JP2011082669A - Digital broadcast receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a digital broadcast receiver for improving receiving performance by suppressing adjacent interference waves in an inexpensive configuration. <P>SOLUTION: A control part 112 is configured so as to perform control that shifts, when a signal of the same channel is received by a reception system, one local oscillation frequency of the reception system in accordance with a receiving state detected by a receiving state-detecting means 111. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an in-vehicle digital broadcast receiving apparatus, for example.

Unlike a home receiver, an in-vehicle digital broadcast receiver generally uses a diversity system that synthesizes and receives signals from a plurality of front end units. In the diversity system, it is necessary to receive the same channel at the front end units of a plurality of systems.
However, it is known that the local oscillator of the front end unit malfunctions due to interference (mutual interference) between the local oscillation frequencies of each other when a local oscillator of the same channel is present nearby.
For such a problem, in Patent Document 1, when the same frequency is selected by two local oscillators, the local oscillation frequency of any local oscillator is displaced so that the frequency difference is 100 kHz or more. A technique for shifting the local oscillation frequency of the local oscillator so as not to interfere with each other is disclosed.

JP 2006-173922 A

In conventional digital broadcast receivers, in order to suppress mutual interference of local oscillation frequencies, measures such as shielding the front end parts and separating the distances from each other are taken, which hinders downsizing of the apparatus. There was a problem.
Although it is conceivable to shift the local oscillation frequency so as not to interfere as in Patent Document 1, if the center frequency of the narrowband filter is not shifted for each reception system, reception performance may be adversely affected.
In addition, a configuration using two types of narrow band filters (for example, SAW (Surface Acoustic Wave) filters) having different center frequencies so as not to adversely affect the cost is high.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a digital broadcast receiver that improves reception performance by suppressing adjacent interfering waves according to a reception state with a low-cost configuration. To do.

  The digital broadcast receiving apparatus according to the present invention is a digital broadcast receiving apparatus having at least two reception systems, and a reception state detection means for detecting a reception state of a reception signal of the reception system, and a signal of the same channel is received by the reception system. Then, a control unit that performs control to shift the local oscillation frequency of one of the reception systems according to the reception state detected by the reception state detection unit is provided.

  According to the digital broadcast receiving apparatus according to the present invention, when a signal of the same channel is received by the receiving system, control is performed to shift one local oscillation frequency of the receiving system according to the reception state. The reception performance can be improved without increasing the cost.

1 is a block diagram illustrating a configuration of a digital broadcast receiving apparatus according to Embodiment 1. FIG. 3 is a flowchart for explaining the operation of the digital broadcast receiving apparatus according to the first embodiment. 6 is a diagram showing changes in the waveform of a received signal when the local oscillation frequency is shifted in the first embodiment. FIG. 6 is a flowchart for explaining the operation of the digital broadcast receiving apparatus according to the second embodiment. It is a figure which shows the change of the waveform of a received signal at the time of shifting a local oscillation frequency. 6 is a block diagram illustrating a configuration of a digital broadcast receiving apparatus according to Embodiment 3. FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Embodiment 1 FIG.
FIG. 1 is a block diagram showing a schematic configuration of a digital broadcast receiving apparatus according to Embodiment 1 of the present invention. As shown in FIG. 1, the digital broadcast receiving apparatus includes a first reception system 100, a second reception system 200, a reception state detection unit 111, and a control unit 112. Receiving systems 100 and 200 having the above configuration receive digital broadcast signals, respectively, and display images based on the synthesized signals.

  The first receiving system 100 includes an antenna 101, a mixer 102, a narrow band filter 103, a demodulating means 104, a video / audio output means 105, a local oscillator 106, a reference oscillator 107, and a PLL (Phase Locked Loop) 108. The receiving system 200 includes an antenna 201, a mixer 202, a narrow band filter 203, a demodulation unit 204, a video / audio output unit 205, a local oscillator 206, a reference oscillator 207, and a PLL 208.

  The antennas 101 and 201 receive an RF (Radio Frequency) signal as a digital broadcast signal. The local oscillators 106 and 206 generate a local oscillation frequency for converting the frequency of the RF signal.

The mixer 102 mixes and converts the RF signal (for example, the frequency of the RF signal is 470 MHz to 770 MHz) received by the antenna 101 and the local oscillation frequency from the local oscillator 106, and converts the RF signal to IF (Intermediate Frequency; intermediate). Frequency) signal (for example, IF signal frequency is 57 MHz) and output.
The mixer 202 mixes the RF signal received by the antenna 201 and the local oscillation frequency from the local oscillator 206, converts the frequency, converts the RF signal into an IF signal, and outputs the IF signal.

  The narrowband filters 103 and 203 are filters that allow only a signal having a narrow band frequency to pass therethrough. For example, an interference signal included in the IF signal is removed, and an IF signal as a desired wave necessary as a digital broadcast signal is allowed to pass. Output.

  The demodulation means 104 and 204 have a function of synthesizing input IF signals, a function of demodulating IF signals, and a function of analyzing IF signals. As a function of combining IF signals, the demodulating means 104 receives the IF signal input from the narrowband filter 103 and the demodulating means 204 at a ratio calculated based on the analysis result of the IF signal when the received signal is the same channel. Synthesizes the input IF signal. As a function of combining IF signals, the demodulating unit 204 receives the IF signal input from the narrowband filter 203 and the demodulating unit 104 at a ratio calculated based on the analysis result of the IF signal when the received signal is the same channel. Synthesizes the input IF signal.

  Further, the demodulation means 104 and 204 demodulate the synthesized IF signal into a TS (Transport Stream) signal including a video signal, an audio signal, and a data signal as a function of demodulating the IF signal. If the received signals are not in the same channel, the demodulating means 104 demodulates the IF signal input from the narrowband filter 103 without synthesizing the IF signal, and the demodulating means 204 does not synthesize the IF signal. The IF signal input from the narrowband filter 203 is demodulated.

  Further, in the demodulation means 104 and 204, as a function of analyzing the input IF signal, the waveform of the IF signal is extracted, and at the time of error correction in the demodulation process, a bit error rate (BER), carrier wave and A CN (Carrier to Noise) ratio indicating the ratio to noise is calculated.

  The video / audio output means 105 and 205 are components that decompress the demodulated TS signal, extract the video signal, audio signal, and data signal, and output them as video, audio, and data. The audio / video output means 105 and 205 have a concept including a monitor and a speaker for outputting video, audio and data. For example, the monitor and the speaker of the audio / video output means 105 are provided on the front seat side in the vehicle interior. The monitor and speaker of the audio / video output means 205 are provided on the rear seat side of the vehicle interior.

  The local oscillator 106 outputs a signal having a predetermined frequency (local oscillation frequency) in accordance with an instruction from the PLL 108, and the local oscillator 206 outputs a signal having a predetermined frequency in accordance with an instruction from the PLL 208.

  The reference oscillators 107 and 207 output a signal having a reference frequency (reference frequency). For example, a crystal oscillator XO (Xtal Oscillator) is used. Further, a VCXO (Voltage Controlled Xtal Oscillator) capable of changing the frequency may be used.

  PLLs 108 and 208 are electronic circuits that synchronize the reference frequency and the local oscillation frequency. Based on a control signal from the control unit 112, the PLLs 108 and 208 respectively change the reference frequency of the reference oscillators 107 and 207 and the local oscillation frequency of the local oscillators 106 and 206, respectively. By dividing, multiplying, and comparing, the local oscillation frequencies of the local oscillators 106 and 206 are controlled so that a desired channel can be received. The PLLs 108 and 208 perform frequency division processing on the local oscillation frequency using the frequency division ratio N of the local oscillation frequency, and frequency division processing on the reference frequency using the frequency division ratio R.

  The reception state detection unit 111 detects, for example, BER and C / N from the demodulation units 104 and 204 as reception states. The control unit 112 compares the data indicating the reception state (for example, BER, C / N) detected by the reception state detection unit 111 with a preset threshold value, and determines the adjacent interference wave as the reception state from the comparison result. The presence or absence of is determined. In addition, the control unit 112 controls the local oscillator so as to shift the local oscillation frequency according to the reception state.

Next, an example of the operation of the digital broadcast receiving apparatus according to Embodiment 1 will be described using the flowchart of FIG. As shown in FIG. 2, control section 112 determines whether or not channel selection of the same reception channel is instructed in the first reception system and the second reception system (step ST101). At this time, if the same channel is not selected in the first reception system and the second reception system (step ST101 “NO”), the control unit 112 sets the local oscillation frequency to the center frequency in the PLL 108 and the PLL 208, respectively. Instruct them to do so.
The local oscillator 106 outputs the local oscillation frequency as the center frequency in accordance with control by the PLL 108 whose frequency is instructed from the control unit 112. The local oscillator 206 outputs the local oscillation frequency as the center frequency in accordance with the control by the PLL 208 instructed by the control unit 112 (step ST105). Thereafter, the process is terminated.

  When channel selection of the same channel is instructed in the first reception system and the second reception system (step ST101 “YES”), the control unit 112 shifts the local oscillation frequency upward by a preset frequency. Instructs the PLL 208 to oscillate. The PLL 208 controls the local oscillator 206 so as to oscillate the local oscillation frequency in accordance with an instruction from the control unit 112. The local oscillator 206 oscillates the local oscillation frequency by shifting the frequency upward from the center frequency (step ST102). In the following, a case where the local oscillation frequency oscillated by the local oscillator 206 is shifted will be described. However, the local oscillation frequency on the local oscillator 106 side may be shifted without changing the local oscillator 206 side.

Subsequently, the control unit 112 determines whether or not the reception state is good based on the reception state detected by the reception state detection unit 111 (step ST103). If it is determined that the reception state is good (step ST103 “YES”), the process ends.
On the other hand, when the reception state is not good (step ST103 “NO”), control unit 112 instructs PLL 208 to oscillate with the local oscillation frequency shifted downward from the center frequency. The PLL 208 controls the local oscillator 206 so as to oscillate the local oscillation frequency in accordance with an instruction from the control unit 112. The local oscillator 206 oscillates the local oscillation frequency by shifting downward from the center frequency (step ST104). Thereafter, the process is terminated.

Here, a change in the waveform of the received signal when the local oscillation frequency is shifted in the first embodiment will be described. FIG. 3A is a diagram showing a waveform of a received signal before shifting the local oscillation frequency, and FIG. 3B is a diagram showing an output waveform in the case of FIG. FIG. 3C is a diagram showing the waveform of the received signal after shifting the local oscillation frequency, and FIG. 3D is a diagram showing the output waveform in the case of FIG. 3C.
As shown in FIG. 3A, adjacent interference waves are generated, and the adjacent interference wave A is included in the range of the characteristics of the narrowband filter together with the desired wave. In the output waveform in this state, the adjacent interfering wave remains largely as shown in FIG.

  The control unit 112 controls the local oscillator 206 in accordance with the reception state detected by the reception state detection unit 111, and as shown in FIG. 3A, the adjacent interference wave is generated from the center frequency by a preset frequency. The local oscillation frequency is shifted in the a direction (upper side) to be attenuated (step ST102 in FIG. 2). As a result, the adjacent interfering wave A transmitted through the narrow band filter becomes small as shown in FIG.

  On the other hand, as shown in FIG. 3C, a part of the desired wave is attenuated, but the frequency amount to be shifted is set so as to obtain the best reception state. For example, the adjacent interference wave A and the desired wave B It is set in advance as a ratio of the attenuation amount of the portion. By shifting the local oscillation frequency in this way, depending on the level of the adjacent interference wave, the influence of the adjacent interference wave can be suppressed as shown in FIG.

  As described above, according to the first embodiment, when a signal of the same channel is received by the reception system, the control unit 112 determines the reception system according to the reception state detected by the reception state detection unit 111. Since control for shifting one of the local oscillation frequencies is performed, the influence of adjacent interference waves can be suppressed without increasing the number of narrow-band filters, and the reception performance can be improved without increasing costs.

  In the first embodiment, the control unit 112 controls the PLL to shift the local oscillation frequency from the local oscillator. However, as shown by the broken line in FIG. 1, the control unit 112 controls the reference oscillator to set the reference frequency. The local oscillation frequency from the local oscillator may be shifted by shifting.

  In addition, a plurality of reference oscillators having different reference frequencies may be provided in one reception system, and the control unit 112 may be configured to switch the reference oscillator according to the reception state.

Embodiment 2. FIG.
In the second embodiment, a configuration in which the local oscillation frequency is shifted by changing the shift amount according to the reception state will be described. The configuration of the digital broadcast receiving apparatus according to the second embodiment is the same as that of the digital broadcast receiving apparatus according to the first embodiment, and the description of the configuration that performs the same processing is omitted.

  FIG. 4 is a flowchart for explaining the operation of the digital broadcast receiving apparatus according to the second embodiment. As illustrated in FIG. 4, the control unit 112 determines whether or not channel selection of the same channel is instructed in the first reception system and the second reception system (step ST101a). Here, when channel selection of the same channel is not instructed in the first reception system and the second reception system (step ST101a “NO”), the control unit 112 proceeds to step ST105a and focuses on the local oscillation frequency. Control to oscillate at frequency. Thereafter, the process is terminated.

  When channel selection of the same channel is instructed in the first reception system and the second reception system (step ST101a “YES”), control unit 112 oscillates the local oscillation frequency by shifting downward from the center frequency. Instruct the PLL 208 as follows. When the PLL 208 controls the local oscillator 206 in accordance with the instruction from the control unit 112, the local oscillator 206 oscillates the local oscillation frequency shifted downward from the center frequency (step ST102a).

  Next, control section 112 determines whether or not the reception state is good based on the reception state detected by reception state detection means 111 (step ST103a). At this time, when it is determined that the reception state is good (step ST103a “YES”), the control unit 112 ends the process.

  On the other hand, when determining that the reception state is not good (step ST103a “NO”), control unit 112 instructs PLL 208 to oscillate with the local oscillation frequency shifted upward from the center frequency. The PLL 208 controls the local oscillator 206 in accordance with an instruction from the control unit 112. Local oscillator 206 oscillates the local oscillation frequency shifted upward (step ST104a).

  Subsequently, the control unit 112 determines whether or not the reception state is good based on the reception state detected by the reception state detection unit 111 (step ST106a). When it is determined that the reception state is good (step ST106a “YES”), control unit 112 ends the process.

  When the reception state is not good (step ST106a “NO”), the control unit 112 changes the frequency shift amount to, for example, a smaller amount than before (step ST107a), and oscillates by shifting the local oscillation frequency downward. (Step ST108a).

  Thereafter, the control unit 112 returns to the process of step ST106a, and ends the process when the reception state becomes good. If the reception state does not improve, the control unit 112 increases the local oscillation frequency in step ST108a while changing the frequency shift amount in step ST107a until the reception state converges to a good state. Alternatively, the process of shifting downward is repeated.

  As described above, according to the second embodiment, the control unit 112 shifts the local oscillation frequency while changing the frequency amount to be shifted according to the reception state until the reception state is good. As compared with the configuration of the first embodiment, the reception performance can be further improved.

In the first and second embodiments, when adjacent interfering waves exist on both the upper and lower sides of the desired wave, the control unit 112 shifts the local oscillation frequency upward and downward so that the upper desired wave and the lower wave One desired wave may be acquired by combining the desired wave.
FIG. 5 is a diagram showing a change in the waveform of the received signal in the case described above. FIG. 5A is a diagram showing the waveform of the received signal before shifting the local oscillation frequency, and FIG. 5B is a diagram showing the output waveform in the case of FIG. 5A. FIG. 5C is a diagram showing a waveform of a received signal when the local oscillation frequency is shifted in the b direction, and FIG. 5D is a diagram of the received signal when the local oscillation frequency is shifted in the c direction. It is a figure which shows a waveform. Further, FIG. 5 (e) is a diagram showing a composite wave of the output waveforms of FIG. 5 (c) and FIG. 5 (d).

  As shown in FIG. 5A, adjacent disturbing waves are generated on both upper and lower sides of the desired wave, and the upper adjacent disturbing wave A1 and the lower adjacent disturbing wave are included in the range of the characteristics of the narrowband filter together with the desired wave. A2 is included. In the output waveform in this state, the adjacent interfering wave remains largely as shown in FIG. The control unit 112 controls the local oscillator 206, for example, and shifts the local oscillation frequency in the b direction (upper side) from the center frequency shown in FIG. The IF signal is shifted as shown in FIG. 5C, and the demodulating unit 104 acquires the desired wave C on the upper side of the IF signal that has passed through the narrowband filter 103. Next, the control unit 112 controls the local oscillator 206 to shift the local oscillation frequency in the c direction (downward) from the center frequency shown in FIG. When the IF signal is shifted as shown in FIG. 5D, the demodulator 104 acquires the desired wave D below the IF signal that has passed through the narrowband filter 103.

  When the demodulating means 104 acquires the upper desired wave C and the lower desired wave D, the demodulating means 104 synthesizes the upper desired wave C and the lower desired wave. Thereby, depending on the level of the adjacent interference wave, a waveform as shown in FIG. Also by doing so, the reception performance of the digital broadcast receiving apparatus can be improved.

Embodiment 3 FIG.
In the third embodiment, a configuration including three or more reception systems will be described.
FIG. 6 is a block diagram showing a configuration of the digital broadcast receiving apparatus according to the third embodiment. In FIG. 6, the same components as those in the first and second embodiments are denoted by the same reference numerals as those in FIG. As shown in FIG. 6, the configuration of the digital broadcast receiving apparatus according to the first and second embodiments includes a third receiving system 300, which includes an antenna 301, a mixer 302, and a narrowband filter 303. The demodulating unit 304 and the video / audio output unit 305 are included.

  The mixer 302 is connected to the local oscillator 106 and shares the local oscillator 106 with the first receiving system 100. Further, the mixer 302 mixes the RF signal received by the antenna 301 and the local oscillation frequency from the local oscillator 106, converts the frequency, converts the RF signal into an IF signal, and outputs the IF signal.

  The narrow band filter 303 is a filter that transmits only a signal having a narrow band frequency. For example, the adjacent band included in the IF signal is removed, and the IF signal is transmitted as a desired wave as a digital broadcast signal and output. . The narrowband filter 303 is connected to the demodulation unit 304 and outputs the transmitted IF signal to the demodulation unit 304.

  The demodulator 304 has a function of synthesizing the input IF signal, a function of demodulating the IF signal, and a function of analyzing the IF signal. As a function of combining IF signals, the demodulator 304 combines the IF signal input from the narrowband filter 303 and the demodulator 104 at a ratio calculated based on the analysis result of the IF signal when the received signal is the same channel. Synthesizes the input IF signal.

  The demodulator 104 combines the IF signal input from the narrowband filter 303 and the IF signal input from the demodulators 204 and 304 and receives the IF signal input from the narrowband filter 303 when the received signal is the same channel. An IF signal obtained by combining the signal and the IF signal input from the demodulation unit 204 is output to the demodulation unit 304, and an IF signal obtained by combining the IF signal input from the narrowband filter 303 and the IF signal input from the demodulation unit 304 is demodulated 204. Output to.

  The reception state detection unit 111 detects, for example, BER and C / N as reception states from the demodulation units 104, 204, and 304. As in the first and second embodiments, the control unit 112 compares the data indicating the reception state detected by the reception state detection unit 111 with a preset threshold value, and determines the reception state as the reception state based on the comparison result. Determine the presence or absence of interference.

  The video / audio output unit 305 is a component that decompresses the TS signal demodulated by the demodulating unit 304 to extract a video signal, an audio signal, and a data signal, and outputs them as video, audio, and data. Similar to the first and second embodiments, the video / audio output means 305 has a concept including a monitor and a speaker for outputting video, audio, and data.

  As described above, according to the third embodiment, since at least three reception systems are provided and the local oscillator is shared by some of the reception systems, the same effects as in the first and second embodiments can be obtained. The reception performance can be improved without adding a local oscillator.

  100 First receiving system 101, 201, 301 Antenna, 102, 202, 302 Mixer, 103, 203, 303 Narrow band filter, 104, 204, 304 Demodulating means, 105, 205, 305 Video / audio output means, 106, 206 Local oscillator, 107, 207 Reference oscillator, 108, 208 PLL, 111 Reception state detection means, 112 Control unit, 200 Second reception system, 300 Third reception system

Claims (9)

In a digital broadcast receiving apparatus having at least two receiving systems,
A reception state detecting means for detecting a reception state of a reception signal of the reception system;
A control unit that controls to shift one local oscillation frequency of the reception system according to the reception state detected by the reception state detection unit when a signal of the same channel is received by the reception system; A digital broadcast receiver characterized by that.   2. The digital broadcast receiving apparatus according to claim 1, wherein the control unit changes a frequency amount to be shifted according to the reception state detected by the reception state detection unit.   3. The digital broadcast receiving apparatus according to claim 1, wherein the reception state detecting means detects the presence / absence of an adjacent interfering wave as a reception state based on a waveform of a reception signal.   The digital broadcast receiving apparatus according to claim 1 or 2, wherein the reception state detecting means detects a bit error rate or a CN (Carrier to Noise) ratio of a received signal.   5. The digital broadcast receiving apparatus according to claim 1, wherein the control unit performs control to shift a local oscillation frequency by changing a frequency division ratio. 6.   5. The digital broadcast receiver according to claim 1, wherein the control unit performs control to shift a local oscillation frequency by shifting a reference frequency of a reference oscillator. 6.   7. The digital broadcast receiving apparatus according to claim 6, wherein the reference oscillator is a VCXO (Voltage Controlled Xtal Oscillator). The reception system includes a plurality of reference oscillators having different reference frequencies,
7. The digital broadcast receiving apparatus according to claim 6, wherein the control unit performs control to switch the reference oscillator to shift a local oscillation frequency.   9. The digital broadcast receiving apparatus according to claim 1, comprising at least three receiving systems, wherein some receiving systems share the local oscillator.

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