is the difference frequency value Δf at that time,
r is considered to be appropriate, and the demodulation carrier frequency Fsca at that time is set to the frequency Fs of the carrier signal Sca.
It is determined as ca.

On the other hand, if the target difference frequency value ΔFtar is not stable, the current demodulation carrier frequency Fsc
a is reduced by a predetermined frequency Fstep, that is, the demodulation carrier frequency Fsca is corrected so that the difference frequency value Δf is increased by fstep to generate a demodulation carrier signal Sca. Then, the QPSK modulation signal Sif is QPSK-demodulated with the demodulation carrier signal Sca,
It is determined whether the target difference frequency value ΔFtar1, which is the difference frequency value Δf obtained as a result, is stable.

As described above, the demodulation carrier frequency Fsc
a is incremented by fstep to generate a carrier signal Sca, and the QPSK modulated signal Sif is QPSK demodulated with the carrier signal Sca, and the differential frequency value at that time is
The demodulation carrier frequency FscaN (Fsca + N × Fstep) when the target difference frequency value と FtarN (N is a positive integer), which is f, is determined to be stable is set as the frequency Fsca of the carrier signal Sca.

As shown in FIG. 5, the carrier frequency for demodulation FscaN is higher than the ideal boundary difference frequency Fdbi. In this case, the excess difference frequency value Dep is equal to the correction frequency Fdbi.
It is smaller than step. That is, the excess frequency difference De and F
The steps have the relationship shown in the following equation (2). 0 ≦ De ≦ Fstep (2) As is clear from equation (2), by reducing the value of Fstep, the excess frequency difference De can be reduced without limit, and the target difference frequency value △ FtarN can be set without limit. It can be close to the ideal boundary difference frequency Fdbi. If the correction frequency Fstep is set to the minimum difference frequency value Δf (min), the ideal boundary difference frequency Fdbi itself can be detected. As described above, in the present invention, the ideal boundary difference frequency Fdbi that varies with the individual digital broadcast receiving apparatuses and varies with time can be easily and accurately detected even with the same digital broadcast receiving apparatus.

Hereinafter, the structure and operation of the digital broadcast receiving apparatus according to the embodiment of the present invention will be described in detail with reference to FIG. 1, FIG. 2, FIG. 3, and FIG. First, a digital broadcast receiving apparatus (hereinafter abbreviated as “receiving apparatus R”) will be described with reference to FIG. The receiving device R
It includes a tuner 1, a QPSK demodulator 3, a reception controller 13, and a memory 15. The tuner 1 receives the digital broadcast wave Srf ′ (not shown) transmitted from a predetermined broadcast station by the antenna 17 and outputs the digital broadcast wave Srf to the reception channel selection signal output from the reception control unit 13. It downconverts based on Sf and outputs QPSK modulated Sif which is an intermediate frequency signal. QPS
The K demodulation unit 3 performs QPSK demodulation on the QPSK modulation signal Sif input from the tuner 1 to generate a demodulation reception signal Srd, and outputs the demodulation reception signal Srd to a decoder unit (not shown). QPSK
The demodulation unit 3 further generates various control signals based on the QPSK modulation signal Sif and the demodulation reception signal Srd and outputs the control signals to the reception control unit 13.

The QPSK demodulation unit 3 includes a mixer 5, a demodulation carrier generator 7, a difference frequency detector 9, a QPSK lock detector 11, and a digital PLL 12. The digital PLL 12 outputs Q based on the demodulated received signal Srd.
The frequency difference between the QPSK modulation signal Sif used for PSK modulation and the demodulation carrier signal is detected. Digital P
LL12 further outputs the demodulated carrier signal S output from demodulated carrier generator 7 at the detected frequency difference.
The frequency of ca is corrected, and the corrected demodulation carrier signal Sc is corrected.
a ′ is generated. The mixer 5 is connected to the tuner 1 and the digital PLL 12, and receives the input QP
SK modulation signal Sif and correction demodulation carrier signal Sca '
Are mixed to generate a demodulated received signal Srd.

The digital PLL 12 includes a frequency corrector 6, an adder 8, and an NCO 10. The frequency corrector 6 has a loop filter, and converts the demodulated received signal Srd input from the mixer 5 into a QPSK modulated signal Sid.
frequency f (Sif) of f and carrier signal Sc for correction demodulation
The difference frequency value fgap of the frequency F (Sca ′) of a ′ =
F (Sif) -F (Sca ')) is detected. The digital PLL 12 further generates a frequency correction signal Sgap representing a frequency value such that the difference value becomes zero,
Output to the adder 8.

The adder 8 generates a frequency correction signal Sgap,
The demodulation carrier signal Sca input from the demodulation carrier generator 7 is added, and the frequency Fsc of the corrected demodulation carrier signal Sca ′ actually used in the mixer 5 for demodulation is added.
generates frequency data Dfsca 'indicating a'
Enter 10 This frequency Fsca 'is called a carrier frequency for correction demodulation.

The NCO 10 generates the frequency data Dfsca '
, A corrected demodulation carrier signal Sca ′ having the corrected demodulation carrier frequency Fsca ′ is generated and output to the mixer 5. Thus, the corrected demodulation carrier signal Sca ′ output from the NCO 10 is actually used in the mixer 5 for QPSK demodulation.

The QPSK lock detector 11 detects the QPSK lock on the demodulated reception signal Srd output from the mixer 5 and generates a lock detection signal Slo having a binary value which becomes high when the lock is detected. Output to the reception control unit 13.

The difference frequency detector 9 calculates the frequency F (Sif) of the QPSK modulated signal Sif input from the tuner 1.
And a difference frequency value Δf (Δf = F (Sif) −F (Sca)) which is a difference value between the frequency F (Sca) of the demodulation carrier signal Sca input from the demodulation carrier generator 7.
Is detected. The difference frequency detector 9 further generates difference frequency information I △ f representing the detected difference frequency value △ f, and outputs it to the reception control unit 13.

Based on lock detection signal Slo and difference frequency information I △ f input from QPSK demodulation section 3, reception control section 13 controls the frequency of a carrier signal to be used for QPSK demodulation of QPSK modulated signal Sif in mixer 5. Is determined as the demodulation carrier frequency Fsca. Then, the reception control unit 13 generates demodulation carrier frequency information Ica defining the determined demodulation carrier frequency Fsca, and outputs it to the QPSK demodulation unit 3.

The demodulation carrier generator 7 of the QPSK demodulation unit 3 generates a demodulation carrier signal Sca that is mixed by the mixer 5 for QPSK demodulation of the QPSK modulation signal Sif based on the demodulation carrier frequency information Ica. . The demodulation carrier signal Sca is generated so as to have a frequency defined by the demodulation carrier frequency information Ica.

Next, the operation of the receiving apparatus R according to the present invention will be described with reference to the flowchart shown in FIG. After the power is turned on to the receiving apparatus R, first, the user instructs the receiving control unit 13 on a broadcasting station to listen to. Then, in step S1, the reception control unit 13 outputs to the tuner 1 a reception channel selection signal Sf corresponding to the frequency of the digital broadcast wave Srf 'assigned to the selected broadcast channel in response to a user's instruction. The tuner 1 down-converts the digital broadcast Srf to an intermediate frequency based on the reception channel selection signal Sf to generate a QPSK modulated signal Sif. Then, the process proceeds to the next step S3.

In step S3, the reception control unit 13
Is the QPSK modulation signal Sca, which is previously defined as an intermediate frequency for the receiving apparatus R, as the frequency of the demodulation carrier signal Sca with respect to the QPSK modulation signal Sif.
It generates demodulation carrier frequency information Ica indicating the specified frequency Fth of if, and outputs it to QPSK demodulation section 3.

The demodulation carrier generator 7 of the QPSK demodulation section 3 generates a demodulation carrier signal Sca having a specified frequency Fth based on the demodulation carrier frequency information Ica, and outputs the signal to the digital PLL 12. In the digital PLL 12, the frequency correction signal Sgap output from the frequency corrector 6 is initially zero, so that the demodulation carrier signal Sca input from the carrier generator 7 is corrected as the corrected demodulation carrier signal Sca '. Output to mixer 5. The mixer 5 uses the corrected demodulation carrier signal Sca ′ to generate a QPSK signal output from the tuner 1.
The modulated signal Sif is demodulated and a demodulated received signal Srd is output. Then, the process proceeds to the next step S5.

In step S5, the reception control unit 13
Is a lock detection signal S input from the QPSK demodulation unit 3.
Based on lo, it is determined whether or not the QPSK lock has been detected. When the lock is detected, that is, when the broadcast of the channel designated by the user is received, it is determined as Yes, and the process proceeds to the next step S7. On the other hand, if the lock is not detected, that is, if the channel designated by the user has not been received, it is determined to be No and step S
Step 5 is repeated.

That is, the frequency of the actual QPSK modulated signal Sif and the frequency of the demodulation carrier signal Sca are not equal to each other. Therefore, both signals Sif and Sca ′ detected by the frequency corrector 6 of the digital PLL 12 based on the demodulated received signal Srd (first time, Fsca = Fth)
Based on the frequency correction signal Sgap generated so that the frequency difference value △ f ′ (that is, fgap) of the
Demodulated carrier signal S input from carrier generator 7
frequency Fsca (Fst) of the adder 8 and the NC
Corrected demodulation carrier signal Sc corrected by O10
a ′ is input to the mixer 5. By repeating this process (Step S5: No), QPSK
The frequency difference Δf ′ (that is, fgap) existing between the modulation signal Sif and the carrier signal for correction demodulation Sca ′ gradually decreases, and the QPSK lock is finally established (Step S5: Yes).

As described above, in this step, the QPS
When the K synchronization is confirmed, a lock detection signal Slo is output. Then, the process proceeds to the next step S7. In addition,
When the QPSK lock is detected, the presence of the broadcast wave or its occupied band is always confirmed on the selected channel being received. In this case, Δf is F (Sca ′)
= F (Sca) + F (S △ f)) = F (Sif).

The fact that the QPSK lock is detected, that is, that the synchronization can be confirmed by the QPSK lock detector 11 means that the broadcast channel currently being received is within the occupied band in the QPSK transmission. In order to confirm that the broadcast channel is actually broadcasting the content, it is desirable to confirm the QPSK frame synchronization with the demodulated received signal Srd. However,
As described above, in this example, since the frequency of a known broadcast station that is actually broadcasting the content is specified, the QP
It is sufficient to confirm only the QPSK lock detection by the SK lock detector 11.

When the present invention is applied to the reception of a digital broadcast wave Srf 'from an unknown broadcast station within the QPSK broadcast band, as shown in FIG.
The frame synchronization detector 19 that detects frame synchronization based on the demodulated reception signal Srd output from the controller and generates a frame synchronization detection signal SF and outputs the frame synchronization detection signal SF to the reception control unit 13 includes:
What is necessary is just to newly provide in the receiver R. In this case, QPSK
In addition to the QPSK lock detection by the lock detector 11,
This step may be changed so that the determination is Yes only when synchronization is detected by the frame synchronization detector 19.

In step S7, the difference frequency detector 9 outputs the QPSK demodulated signal Sif (the frequency is the same as the corrected demodulated carrier signal Sca ') and the demodulated carrier signal Sc.
A difference value (difference frequency value Δf) of each frequency of a is measured, and difference frequency information IΔf is output to the reception control unit 13. Then, the process proceeds to the next step S9.

In step S9, the reception control unit 13
Determines whether the measurement of the difference frequency value Δf in step S7 has been performed a predetermined number of times L (L is a positive integer) based on the difference frequency information IΔf. If No, the process returns to step S7, and the difference frequency value Δf is measured again. Then, in step S7, after the difference frequency value Δf has been measured a predetermined number of times L, it is determined to be Yes in this step, and the process proceeds to the next step S11.

In step S11, the reception control unit 13
Calculates an average of L difference frequency values Δf based on the difference frequency information IΔf input L times a predetermined number of times, and calculates an average difference frequency ΔF1st. As described above, in steps S7, S9, and S11, the average of the difference frequency value Δf is obtained, thereby suppressing the influence of the exceptional variation of the difference frequency value Δf due to the variation in the quality of the receiver R.
We are aiming for stable processing. Then, the process proceeds to the next step S13.

In step S13, the reception control unit 13
Is the target difference frequency value △ Ftar and the average difference frequency △ F
The difference from 1st is obtained. Then, the process proceeds to the next step S15.

In step S15, the reception control unit 13
Sets the demodulation carrier frequency Fsca of the demodulation carrier signal Sca by adding the difference value obtained in step S13 to the specified frequency Fth. The reception control unit 13 further includes:
The demodulation carrier frequency information Ica that defines the set demodulation carrier frequency Fsca is generated and output to the demodulation carrier generator 7. Then, the process proceeds to the next step S16.

In step S16, the demodulation carrier generator 7 generates a demodulation carrier signal Sca based on the demodulation carrier frequency information Ica input from the reception control unit 13. By demodulating the QPSK modulation signal Sif with the demodulation carrier signal Sca generated in this way, the difference frequency value Δf becomes the target difference frequency value ΔFtar. Then, the process proceeds to the next step S17.

In step S17, it is determined whether or not QPSK lock has been detected based on the lock detection signal Slo input from the QPSK demodulation unit 3, as in the process in step S5. When the lock is detected, that is, when the broadcast of the channel specified by the user is received, it is determined as Yes, and the process proceeds to the next step S19.
Proceed to. On the other hand, if the lock is not detected, that is, if the channel designated by the user has not been received, No is determined and the process of step S17 is repeated.

In step S19, similarly to the process in step S7, the differential frequency detector 9 detects the demodulated received signal Srd and the demodulated carrier signal Sca.
The difference value (difference frequency value Δf) of each frequency of (correction demodulation carrier signal Sca ′) is measured, and difference frequency information IΔf is output to reception control unit 13. Then, the process proceeds to the next step S21.

In step S21, the reception control unit 13
Is calculated based on the difference frequency information I △ f in step S19.
The difference frequency value Δf measured only once in the non-permissible region N
It is determined whether or not it is within the AR. If the difference frequency value Δf is outside the non-permissible region NAR, that is, within the permissible range, it is determined as No, and the process proceeds to the next step S23.

In step S23, the difference frequency value Δf measured in step S19 is determined by the predetermined number M
It is determined whether or not it is determined in step S21 that M is within the allowable range continuously (M is a positive integer). In the case of No, the process returns to step S19, and in this step, Y
Until determined to be es, the processing of step S19 and step S21 is repeated. On the other hand, in this step, Ye
s, that is, the difference frequency value measured in step S19 △
If f is within the allowable range continuously for a predetermined number of times M, the frequency Fsc of the demodulation carrier signal Sca at this time is
a is considered appropriate for stably demodulating the QPSK modulated signal Sif stably, and no further measurement of the difference frequency value Δf is performed. Then, the process proceeds to the next step S
Go to 25.

In step S25, the demodulation carrier frequency information Ica corresponding to the demodulation carrier frequency Fsca for which the difference frequency value Δf is considered to be stable in the previous step S23 is stored in the memory 15, and the process is terminated. I do. Note that the memory 15 is desirably nonvolatile.

On the other hand, if Yes in step S21, that is, if it is determined that the difference frequency value Δf measured in step S19 is within the non-permissible region NAR, the process proceeds to step S27.

In step S27, it is determined whether or not the demodulation carrier frequency Fsca has been corrected by a predetermined number N (N is a positive integer) in step S29 described later. In the case of Yes, in this receiver R, Q
In order to stably demodulate the PSK modulation signal Sif, the demodulation carrier frequency Fsc of the demodulation carrier signal Sca is used.
It is determined that it is impossible to correct a, error processing is performed, and the processing ends. If the determination is No in step S27, the process proceeds to step S29.

In step S29, after the current demodulation carrier frequency Fsca is increased by a predetermined frequency Fstep, the process returns to step S17. Thereafter, the processes in steps S17 to S29 described above are repeated.
This is because the difference frequency value Δf obtained by the current correction is out of the allowable range (S21), but there is still a possibility that the difference frequency value Δf can be corrected. The correction of the frequency Fsca is continued for each correction frequency Fstep. In this sense, the frequency Fstep is defined as a correction frequency for the demodulation carrier frequency Fsca. Also, the correction frequency Fst
By setting the value of ep appropriately, the excessive difference frequency value De shown in FIG. 5 can be reduced.

The method of setting the optimum guaranteed ideal difference frequency value Dr for each receiver R has been described with reference to FIGS. 1, 2, 4, 5, and 6. However, when the product quality of the receiving device R is stable based on the design quality and the manufacturing process capability, in order to obtain the demodulation carrier frequency information Ica indicating the proper demodulation carrier frequency Fsca of the demodulation carrier signal Sca. Without repeating the processing shown in the above-mentioned flowchart, the demodulation carrier frequency information Ica stored in the memory 15 is read out at the time of activation of the receiver R, and the demodulation carrier signal Sca is read out.
And QPSK demodulation may be started immediately.

Referring to FIG. 3, a method of performing QPSK demodulation using demodulation carrier signal Sca generated based on demodulation carrier frequency information Ica stored in memory 15 will be described. Note that the configuration of the receiving device R is the same as that shown in FIGS. When the power is turned on to the receiving device R, in step S100, the memory 15
From the reception control unit 13
Is read in. The reception control unit 13 outputs the read demodulation carrier frequency information Ica to the QPSK demodulation unit 3. Then, the process proceeds to the next step S103.

In step S103, the demodulation carrier generator 7 of the QPSK demodulation unit 3 generates a demodulation carrier signal Sca having the demodulation carrier frequency Fsca specified by the input demodulation carrier frequency information Ica. Output to the digital PLL 12. Then, the process proceeds to the next step S105.

In step S105, the demodulated carrier signal Sca is output to the mixer 5 without frequency correction by the digital PLL 12, and immediately subjected to QPSK demodulation of the QPSK modulated signal Sif. This is because the demodulation carrier signal Sca generated in step S103 is different from the above-described steps S17 to S17.
This is because, at 25, establishment of the QPSK lock and stable demodulation of the QPSK modulated signal Sif have already been confirmed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the structure of a digital broadcast receiving apparatus according to the present invention.

FIG. 2 is a flowchart showing an operation of the digital broadcast receiving apparatus shown in FIG.

FIG. 3 is a flowchart showing a further operation of the digital broadcast receiving apparatus shown in FIG.

FIG. 4 is a block diagram showing a modification of the digital broadcast receiving apparatus shown in FIG.

FIG. 5 is an explanatory diagram of a basic concept of a method for setting a difference frequency value according to the present invention.

FIG. 6 is an explanatory diagram of a basic concept of a method of setting a difference frequency value according to the present invention.

FIG. 7 is a correlation diagram showing a general relationship between a difference between an intermediate frequency and a carrier frequency for demodulation, and a QPSK synchronization time.

[Explanation of symbols]

 R receiver 1 tuner 3 QPSK demodulation unit 5 mixer 7 demodulation carrier generator 9 difference detector 11 synchronization detector 13 reception control unit 15 memory 17 antenna 19 frame synchronization detector Sf reception channel selection signal Srf broadcast wave Sif QPSK modulation signal Srd demodulation reception signal Slo lock detection signal I △ f difference frequency information Ica demodulation carrier frequency information

Claims (9)

[Claims] In the demodulation of a digital broadcast wave, a change rate of a synchronization time with respect to a difference frequency value between an intermediate frequency and a demodulation carrier frequency is a first difference frequency region that is a first value, and the change rate is a first difference frequency region. A digital broadcast receiving apparatus having a second difference frequency region that is a second value larger than a first value, wherein a difference frequency value between the intermediate frequency value and the demodulated carrier frequency is measured to obtain difference frequency information. And a demodulation carrier frequency correction unit that corrects the demodulation carrier frequency based on the difference frequency information so that the difference frequency value is within the first difference frequency region. The demodulation carrier frequency correction means, the demodulation carrier frequency is defined as a predetermined frequency as an intermediate frequency according to the digital broadcast wave,
First demodulation carrier frequency setting means for setting a first demodulation carrier frequency; a difference frequency value between the intermediate frequency and the first demodulation carrier frequency based on the difference frequency information; Difference detection means for obtaining a difference frequency from a predetermined target difference frequency; and a second demodulation carrier for setting a second demodulation carrier frequency, wherein a value obtained by adding the difference frequency to the specified frequency is used as the demodulation carrier frequency. A digital broadcast receiving apparatus, comprising: frequency setting means, wherein a synchronization time during demodulation of the intermediate frequency with the corrected demodulated carrier frequency is suppressed within a predetermined time. 2. When the difference frequency value between the corrected demodulated carrier frequency and the intermediate frequency is within the second difference frequency region even once within a first predetermined number of consecutive times, 2. The apparatus according to claim 1, further comprising: first demodulation carrier frequency correction control means for controlling said demodulation carrier frequency correction means so that said corrected demodulation carrier frequency is changed by a predetermined frequency and further corrected. Digital broadcast receiver as described. 3. The first demodulation carrier frequency correction control means, after the demodulation carrier frequency correction means corrects the demodulation carrier frequency for a second predetermined number of times, further comprising the corrected demodulation carrier frequency and the intermediate frequency. When the difference frequency value is within the second difference frequency region even once in the first predetermined number of times, it is determined that correction is impossible, and further correction is not performed. The digital broadcast receiving apparatus according to claim 2. 4. When the difference frequency value between the corrected demodulation carrier frequency and the intermediate frequency is within the first difference frequency region for a first predetermined number of consecutive times, the corrected demodulation carrier frequency 2. The apparatus according to claim 1, further comprising a second demodulation carrier frequency correction control unit that controls the demodulation carrier frequency correction unit so as to generate corrected demodulation carrier frequency information representing a frequency and not perform further correction of the demodulation carrier frequency. Digital broadcast receiver as described. 5. The digital broadcast receiving apparatus according to claim 4, further comprising a nonvolatile memory for storing the corrected demodulated carrier frequency information. 6. The apparatus according to claim 5, wherein at the time of startup, said first demodulated carrier frequency setting means determines said demodulated carrier frequency based on said corrected demodulated carrier frequency information stored in said nonvolatile memory means. Digital broadcast receiver according to the above. 7. The target difference frequency value is a difference from a broadcast receiving apparatus in which a difference frequency value Δf is estimated to be in the first difference frequency region and close to zero from a manufacturing process capability and product accuracy. The digital broadcast receiving device according to claim 1, wherein the digital broadcast receiving device is a frequency value. 8. In the demodulation of a digital broadcast wave, a change rate of a synchronization time with respect to a difference frequency value between an intermediate frequency value and a demodulated carrier frequency is a first difference frequency region that is a first value, and the change rate is a first difference frequency region. A digital broadcast receiving method having a second difference frequency region that is a second value larger than the first value, wherein a difference frequency value between the intermediate frequency value and the demodulated carrier frequency is measured. A difference frequency value detection step of generating information; and a demodulation carrier frequency correction step of correcting the demodulation carrier frequency so that the difference frequency value is within the first difference frequency region based on the difference frequency information. Digital broadcast reception, characterized in that a synchronization time during demodulation of the intermediate frequency with the corrected demodulated carrier frequency is suppressed within a predetermined time. Method. 9. The demodulation carrier frequency correcting step includes: setting a first demodulation carrier frequency to set a predetermined frequency, which is predetermined as an intermediate frequency according to the digital broadcast wave, as the demodulation carrier signal. A carrier frequency setting step, based on the difference frequency information, determining a difference frequency between a difference frequency value between the intermediate frequency and the first demodulation carrier frequency and a target difference frequency predetermined as a correction target value. The digital signal according to claim 8, further comprising: a detection step; and a second demodulation carrier frequency setting step of setting a second demodulation carrier frequency, wherein a value obtained by adding the difference frequency to the specified frequency is used as the demodulation carrier frequency. Broadcast reception method.