KR100407976B1 - Digital TV receiver - Google Patents

Abstract

A digital TV receiver recovering a symbol clock from received data, wherein the center frequency of the NCO is varied to a specific frequency (3.31 MHz), and then a passband I, Q signal is applied to a complex carrier generated around the changed center frequency. Multiplying to generate a second baseband signal such that a pilot component exists in the fs / 2 frequency portion, and performing timing recovery using the second baseband signal, so that even when a ghost signal delayed by one symbol is received, Can be obtained stably and accurately so that timing recovery can be performed accurately.

Description

Digital TV receiver {Digital TV receiver}

The present invention relates to a digital TV receiver, and more particularly, to a timing recovery apparatus for recovering a symbol clock from received data.

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. Figure 2 shows the spectrum of the I-channel signal in the 6MHz band, the pilot signal is located at 8.69MHz when the center frequency of the signal is located at 6MHz.

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 carrier recovery unit 109 includes a frequency phase locked loop (FPLL) 109a, a loop filter 109b, and an NCO1 109c. The complex multiplier 108 may be included in the carrier recovery unit.

The FPLL 109a is a frequency locked loop (FLL) process that removes a frequency difference between a carrier component of a received signal and a reference carrier component of the receiver itself, and a PLL that removes a phase error between the two carrier signals from which the frequency difference is removed. (Phase Locked Loop) process is executed at the same time.

That is, the FPLL unit 109a detects the frequency offset and the phase error from the baseband pilot signal output from the complex multiplier 108 and outputs the frequency offset and the phase error to the loop filter 109b.

The loop filter 109b filters and integrates the frequency offset and phase error and outputs the result to NCO1 109c. The NCO1 109c generates a complex sine wave proportional to the output of the loop filter 109b and outputs it to the complex multiplier 108.

In this case, the spectrum of the I channel signal when the carrier recovery unit 109 transitions the 6 MHz passband signal of FIG. 2 to baseband with the center frequency of NCO1 109c as 8.69 MHz is shown in FIG. 3.

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 includes a prefilter 113a, a timing error detector 113b, a loop filter 113c, and a numerically controlled oscillator NCO2 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. It is assumed that the timing error detector 113b uses a gardner method as an example 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 a difference value between 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 the low-band signal component among the timing error information extracted by the timing error detector 113b and outputs the low-band signal component to the NCO2 113d. The NCO2 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.

At this time, the Gardner method of the timing error detection unit 110c uses the zero crossing characteristic of the data, and when the spectrum is viewed on the spectrum, the information is provided at the point where the spectrums of two consecutive symbols overlap.

This spectrum is shown in FIG. 4 when viewed in a VSB type digital TV receiver as shown in FIG. 1.

In FIG. 4, the portion where the spectrums of two consecutive symbols overlap is near the frequency fs / 2, and information necessary for obtaining timing error using the zero crossing characteristic of the received data in the Gardner method is It is located only here.

Therefore, the timing recovery unit 113 of the digital TV receiver as shown in FIG. 1 uses the prefilter 113a to detect more accurate timing error in this portion, that is, to obtain zero crossing information of a required signal.

However, when a ghost signal with one symbol delay (about 0.1usec) comes in, the fs / 2 frequency portion of the spectrum is greatly distorted. This means that the zero crossing component of the data required for detecting timing errors in the Gardner method is greatly reduced.

Therefore, in such a situation, the timing recovery unit algorithm of the current digital TV receiver using the Gardner method not only degrades the performance much, but also fails to recover the accurate clock, resulting in performance degradation 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 capable of sufficiently obtaining zero crossing information of data even when a ghost signal delayed by one symbol is received.

1 is a block diagram of a general digital TV receiver

FIG. 2 is a diagram illustrating a spectrum of a passband I signal in a 6 MHz band input to a carrier recovery unit of FIG. 1. FIG.

FIG. 3 is a diagram illustrating a spectrum of a baseband I channel signal output from the carrier recovery unit of FIG. 1. FIG.

4 is a diagram illustrating a spectrum of an example of pre-filtering to obtain an fs / 2 frequency component in the timing recovery unit of FIG. 1.

5 is a conceptual diagram of a digital TV receiver according to the present invention;

6 is a detailed block diagram of FIG.

7 is a diagram illustrating a spectrum of a baseband I channel signal output from a pilot position converter of the present invention;

8 is a diagram illustrating a spectrum of an example of pre-filtering to obtain an fs / 2 frequency component in a timing recovery unit according to the present invention.

Explanation of symbols for main parts of the drawings

101: antenna 102: tuner

200: digital processing unit 300: carrier recovery unit

400: pilot position converter 500: channel decoder

600: timing recovery unit

According to an aspect of the present invention, there is provided a digital TV receiver comprising: a digital processing unit for selecting a desired channel frequency through an antenna, converting the desired frequency into an intermediate frequency, and then digitizing only a predetermined band of the intermediate frequency; A carrier recovery unit for converting the digitized passband signal to a first baseband signal by multiplying a complex carrier generated using a first center frequency; A pilot position converter for converting the digitized passband signal to a second baseband signal by multiplying a complex carrier generated using a second center frequency; A resampler for receiving timing errors of current symbols and interpolating the second baseband signal output from the pilot position converter to reduce an error between the signals; And a timing recovery unit for obtaining timing errors of current symbols from an output of the resample unit and outputting the timing errors to the resample unit.

The carrier recovery unit includes a complex multiplier for multiplying the passband signal by a complex carrier generated around the first center frequency to shift the passband signal to a baseband signal, and a frequency from a baseband pilot signal output from the complex multiplier. A FPLL for detecting offset and phase errors, a loop filter for filtering and integrating the frequency offset and phase errors, and a complex carrier that is proportional to the output of the loop filter is generated based on a first center frequency and output to the complex multiplier. It characterized in that it is composed of a numerically controlled oscillator.

The pilot position converter includes a numerically controlled oscillator for generating and outputting a complex carrier, which is proportional to the output of the loop filter of the carrier recovery unit, based on a second center frequency, and a complex generated around the passband signal and the second center frequency. And a complex multiplier for multiplying the carrier to transition the passband signal to a second baseband signal.

The second center frequency is characterized in that the 3.31MHz.

The pilot component included in the second baseband signal is located at a frequency portion of fs / 2 (where fs is a sampling frequency).

The timing recovery unit extracts information on a timing error by multiplying a pre-filter passing only an edge portion of the spectrum from the output of the resample unit and a difference value between two symbol samples passing through the pre-filter by one intermediate sample. An error detector, a loop filter for filtering only low-band signal components among the timing error information extracted by the timing error detector, and an output frequency converted according to the low-band component of the timing error information to adjust sampling timing of the resample unit. It is characterized by consisting of NCO.

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.

According to the present invention, by placing a pilot signal in a specific portion of a received signal, that is, an fs / 2 frequency component, even when a ghost signal delayed by one symbol is input, the crossover information of data necessary for timing error detection is accurately obtained.

5 is a conceptual block diagram of a digital TV receiver according to the present invention, and FIG. 6 is a detailed block diagram.

5 and 6, the pilot signal is positioned in the fs / 2 frequency portion on the frequency spectrum shifted to the baseband by changing the center frequency of the NCO. This is performed by the pilot position converting unit 400. In this case, the carrier recovery unit 300 performs a carrier recovery process using the FPLL algorithm as in the prior art without being affected by the pilot position converter 400.

In the present invention, for convenience of description, the baseband I, Q signal demodulated by the carrier recovery unit 300 is called a first baseband I, Q signal, and the baseband I, Q demodulated by the pilot position converter 400. The signal is called a second baseband I, Q signal.

The timing recovering unit 500 according to the present invention receives the second baseband signal converted by the pilot position converting unit 400 and detects a timing error to generate a clock as used in transmission.

Referring to FIG. 6, the pilot position converting unit 400 has a center frequency different from that of NCO1 304 of the carrier recovering unit 300, and a frequency offset from the loop filter 303 of the carrier recovering unit 302. And multiplying the carriers of the NCO3 (401) by multiplying the NCO3 (401) for generating and outputting a complex sine wave proportional to the phase error, and the passband I, Q signals outputted through the retarder (106) and the Hilbert transformer (107). A complex multiplier 403 outputs to the resample unit 501 of the channel decoder 500.

In general, when timing error detection is performed by the Gardner method, the zero crossing component of the data used in the Gardner method is present in a portion where two consecutive spectra overlap.

The pilot position converting unit 400 of the present invention allows the pilot component to exist in the overlapped portion.

By doing so, even if the one-signal delayed ghost (eg, 0.1usec) signal is included in the received signal, distortion of the portion where the spectrums of two consecutive symbols overlap can be greatly reduced.

That is, the passband I and Q signals output from the delay unit 106 and the Hilbert converter 107 of the digital processing unit 200 are output to the complex multiplier 301 of the carrier recovery unit 300.

The complex multiplier 301 multiplies the passband I, Q signals by the complex carriers output from the NCO1 304 to transition to the baseband I, Q signals and outputs them to the FPLL 302.

The FPLL 302 is a frequency locked loop (FLL) process that removes a frequency difference between a carrier component of a received signal and a reference carrier component of a receiver itself, and a PLL that removes a phase error between the two carrier signals from which the frequency difference is removed. (Phase Locked Loop) process is executed at the same time.

That is, the FPLL 302 detects the frequency offset and the phase error from the baseband pilot signal output from the complex multiplier 301 and outputs the frequency offset and phase error to the loop filter 303.

The loop filter 303 filters and integrates the frequency offset and the phase error and simultaneously outputs the NCO1 304 of the carrier recovery unit 300 and the NCO3 401 of the pilot position converter 400. The NCO1 304 generates a complex sine wave proportional to the output of the loop filter 303 and outputs the complex sine wave to the complex multiplier 301, where the center frequency of the NCO1 304 is 8.69 MHz.

The NCO3 401 of the pilot position converter 400 generates a complex sine wave proportional to the output of the loop filter 303 and outputs the complex sine wave to the complex multiplier 403. The center frequency is 3.31 MHz. That is, the NCO3 401 changes the complex carrier within a predetermined range around the center frequency (ie, 3.31 MHz) according to the output of the loop filter 302 and outputs the complex carrier to the complex multiplier 403.

The complex multiplier 403 multiplies the complex carriers output from the NCO3 401 by the I and Q signals output from the delay unit 106 and the Hilbert transformer 107 to resample the unit 501 of the channel decoder 500. )

That is, a complex carrier is generated by setting the center frequency of the NCO3 401 to 3.31 MHz, and the passband I and Q signals output from the delayer 106 and the Hilbert converter 107 are generated using the generated complex carrier. Transitioning to two baseband I, Q signals yields a spectrum as shown in FIG.

Referring to FIG. 7, the pilot signal is located in the fs / 2 portion on the frequency spectrum shifted to the baseband in the complex multiplier 401.

In the channel decoder 500, a portion where the spectrums of two consecutive symbols overlap in demodulation is as shown in FIG. 8.

That is, the resampler 501 of the channel decoder 500 is not the first baseband signal demodulated by the carrier recovery unit 300 but the second baseband signal and the signal demodulated by the pilot position converter 400. Interpolation is performed in a direction of reducing errors therebetween, and timing information is received from the timing recovery unit 600.

When the output of the resample unit 501 passes through the matched filter 502, the SNR at the symbol position output from the resample unit 501 becomes maximum.

The signal output from the matched filter 502 is added by the adder 503 so that only the signal of the real component is output for channel equalization and output to the timing recovery unit 600.

The prefilter 601 of the timing recovery unit passes only the edge portion of the spectrum from which timing information can be obtained and outputs the result to the timing error detector 602.

In this case, when the signal converted into the baseband by the pilot position converter 400 is demodulated while passing through the channel decoder 500, a spectrum as shown in FIG. 8 is obtained.

The frequency band filtered by the prefilter 601 is an fs / 2 frequency band in which two symbols of the 6 MHz band overlap with each other as shown in FIG. 8.

That is, when timing error detection is performed by the timing recovery unit 600 in the Gardner method, since the zero crossing component of the data used in the Gardner method is present in the portion where two consecutive spectra overlap, the pre-filter 601 Extract only this part and print it out.

In this case, the portion where the spectrums of the two consecutive symbols overlap is hardly distorted even when a ghost (eg, 0.1usec) signal delayed by one symbol is included in the received signal, and thus is output from the prefilter 601. The signal contains enough information for timing error detection.

The timing error detection unit 602 detects information on timing errors (ie, compensation values for timing offsets) in various ways, and according to the present invention, it is assumed that a garner method is used.

That is, the timing error detector 602 obtains information on the timing error by multiplying a difference value between two adjacent symbol samples by one intermediate sample value and outputs the information about the timing error to the loop filter 603. The loop filter 603 filters out only low-band signal components of the timing error information extracted by the timing error detection unit 602 and outputs the same to the NCO2 604. The NCO2 604 adjusts the sampling timing of the resample unit 501 by converting an output frequency according to the low band component of the timing error information.

In this way, the present invention can place the pilot component in a specific portion of the received signal, that is, the fs / 2 frequency component, to obtain a more robust fs / 2 frequency component even when a ghost signal delayed by one symbol is received. have.

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

As described above, according to the digital TV receiver according to the present invention, the center frequency of the NCO is varied to a specific frequency (3.31 MHz), and then the complex carriers generated around the center frequency are multiplied by the passband I, Q signals to form a second. By generating a baseband signal and performing timing recovery using the second baseband signal, it is possible to stably and accurately obtain data crossing information even when a ghost signal delayed by one symbol is received. Therefore, the timing recovery can be performed accurately, thereby improving the performance of the system.

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)

In a digital TV receiver for receiving a signal that is modulated and transmitted in a residual side band (VSB) method, A digital processor which selects a desired channel frequency through an antenna, converts the desired channel frequency into an intermediate frequency, and then digitizes only the predetermined band of the intermediate frequency; A carrier recovery unit for converting the digitized passband signal to a first baseband signal by multiplying a complex carrier generated using a first center frequency; A pilot position converter for converting the digitized passband signal to a second baseband signal by multiplying a complex carrier generated using a second center frequency; A resampler for receiving timing errors of current symbols and interpolating the second baseband signal output from the pilot position converter to reduce an error between the signals; And And a timing recovery unit for obtaining timing errors of current symbols from an output of the resample unit and outputting the timing errors to the resample unit. The method of claim 1, wherein the carrier recovery unit A complex multiplier for multiplying the passband signal by a complex carrier generated around a first center frequency to transition the passband signal to a baseband signal; An FPLL for detecting a frequency offset and a phase error from a baseband pilot signal output from the complex multiplier; A loop filter for filtering and integrating the frequency offset and phase error; And a numerically controlled oscillator for generating a complex carrier wave proportional to the output of the loop filter about a first center frequency and outputting the complex carrier to the complex multiplier. The method of claim 2, wherein the pilot position converter A numerically controlled oscillator for generating and outputting a complex carrier with respect to the output of the loop filter of the carrier recovery unit based on a second center frequency; And a complex multiplier for multiplying the passband signal by a complex carrier generated around a second center frequency to transition the passband signal to a second baseband signal. The method of claim 1, wherein the timing recovery unit A pre-filter passing only an edge portion of the spectrum from the output of the resample section; A timing error detector for extracting information on timing errors by multiplying a difference value between two symbol samples passing through the prefilter by one intermediate sample; A loop filter for filtering only low-band signal components of the timing error information extracted by the timing error detector; And an NCO for converting an output frequency according to a low band component of the timing error information to adjust a sampling timing of the resample unit.