JP2004304756A - Quadrature detection circuit and offset beat canceller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To execute the quadrature detection of a received signal highly precisely by setting a carrier used for the quadrature detection and the received signal in a regular phase in a quadrature detection circuit for applying the quadrature detection to the received signal by using a carrier recovered from the received signal. <P>SOLUTION: In an offset beat canceller wherein quadrature detection is applied to a video IF signal obtained by selecting a television broadcast signal of a prescribed broadcast channel from a received signal, a interference wave signal components are produced from a Q signal after the quadrature detection, and the signal components are eliminated from the I signal after the quadrature detection to produce a video signal with no interference wave signal components, the quadrature detection section 32 used for applying quadrature detection to the video IF signal is configured so that the video IF signal is subjected to quadrature detection by using the video carrier recovered from the video IF signal and a phase adjustment section 80 applies feedback control to the phase of the video carrier so that a voltage (average voltage) of the Q signal after the quadrature detection is almost zero. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a quadrature detection circuit that performs quadrature detection on a received signal using a carrier reproduced from the received signal, and an offset beat canceller using the quadrature detection circuit.

  2. Description of the Related Art Conventionally, when performing a television broadcast using the same broadcast channel in an adjacent area, an offset of ± 10.01 kHz is provided to a transmission frequency of each television broadcast signal, and a video signal is reproduced by a television receiver. To make the stripes (beats) appearing on the screen less noticeable. However, if the amount of the interfering wave is large, the beat will appear significantly, and there is a demand for better image quality from the viewer.

Therefore, in recent years, in order to prevent such a beat failure, a TV intermediate signal (hereinafter, also referred to as a video IF signal) obtained by frequency-converting a television broadcast signal of a broadcast channel in which a beat failure occurs into a predetermined frequency band is used. The Q carrier including the interference wave signal component is generated by reproducing the video carrier of the above and the quadrature detection of the video IF signal is performed using the video carrier, and further, the interference is generated from the generated Q signal using the analog filter. There has been proposed an offset beat canceller that generates a wave signal component and removes this interference wave signal component from the video IF signal (for example, see Patent Documents 1 and 2).
JP-A-8-98061 JP-A-9-55671

  By the way, in the proposed offset beat canceller, in order to generate an interference wave signal component from a video intermediate frequency signal obtained by selecting a received television broadcast signal, a video carrier is reproduced from the video intermediate frequency signal, The video intermediate frequency signal is subjected to quadrature detection using the reproduced video carrier, but if the phase of the video carrier used for the quadrature detection and the video intermediate frequency signal are shifted, the Q signal obtained by the quadrature detection becomes the original signal. Therefore, there is a problem that an interference wave signal component cannot be accurately generated from the Q signal.

  The present invention has been made in view of such a problem, and is used in the above-described offset beat canceller and the like, and is used in quadrature detection in a quadrature detection circuit that performs quadrature detection of a received signal using a carrier reproduced from the received signal. It is an object of the present invention to set a carrier and a received signal to normal phases so that quadrature detection of the received signal can be performed with high accuracy.

  In order to achieve the above object, the invention according to claim 1 provides a carrier regenerating unit for regenerating a carrier contained in a received signal, and mixing the carrier reproduced by the carrier regenerating unit and the received signal in phase. And a second detector for generating a Q signal by mixing the carrier recovered by the carrier recovery unit and the received signal by shifting the phase of each signal by 90 degrees. A quadrature detection circuit including a detection unit, wherein the Q signal generated by the second detection unit is reproduced by the carrier reproduction unit such that the voltage (specifically, the average voltage) of the Q signal becomes substantially zero. A phase adjuster for adjusting the phase of the carrier is provided, and the carrier adjusted in phase by the phase adjuster is input to the first detector and the second detector.

  That is, in the quadrature detection circuit of the present invention, the Q signal generated in the second detection section is fed back, and the phase of the carrier reproduced from the reception signal is adjusted so that the average voltage becomes substantially zero. , Q signal is a sine wave consisting of only true interference signal components, and adjusts the phase of the carrier used for quadrature detection so that the phase of the carrier used for quadrature detection and the phase of the received signal have the same phase or a 90 degree phase difference You do it.

  As a result, according to the quadrature detection circuit of the present invention, the quadrature detection of the received signal can always be executed with high accuracy. For example, the characteristics of the circuit elements constituting the quadrature detection circuit may be changed over time or temperature. , It is possible to execute highly accurate quadrature detection without being affected by the characteristic change.

  In the quadrature detection circuit of the present invention, when performing quadrature detection on a received signal, the first detection unit mixes the carrier and the reception signal, and the second detection unit shifts the phase of the carrier by 90 degrees (delay). The received signal and the received signal may be mixed. Alternatively, the carrier and the received signal are mixed in the first detector, and the phase of the received signal is shifted (delayed) by 90 degrees in the second detector. And a carrier may be mixed.

  Then, as in the latter case, in the case where the Q signal is generated by mixing the carrier obtained by shifting the phase of the received signal by 90 degrees (delay) with the carrier in the second detector, It is necessary that the phase of the received signal mixed with the carrier in the first detector is shifted from the received signal mixed with the carrier in the second detector by 90 degrees in the entire frequency domain. It is desirable that the quadrature detection circuit is configured as described in claim 2.

  That is, in the quadrature detection circuit according to the second aspect, in the quadrature detection circuit according to the first aspect, the second detection unit passes through the phase shifter that shifts the phase of the received signal by 90 degrees and the phase shifter. A mixer that mixes the received signal with the carrier wave whose phase has been adjusted by the phase adjustment unit, wherein the first detection unit detects that the phase of the reception signal mixed with the carrier wave has passed through the phase shifter of the second detection unit; A delay line for delaying the received signal in accordance with the operation characteristics of the phase shifter so that the received signal is shifted by 90 degrees in the entire frequency range, and the phase of the received signal passing through the delay line is adjusted by a phase adjusting unit A mixer for mixing the carrier with the carrier.

  Therefore, according to the quadrature detection circuit of the second aspect, the phase shifter of the second detection unit cannot accurately shift (delay) the phase of the received signal by 90 degrees in the entire frequency domain. Therefore, the phase difference of the received signal input to the mixer in each detector can be made a phase difference of 90 degrees in the entire frequency domain, and the I signal and the Q signal can be accurately corrected in each detector. Can be generated.

  Next, according to a third aspect of the present invention, a television broadcast signal of a predetermined broadcast channel including an interference wave having a transmission frequency offset by a predetermined frequency from a desired wave is selected from the reception signals input from the reception antenna. Tuning means for outputting a video intermediate frequency signal and an audio intermediate frequency signal of the television broadcast signal; and quadrature detection of the video intermediate frequency signal output from the channel selecting means, thereby obtaining the video intermediate frequency signal. A video signal processing means for generating a video signal or a video intermediate frequency signal from which the generated interference signal component has been removed, and a video signal or a video signal generated by the video signal processing means. A television broadcast signal generating means for generating a television broadcast signal of a predetermined broadcast channel based on a video intermediate frequency signal and an audio intermediate frequency signal output from the channel selecting and demodulating means; An offset beat canceller that outputs the generated television broadcast signal as a reception signal, wherein the video signal processing means is a quadrature detection circuit used for quadrature detection of the video intermediate frequency signal. A quadrature detection circuit according to claim 1 or 2.

  As described above, in the offset beat canceller of the present invention, the quadrature detection circuit according to claim 1 or 2 is used when quadrature detection of the video intermediate frequency signal is performed by the video signal processing means. Therefore, the video carrier used for quadrature detection and the video intermediate frequency signal can be accurately set to the same phase or a phase difference of 90 degrees, and the quadrature detection of the video intermediate frequency signal can be performed with high accuracy.

  Therefore, the video signal processing means accurately generates an interference signal component contained in the video intermediate frequency signal from the Q signal obtained by the quadrature detection, and converts the interference signal component from the video intermediate frequency signal or the baseband video signal into an interference signal. The signal component can be accurately removed.

  Here, in the offset beat canceller according to claim 3, as the video signal processing means, similarly to the conventional offset beat canceller described in the section of the related art, the video intermediate frequency signal is obtained by using the above quadrature detection circuit. A quadrature detection generates a Q signal including an interference signal component, generates an interference signal component from the generated Q signal using an analog filter, and removes the generated interference signal component from the video intermediate frequency signal. May be configured.

  However, if an analog filter is used to generate an interference wave signal component from a Q signal obtained by quadrature detection as in the related art, an offset beat canceller is used to stabilize the filter characteristics of the analog filter. There is a problem that it must be used in an environment where temperature changes are small.

  Therefore, in order to enable the offset beat canceller described in claim 3 to be used in an environment with a large temperature change, the video signal processing means may be configured as described in claim 4.

  That is, in the offset beat canceller according to claim 4, the video signal processing means generates an I signal and a Q signal by performing quadrature detection on the video intermediate frequency signal using the quadrature detection circuit. A / D conversion and digital processing of the Q signal generate an interference signal component included in the I signal, and the generated interference signal component is removed from the I signal, thereby obtaining the interference signal component. It is configured to generate a video signal from which is removed.

  Therefore, according to the offset beat canceller of the fourth aspect, the video signal processing means generates an interference wave signal component by digitally processing the Q signal obtained by orthogonally detecting the video intermediate frequency signal. Therefore, it is possible to stably generate the interference wave signal component without being affected by the ambient temperature, for example, even if installed in an environment with a large temperature change to perform home joint reception and the like, The interference wave signal component can be satisfactorily removed from the received television broadcast signal.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram showing a configuration of an entire television broadcast receiving system according to a first embodiment to which the present invention is applied. It should be noted that the television broadcast receiving system of the present embodiment is for domestic use in Japan, and television broadcasts in the VHF band and the UHF band described below are performed by the NTSC system having a bandwidth of 6 MHz.

  As shown in FIG. 1, the television broadcast receiving system according to the present embodiment is a joint receiving system for transmitting a reception signal from an antenna installed outdoors to each room in a building via a transmission line. VHF antenna 2 and UHF antenna 4 for receiving VHF band and UHF band broadcast waves transmitted from a ground station, respectively, and receive transmission waves from a broadcast satellite (BS) and a communication satellite (CS). A BS / CS antenna 6;

  The BS / CS antenna 6 includes a reflecting mirror 6a and a receiving unit 6b disposed at a focal point of the reflecting mirror 6a via a supporting arm. The received signal is transmitted to a BS / CS by a converter built in the receiving unit 6b. / CS-IF signal is frequency-converted (down-converted) and output.

  The received signals (VHF received signal, UHF received signal, BS / CS-IF signal) from each of these receiving antennas 2 to 6 are transmitted to a booster (amplifier) 8 via a transmission line composed of a coaxial cable. The booster 8 amplifies the signal to a predetermined level. Each of the received signals (VHF received signal, UHF received signal, BS / CS-IF signal) amplified by the booster 8 is mixed in the booster 8 and input to an offset beat canceller 20 at a subsequent stage, where The signal is output from the beat canceller 20 to the transmission line on the terminal side.

  A distributor 10 is connected to the transmission line on the terminal side, and the received signal output from the offset beat canceller 20 is distributed by the distributor 10 to a plurality of systems (four systems in the figure). The signals are transmitted to the receiving terminals in the rooms where the respective serial units 12 are installed, via the plurality of serial units 12 connected in series on the distributed transmission lines of the respective systems.

Next, the configuration of the offset beat canceller 20 will be described in detail with reference to FIG.
As shown in FIG. 2, the offset beat canceller 20 includes an input terminal Tin for inputting a reception signal output from the booster 8 via a transmission line (coaxial cable), and an output terminal Tout for outputting a reception signal. And

  The BS / CS-IF signal among the received signals input to the input terminal Tin is internally provided via a high-pass filter (hereinafter, a high-pass filter is referred to as an HPF) 24 that selectively passes only this signal. The signal is fetched and transmitted to the output terminal Tout via the BS / CS-IF signal passing path formed in the beat canceller 20 and the HPF 26 provided on the output terminal Tout side, and transmitted from the output terminal Tout to the terminal. Output to the side.

  Also, of the received signals input to the input terminal Tin, the VHF received signal and the UHF received signal are low-pass filters that selectively pass only received signals in the VHF and UHF bands (hereinafter, the low-pass filter is referred to as LPF). The signal is taken into the inside via the circuit 22 and is divided into two by the distribution circuit 28. One of the received signals (VHF / UHF signals) distributed by the distribution circuit 28 passes through a VHF / UHF signal passing path formed in the beat canceller 20, and is output to the output terminal Tout side mixing circuit. 42.

  On the other hand, the other reception signal distributed by the distribution circuit 28 is input to the UHF tuning unit 30. The UHF tuning unit 30 tunes a television broadcast signal of a predetermined broadcast channel in the UHF band specified by the control channel control signal from the control unit 50, and the video carrier becomes a predetermined frequency (for example, 58.75 MHz). It outputs a video intermediate frequency signal (video IF signal) and an audio intermediate frequency signal (audio IF signal) whose audio carrier has a predetermined frequency (4.5 MHz) specified by the NTSC system. The UHF tuning unit 30 corresponds to a tuning unit of the present invention.

  The video IF signal output from the UHF tuning unit 30 is input to the quadrature detection unit 32, where the quadrature detection unit 32 performs quadrature detection using the video carrier included in the video IF signal. The I signal and the Q signal that have been subjected to quadrature detection by the quadrature detection unit 32 are input to a beat cancellation digital processing unit 34, and the digital processing unit 34 removes the baseband signal component from the interference signal component. Video signal.

  Then, the video signal and the audio IF signal output from the UHF tuning unit 30 are respectively input to the UHF modulation unit 36, where the UHF modulation unit 36 specifies the video IF signal by the output channel control signal from the control unit 50. It is converted into a UHF band television broadcast signal of the predetermined broadcast channel (output channel).

  The UHF modulation unit 36 corresponds to the television broadcast signal generation unit of the present invention. However, the UHF modulation unit 36 is not necessarily a UHF band like the UHF modulation unit 36 of the present embodiment. It is not necessary to generate a TV broadcast signal, and a TV broadcast signal of a VHF band channel or a CATV channel may be generated.

  Next, the television broadcast signal generated by the UHF modulation section 36 passes through a band-pass filter 38 (hereinafter, the band-pass filter is referred to as BPF) 38 that selectively allows only the UHF band television broadcast signal. Is input to an amplifying unit 40 having a gain control (GC) volume VR, and is amplified to a predetermined level by the amplifying unit 40 before being input to a mixing circuit 42.

  As a result, the mixing circuit 42 mixes the VHF / UHF signal passed through the VHF / UHF signal passage and the television broadcast signal of the predetermined output channel generated by the UHF modulator 36.

  The VHF / UHF signal mixed by the mixing circuit 42 is further amplified to a predetermined level by the amplifier circuit 44, and then passed through the LPF 46 that selectively passes only the reception signals in the VHF and UHF bands. The signal is transmitted to the output terminal Tout, and output from the output terminal Tout to the terminal together with the BS / CS-IF signal.

  Here, the digital processing unit 34 and the quadrature detection unit 32 correspond to video signal processing means of the present invention. In the present embodiment, the digital processing unit 34 digitally processes the Q signal, An interference signal component included in the signal is generated, and the interference signal component is removed from the I signal.

That is, the desired wave video signal included in the video IF signal is A (t), its carrier (video carrier) is cos (ωt), the interference wave video signal is B (t), and its carrier (video carrier) is cos ｛. If (ω + δ) t + Φ｝, the video IF signal is
Video IF signal = A (t) cos (ωt)
+ B (t) cos {(ω + δ) t + Φ}
And the I signal and Q signal after quadrature detection are
I signal = A (t) + B (t) cos (δt + Φ)
Q signal = B (t) sin (δt + Φ)
Accordingly, the digital processing unit 34 digitally processes the Q signal to generate “B (t) cos (δt + Φ)” which is an interference signal component included in the I signal, and generates the interference signal component. Is removed from the I signal.

  Specifically, in order to remove beats from a reproduced television image, it is sufficient to remove an interfering signal component with respect to a low-frequency component (frequency: 0 to several tens of kHz) of the video signal. Then, as shown in FIG. 3, first, a Q signal is captured as digital data via an A / D converter 60, and the captured Q signal is filtered by a filter 62 functioning as an LPF. Only the low-frequency component of the Q signal is extracted, and the beat component generation unit 64 generates the interference signal component “B (t) cos (δt + Φ)” from the extracted low-frequency component of the Q signal.

  Further, the digital processing unit 34 fetches the I signal as digital data via the A / D conversion unit 61, and converts the fetched I signal into a filter unit 63 functioning as an LPF and a filter unit 67 functioning as an HPF. To separate the low frequency component and the high frequency component of the I signal.

  Then, the interference wave signal component output from the beat component generation unit 64 is delayed by the processing operation of the beat component generation unit 64 from the low-frequency component and the high-frequency component of the I signal that has passed through each of the filter units 63 and 67. In order to synchronize the low-frequency component and the high-frequency component of the I signal passed through the filter units 63 and 67 with the interference signal component generated by the beat component generation unit 64, the low-frequency component and the high-frequency component of the I signal The components are delayed by delay processors 65 and 68, respectively.

  Finally, the subtraction unit 66 performs a subtraction process of subtracting the interference signal component generated by the beat component generation unit 64 from the low-frequency component of the I signal after the delay process. The low frequency component of the I signal and the high frequency component of the I signal after the delay processing are added by the addition processing unit 69 to generate a video signal (specifically, video data) from which the interference signal component is removed. After this is converted into an analog video signal by the D / A converter 69a, it is output to the BPF 38.

  Therefore, the digital processing unit 34 outputs a video signal from which the interference wave signal component causing the offset beat failure is removed, and the digital processing unit 34 outputs the I signal and the Q signal after quadrature detection. Is converted to digital data and digitally processed to generate a video signal from which the interference signal component has been removed, so that the video signal from which the interference signal component has been removed can be stabilized without being affected by the ambient temperature. Can be generated.

  Next, the offset beat canceller 20 is provided with an output channel setting section 48 so that the broadcast channel (output channel) of the television broadcast signal generated by the UHF modulation section 36 can be set by an external operation.

  The control unit 50 is configured by a microcomputer, and in accordance with an output channel setting command input from the output channel setting unit 48, a broadcast channel (output) when the UHF modulation unit 36 generates a television broadcast signal. Channel).

  The channel selected by the UHF channel selector 30 is stored in the EEPROM 52 in advance, and the controller 50 fixes the channel selected by the UHF channel selector 30 to the channel stored in the EEPROM 52.

  The offset beat canceller 20 is provided with a power input terminal Tdc for supplying a DC power of, for example, 15 V from a DC adapter or the like (not shown). Each of the internal circuits described above has a power input terminal Tdc. A power supply voltage for operation is supplied from a supplied DC power supply via a power supply unit 56 that generates various power supply voltages for operating the above-described internal circuit.

  By the way, in the offset beat canceller 20 of the present embodiment, the digital processing unit 34 digitally processes the Q signal obtained by the quadrature detection unit 32 to generate an interference wave signal component included in the video signal. Is removed from the I signal, so that the interference signal component can be removed without being affected by the ambient temperature, as compared with a conventional offset beat canceller that generates an interference signal component using an analog filter. However, if the phase of the carrier used for orthogonal detection of the video IF signal in the orthogonal detection unit 32 deviates from the normal phase, the quadrature detection of the video IF signal can be accurately performed. However, there is a problem that the characteristic of removing the interference wave signal component is eventually deteriorated.

Therefore, in the offset beat canceller 20 of the present embodiment, the quadrature detection unit 32 is configured as shown in FIG. 4 so that the quadrature detection of the video IF signal can always be optimally executed.
That is, as shown in FIG. 4, the quadrature detection unit 32 of the present embodiment includes a distribution circuit 70 that distributes the video IF signal output from the UHF tuning unit 30 into two, and one of the distribution circuits 70 that is distributed by the distribution circuit 70. An amplification circuit 71 for amplifying the video IF signal, a distribution circuit 72 for further dividing the video IF signal amplified by the amplification circuit 71 into two, and a phase of one of the video IF signals distributed by the distribution circuit 72 is set to 90 degrees. The phase of the other video IF signal distributed by the (π / 2) phase shifter 74 and the distribution circuit 72 is 90 degrees in the entire frequency domain with respect to the video IF signal passed through the phase shifter 74. A delay line 73 for delaying the other video IF signal in accordance with the operation characteristics of the phase shifter 74 so as to be shifted, a video IF signal passing through the delay line 73 and the phase shifter 74, and a carrier reproduction unit 77 described later. Video playback played on It comprises a pair of mixers 75 and 76 for mixing preparative respectively.

  The quadrature detection unit 32 also transfers a carrier reproduction unit 77 that reproduces a video carrier from the other video IF signal distributed by the first-stage distribution circuit 70, and transfers the video carrier reproduced by the carrier reproduction unit 77. There is provided a variable phase shifter 78 for phase-shifting, and a distribution circuit 79 for splitting the video carrier wave having passed through the variable phase shifter 78 into two and outputting the same to the mixers 75 and 76.

  Here, the mixers 75 and 76 perform quadrature detection of the video IF signal by mixing the video IF signal passed through the delay line 73 and the phase shifter 74 with the video carrier input from the distribution circuit 79, respectively. belongs to. That is, the mixer 75 generates an I signal by mixing the video IF signal passing through the delay line 73 and the video carrier having the same phase as the video IF signal, and the mixer 76 generates the I signal by passing through the phase shifter 74. A Q signal is generated by mixing with a video carrier having a phase advanced by 90 degrees (π / 2).

  Then, the I signal and the Q signal after the synchronous detection generated by these mixers 75 and 76 are input to amplification circuits 83 and 84 via LPFs 81 and 82 that selectively pass the signal components. After being amplified to a predetermined level by the amplifier circuits 83 and 84, the signal is output to the digital processing unit 34.

  Further, the Q signal output from the amplifier circuit 84 is taken into the quadrature detection unit 32 of the present embodiment, and the voltage of the variable phase shifter 78 is set so that the voltage of the Q signal (specifically, the average voltage) becomes substantially zero. A phase adjuster 80 is provided for adjusting the phase of the video carrier input to each of the mixers 75 and 76 by controlling the amount of phase shift of the video carrier.

  As a result, in the quadrature detection section 32 of the present embodiment, the operation of the phase adjustment section 80 allows the video IF signals input to the mixers 75 and 76 and the video carrier to have the same phase or a phase difference of 90 degrees. The video IF signal can be accurately orthogonally detected using the video carrier reproduced by the carrier reproducing unit 77.

  Therefore, according to the offset beat canceller 20 of the present embodiment, the digital processing unit 34 uses the Q signal obtained by the quadrature detection unit 32 to accurately generate an interference wave signal component included in the video IF signal. By removing the interference signal component from the I signal, it is possible to accurately restore a video signal free of the interference signal component.

  In the present embodiment, the quadrature detection unit 32 corresponds to the quadrature detection circuit of the present invention. Further, the delay line 73 and the mixer 75, and the phase shifter 74 and the mixer 76 used for orthogonally detecting the video IF signal in the orthogonal detection unit 32 are respectively provided in the present invention (specifically, described in claim 2). It corresponds to a first detector and a second detector.

As mentioned above, although one Example of this invention was described, this invention is not limited to the said Example, A various aspect can be employ | adopted.
For example, in the quadrature detection unit 32 of the above embodiment, the I signal is generated by the mixer 75 and the Q signal is generated by the mixer 76, so that the input path of the video IF signal to each of the mixers 75 and 76 is Although the delay line 73 and the phase shifter 74 have been described as being provided, as shown in FIG. 5, if the phase shifter 74 is provided on the input path of the video carrier to the mixer 76, Without providing the delay line 73 and the phase shifter 74 in the input path of the video IF signal, the mixer 75 can generate the I signal and the mixer 76 can generate the Q signal.

  In the above-described embodiment, the digital processing unit 34 is described as separating the I signal into a low-frequency component and a high-frequency component. However, the I signal does not necessarily need to be separated, and the A / D converter 61 Alternatively, the I / A signal obtained by the A / D conversion may be directly delayed by the delay processing unit to remove the interference signal component from the I signal.

  In the above embodiment, the digital processing unit 34 is used to remove the interference wave signal component. However, as in the above-described conventional apparatus, the Q signal obtained by performing quadrature detection on the video IF signal is used. An interference filter is generated using an analog filter, the interference signal is up-converted to a frequency corresponding to the video IF signal, and the up-converted interference signal is removed from the video IF signal. You may. However, in this case, it is necessary to use the offset beat canceller in an environment where the temperature change is small so that the characteristics of the offset beat canceller do not change.

  Furthermore, in the above embodiment, the case where the present invention is applied to the offset beat canceller has been described. However, the present invention is not limited to the quadrature detection circuit used in the offset beat canceller, and the present invention is applied to the reception using the carrier reproduced from the received signal. If it is a quadrature detection circuit that performs quadrature detection of a signal, the same effect can be obtained by applying the same as in the above embodiment.

FIG. 1 is a schematic configuration diagram illustrating a configuration of an entire television broadcast receiving system according to an embodiment. FIG. 2 is a block diagram illustrating a configuration of an offset beat canceller illustrated in FIG. 1. FIG. 3 is a block diagram illustrating a configuration of a digital processing unit illustrated in FIG. 2. FIG. 3 is a block diagram illustrating a configuration of a quadrature detection unit illustrated in FIG. 2. FIG. 5 is a block diagram illustrating another configuration example of the quadrature detection unit illustrated in FIG. 2.

Explanation of reference numerals

2 VHF antenna, 4 UHF antenna, 6 BS / CS antenna, 8 booster, 10 distributor, 12 serial unit, 20 offset beat canceller, 22, 46, 81, 82 LPF, 24, 26 .. HPF, 28 distribution circuit, 30 UHF tuner, 32 quadrature detector, 34 digital processor, 36 UHF modulator, 38 BPF, 40 amplifier, 42 mixing circuit, 44, 83, 84 amplifier circuit, 48 output channel setting unit, 50 control unit, 52 EEPROM, 56 power supply unit, 60, 61 A / D converter unit, 62, 63, 67 filter unit, 64 beat component generation , 65, 68 ... delay processing section, 66 ... subtraction processing section, 69 ... addition processing section, 69a ... D / A conversion section, 70, 72, 79 ... distribution circuit, 71 ... amplification circuit, 73 ... delay line, 74 Phase shifter, 75 and 76 ... mixer, 77 ... carrier recovery unit, 78 ... variable phase shifter, 80 ... phase adjustment portion, Tdc ... power input terminal, Tin ... input terminal, Tout ... output terminal, VR ... volume.

Claims (4)

A carrier recovery unit that recovers a carrier wave included in the received signal;
A first detector that generates an I signal by mixing the received signal and the carrier reproduced by the carrier reproducer in phase.
A second detection unit that generates a Q signal by mixing the carrier reproduced by the carrier reproduction unit and the received signal while shifting the phase of each signal by 90 degrees;
A quadrature detection circuit comprising:
A phase adjuster that adjusts the phase of the carrier reproduced by the carrier reproducer so that the voltage of the Q signal generated by the second detector becomes substantially zero;
A quadrature detection circuit configured to input the carrier wave adjusted in phase by the phase adjustment unit to the first detection unit and the second detection unit. The second detector includes a phase shifter that shifts the phase of the received signal by 90 degrees, and a mixer that mixes the received signal that has passed through the phase shifter with the carrier that has been phase adjusted by the phase adjuster. ,
The first detection unit, the received signal mixed with the carrier, the received signal passed through the phase shifter of the second detection unit 90 degrees in the entire frequency range of the received signal, the received signal, the received signal A delay line that delays according to the operation characteristics of the phase shifter, and a mixer that mixes the reception signal that has passed through the delay line and the carrier wave that has been phase adjusted by the phase adjustment unit,
The quadrature detection circuit according to claim 1, wherein From among the received signals input from the receiving antenna, a TV broadcast signal of a predetermined broadcast channel including an interference wave whose transmission frequency is offset by a predetermined frequency with respect to a desired wave is selected, and a video intermediate frequency of the TV broadcast signal is selected. Channel selecting means for outputting a signal and an audio intermediate frequency signal,
By performing quadrature detection on the video intermediate frequency signal output from the channel selection means, an interference signal component contained in the video intermediate frequency signal is generated, and the generated video signal or video intermediate signal is removed. Video signal processing means for generating a frequency signal;
TV broadcast signal generation for generating a TV broadcast signal of a predetermined broadcast channel based on a video signal or a video intermediate frequency signal generated by the video signal processing means and an audio intermediate frequency signal output from the channel selection demodulation means. Means,
Comprising, an offset beat canceller that outputs the generated television broadcast signal as a received signal,
3. The offset beat canceller according to claim 1, wherein said video signal processing means includes a quadrature detection circuit according to claim 1 or 2 as a quadrature detection circuit used for quadrature detection of said video intermediate frequency signal. The video signal processing means generates an I signal and a Q signal by performing quadrature detection on the video intermediate frequency signal using the quadrature detection circuit, and A / D converts the generated Q signal to perform digital processing. Generating an interference signal component included in the I signal, and removing the generated interference signal component from the I signal, thereby generating a video signal from which the interference signal component has been removed. The offset beat canceller according to claim 3, wherein

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