JP2010226757A - Channel level control unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To output a terrestrial digital broadcast signal after canceling distortion such as level gradient in each channel band of the terrestrial digital broadcast signal. <P>SOLUTION: In a channel level control unit 2, a received terrestrial digital broadcast signal is branched and then output as broadcast channel signals adjusted into specified level for each broadcast channel by channel level controllers 2a-2n, and the output broadcast channel signals are mixed by a mixer 30. In the channel level controller 2a, a specific broadcast channel signal separated by a band pass filter 16 is down-converted into an intermediate frequency (IF) signal by a mixer 18. For the IF signal, level tilting is then corrected to be flat by tilt circuits 24a, 24b and an unwanted component is removed by a SAW filter 25. The IF signal is up-converted into a frequency of the original broadcast channel signal by a mixer 26, and the broadcast channel signal is further level-adjusted into specified level by a level adjuster 28 and output through a band pass filter 29 to the mixer 30. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a channel level control unit that adjusts a terrestrial digital broadcast signal received by an antenna to a specified level for each broadcast channel and sends it to a joint reception facility such as an apartment house.

  From December 2003, even in a joint reception facility such as an apartment house with digital terrestrial broadcasting in Tokyo, Osaka, and Nagoya, a dedicated UHF antenna is installed to receive digital terrestrial broadcasting. It is mixed with the terrestrial analog broadcast signal and the BS / CS broadcast signal for distribution.

  FIG. 9A shows frequency allocation at the transmission point of terrestrial digital broadcasting, and shows 20 to 28 channels corresponding to nine channels from 512 MHz to 566 MHz, taking terrestrial digital broadcasting in the Tokyo area as an example.

  When such terrestrial digital broadcasting is received at a joint reception facility such as an apartment house, the reception level undulates in the frequency direction as shown in FIG. Distortion and level difference occurs between each channel.

  For this reason, in order to adjust the level difference between channels in the terrestrial digital broadcast signal received by the UHF antenna, a head end device as a channel level controller is provided in the signal line from the antenna. The head end device individually extracts signals of each channel in the terrestrial digital broadcast signal with a filter, removes unnecessary signals and adjusts them to a specified level, and then outputs them again.

  In the level adjustment in the head end device, the signal level is measured for each channel, and control is performed so that the measured signal level becomes a specified level.

JP 2003-309739 A

  However, the control in the conventional channel level controller is based on a level obtained by averaging the entire channel band for each channel band, and there is a problem that the signal level of each channel is not flat.

  FIG. 10A shows a case where the signal level in the channel band of 5.6 MHz is flat, and the signal level obtained by averaging the entire channel band matches the signal level in the channel band. However, as shown in FIG. 10B, when the signal level is distorted and changes obliquely in the channel band, the signal level obtained by averaging the entire channel band is accurate to the signal level in the channel band. Not shown in

  For this reason, when the antenna reception point where the signal level undulates in the frequency direction as shown in FIG. 9B is adjusted to the specified level based on the average level of each channel, as shown in FIG. The average level is adjusted so that there is no level difference while maintaining the slope of the signal level in the frequency direction as it is, and the distortion in the frequency direction remains in each channel signal after the level adjustment.

  For this reason, when a terrestrial digital broadcast signal whose level has been adjusted as shown in FIG. 9C is amplified using a transmission amplifier, the signal is inclined, so that the signal is excessively input at a high level portion in the channel. As a result, distortion and low-level parts are easily affected by noise, and problems such as reception failure may occur on the dwelling unit side.

An object of the present invention is to provide a channel level control unit that removes distortion such as level inclination in each channel band of a terrestrial digital broadcast signal and outputs the signal.

  In order to achieve this object, the present invention is configured as follows.

  The present invention branches a terrestrial digital broadcast signal received by an antenna to a plurality of channel level controllers by a branching device, and the plurality of channel level controllers bring a specific broadcast channel signal separated from the branched terrestrial digital broadcast signal to a specified level. The target is a channel level control unit that is adjusted and then mixed in a mixer and output to a joint reception facility.

In such a channel level control unit for digital terrestrial broadcasting, each of a plurality of channel level controllers
A band-pass filter that separates a specific broadcast channel signal from a terrestrial digital broadcast signal branched by a branching device;
An oscillator that oscillates a channel setting signal of a natural frequency corresponding to a broadcast channel signal separated by a bandpass filter;
A first frequency converter for down-converting a specific broadcast channel signal separated by a band-pass filter into an intermediate frequency signal having the same frequency in all channel level controllers by a channel setting signal from an oscillator;
A SAW filter for removing unnecessary components outside the channel band from the intermediate frequency signal from the first frequency converter;
A second frequency converter for upconverting the intermediate frequency signal from the SAW filter to the frequency of the original broadcast channel signal by the channel setting signal from the oscillator;
A level adjuster for adjusting the level of the broadcast channel signal from the second frequency converter to a specified level and then outputting the signal to the mixer through a bandpass filter;
A tilt circuit that is provided between the first frequency converter and the second frequency converter and that flatly corrects the level gradient in the channel frequency band of the intermediate frequency signal;
The tilt circuit
A first tilt circuit that flatly corrects a tilt characteristic whose level increases with an increase in frequency;
And a second tilt circuit that flatly corrects a tilt characteristic whose level decreases with increasing frequency.

Here, the first tilt circuit and the second tilt circuit are provided separately in the front stage and the rear stage of the SAW filter. Alternatively, the first tilt circuit and the second tilt circuit may be provided before the SAW filter, or may be provided after the SAW filter.

  According to the channel level control unit of the present invention, by providing the tilt circuit in the channel level controller, it is possible to flatly correct and output the slope of the signal level generated in the channel band, thereby flattening the signal level. By measuring the output level after correction, the measurement level obtained by averaging the levels of the entire channel band accurately represents the signal level, and the level is adjusted so that the measurement level matches the specified level for each channel. Therefore, it is possible to obtain an appropriate adjustment output that eliminates the level difference between channels, and the generation of signal distortion and noise when passing through the transmission amplifier while leaving the high and low signal levels in the channel band. The problem of being affected can be solved.

  In addition, when tilt correction is performed using a tilt circuit with a high-frequency signal, it is difficult to design a tilt circuit having a different frequency for each channel. In the present invention, a tilt circuit is provided at a portion converted to an intermediate frequency. As a result, the circuit design of the tilt circuit can be easily performed because of the same frequency even if the channels are different.

Furthermore, by providing a tilt circuit that corrects the upper-right tilt in the channel band and a tilt circuit that corrects the upper-left tilt, the level distortion in the channel band can be handled appropriately regardless of whether it rises to the right or to the left. it can.

Explanatory drawing of the joint reception equipment in which the channel level controller of the present invention is installed The circuit block diagram which showed the embodiment of the channel level controller of this invention A circuit diagram showing an embodiment of the tilt circuit of FIG. Explanatory drawing of left-up slope correction by the tilt circuit of FIG. Explanatory drawing of the upper right slope correction by the tilt circuit of FIG. Characteristic diagram showing digital terrestrial broadcast transmission point, antenna reception point, and channel level controller output of the present invention The circuit block diagram which showed other embodiment of the channel level controller by this invention The circuit block diagram which showed other embodiment of the channel level controller by this invention Characteristic diagram showing the output of digital terrestrial broadcast transmission point, antenna reception point and conventional channel level controller Explanatory diagram of channel band level measurement in a conventional channel level controller

  FIG. 1 is an explanatory diagram of a common reception facility such as an apartment house in which the channel level controller of the present invention is installed. In FIG. 1, a dedicated UHF antenna 1 for receiving terrestrial digital broadcasting is installed in a joint reception facility such as a housing complex, and an antenna reception signal of the UHF antenna 1 is input to a channel level control unit 2 to obtain a level. Adjustments are being made.

  The channel level control unit 2 is provided with the channel level controller of the present invention for each channel of the terrestrial digital broadcast to be received by the joint reception facility, as will be clarified in the following explanation, Channel signals are individually extracted by filters, unnecessary signals are removed, slope correction (tilt correction) is performed by the filter circuit according to the present invention, and level adjustment is performed, and then mixed and output.

  In addition to the UHF antenna 1 dedicated to digital terrestrial broadcasting, in the joint reception facility, in addition to the VHF (Lo) antenna 3, the VHF (Hi) antenna 4 and the UHF antenna 5 for receiving the existing terrestrial analog broadcasting, the BS / CS antenna 6 Is provided.

  The signal from the UHF antenna 1 for terrestrial digital broadcasting passes through the channel level control unit 2 and is mixed with the terrestrial analog broadcast signal from the UHF antenna 5 after being level-adjusted by the antenna level controller 8 and output to the mixer 9b. . The signals from the VHF (Lo) antenna 3 and the VHF (Hi) antenna 4 are mixed by the mixer 9a, adjusted in level by the channel level controller 10, and then mixed by the mixer 9b with the UHF signal. . Further, the signal from the BS / CS antenna 6 is mixed with the signal from the mixer 9b by the mixer 9c.

  The output of the mixer 9c is amplified by the amplifier 10a and then transmitted to the dwelling unit side of the common receiving facility. Branch units 111a and 111b, distributors 11a to 11d, and an amplifier 10b are installed in the system on the dwelling unit side. The equipment of each dwelling unit is shown for one of the distribution terminals of the distributor 11c. In each dwelling unit, the distribution output of the distributor 11d is connected to the TV terminal 12, and then the terrestrial / BS / CS digital tuner is connected from the TV terminal 12. 13 and the TV 14. The output of the terrestrial / BS / CS digital tuner 13 is connected to the television 14.

  FIG. 2 is a circuit block diagram showing an embodiment of the channel level controller of the present invention. The channel level controllers 2a, 2b, 2c... 2n arranged in the channel level control unit 2 shown in FIG. Of these, the circuit configuration of the channel level controller 2a is shown.

  In the channel level control unit 2 of FIG. 2, a signal from the UHF antenna 1 that has received the terrestrial digital broadcast is branched to the channel level controllers 2 a to 2 n by the branching unit 15. The channel level controller 2 a is provided for, for example, 21 channels shown in FIG. 6A, and a signal of a channel band of 518 to 524 MHz is separated by the band pass filter 16 and input to the amplifier 17.

The output of the amplifier 17 is input to a mixer 18 that functions as a first frequency converter. A local oscillation signal having a local oscillation frequency is input to the mixer 18 from the local oscillator 22. If the frequency of the signal input from the amplifier 17 to the mixer 18 is f1, and the frequency of the signal input from the local oscillator 22 is f2, the mixer 18 has a frequency difference Δf = f2−f1 between the two signals.
Produces the output

  Here, the frequency Δf of the mixer 18 is set to an intermediate frequency 56.857 MHz in the television broadcast signal. When the channel level controller 2a is for the 21 channel shown in FIG. 6, the modulation frequency is about 521.143 MHz.

  Assuming that the modulation frequency of 21 channels input from the amplifier 17 to the mixer 18 is f1 = 521.143 MHz and the intermediate frequency Δf = 56.857 MHz which is the output of the mixer 18, the local oscillation frequency from the local oscillator 22 in this case Is f2 = 578 MHz.

  The local oscillation frequency f2 of the local oscillator 22 is set by channel selection by the channel switch 19. That is, when channel 21 is selected by the channel switch 19, the CPU 20 determines this channel setting signal, and the local oscillator 22 oscillates the local frequency f2 = 578 MHz by setting the collector for the PLL 21.

  The 56.857 MHz intermediate frequency signal output from the mixer 18 is applied to an intermediate frequency processing circuit unit in which the tilt circuit 24a, the SAW filter 25, and the tilt circuit 24b are sequentially connected. In the channel level controller 2a, for example, after down-converting the channel signal of the 21 channel into an intermediate frequency signal, unnecessary components other than the 5.6 MHz channel band are removed using the steep cutoff characteristic of the SAW filter 25, Channel interference due to unnecessary signals from adjacent channels is eliminated.

  As a SAW filter 25 having such a steep cut-off characteristic, it is difficult to realize a SAW filter having a sufficient characteristic at a level of the 500 MHz order, which is the UHF band. After down-conversion to a frequency of 56.857 MHz, the unnecessary standby signal component is removed by the SAW filter 25 by a sharp cut-off characteristic.

  A tilt circuit 24a is provided as a first tilt circuit in the preceding stage of the SAW filter 25, and a tilt circuit 24b is provided as a second tilt circuit in the subsequent stage. The tilt circuits 24a and 24b have the circuit configuration shown in FIG.

  FIG. 3 is a circuit diagram of the tilt circuit 24a. A capacitor C1 and a resistor R1 are connected in parallel between the input terminal 31 and the output terminal 32, and a resistor R2, a variable resistor VR, an inductance L1, and a capacitor are connected to the ground side. A ladder circuit by C2 is connected. In such a tilt circuit 24a, the slope characteristic (tilt characteristic) in the channel band of 5.6 MHz can be adjusted by changing the resistance value of the variable resistor VR.

Referring again to FIG. 2, a mixer 26 functioning as a second frequency converter is provided following the tilt circuit 24b, and the intermediate frequency signal from the tilt circuit 24b is up-converted by the local oscillation signal from the local oscillator 22. Bird and convert to the original channel band signal and output. That is, assuming that the local oscillation frequency from the local oscillator 22 is f2 and the intermediate frequency from the tilt circuit 24b is Δf, the frequency f1 of the output signal of the mixer 26 is f1 = f2−Δf.
To perform frequency conversion, that is, frequency up-conversion.

  The signal returned from the intermediate frequency signal to the original frequency by the mixer 26 is amplified by the amplifier 27, passes through the level adjuster 28, and further passes through the band pass filter 29 having a 21-band pass band to the mixer 30. Is output and mixed with signals from the other channel level controllers 2b to 2n.

  The local oscillator 22 of the channel level controller 2a shown in FIG. 2 is composed of one local oscillator. However, in order to separate the input channel and the output channel, the local oscillator 22 may be composed of two.

  FIG. 4 is an explanatory diagram of slope correction by the tilt circuit 24a provided in the previous stage of the SAW filter 25 of FIG. As shown in FIG. 4A, the channel signal in the 5.6 MHz band converted to the intermediate frequency has a distortion of level fluctuation that has an upward slope characteristic with a high level on the low frequency side and a low level on the high frequency side. In such a case, the slope characteristic is flattened by adjusting the variable resistor VR in the tilt circuit 24a shown in FIG. 3 so as to lower the high-frequency low frequency side as shown in FIG. 4B. Can be adjusted.

  FIG. 5 is an explanatory diagram of the slope correction by the tilt circuit 24b provided at the subsequent stage of the SAW filter 25 in FIG. 2. In this case, the high frequency side is high in the 5.6 MHz band of the intermediate frequency as shown in FIG. If the low frequency side has a level distortion with a slope characteristic that rises to the right, the variable resistor VR is applied to the slope circuit 24b having the same circuit configuration as in FIG. By adjusting in the opposite direction, the level on the high frequency side is lowered and corrected to a flat characteristic as shown in FIG.

  In the channel level controller 2a shown in FIG. 2, the level is first adjusted to flat by slope correction in the channel band by the tilt circuits 24a and 24b as shown in FIGS. When adjusting in the tilt circuits 24a and 24b, the output terminal from the band pass filter 29 of the channel level controller 2a is connected to an oscilloscope, and one or both of the tilt circuits 24a and 24b are observed while observing the waveform of the channel band. The level characteristic of the flat channel band is obtained while adjusting the variable resistance VR.

  When the slope adjustment to flatten the channel band is completed by the tilt circuits 24a and 24b, the level is measured by connecting a level measuring device or spectrum analyzer to the output terminal of the mixer 30.

  In the level measurement by the level measuring device, an averaged level of each level in the entire channel band is obtained as a measurement result. In the present invention, the level in the channel band is flattened by adjusting the tilt circuits 24a and 24b prior to the level measurement. Therefore, the measurement result of the average level by the level measuring device accurately represents the signal level in the channel band. When the level measurement by the level measuring device is completed, the level adjuster 28 in FIG. 2 is adjusted so that the measurement level becomes a predetermined specified level.

  When the adjustment of the channel level controller 2a in FIG. 2 has been completed, the remaining channel level controllers 2b to 2n are similarly adjusted to the specified level by correcting the level of the channel band by the tilt circuit to be flat and then measuring the level. Adjust the level.

  In such a state that the channel level controllers 2a to 2n have been adjusted for the tilt circuit and level measured by the level measuring device, the signals of the channels output from the mixer 30 have the same signal level and a level difference. Furthermore, the signal level is flat in each channel band.

  That is, as shown in FIG. 6B, the terrestrial digital broadcasting signals of 20 to 28 channels sent from the transmission point as shown in FIG. 6A are transmitted in the frequency direction as shown in FIG. Even if the signal level has a wavy distortion, the level distortion having a slope in the frequency direction with respect to the channel band is flattened through the channel level controllers 2a to 2n of the present invention shown in FIG. As a result of adjusting the level to a constant level after the adjustment, the output signal from the channel level controller unit 2 is flat in each channel band for 20 channels to 28 channels and has no level difference as shown in FIG. The received signal can be reproduced and sent to the joint receiving facility. .

  Here, the channel level controllers 2b to 2n in FIG. 2 are different from the channel level controller 2a in that the channel frequency is different, so that the local oscillation frequency output from the local oscillator 22 is a frequency unique to each channel. The frequencies of the processing signals in the circuits 24a and 24b and the SAW filter 25 are all the same intermediate frequency 56.857 MHz.

  For this reason, even if the target channels are different, the same circuit can be used as the tilt circuits 24a and 24b for performing the intermediate frequency signal in the channel level controllers 2a to 2n, and the circuit design of the tilt circuits 24a and 24b can be made extremely easy. .

  FIG. 7 is a circuit block diagram showing another embodiment of the channel level controller according to the present invention. The channel level controller 2a for 21 channels is taken as an example. This embodiment is characterized in that tilt circuits 24 a and 24 b are provided before the SAW filter 25.

  Even if the two tilt circuits 24a and 24b are moved to the front stage of the SAW filter 25 as described above, they are used for adjusting different characteristics of the right-up and left-up, respectively. Therefore, the tilt circuits 24a and 24b in FIGS. The slope correction function shown in FIG. 5 is obtained in the same manner as the embodiment of FIG.

  FIG. 8 shows another embodiment of the channel level controller 2a according to the present invention. In this embodiment, two tilt circuits 24a and 24b are provided after the SAW filter 25. In this case, FIG. 4 and FIG. 5 can be corrected to a flat level distortion having a slope in the channel band by the slope adjustment of the left upward and right upward slopes.

  In the above embodiment, the channel allocation of digital terrestrial broadcasting in the Tokyo area was taken as an example. However, the regions of the country starting from now on also correspond to the channel allocation unique to each region, and the present invention is applied to each channel. The channel level controller can be applied as it is.

The present invention is not limited to the above-described embodiment, includes appropriate modifications that do not impair the object and advantages thereof, and is not limited by the numerical values shown in the above-described embodiment.

1: UHF antenna 2: Channel level control units 2a to 2n: Channel level controller 15: Branching device 16, 29: Band pass filter 17, 27: Amplifier 18: Mixer (first frequency converter)
19: Channel SW
20: CPU
21: PLL
22: Local oscillators 24a, 24b: Tilt circuit 25: SAW filter 26: Mixer (second frequency converter)
28: Level adjuster 30: Mixer

Claims (4)

The terrestrial digital broadcast signal received by the antenna is branched into a plurality of channel level controllers by a branching unit, and the plurality of channel level controllers adjust a specific broadcast channel signal separated from the branched terrestrial digital broadcast signal to a specified level. In a channel level control unit that mixes with a mixer and outputs to a common reception facility,
Each of the plurality of channel level controllers includes:
A bandpass filter for separating a specific broadcast channel signal from the terrestrial digital broadcast signal branched by the branching device;
An oscillator that oscillates a channel setting signal of a natural frequency corresponding to a broadcast channel signal separated by the bandpass filter;
A first frequency converter that down-converts a specific broadcast channel signal separated by the band-pass filter into an intermediate frequency signal having the same frequency in all channel level controllers by a channel setting signal from the oscillator;
A SAW filter for removing unnecessary components outside the channel band from the intermediate frequency signal from the first frequency converter;
A second frequency converter for upconverting the intermediate frequency signal from the SAW filter to the frequency of the original broadcast channel signal by the channel setting signal from the oscillator;
A level adjuster that adjusts the level of the broadcast channel signal from the second frequency converter to a specified level and then outputs the signal to the mixer through a band-pass filter;
A tilt circuit which is provided between the first frequency converter and the second frequency converter and which flatly corrects the level gradient in the channel frequency band of the intermediate frequency signal;
With
The tilt circuit is
A first tilt circuit that flatly corrects a tilt characteristic whose level increases with an increase in frequency;
A second tilt circuit that flatly corrects a tilt characteristic whose level decreases with increasing frequency;
A channel level control unit characterized by comprising
2. The channel level control unit according to claim 1, wherein the channel level controller is provided with the first tilt circuit and the second tilt circuit divided into a front stage and a rear stage of the SAW filter. unit.
2. The channel level control unit according to claim 1, wherein the channel level controller is provided with the first tilt circuit and the second tilt circuit in front of the SAW filter.
  2. The channel level control unit according to claim 1, wherein the channel level controller is provided with the first tilt circuit and the second tilt circuit in a subsequent stage of the SAW filter.

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