Timing recovery device

[0001] This application claims the benefit of the Korean Application No. P2002-10562 filed on Feb. 27, 2002, which is hereby incorporated by reference.

[0002] 1. Field of the Invention

[0003] The present invention relates to digital TV receivers, and more particularly, to a timing recovery device in a digital TV receiver which recovers a symbol clock of a received data.

[0004] 2. Background of the Related Art

[0005] Recent digital TV broadcastings are made according to own transmission systems and standards of the USA, Europe, and Japan. For an example, the USA employs a VSB (Vestigial Side Band) type transmission format, an MPEG video compression format, and an AC-3 audio compression format.

[0006] For transmission of a data compressed according to above standards, synchronization signals are inserted into the data at fixed intervals, and a receiver, such as a digital TV receiver, is required to generate a clock identical to the synchronization signal used at the time of transmission for recovery of the data. A part that serves to generate such a clock at the digital TV receiver is a timing recovery part. That is, the timing recovery part reproduces a clock of a symbol stream, and a purpose of the timing recovery lies on correct and accurate prediction of a symbol transition point at the digital TV receiver based on a received data stream.

[0007] A data frame transmitted to a related art digital TV receiver will be described. As shown in FIG. 1, there are two synchronization signals used in data transmission; one is a data segment synchronization signal, and the other one is a field synchronization signal. The data segment synchronization signal, the field synchronization signal, and the data form a unit frame of 313 data segments each with 4 symbols of data segment synchronization signals, and 828 symbols of data.

[0008] The foregoing data is displayed on the digital TV receiver according to the following sequence. As shown in FIG. 2, upon reception of a broadcasting signal having the data through an antenna, a tuner 101 selects a frequency of a specific channel, and converts the frequency into an IF signal, and the IF signal is converted into a digital data through an analog/digital converting part A/D 102.

[0009] Then, the IF signal converted into the digital data is provided to a synchronization signal detecting part 103, which detects the data segment synchronization signal and the field synchronization signal inserted at the time of transmission from the digital IF signal.

[0010] For recovering the data by using the signals from the synchronization signal detecting part 103, the timing recovering part 104 recovers the timing of the synchronization signal used at the time of transmission. That is, the timing recovering part 104 recovers the timing to be applied to an A/D clock of the A/D converting part 102 by using the data segment synchronization signal.

[0011] Then, an FPLL (Frequency Phase Locked Loop) 105 demodulates the digital IF signal into a base band I signal and a base band Q signal. The Q signal is used in recovery of a carrier. Then, a channel equalizing part 106 removes errors, such as ghost, and the like, from the signal from the FPLL 105, and a video decoder 107 decodes, and displays a signal from the channel equalizing part 106 on a screen.

[0012] In a case the timing is recovered by using the data segment synchronization signal, a phase error is erased because the timing is recovered in a state recovery of the carrier is not finished yet, i.e., in a state the phase error of the signal is present still.

[0013] Moreover, the related art timing recovering part requires a long time period for detecting the timing error because a segment synchronization section can not be known when the ghost is present. Eventually, compensation for the timing error is delayed as much, resulting in a vicious circle of failing detection of a proper data segment synchronization signal.

[0014] Accordingly, the present invention is directed to a timing recovery device that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.

[0015] An object of the present invention is to provide a timing recovery device which can capture a timing offset from an average gain of a timing error detecting part within a short time even if a 0 dB ghost presents.

[0016] Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

[0017] To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the timing recovery device includes a filter for passing edges of spectrums of broadcasting signals sampled at fixed intervals at a re-sampling part, a timing error detecting part for obtaining two symbol sample from a signal from the filter and an intermediate sample thereof, and detecting information on a timing error from a result (a value) of multiplication of a difference of the two samples and the intermediate sample, a loop filter for providing a signal of a bandwidth according to a signal from the timing error detecting part, and an NCO for controlling a sampling timing of the re-sampling part in response to a signal from the loop filter.

[0018] The timing error detecting part includes a first delay for delaying a received symbol sample by one clock, a second delay for further delaying a signal from the first delay by one clock, a subtractor for providing a difference of signals from the pre-filter and the second delay, a multiplier for multiplying signals from the first delay and the subtractor, and a sign extractor for extracting a sign which is a timing error value from a signal from the multiplier, or alternatively, the timing error detecting part includes a first delay for delaying an I signal symbol sample by one clock, a second delay for further delaying a signal from the first delay by one clock, a first subtractor for providing a difference of an I signal symbol sample and a signal from the second delay, a first multiplier for multiplying signals from the first delay and the first subtractor, a third delay for delaying a Q signal symbol sample by one clock, a fourth delay for further delaying a signal from the third delay by one clock, a second subtractor for providing a difference of a Q signal symbol sample and a signal from the fourth delay, a second multiplier for multiplying signals from the third delay and the second subtractor, a third subtractor for providing a difference of signals from the first and second multipliers, and a sign extractor for extracting only a sign from the third subtractor.

[0019] The loop filter includes a first bandwidth forwarding part for selectively forwarding one of first positive bandwidth values and first negative bandwidth values in response to a signal from the timing error detecting part, a second bandwidth forwarding part for selectively forwarding one of second positive bandwidth values and second negative bandwidth values in response to the signal from the timing error detecting part, a first adder for adding a signal from the first bandwidth forwarding part to a signal fed back from a delay at a next stage, and a second adder for adding a signal from the first bandwidth forwarding part to a signal from the first adder. The first or the second bandwidth forwarding part includes a first storing part for storing positive bandwidth values, a first multiplexer for selectively providing one of the positive bandwidth values in response to a switching signal, a second storing part for storing negative bandwidth values, a second multiplexer for selectively providing one of the negative bandwidth values in response to the switching signal, and a third multiplexer for selectively providing one of signals from the first and second multiplexers in response to a signal from the timing error detecting part.

[0020] In another aspect of the present invention, there is provided a timing recovery device including a filter for passing components of a broadcasting signal sampled at fixed intervals by a re-sampling part, the component containing timing information only, a timing error detecting part for detecting a polarity form timing error value having a positive () or a negative value from a signal from the filter, a loop filter for selectively providing a signal of a specific bandwidth of a plurality of bandwidths according to a signal from the timing error detecting part, and an NCO for controlling a sampling timing of the re-sampling part in response to a signal from the loop filter.

[0021] The timing error detecting part includes a first delay for delaying an I signal symbol sample from the filter by one clock, a second delay for further delaying a signal from the first delay by one clock, a subtractor for providing a difference of signals between the I signal symbol sample and a signal from the second delay, a multiplier for multiplying signals from the first delay and the subtractor, and a sign extractor for extracting a polarity form timing error value from a signal having a positive () or negative () polarity from the multiplier, or alternatively the timing error detecting part includes a first delay for delaying an I signal symbol sample from the filter by one clock, a second delay for further delaying a signal from the first delay by one clock, a first subtractor for providing a difference of an I signal symbol sample and a signal from the second delay, a first multiplier for multiplying signals from the first delay and the first subtractor, a third delay for delaying a Q signal symbol sample from the filter by one clock, a fourth delay for further delaying a signal from the third delay by one clock, a second subtractor for providing a difference of a Q signal symbol sample and a signal from the fourth delay, a second multiplier for multiplying signals from the third delay and the second subtractor, a third subtractor for providing a difference of signals from the first and second multipliers, and a sign extractor for extracting a polarity form timing error having a positive () or a negative () polarity from a signal from the third subtractor.

[0022] The loop filter accumulates and provides a positive bandwidth signal if the signal from the timing error detecting part is positive (), and a negative bandwidth signal if the signal from the timing error detecting part is negative ().

[0023] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

[0024] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention:

[0025] In the drawings:

[0026] FIG. 1 illustrates a data frame received at a related art digital TV: receiver;

[0027] FIG. 2 illustrates a block diagram of a related art digital TV receiver;

[0028] FIG. 3 illustrates a block diagram of a timing recovery device in accordance with a preferred embodiment of the present invention;

[0029] FIG. 4 illustrates a block diagram of one embodiment of a timing error detecting part by using an I signal in the timing recovery device of the present invention;

[0030] FIG. 5 illustrates a block diagram of one embodiment of a timing error detecting part by using I and Q signals in the timing recovery device of the present invention;

[0031] FIG. 6 illustrates a detailed block diagram of a loop filter in the timing recovery device of the present invention;

[0032] FIG. 7 illustrates an experimental graph comparing average gains of a related art timing error detecting part and a timing error detecting part of the present invention, when no ghost is present; and

[0033] FIG. 8 illustrates an experimental graph comparing average gains of a related art timing error detecting part and a timing error detecting part of the present invention, when a 0 dB ghost is present.

[0034] Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

[0035] When broadcasting signals are received through an antenna, after a frequency of specific channel is selected by a viewer, a broadcasting signal of a selected channel is converted into a digital data through an analog/digital converting part A/D (not shown). Then, the broadcasting converted into a digital data is provided to a re-sampling part 300, the re-sampling part 300 samples the broadcasting signal at fixed intervals, and a signal from the re-sampling part 300 is provided to a carrier recovery part (not shown) or a channel equalizing part (not shown). The signal from the re-sampling part 300 is provided to the re-sampling part 300 through the timing recovery device 301.

[0036] FIG. 3 illustrates a block diagram of a timing recovery device in accordance with a preferred embodiment of the present invention, including a pre-filter 301a for passing a band of a signal from the re-sampling part 300, a timing error detecting part 301b of the Gardner type for detecting a timing error from a signal from the pre-filter 301a, a loop filter 301c for passing a low band component of the signal from the timing error detecting part 301b, and a numerically controlled oscillator (NCO) 301d for changing a frequency to be provided in response to a signal from the loop filter 301c, and controlling a sampling timing of the re-sampling part 300.

[0037] The pre-filter 301a only passes edges of spectrums of a broadcasting signal received at the digital TV receiver, because the edge contains information on the timing of the broadcasting signal.

[0038] FIG. 4 illustrates a first embodiment timing error detecting part 301b, including a first delay 401 for delaying an I signal symbol sample from the pre-filter 301a by one clock, a second delay 402 for delaying a signal from the first delay by one clock, a subtractor 403 for providing a difference of signals from the pre-filter 301a and the second delay 401, a multiplier 404 for multiplying signals from the first delay 401 and the subtractor 403, and a sign extractor 405 for extracting a sign which is a timing error value from a signal from the multiplier 404.

[0039] When the I signal symbol sample is provided to the first delay 401, the first delay 401 delays the I signal symbol sample for one clock and provides to the second delay 402 and the multiplier 404. the symbol sample delayed for one clock is further delayed for one clock at the second delay 402, and provided to the subtractor 403.

[0040] Then, the subtractor 403 calculates a difference of the symbol sample from the pre-filter 301a and the two clock delayed symbol sample from the second delay 402, and provides to the multiplier 404.

[0041] The multiplier 404 multiplies the one clock delayed symbol sample from the first delay 401 and a signal from the subtractor 403, and provides to the sign extractor 405. The sign extractor 405 extracts a sign representing only a polarity of the signal from the multiplier 404, and provides to the loop filter 301c. the sign extractor 405 provides on of 1, 0, or 1.

[0042] Thus, the timing error detecting part 301b multiplies a difference of two symbol samples and an intermediate symbol sample of the two symbol samples, and extracts a sign from a result of the multiplication. The extracted sign is used as a timing error value.

[0043] The operation of the timing error detecting part 301b can be expressed as the following equation. $\begin{array}{cc}{U}_r\left(k\right)=\mathrm{sgn}\left[x\left(-\frac{T}{2}+\mathrm{kT}\right)\left\{x\left(+\mathrm{kT}\right)-x\left(-T+\mathrm{kT}\right)\right\}\right]& \left(1\right)\end{array}$

[0044] where, : timing phase,

[0045] $x\left(-\frac{T}{2}+\mathrm{kT}\right)$

[0046] intermediate samples.

[0047] FIG. 5 illustrates a block diagram of a second embodiment of a timing error detecting part, for, different from the first embodiment, detecting a timing error by using I, and Q signals.

[0048] Referring to FIG. 5, the second embodiment timing error detecting part 301b multiplies a difference of two symbol samples and an intermediate sample value of the two symbol samples to I, and Q signals, respectively.

[0049] That is, upon reception of an I signal symbol sample, the first delay 501 delays the symbol sample for one clock, and provides to a second delay 502 and a first multiplier 504. The symbol sample delayed for one clock is further delayed for one clock at the second delay 502, and provided to the first subtractor 503. Then, the subtractor 503 calculates a difference of the I signal symbol sample and the symbol sample delayed for two clocks from the second delay 502, and provides to the first multiplier 504. The first multiplier 504 multiplies the one clock delayed symbol sample from the first delay 501 and a signal from the first subtractor 503.

[0050] Upon reception of a Q signal symbol sample, the third delay 505 delays the Q signal symbol sample for one clock, and provides to the fourth delay 506 and the second multiplier 508. The symbol sample delayed for one clock is further delayed for one clock at the fourth delay 506 and provided to the second subtractor 507. Then, the second subtractor 507 calculates a difference of the Q signal symbol sample and the two clock delayed symbol sample from the fourth delay 508, and provides to the second multiplier 508. The second multiplier 508 multiplies the one clock delayed symbol sample from the third delay 505 and a signal from the second subtractor 507.

[0051] Then, the third delay 509 calculates a difference of signals from the first multiplier 504 and the second multiplier 508, and provides to the sign extractor 510. The sign extractor 510 extracts a sign of the difference, and provides as a timing error value of a polarity form.

[0052] As described, because the timing error detecting part 301b of the present invention detects a polarity form of timing error, an average gain of the timing errors are significantly greater than a related art timing error detecting part. Moreover, as shown in FIG. 4, the timing error can be obtained by using the I signal only, or as shown in FIG. 5 the timing error can be obtained by using both the I and Q signals. The first embodiment timing error detecting part in which only the I signal is used has a simple circuit system, and the second embodiment timing error detecting part in which only the I and Q signals are used can provide a more accurate timing error, though a circuit system thereof is complicated.

[0053] FIG. 6 illustrates a detailed block diagram of one embodiment of a loop filter 301c which fixes a loop bandwidth depending on a direction of the polarity form of timing error provided through the timing error detecting part 301b.

[0054] The loop filter 301c includes a first bandwidth forwarding part 620 for selectively forwarding one of first positive bandwidth values and first negative bandwidth values, a second bandwidth forwarding part 630 for selectively forwarding one of second positive bandwidth values and second negative bandwidth values, a first adder 606 for adding a signal from the first bandwidth forwarding part 630 to a signal fed back from a delay at a next stage, and a second adder 608 for adding a signal from the first bandwidth forwarding part 620 to a signal from the first adder 606. The loop filter 301c may include more than two of a plurality of bandwidth forwarding parts which forwards bandwidth values different from one another.

[0055] The first bandwidth forwarding part 620 includes first, and second storing part 601a and 602a, and first, second, and third multiplexers 603a, 604a, and 605a, and the second bandwidth forwarding part 630 includes third, and fourth storing part 601b and 602b, and fourth, fifth, and sixth multiplexers 603b, 604b, and 605b.

[0056] The first bandwidth forwarding part 620 and the second bandwidth forwarding part 630 will be described in more detail. The first storing part 601a calculates the first positive bandwidth values Frequency1Bw0Frequency1Bw3 of the plurality of the loop filters in advance and stores therein, and the second storing part 602a calculates the first negative bandwidth values Frequency1Bw0Frequency1Bw3 of the plurality of the loop filters in advance and stores therein. The first multiplexer 603a selects one of the plurality of the first positive bandwidth values stored in the first storing part 601a and forwards to the third multiplexer 605a in response to a lock detecting signal LD2:0 which is a switching signal, and the second multiplexer 604a selects one of the plurality of the first negative bandwidth values stored in the second storing part 602a and forwards to the third multiplexer 605a in response to the lock detecting signal LD2:0. The third multiplexer 605a selects one of signals from the first, and second multiplexers 603a and 604a and forwards to the second adder 608 according to the polarity form timing error value from the timing error detecting part 301c.

[0057] The third storing part 601b calculates the second positive bandwidth values Frequency2Bw0Frequency2Bw3 of the plurality of the loop filters in advance and stores therein, and the fourth storing part 602b calculates the second negative bandwidth values Frequency2Bw0Frequency2Bw3 of the plurality of the loop filters in advance and stores therein. The fourth multiplexer 603b selects one of the plurality of the second positive bandwidth values stored in the third storing part 601b and forwards to the sixth multiplexer 605b in response to a lock detecting signal LD2:0, and the fifth multiplexer 604b selects one of the plurality of the second negative bandwidth values stored in the fourth storing part 602b and forwards to the sixth multiplexer 605b in response to the lock detecting signal LD2:0. The sixth multiplexer 605b selects one of signals from the fourth, and fifth multiplexers 603b and 604b and forwards to the first adder 606 according to the polarity form timing error value from the timing error detecting part 301c. The first adder 606 adds a signal from the sixth multiplexer 605b and a value fed back from the delay 607 at the next stage and provides to the delay 607 at the next stage, and the delay 607 delays a signal from the first adder 606 by one symbol, and feeds the signal back to the first adder 606 and provides the signal to the second adder 608. The second adder 608 adds a signal from the third multiplexer 605a and a signal from the delay 607, and provides to the NCO 301d. The first, and second adders 606 and 608 and the delay 607 are of a kind of integrator, for accumulating results of the third and sixth multiplexers 605a and 605b in symbols. The gear shifting of the filter bandwidth is made automatically in response to the lock detecting signal LD2:0.

[0058] If a polarity of the polarity form timing error is positive (1), the loop filter 301c accumulates and provides the positive bandwidth values, and, opposite to this, if a polarity of the polarity form timing error is negative (1), the loop filter 301c accumulates and provides the negative bandwidth values. Therefore, the bandwidth value from the loop filter 301c is a constant, and a multiplexer can be employed in place of a multiplier for selection of the loop filter bandwidth value, much hardware resource can be saved. This is made possible as the timing error value is not a data form, but a polarity form.

[0059] FIG. 7 illustrates an experimental graph comparing average gains (S curve) of a related art timing error detecting part and a timing error detecting part of the present invention, when no ghost is present, wherein it can be noted that the average gain of the timing error detecting part of the present invention is greater than the related art timing error detecting part of the Gardner type by more than two times.

[0060] FIG. 8 illustrates an experimental graph comparing average gains (S curve) of a related art timing error detecting part and a timing error detecting part of the present invention, when a 0 dB ghost is present, wherein it can be noted that the average gain of the timing error detecting part of the present invention is greater than the related art timing error detecting part of the Gardner type by more than 10 times.

[0061] From the result of experiment, it can be known that the average gain of the timing error detecting part of the present invention is excellent compared to the related art timing error detecting part, which contribute to a performance improvement of the timing recovery device in a digital TV receiver.

[0062] The present invention is applicable to a communication field of VSB/QPSK/QAM.

[0063] The multiplication of a difference signal between two symbol samples and an intermediate sample thereof, and extracting a sign only from a result of the multiplication as a timing error, which permits to provide a very great average gain of the timing error, can shorten a time period required for capturing the timing error. Especially, since a very great gain can be obtained even in a case a 0 dB ghost is present, a timing offset can be captured within a short time period.

[0064] Since the timing error detecting part provides a polarity form timing error, hardware of loop filter can be simplified.

[0065] It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.