JPH0549008A - Dropout correction device - Google Patents

Abstract

PURPOSE:To send information to an output without increasing a processing bit number of a reproduction signal processing circuit such as time axis correction by adding a signal at the outside' of pass band of an LPF when a dropout takes place. CONSTITUTION:Digital data for a period corresponding to a period of dropout in output signal of an A/D converter 3 are replaced into a signal at the outside of pass band of an LPF 2 by a digital data addition circuit 4. Then the signal for the dropout period is interpolated by a signal of a preceding field/frame or a preceding line with a dropout correction circuit 6 in response to an output of a digital data detection circuit 7. That is, after the signal with data added changing from a low level to a high level is processed by a reproduction signal processing circuit 5 for each sample for the dropout period and the result is inputted to the digital data detection circuit 7. Thus, information is sent without increasing the scale of the time axis correction circuit and without decreasing a dynamic range of the signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dropout correction device for correcting a signal dropout (a missing portion or an inaccurate portion of a reproduced video signal) in a recording / reproducing apparatus such as a video tape recorder or a video disc.

[0002]

2. Description of the Related Art In a video tape recorder or the like for recording / reproducing a video signal, a time axis correction circuit for reading a memory with a clock having no time axis fluctuation is used in order to remove the time axis fluctuation of the reproduction signal. ing. Therefore, the timings on the writing side and the reading side of the time-axis correction circuit do not correspond one-to-one, and the timing obtained on the writing side of the time-axis correction circuit can be transferred to the reading side by some method. Must be transmitted. There is also an idea that the write-out side of the time axis correction circuit corrects the dropout, but the interpolation becomes complicated because the number of data in one horizontal scanning period changes according to the speed change of the tape during special reproduction. Also, in the case of multi-channel recording, interpolation is difficult because the interpolated signal is transmitted on other channels with different time axis fluctuations. For this reason, dropout correction is generally performed on the read side of the time axis correction circuit.

FIG. 8 is a block diagram showing a time axis correction circuit. The clock and the reference signal on the writing side are synchronized with the input data, and the clock and the reference signal on the reading side have no time axis fluctuation. It is a signal. Therefore, when a signal as shown in (a) of FIG. 9 is input to the time axis correction circuit, its output signal becomes a signal that is temporally shifted as shown in c of (FIG. 9), and the shift amount is Is constantly fluctuating.

That is, even if a signal indicating dropout as shown in (b) of FIG. 9 (the period of Low is the period of dropout) is obtained at the input side of the time axis correction circuit, it remains as it is. The timing cannot be used on the output side of the time axis correction circuit. Therefore, the time axis correction circuit is configured by newly adding 1 bit to the number of effective bits used for signal processing. That is, as shown in (FIG. 8), the time axis correction circuit is configured by 9 bits, 8 bits for video and 1 bit for dropout.

In the case of such a configuration, the scale of the memory becomes large due to the dropout information transmission,
There is a problem that the memory cost increases.

A method of transmitting dropout information in the time axis correction circuit without newly adding 1 bit is known from Japanese Patent Laid-Open No. 59-198512.
As shown in (a) of FIG. 10, the number of bits is set by setting the data in the period corresponding to the dropout to a value outside the effective data area allocated for signal processing within the 8-bit dynamic range. Transmitting dropout information without increasing.

In the case of such a configuration, there is a problem that the dynamic range when the video signal is digitized cannot be effectively utilized because a predetermined level is assigned to the dropout information transmission.

[0008]

These problems are related to all recording / reproducing devices that perform time axis correction, and the number of bits in the memory is used to transmit dropout information to the read side of the time axis correction circuit. Had to be increased, or the dynamic range of the signal being processed had to be narrowed. Therefore, there is a problem that the scale of the time axis correction circuit increases or the dynamic range decreases.

The present invention solves the above-mentioned drawbacks and transmits dropout information into the time axis correction circuit without increasing the circuit scale of the time axis correction circuit and without reducing the signal dynamic range. It is an object of the present invention to provide a dropout correction device that can be operated.

[0010]

In order to solve the above-mentioned problems, a dropout correction device of the present invention provides an LPF having a predetermined pass band and an output signal of the LPF to the LPF.
An AD converter for converting into digital data at a frequency more than twice the pass band of F, and a digital for replacing the digital data in the period corresponding to the dropout with respect to the output signal of the AD converter with a signal outside the pass band of the LPF. A data addition circuit, a reproduction signal processing circuit for performing signal processing for reproduction on an output signal of the digital data addition circuit, and detecting data added by the digital data addition circuit from the signal after the reproduction signal processing. It comprises a digital data detection circuit and a dropout correction circuit which receives the output signal of the reproduction signal processing circuit as an input and performs a dropout correction operation from a signal indicating the dropout detected by the digital data detection circuit. ..

[0011]

In the present invention, by adopting the above configuration, L
A signal outside the pass band of the PF will be inserted only during the dropout period. Such signals are easy to create. For example, a signal in which the minimum value and the maximum value of the dynamic range are repeated for each sample data corresponds to this. By using such a signal, it is possible to transmit the dropout information into the time-axis correction circuit without increasing the circuit scale of the time-axis correction circuit and without reducing the dimic range of the signal. ..

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the dropout correction device according to the present invention will be described below with reference to the drawings. (Fig. 1)
FIG. 3 is a block diagram showing an example of a dropout correction device of the present invention. FIG. 2 is a block diagram showing an example of the digital data detection circuit of the dropout correction device of FIG. FIG. 3 is a waveform diagram showing the signal waveform of each part.

In FIG. 1, 1 is an input terminal, 2 is an LPF having a predetermined pass band, 3 is an AD converter for converting an input video signal into digital data at a frequency twice or more the pass band of the LPF 2. Is a digital data addition circuit that replaces the digital data in the period (supplied from the terminal 9) corresponding to the dropout with respect to the output signal of the AD converter 3 with a signal outside the pass band of the LPF 2, and 5 is for reproduction. A reproduction signal processing circuit for performing signal processing, for example, de-emphasis or time axis correction, 7 is digital data for detecting a signal outside the pass band of the LPF added by the digital data adding circuit 4 from the output signal of the reproduction signal processing circuit 5. The detection circuit 6 outputs the signal of the dropout period according to the output of the digital data detection circuit 7 to the previous line or the previous line. Dropout compensation circuit for interpolating a signal Irudo / frame, 8 denotes an output terminal.

The video signal input to the input terminal 1 is an LP signal.
The band is limited in F2, and then input to the AD converter 3. A signal converted into digital data by the AD converter 3 is shown in a of FIG. here,
Since the input video signal is band-limited by the LPF 2, there is no wide-band signal that rises from the Low level to the High level with one sample as shown in (FIG. 7).

In (a) of FIG. 3, white circles are accurate data, black circles are data in which dropout occurs, and t1 to t2 are dropouts as shown in (b) of FIG. It has been detected. The signal a in FIG. 3 is input to the digital data adding circuit 4, and as shown in c in FIG. 3, the data in the periods t1 to t2 changes from the low level to the high level in the effective data area every sample. Converted to a changing signal. In this way, during the dropout period, from the Low level to H for each sample.
The signal added with the data that changes to the high level is processed by the reproduction signal processing circuit 5 and then input to the digital data detection circuit 7. A configuration example of the digital data detection circuit 7 is shown in FIG.

In FIG. 2, 10 is an input terminal and 11 is an input terminal.
Is a delay circuit that delays data by the time of one sample,
12 is an adder that takes the difference between the data one sample before and the current data, 13 is an absolute value conversion circuit that calculates the absolute value of the output signal of the adder 12, and 14 is the magnitude of the absolute valued data. It is a comparison circuit for comparing and detecting dropout.

The absolute value of the difference from the data one sample before can be obtained from the data of c input to the digital data detection circuit 7 (FIG. 3). The absolute value of the difference between the adjacent samples is smaller than the dynamic range of the effective data area even in the part that does not correspond to the dropout, as shown in FIG. Also, the drop dropout portion changes from the minimum value to the maximum value of the effective data area as shown in c of (FIG. 3), and the output of the absolute value circuit 13 is the dynamic range of the effective data area. A value corresponding to is obtained. That is, in the comparison circuit 14, a signal indicating the dropout period is obtained in a one-to-one correspondence with the data, and the dropout information is transmitted to the output side of the reproduction signal processing circuit 5.

Another embodiment of the dropout correction device of the present invention will be described below with reference to the drawings. FIG. 4 is a block diagram showing another embodiment of the dropout correction device of the present invention. FIG. 5 is a block diagram showing an example of the dropout start / end signal detection circuit of the dropout correction device of FIG. (Figure 6)
It is a wave form diagram which shows the signal waveform of each part.

In FIG. 4, parts different from the embodiment shown in FIG. 1 will be described. Reference numeral 16 denotes a dropout start / end signal adding circuit for adding predetermined data to the output position of the AD converter 3 at the start position and the end position of the dropout period. It is a dropout start / end signal detection circuit for extracting information.

The signal output from the AD converter 3 is
As shown in (b) of FIG. 6, the dropout start signal is input to the dropout start / end signal addition circuit 16 together with the dropout display signal indicating that t1 is the dropout start time and t2 is the dropout end time. It To this signal, a signal that changes from Low level to High level is added at the start of dropout. Furthermore, at the end of the dropout, from the High level to Lo
A signal that changes to the w level is added. The input signal is output as it is during the period other than the dropout start position and the end position. The signal is shown in c of (FIG. 6).
This signal is processed by the reproduction signal processing circuit and then processed by the dropout start / end signal detection circuit 17, an example of which is shown in FIG.

In FIG. 5, 10 is an input terminal and 11 is an input terminal.
Is a delay circuit that delays data by the time of one sample,
12 is an adder that takes the difference between the data one sample before and the current data, and 18 is the output of the adder 12 is equal to ((maximum value of valid data area)-(minimum value of valid data area)) Comparator circuit A that outputs a predetermined signal when
Reference numeral 19 denotes a comparison circuit B which outputs a predetermined signal when the output of the adder 12 becomes equal to ((minimum value of effective data area)-(maximum value of effective data area)).
Reference numeral 20 denotes a dropout position detection circuit that supplies a dropout period to the correction circuit 6 from the signals indicating the start position and the end position of the dropout supplied from the comparison circuit A18 and the comparison circuit B19.

In the comparison circuit A18 and the comparison circuit B19, a data string added only to the start position and the end position of the dropout, which does not exist in the band-limited video signal, that is, the minimum value of the effective data area in one sample. From the maximum value or from the maximum value to the minimum value is detected, the dropout period can be detected at the output side of the reproduction signal processing circuit 5.

In the above description of each embodiment, the data to be used in the full dynamic range of the effective data area is considered as the signal to be inserted in the dropout period, but even if the signal is outside the pass band of the LPF. Good.

[0024]

As described above, according to the dropout correction device of the present invention, a signal outside the pass band of the LPF is added during the dropout period so that the reproduction signal processing circuit for time axis correction or the like is passed. Even in this case, the dropout information obtained on the input side of the reproduction signal processing circuit is output on the output side without increasing the number of processing bits of the reproduction signal processing circuit and reducing the effective data area. Can be transmitted to.

Further, if the signal added during the dropout period is added with data in which the minimum value and the maximum value of the dynamic range of the effective data area change for each sample, the detection on the output side of the reproduction processing circuit can be easily performed. it can.

As the data to be added, the data of the first part and the data of the last part of the period corresponding to the dropout are set to predetermined values, for example, from the minimum value to the maximum value of the effective data area at the start position and the end position. Then, by replacing the maximum value in the effective data area with the minimum value, the dropout can be detected on the output side of the reproduction processing circuit by only processing a part of the data in the dropout period.

[Brief description of drawings]

FIG. 1 is a block diagram showing a dropout correction device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a digital data detection circuit of the dropout correction device.

FIG. 3 is a waveform diagram showing a signal waveform of each part of the dropout correction device.

FIG. 4 is a block diagram showing a dropout correction device according to another embodiment of the present invention.

FIG. 5 is a block diagram showing a digital data detection circuit of another embodiment.

FIG. 6 is a waveform diagram showing signal waveforms of respective parts of the dropout correction device according to the other embodiment.

FIG. 7 is a waveform diagram showing a signal waveform of a conventional example.

FIG. 8 is a block diagram showing a time axis correction circuit.

FIG. 9 is a timing chart of signals at various parts of the time axis correction circuit.

FIG. 10 is a timing chart of signals at various parts of the time axis correction circuit.

[Explanation of symbols]

 1 Input Terminal 2 LPF 3 AD Converter 4 Digital Data Addition Circuit 5 Playback Signal Processing Circuit 6 Dropout Correction Circuit 7 Digital Data Detection Circuit 8 Output Terminal 9 Dropout Signal Input Terminal 10 Digital Data Detection Circuit Input Terminal 11 Delay Circuit 12 Addition Device 13 Absolute value conversion circuit 14 Comparison circuit 15 Output terminal of digital data detection circuit 16 Dropout start end signal addition circuit 17 Dropout start end signal detection circuit 18 Comparison circuit A 19 Comparison circuit B 20 Dropout position detection circuit 21 Time axis Correction circuit

Claims (2)

[Claims] 1. An LPF having a predetermined pass band, an AD converter for converting an output signal of the LPF into digital data at a frequency twice or more the pass band of the LPF, and an output signal of the AD converter. A digital data addition circuit that replaces digital data in a period corresponding to dropout with a signal outside the pass band of the LPF; and a reproduction signal processing circuit that performs signal processing for reproduction on the output signal of the digital data addition circuit. A digital data detection circuit for detecting the data added by the digital data addition circuit from the signal after the reproduction signal processing; and a dropout detected by the digital data detection circuit using the output signal of the reproduction signal processing circuit as an input. Dropout correction that performs dropout correction operation from the indicated signal Dropout compensation device is characterized in that a road. 2. An LPF having a predetermined pass band, an AD converter for converting an output signal of the LPF into digital data at a frequency twice or more the pass band of the LPF, and an output signal of the AD converter. A dropout start / end signal addition circuit that replaces the data of the first part and the data of the last part of the period corresponding to the dropout with a predetermined value, and for reproduction with respect to the output signal of the dropout start / end signal addition circuit A reproduction signal processing circuit for performing the signal processing of, a dropout start and end signal detection circuit for detecting the dropout start and end data added by the dropout start and end signal adding circuit from the signal after the reproduction signal processing, and The output signal of the reproduction signal processing circuit is input and detected by the dropout start / end signal detection circuit. A dropout correction circuit that performs a dropout correction operation from a signal indicating the generated dropout.