JPH06164990A - Signal waveform equalizing method - Google Patents

Abstract

PURPOSE:To suppress the decline of equalization accuracy at minimum even for transmission distortion for which delay time is large and to perform an equalizing processing in a short period of time at the time of equalizing the waveform of MUSU signals by using an adaptive equalization type filter 5. CONSTITUTION:The maximum delay time T of the transmission distortion more than the prescribed level of VIT signals is detected 10 and depending on whether or not the maximum delay time is within a prescribed period tine To provided with the VIT signals in an approximate center, whether the transmission distortion of the maximum delay time T is equalizable or not is judged 11 by operating the entire tap stages of the adaptive equalization type filter 5 by a high-speed clock phi1. Corresponding to a judged result, whether the filter 5 performs an equalizing operation by using only the high-speed clock or the filter 5 performs the equalizing operation by selectively using the high-speed clock phi1 and a low-speed clock phi2 for the respective tap stages of the filter 5 is switched.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal waveform equalizing method used in a transmission system of MUSE signals obtained by band-compressing high-definition signals.

[0002]

2. Description of the Related Art CA for transmitting NTSC signals and MUSE signals through a transmission system such as a coaxial cable or an optical cable.
In a TV system, a so-called waveform equalizer is used to correct the waveform distortion (transmission distortion) of the signal in the above transmission system.

Among others, a waveform equalizer for MUSE signals is disclosed in, for example, Japanese Unexamined Patent Publication No. 64-82778 (H0).
4N 7/13) etc., transmission distortion is detected using the VIT signals inserted in the first and second lines in the vertical blanking period of the MUSE signal, and a waveform is detected according to the detected output. There is one that controls the tap coefficient of the equalization filter.

FIG. 6 shows a schematic configuration of such a conventional MUSE signal waveform equalizer, in which 1 is an input analog M.
Low-pass filter for cutting USE signal transmission bandwidth (8.1MHz) or more, 2 is MUSE from this filter
The A / D converter 3 for converting the signal into a digital signal is A
A sync detector for separating and detecting horizontal and vertical sync signals in the MUSE signal after D conversion, 4 is a timing generator for generating clock pulses and various timing pulses with each sync signal as a time reference, and 5 is for AD conversion Is an adaptive equalization type filter including a multi-stage transversal filter to which the MUSE signal of is input.

Further, 6 is an MU which has passed through the filter 5.
A VIT signal capturing section for separating and extracting the VIT signal from the SE signal, a transmission distortion detecting section for detecting transmission distortion such as ghost and waveform distortion of the extracted VIT signal, and 8 for the filter 5 based on the error signal. A tap coefficient calculator for calculating the tap coefficient of each stage, and a tap coefficient memory 9 for writing / reading the tap coefficient by the clock from the timing generator 4.

[0006]

In this waveform equalizer, as described above, the transmission distortion of the MUSE signal is suppressed by using the VIT signal shown in FIG. 3 inserted in the first and second lines of the vertical blanking period. It is detecting. That is, this VIT
The waveform distortion of the signal itself, the ghost of the VIT signal, etc. are detected, and the waveform equalization of the MUSE signal is performed according to the detection result.

By the way, the MUSE signal input to such a waveform equalizer may have very little ghost or waveform distortion, such as the MUSE signal reproduced from an optical disc, or the case of satellite broadcasting. Some are subject to large transmission and time distortions. In such a case, the delay time in the filter 5 in FIG. 6 is increased and the VIT
If the VIT signal capturing period in the signal capturing section 6 is lengthened and the tap coefficient of the filter is set in correspondence with the entire period, the VIT signal is present at a position greatly separated from the true VIT signal in time. Transmission distortion can be removed.

For this reason, conventionally, an equalization filter having a large number of tap stages is used, or the driving clock cycle of this filter is made long (that is, a low-speed clock is used). However, in this case, when the MUSE signal from the above-mentioned optical disk or the like is input, waveform equalization is performed for a longer time than necessary, and further, when a low-speed clock is used, etc. It was not a good idea because the accuracy of the conversion decreased.

Therefore, it is an object of the present invention to efficiently perform equalization operation, to prevent the equalization precision from being lowered more than necessary, and to complete the waveform equalization in a short time.

[0010]

According to the present invention, each of the adaptive equalization filters in which the transmission distortion of the reference signal in the input signal to be waveform-equalized is detected and the input signal is input according to the detected output. In a waveform equalization method for setting the tap coefficient of a stage, the maximum delay time of the transmission distortion above a predetermined level is detected, and the maximum delay time is determined depending on whether or not the maximum delay time is within a predetermined time including a reference signal at substantially the center. It is determined whether the transmission distortion of the maximum delay time can be equalized by operating all stages of the filter with a high-speed clock, and if it is determined that they can be equalized, each stage of the filter is operated with a high-speed clock. , The tap coefficient calculated for each cycle of the high-speed clock is set in each stage of the filter, and when it is determined that equalization is not possible, each stage in the center of the filter is operated by the high-speed clock, This high The tap coefficient calculated for each cycle of the clock is set in each stage of the central part, and each stage other than the central part is operated by a low-speed clock having K times the high-speed clock period (K is an integer). The tap coefficient calculated for each cycle of the low-speed clock is set in each stage other than the central portion.

[0011]

According to the present invention, when the transmission distortion of the maximum delay time can be equalized by the high-speed clock, the equalization operation is performed only by the high-speed clock, and the transmission distortion of the maximum delay time is the above-mentioned high-speed clock. If the equalization cannot be performed only by itself, the section near the reference signal performs the equalization operation with high accuracy by the high-speed clock, and the equalization operation by the low-speed clock in the other sections, depending on the transmission distortion of the input signal. Waveform equalization will be executed efficiently.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiment of FIG. 1 showing the case of waveform equalizing a MUSE signal according to the present invention will be described below.

In the waveform equalizer shown in FIG. 1, the same parts as those in FIG. 6 are designated by the same reference numerals and their explanations are omitted, but the following parts are added in comparison with FIG. That is, in FIG.
Reference numeral 10 denotes a maximum delay time detection unit that detects a time position of the transmission distortion at the farthest position among the transmission distortions detected by the transmission distortion detection unit 7 which is equal to or higher than a predetermined level, that is, a delay time T from the true VIT signal. It is determined whether or not the detected maximum delay time T is within a predetermined time To shown in FIGS. 4 and 5, and a determination / control for controlling the tap coefficient calculation unit 8 and a clock switching unit 12 described later according to the determination result. It is a control unit.

Since the predetermined time To is set to the delay time in this filter when all stages of the filter 5 are driven by the clock of 32.4 MHz, To = N / 32.
It is expressed in 4 microseconds.

Further, 12 is a high-speed clock φ1 of 32.4 MHz and 16.2 MHz output from the timing generator 4.
Is a clock switching unit for selectively applying the low-speed clock φ2 and the low-speed clock φ2 to each tap stage of the equalization filter 5 in accordance with the output of the determination / control unit 11. The switching unit 12 is configured in detail as shown in FIG. ing.

That is, in FIG. 2, the equalization filter 5
As is well known, it comprises N delay elements D, coefficient multipliers M and one adder A, respectively, and the clock switching unit 12 has the above-mentioned high-speed clock φ1 and low-speed clock φ2.
Is provided to each of the delay elements D, and N switching elements S for selectively supplying the delay elements D and a decoder section De for switching each switching element S in accordance with the output of the determination / control section. .

The embodiment of FIG. 1 is configured as described above, and its operation will be described below. Now, if the maximum delay time T of the transmission distortion detected by the maximum delay time detecting unit 10 is within the above-mentioned predetermined time To, the transmission distortion of the maximum delay time T can be obtained by using a high-speed clock at all tap stages of the filter 5. Even if it is operated, it will be possible to equalize, so in this case judgment /
The control unit 11 switches all the switching elements S (FIG. 2) in the clock switching unit 12 to the high speed clock φ1 side. Further, at this time, the determination / control unit 11 controls the tap coefficient calculation unit which operates by the high speed clock φ1 to store each tap coefficient calculated for each cycle of the high speed clock in the tap coefficient memory 9. Then, the stored tap coefficients are set in the tap stages (the multipliers M in FIG. 2) of the filter 5, respectively. FIG. 4 shows the operation in this case. The VIT signal fetching section 6 always performs sampling operation by the high speed clock φ1.

On the other hand, the maximum delay time T of the transmission distortion detected by the maximum delay time detector 10 is the above-mentioned predetermined time To.
If it is larger, the determination / control unit 11 performs the following operation. That is, at this time, the determination / control unit 11 first

[0019]

Of x and y satisfying the above, the maximum value of x
(Integer) and y value (integer) determined by it are calculated.

Next, when the value of x is determined in this way, the judging / controlling section 11 operates the clock switching section 12 and the tap coefficient calculating section 8 according to the value of x as follows. Control. That is, the decoder De in the clock switching unit 12
When the value of x is given from the determination / control unit 11, the central portion of the filter 5 among the N switching elements S (where the central tap is from the first stage to the nth stage is approximately n ± x / 2). Range)), only x switching elements S respectively corresponding to x tap stages are switched to the high speed clock φ1 side, and y = N−x switching elements S corresponding to the remaining tap stages at both ends are low speed. Switch to clock φ2 side.

On the other hand, when the above-mentioned value of x is given, the tap coefficient calculation unit 8 is fast in the sampling interval (ax interval in FIG. 5) corresponding to the x tap stages in the central part of the equalization filter 5. The calculation result for each cycle of the clock φ 1 is passed through the tap coefficient memory 9 to each of the x tap stages (that is,
It is set in each of the coefficient multipliers M) in FIG. In addition, in the sampling section (by section in FIG. 5) corresponding to y tap stages at both ends, the tap coefficient memory 9 stores the calculation result every two cycles of the high-speed clock φ1, that is, every one cycle of the low-speed clock φ2. To each of the y tap stages.

Therefore, as shown in FIG. 5, the equalizing filter 5 performs the equalizing operation in the cycle of the high speed clock φ1 in the ax section and the equalizing operation in the cycle of the low speed clock φ2 in the by section. The transmission distortion existing at the position exceeding the above-mentioned predetermined time To can also be waveform-equalized.

The calculation for tap coefficient calculation in the tap coefficient calculation unit 8 is performed by the LMS (Least Mean Square) method by multiplication of the error signal and the input signal.
Since this point is the same as the conventional one, detailed description will be omitted.

Each functional block of the VIT signal capturing section 6 to the judgment / control section 11 can be constructed by software of a personal computer, but may be realized by a hardware configuration by a dedicated circuit.

Although the embodiment for waveform equalization of the MUSE signal has been described above, the present invention is also applicable to waveform equalization of an NTSC television signal. In such a case, for example, a vertical synchronization signal of The leading edge or the like may be used as the reference signal.

[0027]

According to the waveform equalization method of the present invention, the equalization operation is performed by the low speed clock only during the minimum necessary period, and the equalization operation is performed by the high speed clock during other periods. Even for transmission distortion with a large delay time, the equalization accuracy and the equalization time can be minimized to perform the equalization processing.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram showing details of a main part thereof.

FIG. 3 is a signal waveform diagram of a VIT signal and a period before and after the VIT signal.

FIG. 4 is a diagram for explaining the operation of the present invention when the maximum delay time is small.

FIG. 5 is a diagram for explaining the operation of the present invention when the maximum delay time is large.

FIG. 6 is a block diagram showing a schematic configuration of a conventional waveform equalizer.

[Explanation of symbols]

 8 Tap coefficient calculation unit 10 Maximum delay time detection unit 11 Judgment / control unit 12 Clock switching unit De decoder

Claims (2)

[Claims] 1. A waveform for detecting a transmission distortion of a reference signal in an input signal to be waveform-equalized and setting a tap coefficient of each stage of an adaptive equalization filter to which the input signal is input according to the detected output. In the equalization method, the maximum delay time of the transmission distortion above a predetermined level is detected, and the transmission distortion of the maximum delay time is determined depending on whether or not the maximum delay time is within a predetermined time including a reference signal in the center. All stages of the filter are operated with a high-speed clock to determine whether equalization is possible. If it is determined that equalization is possible, each stage of the filter is operated with a high-speed clock, and each cycle of this high-speed clock is determined. The tap coefficient calculated in step S1 is set in each stage of the filter, and when it is determined that equalization is not possible, each stage in the center of the filter is operated with a high-speed clock, and at each cycle of this high-speed clock. Arithmetic The tap coefficient output is set in each stage of the central part, and each stage other than the central part is operated by a low speed clock having K times the high-speed clock period (K is an integer), and at each low-speed clock period. The signal waveform equalization method, wherein the tap coefficient calculated in step 1 is set in each stage other than the central portion. 2. The signal waveform equalizing method according to claim 1, wherein the input signal is a MUSE signal, and the reference signal is a VIT signal in the MUSE signal.