EP0573407A1

EP0573407A1 - Detection of the presence of digital data in a video signal

Info

Publication number: EP0573407A1
Application number: EP19900913491
Authority: EP
Inventors: Gérard Korahnke; Michel Laurent
Original assignee: TONNA ELECTRONIQUE
Current assignee: TONNA ELECTRONIQUE
Priority date: 1989-09-06
Filing date: 1990-09-05
Publication date: 1993-12-15
Also published as: WO1991003907A1; FR2651632A1; FR2651632B1

Abstract

La détection de la présence de données numériques, notamment les mots de synchronisation de signaux de la famille MAC, comprend les étapes suivantes: générer séquentiellement (100, 112) une fenêtre temporelle T2 (132) de prévision d'apparition des données numériques (20) et détecter le début des données numériques par détection de seuil (114, 123, 124) pendant chaque fenêtre temporelle T2, tout en vérifiant que le seuil soit franchi dans au moins une fenêtre sur x fenêtres consécutives (102, 116) et que la génération de fenêtre soit recalée après un tel franchissement. La détection peut être appliquée au contrôle du niveau de composante continue du signal vidéo et de son amplitude.Detecting the presence of digital data, in particular the MAC family of signal synchronization words, comprises the following steps: sequentially generating (100, 112) a time window T2 (132) for predicting the appearance of digital data (20 ) and detect the start of the digital data by threshold detection (114, 123, 124) during each time window T2, while verifying that the threshold is crossed in at least one window over x consecutive windows (102, 116) and that the window generation is readjusted after such a crossing. Detection can be applied to control the level of the DC component of the video signal and its amplitude.

Description

DETECTION OF THE PRESENCE OF DIGITAL DATA IN A VIDEO SIGNAL

The present invention relates to the field of video signal processing.

The present invention relates more precisely to a method and a device for detecting the presence of recurrent digital data in a video signal, as well as to the applications of these method and device.

The present invention finds particular application in the processing of video signals comprising digital baseband data and more precisely the signals of the MAC family (multiplexing

"Of analog components).

Essentially, these MAC family video signals include, as shown in the attached FIG. 1, sequences comprising a recurring packet 20 of digital data useful for the synchronization and definition of sound, then analog information 21 of chrominance followed by analog luminance information 22.

- These. Video signals are well known to those skilled in the art and will therefore not be described further _. detail later. It will be noted, however, that these video signals generally comprise a so-called "clamp" period providing a reference level for the alignment of the signals between the packet of digital data and the analog information ^' chromi¬ nance.

The present invention can be used in particular, but not exclusively, for the alignment of a video signal with respect to a voltage reference.

The problem, well known to those skilled in the art, posed by this kind of video signal comes from the fact that, in order to safely detect digital data, in particular digital image synchronization words, it would be necessary to check correctly beforehand. the level of the so-called continuous component of the signal and its amplitude, while in order to control these quantities, it is planned to be based on reference voltage stages which can only be exploited correctly after having detected synchronization. Different systems have already been proposed in an attempt to resolve the dilemma thus posed. The various systems hitherto proposed, in particular for the alignment of signals, require complex processing and decoding of the signal for the extraction of digital data. EP-A-0167430 has proposed a system comprising, as shown in FIG. 2 appended, an input amplifier 30 with variable gain followed by an adder 31.

The output of the summator 31 attacks several routes.

A first channel 32 comprises means capable of estimating the amplitude and the average value of the data signal from the whole of the video signal. For this, the first channel 32 comprises a positive peak detector 33 and a negative peak detector 34 associated with a summator 35 and a subtractor 36.

The estimated amplitude of the data signal is available at the output of the subtractor 36. The output of the subtractor36 is thus used to drive the variable gain amplifier - input 30.

The estimated average value of the data signal is available at the output of the summer 35. The output of the summer 35 is thus used to apply a correction voltage for the alignment of the video signal on the summer 31, via '' an integrator 39.

A second channel connected to the output of the adder 31 is formed by a processing and decoding module 37 capable of recovering the clock of the video signal, and of providing digital data sampled. A third channel connected to the output of the adder 31 is formed by a "clamp" level sampler 38 capable of applying the "clamp" level of the video signal to the adder 31 via the integrator 39, to the place of the output signal of the adder 35, when it is commanded to close by the processing and decoding module 37. The system proposed in document EP-A-0167430 thus operates in two successive modes for the alignment of the signal video.

In a first mode, which corresponds to an acquisition phase, the video signal is roughly aligned on the basis of the estimate of the average value of the data signal coming from the summator 35. Similarly the signal is regulated by the input amplifier 30 using the estimate of the amplitude of the data signal from the subtractor 36.

When the synchronization pattern is assumed to be extracted, the system goes into the second mode which corresponds to a holding phase during which the processing and decoding module 37 sequentially aligns the signal from the detected "clamp" level, by closing sequence of switch 38 and regulates s <_. amplitude thanks to the amplifier 30 according to black and white steps transmitted by the video signal to each frame. Another system is described in document EP-A-02S 2 106.

This system comprises, as shown in the attached FIG. 3, a variable gain input amplifier 40, a summator 41, a peak detector 42, averaging means 43, an inverter switch 44, a module for processing and decoding 45 and a module 46 for aligning the video signal on a "clamp" level.

The system described in document EP-A-C2S2106 comprises three successive modes of operation with a view to aligning ¹ "the video signal.

During the first mode, installed at the start of the system, the module 45 permanently activates the peak detector ^ 2 and the averaging means 43, as well as the associated means for adjusting the gain using the amplifier 40 and the DC component at lA of the summator 41. This first mode makes it possible to roughly extract the digital data. During the second consecutive mode, the processing and decoding module 45 validates the peak detector 42 only during the digital signal periods. The second mode is only installed after recognition of an image synchronization word.

Thereafter, during the third mode, the module 45 commands a change of state of the reversing switch 44 to activate the means 46 in order to use the reference stages of the video signal.

Finally, the document EP-.A-0305772 has proposed a system comprising, as shown in the figure - attached a variable gain input amplifier 50. a processing and decoding module 51, averaging means 52 and an interrupter 53. The switch 53 is designed to validate or inhibit the averaging means 52 according to its state. More precisely, the interrup¬ tor 53 is controlled by the processing and decoding means 51 so that it validates the averaging means 52 when the processing module e: decoding 51 detects the presence of digital data. The average signal from the means 52 is applied to the input summator _ to align the signal.

The means for decoding digital data proposed in the aforementioned prior documents are very complex and do not give full satisfaction. The object of the present invention is to provide a new method and a new device for detecting the presence of recurrent digital data in a video signal which eliminate the drawbacks of the prior art.

After numerous tests and studies, the Applicant has shown that it is possible to detect the presence of digital data by simple analog processing and therefore that it is possible to get out of the aforementioned diithesis under the terms of which it would first be necessary to correctly check the level of DC component of the signal and its amplitude to detect the digital data while for control ^” - these quantities, it would be necessary to be based on reference voltage steps which could only be exploited after detecting synchronization .

The method for detecting the presence of recurrent digital data in a video signal thus proposed in the context of the present invention comprises the steps consisting in:

- sequentially generate a time window for predicting the appearance of digital data, and

- detect the start of digital data by a threshold detection. According to an advantageous characteristic of the present invention, the step of detecting the start of the digital data is operated by a double threshold detection.

According to another advantageous characteristic of the present invention, the method comprises the step of generating a digital data detection signal at the end of each time window.

According to another advantageous characteristic of the present invention, the method further comprises the steps consisting in:

- check the threshold crossing in at least one window on X consecutive windows, and

- close the window thus opened and reset the sequential generation of “forecast time windows, when a threshold crossing is detected during the open window.

The present invention also provides a device for implementing the above-mentioned detection method.

As indicated above, the present invention finds particular application to the alignment of a video signal. It is however not limited to this application. The present invention may for example be applied ^to the years AGC amplifier of a ^video or in the modulation depth control.

Other characteristics, aims and advantages of the present invention will appear on reading the detailed description which follows and with reference to the appended drawings given by way of nonlimiting examples and in which:

FIG. 1 previously described diagrammatically represents video signals comprising digital data capable of being processed using the device according to the present invention,

FIG. 2 previously described schematically represents the prior system proposed in document EP-A-0167430,

FIG. 3 previously described schematically represents the structure of the prior system proposed in document EP-A-0282106,

FIG. 4 previously described schematically represents the structure of the prior system proposed in document EP-A-0305772, - Figure 5 shows in the form of a flowchart the method of detecting the presence of digital data in accordance with this present. ention,

FIG. 6 represents in the form of functional blocks the basic structure of the device for detecting the presence of digital data according to the present invention,

- Figure 7 schematically shows the structure of an embodiment of a device for detecting the presence of digital data according to the present invention.

FIG. 8 represents a timing diagram illustrating the operation of the device for detecting the presence of digital data in accordance with the present invention, and

- Figures 9 and 10 schematically show two examples of application of the device for detecting the presence of digital data to the alιgneme <"- of video signals. We will first describe the method of detecting the presence of recurrent digital data in a video signal, in accordance with the present invention, with reference to FIG. 5 appended.

This method comprises a first step 100 ^″ consisting in sequentially generating a time window for predicting the appearance of digital data. The period of generation of said time windows substantially coincides with the period of the sequences of the video signal.

Even more precisely, as will be described in more detail below, preferably the period of generation of the time windows is slightly less than the period of the sequences of the video signal.

The above-mentioned step 100 is followed by a step 102 consisting in detecting the crossing of at least one threshold during at least one window on X consecutive windows. Preferably step 102 consists in detecting the crossing by the video signal of a minimum threshold or a maximum threshold.

The number X of consecutive windows can be adapted according to each particular application.

By way of nonlimiting example X can be equal to six. If during step 102 a threshold crossing is detected during at least one window on X windows consecu es. test step 102 and followed by step 1 04 during which the output signal indicative of a detection of digital data is generated at the end of each time window for forecasting the appearance of digital data. ques.

On the other hand, if the test step 102 is negative, that is to say: no threshold crossing is detected for X consecutive windows, the test step 102 is followed by a step 1 06 during which the time window is opened. Step 106 is followed by a step AS which consists in detecting a threshold crossing by the udeo signal. The window is kept open as long as such a threshold crossing is not detected in step 108.

On the other hand, when during the test step 1 8 a crossing of threshold is detected, the method proceeds to step 1 10 during which the window previously forced to open is closed and the generation period sequential of time windows for forecasting the appearance of digital data is reset when this window is closed. The method 110 is followed by the step 104 of generating a digital data detection signal.

Step 104 of signal generation is looped back to step 100 of sequential generation of time windows.

Schematically illustrated in Figure 6 the structure of the detection device 1 1 1 able to implement the above method. We see in this figure 6 a module 1 1 2 which sequentially generates time windows for predicting the appearance of digital data according to a period advantageously slightly less than the period of the sequences of the video signal. A module 1 14 detects the crossing by the video signal of at least one threshold, advantageously a minimum threshold or a maximum threshold during said time windows.

A third module 1 16 monitors the threshold crossing during at least one window on X consecutive windows. Module 1 16 forces the time window to open if such threshold crossing is not detected at least once during X f consecutive windows.

Finally we see in Figure 6 a fourth module I I S forming an output signal generator. The module 1 1 8 is validated at the end of each time window.

We will now describe the particular structure of the device 1 1 1 for detecting digital data shown in FIG. 7 appended.

This FIG. 7 shows the time window generator module 1 1 2, the module 1 14 threshold crossing detector, the module 1 1 6 for monitoring the crossing of threshold for at least one window on X consecutive windows and the module 1 1 8 output signal generator.

The module 1 14 includes two buffer amplifiers 1 20, 1 22, a low-pass video filter 121, two comparators 1 23, 1 2- arranged respectively as high threshold detector and low threshold detector. two flip-flops 125, 126 and an AND gate 127.

The module 1 1 6 surveillance is formed essentially of a shift register 128 and a NAND gate 129. The time window generator module 1 12 comprises essentially a clock ^"quartz 1 30, a counter 1 31 and a generator pulse or monostable 132.

The module 1 18 output signal generator is formed by a pulse generator or monostable. The input video signal is taken through a ^m plificateur buffer 120, video low pass filter 121 and buffer amplifier 122 connected in series. This arrangement improves the immunity of the system against noise.

The video signal is then routed simultaneously to the high threshold detector 123 and the low threshold detector 124. The comparator 123 compares the signal from the buffer amplifier 122 to a high reference level Ul, while the comparator 124 compares the same video signal at a low reference level U2.

Comparators 123, 124 thus generate on their output clock pulses, when detecting the crossing of the high threshold or the low threshold. These clock pulses are applied to the flip-flops 1 25 and 1 26. They also receive, on their reset input, a T2 signal from the pulse generator or monostable 132. This T2 signal shown schematically on the first line of figure S corresponds to a time window for forecasting the appearance of digital data. Thus, flip-flops 125 and 1 26 have their output Q which goes to the low state if the pulses generated by the comparators 1 23, 1 2 ^ are during the time window T2. The outputs Q of flip-flops 1 25 and 1 26 are connected to the inputs of gate 127. The output of this latter is connected to the input of shift register 128. Thus the low state at the output of flip-flops 125 and 126 e -st transferred to the shift register 1 2S at each pulse of the time window signal T2. Gate 129 forms a logical combination of six successive outputs from the register. offset 1 28 and of the outputs Q of flip-flops 125 and 126. Gate 129 is connected to the pulse generator or monostable 132. Thus, if for six consecutive lines the threshold detectors 123, 124 are not requested, gate 1 29 forces the output of the pulse generator or monostable 1 32 to the high level, the system is unlocked and the window T2 for detection of data appearance remains open. Gate 129 will stop forcing the pulse generator or. monostable 61 3 at the high level, after detection of the crossing of one of the thresholds. The pulse generator or monostable 1 32 includes a counter which counts the pulses from the quartz clock 130 to generate the time window signal T2. More specifically, the counter integrated into the pulse generator or monostable 13 is reset by the output of the counter 131. The latter also counts the pulses. the quartz clock 130 for generating output pulses at a period such that the period of the time windows T2 is slightly less than the line period of the video signal.

The pulse generator or monostable 1 18 also receives the signal from the quartz clock 130 to generate at its output pulses T3 of determined duration on the falling background of the signal T2. The output of the IIS pulse generator or monostable constitutes the output of the digital data detector.

The pulse generator or monostable 1 1 S is thus emptied only on the falling edges of the signal T2, that is to say when closing each time window for detecting threshold crossing.

As previously indicated, the detection of the presence of recurrent digital data in a video signal can be used in particular for signal alignment. There is shown schematically in Figure 9 attached an alignment device according to the present invention.

We see in Figure 9 an adder 1 50. three buffer amplifiers ic 151, 1 52 and 1 56, a switch 1 53, a level detector 1 54, a comparator 155 and the digital data detector device 1 1 1 mentioned above.

The level detector 1 54 is advantageously of the known type with diode and capacitor.

The digital data detector 1 1 1 receives the input signal v ideo via the buffer amplifier 1 56. The input signal is applied to one of the inputs of the adder 150. The output of the adder 1 50 is connected to the input of the buffer amplifier 1 51. The switch 1 53 is placed between the output of the aforementioned buffer amplifier 151 and the input of the buffer amplifier 152. The output of the buffer amplifier 152 is connected to the input of the level detector 1 54. The output of the level detector 154 is connected to a first input of the comparator 155. The second input of the comparator 155 receives a reference voltage VREF .

The output of comparator 155, on which a correction signal is available, is applied to the second input of adder 150.

The switch 153 is only placed in the closed state when the detector 1 1 1 identifies the presence of digital data. This ensures that the level detector 154 detects one of the extremes of the data digital (the extreme negative according to the orientation of the diode represented schematically in the detector 154 in FIG. 9).

The switch 153 is advantageously closed during the state at the high level of the signal T3 coming from the output generator 1 1 S of the detector 1 1 1.

The device shown in FIG. 9 therefore makes it possible to align the video signal with the negative end of the digital data.

FIG. 10 shows an improved alternative embodiment of the device enabling the video signal to be aligned with the average value of the extremes of the digital data.

For this, the error voltage generated at the output of the comparator, 1 55 is no longer obtained by comparing only one of the extremes of the digital data with a reference voltage, but by comparing, with the reference voltage , the average of the extremes of the numerical data. These extremes of the numerical data are detected respectively in a detector of maximum value 1540 and in a detector of minimum value 1545.

The device shown in Figure 10 includes an adder 1 50, three amplifiers Buffer 1 51, January 52, 1˝ 56, a comparative tor 155, a switch 153, two ^of additional buffer amplifiers 1541, 1546 and 1542 and two resistors R R 1547.

These elements are essentially arranged as described above with reference to FIG. 9.

The maximum value detector 1540 has its input connected to the output of the buffer amplifier 152 while its output is connected to the input of the comparator 155 via the buffer amplifier 1541 and the resistor R I 542.

In parallel, the minimum value detector 1545 has its input connected to the output of the buffer amplifier 152 and to its output connected via the buffer amplifier 1546 and the resistor.

R 1547, with the same value as resistor R 1542, has the same comparator 155 input.

Buffer amplifier 151 takes the output video signal of the adder 1 50. When the detector 1 1 1 of digital data identifies the presence of digital data, at the level of the input signal, it closes the switch 153. Thus the video signal is not present at the input 1540 and 1545 only when digital data is available. The detectors 1540 and 1545 respectively detect the maximum and minimum values of the digital data of the video signal. The resistors RI 542 and RI 547 define an average value of these extremes applied to the comparator 155.

The output video signal is thus aligned with the average value of the extremes of the digital data.

The present invention can also find application in the automatic gain control of a video amplifier. For this, the video amplifier is controlled by the extremes measured on the video signal when detecting the presence of digital signals. As indicated previously, the present invention can also find application in the modulation depth control.

More generally, the present invention can find application in the production of a video signal processing device chosen from the group comprising high frequency reception devices, modulation devices and video transcoding devices.

Of course the present invention is not limited to the particular embodiments which have just been described but extends to all variants in accordance with its spirit.

For example, one can consider operating the de- of digital data during each iron. be temporal by detection of the crossing of a single threshold. In this hypothesis, one of the comparators 123, 124, one of the flip-flops 125, 126 and the AND gate 127 of FIG. 7 must be deleted. This simplification does not however make it possible to detect with certainty the start of the digital data if the first bits of the digital data are of identical level and opposite to that detected when the threshold is crossed. The period of the signal T3 must therefore be reduced accordingly with respect to the variation with double threshold detection.

Claims

1. Method for detecting the presence of recurrent digital data in a video signal, characterized by the fan that it comprises the steps consisting in:

- sequentially generating (100) a time window T2 for predicting the appearance of digital data, and

- detect the start of the digital data by detecting a threshold (1 23, 1 24) during each time window T2.

2. Method according to claim 1, characterized in that the step of detecting the start of the digital data consists of a * double threshold detection (123, 124), respectively high or low, during each time window T2.

3. A method according to one of claims 1 or 2, characterized in that it comprises the additional step ^(the 04) of generating an output signal indicative of digital data detection to f in each window .

.. Method according to one of claims 1 to 3, characterized in that it comprises the additional steps consisting in: - detecting (102) the crossing of threshold during at least one window on X consecutive windows,

- force (1 06) the window to open if a threshold crossing is not detected for at least one window on X consecutive windows, and

- close (1 10) the window thus opened and readjust the sequence of generation of time windows when a threshold crossing is detected during the open window.

5. Method according to one of claims 1 to 4, characterized in that the generation period of the time windows T2 for predicting the appearance of the digital data is substantially equal to the period of recurrence of the sequences of the video signal.

6. Method according to one of claims 1 to 5, characterized in that the generation period of the time windows T2 for predicting the appearance of digital data is slightly less than the period of recurrence of the sequences of the video signal.

7. Device digital Recur ^r ales data presence detection in a video signal, for carrying out the method according to one of claims 1 to 6, characterized in that the i comprises:

a sequential generator of a time window for predicting the appearance of digital data (1 12), and

- Threshold crossing detector means (1 14) during each time window.

8. Detection device according to claim 7, characterized in that it comprises a quartz clock (1 30) and a counter (1 3 1) designed to synchronize the time window for predicting the appearance of digital data T2 with the incident video signal.

9. Device according to one of claims 7 or S, characterized in that the means (1 14) threshold crossing detectors detect the crossing, by the video signal, of a low threshold or a high threshold, during each time window.

10. Device according to one of claims 7 to 9, characterized by the milk which it further comprises:

- Means (1 16) able to check the crossing of the threshold during at least one window on X consecutive windows, - Means (129) able to force the window to open if a crossing of threshold is not detected during at least one window on X consecutive windows, and

- Means (129, 13) able to close the window thus opened and to readjust the sequence of generation of time windows when a threshold crossing is detected during the open window.

11. Device according to one of claims 7 to 10, characterized in that it comprises a pulse generator or monostable (1 18) designed to generate a pulse T3, initiated during the closing of the time window of prediction of the appearance of T2 digital data.

12. Device according to one of claims 7 to 1 1, characterized in that it comprises a filter (121) through which passes the incident video signal before attacking the device (123, 124, 125, 126) of detection of the start of digital data, in order to improve the noise immunity of this detection.

13. Detection device according to one of claims 7 to 12, characterized in that it comprises:

- a set of counters (1 30, 1 31) generating recurrent T2 pulses representative of a time window for predicting the appearance of digital data,

- two detectors (123, 1 24) comparing the input video signal with respective thresholds U l, U2 high and low,

- two flip-flops (125, 126) controlled by the outputs of the detectors (123, 124).

- a shift register (128) which receives as input a logical combination of the outputs of the two flip-flops (1 25, 126),

- A gate (129) which forms a logical combination of the outputs of the shift register (128) to force the time window for predicting the appearance of digital data T2 upon opening, when the respective high and low thresholds do not have not been crossed for a specified number of consecutive scan lines,

- a pulse generator or output monostable (1 18) validated when the time window for predicting the appearance of digital data is closed.

14. Device according to one of claims 7 to 1 3, characterized in that the digital baseband data are the data and synchronization bits of a video signal of the MAC family.

15. Device according to one of claims 7 to 14, characterized in that it further comprises:

- at least one level detector (154; 1540, 1545) designed to detect at least one extreme of the digital signals detected in the video signal,

a comparator (155) able to compare the detected level with a reference voltage VREF to generate an error voltage proportional to the difference between the detected level and the reference voltage, and

- an adder (150) able to add the error voltage to the video signal * in order to control a determined level of the video signal with respect to the reference voltage VREF, and to carry out a non-pinched alignment of the video signals.

16. Device according to claim 15, characterized in that the level detector (1540, 1545) is designed to detect several determined levels and to form a combination of these determined levels.

17. Device according to one of the claims 1 5 or 1 6, characterized in that the level detector comprises a first detector (1 540) designed to detect the maximum values of digital data and a second detector (1 545) designed to detect minimum values of digital data, as well as means (1 54 1. 1 546, RI 542, K i 547) for averaging the maximum and rr '-umale values detected.

18. Device according to one of claims 1 5 or 1 7, characterized in that it comprises an electronic switch (1 A designed to be closed only during the detection of digital data, so that the signal v ideo is applied at the input of the level detector only in the presence of digital data.

19. Device according to one of claims 1 to 1 S, characterized in that it comprises a variable gain input amplifier controlled by the extremes of the digital data detected.

20. Application of the device in accordance with one of claims 7 to 19, in the production of a video signal processing device chosen from the group comprising high-frequency reception devices, modulation devices and video transcoding.