KR20050002177A - Automatic Fine Tuning For Digital Television - Google Patents

Abstract

PURPOSE: An automatic fine tuning apparatus for a digital television is provided to control the tuning frequency of the tuner at a demodulating stage although the central frequencies of a channel and of a signal tuned by the tuner are out of a permitted limit. CONSTITUTION: A demodulator(200) comprises an NTSC(National Television Standards Committee) remove filter(230) and an equalizer(250), processes a central frequency of an IF(Intermediate Frequency) signal outputted from a tuner(100) and checks a lock of a channel. When the channel is locked, the demodulator demodulates the IF signal and then outputs the IF signal into data bit stream. A power detecting member(300) detects power outputted from the NTSC remove filter and equalizer. A microcomputer(400) control the central frequency detected by the tuner on the basis of the channel lock check result and power values detected by the power detecting member.

Description

Automatic Fine Tuning For Digital Television

The present invention relates to an automatic fine tuning device for digital television (hereinafter referred to as AFT; Automatic Fine Tuning).

As shown in Fig. 1, the 8 VSB (Vestigial Sideband) digital terrestrial broadcast channel provides a high quality video, audio and auxiliary data of approximately 19 Mbit / s with a bandwidth of 6 MHz. In order for the receiver to accurately demodulate the digital terrestrial broadcast signal, the tuner frequency and the center frequency of the channel must be exactly matched by the tuner. If the tuning frequency and the center frequency of the channel deviate due to a problem such as a transmission process, the demodulator cannot detect the pilot signal, and thus the demodulator performs a tuning operation to detect the pilot signal. However, there is a problem in that tuning cannot be adjusted in a demodulation stage in which the frequency is set beyond the allowable range in the demodulation stage or the frequency deviates much during the transmission process.

Therefore, there is a need for an automatic fine tuning device for digital television that can control the tuning frequency of the tuner at the demodulation stage even when the center frequency of the channel and the center frequency of the signal tuned by the tuner are out of the allowable range.

Accordingly, the present invention has been made in view of the above circumstances, and an object of the present invention is to adjust the tuning frequency of the tuner at the demodulator even when the center frequency of the channel and the center frequency of the signal tuned by the tuner are out of an allowable range. It is to provide an automatic fine tuning device for digital television that can be controlled.

The automatic fine tuning apparatus for digital television according to the present invention for achieving the above object includes an NTSC cancellation filter and an equalizer, and checks the channel lock by processing the center frequency of the intermediate frequency signal from the tuner, and checking the result. A demodulator for demodulating the intermediate frequency signal to output a data bitstream; A power detector for detecting power of signals output from the NTSC cancellation filter and equalizer; And a microcomputer for controlling the center frequency of the channel detected by the tuner based on the channel lock check result of the demodulator and the detected power values from the power detector. Preferably, when the channel lock check result of the demodulator is unlocked and the detected power value from the power detector is equal to or greater than a predetermined reference value, the microcomputer adds or subtracts the tuning frequency of the tuner by a step frequency. If the tuner controls the tuning frequency of the tuner and the channel lock check result of the demodulator is unlocked and the detected power value from the power detector is less than a predetermined reference value, the broadcast signal is tuned to the tuned frequency by the tuner. It is determined that there is no, and characterized in that the tuner does not control the center frequency.

According to the present invention, when the center frequency of the channel and the center frequency of the signal tuned by the tuner are out of the allowable range or more, it is possible to detect this and fine tune the tuner tuning frequency again.

1 is a diagram illustrating a baseband frequency configuration of an 8 VSB digital broadcast channel.

2 is a block diagram showing an automatic fine tuning apparatus for digital television according to an embodiment of the present invention.

3 and 4 are diagrams for explaining the operation of the automatic fine adjustment device for digital television shown in FIG.

<Explanation of symbols for the main parts of the drawings>

100 tuner 200 demodulator

210: ADC 230: NTSC Rejection Filter

250: equalizer 270: error correction decoder

300: power detector 400: MCU

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

2 is a block diagram showing an automatic fine tuning apparatus for digital television according to an embodiment of the present invention.

3 and 4 are diagrams for explaining the operation of the automatic fine adjustment device for digital television shown in FIG.

2, reference numeral 100 denotes a tuner. The tuner 100 detects a signal of a predetermined channel from an RF signal received through an antenna (not shown) under the control of a microcomputer 400 (hereinafter referred to as MCU), which will be described later, and has an intermediate frequency of 44 MHz. Output the signal. The tuner 100 includes a band currency filter, a first mixer, a first local oscillator, a second mixer, a second local oscillator, and the 44 MHz by the first and second mixers and the first and second local oscillators. Outputs an intermediate frequency signal.

Reference numeral 200 denotes a demodulator 200. The demodulator 200 processes an intermediate frequency signal from the tuner 100 and outputs a data bit string. The demodulator 200 includes an ADC 210, an NTSC cancellation filter 230, an equalizer 250, and an error correction decoder 270. The ADC 210 detects an I signal and a Q signal from the intermediate frequency signal, and outputs a digital signal based on the I and Q signals. The NTSC cancellation filter 230 removes NTSC signal interference from the digital signal from the ADC 210. The equalizer 250 corrects linear channel distortion such as tilt, afterimage, etc. in the signal from the NTSC cancellation filter 230. The error correction decoder 27 detects and corrects an error of the data digital signal through the equalizer 250 and outputs a data bitstream.

Reference numeral 300 denotes a power detector 300. The power detector 300 detects power of processing signals of the NTSC cancellation filter 230 and the equalizer 250, and provides the detected power values to the MCU 400.

The MCU 400 controls the tuner 100 according to the detected power values from the power detector 300. When the MCU 400 detects that the power values detected by the power detector 300 are less than a predetermined reference value, the MCU 400 controls the tuner 100 to control the tuner 100 as shown in FIG. 3. By adjusting the center frequency Fc of the tuner 100 by the minimum adjustable frequency Fs, the demodulator 200 can detect the pilot signal. For example, after the tuner 100 tunes at the first center frequency Fc, the demodulator 200 checks the channel lock, and if it is unlocked, the step frequency Fs of the tuner 100. The tuning of the tuner 100 is retuned by adding or subtracting by. Of course, the demodulator frequency of the demodulator 200 at this time should be larger than the step frequency. In contrast, when the demodulation range is wider than 2 * Fs, the control of "No. 1" shown in FIG. 3 can be omitted and "No. 2" can be executed. It is desirable to decide how many n values should be set in consideration of the tuning time and the desired frequency range. Of course, the larger the value n, the longer the tuning time.

The MCU 400 tunes the tuner 100 when the channel lock check result of the demodulator 200 is unlocked and the detected power values from the power detector 300 are greater than or equal to a predetermined reference value. The tuning frequency of the tuner 100 is controlled by adding or subtracting the frequency by the step frequency Fs. On the contrary, when the channel lock check result of the demodulator 200 is unlocked and the detected power values from the power detector 300 are less than a predetermined reference value, the tuned frequency is tuned by the tuner 100. It is determined that there is no broadcast signal in the signal, and the center frequency control of the tuner 100 is stopped.

On the other hand, as shown in Figure 4, when the power value of the demodulator 200 is provided to the MCU 400 by the power detector 300 so as to distinguish the power (hatched portion) in the range of 2 * Fs, It should be noted that the MCU 400 may determine whether to adjust the tuning frequency of the tuner 100 by applying or decreasing the step frequency.

Therefore, according to the above configuration, when the center frequency of the channel and the center frequency of the signal tuned by the tuner are out of the allowable range or more, it is possible to detect this and fine tune the tuning frequency of the tuner again.

As described above, according to the present invention, even when the center frequency of the channel and the center frequency of the signal tuned by the tuner are out of the allowable range or more, the automatic tuning for the digital television which can control the tuning frequency of the tuner at the demodulation stage is described. The device can be realized.

Although the present invention has been described in detail by the above embodiments, the present invention is not limited thereto, and variations and improvements can be made without departing from the ordinary knowledge of those skilled in the art.

Claims (2)

A demodulator including an NTSC cancellation filter and an equalizer, processing the center frequency of the intermediate frequency signal from the tuner to check the channel lock, and if the result of the check is a lock, demodulate the intermediate frequency signal to output a data bitstream ; A power detector for detecting power of signals output from the NTSC cancellation filter and equalizer; And And a microcomputer for controlling the center frequency of the channel detected by the tuner based on the channel lock check result of the demodulator and the detected power values from the power detector. 2. The method of claim 1, wherein the microcomputer determines that the tuner tunes the tuner by a step frequency when the channel lock check result of the demodulator is unlocked and the detected power value from the power detector is greater than or equal to a predetermined reference value. By controlling the tuning frequency of the tuner, If the channel lock check result of the demodulator is unlocked and the detected power value from the power detector is less than a predetermined reference value, it is determined that there is no broadcast signal at the tuned frequency by the tuner, An automatic fine tuning device for digital television, characterized by no center frequency control.