KR20030077204A - Demodulator for europe digital television system for terrestrial broadcasting signal and cable broadcasting signal - Google Patents

Abstract

PURPOSE: A demodulator of an European digital television system used in common for both ground wave and cable is provided to reduce an area of hardware of the European digital television system. CONSTITUTION: A locking detector(614) obtains a symbol rate of a demodulated signal by using a detecting signal of a QAM(Quadrature Amplitude Modulation) timing error detecting unit(605) to discriminate a ground wave broadcasting signal and a cable broadcasting signal. A selecting element(616) selects one of the detecting signal of the QAM timing error detecting unit and a detecting signal of an OFDM(Orthogonal Frequency Division Modulation) timing error detecting unit(609). A frequency synchronizing unit(608) generates a frequency control signal according to a result of the discrimination of the locking detector. An output signal of a frequency compensating unit is inputted to one of a fast fourier transformer(611) and a QAM equalizer. The ground wave broadcasting signal is inputted to an FEC(Forward Error Correction)(615) via the fast fourier transformer and an OFDM equalizer. The cable broadcasting signal is inputted to the FEC via the QAM equalizer.

Description

Demodulator for europe digital television system for terrestrial broadcasting signal and cable broadcasting signal

The present invention relates to a digital television system, and more particularly, to a demodulator of a European digital television system capable of digitally receiving and demodulating both terrestrial broadcasting and cable broadcasting.

In the existing European digital television (DTV) system, only a part of terrestrial broadcasting is generally received, and cable broadcasting is analog. Thus, there was little demand for digitally receiving cable broadcasts. However, with the spread of digital cable broadcasting reception systems, digital terrestrial and cable common systems are required.

In general, European digital terrestrial broadcasting uses orthogonal frequency division modulation (OFDM), which is a relatively complex modulation method, and European digital cable broadcasting uses quadrature amplitude modulation (QAM). Therefore, circuits for receiving terrestrial broadcasting and cable broadcasting in European DTV systems are generally made independently. This requires two receive front ends, which increases the hardware area itself when building integrated circuits. To solve this problem, there is a need for a DTV system that can reduce the hardware area by sharing a terrestrial system and a cable system.

1 is a block diagram illustrating a general European DTV system. Referring to this, a typical European DTV system includes a tuner 101, an OFDM demodulator 102, a QAM demodulator 103, and an error correction decoder unit 110. The error correction decoder unit 110 includes deinterleavers 111 and 113, a Viterbi decoder 112, a Reed-Solomon (RS) decoder 114, and a descrambler 115.

In the conventional DTV system shown in FIG. 1, a circuit for receiving terrestrial broadcasting and a circuit for receiving cable broadcasting are separately separated, and symbol synchronization is performed separately.

First, the terrestrial broadcast signal goes through an OFDM demodulation process in the OFDM demodulator 102 and goes to an error correction decoder. The cable broadcast signal undergoes QAM demodulation in an additional QAM demodulator 103 to correct errors. It enters the decoder error (forward error correction).

Detailed configurations of the OFDM demodulator 102 and the QAM demodulator 103 according to the prior art are shown in FIGS. 2 and 3, respectively. In the past, analog demodulators were used, but as shown in FIGS. 2 and 3, OFDM demodulators 102 and QAM demodulators using an interpolator are widely used for full digital timing synchronization.

The structure using the interpolator handles all the synchronization parts such as symbol synchronization and frequency synchronization in the purely digital domain, which eliminates the need for external circuits and is easy to integrate.

Referring to FIG. 2, the OFDM demodulator 102 according to the related art is an analog-to-digital converter (ADC) 401 for sampling an intermediate frequency analog terrestrial broadcast signal IF and converting the signal into a digital signal. Is a downlink frequency converter 403 which is converted into an in-phase (I) component and an orthogonal (Q) component, an interpolator filter 405 for synchronizing symbol synchronization of an OFDM signal according to timing control information, and an interpolation timing control information. And a timing synchronizer 404 generated by the radar filter 405.

In addition, the OFDM demodulator 102 according to the related art includes a frequency shifter 406 for compensating for the frequency of an input signal according to the frequency synchronization information, a frequency synchronizer 407 for outputting the frequency synchronization information to the frequency shifter 406, A fast Fourier transformer (FFT) 408 for fast Fourier transforming the input data, and a channel estimator and equalizer 409.

Referring to FIG. 3, the QAM demodulator 103 according to the related art is an analog-to-digital converter (ADC, 501), a downlink frequency converter (503) for sampling an analog cable broadcasting signal IF of an intermediate frequency and converting it into a digital signal. An interpolator filter 505 and a timing synchronizer 504 are included.

In addition, the QAM demodulator 103 according to the related art filters the frequency compensator 506, the frequency synchronizer 507, and the input data to perform the function similar to the frequency shifter 406 of FIG. Matching filters (MF, 508) and a QAM equalizer (509).

As shown in Figures 2 and 3, many of the components of the digital OFDM demodulator 102 and the QAM demodulator 103 serve similar functions. In particular, circuits for timing synchronization and frequency synchronization have many overlapping functionalities, and are suitable for common implementation for OFDM signals and QAM signals.

Therefore, the conventional European DTV system has respective demodulators that independently demodulate the terrestrial broadcast signal and the cable broadcast signal, as shown in Figs. 2 and 3, but the DTV system to be made in the future has a hardware size or a digital cable network. As a result, a system that commonly implements a circuit for demodulating terrestrial broadcast signals and cable broadcast signals on the same chip is required.

Therefore, the technical problem to be achieved by the present invention is to realize a common part of a circuit for receiving and demodulating terrestrial broadcast signals and a circuit for receiving and demodulating cable broadcast signals in a European DTV system, thereby reducing hardware area and simplifying control. It is to provide demodulator for European terrestrial / cable DTV system.

The detailed description of each drawing is provided in order to provide a thorough understanding of the drawings cited in the detailed description of the invention.

1 is a block diagram showing a typical European digital television system.

2 is a block diagram showing a detailed configuration of an OFDM demodulator according to the prior art.

3 is a block diagram showing a detailed configuration of a QAM demodulator according to the prior art.

Figure 4 is a block diagram showing a demodulator of the European terrestrial / cable common DTV system according to an embodiment of the present invention.

One aspect of the present invention for achieving the above technical problem relates to a demodulator of a terrestrial / cable common DTV system for demodulating a terrestrial broadcast signal and a cable broadcast signal in a European digital television (DTV) system. In accordance with an aspect of the present invention, a demodulator for a European terrestrial / cable common DTV system includes: an OFDM demodulator configured to receive and demodulate the OFDM modulated terrestrial broadcast signal; And a QAM demodulator configured to receive and demodulate the QAM-modulated cable broadcast signal, wherein the hardware circuit for symbol synchronization and frequency synchronization of the terrestrial broadcast signal in the OFDM demodulator and the symbol synchronization of the cable broadcast signal in the QAM demodulator; Hardware circuit for frequency synchronization is characterized in that commonly implemented.

Another aspect of the present invention for achieving the above technical problem relates to a demodulator of a terrestrial / cable common DTV system for demodulating a terrestrial broadcast signal and a cable broadcast signal in a European digital television (DTV) system. In accordance with another aspect of the present invention, a demodulator for a European terrestrial / cable DTV system includes: an analog / digital converter configured to sample the terrestrial broadcast signal and an analog signal of an intermediate frequency on which the cable broadcast signal is loaded and sample the signal; A symbol synchronization circuit that receives the sampling signal and outputs the signal in synchronization with a symbol; A frequency synchronizing circuit for receiving an output signal of the symbol synchronizing circuit and outputting the frequency synchronizing signal; A fast Fourier transformer for receiving the terrestrial broadcast signal from an output signal of the frequency synchronization circuit and performing fast Fourier transform; An OFDM equalizer for receiving and equalizing output data of the fast Fourier transformer; And a QAM equalizer configured to receive and equalize the cable broadcast signal among the output signals of the frequency synchronization circuit, wherein the symbol synchronization circuit is embodied in common with the terrestrial broadcast signal and the cable broadcast signal.

In order to fully understand the present invention, the operational advantages of the present invention, and the objects achieved by the practice of the present invention, reference should be made to the accompanying drawings which illustrate preferred embodiments of the present invention and the contents described in the accompanying drawings.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Like reference numerals in the drawings denote like elements.

Figure 4 is a block diagram showing a demodulator of the European terrestrial / cable common DTV system according to an embodiment of the present invention.

The demodulator of the European terrestrial / cable DTV system according to an embodiment of the present invention shares a large portion of hardware required for demodulation of the terrestrial signal and hardware required for demodulation of the cable signal, in particular, a hardware circuit for synchronization. do. That is, some of the blocks of the all-digital synchronous circuit used in the conventional terrestrial OFDM demodulator are shared so that the digital cable synchronous circuit can be configured.

The reception mode for receiving DTV broadcasting is divided into two types. First, the signal is completely converted to baseband and processed, and the intermediate frequency output is sampled to change to baseband within the baseband processing system. I may give it. The demodulator of the DTV system of the present invention corresponds to the latter.

Referring to FIG. 4, a demodulator according to an embodiment of the present invention is an analog / digital converter (ADC) 601, a symbol synchronization circuit 650, a frequency synchronization circuit 660, a fast Fourier converter 611, an OFDM equalizer. 613 and a QAM equalizer 612.

The analog / digital converter (ADC) 601 samples an analog signal IF having an intermediate frequency on which terrestrial broadcast signals and cable broadcast signals are sampled, and outputs them as a sampling signal SS. At this time, the sampling frequency is determined by the sum of the 1/4 of the intermediate frequency and the transmission rate of the data to be sent or determined by finding a frequency without aliasing. Since the signal IF input to the analog / digital converter ADC 601 is an output signal of a tuner (not shown), a signal of a specific channel among terrestrial broadcast signals or cable broadcast signals is selected by the tuner.

The symbol synchronization circuit 650 receives the sampling signal SS and outputs the symbol synchronization in synchronization with the terrestrial broadcast signal and the cable broadcast signal.

The symbol synchronization circuit 650 circuit specifically includes a polyphase filter 602, a downlink frequency converter 603, a matched filter 604, a loop filter 606, and a timing controller 607.

The polyphase filter 602 interpolates the sampling signal SS received according to the timing control signal TCS output from the timing controller 607 to adjust timing synchronization. The downlink frequency converter 603 converts the frequency of the output signal of the multiphase filter 602 into a low frequency and separates the input signal into in-phase (I) and quadrature (Q) components. The output signal of the downlink frequency converter 603 is subjected to a matched filter 604 to find data.

The timing control signal TCS for controlling the polyphase filter 602 is generated by the timing controller 607. The timing controller 607 generates a timing control signal TCS according to the timing error detection signals TEQ and TEO. The loop filter 606 is required to remove high frequency noise of the timing error detection signals TEQ and TEO. Do.

The demodulator of the European terrestrial / cable DTV system according to an embodiment of the present invention is a QAM timing error detector 605, an OFDM timing error detector 609, and two detectors 605 and 609 for generating a timing error detection signal. It is preferable to further include selecting means 616 for selectively inputting the timing error detection signals TEQ and TEO outputted from the loop filter 606.

The frequency synchronizing circuit 660 receives the output signal of the symbol synchronizing circuit 650 and outputs the frequency synchronizing signal, which is commonly implemented for the terrestrial broadcasting signal and the cable broadcasting signal.

In detail, the frequency synchronizing circuit 660 includes a frequency compensating unit 610 and a frequency synchronizing unit 608.

The frequency compensator 610 compensates for the frequency of the output signal of the symbol synchronization circuit 650 according to a predetermined frequency control signal, thereby eliminating an error in the frequency. At this time, the frequency synchronizer 608 outputs a frequency control signal FCS to the frequency compensator 610 to control how much the frequency compensator 610 should compensate for the frequency. Since the frequency compensation degree of the frequency compensator 610 should be different depending on whether the signal to be demodulated is a QAM signal or an OFDM signal, the frequency synchronizer 608 is a frequency compensator (QAM signal / OFDM signal) according to the type of the demodulated signal (QAM signal / OFDM signal). 610 is controlled.

Through the matched filter 604, the QAM data is nearly demodulated. Therefore, in the case of a QAM signal, the frequency is compensated in the frequency compensator 610 and then input to the QAM equalizer 612.

The QAM equalizer 612 equalizes the waveform, which is distorted due to channel noise, in the process of transmitting the QAM signal. The output data of the QAM equalizer 612 is input to the error correction decoder 615 for error correction.

On the other hand, the OFDM signal is recovered data through a fast Fourier transform. Accordingly, in the case of an OFDM signal, data is recovered by the fast Fourier transformer 611 via the frequency compensator 610, and channel estimation and equalization are performed by the OFDM equalizer 613. The output data of the OFDM equalizer 613 is input to the error correction decoder 615 for error correction.

The data recovered through the matched filter 604 or the fast Fourier transformer 611 is fed back and used for timing control.

Looking at the feedback path of the OFDM data, the recovered OFDM data passes through the OFDM timing error detector 609, enters the input of the loop filter 606, eliminates the high frequency components, and then controls the polyphase filter 602. 607). The OFDM timing error detector 609 is a circuit for detecting timing errors of OFDM data.

Looking at the timing control path of the QAM data, the restored QAM data passes through the QAM timing error detection unit 605, enters the input of the loop filter 606, eliminates high frequency components, and then controls the polyphase filter 602. It is used as an input of 607. The QAM timing error detector 605 is a circuit that detects timing errors of the QAM data.

The multiplexer is selected as the selection means 616 for selecting one of the detection signal TEO of the OFDM timing error detection unit 609 and the detection signal TEQ of the QAM timing error detection unit 605 and inputting the same to the loop filter 606. Used.

In the demodulator according to the embodiment of the present invention having the configuration described above, the symbol synchronization circuit 650 and the frequency synchronization circuit 660 are commonly used for demodulation of the cable signal and the demodulation of the terrestrial signal.

Operation of the demodulator of the European terrestrial / cable common DTV system according to an embodiment of the present invention shown in FIG. 4 is performed as follows.

First, it distinguishes whether it is a terrestrial broadcast signal or a cable broadcast signal. To this end, it is preferable that the demodulator of the European terrestrial / cable common DTV system according to an embodiment of the present invention further includes a locking detector 614.

The locking detector 614 automatically determines whether the demodulated signal is a terrestrial broadcast signal or a cable broadcast signal by obtaining a symbol rate of the demodulated signal using the detection signal TEQ of the QAM timing error detector 605. That is, the locking detector 614 compares the symbol rate of the demodulated signal with the set symbol rate to distinguish whether the demodulated signal is a terrestrial broadcast signal or a cable broadcast signal.

The determination result of the locking detector 614 is used to control the path of the other components and the signal.

The selecting means 616 selects either the detection signal TEQ of the QAM timing error detection unit 605 or the detection signal TEO of the OFDM timing error detection unit 609 according to the determination result of the locking detector 614. . The frequency synchronizer 608 generates a frequency control signal FCS in response to the determination of the locking detector 614, and the output signal of the frequency compensator 610 according to the determination result of the locking detector 614. Input is either to transducer 611 or to QAM equalizer 612.

That is, in the case of terrestrial waves, a synchronization process is performed followed by a fast Fourier transform 611 and an OFDM equalizer 613 to enter the FEC 614, and in the case of a cable signal, the FEC 614 via the QAM equalizer 612. The path is controlled to enter.

Although the present invention has been described with reference to one embodiment shown in the drawings, this is merely exemplary, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

According to the present invention, a substantial portion of a circuit for demodulating a terrestrial broadcast signal and a circuit for demodulating a cable broadcast signal is implemented in hardware in a European DTV system. Therefore, according to the present invention, the hardware area of the European DTV system is reduced and the control is simplified.

Claims (9)

In a demodulator of a terrestrial / cable common DTV system that demodulates terrestrial broadcast signals and cable broadcast signals in a European digital television (DTV) system, An OFDM demodulator for receiving and demodulating the OFDM modulated terrestrial broadcast signal; And A QAM demodulator configured to receive and demodulate the QAM modulated cable broadcast signal, European-style terrestrial wave, characterized in that the hardware circuit for symbol synchronization and frequency synchronization of the terrestrial broadcast signal in the OFDM demodulator and the hardware circuit for symbol synchronization and frequency synchronization of the cable broadcast signal in the QAM demodulator are implemented in common. Demodulator for cable-shared DTV systems. In a demodulator of a terrestrial / cable common DTV system that receives and demodulates a terrestrial broadcast signal and a cable broadcast signal in common in a European digital television (DTV) system, An analog / digital converter configured to sample an analog signal of an intermediate frequency carrying the terrestrial broadcast signal and the cable broadcast signal and output the sampled signal as a sampled signal; A symbol synchronization circuit that receives the sampling signal and outputs the signal in synchronization with a symbol; A frequency synchronizing circuit for receiving an output signal of the symbol synchronizing circuit and outputting the frequency synchronizing signal; A fast Fourier transformer for receiving the terrestrial broadcast signal from an output signal of the frequency synchronization circuit and performing fast Fourier transform; An OFDM equalizer for receiving and equalizing output data of the fast Fourier transformer; And A QAM equalizer for receiving and equalizing the cable broadcast signal among the output signals of the frequency synchronization circuit, And the symbol synchronization circuit is embodied in common for the terrestrial broadcast signal and the cable broadcast signal. 3. The symbol synchronization circuit of claim 2, wherein the symbol synchronization circuit A multiphase filter which receives the sampling signal and interpolates according to a predetermined timing control signal to output timing synchronization; A downlink frequency converter for converting the frequency of the output signal of the multiphase filter to a low frequency and separating the in-phase component into quadrature-phase components; And And a matched filter for processing the output signal of the downlink frequency converter to find the data. 4. The symbol synchronization circuit of claim 3, wherein the symbol synchronization circuit A loop filter for removing high frequency noise components of a predetermined timing error detection signal; And And a timing controller for receiving the output signal of the loop filter and outputting the timing control signal. The method of claim 2, The frequency synchronization circuit may include a frequency compensator configured to compensate a frequency of an output signal of the symbol synchronization circuit according to a predetermined frequency control signal; And a frequency synchronizer for generating the frequency control signal according to the type of signal to be demodulated, The frequency synchronization circuit is a demodulator of a terrestrial / cable common DTV system of claim 1, wherein the terrestrial broadcast signal and the cable broadcast signal are implemented in common. The demodulator of claim 3 or 5, wherein the demodulator of the European terrestrial / cable DTV system comprises: A QAM timing error detector for detecting a timing error by receiving an output signal of the matched filter; An OFDM timing error detector for detecting a timing error by receiving output data of the fast Fourier transformer; And And a selection means for selecting one of the detection signal of the QAM timing error detection unit and the detection signal of the OFDM timing error detection unit to output the timing error signal as a demodulator of the European terrestrial / cable common DTV system. . The demodulator of claim 6, wherein the demodulator of the European terrestrial / cable DTV system And a locking detector for determining whether the demodulated signal is the terrestrial broadcast signal or the cable broadcast signal by obtaining a symbol rate of the demodulated signal using the detection signal of the QAM timing error detection unit. Demodulator for European terrestrial / cable DTV systems. 8. The method of claim 7, wherein said selecting means The demodulator of the European terrestrial / cable common DTV system according to the determination result of the locking detector, one selected from the detection signal of the QAM timing error detector and the detection signal of the OFDM timing error detector. According to claim 7, The frequency synchronization unit generates the frequency control signal according to a determination result of the locking detector, And the output signal of the frequency compensator is input to any one of the fast Fourier transformer and the QAM equalizer according to the determination result of the locking detector.