JP2006314011A - Synchronous separation circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the detection efficiency of synchronization signal by precisely detecting the synchronization signal, when a video signal is a weak electric-field signal, and when V-sag is generated. <P>SOLUTION: An effective pixel/VB period determining section 120 determines whether a video signal is in an effective pixel period or in a VB period. Furthermore, a minimum detection section 130 detects a minimum value of a signal level in a detection period determined, according as to whether the video signal is in the effective pixel period or in the VB period. Then a minimum value decision section 140 decides whether the detected minimum value is an adequate value, and then a threshold calculation section 150 finds a threshold for synchronizing the signal detection, according to whether the minimum value is adequate. Once the threshold is found, a synchronization separation section 160 outputs the signal, when the level of the input video signal decreases below the threshold as a synchronization signal. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a synchronization separation circuit that detects a synchronization signal from an input video signal.

The average level of a composite video signal (hereinafter referred to as a video signal) on which a luminance signal (hereinafter referred to as a Y signal) and a color signal (hereinafter referred to as a C signal) are superimposed is always in the vertical blanking period. Lower. For this reason, the video signal has a vertical scanning frequency component (about 59.94 Hz in the case of NTSC). When a video signal is transmitted, a direct current component is generally blocked and transmitted. At this time, when the vertical scanning frequency component is attenuated, the level of the vertical blanking period approaches the average level of the video. As a result, a phenomenon occurs in which the lower end potential of the synchronizing signal in the vertical blanking period becomes higher than the lower end potential of the synchronizing signal in other periods. (In the following description, a signal state in which the lower end potential of the synchronizing signal during the vertical blanking period is increased is referred to as a V sag state. Also, such a state is referred to as “V sag is generated”. To do.)
Therefore, the sync separation circuit that detects the sync signal from the input video signal accurately detects the sync signal from the input video signal even when V sag, which is relatively generated during the vertical blanking period, occurs. It needs to be configured so that it can.

  As a sync separation circuit that can detect a sync signal even when V sag occurs, the minimum value of the level of the video signal in a certain period of the input video signal is detected, and whether or not the minimum value is an appropriate value (minimum value). Depending on whether or not is within a predetermined range), a predetermined offset value is added to (or subtracted from) the minimum value to obtain a threshold value, and the obtained threshold value is compared with the level of the video signal. There is a synchronization separation circuit 300 that detects the portion of the video signal that has become a synchronization signal.

  FIG. 4 is a block diagram showing a configuration of the synchronization separation circuit 300. As shown in FIG. The synchronization separation circuit 300 includes a minimum value detection unit 310, a minimum value determination unit 320, a threshold value calculation unit 330, and a synchronization separation unit 340.

  The minimum value detection unit 310 obtains the minimum value of the signal level in a predetermined detection period of the video signal video signal input from the composite video signal input terminal, and sends the minimum value signal indicating the obtained minimum value to the minimum value determination unit 320. It is designed to output. The period for detecting the minimum value includes, for example, individual patterns depending on circuits such as 110% and 55% with a period during which a video signal for one line of video is output (hereinafter referred to as 1H) as a 100% reference.

  The minimum value determination unit 320 determines whether the minimum value is an appropriate value and outputs a determination result signal indicating the determination result to the minimum value determination unit 320. Specifically, assuming that the minimum value detected in the previous line is X, the range is within the range of X ± α (α is a predetermined constant) (X−α <minimum value <X + α, hereinafter this range is referred to as the allowable range). ) If the minimum value is included, the minimum value is determined to be valid, and if the minimum value is not within the range, it is not valid (for example, if the detected minimum value is due to noise, or the synchronization signal Etc.).

  The threshold value calculation unit 330 calculates a threshold value obtained by adding (or subtracting) a predetermined offset value to the minimum value obtained by the minimum value detection unit 310 according to whether the minimum value is an appropriate value. . Specifically, if the minimum value is a reasonable value, a threshold obtained by adding a predetermined offset value to the minimum value is output as a threshold signal. If the minimum value is larger (or smaller) than a value within the allowable range, it is determined that the level of the video signal is fluctuating (V sag is generated), and the second value is compared with the minimum value. A value obtained by adding (or subtracting) the offset value (Y) is set as a new minimum value, and a threshold value obtained by adding the offset value to the new minimum value is output as a threshold signal.

  The sync separator 340 receives the video signal and the threshold signal output from the threshold calculator 330, and uses the signal when the level of the input video signal is equal to or lower than the level indicated by the threshold signal as a sync signal. The signal is output to the synchronization signal output terminal.

  For example, when the video signal A shown in FIG. 5 is input to a circuit configured to detect the minimum value of the level of the video signal in the 1H period, the video in the 1H period is input by the minimum value detection unit 310. The minimum value of the signal level is detected (see the circled portion of the video signal A in FIG. 5). The validity of the minimum value is determined by the minimum value determination unit 320.

  When it is determined that the minimum value is not valid (see the asterisk mark of the video signal A in FIG. 5), the minimum value is within the range of the determination condition in the next 1H period. When the threshold value is calculated by the minimum value determination unit 320, the second offset value Y is further added to (minimum value + offset value). Thereby, even if V sag is generated, the threshold value is obtained following the signal change (see section V in FIG. 5), and the level of the video signal becomes equal to or lower than the threshold value by the synchronization separation unit 340. The time signal is output as a synchronization signal to the synchronization signal output terminal (see the synchronization signal C in FIG. 5).

  For example, when the video signal A shown in FIG. 6 is input to the circuit configured to detect the minimum value of the level of the video signal in the period of 0.5H, the minimum value detection unit 310 The minimum value of the video signal level in the period of 0.5H is detected (see the circled portion of the video signal A in FIG. 6). The validity of the minimum value is determined by the minimum value determination unit 320.

  If it is determined that the minimum value is not valid (see the asterisk of the video signal A in FIG. 6), the minimum value is within the range of the determination condition in the next 0.5H period. In addition, when the threshold value is calculated by the minimum value determination unit 320, the second offset value (Y) is further added to (minimum value + offset value). As a result, even if V sag is generated, the threshold value is obtained following the signal change (see section V in FIG. 6), and the level of the video signal becomes equal to or lower than the threshold value by the synchronization separation unit 340. The time signal is output as a synchronization signal to the synchronization signal output terminal (see the synchronization signal C in FIG. 6).

  As described above, according to the synchronization separation circuit 300, the threshold value is changed depending on whether or not the V sag is generated, and the synchronization signal can be appropriately detected and output from the input video signal.

  Further, even in the case of a video signal with a low level (for example, a signal of about 30% of the standard video signal level, hereinafter referred to as a weak electric field signal), the video quality can be ensured by being able to detect the synchronization signal. It is an important factor above.

  As a conventional synchronization separation circuit that can detect a synchronization signal even when a weak electric field signal is input, a PLL (Phase-Locked-Loop) circuit is used to monitor the lock state of the synchronization-separated horizontal synchronization signal. Some have adjusted the threshold value for performing synchronous separation (see, for example, Patent Document 1).

  In this synchronization separation circuit, a clock signal obtained by multiplying the horizontal synchronization signal output from the synchronization separation circuit by a predetermined multiplication ratio is generated by the PLL circuit, and it is detected whether or not the PLL circuit is in a locked state. The threshold for performing synchronization separation is adjusted according to the above. For example, when it is determined that the lock state has not been reached, the lock detection signal is not output, and the threshold value in the sync separation circuit is controlled to a level that is strong against noise input and is unlikely to malfunction.

According to this sync separator circuit, the threshold value of the sync separator circuit can be optimally controlled according to the state of the received video signal, and a stable horizontal sync signal and vertical sync signal can be generated even when a weak electric field signal is input. It becomes possible to do.
JP 2002-190964 A (pages 3 to 6, FIG. 1)

  However, in the conventional sync separator that adjusts the threshold according to the minimum value detected in a certain period, the sync signal can be detected accurately when the video signal is a weak electric field signal, and the V sag is generated. It has been difficult to accurately detect the synchronization signal.

  For example, if the period for detecting the minimum value is set to 1H or more, in the period in which the pixels are effectively output (effective pixel period), the synchronization signal is output even if the video signal level is about 30%. Although it can be detected, there is a possibility that the synchronization signal cannot be detected in the vertical blanking period (hereinafter referred to as VB period). That is, in the VB period, since synchronization (equivalent) pulses exist at intervals of 0.5H, tracking of the threshold is delayed by 0.5H. Therefore, even if V sag occurs in the VB period, the change of the threshold value cannot follow the fluctuation of the video signal level, and the synchronization signal may not be detected.

  For example, when the period for detecting the minimum value is 0.5H, even if a V sag occurs in the VB period, it is possible to follow the fluctuation of the video signal level in a timely manner. When the synchronization signal interval is 1H, if there is no synchronization signal within 0.5H of the detection period, the minimum value is erroneously detected. Therefore, the second offset is set to the threshold value in the next detection range. The value (Y) is added. If the video signal level at this time is about 30%, the calculated threshold value exceeds the video signal level, and the synchronization signal may not be detected.

  Further, in the synchronization separation circuit that adjusts the threshold according to the lock state of the PLL circuit, the V sag state is not taken into account even though the synchronization signal can be stably detected for the weak electric field signal. It was.

  The present invention has been made paying attention to the above-mentioned problem, and can detect the synchronization signal accurately when the video signal is a weak electric field signal and a V sag occurs, and can improve the detection efficiency of the synchronization signal. It is an object to provide a synchronization separation circuit.

In order to solve the above problems, the invention of claim 1
A synchronization separation circuit for detecting a synchronization signal from a video signal,
A line counter for counting the number of lines of the video signal;
A period determining unit that determines whether the video signal is an effective pixel period or a vertical blanking period based on the number of lines;
A minimum value detecting unit for detecting a minimum value of the level of the video signal in a detection period determined according to whether the video signal is an effective pixel period or a vertical blanking period;
A minimum value determination circuit for determining whether the minimum value detected by the minimum value detection unit is a value within a predetermined allowable range; and
A threshold value calculation unit for obtaining a threshold value obtained by adding or subtracting an offset value determined according to a determination result of the minimum value determination circuit to the minimum value;
A sync separator that outputs a signal when the level of the video signal is equal to or lower than the threshold as the sync signal;
It is provided with.

  As a result, since the detection period of the minimum value of the video signal level is switched between the effective pixel period and the VB period, the synchronization signal can be accurately obtained even when the video signal is a weak electric field signal and a V sag occurs. Detection and synchronization separation can be performed.

The invention of claim 2
The synchronization separation circuit of claim 1,
Furthermore, a signal level change rate detection unit for detecting a change rate of the level of the video signal,
The minimum value detection unit is configured to widen the allowable range when the change rate detected by the signal level change rate detection unit is larger than a predetermined value,
The threshold calculation unit is configured to increase or decrease the offset value in accordance with the magnitude of the change rate detected by the signal level change rate detection unit.

  Thereby, the minimum value of the video signal level can be detected with higher accuracy.

  According to the present invention, when a video signal is a weak electric field signal and a V sag is generated, the synchronization signal can be detected with high accuracy, and the detection efficiency of the synchronization signal can be improved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Embodiment 1 of the Invention
FIG. 1 is a block diagram showing a configuration of a synchronization separation circuit 100 according to the first embodiment of the present invention. As shown in the figure, the synchronization separation circuit 100 includes a line counter 110, an effective pixel / VB period determination unit 120, a minimum value detection unit 130, a minimum value determination unit 140, a threshold value calculation unit 150, and a synchronization separation unit 160. Configured.

  The line counter 110 counts the number of lines of the video signal based on the synchronization signal output from the synchronization separation unit 160 and outputs a signal indicating the number of lines to the effective pixel / VB period determination unit 120.

  The effective pixel / VB period determination unit 120 determines, based on the number of lines, whether the pixel is effectively output in the video signal (effective pixel period) or a vertical blanking period (VB period). A determination signal indicating the determination result is output to the minimum value detection unit 130.

  The minimum value detection unit 130 obtains the minimum value of the video signal level in the detection period determined according to whether the video signal input from the composite video signal input terminal is an effective pixel period or a VB period. A minimum value signal indicating the minimum value is output to the minimum value determination unit 140. Specifically, when the determination signal indicates an effective pixel period, the detection period is set to 1H or more, and is set to around 0.5H for the VB period. By setting the detection period to 1H or more in the effective pixel period, it is possible to ensure that the synchronization period is included in the detection period. Further, by setting the detection period to around 0.5H in the VB period, it is possible to detect the minimum value following the synchronization pulse existing every 0.5H.

  The minimum value determination unit 140 receives the minimum value signal, determines whether the minimum value indicated by the minimum value signal is an appropriate value, and outputs a determination result signal indicating the determination result to the threshold value calculation unit 150. It has become. Specifically, assuming that the minimum value detected in the previous line is X, the range is within the range of X ± α (α is a predetermined constant) (X−α <minimum value <X + α, hereinafter this range is referred to as the allowable range). ) If the minimum value is included, it is determined that the minimum value is valid. If the minimum value is not within the range, it is determined that the minimum value is not valid (for example, the detected minimum value is due to noise). Is done.

  If the minimum value obtained by the minimum value detection unit 130 is a reasonable value, the threshold calculation unit 150 outputs a threshold obtained by adding a predetermined offset value to the minimum value as a threshold signal, while the minimum value Is a value larger (or smaller) than a value within the allowable range, it is determined that the level of the video signal has fluctuated (V sag has occurred), and a second offset value ( A value obtained by adding (or subtracting) Y) is set as a new minimum value, and a threshold value obtained by adding the offset value to the new minimum value is output as a threshold signal.

  The sync separator 160 receives the video signal and the threshold signal output from the threshold calculator 150, and uses the signal when the level of the input video signal is equal to or lower than the level indicated by the threshold signal as a sync signal. The signal is output to the synchronization signal output terminal.

  The operation of the sync separator circuit 100 configured as described above when the input video signal is a weak electric field signal of about 30% of the standard video signal level and V sag is generated will be described.

  First, in the sync separator circuit 100, when a video signal is input from the composite video signal input terminal, the line counter 110 counts the number of lines, and the result is output to the effective pixel / VB period determination unit 120. The effective pixel / VB period determination unit 120 determines whether it is an effective pixel period or a VB period based on the number of lines, and the determination result is output to the minimum value detection unit 130. In the minimum value detection unit 130, the minimum value in the detection period of 1H is detected in the effective pixel period, and the minimum value in the detection period of 0.5H is detected in the VB period. In other words, since the effective pixel period always includes a synchronization pulse in the detection period, the minimum value is not erroneously detected. In addition, since the minimum value is detected following the synchronizing pulse existing every 0.5H during the VB period, the minimum value can be detected accurately even when a V sag is generated.

  When the minimum value is obtained by the minimum value detection unit 130, the minimum value determination unit 140 determines whether or not the minimum value is an appropriate value. If the minimum value is an appropriate value as a result of the determination, the threshold value calculation unit 150 outputs a threshold value obtained by adding a predetermined offset value to the minimum value. When the minimum value is larger (or smaller) than a value within the allowable range, it is determined that the level of the video signal has fluctuated (V sag is generated), and the minimum value is compared with the minimum value. A value obtained by adding (or subtracting) the second offset value (Y) is set as a new minimum value, and a threshold value obtained by adding the offset value to the new minimum value is output. When the threshold value is output, the sync separator 160 outputs a signal when the level of the input video signal is equal to or lower than the threshold value to the sync signal output terminal.

  As described above, according to the present embodiment, the minimum detection period is switched between the effective pixel period and the VB period. Therefore, even when the video signal is a weak electric field signal and a V sag is generated, the synchronization is performed. It becomes possible to detect a signal accurately and perform synchronization separation, thereby improving the detection efficiency of the synchronization signal.

<< Embodiment 2 of the Invention >>
An example of a circuit configured to detect a synchronization signal with higher accuracy than the apparatus according to the first embodiment will be described.

  FIG. 2 is a block diagram illustrating a configuration of the synchronization separation circuit 200 according to the second embodiment of the present invention. In the following description, components having the same functions as those of the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  The synchronization separation circuit 200 includes a minimum value determination unit 240 instead of the minimum value determination unit 140, a threshold value calculation unit 250 instead of the threshold value calculation unit 150, and a V sag detection unit 270 in the circuit of the first embodiment. It is configured.

  Similar to the minimum value determination unit 140, the minimum value determination unit 240 determines whether or not the minimum value indicated by the input minimum value signal is an appropriate value. However, the determination in the minimum value determination unit 240 is input when the inclination value (see FIG. 3) of the video signal indicated by the input inclination value signal (described later) is greater than or equal to a predetermined value (or less). It is determined that a V sag has occurred in the video signal, and the allowable range is widened. Thereby, it is possible to suppress erroneous determination when a sudden V sag occurs.

  If the minimum value obtained by the minimum value detection unit 130 is a reasonable value, the threshold calculation unit 250 outputs a threshold obtained by adding a predetermined offset value to the minimum value as a threshold signal, while the minimum value Is a value larger (or smaller) than a value within the allowable range, it is determined that the level of the video signal has fluctuated (V sag has occurred), and a second offset value ( A value obtained by adding (or subtracting) Y) is set as a new minimum value, and a threshold value obtained by adding the offset value to the new minimum value is output as a threshold signal. However, in the threshold value calculation unit 250, the offset value is changed according to the inclination value of the video signal.

  The V sag detection unit 270 calculates an inclination value for each predetermined period of the input video signal, and outputs an inclination value signal indicating the inclination value.

  A description will be given of an operation when a video signal in which an abrupt V sag is generated in the VB period as shown in FIG. 3 is input from the composite video signal input terminal to the synchronization separation circuit 200 configured as described above.

  When the video signal is input from the composite video signal input terminal, the minimum value detection unit 130 switches the minimum value detection period between the effective pixel period and the VB period, and detects the minimum value of the signal level.

  On the other hand, the V sag detection unit 270 calculates the inclination of the input video signal every predetermined period. The calculated inclination value is output to the minimum value determination unit 240 and the threshold value calculation unit 250 as an inclination value signal.

  When the slope value is a value greater than or equal to a predetermined value (or less), the minimum value determination unit 240 determines that a V sag has occurred in the input video signal, and in accordance with the slope value. The allowable range is widened. Based on the widened allowable range, the minimum value determination unit 240 determines whether or not the minimum value is appropriate.

  Further, the threshold value calculation unit 250 adjusts the offset value according to the inclination value. The adjusted offset value is added (or subtracted) to the minimum value to obtain the threshold value. When the threshold is obtained, the sync separator 160 outputs a signal when the level of the input video signal is equal to or lower than the threshold to the sync signal output terminal.

  As described above, also in the present embodiment, since the minimum detection period is switched between the effective pixel period and the VB period, it is synchronized even when the video signal is a weak electric field signal and a V sag is generated. It becomes possible to detect a signal accurately and perform synchronization separation, thereby improving the detection efficiency of the synchronization signal.

  In addition, since fluctuations in the level of the video signal (signal slope value) are detected every predetermined period, even if the fluctuation range of the video signal level is very large due to V sag or the like, the threshold is set according to the detected slope value. Adjustment is made so as to follow the fluctuation of the signal level more quickly, and detection efficiency can be further improved.

  The synchronization separation circuit according to the present invention has an effect that the synchronization signal can be detected accurately when the video signal is a weak electric field signal and a V sag is generated, and the detection efficiency of the synchronization signal can be improved. It is useful as a sync separation circuit for detecting a sync signal from an input video signal.

It is a block diagram which shows the structure of the synchronous separation circuit which concerns on Embodiment 1 of this invention. It is a block diagram which shows the structure of the synchronous separation circuit which concerns on Embodiment 2 of this invention. It is a timing chart which shows the level change of a video signal when V sag occurs in a VB period. It is a block diagram which shows the structure of the conventional figure synchronous separation circuit. 10 is a timing chart showing a minimum value detected in each period when the detection period is 1H in the conventional synchronization separation circuit. 10 is a timing chart showing a minimum value detected in each period when the detection period is 0.5H in the conventional synchronization separation circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Sync separation circuit 110 Line counter 120 Effective pixel / VB period determination part 130 Minimum value detection part 140 Minimum value determination part 150 Threshold value calculation part 160 Synchronization separation part 200 Synchronization separation circuit 240 Minimum value determination part 250 Threshold value calculation part 270 V sag detection Unit 300 synchronization separation circuit 310 minimum value detection unit 320 minimum value determination unit 330 threshold value calculation unit 340 synchronization separation unit

Claims (2)

A synchronization separation circuit for detecting a synchronization signal from a video signal,
A line counter for counting the number of lines of the video signal;
A period determining unit that determines whether the video signal is an effective pixel period or a vertical blanking period based on the number of lines;
A minimum value detecting unit for detecting a minimum value of the level of the video signal in a detection period determined according to whether the video signal is an effective pixel period or a vertical blanking period;
A minimum value determination circuit for determining whether the minimum value detected by the minimum value detection unit is a value within a predetermined allowable range; and
A threshold value calculation unit for obtaining a threshold value obtained by adding or subtracting an offset value determined according to a determination result of the minimum value determination circuit to the minimum value;
A sync separator that outputs a signal when the level of the video signal is equal to or lower than the threshold as the sync signal;
A synchronization separation circuit comprising: The synchronization separation circuit of claim 1,
Furthermore, a signal level change rate detection unit for detecting a change rate of the level of the video signal,
The minimum value detection unit is configured to widen the allowable range when the change rate detected by the signal level change rate detection unit is larger than a predetermined value,
The synchronization separation circuit, wherein the threshold value calculation unit is configured to increase or decrease the offset value according to the magnitude of the change rate detected by the signal level change rate detection unit.

Images