JPH04172657A - Skew corrector - Google Patents

Abstract

PURPOSE:To accurately correct a skew conveniently to constitute as an analog signal processor by detecting a phase difference of signals of the same processing stage of first and second signal processing paths for an overlapping period, and controlling variable delay circuits so that the phase difference becomes zero. CONSTITUTION:A switch 12 switches first, second signal selecting states for an overlapping period. A led third signal is input to a first signal processing path 100 formed of a band pass filter 13, a delay circuit 14 and a demodulator 15, and a second signal is always input to a second signal processing path 200 formed of a band pass filter 23, a delay circuit 24 and a demodulator 25 of entirely the same configuration. Skew detectors 31, 33 detect a time difference of FM signals of the outputs of the circuits 14, 24 and a time difference of demodulated outputs of the demodulators 15, 25, control delay amounts of the circuits 14, 24, and controls so that time difference information becomes a minimum value. Thus, an accurate correction convenient for constituting an analog signal processor can be performed.

Description

[Detailed Description of the Invention] "Object of the Invention" (Industrial 111-use packaging) This invention is a magnetic recording and reproducing device capable of recording and reproducing high-quality audio signals, a so-called Hi-Fi~'TR audio reproducing system, etc. The present invention relates to a skew correction device used for.

(Prior Art) In a helical scan type VTR, a stereo audio signal is deeply recorded on the same track as the video recording track on a magnetic tape, and this is reproduced using the so-called H4 Fi V.
TR is widely used. When reproducing an audio signal in the second system, the reproduced signal is alternately reproduced from the first and second playback heads tracing different tracks, so that these first and second signals are combined into a continuous third signal. Is it necessary to connect it to

Therefore, the first and second signals are recorded and reproduced so that there is a partial overlap period, and within the 20 overlap period, the first and second signals have exactly the same content. During this period, selection is made to switch from the first signal to the second signal or from the second signal to the first signal, and a continuous third signal is obtained. The problem here is that a signal is dropped due to switching selection, resulting in so-called switch noise, which remains in the third signal.

In order to solve this problem, various switching noise reduction circuits have been developed.

This mainly involves switching the demodulated outputs of the first and second signals by hold interpolation or linear interpolation, and connecting them while masking noise.

However, in reality, in VTRs, the tape expands and contracts, and the linearity of the head trunking is not ideal in many cases. If linearity cannot be ideally obtained, the head or trace with azimuth may deviate from the center (wavering), and the reproduced output may be deviated (modulated) in the time axis direction.

In such a case, even if the first and second demodulated outputs are connected without any signal loss, the signal may be located between the first and second signals (
Because of the skew, smooth continuity cannot be obtained. This phenomenon becomes more noticeable when the recording VTR and the reproducing VTR are different. Furthermore, even if the tape expands and contracts, this expansion and contraction itself causes skew.

As a means of solving problems caused by such skew,
There is a Japanese Patent Application No. 1-221061 entitled "Skew Correction Device".

An example of the circuit introduced in this book is shown in Figure 3.

First and second signals from first and second playback heads are supplied to input terminals 1a and 1b. During the overlap period, the first and second signals are simultaneously present at input terminals 1a and 1b. The first and second signals are input to delay circuits 8a and 8b via bandpass filters 2a and 2b, respectively. The outputs of delay circuits 8a and 8b are input to demodulation circuits 3a and 3b, respectively, and demodulated. The demodulated outputs A1 and 81 are then switched and selected by the switch 5 during the overlap period, and are derived as a continuous third signal.

The demodulated outputs A1 and 81 are further input to the skinny detection circuit 6.

The skinny detection circuit 6 detects the digit error between the signals A1 and B1 during the overlap period to obtain skinny information. During the overlap period, signals A1 and A8 should
A phase error of 1 is a lotus of zero. The skinny information is input to the control circuit 7 and used as delay amount control information for the delay circuits 8a and 8b. This control is performed so that the phase error between the signals A1 and 81 becomes zero.

FIG. 4 shows a timing chart of the FM signals Ach and Bch output from the bandpass filters 2a and 2b and the switching pulse SWP of the switch 5.

The above system is based on the premise that skew correction is achieved through digital signal processing. However, the Hj of VTR
In the Fi audio recording and playback system, analog signal processing is common and the system is suitable for analog, so if only a part of the system is configured with digital processing, it will be possible to use high-precision analog dental converters, digital-to-analog converters, etc. This results in a significant increase in circuit scale, which inevitably increases costs.

Therefore, when considering converting the system shown in FIG. 3 into a conventional analog signal processing form, it is necessary to match the demodulation circuits 3a and 3b with high accuracy.

The first is the direct current (DC) offset of these demodulation circuits 3a and 3b. Since the skew to be detected is generally a very small amount, less than 1150 of the signal period,
Even if there is a slight C offset between the outputs A1 and 81 of the two demodulation circuits 3a and 3b in FIG. 3, it becomes a major error factor in skew detection, and the accuracy of skew correction is significantly deteriorated. In addition, since the demodulated outputs AI and Bl are switched and selected by the switch 5 after being obtained, a pulse signal is generated at the switching cycle due to the DC offset between the demodulated outputs, and unnecessary periodic signals are generated in the reproduced signal. Otherwise, it will be mixed in.

Second, if there is a difference in demodulation sensitivity between the demodulation circuits 3a and 3b, the outputs A1 and B1 of both circuits can be switched using the switch 5 in the subsequent stage, so that the reproduced signal can be changed from A to A at the switching frequency.
2 and 1 sound as if they had undergone 1 modulation.

In order to avoid the above two problems of DC offset and difference in demodulation sensitivity, offset/node 1 adjustment and demodulation level adjustment are each required. However, in the case of HjFi audio processing, since it is stereo processing, one system, which is the same as that shown in FIG. 3, must be installed in one device.

Therefore, each of the two types of adjustment described above is required for a total of four demodulators, resulting in a significant increase in cost. Furthermore, even if we do all this, the influence of residual off-cuts (adjustment errors) remains, especially when it comes to DC
The offset will have a considerable effect on the correction ability.

(Problems to be Solved by the Invention) As explained above, if a conventional skew correction device is applied as is to an analog signal processing format, it is possible to achieve highly accurate matching of the node and demodulation sensitivity by turning off the DC of the two demodulation circuits. Moreover, if this is to be done by adjusting the χ・I measure, as many as 8 adjustments are required, which is uneconomical.

SUMMARY OF THE INVENTION An object of the present invention is to provide a skew correction device that is convenient to configure as an analog signal processing system, requires fewer adjustment points, and can realize highly accurate skew correction.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides recording signals that are recorded at different positions on a recording medium with signal overlap periods, and a recording signal that is recorded at a first and a second position so that the overlap periods overlap. In the apparatus for obtaining a continuous third signal by alternately switching and selecting this signal in the overlap period, the first and second signals are switched in the overlap period of the first and second signals. selection means for deriving a second signal from the signal or a third signal which is a continuation of the first signal from the second signal; and the third signal derived from the selection means.
signal is input, a bandpass filter, a variable delay circuit,
a first signal path that is sequentially processed by a demodulation circuit; and a second signal processing path that receives either the first signal or the second signal and has the same configuration as the first signal processing path. , a skew detection means for receiving each signal of each intermediate processing stage of the first and second signal processing paths, and detecting a phase difference between the two signals in the automatic/interval period; and means for controlling each variable delay circuit of the first and second signal processing paths so that the phase difference becomes zero based on skew information obtained by the skew detection means.

(Operation) The demodulated signal finally derived by the above means is only the signal from the first signal processing path described above. For this reason, there is no need to worry about the DC offset of the demodulation circuit as in the conventional case of connecting the outputs of a plurality of demodulation circuits, and the problem of DCC offset is eliminated. Also, whether a similar second signal processing path is provided separately from the first signal processing path, or whether this is done through accurate skew detection or whether it is matched with the first signal processing path based on the group delay characteristic. Therefore, it is possible to make the skinny detection circuit section sufficiently small.

(Example) Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of the second invention. A playback signal from the first playback head (first signal 1, for example, an FM audio signal) is introduced into the input terminal 11a, and a playback signal from the second playback head (second signal: For example, F
M audio signal) is introduced. The first and second reproducing heads are provided on a rotating drum of a helical scan type VTR, and alternately trace recording tracks with an overlap period.

The first signal at the input terminal 11a is supplied to the fixed terminal 12a of the switch 12, and the second signal at the input terminal 11b is supplied to the fixed terminal 12b. The switch 2 is switched from the first signal to the second signal selection state or from the second signal to the first signal selection state during the overlap period, and the head switching signal is used as the switching signal. ing. The third signal derived from switch 12
The signal is a combination of the first and second signals, and is input to the bandpass filter 13.

The signal derived from the bandpass filter 13 is input to the demodulation circuit 15 via the delay circuit 14 whose delay amount can be varied.

The above-described system of bandpass filter 13, delay circuit 14, and demodulation circuit 15 constitutes a first signal processing path 100.

A second signal processing path 200 having exactly the same configuration as this first signal processing path 100 is also provided. That is, it is a circuit composed of a bandpass filter 23, a delay circuit 24, and a demodulation circuit 25.

However, the second signal processing path 200 is always manually supplied with, for example, the second signal from the input terminal 11b.

The demodulated output A1 of the first signal processing path 100 is directly delivered to the output terminal 16 as a continuous demodulated output. Further, the second demodulated output A1 and the demodulated output B1 of the demodulation circuit 25 are input to the skew detection circuit 31. The skew detection circuit 31 is a circuit that detects a phase difference (time difference) between two input signals during an overlap period. The time difference information obtained from the second skew detection circuit 31 is input to an adder 32. This adder 32 also receives time difference information from a skew detection circuit 33 . Skinny detection circuit 33
is the output of the previous delay circuits 14 and 24 (FM signal stage)
is used to detect the phase difference. The time difference information obtained by the adder 32 is input to the control circuit 36 via a low pass filter (LPF) 35. The control circuit 36 uses the time difference information to control the amount of delay of the delay circuits 14 and 24 so that the time difference information has a minimum value.

Through the above circuit operation, the demodulated output A1 of the demodulation circuit 15 is outputted as a continuous signal of the A channel and the B channel without skew distortion. especially,
According to this embodiment, since both the A-channel signal and the B-channel signal are constantly demodulated in one signal processing path, compared to a system having two systems that demodulate each channel signal independently, , does not cause the problem of DC offset between each other. Furthermore, compared to a two-system system, there is no need to consider the difference in demodulation sensitivity between the systems.

In this embodiment, skew correction is performed by detecting the time difference between the FM signal output from the delay circuit and the demodulated output from the demodulation circuit. It is known that the skew amount of the FM audio signal of an actual VTR is mostly about 3 μsec or less in compatible playback. This is about 4 cycles at the center frequency of the L channel FM signal, 1.3 MHz, and is a phase difference of about 11" with respect to the 10 KHz signal. The waveform explaining this situation is shown in Figure 2. show.

Block 201 in FIG. 2 shows four examples in which there is a phase difference between the FMM signals 1 and f2, and the phase increases toward the right in the drawing. F M
When skew detection is performed on a signal, either the detection sensitivity is high and accurate correction is possible, or a misalignment point occurs every cycle of 1.3M1lz. Therefore, as shown in block 202 of FIG. 2, the correction amount A based on the output of the skinny detection circuit 33 is
It exhibits a characteristic in which it gradually increases in four cycles and gradually decreases in the next four cycles.

On the other hand, when performing skew detection using the demodulated output, there is no need to worry about mislock, and the detection sensitivity is low, and the detection requires a variety of circuits because the detection has a very small phase of less than a few degrees with the palate. Detection accuracy tends to deteriorate due to error factors. Block 202 in FIG. 2 shows the state of the phase difference of the demodulated output and the characteristics of the correction ff1B obtained thereby. Phase difference 11.1. 'The maximum amount of correction is obtained.

In the embodiment shown in FIG. 1, by using the two systems of skew detection described above in combination, skinny correction is mainly performed on the correction iLA side, and the correction amount B side is used for the purpose of preventing mislocking, thereby achieving high accuracy. You are getting skew correction.

Each delay circuit] If the maximum delay time of 4.24 or 3μ5ec (center delay time 1.
! 1 circuit 15) is delayed by 2 μsec with respect to the detection 1, 1 side (path of bandpass filter 23, delay circuit 24, demodulation circuit 25), the delay time of delay circuit 14 is 0.5 μsec. Then, control is performed to set the delay time of the delay circuit 24 to 2.5 μsec.

In this way, highly accurate skinny correction is possible by delaying the F~1 signal for a certain period of time through feedback control mainly based on phase difference detection using the FN1 signal.

However, if the skew detection circuit has a sufficiently high precision, or if high precision is not required, the skew detection circuit 31 may be extended. In addition, if the FM signal is connected in a continuous phase at the head switching position, most of the pulse noise, which is the main cause of unpleasant switching noise, can be removed, so the skew detection circuit can be used as a skew detection circuit. Even if only one of the output of the detection circuit 33 or the output of the skew pressure detection circuit 31 is used, it is sufficiently practical.

According to this invention, when used for demodulating stereo audio signals, the system shown in Fig. 3 requires four demodulation systems because the same circuit is added in parallel, but the system shown in Fig. 1 can be used for demodulating stereo audio signals. If used, one system of the same path as the first signal processing path may be added. This is because the second signal processing path can be shared as a skew detection section for the left and right channels. Therefore, when this invention is applied to a stereo audio recording and reproducing system, the circuit scale can be reduced to about 3/4 compared to the conventional system.

[Effects of the Invention] As explained above, the skew correction device of the present invention is convenient to configure as an analog signal processing circuit, requires fewer adjustment points, has a small circuit scale, and is highly accurate. correction can be achieved

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is an explanatory diagram for explaining the operation of the circuit in FIG. 1, and FIG.
FIG. 4 is a circuit diagram showing a conventionally proposed skew correction device, and FIG. 4 is a signal waveform diagram shown to explain the operation of the circuit shown in FIG. 3. 12. Switch, IB, 23. Band pass filter, 1
4.24...Delay circuit, 15.25...Demodulation circuit, 3
1.33 - Skew detection circuit, 32... Adder, 35
...low-pass filter, 36 control circuit. Applicant's agent Patent attorney Takehiko Suzue

Claims (2)

[Claims] (1) Recording signals recorded at different positions on a recording medium with overlapping periods of signals are extracted as first and second signals so that the overlapping periods overlap, and this signal is further added to the overlapping period of the recording medium. In the apparatus for obtaining a continuous third signal by alternately switching and selecting in a period, the switching is performed in an overlap period of the first and second signals to switch from the first signal to the second signal or the second signal. A selection means for deriving a third signal that is a continuation of the first signal from the signal, and the third signal derived from the selection means is input and sequentially processed by a bandpass filter, a variable delay circuit, and a demodulation circuit. a second signal processing path into which either the first signal or the second signal is input and which has the same configuration as the first signal processing path; skew detection means for receiving each signal of the same processing stage of the second signal processing path and detecting the phase difference between the two signals in the overlap period; and skew information obtained by the skew detection means. A skew correction device comprising: control means for controlling each variable delay circuit of the first and second signal processing paths so that the phase difference becomes zero based on the following. (2) The skew detection means includes: a first skew detection circuit that obtains time difference information between the demodulated outputs of each demodulation circuit of the first and second signal processing paths; a second skew detection circuit for obtaining time difference information between the outputs of each of the bandpass filters; and an addition means for adding the outputs of the first and second skew detection circuits and inputting the result to the control means. The skew correction device according to claim 1, characterized in that: