JPH02249165A - Tracking error detection circuit - Google Patents

Abstract

PURPOSE:To easily detect a tracking error by extracting the high-frequency component of the reproduced signal of a magnetic tape, and taking out the DC component from detected output after detecting the high-frequency component. CONSTITUTION:A first detection circuit 8 to peak-detect the high-frequency component performs the full-wave rectification or half-wave rectification of the high-frequency component of the reproduced signal, and performs peak- detection (envelope detection) by a low-pass filter. Also, a second detection circuit 9 which takes out a DC(DC component) with negative polarity as a noise level by deciding a new virtual zero point at a level larger than the detection output of the first detection circuit 8 by a reference voltage Vo and detecting the detected output further performs negative half-rectification on the detected output peak-detected by the first detection circuit 8 by the reference voltage Vo, and furthermore, performs integration, then, detects the noise level corresponding to the change of an S/N. Thereby, the tracking error can be easily detected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a tracking error detection circuit for detecting a tracking error of a head in a VTR or the like.

[Summary of the Invention] The present invention provides a tracking error detection circuit for a head such as a VTR, which first detects the high frequency component of a reproduced signal, and then extracts the DC component of this detection output to detect the noise level. This makes it possible to easily detect tracking errors in VTRs and the like that have a multi-channel configuration with multiple heads.

[Prior Art] Conventionally, when reproducing video signals from a VTR (video tape recorder), etc., it has been necessary to optimally adjust the tracking of the head relative to the magnetic tape. There are known devices that display errors using indicators such as meters. Most conventional VTRs have a 1-head 1-channel or 2-head 1-channel (S-VH8 format) configuration, and the RF double signal reproduction level is displayed with a meter, and the S/V It was determined that N was the best and the tracking adjustment state was optimal.

On the other hand, when using PCM recording and playback using a VTR, VT
As a technique for detecting the tracking state of R, there is a technique disclosed in Japanese Unexamined Patent Publication No. 1987-78666 filed by the present applicant. This method focuses on the fact that the S/N of the pedestal portion on which no data is superimposed in the PCM signal changes greatly depending on the tracking state, and attempts to detect the tracking state by detecting the noise level of that portion.

[Problems to be Solved by the Invention] However, the tracking error detection circuit in the above-mentioned conventional technology is capable of handling multiple channels (4 heads and 2 heads) like a VTR compatible with HD TV (high definition television).
When attempting to apply this method to a VTR which has a narrow track width and a narrow head gap, the following problems must be solved.

(1) The VTR described above has a multi-head multi-channel configuration, the track width is narrow at about 20 microns, and the head gap is narrow at about 0.3 microns, so the RF reproduction output differs from channel to channel. To give a simple example, there are factors such as ■Difference in head depth (playback efficiency) 3 dB/10 microns ■Head mounting error approximately ±2 microns (approximately IdB) ■Gain difference between recording/playback amplifiers 3 dB, etc. Considering compatibility and changes over time (head depth, etc.), it is difficult to simply adjust tracking optimally from the RF reproduction signal level.

(2) When amplifier noise and head noise are small compared to tape noise, what changes due to tracking error is the S/N of the video signal and the RF multiplied signal playback level, but in the case of a multi-channel head configuration, , since the RF reproduction signal level differs for each channel, the RF' reproduction signal level and S/N are different from each other as when using the same head.
Pair 1 does not correspond, and the tracking error and the change in the RF reproduction signal level do not clearly correspond to each other. Therefore, even by looking at the maximum meter deflection, it cannot be shown that all heads are in the optimal tracking state. This makes it difficult to optimally adjust the tracking, and if the adjustment cannot be achieved, a S/N difference occurs between channels, resulting in line crawling and the like.

(3) In the conventional example of JP-A-57-78666, P
Since this method uses a pedestal portion where relatively long data peculiar to a CM signal is not superimposed, it cannot be applied to an analog VTR, etc., which performs efficient transmission by eliminating signal gaps as much as possible.

The present invention was devised to solve the above-mentioned problems, and an object of the present invention is to provide a tracking error detection circuit that can easily detect tracking errors in a VTR or the like having a multi-channel configuration with a plurality of heads. shall be.

[Means for Solving the Problems] A tracking error detection circuit according to the present invention for achieving the above object includes an extraction means for extracting a high frequency component of a reproduction signal of a magnetic tape; It is characterized by comprising a first detection means for detecting a wave, and a second detection means for extracting a DC component of the detection output of the first detection means.

[Operation] The present invention extracts and detects the high frequency components of the reproduced signal, extracts the so-called large triangular noise components in the high frequency range along with the discrete high frequency signal components with small energy, and then reproduces those DC components. It is extracted as the noise level that occupies the high frequency components of the signal. This noise level indicates the S/N in high-frequency components, and is the minimum level when tracking is in the best condition, so it can indicate a tracking error state, and it can also indicate a degraded signal component with low energy and a large noise component. Since the S/N ratio is shown, the tracking error state can be displayed without being affected even if there is a difference in the level of the reproduced signal depending on each channel.

[Example] Hereinafter, an example of the present invention will be described in detail based on the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. In the figure, l is a head that reproduces the recording signal recorded on the tape, 2 is a head amplifier, 3 is an equalizer that corrects so that the amplitude characteristics of head l when playing back is flat, and 4 is head 1 and head amplifier 2. 5 is a low-pass filter; 5 is a low-pass filter;
6 is an amplifier. In this embodiment, the noise level is detected from the reproduced signal reproduced through each of the above sections using the following configuration, and the tracking error state is displayed. 7 is a bandpass filter which is an extraction means for extracting the high frequency component of the reproduced signal (video signal), 8 is a first detection circuit that peak detects the high frequency component, and 9 is a detection circuit of the first detection circuit 8. Set the new virtual zero to a level greater than the output reference voltage V. The second detection circuit extracts the DC (direct current component) as a noise level with the opposite polarity by roughly detecting the detection output, and IO is its reference voltage V. 11 is an amplifier for the noise level, and 12 is a noise level display device including a meter and the like and driven by the amplifier 11. The first detection circuit 8 performs full-wave rectification or half-wave rectification of the high-frequency component of the reproduced signal, and performs peak detection (envelope detection) using a low-pass filter or the like.

Further, the second detection circuit 9 has a reference voltage ■ with respect to the detection output peak-detected by the first detection circuit 8.

Negative half-wave rectification is performed by
A noise level corresponding to a change in N is detected. A bypass filter may be used as the band-pass filter 7 if filter processing has already been performed by a low-pass filter during the demodulation process.

The operation of the embodiment configured as described above is shown in FIGS. 2 and 3.
This will be explained with reference to the figures. FIG. 2 is a distribution diagram of signal components and noise components in a reproduced signal, and FIG. 3 is an explanatory diagram for explaining the operation of this embodiment.

First, the principle of the noise level measurement method in this embodiment will be explained. FIG. 2 shows the distribution of the signal component S and the noise component N in the reproduced signal of an analog VTR, with the horizontal axis representing the frequency and the vertical axis representing the response. As can be seen from this figure, the energy of the signal component S becomes smaller and more discrete as the frequency becomes higher. On the other hand, the noise component N
This is so-called triangular noise, and the high frequencies become louder. Therefore, although the spectrum of the signal component S exists over all frequencies in the transmission band, there is a gap in the high frequency portion with respect to the transmission time axis, and the noise component N is easy to catch. Further, the noise level occupying the high frequency portion of the reproduced signal at this time becomes the minimum when the S/N is the best.

Focusing on the above, this embodiment separates and extracts the transmission high-frequency component from the reproduced signal using band-pass filter characteristics instead of using BPF, and performs detection processing to detect the noise level that changes depending on the S/N. To detect.

In this embodiment, the bandpass filter 7 having the characteristics shown in FIG. 2 extracts high-frequency components of the reproduced signal having a waveform as shown in FIG. 3. However, FIG. 3 is an example of a convergence signal.

By doing so, the extracted signal becomes only a high-frequency signal component S and a high-frequency noise component N, making it possible to create a gap T on the transmission time axis.

Furthermore, in this high frequency component, the noise component N is large and the signal component S is small, so that deterioration of S/H can occur. When such a high-frequency component is peak-detected by the first detection circuit 8, part A of the waveform shows the level of the signal component S, and part 8 shows the level of the noise component N. This first
The second detection circuit 9 outputs the detection output from the reference voltage V, which is higher than that of the section A. When negative half-wave rectification and integration are performed using 0 as a virtual zero point and the DC component is extracted, the resulting signal represents the noise level that occupies the high-frequency component of the reproduced signal. Here, if tracking is optimal, the signal component S
becomes relatively large, so the noise level becomes small, and conversely, when a tracking error occurs, the signal component S becomes small and the noise level becomes large. That is, the above noise level changes depending on the S/H, and the noise level changes depending on the S/H.
/N indicates the best state when tracking is optimal, and changes in close relation to the tracking state. Therefore, if the noise level detected in this embodiment is displayed on the appropriate display 12 as described above, the noise level will increase when a tracking error occurs, and the noise level will be at its minimum when the tracking error is optimal. Therefore, tracking errors can be displayed. Moreover, in this embodiment, since the S/N is detected in a portion where the energy of the signal is small, the tracking error can be displayed without being affected by the level of the FM reproduction signal.

As a result, VTRs with multi-channel configurations with multiple heads
In this case, by adjusting the tracking of each head so that the display on one display 12 is minimized, the tracking state can be optimally adjusted.

Note that in the second detection circuit in the above embodiment, detection was performed by negative rectification so that the minimum value displayed (noise level) on the display 12 was the best point of S/N.
Detection is performed using normal positive rectification, and the maximum value displayed is S/
It may be set to the best point of N. Further, the present invention can also be applied to a tracking error detection circuit when automatically adjusting tracking such as dynamic tracking. As described above, the present invention can be applied in various ways and can take various embodiments in accordance with its gist.

[Effects of the Invention] As is clear from the above description, the tracking error detection circuit of the present invention provides the following effects.

(1) VTr with multi-head multi-channel configuration (for example,
When the tracking error state was displayed using the RF signal level, the RF signal level differed depending on the channel, so it was impossible to accurately display the dragging state and it was difficult to achieve optimal tracking. However, the present invention's noise level Since all channels can be displayed in the same way, optimal tracking adjustments can be made easily.

(2) In the display based on RF signal level, the RF signal level decreases/increases as the head depth increases/decreases, so it is necessary to adjust the display due to changes over time, etc. However, in the present invention, it depends on the S/N. However, since the noise depends on the tape, there is no such change, and there is no need for adjustment.

(3) In VTRs with multiple heads and multiple channels, it is difficult to optimally adjust tracking, so
Although line crawling is likely to occur due to the N difference, in the present invention, since the tracking adjustment is 5 times, line crawling can be easily prevented from occurring.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a distribution diagram of signal components and noise components of a reproduced signal, and FIG. 3 is an explanatory diagram of the operation of this embodiment. l...Head, 2...Head amplifier, 4...Demodulator,
7... Bandpass filter, 8... First detection circuit,
9. Second detection circuit.

Claims (1)

[Claims] (1) An extraction means for extracting a high frequency component of a reproduced signal of a magnetic tape, a first detection means for detecting the high frequency component, and a second detection means for extracting a DC component of the detection output of the first detection means. A tracking error detection circuit comprising: detection means.