JPH04258807A - Tracking error detector - Google Patents

Abstract

PURPOSE:To enable characteristics equivalent to those obtained when the band for a BPF is narrowed and to improve the S/N of a pilot frequency for tracking error detection by multiplying a regenerative signal by a signal with same frequency as the pilot frequency and narrowing the band for the LPF. CONSTITUTION:Two signals whose frequencies are the same as the pilot frequency and whose phases are different from each other by 90 deg. are generated in a pilot frequency generation circuit 1, and multiplied with the regenerative signal, respectively, in multiplication circuits 3 and 4. Unnecessary components are removed in LPFs 7 and 8, and the obtained signals are squared, respectively, in square circuits 11 and 12, added, and the square root of the sum is taken in a square root circuit 17. On the other hand, two signals whose frequencies are the same as the frequency three times the pilot frequency and whose phases are different from each other by 90 deg. are generated in a pilot frequency oscillation circuit 2, and they are processed similarlly. Also the difference between them are obtained in a subtraction circuit 19 from the outputs of the square root circuits 17 and 18 and the tracking error is detected. Thus, the characteristics equivalent to those obtained when the band for the BPF is narrowed or above can be obtained and the S/N can be improved.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention records and reproduces a pilot signal for tracking error detection on a magnetic recording medium together with a main signal, and upon reproduction, the reproduction output level of the pilot reproduced as a crosstalk signal from both adjacent tracks. This invention relates to a tracking error detection device that detects a tracking error by comparing the following.

0002

[Prior Art] Conventionally, in a tracking error detection device used for 8mm video, four low frequency pilots with different frequencies are set, and one low frequency pilot is frequency-multiplexed onto a video signal for each video track and recorded. do. During playback, two low frequency pilots recorded on both adjacent video tracks are detected as crosstalk from adjacent video tracks, and tracking errors are detected by comparing the playback output levels of the two low frequency pilots. (For example, Author: Akira Hirota, About 8mm Video (1), Television Society Technical Report VR
61-1).

FIG. 5 is a block diagram showing the configuration of a tracking error detection device used for conventional 8 mm video.

In FIG. 5, a signal recorded on a magnetic recording medium 21 is reproduced by a magnetic head 22 and an amplifier circuit 23. The reproduced signal contains pilots from both adjacent tracks, and in the four-frequency generator circuit,
Using the clock output from the color APC of the 8mm video and the PG (rotational position detection pulse) of the 8mm video, a signal having the same time fluctuation and the same frequency as the pilot of the playback track is generated. is generated and multiplied by the pilots from both adjacent tracks in multiplier circuits 25 and 26. Therefore, the multiplication circuits 25 and 26
The output signal includes a signal having the same frequency as the horizontal synchronization signal from the pilots from both adjacent tracks and a signal having a frequency three times that of the horizontal synchronization signal, which has been corrected for fluctuations due to time axis fluctuations. Ru.

Next, band pass filters (hereinafter referred to as BPF) 27 and 28 extract a signal having the same frequency as the horizontal synchronizing signal and a signal having a frequency three times that of the horizontal synchronizing signal.

Next, the detection circuits 29 and 30 detect the amplitude level of the signal outputted from the BPF by square law detection or full wave detection, and pass it through a low pass filter (hereinafter referred to as L).
A tracking error signal is detected by removing unnecessary components using LPFs 31 and 32 (referred to as PF), and taking the difference between the outputs of LPFs 31 and 32 using a subtraction circuit 33.

[0007] Here, the bands of BPF27 and 28 are set to 200
If the band is set to about Hz and the band is narrowed, the Q of the circuit will be about 80 to about 200, making it difficult to implement hardware. In addition, even if the frequency band is limited to several tens of Hz with the LPFs 31 and 32, since the detection circuits 29 and 30 use square law detection or full wave detection, the frequency outside the BPF band is converted to near DC. Therefore, the SN ratio of the tracking error detection pilot cannot be improved much by narrowing the band of the LPF.

[0008]

However, if the tracking error detection device shown in FIG. It needs to be narrowband.

However, even if a tank circuit with a high Q is used for the BPF, Q=20 is a practical range at most, and beyond that it becomes difficult to implement hardware.

[0010] Furthermore, when a digital signal is used as the main signal and a tracking pilot signal is generated during recording modulation for recording and reproducing, the digital signal has signal components up to low frequencies, so the BPF is further narrowband. It is necessary to

The present invention has been made in view of the above points, and provides a tracking error detection device that has characteristics equivalent to or better than a narrow-band BPF without using a narrow-band BPF, and that can be easily implemented in hardware. is intended to provide.

0012

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a pilot frequency oscillation circuit that generates two signals having the same frequency as the pilot frequency for tracking error detection but with a phase difference of 90 degrees, and a magnetic recording medium. two multiplier circuits that respectively multiply the signal reproduced from the two signals having a phase difference of 90 degrees; two low-pass filters that extract only low frequency components from the outputs of the two multiplier circuits; two squaring circuits that square the two outputs from the two low-pass filters, an addition circuit that adds the outputs of the two squaring circuits, and a square root circuit that takes the square root of the output of the addition circuit. It is equipped with the following.

[0013]

[Operation] Instead of making the BPF a narrow band, the present invention multiplies the reproduced signal by a signal of the same frequency as the pilot frequency to make the LPF a narrow band.
Characteristics equivalent to narrowband F can be achieved, and hardware can be realized without difficulty and narrowband can be achieved.

Further, the phase of the tracking error pilot recorded and reproduced on the adjacent track is not constant due to errors in the head mounting height position and the like.

Therefore, even if the signal is multiplied by the same signal as the pilot frequency, the level of the signal output from the LPF will vary due to the phase error.

Therefore, in order to prevent level fluctuations, two signals having the same frequency as the pilot frequency but having a phase difference of 90 degrees are vector-decomposed by multiplying them by the main signal to which the pilot reproduced from the magnetic recording medium is added. two L's
High-frequency components are removed by the PF, and these two outputs are squared and added to perform vector synthesis, and the absolute level of the reproduced pilot is detected regardless of the phase error.

In addition, in the square root circuit, by squaring
This is to inversely transform the doubled frequency during reproduction into the original frequency component.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of the main parts of a tracking error detection device according to a first embodiment of the present invention. By replacing the blocks after BPF 27 and 28 in FIG. 5 with the blocks of this embodiment, the hardware can be improved. This configuration is easy to use and can provide the same characteristics as a narrow-band BPF.

The first embodiment will be explained below. The pilot frequency oscillation circuit 1 generates two signals having the same frequency as the horizontal synchronizing signal and having phases different by 90 degrees. Similarly, the pilot signal oscillation circuit 2 generates two signals having three times the frequency of the horizontal synchronizing signal and having phases different by 90 degrees.

Next, the multiplier circuits 3, 4, 5, and 6 combine signals with the same frequency as the horizontal signal containing tracking error information, which is the output of the multiplier circuits 25 and 26 (see FIG. 5). Multiplication is performed by a signal having a frequency three times that of the horizontal signal, and the amplitude component of the tracking error signal is vector-decomposed.

Here, the reason why vector decomposition is performed is that the phase of the signals output from the multiplier circuits 25 and 26 is affected by the error in the mounting height position of the magnetic head and the 18
Tracking is difficult because the phase of the signal output from the pilot signal frequency oscillator circuits 1 and 2 cannot be uniquely determined due to variations in the 0 degree index mounting position error and the width of the magnetic head stepping on the adjacent track. This is because it is not possible to prevent compatibility offsets and effects on detection sensitivity when error detection is performed. Therefore, vector decomposition is performed to remove the influence of phase fluctuations and accurately detect the amplitude component of the tracking error.

Next, the LPFs 7, 8, 9, and 10 extract the low frequency components of the tracking error signal and output them to the square circuits 11, 12, 13, and 14.

Here, if the frequency bands of LPFs 7, 8, 9, and 10 are made narrow, the multiplier circuits 3, 4, 5, and 6 will have
Since only the pilot frequency signal component is converted to a frequency near the low frequency, an effect equivalent to a narrow band BPF can be obtained. In addition, if LPF7, 8, 9, and 10 were originally intended to be followed by a capstan servo,
It is realized in a band of several tens of Hz and can be easily made into hardware.

Next, squaring circuits 11, 12, 13, and 14 square the outputs of LPFs 7, 8, 9, and 10, respectively, and output them to adder circuits 15 and 16. Addition circuits 15 and 16 add the outputs of squaring circuits 11, 12, 13, and 14, respectively, vector-compose the vector-decomposed components, and detect accurate tracking information.

Next, square root circuits 17 and 18 take the square root of the outputs of adder circuits 15 and 16. The reason for taking this square root is that the tracking error component is squared in the squaring circuits 11, 12, 13, and 14, so that the frequency is doubled. Therefore, the square root is taken, converted to the original frequency component, and output.

Finally, in the subtraction circuit 19, the square root circuit 17
, 18 and detects and outputs the tracking error.

Next, a second embodiment of the present invention will be described with reference to the drawings. Here, the second embodiment is a method in which a digital signal is recorded in the main signal, and a pilot for tracking error detection is premised on a method in which a DSV (digital integrated value) is changed and inserted when performing recording modulation.

For example, the two magnetic heads A0, B0 shown in FIG. 2(a) and A1, B1 facing each other by 180 degrees are arranged in a staggered manner, and the pilot for tracking error detection is set as shown in FIG.
Continuous f1, f2 at low frequency shown in (b) (however, f
1 and f2 are not equal. For example, f1=180kHz,
Let f2=120kHz. ) is generated and inserted.

During reproduction, the magnetic heads B0 and B1 generate pilots f1 and f as crosstalk from both adjacent tracks.
2, and the tracking error is detected by taking the difference between f1 and f2.

FIG. 3 is a block diagram showing the main structure of a second embodiment of the present invention. Data recorded on the magnetic recording medium 41 is reproduced via the magnetic head 42 and the amplifier circuit 43, and the tracking error detection pilot signal is reproduced as crosstalk from both adjacent tracks.

Next, the reproduced signal is sent to the PLL circuit 44 and the BP
It is output to F47 and F48. The PLL circuit 44 reproduces a reproduced clock of the digital signal, which is the main signal, and outputs it to the frequency dividing circuits 45 and 46.

Here, since the pilot is inserted during recording modulation, the frequency of the pilot is one integer fraction of the reproduced clock. Therefore, the frequency dividing circuit 45,
At 46, the frequency of the recovered clock is divided by an integer to generate two signals that match the pilot frequency and have a phase difference of 90 degrees. Furthermore, since the reproduced clock includes time axis fluctuations during reproduction, the signals output from the frequency dividing circuits 45 and 46 simultaneously include time axis fluctuations during reproduction.

Next, the BPFs 47 and 48 are constructed of tank circuits whose Q is not so high, and roughly detect the pilot frequency band and remove unnecessary components.

Here, the reason for inserting the BPFs 47 and 48 is that when the frequency dividing circuits 45 and 46 are constructed of digital circuits, the output becomes a square wave, so harmonics exist at odd number times.
When multiplied by the multiplier circuits 49, 50, 51, and 52, there is a component that is converted from an odd harmonic component to a low frequency,
This is because noise is a tracking error component, so noise can be prevented by band-limiting in advance.

Further, as shown in FIG. 4, the output binary waveform from the frequency dividing circuit 45 or the frequency dividing circuit 46 shown in FIG. Convert to waveform,
For example, if the m:n ratio is 1:2, the third harmonic component becomes infinitely small, and only harmonic components of the fifth or higher order exist. Therefore, if the ternary waveform of FIG. 4(b) is used, further effects can be obtained, and
can be constructed using a simple digital circuit.

Next, multiplier circuits 49, 50, 51, and 52 multiply the outputs of BPFs 47 and 48 by the outputs of frequency divider circuits 45 and 46, and perform vector decomposition as described above.

Here, as described above, the two signals outputted from the frequency dividing circuit 45 or the frequency dividing circuit 46 and having the same frequency as the pilot frequency with a phase difference of 90 degrees simultaneously contain time axis fluctuations during reproduction. I'm here. Therefore, the signals output from the multiplication circuits 49, 50, 51, and 52 are signals whose time axis fluctuations have been corrected. Especially during special playback, the VTR
Since the relative speed of the BPF varies by about 4%, if a narrowband BPF is used, the pilot frequency may vary outside the BPF band, and tracking errors may not be detected. However, as mentioned above, Frequency dividing circuit 45, 4
If the output of No. 6 includes time axis fluctuations during reproduction, it will be corrected naturally and the above-mentioned problem will not occur.

Next, the LPFs 53, 54, 55, and 56 extract the low frequency components of the tracking error signal, and
It is output to multiplication circuits 57, 58, 59, and 60.

Here, if the frequency bands of the LPFs 53, 54, 55, 56 are made narrow, the multiplication circuits 49, 50, 5
In the case of No. 1 and 52, only the pilot frequency signal component is converted to a frequency near the low frequency, so an effect equivalent to that of narrow band BPF can be obtained. Also, LPF53, 54, 55,
56 is originally realized in a band of several tens of Hz when a capstan servo is used for tracking, and it can be easily made into hardware.

Next, squaring circuits 57, 58, 59, and 60 square the outputs of LPFs 53, 54, 55, and 56, respectively, and output them to adder circuits 61 and 62. Addition circuit 61, 6
2, the outputs of the squaring circuits 57, 58, 59, and 60 are added, vector-decomposed components are vector-combined, and accurate tracking information is detected.

Next, square root circuits 63 and 64 take the square root of the outputs of adder circuits 61 and 62. The reason for taking the square root is that the tracking error component is squared in the squaring circuits 57, 58, 59, and 60, so that the frequency is doubled. Therefore, the square root is taken and converted to the original frequency component and output.

Finally, in the subtraction circuit 65, the square root circuit 63
, 64, and detects and outputs the tracking error.

[0044]

[Effects of the Invention] As described above, according to the present invention, by multiplying a signal of the same frequency as the pilot and passing it through a narrowband LPF, characteristics equivalent to narrowband BPF can be obtained. It can be easily made into hardware, and the S/N ratio of tracking error detection can be improved.

Furthermore, the tracking error component is vector-decomposed by multiplying two signals having the same frequency as the pilot and having different phases by 90 degrees in the multiplication circuit, and the tracking error component is again vector-combined after passing through the LPF. , the tracking error can be detected regardless of the phase of the recorded pilot.

[0046] Even if a digital signal is used for recording and a pilot is inserted during recording modulation, the reproduced clock is regenerated by a PLL, and two signals having the same frequency as the pilot but with a phase difference of 90 degrees, including time axis fluctuations, are generated. , the time axis fluctuation can be corrected by a multiplier circuit.

Furthermore, even if the digital signal has signal components at low frequencies, the band can be easily limited using the present invention, so the S/N ratio for tracking error detection can be improved.

[0048] Also, by inserting a BPF with a small Q, two signals having the same frequency as the pilot but with a phase difference of 90 degrees are
By using a value digital signal, the frequency divider circuit can be constructed with a simple digital circuit.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of main parts of a tracking error detection device in a first embodiment of the present invention.

[Figure 2] (a)
Diagram showing an example of magnetic head arrangement when recording digital signals (b) Diagram showing recording arrangement of tracking error detection pilots when recording digital signals

FIG. 3 is a block diagram showing the configuration of a tracking error detection device in a second embodiment of the present invention.

FIG. 4 is a waveform diagram showing the output waveform of the frequency divider circuit in the second embodiment.

[Fig. 5] Block diagram showing the configuration of a conventional tracking error detection device

[Explanation of symbols]

1, 2 Pilot frequency oscillation circuit 3-6, 25, 26, 49-52 Multiplying circuit 7-10
,31,32,53~56 LPF11~14 2
Multiplication circuits 15, 16, 61, 62 Addition circuits 17, 18, 63, 64 Square root circuits 19, 33, 6
5 Subtraction circuit 21, 41 Magnetic recording medium 22 Magnetic head 23, 43 Amplification circuit 24 4-frequency generation circuit 27, 28, 47, 48 BPF 29, 30 Detection circuit 44 PLL circuit 45, 46 Frequency division circuit 57, 58, 59, 60 square circuit

Claims (4)

[Claims] 1. A pilot for tracking error detection is added to the main signal and recorded on a magnetic recording medium, and during playback, tracking is performed by comparing the playback output level of the pilot played back as a crosstalk signal from both adjacent tracks. A tracking error detection device for detecting an error, which includes a pilot frequency oscillation circuit that generates two signals having the same frequency as the pilot frequency and having a phase difference of 90 degrees, and the pilot reproduced from the magnetic recording medium. two multiplier circuits that respectively multiply the main signal and the two signals having a 90 degree phase difference; two low-cut filters that extract only low frequency components from the outputs from the two multiplier circuits; Two squaring circuits that square the two outputs from the band cutoff filter, an adding circuit that adds the outputs of the two squaring circuits, and a square root circuit that takes the square root of the output of the adding circuit. tracking error detection device. Claim 2: A pilot for tracking error detection is generated by changing the digital integrated value during recording modulation of the digital signal of the main signal, and is recorded on the magnetic recording medium together with the main signal, and during playback, the pilot is generated by changing the digital integration value, and during reproduction, the pilot is a tracking error detection device that detects a tracking error by comparing the reproduced output level of the pilot reproduced as a talk signal, and a phase-locked loop circuit that generates a reproduced clock from a digital signal of the reproduced main signal;
a frequency dividing circuit that divides the output of the phase-locked loop circuit to generate two signals having the same frequency as the pilot frequency and having a phase difference of 90 degrees; and a digital signal containing the pilot reproduced from the magnetic recording medium. Said 90
two multiplier circuits that multiply two signals with different degrees and phases, two low-frequency cut-off filters that extract only low-frequency components from the outputs of the two multiplier circuits; 2 outputs each
A tracking error detection device comprising: two squaring circuits that multiply, an adding circuit that adds the outputs of the two squaring circuits, and a square root circuit that takes the square root of the output of the adding circuit. 3. A bandpass filter for limiting the band of a digital signal including a pilot reproduced from a magnetic recording medium is provided before the two squaring circuits, and the output of the bandpass filter and the 90% frequency generated from the frequency dividing circuit are provided. 3. The tracking error detection device according to claim 2, wherein said two multiplier circuits respectively multiply two binary digital signals having different degrees and phases. 4. A bandpass filter for limiting the band of a digital signal including a pilot reproduced from a magnetic recording medium is provided before the two squaring circuits, and the output of the bandpass filter and the 90% signal generated from the frequency dividing circuit are provided. 3. The tracking error detection device according to claim 2, wherein two ternary digital signals having different degrees and phases are respectively multiplied by two multiplier circuits.