KR0183168B1 - Ntsc interference rejection method using notch filter - Google Patents

Abstract

1. The technical field to which the invention described in the claims belongs:

In the GA-VSB system, the present invention relates to a circuit for eliminating NTSC mixing that may occur in simultaneous broadcasting of NTSC and ATV.

2. The technical problem to be solved by the invention:

The present invention provides a circuit and a method capable of simply preventing deterioration of ATV broadcasting by NTSC signals without greatly increasing hardware complexity.

3. Summary of the solution of the invention:

The NTS mixing elimination circuit includes: means for detecting whether NTS is mixed and generating an NTS mixing detection signal in a television broadcast receiving system; means for inputting and filtering the received TV broadcasting signal; And a means for switching the notch-filtered signal when the mixing occurs according to the state of the NTS mixing detection signal, and when the mixing does not occur, the received television broadcast signal is output as it is.

4. Important uses of the invention:

It is used in general reception system related to high definition television.

Description

Removal method of NTS mixing using a odor filter

1 is an exemplary diagram of an NTSC signal.

2 is an exemplary error diagram of a modulated NTSC signal and an equalizer.

3 is a diagram illustrating a frequency spectrum of a modulated NTSC signal.

4 is a diagram illustrating a frequency spectrum according to characteristics of an NTSC incorporation removal filter.

5 is a block diagram of the NTSC filter and equalizer in the GA-VSB system.

6 is a block diagram of a conventional NTSC removal filter and equalizer using a comb filter in the GA-VSB system.

7 is a block diagram of an NTSC removal filter and an equalizer according to the present invention using a notch filter in a GA-VSB system.

8 is a block diagram of a notch filter using a band filter.

9 is a block diagram of an NTSC removal filter using an equalizer filter.

* Explanation of symbols for main parts of the drawings

72: delay unit 74: notch filter

76 switch 82, 84, 86 band filter

88: adder

The present invention provides a circuit and method for eliminating NTSC interference that may occur in simultaneous broadcasting of NTSC and ATV (Advance TV-HDTV; ATV) in a Grand Alliance (VSB) system. In particular, the present invention provides a circuit and a method capable of simply preventing deterioration of ATV broadcasting by NTSC signals without greatly increasing hardware complexity.

Recently, the GA-VSB method was decided as a transmission / reception method of ATV, the next generation TV method in the United States. This method also considers simultaneous broadcasting with the existing NTSC method. In this case, separate processing related to NTSC Rejection Filter (hereinafter referred to as NRF) in order to reduce the incorporation of potentially NTSC components into ATV. I put it. In other words, NRF effectively prevents ATV broadcast deterioration due to NTSC mixing in a co-channel situation in which both ATV and NTSC broadcast simultaneously, and the basic idea is to remove carrier parts of NTSC signal. Doing.

The reason why the NTSC removal filtering is required in the GA-VSB system and the problem of the operation will be described in detail.

Figures 1 to 4 show the results of the GA-VSB simulation, Figure 1 shows the NTSC signal, Figure 2 shows the modulated NTSC signal and the error of the equalizer, and Figure 3 shows the frequency spectrum of the modulated NTSC signal. Figure 4 shows the frequency spectrum according to the characteristics of the NTSC mixing filter.

First of all, the characteristics of NTSC signal and NTSC rejection filtering results show that in simultaneous broadcasting of NTSC and ATV, NTSC signal has VSB signal and constant carrier frequency offset (approximately 0.89MHz). In the case of the baseband, it is the same as modulating the frequency by the frequency offset with the VSB signal. That is, when the color bar signal of FIG. 1 is modulated in this manner, it is as shown in FIG. The NTSC signal has a frequency characteristic as shown in FIG. 3, and it can be seen that almost all energy is concentrated in the original DC component (modulated carrier). Therefore, the removal of these parts alone can achieve significant NTSC incorporation. That is, when the NTSC incorporation component of FIG. 3 passes through the NRF having the configuration as shown in FIG. 5, the energy value of about 430 in FIG. 3 is reduced to about 46 as shown in FIG. Since the component is removed, the influence of the MTSC signal on the ATV signal is reduced. However, no sub-modulation or modulation rate of the signal is taken into consideration, and FIGS. 3 and 4 show the results of the Fast Fourir Transform of 4096 samples.

NTSC rejection filtering proposed in the GA-VSB system is a method using a reference signal (field synchronization signal). That is, as shown in FIG. 5, the received reference signal is compared with the reference signal stored in the receiver, and the NRF is driven or not by using the accumulated power difference of the difference to determine whether the NRF is 12 symbol delays. Use a comb filter with The characteristics of such a comb filter are as shown in FIG. Such NTSC removal filtering is described in detail in the Grand Alliance HDTV System Specification, submitted to the ACATS Technical Subgroup, Feb., 1994.

Referring to FIG. 5, the NTSC removal filtering operation will be briefly described. Reference numeral 100 denotes an NTSC mixing detection unit for detecting the mixing of NTSC signal components, and 100 denotes an equalizer. The front end of the NTSC mixing detection unit 100 is connected to a frequency phase locked loop (FPLL) (not shown), and the equalizer 200 is connected to a phase tracker loop (PTL) not shown at the rear end. The NTSC mixing detection unit 100 includes a matched filter 12, a first NRF 13 and a second NRF 14, a first adder 15 and a second adder 19, a first square multiplier 16, a second square multiplier 17, a first accumulator 26 and a first filter. 2 It consists of an accumulator 27, an error detector 18, and a multiplexer 29.

Referring to the operation of the NTSC mixing detector 100, the signal B 'output from the matched filter 12 is input to the input terminal 0 of the multiplexer 29, and the signal B' is the signal A 'from which the NTSC signal component is removed by the first NRF 13. Is input to the input terminal 1 of the multiplexer 29. Meanwhile, the first path formed by the first adder 15, the first square multiplier 16, and the first accumulator 26 is a path without NTSC removal filtering, and the second adder is 19, the second square multiplier 17, and the second accumulator 27. The formed second path is a path in which the reference signal Fsync is NTSC removed filtered by the second NRF 14.

First, when the first path is examined, the difference between the input signal B 'and the reference signal Fsync is output through the first adder 15, squared through the first square multiplier 16, and accumulated through the first accumulator 26. Since the reference signal Fsync is a field synchronization signal, the output of the first adder 15 becomes an error value. If the input B 'signal is not very different from the reference signal Fsync, it means that there is little error, and if there is much difference, it means that there are many errors. Therefore, the output value B of the first accumulator 26 becomes an error power value.

Next, when the second path is examined, the input signal B 'is filtered through the second adder 19 to the NTSC rejection filtered signal A' by the first NRF 13 and the reference signal Fsync 'is applied to the NTSC rejection filtered reference signal Fsync'. The difference is output and squared through the second power multiplier 26 and accumulated through the second accumulator 28. Since the reference signal Fsync 'is an NTSC elimination filtered field synchronization signal, the output of the second adder 24 becomes an NTSC elimination filtered error value. At this time, if the input signal 'A' is not much different from the reference signal Fsync, it means that the NTSC elimination filtered error is small. If the difference is large, it means that the NTSC elimination filtered error is large. Therefore, the output value A of the second accumulator 28 becomes the NTSC removal filtered error power value.

When the error power value B. A is applied to the error detector 18, the error detector 18 compares the error power values B and A to detect the degree of the mixed NTSC signal component on the channel. The more NTSC signal components, the larger the error power value B is. This is because the A value is NTSC elimination filtered error power value.

The error detector 18 compares the error power values B and A of the difference and controls the multiplexer 29 to select a signal of a path corresponding to a low value. That is, if AB, the error detector 18 outputs 0 to the selected terminal S of the multiplexer 29, and the multiplexer 29 selects and outputs a signal B applied to the input terminal 0 in response thereto. When the signal B 'is selected, the equalizer 200 at the rear stage operates as an eight-level equalizer. If the signal is AB, the error detector 18 outputs 1 to the selected terminal S of the multiplexer 29, and the multiplexer 29 selects and outputs a signal A 'applied to the input terminal 1 in response thereto. The output of the error detector 29 is also applied to the equalizer 200.

When the multiplexer 29 selects signal A ', the equalizer 200, which is at a later stage, operates as a 15 level equalizer in response to the output of the error detector 18. When the multiplexer 29 selects the signal B ', the equalizer 200 at the rear stage operates as an eight-level equalizer in response to the output of the error detector 18.

When the equalizer 200 operates as a 15 level equalizer, there is an advantage of eliminating the mixed NTSC signal components, while the noise performance (3db) is reduced, and when the equalizer 200 operates as an 8 level equalizer, the 15 level It has advantages and disadvantages complementary to the equalizer. Reference numeral 11 denotes a symbol timing recovery and field synchronization signal detection unit, and serves to apply a field synchronization signal to the equalizer 200.

However, although NRF has the advantage of minimizing the effects of NTSC mixing, the noise performance (S / N ratio) of ATV system is reduced by about 3db. Therefore, NRF should not be operated when there is no NTSC mixing. . In order not to drive the NRF, it is necessary to check the presence and strength of NTSC incorporation to determine whether to drive the NRF. We also need to implement a processor with two 15-level paths using a comb filter. Equalizer and trellis decoding both have two paths.

In this way, the complexity of hardware increases when two paths are used, such as the decision level of the equalizer being changed from 8 to 15 when driving the NRF. In addition, when processing 15 levels, it is impossible to equalize using stop go algorithm due to decision error due to noise or relative increase of multipath compared to 8 levels of processing. There is a restriction to perform equalization. In addition, since the VSB signal has a reference signal of about 0.75% including segment synchronization, the data utilization efficiency decreases significantly, and when only the reference data is used, the VSB signal cannot cope with a multipath environment that changes with time.

Accordingly, it is an object of the present invention to provide a circuit and method for simply eliminating NTSC mixing without increasing hardware complexity. Another object of the present invention is to provide an NTSC incorporation elimination circuit and method capable of blind equalization.

The present invention for achieving the above object is to use blind equalization without increasing the hardware complexity by using only the eight-level path, and to remove the NTSC mixed carrier portion by using a notch filter instead of a comb filter. .

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

First, in adding reference numerals to the components of each drawing, it should be noted that the same reference numerals have the same reference numerals as much as possible even if displayed on different drawings. In addition, in the following description, many specific (specific) matters such as components of a specific circuit are shown, which are provided to help a more general understanding of the present invention, and the present invention may be practiced without these specific matters. It will be obvious to those who have a knowledge of career in the field. In the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

FIG. 7 shows the structure of the NTSC mixing cancellation circuit according to the present invention. A filter for removing each carrier (image carrier, color subcarrier, voice carrier) portion, which is a high energy component of NTSC mixing, as shown in the frequency characteristics shown in FIG. In the channel environment where NTSC mixing is large, the switch 76 selects the notch filter path to effectively eliminate NTSC mixing. The control signal CS indicates the presence or absence of NTSC mixing, and controls the switch 76 to select the output of the notch filter 74 when the NTSC mixing exceeds a predetermined level. Such control signal CS is described in the above-mentioned document, Grand Alliance HDTV System Specification, submitted to the ACATS Technical Subgroup, Feb., 1994 and the patent application No. 'Devices and Methods for Controlling the Drive Selection of NTC Rejection Filters'.

On the other hand, it is also possible to implement a method for the control signal CD to always select the notch filter output, to reduce the complexity of the hardware. No additional circuitry is required for this, and even if there is no NTSC mixing, this can be realized because the signal characteristics damaged by the notch filter can be compensated by the equalizer.

In addition, the configuration of the NRF by the notch filter is possible for both analog and digital. In case of an analog configuration, the switch 76 is an analog switch. The control signal CS selects one of the original path B ', that is, the path passing through the delay unit 72 or the path A' passing through the notch filter 74. Generate the output signal SO.

Delay matching with the notch filter 74 requires a delay of 1/2 of the filter length of the notch filter 74, but a zero delay may be used. Zero delay simply means to pass the signal. In the case of zero delay, no delay matching is performed with the notch filter. Such delay matching is necessary only when the NRF shown in FIG. 7 affects the operation of the equalizer.

Even if you do not use a sharp bandstop filter, which is difficult to construct, you can use a number of band-pass filters to subtract its output from the original signal as shown in FIG. It is also possible to implement a notch filter of characteristics. In the present embodiment, three first to third band filters 82, 84, and 86 are used.

FIG. 9 illustrates a method of implementing a notch filter using the filter of the equalizer 200 shown in FIG. 5 to reduce the complexity of hardware due to a separate notch filter configuration. This is because the equalizer 200 uses the characteristics of the filter groups L1 and L2, and the filter L1 of the filter groups L1 and L2 is used to implement the notch filter, so that a separate filter does not need to be added to the input stage. You will find the significance. That is, in the system reset, the filter coefficient calculator 45a is a coefficient of the L1 tap filter 41a in response to the input of the control signal CS according to the NTSC mixing detection. The initial coefficient-second machine number is only the reference point of the L1 tap filter. If the coefficients are all zeros, either apply a load or apply a notch filter coefficient, implemented by the appropriate filter design software, to cope with changes in the channel state during the system's operation-changes in NTSC incorporation. Since the filter coefficient calculation unit 45a needs to correct the coefficient value of the notch filter, the control signal CS detects a change from the input and multiplies or divides the coefficient of the notch filter by the calculated coefficient. By loading the reflected coefficient), it is possible to obtain the same effect of eliminating NTSC mixing as in the case of a notch filter without a separate notch filter. However, in most cases, since the channel environment will not change drastically, the presence of NTSC can be detected only in the initial state, and accordingly, the initial state of the equalizer may be set to the coefficient of the notch filter.

On the other hand, since the notch filter coefficient calculation block is generally composed of DSP, it is easy to adaptively determine the notch filter according to the degree of NTSC mixing.

On the other hand, it is not necessary to remove all carrier components of NTSC incorporation in the implementation of NRF using a notch filter. As can be seen from the frequency characteristic of FIG. 3, since most of the energy is concentrated in the image carrier portion, in order to simply configure the notch filter, it is possible to obtain a sufficient removal performance of NTSC mixing only by removing this portion.

As described above, the present invention does not cause the problem of increasing the NRF to 15 levels when using the comb filter using only 8-level paths, thereby simplifying hardware and applying blind equalization algorithms. There is an advantage.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications may be made without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined not only by the scope of the following claims, but also by the equivalents of the claims.

Claims (10)

A television broadcast receiving system, comprising: means for detecting whether or not an NTS is mixed and generating an NTS mixing detection signal, means for inputting and filtering the received TV broadcasting signal, and a state of the NTS mixing detection signal; And a means for switching to output the notch-filtered signal when the mixing occurs, and to output the received television broadcast signal as it is when the mixing does not occur. 2. The NC seed mixing elimination circuit according to claim 1, further comprising means for delaying the notch filter length by 1/2 for delay matching with the notch filtering means. The method of claim 2, wherein the switching means selects the notch filtered signal when the mixing occurs, and selects and outputs the delayed signal when the mixing does not occur according to the state of the NC mixing detection signal. NTS mixing elimination circuit characterized in. The filter according to any one of claims 1 to 3, wherein the notch filter comprises: first to third band filters for inputting the received television broadcast signals and filtering the first, second, and third bands; And a means for subtracting the output of the first to third band pass filters from the received television broadcast signal. A television broadcast receiving system having an equalizer, comprising: means for notably filtering received television field synchronization signals, and obtaining and filtering the difference between an average power level of the received television broadcast signal and a field synchronization signal and notch filtering the television broadcast. The difference between the average power level of the signal and the field-filtered field-synchronized signal is obtained, and the two differences are compared for a predetermined period to detect the degree of NTS mixing, and the selection having the first or second state as the number is less. Means for generating a control signal, selecting the notch filtered signal in response to the selection control signal having the second state, and selecting the received television broadcast signal in response to the selection control signal having the first state; An NTS mixing elimination circuit, characterized in that configured to output to the equalizer. 6. The anti-CNC mixing elimination circuit according to claim 5, further comprising means for delaying a half of a notch filter length for delay matching with the notch filtering means. 7. The method of claim 6, wherein the notch filtered signal is selected in response to the selection control signal having the second state, and the delayed television broadcast signal is selected and output to the equalizer in response to the selection control signal having the first state. An NTS mixing elimination circuit further comprising a means for. 8. The filter according to any one of claims 5 to 7, wherein the notch filtering means comprises: first to third band filters for inputting the received television broadcast signals, respectively, and filtering in the first, second and third bands; And means for subtracting the output of the first to third band pass filters from the received television broadcast signal. A television broadcast receiving system comprising means for detecting whether an NTS is mixed from a received TV broadcast signal and generating an NTS mixing detection signal, wherein the initial state filter coefficient or the notch filter coefficient is calculated according to the frame synchronization signal. Means for outputting an initial state filter coefficient if there is no mixing, and outputting a notch filter coefficient if there is mixing, and filtering the received television broadcast signal according to the output initial state filter coefficient. And a TS filter, comprising: a predetermined tap filter. A television broadcast receiving system having an equalizer, comprising: means for notably filtering received television broadcast signals and field synchronization signals, and obtaining and filtering the difference between the average power levels of the received television broadcast signals and field synchronization signals. Means for obtaining a difference between the average power level of the television broadcast signal and the field-filtered field-synchronized signal, comparing the two differences for a predetermined period of time to detect NTS mixing, and generating a predetermined control signal when the mixing is detected; And means for transmitting the notch filtered signal to the equalizer in response to the generation of the control signal.