JPH10126287A - Television broadcast receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent sharpness of a contour from being lost to limit a high-frequency band by an automatic gain control(AGC) circuit in the case of emphasizing a video signal around a video carrier frequency and a chrominance subcarrier frequency so as to relieve a multi-path disturbance. SOLUTION: The receiver has an automatic again control circuit that receives a video signal, including a video carrier signal, a chrominance subcarrier signal and a horizontal synchronization signal and uses the horizontal synchronization signal, is provided with a Q (sharpness of resonance for turning circuit) variable filter 6 that emphasizes the video signal around the video carrier frequency and the chrominance subcarrier frequency, a frequency characteristic correction circuit 13 that recovers the video signal whose high-frequency component is limits by an automatic gain circuit 16 and with a control circuit 11 that detects a multi-path signal from the reception state of the horizontal synchronization signal and uses a control signal from which the high-frequency component is eliminated to control the operation of the Q-variable filter 6 and the frequency characteristic correction circuit 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile receiver for terrestrial television broadcasting transmitted by an amplitude modulation method, and more particularly to an image near a video carrier frequency and a color subcarrier frequency for relieving multipath interference. The present invention relates to preventing loss of sharpness of a contour due to restriction of a high frequency range by a filter circuit when enhancing a signal.

[0002]

2. Description of the Related Art As the above-mentioned television broadcast receiving apparatus,
There is one described in Japanese Patent Application No. 6-130698. 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, and a horizontal synchronization signal (about 15.7 kHz)
The multipath is detected from the disturbance and the resonance characteristic of the filter is changed to emphasize 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 anti-phase multipath (multipath propagation) in the vicinity of the video carrier frequency, the reception level in the vicinity is lowered, synchronization is lost, the hue is changed, and the color This is because if the signal is affected by multi-paths having a reversed phase near the carrier frequency, color erasure (monochrome conversion) occurs and disturbance of the received image occurs. Therefore, even if there is multipath interference and the reception level is reduced, the effect 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]

By the way, in the above-described television broadcast receiving apparatus, as described above, when a multipath is detected, the transmission characteristic changes 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, when 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 by the multipath operates, the high-frequency band of the video signal is restricted, and the outline of the received video, particularly the sharpness of 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 in the image contour portion, and a wide band is required for faithful reproduction.

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 contour due to band limitation of frequency characteristic correction.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, an object of the present invention is to provide an automatic gain control system which receives a video signal including a video carrier signal, a color subcarrier signal, and a horizontal synchronization signal, and uses the horizontal synchronization signal. In a television broadcast receiving apparatus having a circuit, a first video signal enhancing means for enhancing a video signal near the video carrier frequency and the color subcarrier frequency, and a video signal whose high frequency component is limited by the automatic gain circuit is recovered. A frequency characteristic correction circuit detects a multipath signal from a reception state of the horizontal synchronization signal, and controls the operation of the first video signal enhancement means and the frequency characteristic correction circuit with a control signal from which a high frequency component is removed. A control circuit is provided. 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.

The first video signal enhancing means varies the enhancement of the video signal in the vicinity of the video carrier frequency and the color sub-carrier frequency according to the magnitude of the multipath state, and the frequency characteristic correction circuit comprises The video signal is recovered in conjunction with. By this means, it is possible to always obtain an optimal received video. The control circuit operates the first video signal emphasis unit despite the fact that 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, contour blur is effectively corrected when a malfunction occurs due to a control delay of the control circuit, where contour blur of the received video is most noticeable.

If 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]

Embodiments of the present invention will be described below 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, a 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 which is a first video signal enhancement means for controlling Q (sharpness of resonance of the tuning circuit) so that the video carrier frequency fv and the color sub-carrier frequency fsc become resonance frequencies so as to enhance them. , An intermediate frequency amplifier 7 connected thereto for amplifying an intermediate frequency region
And a video detector 8 connected thereto for detecting a video signal
And a synchronization signal processing unit 9 connected thereto for extracting a synchronization signal from a video signal, and a reception state connected to the synchronization signal processing unit 9 for disturbing a horizontal synchronization signal among the synchronization signals (a large signal is output when multipath interference increases). And a Q-variable filter 6 which is connected thereto and controls the Q variable filter 6 when there is a disturbance in the horizontal synchronizing signal, thereby controlling the video carrier frequency fv.
Control circuit 11 for enhancing the color subcarrier frequency fsc
A YC separation unit 12 connected to the video detector 8 for separating the video signal y and the color signal c, and a frequency characteristic correction circuit (enhancer) connected to the YC separation unit 12 for correcting the frequency characteristic emphasized by the Q variable filter 6 13) and a comparator 14 for controlling the operation of the frequency characteristic correction circuit 13 by inputting the signal from the control circuit 11 to the inverting terminal and the threshold value VTH0 to the non-inverting terminal.
And the synchronization signal from the synchronization signal processing unit 9 and the YC separation unit 1
And a display unit 15 for inputting the color signal c from the second and the video signal y from the frequency characteristic correction circuit, and the intermediate wave amplifier 7 using the peak value of the horizontal synchronization signal from the synchronization signal processing unit 9.
AGC circuit 16 for controlling the gain of

FIG. 2 is a diagram for explaining the characteristics of the Q variable filter 6 shown in FIG. FIG. 3A shows frequency characteristics input from the band limiting filter 5 to the Q variable filter 6. FIG. 3B shows the frequency characteristics 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. This figure (c)
Indicates the characteristic 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 range (1 to 2 MHz) indicated by the solid line with respect to the dotted line in the case where the Q variable filter 6 has no correction, in the case where the correction has been 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 subcarrier frequency.

The synchronization signal processing section 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-locked loop, which is applied to the voltage-controlled oscillator, amplifies the output, and changes the voltage level of the signal detected by AM detection to synchronize the reception state with the reception state. Detect as disturbance.

FIG. 3 is a diagram showing an example of the control circuit 11.
As shown in the figure, the control circuit 11 includes a reception state circuit 10
An amplifier 111 for amplifying the signal from the receiver, an integrator 112 for removing the high-frequency component of the reception state signal from the reception state detector 10 to stabilize the signal, and connected to the Q variable filter 6 and the comparator. Buffer amplifier 1 to output to 14
13 is provided.

FIG. 4 is a diagram showing a configuration example of the frequency characteristic correction circuit 13 of FIG. As shown in the figure, the 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, a 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 and removing a high-frequency component, and a low-pass filter 136B and the limiter 135. A summing amplifier 136A for summing the output, and selecting an output of the summing amplifier 136A and an 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

FIG. 5 is a diagram for explaining the characteristics of the frequency characteristic correction circuit 13 shown in 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 0 MHz and the chrominance carrier frequency 3.58 MHz. That is, Q
Correction is performed so that the frequency characteristics of the variable filter 6 are opposite to the frequency characteristics. Therefore, it is possible to recover the level drop in the high frequency range shown in FIG.

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 an outline. FIG. 6 is a diagram showing another example of the television broadcast receiving device according to the present invention. As shown in FIG.
The level changing unit 17 differs from the example of FIG. Control circuit 1
1 controls the Q of the Q variable filter 6 according to the degree of the synchronization disturbance in the reception state as described below, and responds to this control via the level conversion unit 17 to the correction unit of the frequency characteristic correction unit 13. The circuit constant of 134 is changed.

FIG. 7 is a diagram for explaining the characteristics of the Q variable filter 6 and the frequency characteristic correction circuit 13 of FIG. This figure (a)
As shown in (5), the Q variable filter 6 performs enhancement by flat correction OFF as the synchronization disturbance increases, and corrections 1, 2 and 3 whose peaks gradually increase. On the other hand, the frequency characteristic correction circuit 13 also has a flat correction OF.
The peak is gradually increased (enhanced) as in F, Correction 1, Correction 2 and Correction 3.

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. That is, 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 is provided 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,
This averaged signal is applied to the inverting terminal and to the threshold VTH1.
20 to the non-inverting terminal, the comparator 21 to input the output of the control circuit 11 to the non-inverting terminal and the threshold VTH2 to the inverting terminal, and input the outputs of the comparators 20 and 21 to the analog An AND circuit 22 for turning on the switch 18 at "H (high)", and an output of the AND circuit 22 are inverted to replace the comparator 14 of FIG.
And an inverter 23 for controlling the operation of the third embodiment.

That is, the multipath is detected when the voltage for controlling (instructing) the amount of amplification to the Q variable filter 6 for enhancing and amplifying the nearby frequency component of the video carrier frequency is equal to or higher than a predetermined threshold value VTH2. The detection signal from the reception state detection circuit 10 is not more than the threshold value VTH1 (not detected)
Only in the case of (1), the enhancement is performed by the frequency characteristic correction circuit 13 of the demodulation stage. 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. That is, when there is a synchronization disturbance in the reception state, the emphasis is performed. However, during the period of emphasis and the synchronization disturbance in the reception state is not yet corrected, there is disturbance in the received image. 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 enhancement 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. According to the present invention, it is possible to correct the blur of the received video when the blur of the received video is most noticeable.

FIG. 9 is a diagram showing still another example of the television broadcast receiving apparatus according to the present invention. As shown in this figure, the configuration different from that of FIG. 1 is that a switch 24 between the comparator 14 and the frequency characteristic correction circuit 13 and the output of the AGC circuit 16 are inputted to the non-inverter and the threshold value VTH3 is inputted to the inverting terminal. And a comparator 25 for controlling the operation of the switch 24. The threshold value VTH3 is varied by the operation setting.

That is, the input signal strength of the receiver is detected by the AGC circuit 16, and when 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 low, the so-called received image is in a sandstorm state.
, The noise of the received video increases, and the noise rises. 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 showing an example of a television broadcast receiving device 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;

5 is a diagram illustrating characteristics of the frequency characteristic correction circuit 13 in FIG.

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

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hidemori Tsuka 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation

Claims (4)

[Claims] 1. A television broadcast receiving apparatus which receives a video signal including a video carrier signal, a color sub-carrier signal, and a horizontal synchronization signal, and has an automatic gain control circuit using a horizontal synchronization signal. First video signal enhancement means for enhancing a video signal near a 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 multipath signal from a reception state of the horizontal synchronization signal. And a control circuit that controls the operation of the first video signal enhancement means and the frequency characteristic correction circuit with a control signal from which the high-frequency component has been removed. 2. The image processing apparatus according to claim 1, wherein the first video signal enhancement unit varies enhancement of the video signal near the video carrier frequency and the color sub-carrier frequency in accordance with the magnitude of the multipath state. The television broadcast receiving apparatus according to claim 1, wherein the video signal is recovered in conjunction with the emphasis. 3. The first video signal enhancement means, despite the fact that multipath is eliminated due to a control delay caused by a circuit time constant for removing the high frequency component. The television broadcast receiving apparatus according to claim 1, wherein the frequency characteristic correction circuit is operated only when is operated. 4. The television broadcast reception according to claim 1, wherein 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. apparatus.