TWI454152B - Video standard detector and operation method thereof and intermediate frequency demodulator - Google Patents

Description

Video standard detector and its operation method and intermediate frequency demodulator

The present invention relates to a television demodulation, and more particularly to a video standard detector and a video standard detection method for determining a video standard to which a baseband signal belongs.

In general, in analog TV applications, a tuner is usually used to downconvert a television signal from a radio frequency (RF) band to an intermediate frequency (IF) band. The IF demodulator is used to demodulate the IF signal into a composite video broadcast signal (CVBS) and a sound signal.

Composite video broadcast signals have various standard specifications due to regionality. The current composite video broadcast signal contains three specifications, the National Television Systems Committee (NTSC), the Phase Alternating Line (PAL), and the sequential transmission of color and storage ( Couleur , SECAM). All of the above methods adopt Amplitude Modulation (AM) mode, and the amplitude modulation mode can be divided into two modes: Positive Modulation Mode and Negative Modulation Mode.

The NTSC video standard is a negative modulation mode with a field period of approximately 16.67 milliseconds. The PAL video standard is a negative modulation mode with a field period of approximately 20 milliseconds. The SECAM-L video standard is one of the branches of the SECAM video standard. It belongs to the positive modulation mode and has a field period of approximately 20 milliseconds.

Therefore, in the stage of signal intermediate frequency demodulation, it is necessary to discriminate the composite video broadcast signal specification to which it belongs, in order to demodulate the correct composite video broadcast signal.

The invention provides a video standard detector and an operation method thereof and an intermediate frequency demodulator, which can determine which video standard the baseband signal belongs to.

The invention provides a video standard detector comprising a low pass filter and a feature detector. A low pass filter filters the baseband signal. The feature detector detects the vertical synchronization information and the horizontal synchronization information of the baseband signal by using the output of the low-pass filter, and determines which video standard the baseband signal belongs to according to the vertical synchronization information and the horizontal synchronization information.

The invention also proposes a video standard detection method, which comprises filtering a fundamental frequency signal to obtain a filtering result. Filter the result to detect vertical sync information. By using the filtered result to detect horizontal synchronization information. The vertical synchronization information and the horizontal synchronization information are used to determine which video standard the baseband signal belongs to.

The invention provides an intermediate frequency demodulator comprising an analog digital converter, a frequency shifting unit, a low pass filter, a feature detector and a baseband processor. The analog digital converter converts the intermediate frequency signal into a digital signal. The frequency shifting unit shifts the digital signal to output a baseband signal. The low pass filter filters the fundamental frequency signal. The feature detector detects the vertical synchronization information and the horizontal synchronization information of the baseband signal by using the output of the low-pass filter, and determines which video standard the baseband signal belongs to according to the vertical synchronization information and the horizontal synchronization information. The baseband processor processes the baseband signal according to the video standard to generate a composite image broadcast signal and a sound signal.

Based on the above, the present invention converts an intermediate frequency signal into a digital signal by an analog digital converter and a frequency shifting unit. Then, the low-pass filter and the feature detector in the video standard detector are used to determine which standard the baseband signal converted by the intermediate frequency signal belongs to, and correspondingly process the fundamental video signal.

The above described features and advantages of the present invention will be more apparent from the following description.

The dynamic image transmission method of the traditional analog television broadcasting system is composed of a series of static pictures. A static picture is also called a frame, which is composed of hundreds of horizontal scanning lines. For the interlaced scanning method, these horizontal scanning lines are further divided into odd lines and even lines. All odd lines form an odd field (Odd Field), and all even lines form an even field (Even Field). Part of the horizontal scanning line in each field is set to Vertical Synchronization. Each horizontal scan line has a horizontal synchronization (Horizontal Synchronization).

The NTSC video standard is a negative modulation mode with about 30 frames per second (ie, about 60 fields per second), so the vertical scanning frequency is about 60 Hz, and the field period is about 16.67 milliseconds. The NTSC video standard contains 525 horizontal scan lines per frame, so the horizontal scan frequency is approximately 15.734 kHz. The PAL video standard is a negative modulation mode with about 25 frames per second (ie, about 50 fields per second), so the vertical scanning frequency is about 50 Hz, and the field period is about 20 milliseconds. The SECAM-L video standard is one of the branches of the SECAM video standard. It belongs to the positive modulation mode, which has about 25 frames per second (ie, about 50 fields per second), so the vertical scanning frequency is about 50 Hz, and the field period is about Slightly 20 milliseconds. The PAL video standard and the SECAM-L video standard contain 625 horizontal scan lines per frame, so the horizontal scanning frequency is approximately 15.625 kHz.

1 is a block diagram showing an intermediate frequency demodulator in accordance with an embodiment of the present invention. Referring to FIG. 1, the intermediate frequency demodulator 100 includes an analog digital converter 101, a frequency shifting unit 102, a video standard detector 200, and a baseband processor 103. The analog-to-digital converter 101 receives and converts the analog intermediate frequency signal IFA to a digital signal IED. The frequency shifting unit 102 is coupled to the analog-to-digital converter 101, and shifts the digital signal IFD from the intermediate frequency to the fundamental frequency to output a baseband signal BB. The video standard detector 200 receives the baseband signal BB, determines which video standard the baseband signal BB belongs to, and then outputs a determination result R1. The baseband processor 103 is coupled to the frequency shifting unit 102 and the video standard detector 200, and correspondingly processes the baseband signal BB to obtain the baseband video signal BBV according to the determination result R1 of the video standard detector 200. The baseband video signal BBV includes a composite video broadcast signal (CVBS) and an audio signal.

The analog digital converter 101, the frequency shifting unit 102 and the baseband processor 103 described above can be implemented in any manner. For example, an analog digital converter 101 is implemented with a pipeline analog digital converter. Those skilled in the art should be familiar with the analog-to-digital converter 101, the frequency shifting unit 102, and the baseband processor 103, and therefore will not be described herein.

The video standard detector 200 includes a low pass filter (LPF) 201 and a feature detector 202. The low pass filter 201 filters the fundamental frequency signal BB to output a filtered result BBL. The feature detector 202 is coupled to the low pass filter 201. The feature detector 202 detects the vertical synchronization information and the horizontal synchronization information, and determines which video standard the baseband signal BB belongs to according to the vertical synchronization information and the horizontal synchronization information. The vertical synchronization information includes a field period of the baseband signal BB, and the horizontal synchronization information includes a horizontal synchronization number (horizontal line number) in the field period and a modulation mode of the filtering result BBL. Therefore, the feature detector 202 generates the determination result R1 to the baseband processor 103. The baseband processor 103 processes the baseband signal BB in accordance with the determination result R1.

2 is a block diagram showing the video standard detector 200 of FIG. 1 in accordance with an embodiment of the present invention. The low pass filter 201 includes a narrow band low pass filter 301 and a wide band low pass filter 302. The filter result BBL output by the low pass filter 201 includes the narrowband signal BBL1 output by the narrowband low pass filter 301 and the wideband signal BBL2 output by the wideband low pass filter 302. The feature detector 202 includes a vertical sync finder 303, a horizontal sync finder 304, and a decision unit 305. The narrowband low pass filter 301 receives and filters the baseband signal BB to output a narrowband signal BBL1 to the vertical sync detector 303 of the feature detector 202. The vertical sync detector 303 detects the filter result BBL (ie, the narrowband signal BBL1) to obtain the vertical sync information including the field period to the decision unit 305. The aforementioned field period is determined by counting the time interval between two adjacent field peaks. The horizontal sync detector 304 detects the filter result BBL (ie, the wideband signal BBL2) to obtain the horizontal sync information to the decision unit 305. The horizontal synchronization information includes the horizontal synchronization number (the number of horizontal lines) and the modulation mode. In addition, when the vertical synchronization information is detected, the vertical synchronization detector 303 further notifies the horizontal synchronization detector 304 to detect the horizontal synchronization information.

FIG. 3 is a timing diagram showing the narrowband signal BBL1 outputted by the narrowband low-pass filter 301 of FIG. 2 when the baseband signal BB is a signal of a video standard such as NTSC, PAL, and SECAM-L, respectively, according to another embodiment of the present invention. In Figure 3, the NTSC and PAL video standards are both in the negative modulation mode, while the SECAM-L video standard is in the positive modulation mode.

Referring to FIG. 2 and FIG. 3, after the fundamental frequency signal BB passes through the narrowband low pass filter 301, the characteristics of the signal can be visualized. As shown in FIG. 3, after the fundamental frequency signal BB of various video standards passes through the narrowband low-pass filter 301, periodic field peaks (maximum or minimum values) appear in the vertical sync region. For example, in the NTSC video standard, after the narrowband low-pass filtering, the baseband signal BB will appear on the 4th, 5th, and 6th scan lines (in the even field) and the 267th, 268th, and 269th scan lines (in the odd field). Sexual field peaks (maximum values). For example, under the PAL video standard, after the narrowband low-pass filtering, the baseband signal BB is on the first, second, and third scan lines (in the even field) and the 313th, 314, and 315th scan lines (in the odd field). ) Periodic field peaks (maximum values) appear. For the SECAM-L video standard, since it belongs to the positive modulation mode, the fundamental frequency signal BB passes through the narrowband low-pass filtering, and will be on the first, second, and third scan lines (in the even field) and the third and third lines, Periodic field peaks (minimum values) appear on 315 scan lines (in odd fields).

Therefore, the vertical sync detector 303 can detect the narrowband signal BBL1 to learn the field peak of the fundamental frequency signal BB, and count the time interval of the adjacent two field peaks to output the field period (as vertical synchronization information) to the decision unit 305. In fact, the aforementioned field period includes the positive field period obtained in the positive modulation mode, and/or the negative field period obtained in the negative modulation mode. For example, if the baseband signal BB belongs to the NTSC video standard, the vertical sync detector 303 can detect that the negative field period of the narrowband signal BBL1 is about 16.67 milliseconds (60 Hz). If the baseband signal BB belongs to the PAL video standard, the vertical sync detector 303 can detect that the negative field period of the narrowband signal BBL1 is about 20 milliseconds (50 Hz). If the baseband signal BB belongs to the SECAM-L video standard, the vertical sync detector 303 can detect that the positive field period of the narrowband signal BBL1 is about 20 milliseconds (50 Hz). Therefore, depending on the field period (positive field period and/or negative field period), the system can be distinguished as the NTSC video standard, the PAL video standard or the SECAM-L video standard.

Regardless of the system, each visible line (horizontal line) will have horizontal synchronization at the beginning. Therefore, in this embodiment, by adding a mechanism for detecting horizontal synchronization, a horizontal synchronization check window (HSync check window) is set between adjacent two vertical synchronizations. The number of horizontal syncs (ie, horizontal scan lines) is calculated during this period to increase the reliability of the video standard detection.

Finally, the determining unit 305 uses the vertical synchronization information (field period) output by the vertical synchronization detector 303 and the horizontal synchronization information (including the horizontal synchronization number and the modulation mode) output by the horizontal synchronization detector 304 as the judgment of the detection video standard. in accordance with. In an application example, referring to FIG. 2 and FIG. 3, video standards such as PAL, SECAM-L, and NTSC can be utilized in different channels. If the negative field period is approximately 20 milliseconds, and the number of horizontal synchronizations in the negative modulation mode (hereinafter referred to as negative horizontal synchronization) is greater than the first preset value, it is determined that the fundamental frequency signal BB belongs to the PAL video standard, that is, the channel is PAL. Standard channel. If the negative field period of the other channel is approximately 16.67 milliseconds and the negative horizontal synchronization number is greater than the third predetermined value, it is determined that the fundamental frequency signal BB belongs to the NTSC video standard, that is, the channel is an NTSC standard channel. If the positive field period of another channel is approximately 20 milliseconds, and the horizontal synchronization number (hereinafter referred to as positive horizontal synchronization) in the positive modulation mode is greater than the second preset value, it is determined that the fundamental frequency signal BB belongs to the SECAM-L video standard. That is, this channel is the standard channel of SECAM-L. The video standard corresponding to the baseband signal BB is determined by the decision unit 305 based on at least one of a field period (including at least one of a positive field period and a negative field period) and a horizontal synchronization number (including both positive horizontal synchronization and negative horizontal synchronization). ) decided. In addition, the foregoing first preset value may be any integer (for example, 300) less than or equal to the number of PAL field lines, and the foregoing second preset value may be any integer less than or equal to the number of SECAM-L field lines ( For example, 300), and the aforementioned third preset value may be any integer (eg, 250) that is less than or equal to the number of NTSC field lines.

The operation of the horizontal sync detector 304 described above can be referred to FIG. 4 and FIG. 5. Fig. 4 is a waveform diagram of a scanning line having a horizontal modulation of positive modulation mode in the present embodiment. Referring to FIG. 4, the horizontal synchronization detector 304 searches for the horizontal synchronization minimum value HsyncPeak of the filtering result BBL (ie, the wideband signal BBL2), wherein the horizontal synchronization minimum value HsyncPeak must conform to the characteristics of the periodic occurrence, and if not, re-search. Next, a fixed-width entry observation window BkPorchWindow is set in the vicinity of the horizontal synchronization minimum value HsyncPeak of the filtering result BBL. The horizontal synchronization threshold HsyncThreshold is determined based on the average value of the filtering result BBL in the entry observation window BkPorchWindow and the horizontal synchronization minimum value HsyncPeak. Wherein, the average value is obtained based on the average of the broadband signal BBL2 in the BkPorchWindow.

Fig. 5 is a waveform diagram of a scanning line for determining whether or not positive horizontal synchronization is effective in the positive modulation mode in the embodiment. Referring to FIG. 5, if the value of the filtering result BBL (ie, the wideband signal BBL2) is less than the horizontal synchronization threshold HsyncThreshold, the horizontal synchronization segment output HsyncSlicerOut is a high level. A fixed-width error observation window HsyncErrWindow is opened in the vicinity of the horizontal synchronization minimum value HsyncPeak of the filtering result BBL, and the sample sum St of the high-level HsyncSlicerOut in the window is calculated. Finally, if the analysis sample sum St is within the criterion of positive horizontal synchronization, it is considered to be a valid positive horizontal synchronization. The horizontal sync detector 304 detects positive horizontal sync in the field period according to the above method, and further counts the number of positive horizontal syncs.

Similarly, in order to count the number of negative horizontal synchronizations of the filtering result BBL, first, the maximum value of the filtering result BBL (ie, the wideband signal BBL2) is searched for, and it must conform to the characteristics of the periodic occurrence, and if not, the search is re-searched. Next, the observation window of the fixed width is opened in the vicinity of the maximum value of the filtering result BBL, and the sum of the samples valid in the window is calculated according to the maximum value of the searched filtering result BBL, the above-mentioned HsyncSlicerOut, and the video standard. Next, analyze whether the sum of the samples is within the criterion of the negative level synchronization. If the sum of the sampled samples is within the criteria for the negative level synchronization, then it is considered a valid negative level synchronization. The horizontal sync detector 304 detects negative horizontal sync in the field period in accordance with the above method and further counts the number of negative horizontal syncs.

The feature detector 202 is not limited to the implementation shown in FIG. 2. FIG. 6 is a block diagram showing the feature detector 202 of FIG. 2 in accordance with another embodiment of the present invention. Referring to FIG. 6, the feature detector 202 includes a positive vertical sync detector 401, a positive horizontal sync detector 402, a negative vertical sync detector 403, a negative horizontal sync detector 404, and a decision unit 405. Since NTSC and PAL are both negative modulation mode systems, in order to save hardware area, the same set of hardware (ie, negative vertical sync detector 403 and negative horizontal sync detector 404) can be used for detection.

The positive vertical sync detector 401 operates in a positive modulation mode. The positive vertical sync detector 401 detects the filter result BBL (ie, the narrowband signal BBL1) to learn the positive vertical sync (ie, the minimum value) of the baseband signal BB, and counts the time intervals of two adjacent positive vertical syncs to output the positive field. cycle. The positive horizontal sync detector 402 operates in a positive modulation mode. The positive horizontal sync detector 402 detects the filtered result BBL (ie, the wideband signal BBL2) and learns the positive horizontal synchronization of the baseband signal BB, and counts the positive horizontal synchronization of the baseband signal BB in the positive field period to output the positive horizontal synchronization number. In addition, when the positive field period is detected, the positive vertical sync detector 401 further informs the positive horizontal sync detector 402 to detect the number of positive horizontal syncs.

The negative vertical sync detector 403 operates in a negative modulation mode. The negative vertical sync detector 403 detects the filtered result BBL (ie, the narrowband signal BBL1) to learn the negative vertical sync (ie, the maximum value) of the baseband signal BB, and counts the time interval between two adjacent negative vertical syncs to output a negative field. cycle. The negative horizontal sync detector 404 operates in a negative modulation mode. The negative horizontal sync detector 404 detects the filtered result BBL (ie, the wideband signal BBL2) and learns the negative horizontal synchronization of the baseband signal BB, and counts the negative horizontal sync of the baseband signal BB in the negative field period to output the negative horizontal sync number. In addition, when the negative field period is detected, the negative vertical sync detector 403 further notifies the negative level sync detector 404 to detect the number of negative horizontal syncs.

The aforementioned positive vertical sync detector 401 and negative vertical sync detector 403 can be implemented with reference to the related description of vertical sync detector 303. Additionally, the aforementioned positive horizontal sync detector 402 and negative horizontal sync detector 404 can be implemented with reference to the related description of horizontal sync detector 304.

The decision unit 405 is coupled to the positive vertical sync detector 401, the positive horizontal sync detector 402, the negative vertical sync detector 403, and the negative horizontal sync detector 404. Wherein, if the negative field period is approximately 20 milliseconds and the negative horizontal synchronization number is greater than the first preset value, it is determined that the fundamental frequency signal BB belongs to the PAL video standard. If the positive field period is approximately 20 milliseconds and the positive horizontal synchronization number is greater than the second predetermined value, it is determined that the fundamental frequency signal BB belongs to the SECAM-L video standard. If the negative field period is approximately 16.67 milliseconds and the negative horizontal synchronization number is greater than the third predetermined value, it is determined that the fundamental frequency signal BB belongs to the NTSC video standard. The first preset value, the second preset value, and the third preset value are arbitrary integers, and can be set according to design requirements.

To further confirm the judgment result, the decision unit 405 can add more judgment conditions. That is, in other embodiments, if the negative field period and/or the positive field period is approximately 20 milliseconds, and the negative horizontal synchronization number is greater than the first preset value, and the positive horizontal synchronization number is less than or equal to the fourth preset value ( For example, if it is 0), it is judged that the fundamental frequency signal BB belongs to the PAL video standard. If the number of positive horizontal synchronizations is greater than the second preset value, and the number of negative horizontal synchronizations is less than or equal to the fourth predetermined value, it is determined that the fundamental frequency signal BB belongs to the SECAM-L video standard. If the negative field period is approximately 16.67 milliseconds, and the negative horizontal synchronization number is greater than the third preset value, and the positive horizontal synchronization number is less than or equal to the fourth predetermined value, it is determined that the fundamental frequency signal BB belongs to the NTSC video standard.

Feature detector 202 can also be implemented with reference to FIG. FIG. 7 is a block diagram showing the feature detector 202 of FIG. 2 in accordance with another embodiment of the present invention. Referring to FIG. 7, the feature detector 202 includes a first positive vertical sync detector 501, a first positive horizontal sync detector 502, an inverting unit 503, a second positive vertical sync detector 504, and a second positive horizontal sync detector 505. And determining unit 506.

The first positive vertical sync detector 501 detects the filtered result BBL (ie, the narrowband signal BBL1) to learn the positive vertical sync of the baseband signal BB, and counts the time intervals of two adjacent positive vertical syncs to output a positive field period. The first positive horizontal synchronization detector 502 detects the filtering result BBL (ie, the wideband signal BBL2) to learn the positive horizontal synchronization of the fundamental frequency signal BB, and counts the positive horizontal synchronization of the fundamental frequency signal BB in the positive field period to output a positive level. The number of synchronizations. In addition, when the positive field period is detected, the first positive vertical sync detector 501 further notifies the first positive horizontal sync detector 502 to detect the positive horizontal sync number.

The inverting unit 503 inverts the filtering result BBL to output an inverted result, and the inverted result thereof is inverted from the filtered result BBL. The second positive vertical sync detector 504 detects the inverted result of the filtered result BBL to learn the negative vertical sync of the baseband signal BB, and counts the time interval of two adjacent negative vertical syncs to output a negative field period. The second positive horizontal sync detector 505 detects the inverted result of the filtered result BBL to learn the negative horizontal synchronization of the fundamental frequency signal BB, and counts the negative horizontal synchronization of the fundamental frequency signal BB in the negative field period to output the negative horizontal synchronization number. In addition, when the negative field period is detected, the second positive vertical sync detector 504 further notifies the second positive horizontal sync detector 505 to detect the number of positive horizontal syncs. In particular, the inverting unit 503, the second positive vertical sync detector 504, and the second positive horizontal sync detector 505 are implemented as the negative vertical sync detector 403 and the negative horizontal sync detector 404 of FIG.

The determining unit 506 is coupled to the first positive vertical sync detector 501, the first positive horizontal sync detector 502, the second positive vertical sync detector 504, and the second positive horizontal sync detector 505. The decision unit 506 is similar to the decision unit 405 in FIG. 6, and its function will not be described herein. The first positive vertical sync detector 501 and the second positive vertical sync detector 504 can be implemented with reference to the related description of the vertical sync detector 303. In addition, the aforementioned first positive horizontal synchronization detector 502 and second positive horizontal synchronization detector 505 can be implemented with reference to the related description of horizontal synchronization detector 304.

FIG. 8 is a block diagram showing the video standard detector 200 of FIG. 1 in accordance with another embodiment of the present invention. The video standard detector 200 includes an inverter 205, a switch 206, a low pass filter 201, and a feature detector 202. The inverter 205 receives the down-converted signal (ie, the baseband signal BB output by the frequency shifting unit 102) to output an inverted signal, wherein the inverted signal and the down-converted signal are inverted from each other. The first input of the switch 206 receives the down-converted signal, the second input of the switch is coupled to the inverter 205, and the output of the switch is coupled to the low-pass filter 201. The switch 206 selects the inverted signal or the down-converted signal as the baseband signal BB' according to the selection signal and outputs it to the low-pass filter 201.

In the present embodiment, the feature detector 202 has only a positive/negative vertical sync detector and a positive/negative horizontal sync detector. Feature detector 202 provides switch 206 selection signals. First, the feature detector 202 controls the switch 206 to select the down-converted signal as the baseband signal BB'. The low pass filter 201 filters the fundamental frequency signal BB' and outputs a filtered result BBL. The feature detector 202 detects the filtered result BBL to know the positive field period of the down-converted signal (ie, the baseband signal BB output by the frequency shifting unit 102) and the number of positive horizontal synchronizations in the field period.

Next, the feature detector 202 controls the switch 206 to select the inverted signal output from the inverter 205 as the base frequency signal BB'. The low pass filter 201 filters the high frequency component of the fundamental frequency signal BB' and outputs a filtered result BBL. The feature detector 202 detects the filtering result BBL to know the negative field period of the down-converted signal (ie, the baseband signal BB output by the frequency shifting unit 102) and the number of negative horizontal synchronizations in the field period.

After the feature detector 202 completes the above operation, a positive field period, a negative field period, a positive horizontal synchronization number, and a negative horizontal synchronization number can be obtained. Therefore, the feature detector 202 can determine which video standard the baseband signal BB belongs to according to the positive field period, the negative field period, the positive horizontal synchronization number, and the negative horizontal synchronization number, and then output the determination result R1 to the baseband processor 103. For how the feature detector 202 detects the positive field period, the negative field period, the positive horizontal synchronization number, and the negative horizontal synchronization number, and how to determine which video standard the basic frequency signal BB belongs to, the feature detectors of FIG. 2 to FIG. 7 can be referred to. 202, so I won't go into details here. In the embodiment of Figure 8, feature detector 202 is implemented with only a positive/negative vertical sync detector and a positive/negative horizontal sync detector to save hardware area.

FIG. 9 is a flow chart of a method for detecting a video standard according to an embodiment of the invention. Please refer to FIG. 1 and FIG. 9 together. In step S901, the low pass filter 201 filters the fundamental frequency signal BB to obtain a filtered result BBL. The feature detector 202 detects the filter result BBL to learn the negative field period of the baseband signal BB (step S902), and learns the positive field period of the baseband signal BB (step S913). After step S902 is completed, steps S903 to S912 are performed. After step S913 is completed, steps S914 to S919 are performed.

The feature detector 202 determines in step S903 what the negative field period is. If the negative field period is approximately 16.67 milliseconds (e.g., in the range of 16-17 milliseconds), feature detector 202 proceeds to steps S904-S902. If the negative field period is approximately 20 milliseconds (e.g., in the range of 19.5 to 20.5 milliseconds), the feature detector 202 proceeds to steps S909 to S910. If the negative field period does not fall within the above two ranges, it means that it is impossible to detect which video standard the basic frequency signal BB belongs to (step S908).

In step S904, the feature detector 202 detects the filtering result BBL to know the number of negative horizontal synchronizations in the negative field period of the baseband signal BB. In step S905, the feature detector 202 determines whether the number of negative horizontal synchronizations is greater than a third preset value. If the number of times of the negative horizontal synchronization is greater than the third preset value, it is determined that the fundamental frequency signal BB belongs to the NTSC video standard (step S906), otherwise it indicates that it is impossible to detect which video standard the basic frequency signal BB belongs to (step S907).

In step S909, the feature detector 202 detects the filtering result BBL to know the number of negative horizontal synchronizations in the negative field period of the baseband signal BB. In step S910, the feature detector 202 determines whether the number of negative horizontal synchronizations is greater than a first preset value. If the number of negative horizontal synchronizations is greater than the first preset value, it is determined that the baseband signal BB belongs to the PAL video standard (step S911), otherwise it indicates that it is impossible to detect which video standard the basic frequency signal BB belongs to (step S912).

In step S914, the feature detector 202 determines the positive field period. If the positive field period is approximately 20 milliseconds (e.g., in the range of 19.5 to 20.5 milliseconds), the feature detector 202 proceeds to steps S916 through S917. If the positive field period does not fall within the above range, it means that it is impossible to detect which video standard the basic frequency signal BB belongs to (step S915). In step S916, the feature detector 202 detects the filtering result BBL to know the number of positive horizontal synchronizations in the positive field period of the baseband signal BB. In step S917, the feature detector 202 determines whether the number of positive horizontal synchronizations is greater than a second preset value. If the number of positive horizontal synchronizations is greater than the second preset value, it is determined that the fundamental frequency signal BB belongs to the SECAM-L video standard (step S918), otherwise it indicates that it is impossible to detect which video standard the basic frequency signal BB belongs to (step S919).

Based on the above, the embodiment of the present invention converts the intermediate frequency signal IFA into a digital signal IFD by the analog digital converter 101 and the frequency shifting unit 102. Then, the low-pass filter 201 and the feature detector 202 in the video standard detector 200 are used to determine which standard the baseband signal BB converted by the intermediate frequency signal IFA belongs to, and the baseband processor 103 correspondingly processes the fundamental frequency. The signal BB is obtained to obtain a fundamental video signal BBV.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the invention, and any one of ordinary skill in the art can make some modifications and refinements without departing from the spirit and scope of the invention. The scope of the invention is defined by the scope of the appended claims.

100. . . IF demodulator

101. . . Analog digital converter

102. . . Frequency shifting unit

200. . . Video standard detector

103. . . Baseband processor

201, 203. . . Low pass filter

202. . . Feature detector

205, 503. . . inverter

206. . . Switcher

301. . . Narrowband low pass filter

302. . . Wideband low pass filter

303. . . Vertical sync detector

304. . . Horizontal sync detector

305, 405, 506‧‧‧Decision unit

401‧‧‧Vertical vertical sync detector

402‧‧‧Positive horizontal synchrotron

403‧‧‧negative vertical sync detector

404‧‧‧negative horizontal synchrotron

501‧‧‧First Positive Vertical Synchronizer

502‧‧‧First positive horizontal synchrotron

504‧‧‧Second positive vertical sync detector

505‧‧‧Second positive horizontal synchronous detector

HsyncPeak‧‧‧ horizontal synchronization minimum

BkPorchWindow‧‧‧ entrance observation window

HsyncThreshold‧‧‧ horizontal synchronization threshold

HsyncSlicerOut‧‧‧ horizontal sync segment output

HsyncErrWindow‧‧‧Error Viewing Window

St‧‧‧ sample sum

S901~S908‧‧‧ steps of the video standard detection method

S1001~S1013‧‧‧Steps of another video standard detection method

IFA‧‧‧IF signal

IFD‧‧‧ digital signal

BB‧‧‧ fundamental frequency signal

R1‧‧‧ judgment result

BBV‧‧‧ fundamental video signal

BBL‧‧‧Filter results

BBL1‧‧‧ narrowband signal

BBL2‧‧‧ Wideband signal

1 is a block diagram showing an intermediate frequency demodulator in accordance with an embodiment of the present invention.

2 is a block diagram showing the video standard detector of FIG. 1 in accordance with another embodiment of the present invention.

FIG. 3 is a schematic diagram showing the fundamental frequency signal and the filtering result of FIG. 2 according to another embodiment of the present invention.

Fig. 4 is a waveform diagram of a scanning line having positive horizontal synchronization in the embodiment.

Fig. 5 is a waveform diagram of the scanning line for determining effective positive horizontal synchronization in the positive modulation mode of Fig. 4 in the embodiment.

Figure 6 is a block diagram showing the feature detector of Figure 2 in accordance with an embodiment of the present invention.

Figure 7 is a block diagram showing the feature detector of Figure 2 in accordance with another embodiment of the present invention.

FIG. 8 is a block diagram showing the video standard detector of FIG. 1 according to an embodiment of the invention.

FIG. 9 is a flow chart of a method for detecting a video standard according to an embodiment of the invention.

100. . . IF demodulator

101. . . Analog digital converter

102. . . Frequency shifting unit

103. . . Baseband processor

200. . . Video standard detector

201. . . Low pass filter

202. . . Feature detector

IFA. . . IF signal

IFD. . . Digital signal

BB. . . Baseband signal

R1. . . critical result

BBV. . . Fundamental video signal

BBL. . . Filter result

Claims (15)

A video standard detector for detecting a video standard to which a baseband signal belongs, the video standard detector comprising: a low pass filter for filtering the baseband signal; and a feature detector coupled to the low a pass filter, using the output of the low pass filter to detect vertical synchronization information and horizontal synchronization information of the baseband signal, and determining, according to the vertical synchronization information and the horizontal synchronization information, which video standard the baseband signal belongs to The low pass filter includes: a narrowband low pass filter that filters the baseband signal to output a narrowband signal to the feature detector, wherein the feature detector uses the narrowband signal to detect the vertical sync information And a broadband low-pass filter that filters the baseband signal to output a wideband signal to the feature detector, wherein the feature detector uses the wideband signal to detect the horizontal synchronization information, wherein the narrowband signal The wideband signals together form the output of the low pass filter. The video standard detector of claim 1, wherein the feature detector comprises: a vertical sync detector coupled to the low pass filter, and the vertical sync information is detected by using the narrowband signal; a synchronous detector coupled to the low pass filter to detect the horizontal synchronization information using the broadband signal; A determining unit is coupled to the vertical sync detector and the horizontal sync detector to determine the video standard according to the vertical sync information and the horizontal synchronization information. The video standard detector of claim 2, wherein the vertical synchronization information includes a field period of the baseband signal, the horizontal synchronization information includes a number of horizontal lines in the field period and an output of the low pass filter. Modulation mode. The video standard detector of claim 2, wherein when the vertical synchronization information is detected, the vertical synchronization detector further notifies the horizontal synchronization detector to detect the horizontal synchronization information. An intermediate frequency demodulator comprising: an analog-to-digital converter that converts an intermediate frequency signal into a digital signal; a frequency shifting unit coupled to the analog digital converter, shifting the digital signal to output a fundamental frequency a low-pass filter coupled to the frequency shifting unit to filter the baseband signal; a feature detector coupled to the low pass filter, detecting the base using the output of the low pass filter Vertical synchronization information and horizontal synchronization information of the frequency signal, and determining which video standard the baseband signal belongs to according to the vertical synchronization information and the horizontal synchronization information; and a baseband processor coupled to the frequency shifting unit and the The feature detector processes the baseband signal according to the video standard to generate a composite image broadcast signal and a sound signal, wherein the low pass filter comprises: a narrowband low pass filter that filters the baseband signal to output a narrowband signal to the feature detector, wherein the feature detector uses the narrowband signal to detect the vertical sync information; and a wideband low pass filter, Filtering the baseband signal to output a wideband signal to the feature detector, wherein the feature detector uses the wideband signal to detect the horizontal synchronization information, wherein the narrowband signal and the wideband signal together comprise the low pass filter Output. The IF demodulator of claim 5, wherein the feature detector comprises: a vertical sync detector coupled to the low pass filter, and detecting the vertical sync information by using the narrowband signal; a horizontal synchronization detector coupled to the low-pass filter to detect the horizontal synchronization information by using the broadband signal; and a determining unit coupled to the vertical synchronization detector and the horizontal synchronization detector to be based on the vertical synchronization The information is synchronized with the level to determine the video standard. The intermediate frequency demodulator according to claim 6, wherein the vertical synchronization information includes a field period of the fundamental frequency signal, the horizontal synchronization information includes a horizontal line number in the field period, and the low pass filter The modulation mode of the output. The intermediate frequency demodulator according to claim 6, wherein the vertical synchronization detector further informs the horizontal synchronization detector to detect the horizontal synchronization information when the vertical synchronization information is detected. A video standard detection method for detecting a video standard to which a baseband signal belongs, and the video standard detection method includes: Filtering a baseband signal to obtain a narrowband signal and a wideband signal; detecting the vertical synchronization information by using the narrowband signal; detecting the horizontal synchronization information by using the broadband signal; and according to the vertical synchronization information The horizontal synchronization information is used to determine which video standard the baseband signal belongs to. The video standard detection method of claim 9, wherein the vertical synchronization information includes a field period of the baseband signal. The method for detecting a video standard according to claim 10, wherein the field period is determined by counting time intervals of adjacent two field peaks. The video standard detection method of claim 10, wherein the horizontal synchronization information includes a horizontal line number in the field period and a modulation mode of an output of the low pass filter. The method for detecting a video standard according to claim 12, wherein if the field period is approximately 16.67 milliseconds, it is determined that the baseband signal belongs to the NTSC video standard. The video standard detection method according to claim 12, wherein if the field period is approximately 20 milliseconds and the modulation mode is negative modulation, it is determined that the fundamental frequency signal belongs to a PAL video standard. The video standard detection method according to claim 12, wherein if the field period is approximately 20 milliseconds and the modulation mode is positive modulation, it is determined that the baseband signal belongs to the SECAM-L video standard.