JPH0154791B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a data separation circuit that separates digital data from a pseudo video signal of an audio PCM recorder.

The prior art and its problems will be explained with reference to FIGS. 1 to 3. For audio using VTR
NTSC is used for data transmission of PCM recorders.
The video format is compliant with the National Television System Commitee (National Television System Commitee) system.
Therefore, from a pseudo video signal containing horizontal synchronization signals and PCM data signals, synchronization signals and PCM
It is necessary to separate each data signal. 1st
The figure shows an example of a data signal synchronization signal separation circuit.
In Figure 1, 1 is a video signal input terminal, 2 is a data separation output terminal, 3 is a synchronization separation output terminal, and 4
5 is a video amplifier circuit, 5 is a data separation circuit, and 6 is a synchronous separation circuit. A more specific example of the separation circuit is shown in FIG. 2a.

In FIG. 2a, 7 is a resistor, 8 is a semi-fixed resistor, and the others are the same as in FIG. 1. Further, FIG. 2b shows an NTSC video signal form for reference. In Figure 2b, 9 is a horizontal synchronization signal, 10 is a pedestal signal, and 11 is an NRZ signal.
(Non Return to Zero) system PCM data signal, 12 is a white peak signal for VTR brightness automatic gain control, 13 is a synchronization signal separation level, 1
4 is the PCM data separation level.

The circuit shown in FIG. 2a operates as follows.
A video signal input from input terminal 1 is amplified by video amplifier circuit 4 and input to one input terminal of separation circuits 5 and 6. At the other input terminals of the separation circuits 5 and 6, voltage levels serving as comparison standards for separation, ie separation levels 13 and 14, are connected to the power supply voltage.
Vcc, - Vcc and the semi-fixed resistor 8 are determined and given. The separation circuits 5 and 6 compare the amplified video signal level with the separation level and output a logic signal of 1 or 0 depending on the comparison result, as shown in FIG. Perform PCM data separation or homogroup separation.

Next, Figure 3 shows the two-head helical scan type.
This figure shows a block diagram from the video head of a VTR to the video output. In Figure 3, 15 is the CH1 video head, 16 is the CH2 video head, and 17 is the CH1 video head.
CH1 rotary transformer, 18 is CH2 rotary transformer, 19 is CH1 preamplifier, 20 is
CH2 preamplifier, 21 is channel switch,
22 is an AGC amplifier, 23 is a dropout detector, 24 is an adder, 25 is a dropout switch, 26 is a 1H delay circuit, 27 is an FM equalizer, 28 is an FM demodulator, 29 is a de-emphasis circuit, and 30 is a video amplifier. , 31 are video output terminals. In FIG. 3, when the dropout detector 23 is turned on, that is, when a dropout is detected, the dropout switch 25 is turned on.
Connected to the 1H delay circuit 26 side, adder 24
The signal from 1H before continues to be sent until the dropout detector 23 turns off. This method is a very effective method to prevent dropouts on actual television screens, and is standardly equipped in consumer VTRs as a dropout canceler circuit (DOC circuit).

However, the DOC circuit described above has the following problems when used in a VTR as part of an audio PCM recorder. An audio PCM recorder adds six standardized signal words, one error correction word P and Q each, and one error detection word (hereinafter referred to as CR) generated from these eight words within 1H of the video signal. The data is transmitted as one data block. Further sampled signal word 6
The error correction words P and Q are interleaved with D=16H, and the 8 words within 1H have no correlation as data by themselves. Now, as mentioned above, when there is a dropout on the magnetic recording tape, the DOC circuit sends the data signal from 1H earlier as the video signal, but the data that should originally be considered as an error is sent to the CRC. If the data is read as correct including the
The error will affect the data after ×6H. Failure to detect such errors can cause PCM
This leads to the generation of noise, which can be fatal to high-quality playback by recorders, and a countermeasure is needed.

The purpose of the present invention is to solve the above problems and to
An object of the present invention is to provide a data separation circuit which can detect data as an error so that data that should originally be considered as an error is not sent as correct data by the circuit.

The feature of the present invention is that a gate circuit is provided at the PCM data output of the data separation circuit, and by closing this gate while the DOC circuit is working, 1H
This should be considered an error due to the delay circuit.
The point is that data from 1H ago is not sent to the PCM data output terminal.

The present invention will be explained in detail below with reference to the drawings.

FIG. 4 shows an improved circuit of FIG. 1 according to the present invention, where 33 is a gate control signal and 32 is an output gate circuit. By embodying Figure 4,
FIG. 5 shows the connection relationship with the figure. Fifth
In the figure, 34 is a gate control signal generator, and the other parts are the same as in FIGS. 2, 3, and 4.

FIG. 5 operates as follows. Dropout detector 23 operates to notify dropout switch 25 and gate control signal generator 34 of the presence of a dropout. The dropout switch 25 is connected to the 1H delay circuit 26 side, and the data from 1H before is sent to the adder 24, and as a result, the data from 1H before is output to the video output terminal 31, which should originally be considered as an error. Ru. On the other hand, the gate control signal generator 34 receives a signal that there is a dropout and outputs a gate control signal 33 to close the output gate circuit 32. The output gate circuit 32 will be closed as long as dropout is detected by this signal 33, and during this time all data output to the data output terminal 2 will be 0.
becomes. 1H interval, i.e. 6 standardized signal words, error correction words P, Q and CRC total 128
When all bits become 0, these eight words are determined to be errors in MC correction, and are corrected to original correct data. Since interleaving is performed, the output gate circuit 32 is closed continuously due to dropout (16H x 2).
-1H, that is, 31H, the output data can be corrected to correct data.

In addition, in the above explanation, a VTR is used.
Although the explanation has been made regarding a PCM recorder, it goes without saying that it can also be applied to a PCM recording/playback device using a video disk.

As explained above, according to the present invention, it is possible to protect data from error correction errors caused by the DOC circuit, and when combined with interleaving, this invention becomes a very effective data protection means against data loss due to dropouts. .

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional data signal synchronization signal separation circuit, Fig. 2a is a circuit diagram of an example separation circuit,
Figure 2b shows the NTSC video signal format, Figure 3 is a block diagram of a general home VTR, Figure 4 is a basic block diagram of the data signal synchronization signal separation circuit according to the present invention, and Figure 5 shows the VTR and main unit. FIG. 2 is a block diagram showing the connection relationship of the data separation circuit according to the invention. 5...Data separation circuit, 32...Output gate circuit, 33...Gate control signal, 34...Gate control signal generator.

Claims (1)

[Claims] 1 A magnetic head for reproducing information signals including PCM data signals, a 1H (H: horizontal scanning period) delay circuit, a dropout switch, and an adder circuit, and the information signal reproduced by the magnetic head. dropout compensating means for detecting dropout and compensating for the dropout, a demodulator for demodulating the dropout compensated information signal, data separating means for separating the PCM data signal from the information signal, and a PCM data signal separated by the data separating means. P.C.M.
A data output terminal from which a data signal is output is connected to the data separation means and the data output terminal, and is controlled by a dropout compensation means, and when the dropout compensation means detects a dropout, the PCM data is A data separation circuit comprising output gate means for prohibiting a signal from being output to a data output terminal.