JP2006295406A - Method and device for receiving digital broadcasting signal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a good reception image and reception sound quality by reducing the effect of signal of the frequency which is a jamming in a digital television system. <P>SOLUTION: A digital broadcast signal receiving device 1 comprises a DAC14 for generating a control voltage which controls a tracking filter 3 according to the level of IF signal, a memory 15, and a control part 16 for controlling respective parts. A bit error rate (BER) at demodulation at a signal demodulating part 10 is corresponded to a control DC voltage of the tracking filter 3, which is written in the memory 15. The control part 16 receives the bit error rate (BER) at demodulation process from the signal demodulating part 10, and changes the control voltage of the tracking filter according to the value. The central frequency of the filter is changed so that a target frequency is extracted from the RF signal that is received. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a broadcast signal receiving apparatus such as a television receiver and a broadcast signal receiving method, and more particularly, to a digital broadcast signal receiving apparatus for reducing the influence of a signal having a frequency that becomes a disturbing wave in a broadcast signal transmitted in a digital manner. The present invention relates to a digital broadcast signal receiving method.

  In recent years, television broadcasting is shifting to a digital system in which digital video signals are digitally transmitted in the same transmission band as conventional analog modulation after high-efficiency encoding of digital video signals. Many new broadcasting services have begun, including the beginning. Digital television broadcasting has advantages such as being able to transmit more information than analog systems and being less susceptible to transmission noise.

  Broadcast radio waves of a broadcasting satellite (BS: Broadcasting Satellite, hereinafter referred to as BS) digital broadcasting and a communication satellite (CS: Communications Satellite, hereinafter referred to as CS) are received by a parabolic antenna or the like, for example, 1 After being converted into a high frequency signal (referred to as RF (Radio Frequency) signal) of ˜2 GHz, it is sent to a broadcast signal receiving apparatus such as a so-called set top box or a tuner with a satellite broadcast receiving function. The broadcast signal receiving apparatus is called a voltage controlled oscillator (hereinafter referred to as a VCO (Voltage Controlled Oscillator)) that includes a tracking filter that selectively amplifies a desired signal from an RF signal received by an antenna and whose oscillation frequency is variable depending on an applied voltage. The local oscillation signal oscillated from) is mixed with the RF signal received from the antenna, and frequency conversion is performed to down-convert the signal to a predetermined intermediate frequency (IF) signal.

  As the tracking filter, a filter (VCF (Voltage Controlled Filter)) whose center frequency is variable by an applied voltage is used in order to selectively amplify a desired signal. As a method for controlling the center frequency of the tracking filter, for example, a method of monitoring the IF signal and using the control voltage of the VCO (see FIG. 3), or a method of monitoring the IF signal and generating a control voltage (FIG. 4). See).

  A broadcast receiving apparatus 100 shown in FIG. 3 is an example of a digital television broadcast wave receiving apparatus. A receiving apparatus 100 includes a receiving antenna 101 that receives a broadcast wave transmitted from a broadcasting station, a tracking filter 102 that extracts a target frequency from a received signal, and an RF amplifier that amplifies the extracted frequency 103, a tracking filter 104 for extracting a target frequency from the amplified signal, a desired signal frequency extracted by the tracking filter 104 and a local frequency signal, and an intermediate frequency signal (hereinafter referred to as an IF signal). ), An IF amplifier 106 that amplifies the IF signal, an IF bandpass filter 107 that defines the center frequency of the passband that passes the target frequency of the amplified IF signal, and the IF signal that has passed through the filter IF amplifier 108 for amplifying the amplified IF signal Is output to the signal demodulator 109.

  The receiving apparatus 100 includes a PLL control circuit 110, a VCO 111, and a tank circuit 112. The PLL control circuit 110 oscillates the VCO 111 based on the PLL setting data and the local oscillation frequency currently output by the VCO 111. A control voltage for controlling the frequency to an oscillation frequency corresponding to the PLL setting data is generated. In the receiving apparatus 100, the above-described units are centrally controlled by the control unit 113.

  The receiving apparatus 100 uses the control voltage of the VCO 111 to generate a tracking filter control voltage according to the VCO control voltage, and controls the center frequencies of the tracking filters 102 and 104.

  4 includes a receiving antenna 201 that receives a broadcast wave transmitted from a broadcasting station, a tracking filter 202 that extracts a target frequency from the received signal, and an RF amplifier that amplifies the extracted frequency. 203, a tracking filter 204 that extracts a target frequency from the amplified signal, a mixer 205 that mixes a desired signal frequency extracted by the tracking filter 204 and a local frequency signal and outputs an IF signal, and an IF signal IF amplifier 206 that amplifies, IF bandpass filter 207 that defines the center frequency of the passband that passes the target frequency of the amplified IF signal, IF amplifier 208 that amplifies the IF signal that has passed through the filter, and PLL control circuit 209, VCO 210, and tank circuit 211, Width IF signal is output to the signal demodulation unit 212.

  The receiving apparatus 200 includes a DAC 213 that generates a control voltage for controlling the tracking filter 202 in accordance with the signal level of the IF signal, and a memory 214, and the above-described units are centrally controlled by the control unit 215.

  The receiving apparatus 200 detects the IF signal output from the IF amplifier 208, and supplies a control voltage for controlling the center frequency of the pass band that is passed through the tracking filter 202 so that the output IF signal (IF OUT) is maximized. Is generated.

  Specifically, for example, as a method for controlling the center frequency of the tracking filter, an example in which a VCO control voltage is used is disclosed in Patent Document 1 below, and an example in which a control unit generates a VCO control voltage is disclosed in Patent Document 2 below. Has been. 3 and 4 described above, and the tuners disclosed in Patent Document 1 and Patent Document 2 generally detect the signal level of the RF signal (or IF signal) and obtain a peak value. Thus, a method of controlling the filter coefficient of the tracking filter is employed.

JP 2000-032361 A Japanese Patent Laid-Open No. 2004-215034

  In digital television broadcasting, if there is a strong interference wave in the vicinity of a desired frequency at the time of reception, the interference wave that has passed through the tracking filter may be amplified and adversely affect signal demodulation. The interference signal that caused a bit error during signal demodulation can be corrected by error correction processing provided after the demodulator, but it can be handled by error correction processing depending on the amplified noise level. It will also cause deterioration of the received picture sound quality that can not be.

  Especially when there is an interference wave near the peak value of the signal level of the desired intermediate frequency, the tracking filter will also amplify the interference wave, so that the signal level of the desired intermediate frequency becomes the peak value. It is not always best to adjust the tracking filter.

  Therefore, the present invention has been proposed in view of the above-described conventional situation, and in a digital television system, it is possible to reduce the influence of a signal having a frequency as an interference wave and obtain a good received image and received sound quality. An object is to provide a broadcast signal receiving apparatus.

  In order to achieve the above-described object, a digital broadcast signal receiving apparatus according to the present invention is a digital broadcast signal receiving apparatus that receives a broadcast signal transmitted in a digital manner from a broadcast station, converts it into a predetermined intermediate frequency signal, and demodulates it. A filter means for selectively extracting a radio frequency signal in a target frequency band from a broadcast signal, wherein the center frequency of the transmission signal is variable according to the applied voltage, and voltage controlled oscillation whose oscillation frequency is variable depending on the applied voltage Means for mixing the local oscillation signal transmitted from the voltage controlled oscillation means with the radio frequency signal extracted by the filter means to generate a predetermined intermediate frequency signal, and a signal for demodulating the intermediate frequency signal from the mixing means Demodulation means, filter voltage generation means for generating a voltage applied to the filter means, and bit error rate during demodulation processing in the signal demodulation means And control means for controlling a filter voltage generating means in accordance with the detected said bit error rate.

  The digital broadcast signal receiving apparatus may further include storage means for storing the bit error rate and a control voltage value for controlling the center frequency of the filter means in association with each other. At this time, the control means stores the control voltage value that minimizes the bit error rate in the storage means. Further, the control means stores in the storage means a control voltage value that minimizes the bit error rate for all receivable channels.

  According to the present invention, it is possible to slightly shift the center frequency of the tracking filter while avoiding interference waves. As a result, the bit error rate is improved, and a better received image and received sound quality can be obtained. Furthermore, by adjusting the center frequency of the tracking filter based on the bit error rate value that determines the reception quality in the actual radio wave reception environment, the interference wave is amplified even when there is a strong interference wave near the desired wave. It is possible to make an optimal adjustment such as taking out the desired wave without doing so. In addition, since the center frequency of the tracking filter can be dynamically adjusted, it is possible to adjust the optimum value corresponding to the radio wave reception environment at the actual usage place as well as at the time of manufacture.

  A digital broadcast signal receiving apparatus 1 shown as a specific example of the present invention will be described with reference to the drawings.

  A digital broadcast signal receiving apparatus 1 shown in FIG. 1 is a 12 GHz band digital signal from a broadcast satellite (BS) and a 110 ° communication satellite (CS). This is a tuner that converts a high frequency signal of 1 to 2 GHz obtained from a broadcast signal into a baseband signal. The digital broadcast signal receiving apparatus 1 inputs a target broadcast channel frequency as a local oscillation output signal to a mixer circuit, converts an RF signal input via an antenna into an intermediate frequency signal (IF signal), and generates a baseband signal. Can be downconverted to signal.

  A digital broadcast signal receiving apparatus 1 shown in FIG. 1 includes a receiving antenna 2 that receives a broadcast wave transmitted from a broadcasting station, a tracking filter 3 that extracts a target frequency from the received signal, and an extracted frequency. An RF amplifier 4 and a tracking filter 5 for extracting a target frequency from the amplified signal.

  Further, the desired signal frequency extracted by the tracking filter 5 and the local frequency signal are mixed to output an intermediate frequency signal (hereinafter referred to as IF signal), an IF amplifier 7 for amplifying the IF signal, and the amplified signal. An IF bandpass filter 8 that defines the center frequency of the passband that passes the target frequency of the IF signal, and an IF amplifier 9 that amplifies the IF signal that has passed through the filter are provided. The amplified IF signal is output to the signal demodulation unit 10.

  The digital broadcast signal receiving apparatus 1 further includes a PLL control circuit 11, a VCO 12, and a tank circuit 13. The PLL control circuit 11 uses the VCO 12 based on the PLL setting data and the local oscillation frequency currently output by the VCO 12. A control voltage for controlling the oscillation frequency to the oscillation frequency corresponding to the PLL setting data is generated.

  The digital broadcast signal receiving apparatus 1 includes a DAC 14 that generates a control voltage for controlling the tracking filter 3 according to the signal level of the IF signal, a memory 15, and a control unit 16 that controls each unit. The bit error rate (BER) value at the time of demodulation and the control voltage are written in the memory 15 in association with each other. The local oscillation frequency generated by the VCO 12 is controlled by the control unit 16 so as to receive the initial channel.

  In the digital broadcast signal receiving apparatus 1, the control voltage value of the tracking filter for each channel is given to the memory 15 in the initial state, and the control unit 16 receives the bit error rate (BER) during the demodulation process from the signal demodulation unit 10. ) And the control voltage of the tracking filter is changed according to this value, and the center frequency of the tracking filter 3 is changed so that the target frequency is extracted from the received RF signal.

  More specifically, in the initial state, the control DC voltage of the tracking filter for all channels is written in the memory 15. The VCO 12 first generates a local oscillation frequency for receiving the channel A based on a signal from the PLL control circuit 11 controlled by the control unit 16. The RF input signal input from the receiving antenna 2 passes through the tracking filter 3 and the frequency of the target channel is extracted. The extracted frequency signal is amplified through the RF amplifier 4 and sent to the tracking filter 5. The desired signal frequency finally extracted by the tracking filter 5 is mixed with the local frequency signal generated by the tank circuit 13 and the VCO 12 in the mixer 6 to generate an IF signal.

  The IF signal is amplified by the IF amplifier 7, the IF bandpass filter 8 defines the center frequency of the pass band, and the IF signal in the desired frequency band is amplified by the IF amplifier 9. The amplified IF signal is output to the signal demodulator 10.

  The control unit 16 stores a pair of the BER value in the signal demodulation unit 10 and the control voltage value of the tracking filter 3 corresponding to the BER value in the memory 15. Then, the control unit 16 performs a reception operation by increasing or decreasing the control voltage value of the tracking filter 3 by a predetermined amount d with respect to the initial value V. While comparing with the minimum value of BER written in the memory 15, the receiving operation is repeatedly performed in increments of d from the initial DC voltage value V to the maximum or minimum usable voltage, and the control voltage value that minimizes the BER is set to the A channel. The control DC voltage value is updated. Here, the maximum or minimum voltage that can be used from the initial DC voltage value V is the maximum or minimum voltage that can still receive a signal of the target frequency even if the center of the pass band of the tracking filter 3 deviates from the target frequency. This is the control voltage value when selecting the frequency.

  Next, a process in which the digital broadcast signal receiving apparatus 1 shown in FIG. 1 sets tracking filter control voltage values for all channels will be described with reference to FIG.

  As an initial state, the tracking filter control DC voltage values V1 to Vn are written in the memory 15 for all the channels. It is assumed that the digital broadcast signal receiving apparatus 1 executes the tracking filter voltage optimization process in order from the channel A.

  The controller 16 selects channel A as step S1. The control unit 16 sends a control signal for receiving the initial channel A to the PLL control circuit 11, and a local oscillation frequency for receiving the channel A is generated in the VCO 12.

  Further, the control unit 16 selects the initial DC voltage V for the A channel from the memory 15 as step S2. A selected initial DC voltage is generated at the DAC 14. As step S <b> 3, the control DC voltage generated from the DAC 14 is applied to the tracking filter 3.

  The control unit 16 is sent from the signal demodulator 10 the BER when the IF signal converted from the RF input signal when the control DC voltage of the tracking filter 3 is the initial DC voltage is demodulated. In step S <b> 4, the control unit 16 writes the BER value and the control DC voltage value at this time as a set to the memory 15.

  Subsequently, if the control DC voltage does not exceed the maximum available value (Vmax) of the tracking filter 3 in the determination in step S5, the control unit 16 increases the control DC voltage value of the tracking filter by d in step S6. , V + d is a control DC voltage, the value of the area in the memory 15 that the DAC 14 reads is changed, and steps S3 and S4 are repeated from the initial DC voltage value to the maximum available voltage.

  When the control unit 16 reaches the maximum available value (Vmax) of the tracking filter 3 in step S5, the control unit 16 compares the BER value for each control DC voltage written in the memory 15 in step S7, and determines the minimum BER. The control DC voltage value when the value is obtained is stored in the memory 15 as the tracking filter control DC voltage for the A channel.

  Subsequently, if there is an unset channel by the determination in step S8, the control unit 16 increments the channel number by 1 in step S9, and the optimum value of the control DC voltage of the tracking filter 3 is stored in the memory 15 for all channels. The above operation is repeated until the data is written to.

  As described above, the digital broadcast signal receiving apparatus 1 executes the adjustment process of the control DC voltage of the tracking filter 3 to obtain the optimum value in the radio wave reception environment in which the digital broadcast signal receiving apparatus 1 is actually used. You can choose.

  In addition, when the radio wave is actually received, the radio wave condition may change and the reception state may deteriorate in a specific channel. Therefore, the tracking DC control DC voltage adjustment process described above is executed and set as an initial value. Then, the adjustment process may be executed only for a specific channel. Further, this adjustment process may be executed at regular intervals or based on a user instruction. Thereby, even if the reception state changes according to the use environment of the digital broadcast signal receiving apparatus 1, it is possible to automatically improve the received signal.

  In addition, when adjustment processing is performed in advance at the time of manufacture, it is generally necessary to prepare a signal source and output a signal for the A channel in synchronization when, for example, a reception operation for the A channel is performed. The digital broadcast signal receiving apparatus 1 can be easily realized only by outputting a signal from the control unit 16.

It is a block diagram explaining the digital broadcast signal receiver shown as a specific example of this invention. It is a flowchart explaining the control process of the tracking filter in the digital broadcast signal receiver shown in FIG. It is a block diagram explaining the conventional receiver which diverts the control voltage of a local oscillation circuit and controls a tracking filter. It is a block diagram explaining the conventional receiver which produces | generates the control voltage which controls a tracking filter according to the output value of IF signal.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Digital broadcast signal receiver, 2 Receiving antenna, 3 Tracking filter, 4 RF amplifier, 5 Tracking filter, 6 Mixer, 7 IF amplifier, 8 IF band pass filter, 9 IF amplifier, 10 Signal demodulation part, 11 PLL control circuit, 12 VCO, 13 tank circuit, 14 DAC, 15 memory, 16 control unit

Claims (4)

In a digital broadcast signal receiving apparatus that receives a broadcast signal transmitted in a digital manner from a broadcast station, converts it to a predetermined intermediate frequency signal, and demodulates it,
Filter means for selectively extracting a radio frequency signal of a target frequency band from the broadcast signal, the center frequency of the transmission signal being variable according to the applied voltage;
Voltage-controlled oscillation means whose oscillation frequency is variable according to the applied voltage;
Mixing means for generating a predetermined intermediate frequency signal by mixing the local oscillation signal transmitted from the voltage controlled oscillation means with the radio frequency signal extracted by the filter means;
Signal demodulating means for demodulating the intermediate frequency signal from the mixing means;
Filter voltage generating means for generating an applied voltage to the filter means;
A digital broadcast signal receiving apparatus comprising: control means for detecting a bit error rate during demodulation processing in the signal demodulating means and controlling the filter voltage generating means in accordance with the bit error rate.   Storage means for storing the bit error rate in association with a control voltage value for controlling the center frequency of the filter means is provided, and the control means stores a control voltage value that minimizes the bit error rate in the storage means. The digital broadcast signal receiver according to claim 1.   3. The digital broadcast signal receiving apparatus according to claim 2, wherein the control means stores in the storage means a control voltage value that minimizes a bit error rate for all receivable channels. In a digital broadcast signal receiving method for receiving a broadcast signal transmitted in a digital manner from a broadcast station, converting it to a predetermined intermediate frequency signal and demodulating it,
A step of selectively extracting a radio frequency signal in a target frequency band from the broadcast signal in the filter means in which the center frequency of the transmission signal is variable according to the applied voltage;
Mixing a local oscillation signal with the extracted radio frequency signal to generate a predetermined intermediate frequency signal;
A signal demodulation step of demodulating the intermediate frequency signal,
A digital broadcast signal receiving method comprising: detecting a bit error rate at the time of demodulation processing in the signal demodulating step, and controlling a voltage applied to the filter means according to the bit error rate.

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