KR100282944B1 - Carrier wave a fine recovery apparatus and method - Google Patents

Abstract

end. TECHNICAL FIELD The invention described in the claims pertains to a receiver capable of receiving a television signal carrying a pilot signal.

I. The present invention has been made in an effort to provide a carrier fine recovery apparatus and method for recovering a carrier by tracking a frequency offset even if a frequency offset of a received television signal exceeds a carrier recovery range.

All. Summary of the Invention: A numerically controlled oscillator for generating a first local oscillation signal necessary for converting a carrier carrying a pilot signal to a baseband frequency, and a second local oscillation signal for applying a radio signal received through an antenna. A method for fine carrier recovery of a television signal receiving system having a tuner tuned to and converted into an intermediate frequency signal, the method comprising: a first process of detecting a first local oscillation signal generated from the numerically controlled oscillator; And a third step of calculating an offset between the frequency of the oscillation signal and a preset reference frequency, and a third step of adjusting the frequency of the second local oscillation signal to remove the frequency offset.

la. Important Uses of the Invention: Can be used in digital television receivers.

Description

Carrier fine recovery device and method thereof {CARRIER WAVE A FINE RECOVERY APPARATUS AND METHOD}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to tuning of a television signal receiving system, and more particularly, to an apparatus and method for recovering carrier fines for recovering a frequency offset of a digital television reception signal.

In the reception of digital television signals, there is always a frequency offset between the various frequency oscillators used in the transmission process and the frequency synthesizer of the receiving tuner. Ideally, the tolerances of the oscillators used during transmission and reception are within a few KHz, so the frequency offset of the received signal measured by the receiver is within tens of KHz. However, in a transmission and reception environment in which actual TV radio waves are transmitted, the frequency offset of a received signal may be hundreds of KHz due to deterioration of devices and components. Therefore, in the digital television signal receiving system, the frequency offset of the received signal must be tracked and corrected.

Frequency tracking is a technique that tracks and corrects a received signal if it has a frequency offset beyond the original received frequency due to various reasons on the transmission. Auto frequency tracking (AFT) methods employed in television receivers can be broadly classified according to television reception systems as follows.

First, a typical analog television receiver generates a voltage signal that is proportional to the difference between the visual carrier frequency value of the received signal and the frequency synthesizer frequency value of the receive tuner in the IF band. Detects how much frequency offset it has. The detected frequency offset value is transmitted to the channel tuning controller inside the receiver, and the channel tuning controller corrects the frequency offset by adjusting the frequency of the frequency synthesizer in a direction of decreasing the frequency offset value.

In the VSB (Vestigial Side Band) receiver, a digital television signal transmission method currently proposed in the United States, the received signal is demodulated to the baseband, and then AFC (Auto Frequency Control) LPF and APC LPF (Auto Phase Control Low) at the baseband. Pass filter) is used to calculate the frequency offset value. The frequency of the double conversion tuner 12 is changed according to the output value of the APC LPF to perform overall frequency tracking and carrier recovery. This is a frequency offset correction circuit proposed by Zenith, which is described in detail in 'Guide to the use of the ATSC Television Standard A / 54' issued in 1995 by the United States Advanced Television System Committee.

FIG. 1 shows a block diagram of a general digital television signal receiver employing a digital scheme to recover a carrier wave. Such a configuration is disclosed in detail in Korean Patent Application No. 95-20772 filed by the applicant of the present application. Since the digital television signal receiver shown in Fig. 1 performs carrier recovery after A / D conversion, the oscillation frequency of the second local oscillator 16 of the double conversion tuner 12 is fixed, and the ADC (Analog-to-Digital Converter) The frequency offset is corrected by a NCO (Numerically Controlled Oscillator) 38 located at the rear end of the NPC.

However, in the carrier recovery apparatus having the above-described configuration, frequency distortion may be included in a signal transmitted up to the NCO 38. If the width is large, the frequency recovery is already received by the SAW filter or the like even if the NCO 38 performs the frequency tracking. Since a loss of a signal may occur, carrier recovery may not be possible, and even if carrier recovery is performed, signal quality may deteriorate.

Accordingly, an object of the present invention is to provide a carrier fine recovery apparatus and method for recovering a carrier by tracking a frequency offset even if a frequency offset of a received television signal exceeds a carrier recovery range.

It is still another object of the present invention to provide a carrier fine repair apparatus and a method for compensating a frequency offset by adjusting a tuner frequency corresponding to a frequency component detection amount made for frequency tracking in a television signal receiving system.

It is still another object of the present invention to provide a carrier fine recovery apparatus and method for improving the reception performance of a digital television reception system.

The present invention for achieving the above object is a numerically controlled oscillator for generating a first local oscillation signal required for converting a carrier carrying a pilot signal to a baseband frequency, and a second local oscillation for applying a radio signal received through an antenna In a carrier fine recovery method of a television signal receiving system having a tuner tuned to a signal and converted into an intermediate frequency signal,

A first process of detecting a first local oscillation signal generated from the numerically controlled oscillator;

Calculating a offset between a frequency of the detected first local oscillation signal and a preset reference frequency;

And a third process of adjusting the frequency of the second local oscillation signal to remove the frequency offset.

1 is a partial block diagram of a general digital television signal receiver employing a digital scheme to recover carriers.

2 is a partial block diagram of a digital television signal receiver including a carrier fine recovery apparatus according to an embodiment of the present invention;

3 is a flowchart illustrating carrier fine recovery according to an embodiment of the present invention.

4 is a partial block diagram of a digital television signal receiver including a carrier fine repair apparatus according to another embodiment of the present invention.

Hereinafter, an operation according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that in the following description the same elements in the figures are denoted by the same reference signs wherever possible. In addition, a detailed description of well-known functions and configurations that may unnecessarily obscure the subject matter of the present invention will be omitted.

Figure 2 shows a block diagram of a part of a digital television signal receiver including a carrier fine recovery apparatus according to an embodiment of the present invention.

Referring to FIG. 2, the configuration and operation of a carrier fine repair apparatus according to an exemplary embodiment of the present invention will be described. The RF signal received through the antenna 10 is applied to the dual conversion tuner 12. The double conversion tuner 12 converts the received RF signal into a primary IF signal of 920 MHz by tuning to a local oscillation signal applied from the frequency synthesizer 14. In this case, the double conversion tuner 12 also performs gain control of the output signal in response to the auto gain control AGC of the receiver. The frequency synthesizer 14 generates a local oscillation signal that is varied in steps of a predetermined frequency unit (for example, 62.5 KHz) according to the frequency adjustment data output from the channel selection controller 90 and applies it to the double conversion tuner 12. do.

The IF signal output from the double conversion tuner 12 is then filtered by the SAW filter 18 into an IF signal of a predetermined bandwidth. The SAW filter 18 is a bandpass filter for blocking a signal of an adjacent channel, and has a characteristic of filtering an IF signal with a bandwidth of 6 MHz. The IF signal having the 6 MHz bandwidth passed through the SAW filter 18 is amplified by the IF amplifier 20 and then applied to the mixer 22. The amplification gain of the IF amplifier 20 is determined by the automatic gain control AGC provided by the receiver.

Meanwhile, the IF signal applied to the mixer 22 is mixed with the local oscillation signal generated by the third local oscillator 24 so that the frequency is down converted to a signal near the baseband. As the signal passes through the LPF 26, the second harmonic component (image frequency component) is removed and then converted into a digital signal by the ADC 28. The digitally converted signal is Hilbert filtered by a Hilbert Transform Filter (HFT) 32 in the carrier fine recovery device 60 to generate an imaginary component of the received signal. Through the delay unit 30 in order to match the delay caused by (32), it is generated as a real component. Real component ( ) And imaginary components ( The complex signal consisting of the < RTI ID = 0.0 > At this time, the NCO 38 generates and outputs an oscillation frequency corresponding to the frequency offset value output from the APC LPF 50. Meanwhile, the digital signal converted from the ADC 28 is a complex signal through a low pass filter (LPF) and a phase separator 40. Complex signal of the oscillation frequency of the NCO 38 in the mixer 42 Multiplied by and frequency converted to baseband.

The US-type GA-HDTV signal includes a pilot signal for assisting the receiver in recovering a carrier. The AFC LPF 44 includes a signal between the frequency of the pilot signal frequency-converted to the baseband and the frequency generated by the third local oscillator 24. Used as a filter to detect frequency differences. If there is almost no difference in frequency detected by the AFC LPF 44, the output of the AFC LPF 44 is a positive or negative value fixed by a limiter 46 at its rear end (e.g., + 1 or -1). However, when there is a difference in the frequency detected by the AFC LPF 44, the output value of the limiter 1 46 alternates with +1 and -1. If the output value of the limiter 1 46 alternates with +1 and -1, it means that there is a carrier frequency offset, and if the output value of the limiter 1 46 is fixed to +1 or -1, the carrier is frequency offset. This means no.

On the other hand, the signal output from the limiter 1 46 is multiplied by the imaginary component output from the mixer 42 in the multiplier 48 and applied to the APC LPF 50. Accordingly, the APC LPF 50 outputs a frequency offset value corresponding to the output of the multiplier 48. If the carrier has almost no frequency offset, i.e., there is no difference between the carrier frequency and the demodulation frequency, the signal output from the limiter 1 46 and applied to the multiplier 48 is generated with a fixed positive or negative value. . Therefore, since only the output of the mixer 42 acts on the multiplier 48, the carrier fine recovery apparatus 80 can be regarded as acting as one PLL.

The channel selection controller 90 inputs the frequency component generated by the NCO 38 to output frequency adjustment data for reducing the difference from the reference frequency (2.69 MHz). That is, because the frequency component generated by the NCO 38 for frequency tracking can be seen as the current frequency offset degree, the channel tuning controller 90 outputs the frequency adjustment data in a direction to reduce the difference from the reference frequency. Just do it. It is assumed that the relationship between the frequency adjustment data and the frequency component generated in the NCO 38 is already tabled and stored in the channel selection controller 90.

3 is a flowchart illustrating a carrier fine recovery performance according to an embodiment of the present invention. Hereinafter, a detailed description of the carrier fine recovery is performed with reference to FIGS. 2 and 3.

First, when the power of the receiver is applied, the channel selection controller 90 detects the local oscillation frequency component generated by the NCO 38 to recover the carrier in step 100, and proceeds to step 102. Check if there is a difference (offset) between 2.69 MHz). If there is no difference between the local oscillation frequency generated in the NCO 38 and the reference frequency, the local oscillation frequency of the NCO 38 is locked to the reference frequency. Therefore, the channel tuning controller 90 proceeds to step 106 to set the current. Set the preset frequency to the optimal tuning frequency.

However, if there is a difference between the local oscillation frequency of the NCO 38 and the reference frequency as a result of step 102, the channel tuning controller 90 proceeds to step 104 to reduce the difference between the local oscillation frequency and the reference frequency of the NCO 38. After outputting the frequency adjustment data, go back to step 100. As a result, a local oscillation signal is varied from the frequency synthesizer 14 in unit steps (62.5 KHz) according to the frequency adjustment data and applied to the double conversion tuner 12. Thereafter, the channel selection controller 90 detects the local oscillation frequency generated by the NCO 38 and outputs frequency adjustment data in a direction of decreasing the difference from the reference frequency, thereby finally local oscillating frequency of the NCO 38. Allows to lock at the frequency closest to the reference frequency. If there is no difference between the local oscillation frequency generated in the NCO 38 and the reference frequency in step 102, the present tuning frequency is set to an optimal frequency and the carrier fine recovery method according to the embodiment of the present invention is terminated.

The above-described carrier fine recovery method is an example in which the carrier recovery apparatus has a carrier recovery range of about -250 KHz to 250 KHz. If the frequency offset is out of the range, that is, the frequency offset is large, The carrier fine recovery apparatus shown in FIG. 2 cannot operate normally. A configuration for solving this problem is shown in FIG.

4 is a block diagram of a part of a digital television signal receiver including a carrier fine recovery apparatus according to still another embodiment of the present invention, except for the DC detector 95. FIG. Same as the receiver. For reference, the US GA-HDTV signal includes a pilot signal (DC component) to help the receiver recover the carrier. The DC detector 95 has a wide tuning of the 'high' level when a DC level of a predetermined size or more is detected. Tunning) Output complete signal. The wide tuning completion signal is defined as a signal generated when a frequency offset degree has a value within a carrier recovery range (-250 KHz to 250 KHz). Accordingly, the channel tuning controller 90 first controls the frequency synthesizer 14 so that the 'high' level wide tuning completion signal is input at the time of channel tuning, and after the wide tuning completion signal of the 'high' level is inputted in FIG. Frequency tracking may be completed by performing a carrier fine recovery method as shown in the flowchart. That is, when the frequency offset exceeds the carrier recovery range, the channel selection controller 90 checks whether a wide tuning completion signal having a 'high' level is input while sequentially changing the local oscillation signal output from the frequency synthesizer 14. When the wide tuning completion signal is input, the frequency offset degree is a value within the carrier recovery range, and thus the oscillation frequency of the frequency synthesizer 14 is removed in a direction to eliminate the difference between the local oscillation frequency generated by the NCO 38 and the reference frequency. Fine tune it.

Therefore, even if the frequency offset is out of the carrier recovery range, the received signal frequency offset in the television signal receiver can be stably corrected.

In the above description of the present invention, specific embodiments have been described, but various modifications can be made without departing from the scope of the present invention. Therefore, the scope of the present invention should not be defined by the described embodiments, but should be defined by the claims and their equivalents.

As described above, the present invention can remove the signal distortion at the previous stage of carrier recovery by making the oscillation frequency generated in the NCO the reference frequency, thereby improving the carrier recovery performance and the reception performance of the television signal receiver. There is an advantage. In addition, even if the frequency offset of the received signal is out of the carrier recovery range there is an advantage that the carrier can be recovered.

Claims (5)

A numerically controlled oscillator for generating a first local oscillation signal necessary for converting a carrier carrying a pilot signal to a baseband frequency, and converting a radio signal received through an antenna into an applied second local oscillation signal and converting it into an intermediate frequency signal. In the carrier fine recovery method of a television signal receiving system having a tuner, A first process of detecting a first local oscillation signal generated from the numerically controlled oscillator; Calculating a offset between a frequency of the detected first local oscillation signal and a preset reference frequency; And a third process of adjusting the frequency of the second local oscillation signal to remove the frequency offset. A numerically controlled oscillator for generating a first local oscillation signal necessary for converting a carrier carrying a pilot signal to a baseband frequency, and converting a radio signal received through an antenna into an applied second local oscillation signal and converting it into an intermediate frequency signal. In the carrier fine recovery method of a digital television signal receiver having a tuner, A first process of detecting a first local oscillation signal generated from the numerically controlled oscillator; Calculating a offset between a frequency of the detected first local oscillation signal and a preset reference frequency; A third step of wide tuning the frequency of the second local oscillation signal so that the calculated frequency offset has a value within the carrier recovery range if the calculated frequency offset exceeds the carrier recovery range; And a fourth step of removing the frequency offset by adjusting the second local oscillation signal by a unit step if the frequency offset calculated during the wide tuning adjustment has a value within the carrier recovery range. In the carrier fine recovery apparatus of a system for receiving a television signal carrying a pilot signal, A tuner for tuning and outputting the received television signal to an intermediate frequency signal according to the input frequency adjustment data; An SAW filter for filtering only a predetermined frequency band among the tuned intermediate frequency signals; Frequency converting means for frequency converting the output of the SAW filter into a frequency band capable of digital signal processing; Signal conversion means for converting the output of the frequency conversion means into a digital signal; The output of the signal converting means is separated into a complex signal, the separated signal is multiplied by a local oscillation signal that is variable according to a frequency offset value, and frequency converted to a baseband, and then the frequency offset based on the pilot signal from the baseband complex signal. A carrier recovery unit for detecting an over-phase offset, And a channel tuning controller configured to calculate an offset between the local oscillation signal and the reference frequency generated by the carrier recovery device, and output frequency adjustment data for removing the calculated offset. 4. The apparatus of claim 3, further comprising a DC detector for outputting a wide tuning completion signal in an active state when detecting a pilot signal having a DC level of a predetermined size or more. The frequency tuning channel of claim 4, wherein the channel selection controller performs a wide tuning adjustment mode until input of a wide tuning completion signal in an active state, and a frequency for adjusting a tuning frequency for each unit step after input of the wide tuning completion signal in an active state. Carrier fine recovery device characterized in that for outputting the adjustment data.