JP4749301B2 - Digital broadcast receiver - Google Patents

Description

  The present invention relates to a digital broadcast receiver that receives broadcast signals of an Orthogonal Frequency Division Multiplex (OFDM) transmission system, and more particularly to a digital broadcast receiver that can receive broadcast signals transmitted with different numbers of segments. The present invention relates to a broadcast receiving apparatus.

  In recent years, various broadcasts have become digital broadcasts, such as a transitional period in which terrestrial television broadcasts have changed from analog to digital. An OFDM transmission method is used as a transmission method in this digital broadcasting. In this OFDM transmission method, on the transmitting side, first, digital data to be transmitted is modulated by a large number of subcarriers (subcarriers) orthogonal to each other, and then subjected to an inverse fast Fourier transform (IFFT) process. To a time domain signal. On the receiving side, when a signal from the transmitting side is received, the signal is converted from a time domain to a frequency domain signal by a fast Fourier transform (FFT) process, and then demodulated for each subcarrier of the obtained signal. Apply. In this OFDM system, when the number of subcarriers used is as large as several hundred to several thousand, the symbol period of each modulated wave becomes extremely long, so that it is less susceptible to multipath interference.

  In particular, in ISDB-T (Integrated Services Digital Broadcasting-Terrestrial), which is terrestrial digital broadcasting, the 6 MHz bandwidth can be divided into 13 segments, and the modulation method of the carrier wave can be made different for each segment. Of these 13 segments, one segment arranged in the center is used for broadcasting for portable devices. Also, in ISDB-TSB (Integrated Services Digital Broadcasting-Terrestrial for Sound Broadcasting), which is a terrestrial digital audio broadcasting, broadcasting of each channel to be used is multiplexed with a plurality of services composed of one segment or three segments. It consists of ~ 13 segments. In other words, a concatenated transmission method, which is a method of transmitting a plurality of services as one channel broadcast, is adopted in terrestrial digital audio broadcasting.

  As described above, the terrestrial digital audio broadcasting includes a three-segment broadcasting service that is a service using three segments and a one-segment broadcasting service that is a service using one segment. In the three-segment broadcasting service, among the three segments arranged on the frequency axis, the central one segment and the two segments on both sides are different in different hierarchical configurations and have different specifications. As a result, even in a digital broadcast receiver dedicated to a one-segment broadcast service, it is possible to receive and reproduce one central segment among the three segments based on the three-segment broadcast service.

  As described above, for a digital broadcast receiving apparatus that receives terrestrial digital audio broadcasting composed of a three-segment broadcasting service and a one-segment broadcasting service, the terrestrial digital whose frequency band occupied by each service is all subcarriers of 6 MHz. Since it is narrower than broadcasting, the receiving circuit can be downsized. Furthermore, 64QAM (Quadrature Amplitude Modulation) or the like is used as a modulation method for each subcarrier in terrestrial digital broadcasting, but 16QAM or QPSK (Quadrature Phase Shift Key) suitable for mobile communication is used in terrestrial digital audio broadcasting. Etc. are used.

  As a digital broadcast receiving apparatus that receives this terrestrial digital audio broadcast, a modulation method suitable for mobile communication as described above is adopted, and the frequency band of each service is narrow, so that mobile phones and PDAs (Personal Digital Assistants) and other mobile devices. As a result, a small-sized and low power consumption digital broadcast receiving apparatus is required, and as shown in FIG. 7, the OFDM demodulator is configured as one system. A conventional digital broadcast receiving apparatus will be described below based on the digital broadcast receiving apparatus having the configuration shown in FIG.

  7 receives an OFDM signal, which is a high-frequency signal (RF signal) propagating in the air, by the antenna 50, the frequency is changed from a high-frequency frequency (RF frequency) to an intermediate frequency (IF frequency) by the tuner 51. Conversion (down-conversion) is performed. When receiving a three-segment broadcasting service, the tuner 51 limits the frequency band for three segments, and an analog OFDM signal with a frequency band for three segments that becomes the IF frequency IF3 as shown in FIG. Is output. When the analog OFDM signal is converted into a digital OFDM signal by the AD conversion unit 52, a quadrature component is derived from the in-phase component by the Hilbert conversion unit 53 to generate a complex OFDM signal, and then, as shown in FIG. In addition, an unnecessary frequency component is removed by a BPF (Band Pass Filter) 54 and provided to the frequency converter 55.

  Thereafter, as shown in FIG. 8C, the frequency conversion unit 55 frequency-converts (down-converts) the complex OFDM signal into a baseband signal, and then this baseband signal is given to the 3-segment demodulation unit 56. The 3-segment demodulator 56 establishes symbol synchronization, frequency synchronization, and clock synchronization, and after converting the time axis signal to the frequency axis signal by FFT processing, equalizes the signal assigned to the subcarrier. When this equalized signal is given to an error correction unit (FEC: Forward Error Correction) 57, deinterleaving, Viterbi decoding, and Reed-Solomon decoding for removing signal errors caused by distortion in the transmission path are performed. The MPEG (Moving Pictures Experts Group) -TS (Transport Stream) signal for the three-segment broadcasting service is generated.

  When receiving a one-segment broadcast service (including a one-segment broadcast service arranged in the center of the frequency axis in a three-segment broadcast service), the tuner 51 may or may not limit the band to one segment. . First, when the tuner 51 is not limited to one segment band, the tuner 51 limits the frequency band for three segments as in the case of receiving the three-segment broadcast service. Then, up to the 3-segment demodulator 56, the same operation as when receiving the 3-segment broadcast service is performed, and the FEC 57 corresponds to one segment located in the center of the frequency axis from the signal demodulated by the 3-segment demodulator 56. By extracting the signal to be received, reception of the one-segment broadcasting service is realized. Also, the same operation as when receiving a three-segment broadcast service is performed, and when decoding with FEC57, the MPEG-TS signal for one central segment located at the center of the frequency axis is also extracted. Is realized.

  On the other hand, when the tuner 51 limits the band to one segment, when the tuner 51 performs frequency conversion (down-conversion) from an RF signal to an IF signal, as shown in FIG. An analog OFDM signal with a frequency band is output. At this time, the IF frequency IF1 can be set to a value lower than the IF frequency IF3 because the restricted frequency band is narrower than in the case where the frequency band restriction for three segments is performed. As described above, when the IF frequency is lowered, the sampling frequency in the AD converter 52 can be lowered, so that power saving can be achieved.

Then, when the analog OFDM signal for one segment is converted into a digital OFDM signal by the AD conversion unit 52, the analog OFDM signal is converted into a complex OFDM signal by the Hilbert conversion unit 53, and then, as shown in FIG. Unnecessary frequency components are removed and provided to the frequency converter 55. Then, as shown in FIG. 9C, the frequency conversion unit 55 frequency-converts (down-converts) the complex OFDM signal into a baseband signal, and then this baseband signal is given to the 3-segment demodulation unit 56, so that Equalized to the signal assigned to the carrier. Thereafter, decoding for removing signal errors is performed by the FEC 57, and an MPEG-TS signal for the one-segment broadcasting service is generated.
The Journal of the Institute of Image Media Vol.52, No.11, pp.1562 to 1566 The Journal of the Institute of Image Media Vol.53, No.11, pp.1467 ~ 1471

  In the conventional digital broadcast receiving apparatus configured as shown in FIG. 7, it is possible to receive both the three-segment broadcast service and the one-segment broadcast service, and to switch between the reception of the three-segment broadcast service and the reception of the one-segment broadcast service. it can. However, when switching the reception operation from the three-segment broadcast service to the one-segment broadcast service, if the tuner 51 does not limit the frequency band of one segment, the reception operation can be continued without interruption. It will be operated for a three-segment broadcasting service. Therefore, an unnecessary circuit is operated, and power consumption is increased.

  On the other hand, when the frequency band limitation of one segment is performed by the tuner 51, all the blocks are operated for the one segment broadcasting service, so that it is not necessary to operate an unnecessary circuit. Further, as described above, since the IF frequency can be lowered, the sampling frequency in the AD converter 52 can be lowered, so that further power saving can be achieved. However, since the IF frequency is changed in the tuner 51, when switching between the receiving operation of the three-segment broadcasting service and the receiving operation of the one-segment broadcasting service, the receiving operation is interrupted, and the continuous reception is continued. Can not.

  In view of such a problem, the present invention provides a digital broadcast receiving apparatus that can continuously receive and save power even when a broadcast service with a different number of segments is switched. Objective.

  In order to achieve the above object, a digital broadcast receiver according to the present invention comprises a tuner that receives a high-frequency signal and converts it into an intermediate frequency signal, and a demodulation circuit that demodulates the intermediate frequency signal from the tuner. In the broadcast receiving apparatus, the demodulation circuit uses a plurality of band-pass filters that band-limit the intermediate frequency signal from the tuner in different frequency bands, and a signal band-limited by each of the plurality of band-pass filters is used as a baseband signal. A plurality of frequency conversion units for conversion, a plurality of demodulation units for demodulating the baseband signals from each of the plurality of frequency conversion units, and a plurality of signals obtained by demodulating by the plurality of demodulation units at a predetermined frequency A signal coupling unit coupled to the arrangement, and the band operated according to the frequency band size of the received digital broadcast And selects pass filter and said frequency conversion unit and the demodulation unit.

  In such a digital broadcast receiving apparatus, when switching from reception of a digital broadcast with a wide frequency band to reception of a digital broadcast with the same center frequency as that of the wide digital broadcast and a narrow frequency band, the band is limited at the tuner. Without changing the size of the frequency band, the narrow bandpass filter, the frequency conversion unit, and a part of the demodulation unit that are driven when the wide digital broadcast is received are stopped, so that the narrow The band-pass filter, the frequency converter, and the demodulator according to the size of the frequency band of digital broadcasting are selected and operated.

  Thereby, when receiving a digital broadcast with a narrow frequency band, it is possible to stop the bandpass filter, the frequency conversion unit, and the demodulation unit that do not require operation, and to reduce its power consumption, Since the frequency band to be band-limited by the tuner is not changed, it is possible to continuously reproduce the broadcast without interruption.

  Further, the signal combining unit may combine the plurality of signals output from the plurality of demodulation units by arranging them in time series from the lowest frequency band.

  Further, the digital broadcast is transmitted by an orthogonal frequency division multiplex transmission system and is configured by a high frequency signal composed of one or more segments, and the band pass filter performs frequency band limitation according to one segment, and n segments When receiving a digital broadcast using a high-frequency signal, the n band-pass filters, the n frequency conversion units, and the n demodulation units are selected and operated.

  At this time, the digital broadcast is a three-segment broadcast service and a one-segment broadcast service, and a first bandpass filter for limiting a frequency band for the lowest first segment among the three segments, and of the first segment among the three segments A second bandpass filter for limiting the frequency band for the second lowest segment; a third bandpass filter for limiting the frequency band for the third highest segment among the three segments; and the first to third bandpass filters. First to third frequency converters for generating first to third baseband signals by frequency-converting each of the signals from the first to third bases from the first to third frequency converters A first to a third demodulator that demodulates each band signal may be provided.

  At this time, when receiving the three-segment broadcasting service, the first to third bandpass filters, the first to third frequency conversion units, and the first to third demodulation units are operated, and the first to third bandpass filters are operated. The three-segment broadcasting service is demodulated by combining the signals of the three segments from the first to third demodulating units with the signal combining unit.

  In the case of receiving the one-segment broadcasting service, when switching from the three-segment broadcasting service, the second bandpass filter, the second frequency converting unit, and the second demodulating unit are operated, The one-segment broadcasting service is demodulated based on the one-segment signal from the second demodulator. Thereby, even if it switches from the said 3 segment broadcast service, the received broadcast can be continuously reproduced without interruption.

  On the other hand, when receiving the one-segment broadcasting service from the beginning, the first band-pass filter, the first frequency converting unit, and the first demodulating unit are operated, and one segment from the first demodulating unit is operated. The one-segment broadcasting service is demodulated by the signal of. At this time, the frequency band received by the tuner can be lowered, and the sampling frequency when performing AD conversion can be lowered, so that power saving can be achieved.

  In addition, a decoder unit that decodes the signal output from the demodulator unit, and an output unit that outputs at least one of video and audio based on the analog signal decoded by the decoder unit, The received broadcast video or audio can be reproduced.

  According to the present invention, when a digital broadcast with a narrow frequency band is received, it is possible to stop the bandpass filter, the frequency conversion unit, and the demodulation unit that do not require operation, and to reduce the power consumption. At this time, the received digital broadcast can be changed to one having a narrow frequency band without changing the frequency band to be band-limited by the tuner. Therefore, when switching from a wide frequency band digital broadcast to a narrow frequency band, the broadcast can be reproduced continuously without interruption.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an internal configuration of a digital broadcast receiving apparatus according to this embodiment.

  The digital broadcast receiving apparatus of FIG. 1 is obtained by an antenna 10 that receives an RF signal propagating in the air as a digital broadcast signal, a tuner 11 that selects an RF signal received by the antenna 10, and a tuner 11 that selects a channel. An AD converter 12 that converts the analog IF signal into a digital IF signal, a Hilbert converter 13 that acquires a complex OFDM signal by performing a Hilbert transform on the digital IF signal from the AD converter 12, and a Hilbert transform The BPFs 14a to 14c that limit the frequency band for one segment from the complex OFDM signal from the unit 13, and the frequency conversion unit 15a that performs frequency conversion on the complex OFDM signals that have passed through the BPFs 14a to 14c to obtain a baseband signal To 15c and baseband signals from the frequency converters 15a to 15c, respectively. On the other hand, the 1-segment demodulator 16a-16c that demodulates the signal, the segment combiner 17 that combines the signals of one segment demodulated by each of the 1-segment demodulator 16a-16c, and the signal combined by the segment combiner 17 On the other hand, decoding is performed to remove signal errors to generate an MPEG-TS signal, and an MPEG-TS signal from the FEC unit 18 is decoded by an encoding method such as the MPEG2 method to generate an audio signal. A decoder unit 19 to be generated, and a speaker 20 that reproduces and outputs sound by an audio signal from the decoder unit 19 are provided.

  According to the digital broadcast receiving apparatus configured as described above, the three-segment broadcast service and the one-segment broadcast service can be received as in the conventional digital broadcast receiving apparatus having the configuration shown in FIG. Below, each operation | movement of the digital broadcast receiver of the structure shown in FIG. 1 is demonstrated.

(Receiving operation of 3-segment broadcasting service)
First, the reception operation of the three-segment broadcasting service will be described with reference to the frequency allocation diagram of FIG. When an OFDM signal that is an RF signal propagating in the air is received by the antenna 10, the tuner 11 performs frequency conversion (down-conversion) from the RF frequency to the IF frequency. Then, the frequency band limitation for three segments is performed, and an analog OFDM signal with a frequency band for three segments that becomes the IF frequency IF3 as shown in FIG. That is, if the size of the frequency band of one segment is Δf, an analog OFDM signal having a frequency band of 3 × Δf is given to the AD conversion unit 12. The IF frequency IF3 is the center frequency of the frequency band for three segments.

  The analog OFDM signal from the tuner 11 is analog-to-digital converted by the AD conversion unit 12 to be converted into a digital OFDM signal, and then the Hilbert conversion unit 13 performs Hilbert conversion for deriving a quadrature component from the in-phase component. It is an OFDM signal. A complex OFDM signal having a frequency band of 3 segments (frequency band of 3 × Δf) is transmitted from the Hilbert transform unit 13 to each of the BPFs 14a to 14c.

  In the BPFs 14a to 14c, the complex OFDM signal from the Hilbert transform unit 13 is band-limited by a frequency band for one segment (a frequency band of Δf). At this time, the BPF 14a performs band limitation on the frequency band of Δf that is the center frequency IF3-Δf, the BPF 14b performs band limitation on the frequency band of Δf that is the center frequency IF3, and the BPF 14c performs center limitation on the center frequency. Band limiting is performed on the frequency band of Δf which is IF3 + Δf. Therefore, when the complex OFDM signal S0 having a frequency band of 3 × Δf of the IF frequency IF3 is output from the Hilbert transform unit 13, the BPF 14a outputs Δf of the center frequency IF3-Δf as shown in FIG. The complex OFDM signal S1 band-limited to the frequency band is transmitted from the BPF 14b to the complex OFDM signal S2 band-limited to the frequency band of Δf that becomes the center frequency IF3 as shown in FIG. The complex OFDM signals S3 band-limited to the frequency band of Δf that becomes the center frequency IF3 + Δf as in d) are respectively output.

  Each of the complex OFDM signals S1 to S3 passing through the BPFs 14a to 14c is given to the frequency converters 15a to 15c, respectively. The frequency conversion unit 15a performs frequency conversion (down-conversion) for the frequency IF3-Δf on the complex OFDM signal S1, and the frequency conversion unit 15b performs frequency conversion (down-conversion) for the complex OFDM signal S2 on the frequency IF3. The frequency conversion unit 15c performs frequency conversion (down conversion) for the frequency IF3 + Δf on the complex OFDM signal S3. Therefore, the baseband signal B1 as shown in FIG. 2 (e) is sent from the frequency converter 15a, and the baseband signal B2 as shown in FIG. 2 (f) is sent from the frequency converter 15c from the frequency converter 15c. A baseband signal B3 as shown in FIG. 2 (g) is output.

  When the baseband signals B1 to B3 obtained by the frequency conversion units 15a to 15c are respectively supplied to the 1-segment demodulation units 16a to 16c, first, symbol synchronization, frequency synchronization, and clock synchronization are established. . Thereafter, each of the 1-segment demodulation units 16a to 16c performs FFT processing on each of the baseband signals B1 to B3 with which synchronization is established, thereby converting the time axis signal into a frequency axis signal and assigning it to the subcarrier. Equalize the signal being received. By operating in this way, the equalization signals Sa to Sc obtained by processing each of the baseband signals B1 to B3 are output to the segment combination unit 17 from the 1 segment demodulation units 16a to 16c, respectively. .

  Then, in the segment combination unit 17, the one segment equalization signals Sa to Sc from the one segment demodulation units 16a to 16c are combined to obtain a three segment equalization signal as shown in FIG. The configuration of the segment coupling unit 17 will be described with reference to the block diagram of FIG. As shown in FIG. 3, the segment combination unit 17 includes delay circuits 171 to 173 that delay the equalization signal of one segment by a time T <b> 1 and an addition circuit 174 that adds the equalization signals Sa to Sc. Prepare.

  That is, the delay circuit 171 is connected to the one-segment demodulation unit 16b, delays the equalization signal Sb by time T1, and the two delay circuits 172 and 173 connected in series are connected to the one-segment demodulation unit 16c. The equalization signal Sc is delayed by time 2 × T1. The equalization signal Sa from the one-segment demodulator 16a, the equalization signal Sb delayed by the time T1 from the delay circuit 171 and the equalization signal Sc delayed by the time 2 × T1 from the delay circuit 173 are: The addition circuit 174 adds the values.

  Since the segment coupling unit 17 is configured in this way, the equalization signal Sa is first supplied to the addition circuit 174 among the equalization signals Sa to Sc simultaneously supplied from the one-segment demodulation units 16a to 16c. That is, since there is no signal output from the delay circuits 171 and 173, the equalization signal Sa is output from the adder circuit 174 to the FEC unit 18. When the equalization signal Sa is all output to the FEC unit 18 after the time T1 has elapsed, the equalization signal Sb delayed by the time T1 by the delay circuit 171 is then provided to the addition circuit 174. The equalized signal Sb is output from the adder circuit 174 to the FEC unit 18. When the equalized signal Sb is all output to the FEC unit 18 after the time T1 has elapsed, the equalized signal Sc delayed by the time 2 × T1 by the delay circuits 172 and 173 is then input to the adder circuit 174. Therefore, the equalization signal Sc is output from the adder circuit 174 to the FEC unit 18.

  Thus, since the equalization signals Sa to Sc are sequentially given to the FEC unit 18 from the segment combination unit 17 in time series, as a result, as shown in FIG. Will be combined. Then, the FEC unit 18 performs decoding processing such as deinterleaving, Viterbi decoding, and Reed-Solomon decoding on the equalized signal of the three segments obtained by combining by the segment combining unit 17, and distortion in the transmission path is performed. A signal error caused by the above is removed, and an MPEG-TS signal is generated. In the decoder unit 19, the MPEG-TS signal is subjected to a decoding process based on a compression encoding method such as MPEG2, and an audio signal is generated. Accordingly, the audio signal obtained by the decoder unit 19 is given to the speaker 20, whereby the audio of the program in the received three-segment broadcast service is reproduced.

(First receiving operation of 1-segment broadcasting service)
Next, the first reception operation of the one-segment broadcasting service will be described with reference to the frequency arrangement diagram of FIG. This first reception operation is not switched from the three-segment broadcast service, but is a reception operation when receiving the one-segment broadcast service from the beginning.

  In the first receiving operation of this one-segment broadcasting service, when an OFDM signal that is an RF signal propagating in the air is received by the antenna 10, the tuner 11 changes the RF frequency to the IF frequency by the tuner 11 as in the receiving operation of the three-segment broadcasting service. Frequency conversion (down-conversion) is performed, but frequency band limitation for one segment is performed. As a result, unlike the reception operation of the three-segment broadcast service, an analog OFDM signal in the frequency band for one segment that becomes the IF frequency IF1 as shown in FIG. This IF frequency IF1 is the center frequency of the frequency band for one segment, and is lower than the IF frequency IF3 for the analog OFDM signal in the frequency band for three segments in FIG. . At this time, the IF frequency IF1 is set to IF3−ΔF.

  The analog-to-digital conversion is performed by the AD conversion unit 12 to obtain a digital OFDM signal, and then the Hilbert conversion unit 13 performs the Hilbert conversion to obtain a complex OFDM signal. The complex OFDM signal of the Hilbert transform unit 13 is output to the subsequent stage, but only the BPF 14a, the frequency transform unit 15a, and the one-segment demodulating unit 16a connected to the subsequent stage of the Hilbert transform unit 13 are operated, and no operation is necessary. The BPFs 14b and 14c, the frequency conversion units 15b and 15c, and the 1-segment demodulation units 16b and 16c are stopped to save power.

  Therefore, the complex OFDM signal in the frequency band for one segment subjected to the Hilbert transform is given only to the BPF 14a, and unnecessary frequency components other than the one-segment frequency band of the center frequency IF1 (= IF3-ΔF) are removed. It will be. Then, the complex OFDM signal S1 from which unnecessary frequency components are removed by the BPF 14a as shown in FIG. 4 (b) is frequency-converted (down-converted) by the frequency converter 15a, and as shown in FIG. 4 (c). After being converted to the one-segment baseband signal B1, it is converted to an equalized signal Sa by being equalized to a signal assigned to a subcarrier by the one-segment demodulator 16a.

  The equalized signal Sa from the one segment demodulator 16 a is given to the FEC unit 18 through the adder circuit 174 of the segment combiner 17. When the MPEG-TS signal is generated by performing error decoding on the equalization signal Sa of one segment in the FEC unit 18, the decoder unit 19 performs decoding processing on the MPEG-TS signal. And an audio signal is generated. Accordingly, the audio signal obtained by the decoder unit 19 is given to the speaker 20, whereby the received audio of the program in the one-segment broadcasting service is reproduced.

(Second receiving operation of one segment broadcasting service)
Next, the second reception operation of the one-segment broadcasting service will be described with reference to the frequency allocation diagram of FIG. Unlike the above-described first reception operation, this second reception operation is a reception operation when switching from the three-segment broadcasting service. In the second reception operation of the one-segment broadcast service, unlike the first reception operation described above, the tuner 11, the AD conversion unit 12, and the Hilbert conversion unit 13 are the same as when the three-segment broadcast service is received. A reception operation is performed for the frequency band of the segment.

  In the second reception operation of the one-segment broadcasting service, when an OFDM signal that is an RF signal propagating in the air is received by the antenna 10, the tuner 11 performs frequency conversion (down-conversion) from the RF frequency to the IF frequency. At this time, similarly to the reception operation of the three-segment broadcasting service, the frequency band limitation for three segments is performed. Thus, unlike the first reception operation of the one-segment broadcasting service, an analog OFDM signal in the frequency band for three segments that becomes the IF frequency IF3 as shown in FIG.

  The analog-to-digital conversion is performed by the AD conversion unit 12 to obtain a digital OFDM signal, and then the Hilbert conversion unit 13 performs the Hilbert conversion to obtain a complex OFDM signal. The complex OFDM signal of the Hilbert transform unit 13 is output to the subsequent stage, but only the BPF 14b, the frequency transform unit 15b, and the one-segment demodulating unit 16b connected to the subsequent stage of the Hilbert transform unit 13 are in operation. The BPFs 14a and 14c, the frequency conversion units 15a and 15c, and the 1-segment demodulation units 16a and 16c are stopped to save power.

  Therefore, unlike the above-described first reception operation, the complex OFDM signal S0 in the frequency band of three segments subjected to the Hilbert transform is given only to the BPF 14b, and Δf that becomes the center frequency IF3 as shown in FIG. The complex OFDM signal S2 band-limited to the frequency band is output. The OFMD signal S2 is frequency-converted (down-converted) by the frequency converter 15b to be converted into a one-segment baseband signal B2 as shown in FIG. 5 (c), and then the one-segment demodulator 16b. By being equalized to the signal assigned to the subcarrier, it is converted into an equalized signal Sb.

  The equalized signal Sb from the one-segment demodulator 16b is given to the FEC unit 18 through the delay circuit 171 and the adder circuit 174 of the segment combiner 17. When the MPEG-TS signal is generated by performing error decoding on the equalized signal Sb of one segment in the FEC unit 18, the decoder unit 19 performs decoding processing on the MPEG-TS signal. And an audio signal is generated. Therefore, the audio signal obtained by the decoder unit 19 is given to the speaker 20, whereby the audio of the program in the hierarchy of one segment arranged at the center in the received three-segment broadcasting service is reproduced.

(Switching operation from reception of 3 segment broadcast to reception of 1 segment broadcast service)
Further, a switching operation from reception of the 3-segment broadcast service to reception of the 1-segment broadcast service will be described. When such a switching operation of the broadcast service to be received is performed, the reception operation of the one-segment broadcasting service after the switching is the above-described second reception operation.

  First, as described above, by driving each of the BPFs 14a to 14c, the frequency conversion units 15a to 15c, and the 1 segment demodulation units 16a to 16c, one segment of the OFDM signal selected by the tuner 11 can be obtained. Equalization signals Sa to Sc are generated. When the equalized signals Sa to Sc are combined by the segment combining unit 17 to generate a three-segment equalized signal, the FEC unit 18 and the decoder unit 19 decode the program audio in the three-segment broadcasting service. Playback and output from the speaker 20.

  When switching to the one-segment broadcast service while performing the reception operation of the three-segment broadcast service in this way, the BPF 14b that generates the one-segment equalization signal Sb, the frequency conversion unit 15b, and the one-segment demodulation unit 16b are continued. The BPFs 14a and 14c, the frequency conversion units 15a and 15c, and the one-segment demodulation units 16a and 16c that do not need to be operated are stopped. Thus, a one-segment equalized signal Sb is generated from the three-segment OFDM signal selected by the tuner 11. When the equalized signal Sb is supplied to the FEC unit 18 through the segment combination unit 17, the FEC unit 18 and the decoder unit 19 decode the program signal to reproduce and output the audio of the program in the one-segment broadcasting service from the speaker 20.

  By operating in this way, it is possible to switch from the three-segment broadcast service to the one-segment broadcast service based on the segment arranged in the center of the three-segment broadcast service. Note that the switching of the broadcast service to be received may be performed by operating a user interface (not shown), and the decoder unit 19 determines the reproduction time and reception time of the MPEG-TS signal. It may be executed when the occurrence of a decoding delay is detected from the relationship, or may be executed when it is detected that the reception state at the tuner 11 has deteriorated.

(Switching operation from reception of 1-segment broadcast to reception of 3-segment broadcast service)
The switching operation from the reception of the 1-segment broadcast service to the reception of the 3-segment broadcast service will be described. When such a broadcast service switching operation to be received is performed, the reception operation of the one-segment broadcast service before switching is the above-described second reception operation.

  First, as described above, the BPFs 14a and 14c, the frequency conversion units 15a and 15c, and the one-segment demodulation units 16a and 16c are stopped, and the BPF 14b, the frequency conversion unit 15b, and the one-segment demodulation unit 16b are driven. Then, a one-segment equalized signal Sb is generated from the three-segment OFDM signal selected by the tuner 11. When this equalized signal Sb is provided to the FEC unit 18 via the segment combination unit 17, the FEC unit 18 and the decoder unit 19 decode the program audio from the speaker 20 for reproduction. To do.

  In this way, when performing the reception operation of the one-segment broadcasting service, when switching to the three-segment broadcasting service, the BPF 14b, the frequency conversion unit 15b, and the one-segment demodulation unit 16b are continuously driven and the BPFs 14a, 14c, The frequency conversion units 15a and 15c and the one segment demodulation units 16a and 16c are also driven. Thereby, one-segment equalized signals Sa to Sc are generated from the three-segment OFDM signal selected by the tuner 11. When the equalized signals Sa to Sc are combined by the segment combining unit 17 to generate a three-segment equalized signal, the FEC unit 18 and the decoder unit 19 decode the program audio in the three-segment broadcasting service. Playback and output from the speaker 20.

  By operating in this way, it is possible to switch from the one-segment broadcasting service based on the segment arranged in the center of the three-segment broadcasting service to the three-segment broadcasting service. Note that the switching of the broadcast service to be received may be performed by operating a user interface (not shown), and the decoder unit 19 determines the reproduction time and reception time of the MPEG-TS signal. Depending on the relationship, it may be executed when it is detected that the occurrence of decoding delay can be avoided, or it may be executed when it is detected that the reception state at the tuner 11 has improved. I do not care.

  In the present embodiment, in the first receiving operation of the one-segment broadcasting service, the BPF 14b, the frequency converting unit 15b, and the one-segment demodulating unit 16b may be operated as in the second receiving operation. At this time, an analog OFDM signal is output from the tuner 11 in a frequency band for one segment that becomes the IF frequency IF3.

  Further, the segment coupling unit 17 is not limited to the configuration of FIG. 3, and for example, as shown in FIG. 6, it is switched whether the equalization signal Sa from the one-segment demodulation unit 16 a is applied to the input or output of the addition circuit 174. The switch SW1 and the switch SW2 that switches whether the equalized signal Sb from the one-segment demodulator 16b is applied to the input of the delay circuit 171 or the output of the adder circuit 174 may be provided.

  At this time, when receiving the three-segment broadcasting service, the equalization signal Sa is input to the addition circuit 174 by the switch SW1, and the equalization signal Sb is input to the delay circuit 171 by the switch SW2. On the other hand, when performing the first reception operation of the one-segment broadcast service, the equalization signal Sa is directly input to the FEC unit 18 by the switch SW1, and when performing the second reception operation of the one-segment broadcast service, The equalization signal Sb is directly input to the FEC unit 18 by the switch SW2. Therefore, when receiving the one-segment broadcast service, the operations of the delay circuits 171 to 173 and the adder circuit 174 that constitute the segment coupling unit 17 can be stopped, and the power consumption can be reduced.

  Further, in the present embodiment, a display 21 that reproduces and displays a video by a video signal from the digital decoder unit 19 may be provided. In addition, when the functions of the present embodiment are provided so that a broadcast service with n segments or more can be received, it can be realized by including n BPFs, frequency converters, and 1-segment demodulators. . Then, by driving all n circuits of the BPF, the frequency conversion unit, and the 1-segment demodulation unit, the n-segment broadcasting service is received and the BPF, the frequency conversion unit, and the 1-segment demodulation unit are driven by 3 circuits. By doing so, it is possible to receive a one-segment broadcast service by receiving a three-segment broadcast service and driving one circuit of the BPF, the frequency converter and the one-segment demodulator.

  The present invention can be applied to a digital broadcast receiver that receives digital broadcasts having different numbers of segments such as terrestrial digital audio broadcasts or terrestrial digital broadcasts. As the digital broadcast receivers, small-sized mobile phones, PDAs, etc. Therefore, the present invention can be applied to a mobile terminal device capable of mobile communication. The present invention is also applicable to in-vehicle terminal devices such as car navigation systems and car TVs. Furthermore, the present invention can be applied to a digital broadcast recording apparatus that can record a received digital broadcast.

These are block diagrams which show the internal structure of the broadcast receiving apparatus in embodiment of this invention. These are the frequency arrangement | positioning diagrams of the signal in each part at the time of receiving 3 segment broadcast service in the broadcast receiver of FIG. These are block diagrams which show the structure of the segment coupling | bond part in the broadcast receiver of FIG. These are the frequency arrangement | positioning diagrams of the signal in each part when performing the 1st reception operation | movement of 1 segment broadcast service in the broadcast receiver of FIG. These are the frequency arrangement | positioning diagrams of the signal in each part when performing the 2nd receiving operation of 1 segment broadcast service in the broadcast receiver of FIG. These are block diagrams which show another structure of the segment coupling | bond part in the broadcast receiver of FIG. These are block diagrams which show the internal structure of the conventional broadcast receiving apparatus. These are the frequency arrangement | positioning diagrams of the signal in each part at the time of receiving 3 segment broadcast service in the broadcast receiver of FIG. These are the frequency arrangement | positioning diagrams of the signal in each part at the time of receiving 1 segment broadcast service in the broadcast receiver of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Antenna 11 Tuner 12 AD conversion part 13 Hilbert conversion part 14a-14c BPF
15a to 15c Frequency conversion unit 16a to 16c 1 segment demodulation unit 17 segment combination unit 18 FEC unit 19 decoder unit 20 speaker 171 to 173 delay circuit 174 addition circuit

Claims (4)

In a digital broadcast receiver comprising a tuner that receives a high-frequency signal and converts it to an intermediate frequency signal, and a demodulation circuit that demodulates the intermediate frequency signal from the tuner,
The demodulation circuit is
A plurality of bandpass filters for band-limiting the intermediate frequency signal from the tuner in different frequency bands;
A plurality of frequency converters for converting a band-limited signal into a baseband signal by each of the plurality of bandpass filters;
A plurality of demodulation units for demodulating the baseband signal from each of the plurality of frequency conversion units;
A signal combining unit that combines a plurality of signals obtained by demodulation by the plurality of demodulation units into a predetermined frequency arrangement;
With
When switching from receiving a digital broadcast with a wide frequency band to receiving a digital broadcast with the same center frequency as the wide digital broadcast and a narrow frequency band,
The band pass filter and the frequency conversion unit that are driven when receiving the wide digital broadcast without changing the size of the frequency band to be band limited in the tuner and the intermediate frequency of the intermediate frequency signal And stopping the part of the demodulator to select and operate the bandpass filter, the frequency converter, and the demodulator according to the frequency band of the narrow digital broadcast,
When receiving the narrow digital broadcast from the beginning, the frequency band to be limited by the tuner is narrower and the intermediate frequency of the intermediate frequency signal is lower than when receiving the wide digital broadcast. A digital broadcast receiver characterized by the above. 2. The digital broadcast receiving apparatus according to claim 1, wherein the signal combining unit combines the plurality of signals output from the plurality of demodulation units by arranging them in time series in order from the lowest frequency band . The received digital broadcast is transmitted by an orthogonal frequency division multiplex transmission system, and is configured by a high-frequency signal composed of one or more segments,
The bandpass filter performs frequency band limitation according to one segment,
2. When receiving digital broadcasting using n-segment high-frequency signals, n number of band-pass filters, n number of frequency conversion units, and n number of demodulation units are selected and operated. Or the digital broadcast receiver of Claim 2. A decoder for decoding the signal output from the demodulator;
An output unit that outputs at least one of video and audio based on the analog signal decoded by the decoder unit;
The digital broadcast receiving apparatus according to any one of claims 1 to 3, characterized in that it comprises a.

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