JPH0359840A - Magnetic tape reproducing device - Google Patents

Abstract

PURPOSE:To accurately detect a synchronizing signal and to perform the stable tracking by counting a period of the detected synchronizing signal with counters when the synchronizing signal is detected by a synchronization detecting circuit and controlling the starting time and the ending time of the counters with signals to be outputted from a continuous Hi detecting circuit and a continuous Lo detecting circuit. CONSTITUTION:An output of a comparator 131 tends to generate a beard in the vicinity of its rise and fall. Even in this case, the commencement and completion of two counters 134 and 135 are controlled by using a detecting output of the continuous Hi detecting circuit 132 for detecting the continuation of Hi for a prescribed time and a detecting output of the continuous Lo detecting circuit 133 for detecting the continuation of Lo in level for a prescribed time when a Hi section and a Lo section of the output of the comparator 131 are counted by the two counters 134 and 135. Thus, a malfunction of a time measuring circuit due to noise can be prevented. By this method, the accurate synchronizing signal can be detected, and the accurate tracking is feasible, and hence the stable reproducing device can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a digital audio tape recorder (hereinafter referred to as D
The present invention relates to a playback circuit for a device that records and plays back by forming diagonal tracks on a magnetic tape, such as an AT (hereinafter referred to as an AT) or a video tape recorder (hereinafter referred to as a VTR).

In conventional VTRs and DATs in which tracks are recorded obliquely on a magnetic tape, tracking is the act of causing a reproducing head to trace a desired trajectory over the recorded tracks.

For DAT, ATF (AutomaticTra(+
k (abbreviation for Finding) is recorded.

Furthermore, when recording on a tape that has been previously recorded, DAT employs a method of overlapping recording without providing a head for erasing already recorded signals. Conventionally, in order to detect a synchronization signal from a reproduced signal, the reproduced signal is converted to a digital level by a comparator, and the period, duty ratio, etc. of the signal are determined from the rising edge of the signal.9. Counting is started and ended at the falling edge, and a synchronization signal is detected when the measurement results satisfy the set conditions several times.

Problems to be Solved by the Invention However, in such conventional methods, due to factors such as overwriting of the signals recorded on the tape, other previously recorded signals remain in the original Domei signal at a minute level. , S of the synchronization signal
/N is deteriorated, the output of the comparator is susceptible to noise near both hedges of the original synchronization signal, and the counter that detects the period of the synchronization signal is affected by this noise. Malfunction occurs and normal synchronization signal cannot be generated.

In order to remove these noises, there is a solution by providing the comparator with hysteresis characteristics, but determining the hysteresis width of the hysteresis circuit is extremely difficult considering tapes recorded under various conditions. be.

The present invention has been made in view of the above-mentioned problems, and provides a device that can correctly detect a synchronization signal and perform stable tracking even when the quality of the synchronization signal written on the magnetic tape is poor. It is intended to.

Means for Solving the Problems In order to solve the above problems, the magnetic tape reproducing apparatus of the present invention forms diagonal tracks on a magnetic tape, and at a plurality of predetermined locations on each track of the magnetic tape. Using a magnetic tape on which a tracking signal is recorded, which is composed of two types of signals: a pilot signal for detecting the tracking state by crosstalk and a synchronization signal for detecting the pilot signal, the head and the head are The attached rotary cylinder and the two heads have a reference signal generator for switching the head signal when reproducing the magnetic tape, a comparator for converting the head output signal into a digital level, and an output signal of the comparator. A continuous Hi detection circuit detects that the Hi level continues for a predetermined period of time, and a continuous Hi detection circuit detects that the Hi level continues for a predetermined period of time, and a continuous Hi detection circuit that detects that the Hi level continues for a predetermined period of time
When the continuous Lo detection circuit detects that the level continues and the continuous Hi detection circuit detects the Hi level for a predetermined time, they start measuring the time of the Hi level section of the waveform, and the continuous Lo43. '< When the output circuit detects that it is at Lo level for a predetermined period of time, the time measurement circuit that finishes time measurement of the Hi level section of the waveform and the continuous Lo detection circuit detect that it is at Lo level for a predetermined period of time. Then, time measurement of the Lo level section of the waveform is started, and when the continuous Hi detection circuit detects that the continuous Hi level has continued for a predetermined time f (i), the waveform glue is detected.

Using a time measurement circuit that finishes time measurement for the level section,
When the two time measurement circuits mentioned above satisfy a predetermined condition a predetermined number of times in succession, they output a synchronized 1n pulse, sample and hold the Tl1l KB pilot signal at the timing of the detection pulse, and perform tracking. a tracking detection circuit that outputs a signal for Oi; a tape drive means that rotates the magnetic tape;
The apparatus is configured to include a control circuit that outputs a drive command signal to the drive means using the force of the J rotational speed detection means and the output of the tracking detection circuit.

Function: When the magnetic tape playback device described above fails, the previously recorded signal components may remain as noise due to variations in the recorded information level when the synchronization code input to the comparator is recorded. In the case where the output of the comparator is triggered near the rising edge and falling edge due to a certain period of time, the Hi section and Lo section of the comparator output may be Using the detection output of the circuit that detects that the Hi level continues for the predetermined period of time when the two counters measure, and the detection output of the circuit that detects that the Lo level continues for the predetermined period,
By controlling the start and end of the two counters for time measurement, it is possible to prevent malfunctions of the time measurement circuit caused by the noise. Therefore, even if a tape with a poor quality synchronization signal is played back, the synchronization signal can be reliably detected and stable playback can be performed.

Embodiment Hereinafter, a magnetic tape reproducing apparatus according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a magnetic tape reproducing apparatus according to an embodiment of the present invention.

In Figure 1, 1 is a magnetic tape, 2a is a plus, 2
b is a head with negative azimuth, 3 is head 2a
, 2b is attached with a rotating cylinder 9, 6 and 7 are reels for winding the magnetic tape 1, and 4.6 is a post for winding the magnetic tape 1 around the rotating cylinder 3 to form a desired running path for the magnetic tape 1. be. 131 is the head 2a, 2b
A comparator 132 converts the output reproduced from the comparator 131 into a digital repeater, and 132 is a continuous H level that detects that the Hi level continues for a predetermined period of time in the output of the comparator 131.
The i detection circuit 133 detects that the Lo level continues for a predetermined time in the output of the comparator 131.
o detection circuit, 134 is a counter that measures the time when the output signal of the comparator 131 is at Hi level, and 135 is a counter that measures the time when the output signal of the comparator 131 is at Lo level. Further, 136 is a counter 134. A synchronization signal determination circuit that generates a first sample-and-hold pulse for sampling and holding the ATF signal when a synchronization signal is determined from the time measurement result of the counter 135;
Reference numeral 137 designates a second sample-and-hold pulse path for sampling and holding the ATF signal with a time shift from the sample-and-hold signal generated by the synchronization signal determination circuit 136. Further, 141 is a low-pass filter that extracts an ATF pilot signal, which is a tracking signal, from the output of the heads 2a and 2b, 142 is a rectifier circuit that detects the amplitude of the pilot signal, and 142 is a synchronization signal detection circuit 13.
146 is a sample-hold circuit that samples and holds the output voltage of the subtracter 144 using the pulse generated from the delay circuit 137. . In addition, 11 is a pinch roller, 8 is a capstan shaft, 9 is a capstan motor that shares the shaft with the capstan shaft 8, and 19 is a rotation speed detection flat membrane that detects the rotation speed of the capstan motor 9 (FG).
, 161 is an FV that converts the output frequency of FG17 into voltage.
Converter 162 is an adder that adds the output of the sample-and-hold FV converter 151, and 10 is a drive circuit that drives the capstan motor 9 with the output of the adder 152.

Among the above, the comparator 131, the continuous H1 detection circuit 1
32, continuous Lo detection circuit 133, counter 134, counter 136, synchronization signal determination circuit 136, delay circuit 137
constitutes the synchronization signal detection circuit 13, and the low-pass filter 1
41, rectifier circuit 142, sample hold circuit 143,
, 145, the subtracter 144 is the tracking detection circuit 14
The pinch roller 11, the capstan shaft 8, the capstan motor 9, and the drive circuit 1o constitute a tape drive means 12 for driving the magnetic tape 1, and the FV converter 1
61 and the adder 152 constitute a control circuit 15 that controls the number of rotations of the tape drive means.

The embodiment shown in FIG. 1 is constructed as described above.

Next, a recording example of the magnetic tape used in the embodiment shown in FIG. 1 will be explained.

Referring to FIG. 2, reference numeral 21 indicates tracks recorded on the magnetic tape 1, and hatched areas 22 and 23 indicate areas where ATF signals used as tracking signals are recorded. In each track, ATF signals 22 and 23 are always recorded at the same two predetermined positions. Of course, the number of ATF signals to be recorded is not limited to two, but may be any number if permitted.

Figure 3 shows a specific recording pattern example of areas 22 and 23 where each ATF signal in Figure 2 is recorded. An example of a periodic pattern that repeats is shown.

In this FIG. 3, AI, B1, A2. B2 indicates the distinction between tracks, A1. A2 is a track recorded with positive azimuth, B1. B2 indicates a track recorded with negative azimuth, and the track is B2. A
2. They are played in the order of B1 and AI. Further, 37 indicates a head gap, which moves in the direction of arrow 38. 40 indicates the direction in which the tape 1 moves. Also, 31 and 32 are the S pilot signals recorded by heads with positive and negative azimuths, respectively, for tracking the heads, 33
゜34 are synchronization signals with different recording lengths for pilot detection recorded on the plus azimuth track; 35
．． 36 is a synchronization signal of different recording length for pilot detection recorded on the minus azimuth track, and 39 is an area where the ATF signal is recorded (see Fig. 2).
2 or 23).

Next, the operation when the magnetic tape shown in FIGS. 2 and 3 is reproduced using the embodiment shown in FIG. 1 will be described.

4, 6, and 6 are operational waveform diagrams of the embodiment of FIG. 1 of this publication.

In FIG. 1, a rotating cylinder 31d, a rotating cylinder 31d (which rotates at a constant speed and whose control circuit is not shown),
The heads 2a and 2b attached to the magnetic tape 1
Play the signal recorded above.

The reproduction signals of the heads 2a and 2b are transmitted to the synchronization signal detection circuit 13.
, are input to the tracking detection circuit 14.

The low-pass filter 141 transmits pilot signals 31 and 32 recorded on the magnetic tape 1 to the head 2a.

It is output separately from the output of 2b. Low pass fill 1
The output of 41 is rectified by a rectifier circuit 142, and its amplitude information is output. Therefore, when the head gap 37 travels through the position 38 shown in FIG.
, the output of the rectifier circuit 142, and the output of the rectifier circuit 142 are respectively shown in FIG. This figure shows a case where the head gap 37 is slightly shifted to the left with respect to the traveling direction.

Further, in the synchronization signal detection circuit 13, the signal recorded on the magnetic tape 1 is input to the comparator 131, and the signal converted into a digital signal by the comparator 131 (FIG. 5) is the continuous Hi detection circuit 132 and the continuous Lo detection circuit 13.
3 is input. The continuous Hi detection circuit 132 and the continuous Lo detection circuit 133 detect that the input signal 61 is continuously at the Hf level or the Lo level for a predetermined period of time (52.53 in this case). The counter 134 starts counting from continuous Hi detection time 66, and starts counting from continuous Lo detection time 56.
The count ends at .

Further, the counter 136 starts counting from continuous Lo detection time 66 and ends counting at continuous Hi detection time 57. Measurement results of counter 134 and counter 136 ts/
If the continuous time setting values 62.3 and 63 of the continuous Hi detection circuit 132 and the continuous Lo detection circuit 133 are set equal, the Hi interval 68 and the Lo
They are each equal to section 59. The g counter 132 and the counter 133 can measure the width of the Hi section and the Lo section width of the signal 61, respectively. Next, the synchronization signal determination circuit 136 multiplies the results of the counters 134 and 136 with a predetermined condition, and if this is satisfied, outputs the first sample signal. Delay circuit 1
37, the second sample pulse with a certain time delay with respect to the first sample pulse becomes as shown in FIG. 4, 2 and 4.

As already mentioned, the low pass filter 141 separates and outputs the pilot signals 31 and 32 recorded on the magnetic tape 1 from the outputs of the heads 2a and 2b, and the output of the low pass filter 141 is rectified by the rectifier circuit 142. , its amplitude information is output.

The output of the rectifier circuit 142 and the output of the sample hold-on pull-hold circuit 143 are subtracted by the subtracter 144 by the first pulse output from the synchronizing signal detection circuit 13 (FIG. 4, 2). , delay circuit 137
The voltage sampled and held by the second pulse (Fig. 4 E) generated by the pilot signal (the first two pulses in Fig. 4 This is the difference in the amplitude of the head (of different amplitudes), and corresponds to the deviation of the head center with respect to the track center.

Further, the FGl 7 outputs a signal with a frequency proportional to the rotation speed of the capstan motor 9, and the frequency signal is converted by the FV converter 151 into a voltage difference between it and the desired rotation speed. The output voltage of the FV converter 151 and the output voltage of the tracking detection circuit 14 are added in an adder 152 and input to the drive circuit 1o to drive the capstan motor 9.

The 90 rotations of the capstan motor are equal to the rotations of the capstan shaft 8, and the magnetic tape 1 is caused to travel by being pressed against the pinch roller 11. At this time, the operating point of the control circuit 16 is set so that the output of the tracking detection circuit 14 is zero.

As mentioned above, the embodiment shown in FIG. 1 controls the running of the tape.Next, we will discuss the effects of this embodiment based on the embodiment shown in FIG. 1, and the operation shown in FIG. This will be explained using a waveform diagram. As mentioned above, the effect of this embodiment is that when the S/N of the signal recorded on the tape 1 is extremely poor due to factors such as overwriting, even if the signal has a waveform like the one shown in Figure 6, The point is that the synchronization detection circuit 13 can reliably detect the synchronization signal and generate the first sample-and-hold pulse at an accurate position.

When a waveform in which noise is superimposed on the reproduced waveform is inputted to the comparator 131 as shown in FIG. 6, the output becomes a signal as shown in FIG. 6C. When this signal is input to a synchronization signal detection circuit based on the prior art;'iτ6Figure 6'1.62
(In the conventional synchronous signal detection circuit, the counter starts and stops when the rising edge or falling edge of the signal output from the comparator approaches the 9th edge.)・In order to measure the call and its duty, the measurement results between the edges of the whiskers such as 61 and 62 are input to the subsequent judgment circuit, so the judgment circuit cannot detect the synchronization signal.) However, in the circuit applied to this embodiment, the continuous Hi detection circuit 13
2. Since the counting of the wavelength of the waveform is started and ended by the output of the continuous Lo detection circuit 133, when the waveform shown at the beginning of FIG. The counting start of the counter 132 for measurement is as follows.
The process is performed at time 63 when the continuous Hi detection circuit continuously detects a predetermined period of time H1, and is similarly terminated at 64. Further, a counter 133 measures the wavelength of the waveform Lo section.
For example, measurement starts at 64 and ends at 66.

In this way, in this embodiment, even in the reproduced waveform as shown in Figure 6, the original recording wavelength can be detected and the synchronization signal can be detected accurately, so that even under the bad conditions described in OiJ, This provides stable tracking even when you press the tape playback button.

Effects of the Invention As described above, according to the present invention, the continuous Hi detection circuit button and the continuous L
By providing a detection circuit, the synchronization signal can be detected accurately, and even if the reproduced waveform is overlaid with noise caused by tape overwriting, equipment noise, etc., which was previously difficult to detect, the synchronization signal can be detected accurately. The synchronization signal can be detected.

Therefore, accurate tracking is possible even when playing back a magnetic tape under poor conditions, and this has the great effect of making it possible to provide an extremely stable playback device.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the groove bottom of a magnetic tape reproducing device in an embodiment of the present invention, Fig. 2 is a plan view showing the recording state of the magnetic tape, and Fig. 3 is a diagram showing the recording state of the magnetic tape. 4, 6, and 6 are waveform diagrams for explaining the operation of the embodiment. 2a, 2b...head, 3...rotating cylinder, 131...comparator, 132...
...Continuous Hi detection circuit, 133...Continuous Lo detection circuit, 134°136...Counter,
136... Synchronization signal detection circuit, 143, 145
...Sample and hold circuit, 12...
tape drive means, 13... synchronization signal detection circuit,
14... Tracking detection circuit, 16...
...Control circuit.

Claims (1)

[Claims] Diagonal tracks are formed on a magnetic tape, and a pilot signal for detecting a tracking state by crosstalk and a synchronization signal for detecting the pilot signal are provided at a plurality of predetermined locations on each track of the magnetic tape.
A device for reproducing a magnetic tape on which a tracking signal composed of various types of signals is recorded, comprising a head, a rotating cylinder to which the head is attached, and a comparator for converting the signal reproduced from the head into a digital level. , a continuous Hi detection circuit that detects that the output of the comparator is continuously at Hi level, a continuous Lo detection circuit that detects that the output of the comparator is continuously at Lo level for a certain time, and the time of the Hi interval and the Lo interval. Measure the time of 2
a sync signal detection circuit that detects a sync signal from a signal reproduced from the head using a counter; a tracking detection circuit that samples and holds the pilot signal using the sync signal and outputs a signal for tracking; A tape drive means for running the magnetic tape by rotation, a rotation speed detection means for detecting the rotation speed of the tape drive means, and an output of the rotation speed detection means and an output of the tracking detection circuit. a control circuit for outputting a drive command signal to the means; when the synchronization detection circuit detects a synchronization signal, the period of the detected synchronization signal is measured by the counter; A magnetic tape playback device characterized in that a synchronization signal is detected by controlling the start time and end time of the counter using a signal output from continuous Lo detection.