KR100396672B1 - Digital TV receiver - Google Patents

Abstract

A digital TV receiver of a VSB type, and particularly, a timing recovery using real and imaginary component data after resampling and before matched filtering to reduce delay time caused by passing a conventional matched filter. This can reduce timing acquisition time. Therefore, the performance of the entire timing recovery unit can be improved to capture timing even for a relatively stronger ghost signal for the same time (sample) as that of the current system. In addition, by using both real component and imaginary component data for timing recovery, timing recovery can be performed more accurately.

Description

Digital TV receiver {Digital TV receiver}

TECHNICAL FIELD The present invention relates to digital television, and more particularly, to a digital TV receiver having a fast timing acquisition time in a ghost environment.

Currently, the ATSC (Advanced Television Systems Committee) 8 VSB (Vestigial Side Band) transmission system, which has been proposed for most digital transmission systems and digital TV transmission systems for the United States, carries only data in a transmission signal to improve frequency efficiency. That is, the receiver does not transmit information about the clock necessary for data recovery. Therefore, the receiving side should generate the same clock as used at the time of transmission to recover these data among the received signals in which only data exists. The part which performs this role is a timing recovery part.

FIG. 1 is a block diagram illustrating a general digital TV receiver provided with such a timing recovery unit, and illustrates a VSB transmission scheme as an example.

That is, when a RF (Radio Frequency) signal modulated by the VSB method is received through the antenna 101, the tuner 102 selects only a specific channel frequency desired by the user and then fixes the VSB signal of the RF band loaded on the channel frequency. Lower to the first intermediate frequency band (IF (typically 44 or 43.75 MHz is widely used)) and filter out other channel signals as appropriate.

The output signal of the tuner 102, which lowers the spectrum of an arbitrary channel to a fixed primary IF band, is a surface acoustic wave (SAW) filter 102 employed as a function of removing adjacent channel signals and removing noise signals. Will pass through.

At this time, the digital broadcast signal, for example, since all information is present in the band of 6 MHz from the intermediate frequency of 44 MHz, the SAW filter 103 removes all remaining sections except for the 6 MHz band in which the information exists from the output of the tuner 102. The output is then output to the down converter 104.

The down converter 104 down-converts the signal filtered by the SAW filter 103 to an oscillation frequency for generating a second IF signal, converts the signal into a second IF signal, and then converts the analog / digital (A / D) converter. Output to (105).

The A / D converter 105 samples the output of the down converter 104 at a fixed frequency and outputs the delayed converter 106 and the Hilbert converter 107.

In this case, the Hilbert transformer 107 inverts the signal of the real component input by 90 degrees, converts the signal into an imaginary component signal, outputs the complex component to the complex multiplier 108, and the delay unit 106 outputs the Hilbert transformer. The signal of the real component input by the processing time at 107 is delayed and then output to the complex multiplier 108.

For convenience of description, the signal passed through the delay unit 106 is referred to as an I channel signal, and the signal passed through the Hilbert converter 107 is referred to as a Q channel signal.

The complex multiplier 108 receives a carrier with carrier recovery from the carrier recovery unit 109 and multiplies the I, Q signals of a pass band output from the delayer 106 and the Hilbert transformer 107 to determine the passband. After the I and Q signals are lowered to the baseband, the signals are output to the resampler 110 for conversion into a symbol recovered signal.

The resampler 110 receives the timing error of the current symbols from the baseband signal processing from the timing recovery unit 113 and interpolates in the direction of reducing the error between the digitized signal and the matched filter 111. Will output

The matched filter 111 is a digital matched filter having a roll-off value that is the same as the square root matched filter used in the transmission stage, and a signal output in synchronization with the symbol from the resampler 110 is applied to the matched filter 111. When passed, the SNR at the symbol location is maximized.

The signal output from the matched filter 111 is added by the adder 112 so that only the signal of the real component is output for channel equalization and output to the timing recovery unit 113.

The timing recovery unit 113 is composed of a pre-filter 113a, a timing error detector 113b, a loop filter 113c, and a numerically controlled oscillator (NCO) 113d.

The prefilter 113a passes only the edge portion of the spectrum from which the timing information can be obtained from the signal of the real component output from the adder 112 and outputs the result to the timing error detector 113b. For example, it is assumed that the timing error detector 113b uses a modified gardner method to detect information (ie, a compensation value for timing offset) regarding timing errors in various ways.

That is, the timing error detector 113b multiplies one difference sample value by the difference value of the sign of two adjacent symbol samples, obtains information on the timing error, and outputs the information about the timing error to the loop filter 113c. The loop filter 113c filters only low-band signal components among the timing error information extracted by the timing error detector 113b and outputs the filtered low-band signal to the NCO 113d. The NCO 113d adjusts the sampling timing of the resample unit 110 by converting an output frequency according to the low band component of the timing error information.

However, the digital TV receiver of FIG. 1 described above has the following problems by performing timing recovery using data of the real component that has passed through the matched filter 111.

That is, the Gardner-type timing error detection unit 113b uses the zero-crossing property of the data. In the current system, by using the pre-filter, the Gardner type timing error detection unit 113b does not obtain a great effect of enhancing this property from the matching filter 111. Instead, the acquisition time of the timing recovery unit 113 is delayed as shown in FIG. 2 due to the delay time passing through the matched filter 111.

FIG. 2 is a graph illustrating the timing capturing characteristics of the timing recovery unit 113 in the digital TV receiver as shown in FIG. 1, in which the SNRs of the ghost signal are 1.0 dB, 0.9 dB, 0.8 dB, 0.7 dB, and 0.6 dB from the left. , Timing acquisition characteristic at 0.5dB. 2, it can be seen that the signal size of the ghost that can be captured within 1000000 samples is up to 0.8 dB.

As such, the timing recovery unit 113 may have a very long delay time due to the delay time of the matched filter 111. In addition, as the signal-to-noise ratio (SNR) of the original signal to the ghost signal increases in a ghost channel environment, the delay is increased. It can be seen that the time is longer.

This delay of the acquisition time causes the performance of the timing recovery unit 113 to deteriorate, which means that the overall performance of the digital TV receiver is degraded.

That is, the acquisition time is greatly increased for relatively strong ghost signals, which degrades the performance of the entire system.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a digital TV receiver which improves the performance of the system by shortening the acquisition time by performing timing recovery at the front of the matched filter.

Another object of the present invention is to provide a digital TV receiver that performs timing recovery accurately by performing timing recovery using both real data and imaginary data at the front of the matched filter.

1 is a configuration block diagram of a typical VSB digital TV receiver

2 is a graph illustrating timing acquisition performance of the timing recovery unit of FIG. 1;

3 is a block diagram of a digital TV receiver of a VSB type according to the present invention;

4A is a graph showing the S-curve characteristics of real data components.

4B is a graph showing the S-curve characteristic of an imaginary data component.

5 is a graph illustrating timing acquisition performance of the timing recovery unit of FIG. 3.

6A is a graph illustrating S-curve characteristics of the timing recovery unit of FIG. 1.

6B is a graph illustrating S-curve characteristics of the timing recovery unit of FIG. 3.

Explanation of symbols for main parts of the drawings

301: antenna 302: tuner

303: SAW filter 304: down converter

305: A / D converter 306: Delay

307: Hilbert Converter 308: Complex Number Multiplier

309: carrier recovery unit 310: resample unit

311: matching filter 312: timing recovery unit

312a, 312c: pre-filter 312b, 312d: timing error detector

312e: adder 312f: loop filter

312g: NCO

In the digital TV receiver according to the present invention for achieving the above object, in a digital TV receiver for demodulating the received passband analog signal into a baseband digital signal, the baseband digital signal is received by receiving the timing error of the current symbols The timing error of the current symbols is obtained by using a resampler that performs interpolation in a direction of reducing an error between a sampling time and a desired sampling time, and data of real and imaginary components resampled by the resampler. And a matching filter for outputting the resampler for channel equalization after filtering the output of the resampler to maximize the signal-to-noise ratio at the symbol position output from the resampler. It is characterized by.

Preferably, the timing recovery unit obtains timing error information on data by multiplying an intermediate sample value by a difference value of a sign of two symbol samples output from the resample unit.

Other objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments taken in conjunction with the accompanying drawings.

Hereinafter, with reference to the accompanying drawings illustrating the configuration and operation of the embodiment of the present invention, the configuration and operation of the present invention shown in the drawings and described by it will be described as at least one embodiment, By the technical spirit of the present invention described above and its core configuration and operation is not limited.

3 is a block diagram of a digital TV receiver according to the present invention, in particular, a block diagram related to timing recovery.

3, an antenna 301, a tuner 302, a SAW filter 303, a down converter 304, an A / D converter 305, a delay 306, a Hilbert converter 307, a complex multiplier 308, the carrier recovery unit 309, and the resample unit 310 are the same as those of FIG. 1.

1 is different from the above-described embodiment in that the output of the resample unit 310 is output to the matching filter 311 and to the timing recovery unit 312 for timing recovery. And, the timing recovery is to use both the real component data and the imaginary component data.

To this end, the timing recovery unit 312 outputs the first prefilter 312a and the first prefilter 312a which pass only a predetermined band in the I signal of the real component output from the resample unit 310. The first timing error detector 312b, which obtains information about a timing error by taking the sign value and the intermediate sample value of consecutive symbols from the first signal, passes only a predetermined band in the imaginary component Q signal output from the resample unit 310. A second timing error detector 312d and a first timing error detector 312d which take a sign value and an intermediate sample value of consecutive symbols from the outputs of the second prefilter 312c and the second prefilter 312c to obtain information about a timing error; And an adder 312e for extracting the final timing error information by adding the outputs of the second timing error detectors 312b and 312d, and passing only a low band signal component of information on the timing error output from the adder 312e. Key is composed of a loop filter (312f), the loop filter (312f) NCO (312g) for outputting the timing offset information that needs to be adjusted to the low-band component of the timing error is outputted to the resampler 310 in.

In the present invention configured as described above, an antenna 301, a tuner 302, a SAW filter 303, a down converter 304, an A / D converter 305, a delay 306, a Hilbert converter 307, a complex number Since the operation of the multiplier 308 and the carrier recovery unit 309 is the same, detailed description thereof will be omitted.

That is, the baseband I and Q signals output from the complex multiplier 308 are output to the resample unit 310, and the resample unit 310 is outputted from the NCO 312g of the timing recovery unit 312. The timing error of the output current symbols is used to interpolate in order to reduce the error between the sampling time of the digitized signal output from the complex multiplier 308 and the desired sampling time.

The I and Q signals resampled by the resampler 310 are output to the matched filter 311, and the I signal is the first prefilter 312a of the timing recovery unit 312, and the Q signal is the timing recovery unit. The second prefilter 312c of 312 is output.

The matched filter 311 is a digital matched filter having the same roll-off value as the square root matched filter used in the transmission stage, and a signal output in synchronization with the symbol from the resampler 310 is applied to the matched filter 311. When passed, the SNR at the symbol location is maximized. The signal filtered by the matched filter 311 is output for channel equalization.

On the other hand, the first prefilter 312a of the timing recovery unit 312 outputs only the edge portion of the spectrum to the first timing error detector 312b to enhance the characteristics of the timing error detector from the input I signal. do. Also, the second prefilter 312c passes only the edge portion of the spectrum and outputs it to the second timing error detector 312d to enhance the characteristics of the timing error detector from the input Q signal. As an example, it is assumed that the first and second timing error detectors 312b and 312d detect information about timing errors using a modified Gardner method. That is, the first timing error detector 312b obtains timing error information on the I signal by multiplying the difference value of the sign of the symbol samples of the two I signals passing through the first prefilter 312a by an intermediate sample value. In addition, the second timing error detector 312c obtains timing error information about the Q signal by multiplying a difference value of a sign of symbol samples of two Q signals passing through the second prefilter 312b by an intermediate sample value.

The timing error information for the real and imaginary components detected by the first and second timing error detectors 312b and 312d are added by the adder 312e, and the final timing error information is output to the loop filter 312f. The loop filter 312f filters only the low-band signal components of the timing error information output from the adder 312e and outputs the same to the NCO 312g.

The NCO 312g outputs a timing offset value to the resample unit 310 according to the low band component of the timing error information. Then, the resample unit 310 adjusts the sampling timing according to the timing offset value.

4A is a graph showing an S-curve for a real data component, and FIG. 4B is a graph showing an S-curve characteristic for an imaginary component. The imaginary component is weaker than a real component, but sufficient for use in timing recovery. It can be seen that error characteristics are obtained. In other words, as shown in Fig. 4B, since the S-curve has a slope with respect to the imaginary component, it can be seen that timing error information can also be obtained with respect to the imaginary component.

FIG. 5 is a graph illustrating timing acquisition characteristics in accordance with the present invention. Compared with FIG. 2, for the same magnitude ghost signal of 0.5 dB, the conventional system of FIG. 2 does not converge within 1000000 samples of the present invention. It can be seen that the system is converging at about 850000 samples.

FIG. 6 shows the S-curve characteristics of the conventional system and the system of the present invention, and the timing error for each of the real component and the imaginary component is compared with those of the conventional system of FIG. 6A which used only the real component data passed through the matching filter. It can be seen that the S-curve characteristic of the system of FIG. 6B using the information is further enhanced.

In addition, since the timing recovery unit 312 of the present invention has better capture characteristics than the existing timing recovery unit 113, the convergence time can be shortened.

Here, shortening of the convergence time means that the timing can be stably captured for a relatively strong ghost signal, which means that the performance of the entire loop is improved.

The present invention is applicable to all terrestrial digital broadcast receivers of the ATSC method using VSB modulation.

As described above, according to the digital TV receiver according to the present invention, timing recovery is performed using data of real components and imaginary components that are not matched and filtered after resampling.

That is, the timing acquisition time can be reduced by reducing the delay time caused by passing through the existing matched filter in the present invention. Therefore, the performance of the entire timing recovery unit can be improved to capture timing even for a relatively stronger ghost signal for the same time (sample) as that of the current system.

In addition, since the imaginary component is weaker than the real component but has information that can be used for timing recovery, timing recovery can be performed more accurately by using both real and imaginary component data for timing recovery.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the spirit of the present invention.

Therefore, the technical scope of the present invention should not be limited to the contents described in the embodiments, but should be defined by the claims.

Claims (4)

A receiver of a digital TV that demodulates a received passband analog signal into a baseband digital signal, A resampler configured to receive timing errors of current symbols and perform interpolation in a direction of reducing an error between a sampling timing of a baseband digital signal and a desired sampling timing; A timing recovery unit for calculating timing errors of current symbols by using the real component data and the imaginary component data resampled by the resampler and outputting the timing error to the resampler; And And a matching filter for filtering the output of the resampler to maximize the signal-to-noise ratio at the symbol position output from the resampler and outputting the channel for equalization. The method of claim 1, wherein the timing recovery unit A first pre-filter passing only a predetermined band in the real component data output from the resample unit; A first timing error detector which obtains information on timing errors by taking the sign value of two consecutive symbols and the intermediate sample value from the output of the first prefilter, A second pre-filter passing only a predetermined band in the imaginary component data output from the resample unit; A second timing error detector which obtains information on a timing error by taking the sign value of the two symbols and the intermediate sample value from the output of the second prefilter; An adder for extracting final timing error information from outputs of the first and second timing error detectors; A loop filter for passing only a low band signal component of information on a final timing error output from the adder; And an NCO for generating a timing offset value and outputting the timing offset value to the resampler so as to adjust the sampling timing in accordance with the low band component of the timing error output from the loop filter. The method of claim 2, wherein the first timing error detector And multiplying an intermediate sample value by a difference value of a sign of two consecutive real component symbols passed through the first prefilter to obtain timing error information on data of the real component. The method of claim 2, wherein the second timing error detector And a timing error information for the imaginary component data by multiplying an intermediate sample value by a difference value of a sign of two consecutive imaginary component symbols passing through the second prefilter.