JPH0544904Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a tracking control circuit suitable for use in a rotary head type digital audio tape recorder or the like.

[Prior art and its problems] In a rotating head type magnetic recording/reproducing device, it is necessary for the rotating head to accurately track the track formed during recording during playback, and various tracking control methods have been considered for this purpose. .

A common control method uses control signals found in 1/2-inch VTRs (video tape recorders). In this system, a control signal recorded on one end of the magnetic tape in the width direction is reproduced by a fixed head, and the rotation phase of the rotary head is controlled by this reproduction control signal. However, since this method requires a separate fixed head, a new control method that does not use a fixed head has been adopted for 8mm VTRs. This is a method in which four pilot signals with different frequencies are circulated for each track, frequency-multiplexed recording is performed, and tracking is controlled so that the levels of the pilot signals obtained as crosstalk components from both adjacent tracks are equal during playback. .

Further, recently, rotary head type digital audio tape recorders have been developed, and a tracking control method as shown in FIG. 4 has been considered for use therein.
That is, the reproduction signal from the rotary head H is amplified by the reproduction amplifier 1 and then applied to the bandpass filter 2. FIG. 5(a) shows the reproduction level from one end of the track to the other when the head reproduces one track, that is, the output signal of the reproduction amplifier 1. The above bandpass filter 2 is shown in FIG.
For example, the pilot signal of 130KHz as shown in (b)
It allows only the fp frequency component to pass through, and its output is given to the absolute value circuit 3. The pilot signal fp is recorded near both ends of the track, and is subjected to full-wave rectification in the absolute value circuit 3, and its absolute value is extracted as shown in FIG. 5c. FIG. 5c shows an enlarged view of one of the pilot signals fp, in which a and b are pilot signals of adjacent tracks, and c is a pilot signal of the own track. The pilot signal fp is then sent from the absolute value circuit 3 to the low-pass filter 4, where the envelope component is extracted as shown in FIG. 5d. In this case, the level of pilot signal a is V1,
The level of pilot signal b is V2.
The output signal of the low-pass filter 4 is
Addition circuit 6 via first sample hold circuit 5
It is also sent to the adder circuit 6 via the inverting amplifier 7. The first sample and hold circuit 5 samples and holds the input signal in synchronization with the sampling signal S/H-1 given from a control section (not shown), and outputs the hold signal to the addition circuit 6 as described above. do. This addition circuit 6 is
It detects the level difference between the output of the first sample-and-hold circuit 5 and the envelope signal sent from the low-pass filter 4 via the inverting amplifier 7, and its output is given to the second sample-and-hold circuit 8. This second sample and hold circuit 8 is
Sampling signal S/H- given from the control section
2, and outputs the hold signal as an error signal.

Therefore, during signal recording, the rotary head H forms diagonal recording tracks in the order of A, B, C, and D on the magnetic tape as shown in FIG. 6 without creating a guard band. A PCM audio signal is recorded in each of these tracks A to D, and two blocks of the pilot signal fp for tracking and one block of the synchronization signal fs are recorded in an area different from the recording area of the PCM audio signal. Ru. This pilot signal fp and synchronization signal
fs are different constant frequency signals,
As shown in FIG. 6, recording is performed between three consecutive tracks so that they do not overlap when viewed from a direction perpendicular to the head scanning direction. During reproduction, as shown in FIG. 7, a rotary head H having a gap width wider than the width of the recording track traces the track and reproduces the recorded signal. 7th
In the figure, the width of the track is T, and the width of the rotating head H is
1.5T, where x is the amount of positional deviation between the track center and the head center.

Now, the rotating head H is moving over the track B shown in FIG.
is tracing, the width of the rotary head H is wider than the track width, so that the recording signals of the adjacent tracks A and C are also reproduced together with the recording signal of the track B. When the rotating head H starts tracing the recording area of the synchronization signal fs, at this point the sampling signal S/H-1 is output from the control section, and is output from the low-pass filter 4 in the first sample and hold circuit 5. The envelope signal is sampled as shown in Figure 5e. At this time, since the pilot signal a of the adjacent track C is being reproduced as a crosstalk component, the first sample and hold circuit 5 samples and holds the level V1 of the pilot signal a of the adjacent track C. Further, the envelope signal output from the low-pass filter 4 is inverted by the inverting amplifier 7 as shown in FIG. Then, the rotating head H
starts reproducing the pilot signal b of the adjacent track A as a crosstalk component, the control section outputs the sampling signal S/H-2, and the second sample and hold circuit 8 receives the output of the adder circuit 6 (Fig. 5g). Sample and hold. At the time when this sampling signal S/H-2 is output, the output of the low-pass filter 4 is the pilot signal c of the adjacent track A.
outputs the difference V3 between the level V2 of the track C and the level V1 of the pilot signal a of the adjacent track C already held in the first sample hold circuit 5.
This level V3 (FIG. 5h) is sampled and held by the second sample and hold circuit 8. Therefore, the output of the second sample and hold circuit 8 has a value corresponding to the tracking deviation of the rotary head H, and this output is sent as a tracking error signal to a capstan servo circuit (not shown) to ensure that the level difference is zero. If the amount of tape transport is controlled so that the amount of tape movement is controlled, the rotary head H will trace the track accurately.

The conventional tracking control circuit shown in FIG. 4 is specifically constructed as shown in FIG. 8. This figure 8 shows the main part of figure 4, that is,
The portions of the low-pass filter 4, the first sample-and-hold circuit 5, the adder circuit 6, the inverting amplifier 7, and the second sample-and-hold circuit 8 are shown.
The low-pass filter 4 includes capacitors C1 to C3,
Consisting of resistors R1 to R5 and operational amplifier A1, the pilot signal sent from the absolute value circuit 3 in the previous stage is connected to the high frequency coupling capacitor C1 and resistors R3 and R.
4 to the + terminal of the operational amplifier A1. A reference voltage V0 divided by resistors R1 and R2 is applied to the connection point between the capacitor C1 and resistor R3, and a reference voltage V0 divided by resistors R5 and R6 is applied to the - terminal of operational amplifier A1. V0 is given. In addition, a low-pass filter is configured by a resistor R4, a capacitor C2, an operational amplifier A1, and a capacitor C3.
Through the high frequency negative feedback. The time constant of this low-pass filter is determined by capacitors C2 and C3 and resistor R4. And the above operational amplifier A1
The output becomes the output of the low pass filter 4, and is sent to the first sample hold circuit 5 via the capacitor C4.
and sent to the inverting amplifier 7.

The first sample and hold circuit 5 includes a switching element SW1, a capacitor C5, and a resistor R7, which are turned on and off by the sampling signal S/H-1.
The signal sent from the low-pass filter 4 via the capacitor C4 is sent to the operational amplifier A via the switching element SW1.
It is input to the + terminal of 2. This operational amplifier A2
is, the + terminal is grounded via capacitor C5, and -
A resistor R7 is connected between the terminal and the output terminal. The output of this operational amplifier A2 is then sent to the adder circuit 6 as the output of the first sample and hold circuit 5. On the other hand, the inverting amplifier 7 includes resistors R8 to R10 and an operational amplifier A3, and includes a low-pass filter 4.
A signal sent from the input terminal via the capacitor C4 is inputted to the - terminal of the operational amplifier A3 via the resistor R8. And to the + terminal of operational amplifier A3,
A divided reference voltage V0 is provided by resistors R9 and R10. The output of this operational amplifier A3 is then sent to the adder circuit 6 as the output of the inverting amplifier 7.

The adder circuit 6 includes resistors R11, R12 and an operational amplifier A4, and the outputs of the first sample-and-hold circuit 5 and the inverting amplifier 7 are wire-ORed and input to the - terminal of the operational amplifier A4.
In addition, a resistor R is connected to the + terminal of this operational amplifier A4.
11 and R12 provide a divided reference voltage V0. The output of this operational amplifier A4 is then sent to the second sample and hold circuit 8 as the output of the adder circuit 6. This second sample hold circuit 8 is turned on/off by the sampling signal S/H-2.
It consists of a switching element SW2 which operates in an off state, a capacitor C6, a resistor R13 and an operational amplifier A5, and the signal sent from the adder circuit 6 is inputted to the + terminal of the operational amplifier A5 via the switching element SW2. Also, this operational amplifier A5 is +
The terminal is grounded via a capacitor C6, and a resistor R13 is connected between the - terminal and the output end. The signal output from this operational amplifier A5 becomes the output signal of the second sample and hold circuit 8, that is, the error signal.

The tracking control operation described above is performed by the circuit shown in FIG. 8, but in the conventional tracking control circuit shown in FIG. 8, the V0 voltage is often used as the reference voltage of the operational amplifier. Therefore, there is a problem in that the variation in the reference DC offset voltage increases, and the error voltage of the circuit itself is superimposed on the error output signal. Further, variations in components also affect the error output signal, and there are also problems such as a large number of components.

[Purpose of the invention] The present invention was made in view of the above-mentioned circumstances, and it is an object of the present invention to provide a tracking control circuit that eliminates errors in the circuit itself and can extract pure voltage differences as an error output.

[Key points of the invention] This invention uses a clamp circuit to develop an operational amplifier.
This absorbs variations in DC offset voltage and allows accurate error voltage to be obtained.

[Embodiment of the invention] An embodiment of the invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the overall schematic structure of a tracking control circuit according to the present invention. In FIG. 1, the configuration of the rotary head H, reproducing amplifier 1, bandpass filter 2, absolute value circuit 3, and low-pass filter 4 is the same as the conventional circuit shown in FIG. Explanation will be omitted. Therefore, the envelope component for the pilot signal output from the low-pass filter 4 is transferred to the clamp circuit 11 via the capacitor C4.
sent to. As shown in detail in FIG. 2, this clamp circuit 11 includes a switching element SW that is turned on/off by a sampling signal S/H-1.
1. Resistors R21, R22, R23, operational amplifier A
10, and an envelope signal sent from the low-pass filter 4 via the capacitor C4 is input to the + terminal of the operational amplifier A10. Also,
A resistor R2 is connected to the + terminal of this operational amplifier A10.
A reference voltage V0 obtained by dividing the Vcc voltage by R22 is applied via the switching element SW1. Then, the output signal of the operational amplifier A10 is sent to the sample hold circuit 8 as the output signal of the clamp circuit 11. This sample and hold circuit 8 samples and holds the output signal of the clamp circuit 11 using the sampling signal S/H-2, and outputs it as an error signal.

Next, the operation of the above embodiment will be explained with reference to the timing chart of FIG. Now, suppose that the rotary head H is tracing the track B shown in FIG.
As shown in FIG. 3, first the pilot signal a of the adjacent track C, then the pilot signal b of the adjacent track A, and then the pilot signal c of the own track B are output. In this case, the signal level of the pilot signal a is set to V1, and the level of the pilot signal b is set to V1.
Set it to 2. When the pilot signal a of the track C is being output from the low-pass filter 4, the sampling signal S/H-1 shown in FIG. The output of operational amplifier A10 is clamped to the V0 level as shown in FIG. 3b. Therefore, the pilot signals b and c outputted from the operational amplifier A10 are as shown in FIG. 3b.
As shown in FIG. 2, the difference voltage from the clamp voltage V0 is outputted from the clamp circuit 11 as b' and c'.

Then, at the timing when the pilot signal b' is being outputted from the clamp circuit 11, the sampling signal S/H-2 shown in FIG.
b' is sampled and held in the sample and hold circuit 8 as shown in FIG. 3d. The level V3 of this sampled and held pilot signal b'
is exactly the voltage obtained by subtracting the level V1 of the pilot signal a from the level V2 of the pilot signal b (V3=
V2-V1). The output V3 of this operational amplifier A10 is used as an error signal by the sample and hold circuit 8.
is output from. The error signal output from the sample hold circuit 8 is sent to the capstan servo circuit, and the tape transport amount is controlled so that the error signal becomes zero. This allows the rotating head H to accurately trace the track.

[Effects of the invention] As detailed above, according to the invention, a clamp circuit is used to absorb variations in the DC offset voltage of the operational amplifier, and an accurate error voltage can be obtained. Since the error is limited to only within the circuit, errors in the circuit itself can be eliminated, and a pure voltage difference can be extracted as an error output. In addition, the number of parts can be reduced,
This allows the circuit configuration to be simplified.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a schematic configuration of a tracking control circuit according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing details of the main parts of the embodiment, and FIG. 3 shows the operation of the embodiment. 4 is a block diagram showing a schematic configuration of a conventional tracking control circuit. FIG. 5 is a timing chart for explaining the operation of FIG. 4. FIG. 6 is a pilot signal of a magnetic tape. FIG. 7 is a diagram showing the recording pattern, FIG. 7 is a diagram showing the relationship between the head and the recording track, and FIG. 8 is a circuit configuration diagram showing details of the main parts in FIG. 4. 1... Reproduction amplifier, 2... Band pass filter, 3... Absolute value circuit, 4... Low pass filter, 5, 8... Sample hold circuit, 6... Addition circuit, 7... Inverting amplifier, 11... Clamp circuit, A1-A5, A10... operational amplifier, SW
1, SW2...Switching element.

Claims (1)

[Scope of utility model registration request] The recording signal is obliquely recorded on the track by the rotating head without a guard band, and a pilot signal for tracking is recorded on a part of the track, and most of the recording positions of this pilot signal are on three consecutive lines. In a reproducing apparatus for reproducing magnetic tape recorded in such a way that the tracks do not overlap each other when viewed from the direction orthogonal to the head scanning direction, using a rotary head having a gap width wider than the recording track width, a bandpass filter for selecting the pilot signal from the signals; and envelope detection means for detecting an envelope component of the output of the bandpass filter.
A clamp circuit clamps the output of the envelope detection means to a reference voltage, a sample hold circuit samples and holds the output signal of the clamp circuit, and outputs it as a tracking error signal, and a rotating head detects the tracking error signal during playback of a predetermined track. The clamp circuit is operated when the pilot signal recording position on one of the adjacent tracks is reached, and the sample hold circuit is operated when the pilot signal recording position on the other adjacent track is reached. A tracking control circuit comprising a control means for controlling the tracking control circuit.