JP3560427B2 - Television broadcast receiver - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a mobile receiver for terrestrial television broadcasting transmitted by an amplitude modulation method, and particularly to a filter for emphasizing a video signal near a video carrier frequency and a color subcarrier frequency to relieve multipath interference. The present invention relates to preventing loss of sharpness of a contour due to restriction of a high frequency range by a circuit.
[0002]
[Prior art]
As the television broadcast receiving apparatus, there is one described in Japanese Patent Application No. Hei 6-130699. In this description, a correction circuit is provided on a transmission path between an antenna and a video detection circuit. This correction circuit has a filter for changing the transfer characteristic (intermediate frequency stage or high frequency stage) of the transmission line, detects a multipath from a disturbance of the horizontal synchronization signal (about 15.7 kHz), and detects the resonance characteristic of the filter. To enhance the vicinity of the video carrier frequency and the vicinity of the color subcarrier frequency. This is because, when affected by the selective fading of multi-path (multi-path propagation) in the vicinity of the video carrier frequency, the reception level in the vicinity is reduced, the synchronization is disturbed, the hue is changed, and the color This is because if the signal is affected by a multipath having an opposite phase near the carrier frequency, the color disappears (black and white), and the received image is disturbed. Therefore, even if there is multipath interference and the reception level is reduced, the influence of the multipath interference is reduced by enhancing the vicinity of the video carrier frequency and the vicinity of the color subcarrier frequency by the filter of the correction circuit.
[0003]
[Problems to be solved by the invention]
By the way, in the above-described television broadcast receiving apparatus, as described above, when a multipath is detected, the transmission characteristics change so as to emphasize frequency components near the video carrier frequency. However, since the AGC (automatic gain adjustment circuit) of the television broadcast receiver operates by detecting the peak value of the horizontal synchronization signal, if the low frequency component near the video carrier frequency including the horizontal synchronization signal is emphasized. In the demodulated output, there is a problem that a frequency component in a relatively high frequency band is reduced. That is, it is as if it had been subjected to a kind of low-pass filter. For this reason, when the circuit that corrects the transmission characteristics due to multipath operates, the high-frequency band of the video signal is restricted, and the sharpness of the outline of the received video, particularly a small subject, is reduced, and the character super is difficult to see. The problem occurs. This is because the image luminance signal includes a high frequency in addition to the base signal where the luminance signal changes in a step-like manner at the image contour portion, and a wide band is required for faithful reproduction.
[0004]
SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a television broadcast receiving apparatus capable of preventing loss of sharpness of a contour due to band limitation of frequency characteristic correction.
[0005]
[Means for Solving the Problems]
The present invention provides a television broadcast receiver having an automatic gain control circuit that receives a video carrier signal, a color subcarrier signal, and a video signal including a horizontal synchronization signal, and uses the horizontal synchronization signal in order to solve the above-described problems. A first video signal emphasizing means for emphasizing a video signal near the video carrier frequency and the color sub-carrier frequency, a frequency characteristic correction circuit for recovering a video signal whose high frequency component is limited by the automatic gain circuit, and A control circuit is provided for controlling the operations of the first video signal enhancement means and the frequency characteristic correction circuit with a control signal which detects a multipath signal from a signal reception state and removes its high frequency component. By this means, it is possible to improve the disturbance of the received image at the time of occurrence of the multipath and to improve the contour blur generated in the video signal whose high frequency component is restricted by the automatic gain circuit.
[0006]
The first video signal enhancement means varies the enhancement of the video signal in the vicinity of the video carrier frequency and the color sub-carrier frequency in accordance with the size of the multipath state, and the frequency characteristic correction circuit interlocks with the enhancement. To recover the video signal. By this means, it is possible to always obtain an optimal received video.
The control circuit operates the first video signal emphasizing means even though multipath is eliminated due to a control delay caused by a circuit time constant for removing the high-frequency component. Only when is the frequency characteristic correction circuit operated. By this means, the contour blur is effectively corrected when a malfunction occurs due to the control delay of the control circuit, where the contour blur of the received video is most noticeable.
[0007]
When the automatic gain control circuit determines that the intensity of the input video signal is low, the operation of the frequency characteristic correction circuit is stopped. By this means, it is possible to prevent the noise from rising when the sand storm occurs due to the small input video signal.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing an example of a television broadcast receiving apparatus according to the present invention. As shown in FIG. 1, the television broadcast receiving apparatus includes an antenna 1 for receiving a broadcast wave having a frequency fr, a high-frequency amplifier 2 for amplifying a received signal, and a mixer for receiving the amplified signal and forming an intermediate frequency signal fif. 3, a local oscillator 4 for outputting a local oscillation signal fL0 to the mixer 3 to form an intermediate frequency signal of fif = fL0-fr, and a band limiting filter 5 connected to the mixer 4 for controlling a frequency band. And a Q variable filter 6 as first video signal enhancement means for controlling Q (sharpness of resonance of the tuning circuit) so as to enhance the video carrier frequency fv and the color sub-carrier frequency fsc so that they become resonance frequencies. An intermediate frequency amplifier 7 connected thereto for amplifying an intermediate frequency region, a video detector 8 connected thereto for detecting a video signal, and a synchronization signal extracted from the video signal connected thereto. A synchronization signal processing unit 9 connected thereto, a reception state detector 10 for detecting a reception state (a large signal is output when multipath interference increases) from disturbance of a horizontal synchronization signal among the synchronization signals, and a connection therewith When the horizontal synchronizing signal is disturbed, the control circuit 11 for controlling the Q variable filter 6 to emphasize the video carrier frequency fv and the color sub-carrier frequency fsc, and the video signal y connected to the video detector 8 A YC separation unit 12 for separating into a color signal c, a frequency characteristic correction circuit (enhancer) 13 connected thereto for correcting the frequency characteristic emphasized by the Q variable filter 6, and an inversion terminal for a signal from the control circuit 11 And a comparator 14 for inputting the threshold value VTH0 to the non-inverting terminal to control the operation of the frequency characteristic correction circuit 13, a synchronizing signal from the synchronizing signal processing unit 9, and a synchronizing signal from the YC separating unit 12. A display unit 15 for inputting the color signal c and the video signal y from the frequency characteristic correction circuit, and an AGC circuit 16 for controlling the gain of the intermediate wave amplifier 7 using the peak value of the horizontal synchronization signal from the synchronization signal processing unit 9 And
[0009]
FIG. 2 is a diagram illustrating characteristics of the Q variable filter 6 of FIG. FIG. 3A shows frequency characteristics input from the band limiting filter 5 to the Q variable filter 6. FIG. 3B shows the frequency characteristic of the Q variable filter 6. As shown in FIG. 3B, the Q variable filter 6 has a flat characteristic when there is no correction (Q: minimum), and has a video carrier frequency fv when there is correction (Q: maximum). Have a peak at the color subcarrier frequency fsc. FIG. 3C shows the characteristics of the video signal of the output signal of the video detector 8. As shown in the figure, when the AGC circuit 16 operates, the level decreases in the high frequency band (1-2 MHz) indicated by the solid line with respect to the dotted line in the case where the Q variable filter 6 is not corrected and in the case where the correction is performed. It will be great. In this state, as described above, the sharpness of the contour portion is reduced. Here, 0 MHz corresponds to the video carrier frequency, and 3.58 MHz corresponds to the color sub-carrier frequency.
[0010]
The synchronization signal processing unit 9 and the reception state detector 10 will be further described. The synchronization signal processing section 9 receives the video signal from the video detector 8 and obtains a horizontal synchronization signal using a phase lock loop (PLL: not shown). The reception state detector 10 receives the output of the low-pass filter constituting the phase lock loop, which is applied to the voltage controlled oscillator, amplifies the output, and changes the voltage level of the signal obtained by AM detection, and synchronizes the reception state with the reception state. Detect as disturbance.
[0011]
FIG. 3 is a diagram illustrating an example of the control circuit 11. As shown in the figure, the control circuit 11 includes an amplifier 111 for amplifying a signal from the reception state circuit 10 and an integration for removing a high frequency component of the reception state signal from the reception state detector 10 to stabilize the signal. And a buffer amplifier 113 connected thereto and outputting to the Q variable filter 6 and the comparator 14.
[0012]
FIG. 4 is a diagram showing a configuration example of the frequency characteristic correction circuit 13 of FIG. As shown in the figure, a frequency characteristic correction circuit 13 receives a clamp 131 for clamping a sync tip (a front end of a horizontal synchronization signal) of a horizontal synchronization signal, and inputs the clamped horizontal synchronization signal and a video signal (video signal). A limiter 132 that performs these amplitude controls, a differential control control amplifier 133 that differentiates the amplitude-limited video signal to remove low frequency components, and a correction unit that corrects the frequency characteristics of the video signal from which low frequency components have been removed. 134, a limiter 135 for limiting the amplitude of the corrected result, a low-pass filter 136B for inputting the clamped horizontal synchronizing signal and the video signal to remove high-frequency components, and a low-pass filter 136B and the limiter 135. A summing amplifier 136A for summing the outputs, and selecting between the output of the summing amplifier 136A and the input to the low-pass filter 136B. And a switch control unit 139 for controlling the switch unit 138, a switching unit 140 for externally controlling the switch control unit 139, and externally controlling the operation of the differential control amplifier 133. And
[0013]
FIG. 5 is a diagram illustrating characteristics of the frequency characteristic correction circuit 13 of FIG. As shown in the figure, the frequency characteristic correction circuit 13 corrects the frequency of the video signal y so as to have a peak (enhancement) between the video carrier frequency of 0 MHz and the chrominance carrier frequency of 3.58 MHz. That is, the correction is performed so that the characteristics are opposite to the frequency characteristics of the Q variable filter 6. Therefore, it is possible to recover the level drop in the high frequency range shown in FIG.
[0014]
According to the present invention, it is possible to recover a decrease in level in a high frequency range when a multipath occurs, and thus it is possible to suppress disturbance of a received image accompanied by blurring of a contour.
FIG. 6 is a diagram showing another example of the television broadcast receiving device according to the present invention. As shown in the figure, the level changing unit 17 differs from the example of FIG. The control circuit 11 controls the Q of the Q variable filter 6 in accordance with the magnitude of the synchronization disturbance in the reception state as described below, and responds to this control by controlling the frequency characteristic correction unit 13 via the level conversion unit 17. The circuit constant of the correction unit 134 is changed.
[0015]
FIG. 7 is a diagram for explaining the characteristics of the Q variable filter 6 and the frequency characteristic correction circuit 13 of FIG. As shown in FIG. 6A, the Q variable filter 6 emphasizes the correction OFF with flat correction as the synchronization disturbance increases and the correction 1, correction 2, and correction 3 whose peaks gradually increase. On the other hand, the frequency characteristic correction circuit 13 also gradually increases (enhances) the peak like flat correction OFF, correction 1, correction 2 and correction 3.
[0016]
According to the present invention, by controlling the enhancement correction amount of the frequency characteristic correction circuit 13 of the demodulation stage in conjunction with the enhancement correction amount of the Q variable filter 6 of the intermediate frequency stage, it is possible to always obtain an optimal received image. Can be. That is, the S / N is improved.
FIG. 8 is a diagram showing another example of the television broadcast receiving apparatus according to the present invention. As shown in the figure, the configuration different from FIG. 6 is that an analog switch 18 between the level converter 17 and the frequency characteristic correction circuit 13, an integrator 19 for flattening the output of the reception state detector 10, A comparator 20 for inputting the averaged signal to the inverting terminal and the threshold value VTH1 to the non-inverting terminal, and a comparator 21 for inputting the output of the control circuit 11 to the non-inverting terminal and inputting the threshold value VTH2 to the inverting terminal. And an AND circuit 22 for inputting the outputs of the comparators 20 and 21 and turning on the analog switch 18 at "H (high)", and inverting the output of the AND circuit 22, And an inverter 23 for controlling the operation of the frequency characteristic correction circuit 13.
[0017]
That is, when the voltage for controlling (instructing) the amount of amplification for the Q variable filter 6 for enhancing and amplifying the frequency components near the video carrier frequency is equal to or higher than a predetermined threshold value VTH2, the reception state detection for detecting multipath is performed. The enhancement is performed by the frequency characteristic correction circuit 13 of the demodulation stage only when the detection signal from the circuit 10 is equal to or lower than the threshold value VTH1 (not detected). In this case, the blur of the outline of the received video is most noticeable when a malfunction such as a control delay of the control circuit 11 occurs. In other words, when there is a synchronization disturbance in the reception state, the emphasis is performed. However, during the emphasis and the period in which the synchronization disturbance in the reception state is not yet corrected, there is disturbance in the received video. No correction is needed. Rather, even if the synchronization is restored by the control circuit 11 and the elimination of the synchronization disturbance is detected by the reception state detector 10, the emphasis correction of the Q variable filter 6 is performed due to the large time constant of the control circuit 11. Although there is no disturbance in the synchronization of the received image, the blur of the received image becomes most noticeable due to the enhancement correction. ADVANTAGE OF THE INVENTION According to this invention, when the blur of a received image is most conspicuous, it becomes possible to correct the blur of a received image.
[0018]
FIG. 9 is a diagram showing still another example of the television broadcast receiving apparatus according to the present invention. As shown in the figure, a configuration different from that of FIG. 1 is that a switch 24 between the comparator 14 and the frequency characteristic correction circuit 13 and an output of the AGC circuit 16 are inputted to a non-inverter and a threshold value VTH3 is inputted to an inversion terminal. And a comparator 25 for controlling the operation of the switch 24. The threshold value VTH3 is changed by operation setting.
[0019]
That is, the AGC circuit 16 detects the input signal strength of the receiver, and if the input signal strength of the receiver is lower than a predetermined level, the enhancement of the frequency characteristic correction circuit 13 is stopped. This is because, when the input signal strength of the receiver is small, the so-called received image is in a sandstorm state. In such a case, if the enhancement of the frequency characteristic correction circuit 13 is applied, the noise of the received image becomes large and the noise becomes large. Will rise. According to the present invention, the enhancement of the frequency characteristic correction circuit 13 in such a case is stopped to prevent the noise from floating.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an example of a television broadcast receiving apparatus according to the present invention.
FIG. 2 is a diagram illustrating characteristics of a Q variable filter 6 of FIG.
FIG. 3 is a diagram illustrating an example of a control circuit 11;
FIG. 4 is a diagram illustrating a configuration example of a frequency characteristic correction circuit 13 in FIG. 1;
FIG. 5 is a diagram illustrating characteristics of the frequency characteristic correction circuit 13 of FIG. 1;
FIG. 6 is a diagram showing another example of the television broadcast receiving device according to the present invention.
7 is a diagram illustrating characteristics of a Q variable filter 6 and a frequency characteristic correction circuit 13 in FIG.
FIG. 8 is a diagram showing another example of the television broadcast receiving device according to the present invention.
FIG. 9 is a diagram showing still another example of the television broadcast receiving device according to the present invention.
[Explanation of symbols]
6 Q variable filter 11 Control circuit 13 Frequency characteristic correction circuit 16 Automatic gain control circuit

Claims (4)

Video carrier signal, color sub-carrier signal, receiving a video signal including a horizontal synchronization signal, in a television broadcast receiver having an automatic gain control circuit using a horizontal synchronization signal,
First video signal enhancement means for enhancing the video signal near the video carrier frequency and color sub-carrier frequency,
A frequency characteristic correction circuit for recovering a video signal whose high frequency component is limited by the automatic gain circuit,
A multi-path signal is detected from a reception state of the horizontal synchronization signal, and a control circuit that controls operations of the first video signal enhancement unit and the frequency characteristic correction circuit with a control signal from which a high-frequency component is removed is provided. A television broadcast receiving apparatus characterized by the above-mentioned. The first video signal enhancement means varies the enhancement of the video signal in the vicinity of the video carrier frequency and the color sub-carrier frequency in accordance with the size of the multipath state, and the frequency characteristic correction circuit interlocks with the enhancement. 2. The television broadcast receiving apparatus according to claim 1, wherein the video signal is recovered by performing the recovery. The control circuit operates the first video signal emphasizing means even though multipath is eliminated due to a control delay caused by a circuit time constant for removing the high-frequency component. 2. The television broadcast receiving apparatus according to claim 1, wherein the operation of the frequency characteristic correction circuit is performed only at the time. The television broadcast receiver according to claim 1, wherein the operation of the frequency characteristic correction circuit is stopped when the automatic gain control circuit determines that the intensity of the input video signal is low.

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