JPH0298855A - Tracking control circuit - Google Patents

Abstract

PURPOSE:To perform accurate tracking control by releasing the time constant circuit of an envelope detecting circuit from forcible discharging operation when a pilot signal of an adjacent track is sampled and held, and placing the time constant circuit in the forcible discharging operation at other times. CONSTITUTION:When the pilot signal of the adjacent track is sampled and held, the time constant circuit of the envelope detecting circuit 14 is released from the forcible discharging operation and at other times, the time constant circuit is placed in the forcible discharging operation. Therefore, even when the time constant of the time constant circuit is set large, the time constant circuit can be discharged in a short time after envelope detecting operation. Consequently, the time constant of the envelope detecting circuit 14 can be set large and the ripple of an envelope detection output PENV is reduced to improve the tracking of envelope variation. Consequently, the accurate tracking control is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a tracking control circuit in a magnetic recording/reproducing device such as a rotary head type digital audio tape recorder (DAT).

[Prior art and problems to be solved] Conventionally, in a rotary head type magnetic recording/reproducing device, a pilot signal and a synchronizing signal are recorded in a predetermined area of each track, and a gap width wider than the width of the recording track is created during reproduction. Tracks are traced using a rotary head, and tracking control is performed so that the levels of pilot signals obtained as crosstalk components from both adjacent tracks are equal. When comparing the levels of the pilot signals of both adjacent tracks, the detected pilot signals are rectified, envelope-detected by an envelope detection circuit, and then sampled and held at a predetermined timing for level comparison.

In the envelope detection circuit mentioned above, a time constant circuit is used to detect the envelope of the pilot signal.
If the time constant is made small to improve followability of envelope changes, large ripples will occur in the envelope waveform relative to the pilot signal, and conversely, if the time constant is made large to reduce the ripples, the charging time will be reduced by 7t [because it takes time to discharge the load]. However, there was a problem in that it became impossible to follow envelope changes and the reliability of the tracking error signal could no longer be obtained.

This invention was made in view of the above circumstances, and even if the ripple component is reduced by increasing the time constant of the envelope detection circuit, it is possible to maintain good followability of envelope changes, resulting in highly accurate tracking control. An object of the present invention is to provide a tracking control circuit that can perform the following.

[Means and effects for solving the problem] The present invention provides a forced discharge operation of a time constant circuit in an envelope detection circuit when sample-holding a pilot signal of an adjacent track in a tracking control circuit of a rotary head type magnetic recording/reproducing device. is released, and otherwise the time constant circuit is forced to perform a discharging operation.

In the envelope detection circuit, the charge in the time constant circuit is forcibly discharged at all times, and only during sample hold, the forced discharge operation is canceled and envelope detection is performed on the pilot signal. Therefore, even if the time constant of the time constant circuit in the envelope detection circuit is set to a large value in order to reduce ripples in the envelope signal, envelope changes can be quickly followed.

[Embodiments of the invention] Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

In FIG. 1, reference numeral 11 denotes an input terminal, into which a reproduced signal PBS from a rotary head (not shown) is input. The reproduced signal PBS input to the input terminal 11 is input to an envelope detection circuit 14 via a pilot signal equalizer 12 and a rectifier circuit 13. Furthermore, the reproduced signal PBS inputted to the input terminal 11 is inputted to the synchronization signal detection circuit IG via the synchronization signal equalizer 5. The synchronization signal detection circuit I6 detects the synchronization signal ASY from the output signal of the synchronization signal equalizer 15 and inputs it to the sampling timing generation circuit 17. This sampling timing generation circuit 17 outputs the sampling signal T1 at the time when the synchronization signal ASY is detected (when reproducing the pilot signal for the previous track), and also outputs the sampling signal T1 after a time period of, for example, two blocks has elapsed from the time of detection (when the next track is reproduced). When reproducing a pilot signal for a track), a sampling signal T2 is output, and a timing signal TR, which is an OR signal of the sampling signals TI and T2, is output. The timing signal TR output from the sampling timing generation circuit 17 is sent to the envelope detection circuit 14.

This envelope detection circuit 14 is equipped with a time constant circuit as will be described in detail later, and performs a charging operation according to an input signal when the timing signal TR is at a high level, and forcibly performs a discharging operation when the timing signal TR is at a low level. It is supposed to be done. The detected output PENV of the envelope detection circuit 14 is sent to a sample hold circuit 18 and a differential amplifier 19. The sample and hold circuit 18 outputs the detection output PI? of the envelope detection circuit 14? Nv is sampled and held in synchronization with the fall of the sampling signal TI output from the sampling timing generation circuit 17, and output to the differential amplifier f9. This differential amplifier 19 amplifies the difference signal between the signal held in the sample and hold circuit 18 and the detection output PENV outputted from the envelope detection circuit 14 and outputs it to the sample and hold circuit 20. This sample hold circuit 20 converts the output signal of the differential amplifier 19 into a sampling signal T output from the sampling timing generation circuit 17.
The tracking error signal TE is sampled and held in synchronization with the falling edge of signal TE, and is output to a capstan servo circuit (not shown) as a tracking error signal TE.

The envelope detection circuit 14 is constructed as shown in FIG. In the figure, Q1 is an NPN type transistor, and the reproduced signal PBP sent from the rectifier circuit [3 is inputted to the base of the transistor Q1 from the input terminal 24. This transistor Q1 has a collector connected to the V cell source, an emitter connected to the output terminal 21, and
Grounded via capacitor C. This capacitor C constitutes a time constant circuit together with the internal resistance of the transistor Ql, and is set to a large value so that the ripple in the envelope can be sufficiently reduced. Further, a discharge circuit 22 for discharging the charge stored in the capacitor C is connected to the emitter of the transistor Q1.

This discharge circuit 22 includes, for example, an NPN type transistor Q.
2. Q3. It is composed mainly of Q4, and the transistor Q
The collector of Q2 is connected to the emitter of transistor Ql. Further, the emitter of the transistor Q2 is grounded via the resistor R1, and the base is connected to the Vcct source via the resistor R2 along with the base and collector of the transistor Q3. Further, the emitter and terminal of the transistor Q3 are grounded via the resistor R3, and the collector is connected to the collector of the transistor Q4. This transistor Q4 has an emitter that is grounded, a base that is grounded via a resistor R4, and is also connected to the timing signal input terminal 23 via a resistor R5. A timing signal TR sent from the sampling timing generation circuit 17 is input to this input terminal 23 .

The envelope detection circuit 14 configured as described above is
When the timing signal TR is at a low level, the transistor Q4 is turned off, and the transistors Q2 and Q3 form a current mirror circuit. As a result, a current I2 equal to the collector current %EI3 of the transistor Q3 flows to the emitter of the transistor Q1 and to the collector of the transistor Q2, causing the transistor Ql to operate as a normal emitter follower and forcing the charge charged in the capacitor C by the transistor Q2. Discharged. Furthermore, when the timing signal TR is at a high level, the transistor Q4 is turned on and the resistor R
The current I3 flowing through the transistor Q2 flows through the transistor Q4, and the current I2 of the transistor Q2 becomes zero. Therefore, the transistor Q1 charges the capacitor C until it reaches the peak of the input signal, and then turns off to hold the terminal voltage of the capacitor C at its peak.

Next, the overall operation of the above embodiment will be explained with reference to the timing chart of FIG. Now, if the rotary head H is tracing a track t on the tape as shown in FIG. ,
The recorded signal at t+i will also be reproduced. Note that FIG. 3 shows a state in which the rotary head H is closer to the adjacent track t-1. First, when the rotary head H starts tracing the recording area of the synchronization signal SY, the synchronization signal SY
is reproduced and sent to the synchronization signal detection circuit 1[i via the synchronization signal equalizer I5, and the detection signal ASY shown in FIG. 3 is output from the synchronization signal detection circuit 16. When the synchronization signal detection circuit 16 outputs the detection signal ASY, the sampling timing generation circuit 17 outputs the timing signal TR together with the sampling signal T1 shown in FIG. At this time, the pilot signal p ti of the adjacent track t-1
is reproduced as a crosstalk component and input to the pilot signal equalizer 12. Therefore, from this pilot signal equalizer 12, the output signal P shown in FIG.
The frequency component of the pilot signal PL-1 is extracted as LT, and the rectified output PBP is inputted to the envelope detection circuit 14 via the rectifier circuit 13. The envelope detection circuit 14 includes a sampling timing generation circuit 17
When timing signal TR (high level) is output from , during that time, transistor Q4 in FIG. 2 is turned on and transistor Q2.03 is turned off. Transistor Q2
is turned off, the forced discharge operation of the capacitor C is released, and the pilot signal p input at that time is
The peak of the crosstalk component of ti is held in capacitor C. This peak-held envelope signal P[ENV is sampled and held by the sample-and-hold circuit 18 at the falling edge of the timing signal T1. Therefore, the sample and hold circuit 18 has the adjacent track t-1 which is being reproduced as a crosstalk component.
The level of the pilot signal p ti is sampled and held. Also, at this time, the timing signal TR returns to low level, and the envelope detection circuit 14 turns off the transistor Q4 and the transistors Q2. Q3 is turned on, and the charge stored in the capacitor C is forcibly discharged through the transistor Q2 and the resistor R2, in preparation for the next detection operation.

Then, when the rotary head H starts reproducing the pilot signal p tit of the adjacent track tel as a crosstalk component, the sampling timing generating circuit 17 outputs the sampling signal T2 and the timing signal TR shown in FIG. By outputting this timing signal TR, the forced discharge operation for the time constant circuit of the envelope detection circuit 14 is canceled as described above, and the pilot signal p t of the adjacent track T+1 is supplied to the capacitor C.
The reproduction level value of it is charged by transistor Ql.

Therefore, from the differential amplifier 19, this adjacent track T+1
The difference between the level value of the pilot signal PL+1 and the level value of the adjacent track [-1 pilot signal pt-t already held in the sample and hold circuit 18 is output, and this level difference is used as the level difference of the T2 of the sampling signal. The falling signal is sampled and held by the sample and hold circuit 20. Also, at this time, the timing signal TR returns to low level, the transistor Q4 of the envelope detection circuit 14 is turned off, and the transistors Q2. Q3 is turned on, and the capacitor C is forcibly discharged to prepare for the next detection operation. As described above, the sample and hold circuit 20 holds a value corresponding to the track deviation of the rotary head H, and its output is sent as a tracking error signal TE to a capstan servo circuit (not shown), and the level difference is By controlling the tape transport amount so that the amount is zero, the rotary head H can accurately trace the track. For example, as shown in FIG. 3, when the rotating head H is closer to the adjacent track t-1, the crosstalk component of the pilot signal pt-t is larger than the crosstalk component of the pilot signal t-+1. Therefore, the sample hold circuit 20 has “+
" signal is sampled and held, and this "+" signal is sent to the capstan servo circuit as a tracking error signal TE, and the tape transport amount is controlled so that the rotary head H returns to the adjacent track t+1 side.

As mentioned above, when sampling and holding the pilot signal of the adjacent track, the forced discharge operation of the time constant circuit in the envelope detection circuit 14 is canceled, and at other times, the time constant circuit is forced to perform the discharge operation. Even if the time constant of the constant circuit is set to a large value, the first charge of the time constant circuit can be discharged in a short time after the envelope detection operation.

Therefore, it is possible to set the time constant of the envelope detection circuit 14 to a large value, and the envelope detection output P E
It is possible to reduce ripples in NV and improve followability of envelope changes.

[Effects of the Invention] As described in detail above, according to the present invention, in a tracking control circuit of a rotary head type magnetic recording/reproducing device, when sample-holding a pilot signal of an adjacent track, the time constant circuit in an envelope detection circuit is Since the forced discharge operation is canceled and the above-mentioned time constant circuit is forced to discharge at other times, even if the time constant of the time constant circuit is set to a large value, it is possible to maintain good followability of envelope changes. It is possible to reliably reduce ripples in the envelope signal.

[Brief explanation of the drawing]

1 to 3 show one embodiment of the present invention, in which FIG. 1 is a block diagram showing the overall schematic configuration, FIG. 2 is a circuit configuration diagram showing details of the envelope detection circuit, and FIG. 1 is a timing chart showing a pilot signal recording pattern of a magnetic tape and an operation timing when reproducing this pilot signal. 1! ... input terminal, 12 ... pilot signal equalizer, 13 ... rectifier circuit, 14 ... envelope detection circuit, 15 ... synchronization signal equalizer, 16 ... synchronization signal detection circuit, 17 ... Sampling timing generation circuit, 18... Sample hold circuit, 19... Differential amplifier, 2011. Sample and hold circuit.

Claims (1)

[Claims] In a tracking control circuit of a rotary head type magnetic recording/reproducing device, a detection means for detecting a synchronization signal recorded in a reproduction track, a sampling signal generation means for generating a sampling signal based on the synchronization signal from the detection means, and the above-mentioned first and second adjacent on both sides of the playback track;
an envelope detection means equipped with a time constant circuit for detecting a pilot signal of the truck; and a sampling signal output from the sampling signal generation means to sample and hold the output signal of the envelope detection means to detect the pilot signal of the first and second truck. error signal output means for outputting a tracking error signal according to a level difference between the envelopes of the tracks; and a time constant circuit of the envelope detection means forcibly discharged after the pilot signal of the first track is detected by the envelope detection means. A tracking control circuit characterized in that the tracking control circuit comprises a control means for causing the time constant circuit to release the forced discharge operation of the time constant circuit when starting a next pilot signal detection operation for the second track.