JPH0287355A - Tracking error detecting circuit - Google Patents

Abstract

PURPOSE:To average level fluctuation between plural bits of level difference information by sample holding the level difference information in turn corresponding to four sample-hold circuits respectively and adding up input signals of the individual sample-hold circuits. CONSTITUTION:A level difference signal S4 is inputted to the sample-hold (SH) circuits 10-13 respectively to be subjected to their sample-and-hold operations with timing of 'H' of AND signals S8-S11, and tracking error (TE) voltage signals S51-S54 made by updating sequentially their corresponding difference voltages respectively are outputted to an adder 14. An adding voltage signal S12 of adding up the TE voltage signals S51-S54 is outputted by the adder 14, whereas the voltage level of this adding voltage signal S12 indicates an average position of a head center position for the mean level of the difference voltages to be updated sequentially, changing in accordance with speed variations of a tape. By this method, the level differences can thus be averaged.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a tracking error detection circuit in a helical scan type magnetic recording/reproducing device.

In particular, the present invention relates to a tracking error detection circuit used for ATF control of a DAT.

(Prior Art) DAT tracking control is performed by ATF control, and the principle thereof will be explained using FIGS. 2 to 4.

FIG. 4(a) is a perspective view showing the relationship between the rotating drum 30 and the traveling path of the magnetic tape 31 of the DAT device. It rotates in the direction of arrow J at 2000 revolutions per minute. The magnetic tape 31 is moved by guide rollers 34, 35 and rotating drums 30, 35, 34, 35, and 35, which restrict movement in the width direction. and tilt pin 3
The tape is transported at a predetermined tape speed V in the direction of the arrow along the tape path formed by 2.33.

At this time, the angle of the magnetic tape 31 wrapped around the circumferential surface of the rotating drum 30 is approximately 90 degrees (however, the outer diameter of the rotating drum is 30φ).
Furthermore, this winding is set so that the angle formed between the tape running direction of the tape and the rotating shaft of the rotating drum becomes a reference angle θr.

FIG. 4(b) is a plan view showing the relative angle θ between the tape running direction and the rotating shaft of the rotating drum at the end of one wrap.

On the other hand, FIG. 2 is a partially enlarged view of the ATF area of the track pattern recorded on the magnetic tape.
It is formed at the point E in the same figure.

The section indicates the PCM area in which the PCM signal is recorded. This ATF area includes a block P in which the pilot signal S□ is recorded (indicated by diagonal lines), and blocks A and B in which sync signals s2 of different frequencies are recorded corresponding to the heads ha and hb (respectively indicated by horizontal lines). (indicated by a vertical line) and a block D in which an IBG signal is recorded.

During signal reproduction, heads ha and hb having a scanning width approximately 1.5 times the track width alternately scan adjacent tracks,
The signal recorded on the magnetic tape is reproduced, and FIG. 3 shows the state of the pilot signal S□ reproduced when the head hb scans the lower track 4. At this time, the head hb is connected to each block P5□, P3 of the ATF area E1.
1, P41, and each block P4 of ATF area E2 section
2, P, 2, P, 2 are sequentially scanned, and the pilot signals s1 recorded in these blocks are sequentially reproduced.

FIG. 3(a) shows the reproduction level waveform of the pilot signal S1 when the head hb normally scans the lower track 4. FIG. At this time, in the ATF area E1 section, the reproduction level of each pilot signal S□ of block P3 of the left adjacent track T, and block P, 1 of the right adjacent track TS becomes the same level, and similarly, the reproduction level of each pilot signal S□ becomes the same level. Also, the playback levels of blocks P, 2 and Pl are the same. This means that in each ATF area E2, the width of the head hb scanning the track T is equal to the width of the scanning of the track T, and the width center of the track T4 and the head hb
This shows that the width centers of b are aligned.

Figure (b) shows the playback level waveform when scanning is performed with the head hb shifted to the right track T5, but at this time, the width of the scan of the head hb on the track T5 increases, and conversely, the width of the scan of the track T5 is increased, , the scanning width decreases. Therefore, each track T5. The reproduction level of the pilot signal S recorded in T also increases and decreases. Furthermore, in the same figure (c), the head hb is on the left track T,
The reproduction waveform is shown when scanning is performed with the track shifted to the side, and at this time, the reproduction level of track T increases.

The playback level of track T4 decreases.

As described above, when the head h causes a track deviation, the reproduction level of the pilot signal S reproduced on the adjacent track increases or decreases depending on the direction and magnitude of the deviation.

The ATF control sequentially detects the level difference of the pilot signals S□ reproduced in the blocks P of these adjacent tracks,
The magnetic tape speed V is set so that these playback levels match.
This controls the rotational speed of the capstan, which determines the rotation speed of the capstan.

Figure 7 shows an AT used for conventional general ATF control.
A block diagram of the F control system is shown.

In the figure, the reproduced signal So amplified by the RF amplifier 17 is
a low-pass filter 18 that detects the pilot signal S□;
and a bandpass filter 19 that detects the sync signal s2.
are applied to each. The envelope detection circuit 1 inputs a pilot signal S□ with a reproduction frequency of 130.67 kHz, and outputs a level voltage signal s3 corresponding to this level to a subtracter 2 and a sample hold circuit (hereinafter referred to as an SH circuit) 3. The control circuit 4 inputs the sync signal s2 manually, and when it confirms that this frequency corresponds to the scanning head, outputs a pulse-like control signal S7 at a predetermined timing. For example, in FIG. 2, when head hb scans track T4, block B41
When the sync signal s2 is detected and it is confirmed that this frequency corresponds to the head hb, the control signal sG is output at the timing t shown in FIG. 3, and the control signal s7 is output at the timing t2. . S H circuit 3.20
holds each input signal using these control signals.

Therefore, the SH circuit 3 holds the level voltage of the pilot signal detected from the block P,1 of the right adjacent track T, and the SH circuit 20 detects this level voltage from the block P,1 of the left adjacent track T3. The level difference signal s4 with respect to the level voltage of the pilot signal is held. These hold operations are performed every time each head ha, hb detects the corresponding sync signal s2, so S
The hold signal output from the H circuit 20 is a tracking error voltage signal (hereinafter referred to as TE) indicating a tracking error.
(referred to as a voltage signal) s.

This TE voltage signal s5 is averaged by the smoothing circuit 21 to become an average voltage signal s13, but this average voltage signal 311
is input to a capstan motor drive circuit 15 that drives a capstan motor 16 which is tape transport means. This capstan motor drive circuit 15 rotationally drives the capstan motor 16 so that the input average voltage signal SL3 becomes 0 level, and the tape speed ■ is controlled by negative feedback based on the average voltage signal 513 by the ATF control system. The configuration is as follows.

(Problem to be Solved by the Invention) When the scanning position of the head hb that scans the ATF area E1 moves between the tracks, the sync signal 82' and level corresponding to the head hb are detected. The voltage signal S,′ (as described later, the synchronized sink signal s
2. Since the meaning is somewhat different from that of the level voltage signal s3, ' is added to distinguish it). The change trajectory of each detection level is shown in Figure 5 (a
) and (b).

First, the level change of the sync signal 52' shown in FIG. 5(a) will be explained with reference to FIG. 2.

The level vs4 of the sync signal 52' detected in block B41 is at the maximum level when the center of the head hb scans the center of the track T4, and is at a position d shifted by 174 tracks in the direction (+ direction) of the right adjacent track T. , but as the head hb shifts further in the same direction, the width by which the head hb crosses the block B4 decreases, so the level Vs4 decreases linearly, and eventually the level Vs4 is further 17
When the position d4 is shifted by 41-rack, the level becomes 0.

On the other hand, the level vsI of the sync signal s2' detected in the block B5 of the 1-rack T6 indicates that the head hb is at the position d.
When it exceeds , it increases linearly and reaches the maximum level at position [d, , , and thereafter, similar level changes are repeated as the head hb moves in the ten directions.

Also, head hb is on the left adjacent track T, direction (one direction)
It is clear that the sync signal 52' is detected in the same way even when the signal deviates from the sync signal 52', and changes as shown in the figure. Note that the level Vs2 is the level of the sync signal 82' detected in the block B21 of the track T2.

Next, FIG. 5(b) shows the level change of the level voltage No. 43 53' taken in according to the above-mentioned movement of the head hb.
This will be explained with reference to FIG.

At this time, the control circuit 4 performs control to detect the level of the pilot signal of the adjacent trunk at a predetermined timing shown in FIG. Signal S G + S
Output 'l. Therefore, when the head hb is within the range w2, from the time it passes the block B2□ where the sync signal is detected, and when the head hb is within the range w4, from the time when it passes the block B4□, the head hb is further within the range wG. When the block P is scanned by the head hb, the levels of the voltage signals , / of the block P scanned by the head hb are taken in at predetermined timings t and t2 from the time when the head hb passes through the block B61.

Incidentally, when the control circuit 4 detects the -H sync signal, it outputs a control signal sGs s based on the -H sync signal.

Since the next sync signal is not detected, the sync signal indicated by the dotted line in FIG. 5(a) is not detected.

Therefore, when the scanning center of head hb is at the center of track T4, the level voltage signal taken in at timing t, the level VPI of I (shown by a solid line) and timing t2
The level voltage signal taken in by , the level VP2 of 7 (
(shown by dotted lines) are the detection levels of the pilot signals detected by the head hb in blocks P, 1, and Pl, respectively, and these are at the same level as shown in FIG. 5(b).

Next, when the scanning position of the head hb shifts in the ten directions, the level V
PI increases linearly and level V P 2 decreases linearly. Then, when the position d1 is reached, the level V P 2 becomes 0.
Then, the level VP□ becomes maximum at position d3.

Further, after passing d3, head hb starts detecting the pilot signal of block PG1 at timing t2, so
The level V P z increases linearly again.

Then, when the detection level of the sync signal of block B6□ exceeds Mdt to the extent that it becomes larger than the threshold value Vf, it becomes the above-mentioned range w6, and the level voltage of block P at predetermined timings t and t2 after passing through block B6□. Import the level of the signal , /.

Therefore, the level V P x is in the 0 state from this position d7 to the position dG where the pilot signal of the block P7□ is detected, while the level V P 2 becomes the detection level of the pilot signal of the block P5□ and reaches the maximum until the position d4. It maintains a certain level, and once it exceeds it, it decreases linearly. Eventually, when the scanning center of the head hb reaches the center of the track Tt,
Levels VP and VP2 are again at the same level, but the special number level is the detection level of the pilot signal detected by the head hb in blocks P5 and P7□, respectively. It is clear that even when the head hb shifts in one direction, the levels VPt and VPz of the level voltage signal 53' are detected in the same way and change as shown in the figure.

Next, in the ATF area E2 part, the change locus of the level voltage signal 53' detected when the scanning position of the head hb moves between each track is shown in FIG.
), (C), and FIG. 2.

At this time, the change locus of the sync signal 82' that changes in accordance with the scanning position of the head hb is exactly the same as in the case of the ATF area E2, but the change locus of the level voltage signal s,' is as shown in Fig. 5 (c ) are slightly different as shown in . That is, head h
When the scanning center of b is shifted from the center of track T4 in the ten directions, each level V P x -V p2 changes up to position d3 in the same way as in the case of ATF area E. However, even if the level [d] is exceeded, since there is no block P to be detected at timing t2, the level VPz does not increase as in the ATF area E1, but maintains the O state.

On the other hand, for level Vp engineering, the sync signal detection block is 842.
From position d7, which changes from to 86□, to position d4,
This is the detection level of the pilot signal of block P4□,
As shown in the figure, during this time, as the head hb moves in ten directions, it decreases linearly.

Above, we have explained the level change locus of the pilot signal detected in ATF area E2 when the scanning position of the head hb moves between tracks, but the pilot signal changes in the same way when the head ha moves between tracks. . However, in this case, in the correspondence between the scanning position of the head ha and the level change locus, the track position is shifted by one track, as shown in parentheses in FIG. Furthermore, ATF
The level change locus of the pilot signal in the area E1 is shown in FIG. 4(c), and the level change locus of the pilot signal in the ATF area E2 is the waveform shown in FIG. 3(b). In other words, the relationship is opposite to that for the head hb, but this means that the arrangement n relationship between the sync signal block B and the pilot signal block P corresponding to the head hb in the ATF area E1 is
This is because it matches the arrangement relationship between block A and block P of the sync signal corresponding to head ha in ATF area E2.

TE voltage signal s5 output from the SH circuit 2o in FIG.
is the difference voltage (V
pl-Vpz). Figure 5(d) shows the trajectory of change drawn from the solid line in Figure 5(b) by a dotted line.

In addition, FIG. 5(e) shows a change locus drawn by a dotted line from the solid line in FIG. 4(c). Therefore, when the scanning position of each head ha, hb moves between tracks, the difference voltage Va obtained by the head ha detecting the corresponding sync signal of the ATF area E and the head hb corresponds to the corresponding sync signal of the ATF area E2. The difference voltage vb2 obtained by detecting the sink signal is shown in the same figure (e).
The head hb moves on the change trajectory of ATF area E1.
The difference voltage Vb□ obtained by detecting the corresponding sink signal of
The difference voltage va2 obtained when the head ha detects the corresponding sync signal in the ATF area E2 moves on the change locus shown in FIG.

Now, the rotating drum with the heads ha and hb placed at the same height position (position where the movement trajectory is the same) as during recording is set so that the angle between its axis and the tape running direction is the same reference angle or
When reproducing an ATF signal from a tape that is rotated at 2000 revolutions per minute and transported at a tape speed vp that is approximately the same as that during recording, each head h, which scans the ATF areas E□ and E2,
The scanning positions a and hb have the same positional relationship with respect to the center of the corresponding track Tr. In this case, the differential voltage Vb on each change locus in FIGS. 5(d) and (e)
The differential voltage Va, Va2, and the differential voltage Va, Vb2 are on the same axis and move.

On the other hand, if there is a height difference between the heads ha and hb, the positional relationship that the scanning position of each head makes with respect to the center of the track Tr corresponding to each of the ATF areas E1 will vary depending on the height difference. Error wh occurs, and ATF area E
2, the same amount of height error wh occurs. These errors wh are calculated by the difference voltage V a in FIGS. 5(d) and (e).
1 and vb□.

and can be expressed as an error in the movement positions of Va2 and vb2.

Note that the figure shows a case where the head hb is lower than ha (because the position corresponding to the lower head is shifted in one direction).

In addition, if the angle between the axis of the rotating drum and the tape running direction has an inclination error with respect to the reference angle Or during recording, the scanning direction of each head will not be parallel to the recorded track direction, so the head ha The scanning position is ATF area E.
The positional relationship between the ATF area E2 and the corresponding track center Tr and the positional relationship between the ATF area E2 and the corresponding track center Tr cause a tilt error ws depending on the tilt.

Furthermore, the same amount of tilt error ws occurs in the head hb. These errors ws can be expressed as errors in the movement positions of the differential voltages Va and Va, and between vbl and vb2 in FIGS. 5(d) and (e).

The figure shows a case where the angle relationship shown in FIG. 4(b) is tilted by -Δθ with respect to the recording angle or. In this case, the scanning direction of the head shown in FIG. 2 shifts clockwise, resulting in the relationships shown in FIGS. 5(d) and 5(e).

As described above, the errors wh and ws in the moving position inevitably occur when the height of the head and the inclination of the rotating drum differ during recording and reproduction.

In this case, when the tape speed fluctuates and the relative positional relationship between each head and the trunk shifts, the difference voltages Va□, Va2, vb, and TE voltage signal S output from the SH circuit 2o,
and vb, while maintaining the errors Wh and ws,
It moves along the change locus shown in FIGS. 5(d) and 5(e).

For example, the relationship between the tape speed Vr during recording and the tape speed Vp during playback is Vr(Vp, in the ten direction, and vice versa,
r) When V p, it moves in one direction.

As mentioned above, ATF control generally adjusts the tape speed V so that the average level of this TE voltage signal s5 becomes O level.
Since this is controlled by negative feedback, the level of each differential voltage is usually stabilized at the positions shown in Figures 5(d) and (e).

As described above, the voltage of the TE voltage signal SS output from the SH circuit 20 is such that the voltage of the TE voltage signal SS output from the SH circuit 20 is
, E2 each time the differential voltage shown in FIG.
b 2, Va,, Va2, vb□, vb2, Va engineering...
・Updated in order. Therefore, if there is an error in the height of the head or inclination of the rotating drum during recording and playback,
The level change of each differential voltage increases approximately in proportion to this magnitude, and this level change always appears in the TE voltage signal S.

Therefore, in order to obtain the information necessary for ATF control, that is, the average voltage signal "13" obtained by removing level change components caused by height errors and tilt errors from this TE voltage signal s5, it is necessary to operate each head based on tape speed fluctuations. This has the disadvantage of requiring a smoothing circuit that also slows down the response to positional movement information.

The present invention eliminates the need for smoothing circuits that cause these drawbacks.

(Means for solving the problem) Using a helical scan method, first and second heads arranged on the circumferential surface of a rotating drum scan first and second areas near both ends of each track of a magnetic tape. This is a tracking error detection circuit for reproducing a pilot signal recorded in a 3D device and performing tracking control during reproduction based on the reproduced pilot signal.

a pair of pilot signals of other tracks that the first head detects at different first and second timings in synchronization with the detection of a sync signal recorded on a corresponding first track in the first area; a first sample-and-hold circuit that sequentially samples and holds level difference information;

a pair of pilot signals of other tracks that the first head detects at the first and second timings in synchronization with the detection of the sync signal recorded on the corresponding first track in the second area; a second sample-and-hold circuit that sequentially samples and holds level difference information;

a pair of pilot signals of other tracks that the second head detects at the first and second timings in synchronization with the detection of the sync signal recorded on the corresponding second track in the first area; a third sample and hold circuit that sequentially samples and holds level difference information of the second head; and a third sample and hold circuit that sequentially samples and holds level difference information of the second head; A fourth sample and hold circuit that sequentially samples and holds the level difference information of a pair of pilot signals of other tracks detected at the first and second timings, and the output signals of each of the first to fourth sample and hold circuits are added together. (Operation) The four sample and hold circuits sequentially sample and hold the corresponding level difference information, and by adding the output signals of each sample and hold circuit, the difference between the pair of heads during recording and during playback is It is possible to average out level fluctuations between each level difference information that inevitably occur due to height-related errors and inclination errors of the rotating drum during reproduction with respect to recording.

(Embodiment) Fig. 1 shows a configuration diagram of an embodiment of the present invention, and its operation will be explained with reference to the timing chart of Fig. 6. Parts common to Fig. 7 are given the same reference numerals. Therefore, detailed explanation thereof will be omitted.

In the figure, numeral 5 is a quaternary counter, and when a control signal SG is input, the states of output terminals 5□ to 54 connected to one input terminal of AND circuits 6 to 9 are sequentially changed as shown in Fig. 6. The state is set to “H”. AND circuits 6 to 9 input a control signal s7 that appears in synchronization with control signal s6 to the other input terminals, and use AND signals 86 to S shown in FIG. 6 as control signals for SH circuits 10 to 13, respectively. Output to input terminal.

Each of the SH circuits 10 to 13 inputs the level difference signal s4 and samples and holds it at the "HI+" timing of the AND signal signal -S.Therefore, each SH circuit receives the TE voltage that is successively updated with the corresponding difference voltage. Signal s51~
ss4 is output to the adder 14.

The voltages of these TE voltage signals 851 to sS4 are shown in FIG. 5(d).
Figures 6(k) to 6(k) show how the voltages are sequentially updated based on each differential voltage that is stable in the level state shown in (e).
m). In this case, the difference voltage Val, Va 2, of the TE voltage signals output by each SH circuit 10 to 13,
Although vb, , vb2 do not change, when the positions of the differential voltages shown in FIG. It is clear that changes.

Further, the adder 14 outputs the added voltage signal S□2 obtained by adding the TE voltage signals s5□ to ss4, but the voltage level of this added voltage signal s1□ is the difference voltage V a that is updated sequentially.
, , Va2, vb, , the average level of vb2, that is, the ATF area E1 scanned by each head ha, hb, respectively.
It shows the average position of the head center position relative to the track center of E2, and changes in response to tape speed fluctuations.

The capstan motor drive circuit 15 and the capstan motor 16, which operate based on the added voltage signal 512, are the same as those in FIG. 7, so a description thereof will be omitted.

In the above embodiment, a smoothing circuit was not provided after the adder 14, but a smoothing circuit was provided as necessary for the purpose of achieving desired characteristics of ATF control (effect of the invention). When playing back DAT tapes, there may be a height error between the heads during recording and playback.
If there is an error in the inclination of the rotating drum, each differential voltage of the <TE voltage signal as described above will generate a level difference based on these errors, but according to the present invention, a smoothing circuit that slows down the control response speed, Alternatively, this level difference is averaged out without using a smoothing circuit with steep frequency characteristics that could lead to instability, resulting in a fast response speed and stable ATF.
This allows for control.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, FIGS. 2 to 5 are diagrams for explaining the present invention, FIG. 6 is a timing chart diagram showing signal waveforms of each part of FIG. 1, and FIG. FIG. 7 is a configuration diagram of an ATF control system used for conventional general ATF control. 1...Envelope detection circuit, 2...Subtractor, 3.
20.10-13...Sample hold circuit, 4...
・Route, 14...Adder, 15...Capstan motor drive circuit, 16...Capstan motor, 17...R
F amplifier, 18...Low pass filter, 19...Band pass filter, 21...Smoothing circuit.

Claims (1)

[Claims] By a helical scan method, recording is performed in first and second areas near both ends of each track of a magnetic tape using first and second heads disposed on the circumferential surface of a rotating drum. A tracking error detection circuit for reproducing a pilot signal and performing tracking control during reproduction based on the reproduced pilot signal, wherein the first head detects a corresponding first track in the first area. a first sample and hold circuit that sequentially samples and holds level difference information between a pair of pilot signals of other tracks detected at different first and second timings in synchronization with the detection of a sync signal recorded on the first sample and hold circuit; the level of a pair of pilot signals of another track that one head detects in synchronization with the detection of a sync signal recorded on a corresponding first track in the second area and at the first and second timings; a second sample and hold circuit that sequentially samples and holds difference information; the second head is synchronized with detection of a sync signal recorded on a corresponding second track in the first area; and a third sample and hold circuit that sequentially samples and holds level difference information of a pair of pilot signals of other tracks detected at a second timing; a fourth sample and hold circuit that sequentially samples and holds level difference information between a pair of pilot signals of other tracks that is synchronized with the detection of a sync signal recorded on a track and detected at the first and second timings; A tracking error detection circuit comprising an addition circuit that adds output signals of each of the first to fourth sample and hold circuits.