KR100746588B1 - A carrier recovering apparatus for digital tv receiver - Google Patents

Abstract

 The present invention provides a carrier recovery apparatus for a digital TV receiver that can increase the carrier recovery range and reduce the recovery time by correcting the frequency offset using the amount of power at both ends of the VSB spectrum, estimating the pilot size, and multiplying the gain value according to the pilot size. to provide.

The present invention further comprises a bandpass filter for measuring the amount of power of the left and right ends of the VSB spectrum in the carrier recovery apparatus of the existing digital TV receiver, and measures the amount of power passing through these bandpass filters to obtain an approximate frequency offset. The residual offset is then restored to the existing carrier recovery apparatus, and the residual size is obtained by estimating the size of the pilot by the amount of power passing through the pilot extraction filter of the conventional carrier recovery apparatus and gaining the gain according to the pilot size at the error detector output. This allows for faster offset recovery.

Digital TV, VSB, Pilot Signal, Carrier Recovery Equipment

Description

Carrier recovery device of digital TV receiver {A CARRIER RECOVERING APPARATUS FOR DIGITAL TV RECEIVER}

1 is a block diagram of a general digital TV receiver.

2 is a block diagram of a carrier recovery unit of FIG.

3 is a block diagram of a carrier recovery apparatus of a digital TV receiver according to the present invention;

4 is an installation state diagram of the band pass filter of FIG.

5 and 6 are explanatory diagrams of a frequency offset correction operation of the present invention.

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

10: tuner 20: analog processing unit

30: A / D converter 40: carrier recovery unit

50: symbol timing recovery unit 60: digital processing unit

70: frequency correction unit 71,74: power accumulation and average

72,73: bandpass filter 75: noise power canceller

76,78: gain unit 77: error measuring instrument

The present invention relates to a digital TV receiver, and more particularly, to a carrier recovery apparatus of a digital TV receiver for receiving a transmission signal of a digital TV and recovering a carrier wave from the received signal.

Digital TVs have a much higher screen resolution (e.g., 1080x1920) compared to analog TVs, wider landscape (determined 16: 9 to accommodate the maximum aspect ratio of the movie), and CD-level sound with multiple channels (maximum 5.1 channels).

In the U.S., the transmission format of digital TV adopts the Vestigial Side Band (VSB) method proposed by Zenith in the U.S., and the compression format is MPEG for video compression and Dolby AC for audio compression. -3 is adopted, and the display format is specified to be compatible with existing display methods.

In this case, the VSB modulation is a method of modulating only the remaining part when one sideband signal of the two sidebands generated up and down about the carrier is greatly attenuated when the signal is amplitude modulated.

In other words, the DSB (Double Side Band), which uses both upper and lower sidebands, has a low band efficiency, and a single side band (SSB) using only one side band has emerged.

Currently, Korea's digital TV broadcasting adopts the VSB method by adopting the American standard.

Due to the digital characteristics, when a signal distorted by a transmission channel is restored in a receiver, a clear screen with no noise can be seen, but if it is not restored, it cannot be seen at all. Therefore, there is a need for a receiver capable of recovering a signal in any poor channel environment.

1 is a block diagram of a general digital TV receiver.

VSB modulated RF signal from the transmitter is received through the antenna (ANT) of the receiver and the tuner 10 selects only the frequency of a specific channel desired by the user, and then the first intermediate frequency (IF) band Convert it and print it out.

The analog processor 20 controls passband filtering and gain on the first IF signal to convert the second IF signal, converts the analog signal into a digital signal by the A / D converter 30, and then recovers the carrier. Output to (40).

The carrier recovery unit 40 accurately recovers the position of the pilot frequency, converts it into a baseband signal, and outputs the signal to the symbol timing recovery unit 50 and the digital processing unit 60 including an equalizer, a phase tracker, and error correction. . Therefore, if carrier recovery is not properly performed in the carrier recovery unit 40, data restoration is not performed.

In general, carrier recovery uses a frequency phase locked loop (FPLL) algorithm as shown in FIG. The input signal of the phase separator 41 of the carrier recovery unit 40 may be represented by Equation 1 below.

Equation 1

는 변조전의 데이터 신호이고,

는

의 직교신호 성분이다.

는 파일럿(Pilot) 신호이다.

는 위상 분리기(41)에서 실수성분(

)와 허수성분(

)로 분리된다.

Is the data signal before modulation,

Is

Is an orthogonal signal component of.

Is a pilot signal.

Is the real component in the phase separator 41

) And imaginary components (

Separated by).

Equation 2

는 파일럿 주파수 주위의 성분을 나타낸다.The separated real part and the imaginary part pass through the pilot extraction filter 42 to remove data components in other frequency domains, leaving only components around the pilot frequency.

Denotes the component around the pilot frequency.

Equation 3

I "(t) = [{I (t) + p}] 'cos (w ₂ t + θ)-[Q (t)]' sin (w ₂ t + θ)

Q "(t) =-[{I (t) + p}] 'sin (w ₂ t + θ)-[Q (t)]' cos (w ₂ t + θ)

Components around the pilot frequency passing through the pilot extraction filter 42 are converted by the complex multiplier 43 into a baseband signal.

Equation 4

은 주파수 오프셋 량을 나타낸다. 오차 검출부(44)에서 주파수와 위상의 오프셋 량을 검출해 내고, 오차 검출부(44)의 일시적인 오류를 방지하기 위해 저역통과필터(45)를 통과한다. 저역통과필터(45)의 출력은 수치제어 발진기인 NCO(Numerically Controlled Oscillator)(46)로 입력되어 오차를 수정함으로써 반송파 복구부는

와

를 0으로 만든다.

Denotes the amount of frequency offset. The error detector 44 detects the offset amount of the frequency and phase, and passes through the low pass filter 45 to prevent the temporary error of the error detector 44. The output of the low pass filter 45 is input to a numerically controlled oscillator (NCO) 46, which is a numerically controlled oscillator, and corrects an error so that the carrier recovery unit

Wow

Makes 0

와

는 매우 작기 때문에 오차 검출부(44)의 동작은 파일럿 신호(

)에만 의존한다. 따라서 전송채널에 의해 파일럿 신호(

)의 크기가 0에 가까워지면, 오차 검출부(44)의 입력이 0에 가까워지기 때문에 반송파 복구 범위가 줄어들고 복구하는 시간이 늘어나게 되거나 반송파 복구가 불가능하게 된다.

Wow

Since the operation of the error detector 44 is very small, the pilot signal (

Depends only on Therefore, the pilot signal (

When the magnitude of N is close to zero, since the input of the error detector 44 is close to zero, the carrier recovery range is reduced and the recovery time is increased or carrier recovery is impossible.

That is, the conventional carrier recovery apparatus recovers the carrier using only the pilot signal added before the modulation by the transmitter, so that the carrier recovery range is reduced and the recovery time is long or the carrier recovery is impossible as the pilot signal is distorted by the transmission channel. there was.

The present invention is to solve this problem, an object of the present invention is to increase the carrier recovery range and recovery time by multiplying the gain value according to the pilot size by correcting the frequency offset using the amount of power at both ends of the VSB spectrum The present invention provides a carrier recovery apparatus for a digital TV receiver.

The carrier recovery apparatus of the digital TV receiver for achieving the object of the present invention comprises: a tuner for performing channel tuning on the broadcast signal received from the antenna, and then converting it into a first intermediate frequency signal; An analog processor configured to control passband filtering and gain on the first intermediate frequency signal output from the tuner and convert the gain to a second intermediate frequency signal; An A / D converter converting the output of the analog processor into a digital signal; A carrier recovery unit including a phase separator, a pilot extraction filter, a complex multiplier, an error detector, and a low pass filter to recover a pilot signal from an output of the A / D converter and convert the pilot signal into a baseband signal; And a digital processing unit, the receiving apparatus of a digital TV receiving and demodulating data transmitted by a residual sideband modulation method, the frequency offset being corrected by using the amount of power at the left and right ends of the VSB spectrum from the output of the analog processing unit. In addition, a frequency correction unit for estimating the pilot size from the output of the pilot extraction filter of the carrier recovery unit and multiplying the corresponding gain value according to the pilot size to reduce the influence of the pilot distortion.

The frequency corrector comprises: a first power accumulator and averager for measuring an amount of power passing through a pilot extraction filter of the carrier recovery unit and estimating a pilot size therefrom; First and second band pass filters connected to the analog processing unit and installed at both ends of left and right ends of a VSB spectrum; A second power accumulator and averager for obtaining an accumulated average power of output signals of each of the first and second band pass filters; A noise power remover for removing noise components from the outputs of the second power accumulator and averager; The power according to the pilot distortion according to the pilot magnitude estimated by the first power accumulator and the averager for the signal passed through the first band pass filter located on the left side of the VSB spectrum among the signals from which the noise is removed by the noise power remover. A first gain unit multiplying the gain to reduce the error; And an error measurer for estimating an offset amount from the output of the noise power remover and the first gain unit to change a buffer value of the low pass filter of the carrier recovery unit to correct a frequency offset.

The frequency corrector may reduce the carrier recovery time by multiplying the gain of the error detector by the output of the carrier recovery unit as the pilot size decreases according to the pilot size estimated by the first power accumulator and the averager. It further comprises two gain parts.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the following examples are merely to illustrate the present invention is not limited to the contents of the present invention.

3 is a block diagram of a carrier recovery apparatus of a digital TV receiver according to the present invention.

As shown, the present invention is a carrier recovery device of the digital TV receiver as shown in Figs. 1 and 2, by using the amount of power at both ends of the VSB spectrum to first correct the frequency offset, and also to estimate the pilot size to the pilot size Accordingly, the frequency correction unit 70 is further configured to multiply the gain to reduce the influence of the pilot distortion.

The frequency corrector 70 is sequentially connected to the power accumulator and averager 71 and the analog processor 20 connected to the pilot extraction filter 42 of the carrier recovery unit 40 of the digital TV receiver of FIG. 1. Band pass filter 72, 73, power accumulator and averager 74, noise power remover 75, gain unit 76 and error measuring unit 77 and error recovery unit of carrier recovery unit 40 ( 44, and a gain section 78 connected between the low pass filter 45.

The power accumulator and averager 71 measures the amount of power passing through the pilot extraction filter 42 of the carrier recovery unit 40 and estimates the pilot size therefrom.

The bandpass filters 72 and 73 are installed at both ends of the VSB spectrum as shown in FIG. 4 so as to recover the frequency offset by using the amounts of power at the left and right ends of the VSB spectrum. The average power of each signal passing through the band pass filters 72 and 73 is obtained, and the noise power remover 75 is configured to remove power accumulation and noise in the output of the averager 74.

In addition, the gain unit 76 connected to the noise power remover 75 transmits the power to the signal passing through the band pass filter 72 located on the left side of the VSB spectrum among the band pass filters 72 and 73. The gain is multiplied according to the pilot size estimated by the accumulator and averager 71 so as to reduce the power error due to the pilot distortion, and the error measurer 77 includes the noise power remover 75 and the gain unit 76. By estimating an approximate amount of offset from the output of P, the buffer value of the low pass filter 45 of the carrier recovery unit 40 as shown in FIG. 2 is changed to primarily correct the frequency offset.

The gain unit 78 multiplies the output of the error detection unit 44 of the carrier recovery unit 40 by the corresponding gain as the pilot size decreases according to the power accumulation and the pilot size estimated by the averager 71. It is configured to give.

The present invention configured as described above further comprises bandpass filters 72 and 73 for measuring the amount of power at the left and right ends of the VSB spectrum in the carrier recovery apparatus of the existing digital TV receiver, and these bandpass filters 72 Calibrating the approximate frequency offset by measuring the amount of power passing through (73), and restoring the residual offset to the existing carrier recovery device, and also passing the pilot extraction filter 42 of the existing carrier recovery device. By estimating the size of the pilot, the gain of the error detector 44 outputs the gain according to the pilot size so that the residual offset can be recovered more quickly.

That is, as the band pass filters 72 and 73 are installed at both the left and right sides of the VSB spectrum, the larger the negative frequency offset, the greater the amount of power passing through the band pass filter 72 provided on the left side of the VSB spectrum. As the positive frequency offset increases, the amount of power passing through the bandpass filter 72 located on the right side of the VSB spectrum increases.

Each signal passing through the bandpass filters 72 and 73 is cumulative average power for each signal in the power accumulator and averager 74, and noise is removed through the noise power remover 75. do.

Thereafter, the signal passing through the bandpass filter 72 located on the left side of the VSB spectrum among the outputs of the noise power remover 75 is multiplied by the gain according to the pilot size through the gain unit 76, thereby powering the pilot distortion. Reduce the error

Thereafter, the error measurer 77 estimates an approximate frequency offset amount from the outputs of the gain unit 76 and the noise power remover 75 to obtain a buffer value of the low pass filter 45 of the carrier recovery unit 40. Change the frequency offset first.

The frequency offset is briefly expressed as follows.

: 주파수 오프셋,

: 주파수 오프셋에 따른 필터를 통과한 전력량,

: 필터 천이영역의 기울기,

: 신호의 전력,

: 기본적으로 필터에 있는 전력(도4의 VSB스펙트럼 가장자리+AWGN성분)

Frequency offset,

Is the amount of power passing through the filter according to the frequency offset,

: Slope of the filter transition region,

Is the power of the signal,

: Basically the power in the filter (VSB spectrum edge + AWGN component of Figure 4)

In addition, the low pass filter 45 is a conventional APC low pass filter means that the buffer value of the APC low pass filter 45 is changed.

The residual frequency offset after the first frequency offset correction is corrected by the carrier recovery unit 40 as shown in FIG. 2.

This process extends the carrier recovery range and speeds up by putting a range outside the operation range of the existing carrier recovery apparatus or a recovery speed into a range with a high recovery speed at once.

In Figure 5, the horizontal axis is the frequency offset, the vertical axis is the average of the output value of the low pass filter 45, the larger the frequency offset in the positive direction, the larger the positive voltage value of the vertical axis, the smaller the frequency offset in the negative direction. When the voltage value on the vertical axis has a small value in the negative direction and the frequency offset is 0, a curve having 0 [v] is ideal. However, the characteristic curve of the existing FPLL is shown as shown in Figs. 5 and 6, and Fig. 5 conceptually illustrates that the voltage value of the vertical axis converges to zero when the frequency offset is large according to the present invention. have.

Meanwhile, the amount of power passing through the bandpass filter 72 located at the left end of the VSB spectrum depends on the pilot size. Therefore, the power accumulation and averager 71 estimates the size of the pilot by measuring the amount of power passing through the pilot extraction filter 42, and multiplies the gain in the gain unit 76 as the pilot size decreases, thereby causing pilot distortion. It is possible to reduce the effect of the.

In addition, as the pilot size is reduced, the carrier recovery unit 40 also multiplies the output of the error detector 44 by the gain unit 78 and the gain according to the pilot size estimated by the power accumulator and the averager 71. By doing so, carrier recovery time can be reduced.

In FIG. 6, the voltage value of the vertical axis depends on the size of the received pilot. The present invention conceptually measures frequency of the received pilot and compensates the voltage value of the vertical axis, thereby making it possible to perform frequency correction more quickly. Explaining.

This process reduces the time taken for the second frequency correction by the existing carrier recovery apparatus after the first frequency correction.

As described above, although described with reference to a preferred embodiment of the present invention, those skilled in the art various modifications of the present invention without departing from the spirit and scope of the invention described in the claims below Or it may be modified.

As described above, according to the carrier recovery apparatus of the digital TV receiver according to the present invention, the conventional carrier recovery apparatus after recovering the approximate frequency offset (primary frequency offset correction) using the amount of power at both ends of the VSB spectrum By recovering the carrier (secondary frequency offset correction), the carrier recovery range is widened and the recovery time is also shortened.

In addition, by estimating the size of the pilot using the amount of power passed through the pilot extraction filter and multiplying the gain as the size of the pilot is reduced by the error detector output of the carrier recovery device, the recovery time can be reduced even during the correction of the second frequency offset. It becomes possible.

Claims (3)

A tuner which performs channel tuning on the broadcast signal received from the antenna and converts the first signal into a first intermediate frequency signal; An analog processor configured to control passband filtering and gain on the first intermediate frequency signal output from the tuner and convert the gain to a second intermediate frequency signal; An A / D converter converting the output of the analog processor into a digital signal; A carrier recovery unit including a phase separator, a pilot extraction filter, a complex multiplier, an error detector, and a low pass filter to recover a pilot signal from an output of the A / D converter and convert the pilot signal into a baseband signal; And a digital processing unit, the receiving apparatus of a digital TV for receiving and demodulating data transmitted by a residual sideband modulation method. A first power accumulator and averager for measuring an amount of power passing through a pilot extraction filter of the carrier recovery unit and estimating a pilot size therefrom; First and second band pass filters connected to the analog processing unit and installed at both ends of left and right ends of a VSB spectrum; A second power accumulator and averager for obtaining an accumulated average power of output signals of each of the first and second band pass filters; A noise power remover for removing noise components from the outputs of the second power accumulator and averager; The power according to the pilot distortion according to the pilot magnitude estimated by the first power accumulator and the averager for the signal passed through the first bandpass filter located on the left side of the VSB spectrum among the signals from which the noise is removed by the noise power remover. A first gain unit multiplying the gain to reduce the error; And An error measurer for estimating an offset amount from an output of the noise power remover and the first gain unit and changing a buffer value of the low pass filter of the carrier recovery unit to correct a frequency offset; Carrier recovery apparatus for a digital TV receiver comprising a frequency correction unit comprising a. delete The method of claim 1, wherein the frequency correction unit Further comprising a second gain unit to reduce the carrier recovery time by multiplying the corresponding gain by the output of the error detection unit of the carrier recovery unit according to the pilot size is reduced according to the pilot size estimated by the first power accumulation and the averager A carrier recovery apparatus for a digital TV receiver, characterized in that.

Images