JP2000349848A - Digital broadcast receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a digital broadcast receiver that keeps a synchronization time within a prescribed time so as to attain high-speed channel selection and searching by controlling a carrier frequency to be demodulated in a way that a difference between a frequency of an intermediate frequency signal and the received carrier frequency to be demodulated by a demodulator is a prescribed value. SOLUTION: Difference frequency detectors (9, 13) in the digital broadcast receiver (R) measure a difference destination (ΔF1st) between an intermediate frequency (F(sif)) and a carrier frequency (F(Sca)) to be demodulated. Reception control sections (13, 7) corrects the carrier frequency (F(Sca)) 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 demodulation carrier frequency is small. Thus, the synchronization time (Ts) can be kept within a prescribed time by demodulating the intermediate frequency (F(sif)) with the corrected demodulation carrier frequency (F(Sca)).

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. 8 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

[0003] As shown in the figure, the rate of change of the QPSK synchronization time Ts in the QPSK demodulator is extremely different from a certain point of the difference between the frequency of the input intermediate frequency signal and the frequency of the demodulation carrier signal. . In this example, when the difference frequency value Δf is the minimum value (F (Sif) = F (Sca)), the QPSK synchronization time Ts also becomes the minimum value (zero).
The difference frequency value Δf is positive (F (Sif)> F (Sca))
In the region of, 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
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. in this way,
The difference frequency value Δf, which is a 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 a boundary difference frequency Fdb. Note that the boundary difference frequency Fdb is normally 0 as shown in FIG.

[0005]

SUMMARY OF THE INVENTION A QPSK modulated signal Si
Since there is a relationship as shown in FIG. 8 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 area, as shown by the straight line Lp, it takes more time than when it is located at the boundary difference frequency Fdb, but it is more allowable than when it is located in the negative side area. Synchronization is achieved in the shortest possible time. In addition,
Both the straight lines Ln and Lp represent the characteristics of the frequency difference and 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 Δf is set on or near the boundary difference frequency Fdb in order to reduce the QPSK synchronization time Ts, the difference frequency value Δf is quickly jittered on both the positive and negative sides of the boundary difference frequency Fdb as a boundary. So Q
The PSK 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. 8, 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 represented 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. Thus, a demodulation carrier frequency correction unit for correcting the demodulation carrier frequency is provided, and the synchronization time at the time of demodulation of the intermediate frequency by the corrected demodulation carrier frequency is suppressed within a predetermined time.

As described above, in the first invention, the synchronization time can be suppressed within a predetermined time by setting the difference frequency value in the difference frequency region having a short synchronization time. The operation and the search operation can be sped up.

[0013] In a second aspect based on the first aspect, the demodulation carrier frequency correction section sets a demodulation carrier frequency using a predetermined reference frequency as a demodulation carrier frequency according to the digital broadcast wave. including.

As described above, in the second aspect of the present invention, by demodulating the signal at the demodulation carrier frequency which is the reference frequency, the difference frequency value is near the boundary between the first frequency domain and the second frequency domain. Can be set to

According to a third aspect of the present invention, in any one of the first and second aspects, the difference frequency value between the corrected demodulated carrier frequency and the intermediate frequency is at least once in the first predetermined number of consecutive times. 2 is within the difference frequency domain,
The apparatus further includes 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.

As described above, in the third aspect, 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 fourth aspect, in the third aspect, the first aspect is provided.
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. At least once within the predetermined number of times, if it is within the second differential frequency domain,
It is characterized in that correction is determined to be impossible and no further correction is performed.

As described above, in the fourth invention, even after the demodulation carrier frequency correction in the third invention is performed the second predetermined number of times, the difference frequency value is again increased by the second frequency due to the clock frequency fluctuation. When entering the region, it is prevented that the demodulated carrier frequency is corrected needlessly.

According to a fifth aspect of the present invention, in any one of the first and second aspects, the difference frequency value between the corrected demodulation carrier frequency and the intermediate frequency is a first difference frequency of the first predetermined number of times. A second demodulation carrier that generates a corrected demodulation carrier frequency information representing the corrected demodulation carrier frequency when the frequency is within the region, and controls a demodulation carrier frequency correction unit so that the demodulation carrier frequency is not further corrected. The apparatus further includes a frequency correction control unit.

As described above, in the fifth aspect, if the differential frequency value when demodulated at the specific corrected demodulated carrier frequency is within the first differential 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.

A sixth aspect based on the fifth aspect, further includes a nonvolatile memory unit for storing the corrected demodulated carrier frequency information.

As described above, in the sixth 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 seventh aspect based on the sixth 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 seventh aspect has the same effect as the sixth aspect.

According to an eighth aspect based on the second aspect, the reference frequency is a difference within a first difference frequency range and a minimum synchronization time with respect to the broadcast receiving apparatus in view of manufacturing process capability and product accuracy. This is the frequency value estimated to be closest to the frequency value.

As described above, according to the eighth aspect, the reference frequency estimated to have a difference frequency value that can minimize the synchronization time in the first area based on the manufacturing process capability of the digital broadcast receiver is Since the optimum differential frequency value is searched based on the demodulated carrier frequency, the demodulated carrier frequency that determines the optimum differential frequency value can be effectively and reliably determined.

A ninth 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 ninth 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 tenth aspect based on the ninth aspect, the demodulation carrier frequency correction step is a demodulation carrier frequency setting step of setting a demodulation carrier frequency using a predetermined reference frequency as a demodulation carrier signal according to the digital broadcast wave. including.

As described above, in the tenth aspect,
By performing demodulation at the demodulation carrier frequency that is the reference frequency, the difference frequency value can be set so as to be near the boundary between the first frequency domain and the second frequency domain.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing a digital broadcast receiving apparatus according to the present invention, with reference to FIG. 7, the jitter of a boundary difference frequency generated according to individual variations of the digital broadcast receiving apparatus according to the present invention will be described. The basic concept of the method of setting the difference frequency value while avoiding it will be described.

As described above, the set difference frequency value △
In order to avoid the jitter due to the relative variation between f and the boundary difference frequency Fdb, in the example shown in FIG.
From db, the difference frequency value Di may be set to the difference value Di separated to the positive side by Δf (min) which is the minimum value (resolution) of the difference frequency value Δf. Note that the ideal difference frequency value Di can be expressed by the following equation (1). 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. It is defined as a difference frequency value Di.

With reference to FIG. 7, 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 varies depending on the individual 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 excessive 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 correction frequency Fsca of the proper demodulation carrier signal Sca is determined. decide.

In the following, FIG. 1, FIG. 2, FIG. 3, FIG.
Referring to FIG. 6 and FIG. 6, the structure and operation of the digital broadcast receiving apparatus according to the embodiment of the present invention will be described in detail. First, a digital broadcast receiving apparatus (hereinafter abbreviated as “receiving apparatus R”) will be described with reference to FIG.
The receiving device R includes a tuner 1, a QPSK demodulation unit 3, a reception control unit 13, and a memory 15. The tuner 1 receives a digital broadcast wave Srf ′ transmitted from a predetermined broadcast station.
(Not shown) is received by the antenna 17, the digital broadcast wave Srf obtained is down-converted based on the reception channel selection signal Sf output from the reception control unit 13, and the QPSK modulation Sif as an intermediate frequency signal is converted. Output. The QPSK demodulation unit 3 performs QPSK demodulation on the QPSK modulation signal Sif input from the tuner 1, generates a demodulated reception signal Srd, and outputs it to a decoder unit (not shown). The QPSK demodulation unit 3 further generates various control signals based on the QPSK modulation signal Sif and the demodulation reception signal Srd, and outputs them 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 0, and outputs the frequency correction signal Sgap 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 differential 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 S4.

In step S4, the reception control unit 13
In the digital broadcast receiving apparatus, the QPSK synchronization time Ts when the difference frequency value Δf is most negatively jittered can be set to zero as the frequency of the demodulation carrier signal Sca with respect to the above-described QPSK modulated signal Sif. It generates demodulation carrier frequency information Ica indicating the reference frequency Fst considered to be and outputs it to the QPSK demodulation unit 3. Note that the reference frequency Fst is a value corresponding to the above-described guaranteed ideal difference frequency value Dr.

The demodulation carrier generator 7 of the QPSK demodulation unit 3 generates a demodulation carrier signal Sca having the reference frequency Fst based on the demodulation carrier frequency information Ica, and outputs it 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 S17.

In step S17, 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 specified by the user is received, it is determined as Yes, and the process proceeds to the next step S19. on the other hand,
If no lock is detected, that is, if the channel designated by the user has not been received, it is determined as No, and the process of step S17 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 = Fst)
, The frequency Fsca (Fst) of the demodulation carrier signal Sca input from the carrier generator 7 is calculated based on the frequency correction signal Sgap generated such that the frequency difference value fgap (△ f ′) becomes zero. The corrected demodulation carrier signal Sca ′ corrected by the NCO 10 is input to the mixer 5. This process (step S17:
By repeating (No), the frequency difference fgap (△ f ′) that initially exists between the QPSK modulated signal Sif and the corrected demodulation carrier signal Sca ′ becomes small, and the QPSK lock is finally established (step S17: Ye
s).

In step S17, Q
When the PSK lock is detected, the presence of the broadcast wave or its occupied band is always confirmed on the selected channel being received. Further, Δf is given by F (Sca ′) = F
Ｓf such that (Sca) + F (S △ f)) = F (Sif).

Although not shown, the QPSK lock detector 11 may be replaced with a frame synchronization detector 19. In this case, it goes without saying that in this step, the change is determined to be Yes only when the frame synchronization is detected by the frame synchronization detector 19. Then, the process proceeds to the next step S19.

QPSK lock is detected, that is, QP
The fact that synchronization can be confirmed by the SK lock detector 11 means that the currently received broadcast channel is within the occupied band in 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 QPS
It is sufficient to confirm only the QPSK lock detection by the K 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 S19, the difference frequency detector 9 measures the difference between the QPSK demodulated signal Sif (the frequency is the same as the corrected demodulation carrier signal Sca ') and the demodulation carrier signal Sca, and determines the difference frequency. Find the value Δf. The difference frequency detector 9 outputs difference frequency information I △ f indicating the obtained difference frequency value Δf to the reception control unit 13. Then, the process proceeds to the next step S21.

In step S21, the reception control unit 13
Is based on the difference frequency information I △ f, the difference frequency value △ f measured in step S19 is
It is determined whether it is within. If the difference frequency value Δf is outside the non-permissible region NAR, that is, within the permissible range,
Is determined, and the process proceeds to the next step S23.

In step S23, the difference frequency value Δf measured in step S19 is set to a predetermined number M
It is determined whether or not it is determined in step S21 that the values are within the allowable range continuously. In the case of No, the process returns to Step S19, and the process of Step S19 and Step S21 is repeated until it is determined to be Yes in this step. On the other hand, Yes in this step, that is, the difference frequency value Δf measured in step S19 is a predetermined number M
(M is a positive integer) continuously within the allowable range, the frequency of the demodulation carrier signal Sca at this time is Fs
ca 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 S25.

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 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 a possibility that the correction can still be performed. Of the correction frequency Fstep is continued. In this sense, the frequency Fstep is defined as a correction frequency for the demodulation carrier frequency Fsca. Also, the correction frequency Fst
By appropriately setting the value of ep, the excessive difference frequency value Dep shown in FIG. 7 can be reduced.

Next, with reference to FIG. 5 and FIG. 6, a method for determining the demodulation carrier frequency Fsca in the receiving apparatus R according to the embodiment described with reference to the flowchart shown in FIG. I do. In FIGS. 5 and 6, the set boundary frequency Fdbr is calculated from the boundary difference frequency Fdb shown in FIGS.
The area between p 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.

Reference frequency Fs set in step S4
t, the difference frequency value Δf becomes the ideal difference frequency value Di.
It is set so as to have a larger guaranteed ideal difference frequency value Dr. Therefore, the set boundary frequency Fdbr determined by the reference frequency Fst is set to a value larger than the ideal boundary difference frequency Fdbi, as shown in FIG. However, when the variation of the receiving device R is larger than the guaranteed ideal difference frequency value Dr determined from the design specification and the manufacturing process capability, as shown in FIG. 6, the boundary difference frequency Fdb is smaller than the ideal boundary difference frequency Fdbi. Can be a value. The operation of the receiving device R in each of the two cases will be described below.

In the case shown in FIG. 5, the set boundary frequency Fd
Since br> the ideal boundary difference frequency Fdbi, it is determined as No in step S21, and Yes in step S23.
Is determined, the demodulation carrier frequency information Ica corresponding to the reference frequency Fst is stored in the memory 15 in step S25. On the other hand, in the case shown in FIG. 6, since the set boundary frequency Fdbr <the ideal boundary difference frequency Fdbi,
In step S21, Yes is determined, and in step S27, No is determined. In step S29, the demodulation carrier frequency Fsca is corrected to generate the set boundary frequency Fdbr1. Then, based on the set boundary frequency Fdbr1, steps S17, S19, S21, and S2
The process at 7 is repeated a maximum of a predetermined number N. The set boundary frequency Fdbr is corrected and the set boundary frequency Fdb
By the time rN is generated, the set boundary frequency Fdbrn
When (n is an integer equal to or less than N) exceeds the ideal boundary difference frequency Fdbi, No is determined in step S21, and the process ends through steps S23 and S25. By performing the above-mentioned processing periodically or as needed, the demodulation carrier frequency Fsca is always appropriate even if the characteristic of the differential frequency in the same receiver R fluctuates with the passage of time or a temperature change. Value can be kept.

The method of setting the optimal guaranteed ideal difference frequency value Dr for each receiver R as needed has been described with reference to FIGS. 1, 2, 4, 5, 6, and 7. However, when the product quality of the receiver R is stable based on the design quality and the manufacturing process capability, the demodulation carrier frequency Fsca of the proper demodulation carrier signal Sca is obtained.
In order to obtain the demodulation carrier frequency information Ica indicating the above, the demodulation carrier frequency information Ica stored in the memory 15 is read out at the time of starting the receiving apparatus R without repeating the processing shown in the above-described flowchart, and the demodulation carrier signal Sca 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. The configuration of the receiving apparatus 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 inputted 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 the operation shown in the flowchart shown in FIG. 2;

6 is an explanatory diagram of the operation shown in the flowchart shown in FIG.

FIG. 7 is an explanatory diagram of a basic concept of a method for setting a difference frequency value according to the present invention.

FIG. 8 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 (10)

[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. A digital broadcast receiving apparatus comprising: suppressing a synchronization time during demodulation of the intermediate frequency with the corrected demodulated carrier frequency within a predetermined time. 2. The demodulation carrier frequency correction means according to claim 1, wherein said demodulation carrier frequency correction means includes a demodulation carrier frequency setting means for setting a demodulation carrier frequency using a predetermined reference frequency as said demodulation carrier frequency according to said digital broadcast wave. Digital broadcast receiver. 3. 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 successive times, 2. The apparatus according to claim 1, further comprising: first demodulation carrier frequency correction control means for controlling the demodulation carrier frequency correction means so that the corrected demodulation carrier frequency is changed by a predetermined frequency and further corrected. 3. The digital broadcast receiver according to any one of 2. 4. The first demodulation carrier frequency correction control means, after the demodulation carrier frequency is corrected by the demodulation carrier frequency correction means for a second predetermined number of times, 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 3. 5. 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 times, the corrected demodulation carrier frequency is adjusted. 2. The apparatus according to claim 1, further comprising: a second demodulation carrier frequency correction control unit that generates the corrected demodulation carrier frequency information indicating the frequency and controls the demodulation carrier frequency correction unit so that the demodulation carrier frequency is not further corrected. 3. The digital broadcast receiver according to any one of 2. 6. The digital broadcast receiving apparatus according to claim 5, further comprising a non-volatile memory for storing the corrected demodulated carrier frequency information. 7. The method according to claim 6, 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. The digital broadcast receiving device according to the above. 8. The broadcast receiving apparatus estimates that the reference frequency is closest to a difference frequency value that can minimize the synchronization time within the first difference frequency range from a manufacturing process capability and product accuracy. 3. A frequency value to be set.
3. The digital broadcast receiving device according to claim 1. 9. A 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 demodulation carrier frequency is a first difference frequency region that is a first value, and the change rate is 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. 10. The demodulation carrier frequency correction step includes a demodulation carrier frequency setting step of setting a demodulation carrier frequency using a predetermined reference frequency as the demodulation carrier signal according to the digital broadcast wave. Digital broadcast receiving method.