CN101304477A - Apparatus for separating sync signal in video signal and method thereof - Google Patents

Abstract

An apparatus for separating a sync signal from a video signal. For receiving a video signal to obtain a coupled signal. The level judging circuit receives the coupling signal and compares the voltage of the coupling signal with a plurality of reference voltages. The reference voltage defines a plurality of reference voltage intervals. One of the reference voltage intervals is a predetermined reference voltage interval. The level judging circuit outputs an adjusting signal according to a reference voltage interval corresponding to the minimum voltage of the coupling signal in a preset time section. The level adjusting circuit is provided with a plurality of current sources and is used for receiving the adjusting signals and controlling the current sources to adjust the direct current level of the coupling signals. The synchronous signal separation circuit separates the synchronous signal from the coupling signal when the minimum voltage of the coupling signal is substantially within a predetermined reference voltage interval.

Description

Device and method for separating synchronous signal from video signal

technical field

The invention relates to a device and method for separating synchronous signals in signals, and in particular to a device and method for separating synchronous signals in video signals.

Background technique

Please refer to FIG. 1 , which is a waveform diagram of a video signal. The video signal includes a synchronous signal SYNC and a data signal Data. The level intervals of the data signal Data and the synchronous signal SYNC are different, and generally the possible voltage value of the data signal Data is greater than the voltage value of the synchronous signal SYNC. For the receiver of the video signal, the synchronization signal SYNC in the video signal must be separated first, and the receiver can further generate the pixel clock (Pixel Clock) according to the frequency of the synchronization signal SYNC, and process the video signal.

When transmitting video signals, the output of the transmitter and the DC level that the receiver can receive will often be different. As a result, the video signal received by the receiver may exceed the voltage range in which the receiver can operate normally. Therefore, the conventional video sync separation device first performs capacitive coupling (AC coupling) on the received video signal to isolate the DC voltage between the transmitter and the receiver. Then, the video clamping circuit is used to lock the DC voltage level of the coupled video signal to a required voltage value. Next, because the level intervals of the synchronization signal SYNC and the data signal Data of the video signal are different, the video synchronization separation device uses a comparator and a reference voltage to separate the synchronization signal SYNC from the video signal.

However, the previous design of video clamping circuit is to use the analog circuit loop to fix the capacitively coupled video signal. Since the analog circuit has high requirements on the accuracy of the parameters, this method is easily interfered by the IC process factors. There are phenomena of DC level variation and loop bandwidth drift. The bandwidth of the loop will limit the frequency range of the synchronization signal SYNC that can be processed. In addition, the use of analog circuit loops is also prone to loop instability, thus increasing the complexity of the design. Therefore, how to effectively increase the frequency range of the video signal that the video sync separation device can handle and improve the problem of loop instability is still an unresolved issue.

Contents of the invention

In view of this, the object of the present invention is to provide a device and method for separating synchronous signals from video signals, so as to solve the problem of unstable clamping loop circuits in the past, and to effectively process video signals of different frequency ranges.

According to the purpose of the present invention, a device for separating synchronous signals in video signals is proposed, which is used to receive a video signal. The video signals include a synchronous signal and a data signal, and the level intervals of the data signal and the synchronous signal are different. The device includes a A capacitor, a level judgment circuit, a level adjustment circuit, and a synchronous signal separation circuit. The capacitor is used for receiving the video signal and capacitively coupling the video signal to obtain a coupled signal. The level judging circuit is used for receiving the coupled signal, and comparing the voltage of the coupled signal with multiple reference voltages. The reference voltage defines a plurality of reference voltage intervals. One of the reference voltage intervals is a predetermined reference voltage interval. The level judging circuit outputs an adjustment signal according to the reference voltage interval corresponding to the minimum voltage of the coupling signal within a predetermined time interval. The level adjustment circuit has a plurality of current sources for receiving the adjustment signal and controlling the current sources accordingly to adjust the DC level of the coupled signal until the minimum voltage of the coupled signal is substantially within a predetermined reference voltage range. The synchronous signal separation circuit is used for separating the synchronous signal from the coupling signal according to a separation reference voltage when the minimum voltage of the coupling signal is substantially within the predetermined reference voltage range. The separation reference voltage is adjacent to the predetermined reference voltage interval.

According to the purpose of the present invention, a method for separating synchronous signals in video signals is further proposed, which is suitable for a display device, and the display device is used to receive a video signal. The video signal includes a synchronous signal and a data signal, and the data signal and the synchronous signal The level range of different, this method includes the following steps. First, the video signal is capacitively coupled to obtain a coupled signal. Then, compare the voltage of the coupling signal with a plurality of reference voltages, the reference voltages define a plurality of reference voltage intervals, one of the reference voltage intervals is a predetermined reference voltage interval. Then, an adjustment signal is generated according to the reference voltage interval corresponding to the minimum voltage of the coupling signal within a predetermined time interval. Next, the multiple current sources are controlled according to the adjustment signal to adjust the DC level of the coupled signal until the minimum voltage of the coupled signal is substantially within a predetermined reference voltage range. Afterwards, when the minimum voltage of the coupling signal is substantially within the predetermined reference voltage interval, the synchronization signal is separated from the coupling signal according to a separation reference voltage, the separation reference voltage is adjacent to the predetermined reference voltage interval.

In order to make the above-mentioned purpose, features, and advantages of the present invention more comprehensible, a preferred embodiment will be described in detail below together with the accompanying drawings.

Description of drawings

Figure 1 shows a waveform diagram of a video signal.

FIG. 2 shows a block diagram of an apparatus for separating synchronous signals from video signals according to a preferred embodiment of the present invention.

FIG. 3 shows an example of a detailed circuit diagram of an apparatus for separating synchronous signals from video signals according to a preferred embodiment of the present invention.

FIG. 4 shows a relationship diagram of the reference voltages V1 to V4 and the adjustment signal SAdj according to a preferred embodiment of the present invention.

FIG. 5 shows a timing diagram of the operation control signal P1, the first periodic signal S1 and the second periodic signal S2 according to a preferred embodiment of the present invention.

Fig. 6 shows a diagram of circuit simulation results of the device for separating synchronous signals from video signals according to a preferred embodiment of the present invention.

Description of reference symbols

10: First comparator

20: Second comparator

30: The third comparator

40: The fourth comparator

50: fifth comparator

60: Minimum value detection unit

70: Minimum value recording unit

80: Reference voltage generator

210: capacitance

220: Level judgment circuit

222: Comparison circuit

224: Min recorder

225: Video clamp circuit

230: Level adjustment circuit

232: Coarse adjustment charging current source

234: Fine-tuning the charging current source

236: Fine-tuning the discharge current source

238: Coarse adjustment discharge current source

240: Synchronous signal separation circuit

250: Oscillator

260: Cycle control circuit

Detailed ways

Please refer to FIG. 2 , which shows a block diagram of an apparatus for separating sync signals from video signals according to a preferred embodiment of the present invention. The device 200 for separating the synchronous signal from the video signal is disposed on a display device, such as a liquid crystal screen, for receiving the video signal VS. Wherein, the video signal VS includes a synchronous signal SYNC and a data signal Data, as shown in FIG. 1 . The device 200 includes a capacitor 210 , a video clamp circuit 225 and a sync signal separation circuit 240 . The video clamping circuit 225 includes a level determination circuit 220 and a level adjustment circuit 230 . The capacitor 210 is used for receiving the video signal VS, and performing capacitive coupling (AC Coupling) on the video signal VS to obtain a coupling signal S _C .

The level judging circuit 220 is used for receiving the coupling signal S _C and comparing the voltage of the coupling signal S _C with a plurality of reference voltages, and the reference voltages define a plurality of reference voltage intervals. One of the reference voltage intervals is a predetermined reference voltage interval. The level determination circuit 220 outputs an adjustment signal S _Adj according to the reference voltage interval corresponding to the minimum voltage of the coupling signal within a predetermined time interval.

The level adjustment circuit 230 has a plurality of current sources for receiving the adjustment signal S _Adj and controlling the current sources accordingly to adjust the DC level of the coupling signal S _C until the minimum voltage of the coupling signal S _C is substantially at a predetermined reference up to the voltage range.

The synchronous signal separation circuit 240 is used for separating the synchronous signal from the coupling signal S _C according to a separation reference voltage when the minimum voltage of the coupling signal S _C is substantially within the predetermined reference voltage interval. The separation reference voltage is adjacent to the predetermined reference voltage interval.

Next, how the device 200 for separating synchronous signals from video signals determines whether the minimum voltage of the coupling signal S _C is within a predetermined reference voltage interval will be described in detail. Please refer to FIG. 3 , which shows an example of a detailed circuit diagram of an apparatus for separating synchronous signals from video signals according to a preferred embodiment of the present invention. The level judgment circuit 220 includes a comparison circuit 222 and a minimum recorder 224 . The comparison circuit 222 includes a plurality of comparators, such as the first comparator 10 , the second comparator 20 , the third comparator 30 and the fourth comparator 40 . One terminal of the comparators 10 , 20 , 30 and 40 (for example, the positive input terminal of each comparator) respectively receives the coupling signal S _C . The other end of the first comparator 10 (for example, a negative input end) receives the first reference voltage V1, and the first comparator 10 compares the first reference voltage V1 with the voltage of the coupling signal S _C to output a first indication signal D1. The other end of the second comparator 20 (for example, a negative input end) receives the second reference voltage V2, and the second comparator 20 compares the second reference voltage V2 with the voltage of the coupling signal S _C to output a second indication signal D2. The other end of the third comparator 30 (for example, a negative input end) receives the third reference voltage V 3 , and the third comparator 30 compares the third reference voltage V 3 with the voltage of the coupling signal S _C to output the third Indicates signal D3. The other end of the fourth comparator 40 (for example, a negative input end) receives the fourth reference voltage V4, and the fourth comparator 40 compares the fourth reference voltage V4 with the voltage of the coupling signal S _C to output a fourth indication signal D4. Among them, V1>V2>V3>V4.

As shown in FIG. 4 , the reference voltages V1 to V4 define a plurality of reference voltage ranges R1 to R5 . The reference voltage range R1 is the range whose voltage is greater than V1, the reference voltage range R2 is the range where the voltage is between V1 and V2, the reference voltage range R3 is the range where the voltage is between V2 and V3, and the reference voltage range R4 is the range where the voltage is between V1 and V2. The range between V3 and V4, and the reference voltage range R5 is a range whose voltage is lower than V4.

As shown in FIG. 3 , the minimum value recorder 224 includes a minimum value detection unit 60 and a minimum value recording unit 70 . The minimum detection unit 60 is configured to receive the first indication signal D1 , the second indication signal D2 , the third indication signal D3 and the fourth indication signal D4 to determine the reference voltage interval corresponding to the voltage of the coupling signal. The minimum value recording unit 70 is configured to record a reference voltage interval corresponding to the minimum voltage of the coupling signal S _C within a predetermined time period, and output an adjustment signal S _Adj accordingly. Wherein, the predetermined reference voltage interval is, for example, the reference voltage interval R3.

Please refer to FIG. 4 , which shows a relationship diagram of the reference voltages V1 to V4 and the adjustment signal S _Adj according to a preferred embodiment of the present invention. The adjustment signal S _Adj includes, for example, a first discharge signal UP2 , a second discharge signal UP1 , a lock signal Lock, a first charge signal DN1 and a second charge signal DN2 . When the voltage of the coupling signal Sc is greater than the first reference voltage V1, the indication signals D1-D4 are all enabled. When the voltage of the coupling signal Sc is between the first reference voltage V1 and the second reference voltage V2, the first indication signal D1 is disabled, and the indication signals D2˜D4 are all enabled. When the voltage of the coupling signal Sc is between the second reference voltage V2 and the third reference voltage V3 , the indication signals D1 - D2 are disabled, and the indication signals D3 - D4 are enabled. When the voltage of the coupling signal Sc is between the third reference voltage V3 and the fourth reference voltage V4, the indication signals D1-D3 are disabled, and the fourth indication signal D4 is enabled. When the voltage of the coupling signal Sc is lower than the fourth reference voltage V4, the indication signals D1-D4 are all disabled.

Therefore, the minimum value detection unit 60 can know the reference voltage interval corresponding to the voltage of the coupling signal S _C according to the states of the indication signals D1 - D4 , which is one of the reference voltage intervals R1 to R5 . The minimum value detection unit 60 extracts a plurality of reference voltage intervals corresponding to the voltages of the coupling signal S _C in the predetermined time interval, and finds out the minimum voltage among these reference voltage intervals, which is the minimum voltage of the coupling signal S _C. Corresponding reference voltage range. For example, if the minimum value detecting unit 60 extracts 10 _reference voltage intervals R1, R2, R1, R2, R3, R4, R4, R3, R1 and In the case of R2, since the voltage included in the reference voltage interval R4 is between V3 and V4, which is the smallest of the voltages (above V4) included in R1 to R4, it is known that the reference voltage corresponding to the minimum voltage of the coupling signal S _C The voltage range is R4.

When the reference voltage range corresponding to the minimum voltage of the coupling signal _SC is R1, the first discharge signal UP2 is enabled. When the reference voltage range corresponding to the minimum voltage of the coupling signal _SC is R2, the second discharge signal UP1 is enabled. When the reference voltage interval corresponding to the minimum voltage of the coupling signal _SC is R3, the locking signal Lock is enabled. When the reference voltage interval corresponding to the minimum voltage of the coupling signal _SC is R4, the first charging signal DN1 is enabled. When the reference voltage range corresponding to the minimum voltage of the coupling signal _SC is R5, the second charging signal DN2 is enabled.

As shown in FIG. 3 , the level adjustment circuit 230 further includes a coarse charging current source 232 , a fine charging current source 234 , a fine discharging current source 236 and a coarse discharging current source 238 . When the first discharge signal UP2 is enabled, the coarse discharge current source 238 is enabled to provide the first discharge current as the adjustment current I _Adj to reduce the DC level of the coupling signal S _C . When the second discharge signal UP1 is enabled, the trimming discharge current source 236 is enabled to provide the second discharge current as the adjustment current I _Adj to reduce the DC level of the coupling signal S _C . When the first charging signal DN1 is enabled, the trimming charging current source 234 is enabled to provide the first charging current as the adjusting current I _Adj to increase the DC level of the coupling signal S _C . When the second charging signal DN2 is enabled, the coarse adjustment charging current source 232 is enabled to provide the second charging current as the adjustment current I _Adj to increase the DC level of the coupling signal S _C . Wherein, the absolute value of the second discharging current is smaller than the absolute value of the first discharging current, and the absolute value of the first charging current is substantially smaller than the absolute value of the second charging current.

When the minimum voltage of the coupling signal S _C is substantially outside the predetermined reference voltage range R3, that is, within the reference voltage range R1, R2, R4 or R5, the adjustment signal S _Adj is adjusted according to the minimum voltage of the coupling signal S _C to selectively enable one of the fine-tuning discharge current source 236 , the fine-tuning charging current source 234 , the coarse-tuning discharging current source 238 , and the coarse-tuning charging current source 232 to adjust the DC level of the coupling signal S _C .

When the minimum voltage of the coupling signal S _C is within the predetermined reference voltage range R3, the locking signal Lock is enabled, and the device 200 for separating the synchronous signal from the video signal is in a locked state, and the DC level of the coupling signal S _C does not need to be adjusted. adjustment, so at this time the adjustment signal S _Adj will disable the fine-tuning discharge current source 236, the fine-tuning charging current source 234, the coarse-tuning discharging current source 238, and the coarse-tuning charging current source 232, and the DC level of the coupling signal S _C will be substantially maintained at the original level.

In addition, the synchronous signal separation circuit 240 includes a separation comparator 50 and a reference voltage generator 80 . The separation comparator 50 is used for comparing the coupling signal S _C with the separation reference voltage V5 . When the device 200 for separating the synchronous signal in the video signal is in a locked state, that is, when the minimum voltage of the coupling signal S _C is substantially in the predetermined reference voltage interval R3, the separation comparator 50 separates the reference voltage V5 from the coupling signal S _C separates the synchronous signal SYNC and outputs it. The separation reference voltage V5 is adjacent to the predetermined reference voltage interval R3. In this embodiment, the separation reference voltage V5 is preferably greater than any voltage in the predetermined reference voltage range R3, that is, greater than the reference voltage V2. The reference voltage generator 80 is used for providing reference voltages V1 - V4 and a separate reference voltage V5 .

Please refer to FIG. 5 , which shows a timing diagram of the operation control signal P1 , the first period signal S1 and the second period signal S2 according to a preferred embodiment of the present invention. The video sync separation device 200 further includes an oscillator 250 and a cycle control circuit 260 . The oscillator 250 is used to provide the operation control signal P1 required by the video synchronization device 200 . The period control circuit 260 is used for receiving the operation control signal P1, and down-converting the operation control signal P1 to generate the first period signal S1 and the second period signal S2. The first period signal S1 is transmitted to the minimum value detection unit 60 , and the second period signal S2 is transmitted to the minimum value recorder 224 . The minimum value detection unit 60 of the level determination circuit 220 determines the reference voltage interval corresponding to the voltage of the coupling signal S _C according to the operation control signal P1 . For example, when the control signal P1 is on a rising edge, the minimum detection unit 60 retrieves the reference voltage interval corresponding to the voltage of the coupling signal S _C at that time.

The minimum value detection unit 60 of the level determination circuit 220 determines a predetermined time period according to the period of the first period signal S1. For example, the predetermined time period is the period Δt ₁ of the first periodic signal S1. On the rising edge of the first periodic signal S1 , the minimum detection unit 60 determines the reference voltage interval corresponding to the minimum voltage of the coupling signal S _C from all the reference voltage intervals obtained within the predetermined time interval.

The time length for which the current sources 232 , 234 , 236 , 238 are enabled is determined by the length of time for which the second periodic signal S2 is enabled. For example, if the second charging signal DN2 is enabled, the time length for which the coarse charging current source 232 is enabled can be designed to be equal to Δt ₂ . That is, the coarse charging current source 232 is enabled when the second charging signal DN2 is enabled and the second period signal S2 is enabled. In this way, by enabling the current source only within Δt ₂ , the DC voltage of the coupling signal S _C will not change too rapidly, causing the device 200 to be unstable. Preferably, the frequency of the first periodic signal S1 and the second periodic signal S2 is lower than that of the synchronization signal SYNC.

Please refer to FIG. 6 , which shows a circuit simulation result diagram of an apparatus for separating synchronous signals from video signals according to a preferred embodiment of the present invention. Suppose V1 is set to 60mV, V2 is set to 55mV, V3 is set to 50mV, V4 is set to 45mV, and V5 is set to 40mV. Firstly, the minimum voltage of the coupling signal is about 85mV, which is much higher than any voltage (50mV to 55mV) in the predetermined reference voltage range R3, and is higher than V1, so the first discharge signal UP2 is enabled, and the level adjustment circuit 230 according to The enabled first discharge signal UP2 outputs the adjustment current I _Adj to adjust the DC level of the coupling signal S _C . After several cycles, the minimum voltage of the coupling signal drops to around the predetermined reference voltage range R3, but is still slightly greater than V2, so the second discharge signal UP1 is enabled, and the level adjustment circuit 230 UP1 outputs a small adjustment current I _Adj to fine-tune the DC level of the coupling signal S _C . It can be seen from FIG. 6 that when the second discharge signal UP1 is enabled, the speed of the minimum voltage drop of the coupling signal S _C slows down. After several cycles, the minimum voltage of the coupling signal _SC is within the predetermined reference voltage range R3, so the lock signal Lock is enabled. At this time, the synchronization signal SYNC will be successfully separated by the synchronization signal separation circuit 240 .

The above-mentioned embodiment is exemplified by the level judging circuit 220 including four sets of comparators, but it is not limited thereto.

The device for separating the synchronous signal from the video signal disclosed in the above embodiments of the present invention is used to adjust the DC level of the capacitively coupled video signal, compare the received video signal with a preset reference voltage after capacitive coupling, and Record the reference voltage interval corresponding to the minimum voltage of the capacitive coupling obtained after comparison in the minimum value recorder. The level adjustment circuit adjusts the DC level of the coupled signal according to what is recorded by the minimum recorder. In addition, the level adjustment circuit can have a charging current source and a discharging current source that can provide two different current magnitudes, so that the DC level of the coupling signal can be adjusted more accurately. The device of the present invention is less prone to the problem of inaccurate operation due to the error of the circuit technology, and can also reduce the phenomenon of circuit instability.

In summary, although the present invention has been disclosed as above with a preferred embodiment, it is not intended to limit the present invention. Those skilled in the art of the present invention can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be defined by the patent scope of the present invention.

Claims (16)

1. the device of synchronizing signal in the separating video signal is used to receive a vision signal, and this vision signal comprises a synchronous signal and a data-signal, and this device comprises:

One electric capacity is used to receive this vision signal, and this vision signal is carried out capacitive coupling, to obtain a coupled signal;

One level judging circuit, be used to receive this coupled signal, and voltage and a plurality of reference voltage of this coupled signal compared, described reference voltage defines a plurality of reference voltages interval, one of described reference voltage interval is a preset reference voltage interval, and this level judging circuit is exported one according to pairing this reference voltage interval of the minimum voltage of this coupled signal in the scheduled time section and adjusted signal;

One level adjusting circuit in order to receiving this adjustment signal and to adjust the DC level of this coupled signal according to this, is positioned at this preset reference voltage interval in fact up to the minimum voltage of this coupled signal; And

One synchronous demultiplexing circuit is when being positioned at this preset reference voltage interval in fact in order to the minimum voltage when this coupled signal, according to a separation reference voltage, to isolate this synchronizing signal from this coupled signal.

2. device as claimed in claim 1, wherein, this level judging circuit comprises a reference voltage generator to produce described reference voltage and this separation reference voltage, this separation reference voltage is adjacent to this preset reference voltage interval.

3. device as claimed in claim 1, wherein, when the minimum voltage of this coupled signal during greater than the arbitrary voltage in this preset reference voltage interval, this adjustment signal is used to make this level adjusting circuit to reduce the DC level of this coupled signal; And when the minimum voltage of this coupled signal during less than the arbitrary voltage in this preset reference voltage interval, this adjustment signal is used to make this level adjusting circuit to improve the DC level of this coupled signal.

4. device as claimed in claim 1, wherein, this level judging circuit comprises:

One comparison circuit comprises a plurality of comparators, and an end of described comparator receives this coupled signal respectively, and the other end of described comparator receives described reference voltage respectively; And

One minimum value register, be used for output signal according to described comparator, with the pairing reference voltage of the voltage of judging this coupled signal interval, this minimum value register is more in order to pairing this reference voltage interval of the minimum voltage that writes down this coupled signal in this scheduled time section, and exports this adjustment signal according to this.

5. device as claimed in claim 1, wherein, this level adjusting circuit has a plurality of current sources, adjusting the DC level of this coupled signal, in fact is positioned at this preset reference voltage interval up to the minimum voltage of this coupled signal according to the described current source of this adjustment signal controlling.

6. device as claimed in claim 5, wherein, described current source comprises:

One fine setting discharging current source is in order to reduce the DC level of this coupled signal;

One fine setting charging current source is in order to improve the DC level of this coupled signal;

One coarse adjustment discharging current source is in order to reduce the DC level of this coupled signal; And

One coarse adjustment charging current source is in order to improve the DC level of this coupled signal;

Wherein, this adjusts signal according to pairing this reference voltage interval of the minimum voltage of this coupled signal, optionally to enable one of this fine setting discharging current source, this fine setting charging current source, this coarse adjustment discharging current source and this coarse adjustment charging current source;

Wherein, when the minimum voltage of this coupled signal is positioned in this preset reference voltage interval, this adjusts signal disable should fine setting discharging current source, this finely tunes charging current source, this coarse adjustment discharging current source and this coarse adjustment charging current source.

7. device as claimed in claim 1, wherein, this sync separator circuit comprises:

One separates comparator, is used for relatively that this coupled signal separates reference voltage to export this synchronizing signal with this, and this separates reference voltage in fact greater than the arbitrary voltage in this preset reference voltage interval.

8. device as claimed in claim 1 more comprises:

An operating control signal that provides this device required is provided one oscillator; And

One-period control circuit, be used for produce after this operating control signal frequency reducing a period 1 signal and one second round signal, this level judging circuit is judged pairing this reference voltage interval of voltage of this coupled signal according to this operating control signal, this level judging circuit determines this scheduled time section according to the cycle of this period 1 signal, and the time span that described current source is enabled was determined by the time that enables of this of signal second round.

9. device as claimed in claim 8, wherein, this period 1 signal and this second round signal frequency be lower than the frequency of this synchronizing signal.

10. the method for synchronizing signal in the separating video signal is applicable to a display unit, and this display unit is used to receive a vision signal, and this vision signal comprises a synchronous signal and a data-signal, and this method comprises:

(a) this vision signal is carried out capacitive coupling, to obtain a coupled signal;

(b) the relatively voltage of this coupled signal and a plurality of reference voltage, described reference voltage defines a plurality of reference voltages interval, and one of described reference voltage interval is a preset reference voltage interval;

(c) according to the interval adjustment signal that produces of pairing this reference voltage of the minimum voltage of this coupled signal in the scheduled time section;

(d) according to this adjustment signal adjusting the DC level of this coupled signal, be positioned at this preset reference voltage interval in fact up to the minimum voltage of this coupled signal; And

(e) when the minimum voltage of this coupled signal is positioned at this preset reference voltage interval in fact, according to a separation reference voltage, from this coupled signal, to isolate this synchronizing signal.

11. method as claimed in claim 10, wherein, when the minimum voltage of this coupled signal during greater than the arbitrary voltage in this preset reference voltage interval, reduce the DC level of this coupled signal, and, improve the DC level of this coupled signal when the minimum voltage of this coupled signal during less than the arbitrary voltage in this preset reference voltage interval.

12. method as claimed in claim 10 wherein, in this step (d), adjusting the DC level of this coupled signal, in fact is positioned at this preset reference voltage interval up to the minimum voltage of this coupled signal according to a plurality of current sources of this adjustment signal controlling.

13. method as claimed in claim 12, wherein, described current source comprises a fine setting discharging current source, a fine setting charging current source, a coarse adjustment discharging current source, reaches a coarse adjustment charging current source, this fine setting discharging current source is used to reduce the DC level of this coupled signal, this fine setting charging current source is used to improve the DC level of this coupled signal, this coarse adjustment discharging current source is used to reduce the DC level of this coupled signal, this coarse adjustment charging current source is used to improve the DC level of this coupled signal, and this step (d) comprising:

This adjusts signal according to pairing this reference voltage interval of the minimum voltage of this coupled signal, optionally to enable one of this fine setting discharging current source, this fine setting charging current source, this coarse adjustment discharging current source and this coarse adjustment charging current source; And

When the minimum voltage of this coupled signal is positioned in this preset reference voltage interval, this adjusts signal disable should fine setting discharging current source, this finely tunes charging current source, this coarse adjustment discharging current source and this coarse adjustment charging current source.

14. method as claimed in claim 10, wherein, this separates reference voltage in fact greater than the arbitrary voltage in this preset reference voltage interval, and this separation reference voltage is adjacent to this preset reference voltage interval.

15. method as claimed in claim 10 more comprises:

Produce an operating control signal;

This operating control signal of frequency reducing, with produce a period 1 signal and one second round signal;

Judge pairing this reference voltage interval of voltage of this coupled signal according to this operating control signal; And

Cycle according to this period 1 signal determines this scheduled time section;

Wherein, the time span that is enabled of described current source and this second round signal enable time correlation.

16. method as claimed in claim 15, wherein, this period 1 signal and this second round signal frequency be lower than the frequency of this synchronizing signal.

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