JPS62125561A - Video tape recorder - Google Patents

Abstract

PURPOSE:To fix a noise bar on a screen in an odd-multiple search mode and to obtain an easy-to-see screen by sampling/holding the reference slope wave obtained from a reference signal and performing the tracking control based on said sampling/holding output. CONSTITUTION:In a normal reproduction the output of a comparator 9 is given to a servo circuit as a tracking control signal via a changeover switch 11. Thus the tracking control is carried out. In an odd-multiple speed video search mode a sampling pulse is produced 15 based on the comparison output of the comparator 9. Thus the trapezoidal wave produced from a reference signal is sampled/held 23 by said sampling pulse. Then the tracking control is carried out with said sampling/holding output. Thus the noise bar can be fixed on the screen in an odd-multiple speed search mode. Then an easy-to-see screen is obtained.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a video tape recorder, and more particularly to a helical scan type video tape recorder configured to perform tracking control using pilot signals of four types of sequentially older frequencies. Related to video tape recorders.

<Prior Art> Conventionally, in this type of video tape recorder, for example, an 8 mm video tape recorder, the magnetic tape has a ninth
As shown in the figure, four types of first to fourth pilot signals r, ~r4, low frequency conversion color difference signal St, FM audio signal S2, and FM luminance signal S having different frequencies in sequence are used.
3 is recorded, and the four types of pilot signals f, ~f4 are recorded.
is recorded superimposed on the FM luminance signal etc. while circulating for each track of the magnetic tape 1, as shown in FIG. 1O.

Furthermore, these first to fourth pilot signals f1 to r4
The frequencies of are 6.5fo, 7 as shown in Figure 1I.
．． 5fo, 10.5fo, 9.5ro, (ro is the horizontal synchronization frequency), and the difference in frequency between the pilot signal of the track consisting of the track and the pilot signal of the adjacent tracks on both sides is f, (16kHz ).

3 f, (46kHz). In addition, in FIG. 1O, arrows 30 and 31 indicate magnetic tape I.
The running direction of the rotary magnetic head and the running direction of the rotating magnetic head are respectively shown.

FIG. 8 is a block diagram of a conventional video tape recorder that performs tracking control using such a pilot signal. Based on FIG. 8, tracking control in the normal playback mode of the conventional video tape recorder will be explained. The first to fourth pilot signals r, to r4, etc. are recorded on the magnetic tape 1. The reproduced pilot signals reproduced by the second rotating magnetic heads 2 and 3 are each amplified by a head amplifier 4, and then filtered through a low-pass filter I6.
The signal is then fed to the mixer 17. This mixer 17 has
Four types of reference pilot signals r, -r having the same frequency as the first to fourth pilot signals are sequentially applied from the reference pilot signal generating means 20, and the mixer 17 generates two types of the first to fourth pilot signals. A second beat signal is formed, further having a band frequency of f. , 1st of 3ro. Second bandpass filter 18.
19 to the switching circuit 6. The reference pilot generation means 20 includes a reference pilot signal generation circuit 21 that generates four types of reference pilot signals, and this generation circuit 2.
A selection circuit 22 selectively outputs the output of I in response to a head switching pulse.

The first of these two types. The second beat signal is, for example, the twelfth beat signal.
As shown in the figure, the first. A pilot signal r recorded on the video track on which the second rotating magnetic head 2 or 3 runs, and each pilot signal r recorded on adjacent video tracks on both sides of the video track.
, r, i.e., frequencies f0 and 3r
o signal. The first of these two types. Since the second beat signal has opposite polarity in phase lead and lag in each field, the polarity is switched in the switching circuit 6 for each field by the head switching pulse, and the two types of first and second beat signals are switched. The signal is outputted as a 2 error signal, further detected by a 1.degree. second detection circuit 7.8, and then provided to a comparison circuit 9.

As mentioned above, there are two types of 1st. The second beat signal is a frequency difference signal between the pilot signal recorded on the video track on which the rotating magnetic head runs and the pilot signals recorded on the adjacent video tracks on both sides of the video track. Therefore, if the output levels of both beat signals are equal, it means that the rotating magnetic head or video track is being traced correctly; if they are not equal, it is not being traced correctly. Therefore, the levels of both error signals whose polarities are switched for each field are compared by a comparator circuit 9, and the output of the comparator circuit 9 is applied to a servo circuit (not shown) to perform tracking control.

In this way, tracking control is performed in normal playback mode, but when performing video searches such as fast forwarding or rewinding, the rotating magnetic head normally plays across multiple tracks. There is no tracking control like in playback mode,
As a result, the noise bar on the screen is not fixed, making it difficult to see the screen.

<Objective of the Invention> The present invention has been made in view of the above-mentioned points, and an object of the present invention is to fix the noise bar on the screen to make the screen easy to see in video search.

<Structure of the Invention> In order to achieve the above-mentioned object, the present invention forms two types of beat signals based on a reproduced pilot signal reproduced from a magnetic tape and four types of reference pilot signals,
In a video tape recorder that switches the polarities of both beat signals for each field to form two types of error signals and performs tracking control by comparing these two types of error signals, the phase of the comparison output of the two error signals is , a phase comparison circuit is provided to compare the phase of the head switching pulse with the phase of a reference signal having the same frequency, and when performing an odd-numbered multiple speed video search, a sampling pulse is formed from the comparison output of both error signals, and a sampling pulse is formed from the comparison output of the two error signals. The shaped reference slope wave is sampled and held using the sampling pulse, and tracking control is performed based on this sampled and held output.

<Example> Hereinafter, an example of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram of an embodiment of the present invention,
Portions corresponding to the conventional example in FIG. 8 are given the same reference numerals. The video tape recorder of this embodiment sequentially receives four types of first to first pilot signals having different frequencies.
This is an azimuth recording type helical scan type video tape recorder configured to perform tracking control using signals 1 to r4.

In FIG. 1, ■ is a magnetic tape, and as shown in FIG. Color difference signal s1, PM audio signal S2 and F
An M modulated luminance signal s3 is recorded, and these four types of first to fourth pilot signals -f4 are superimposed on the FM luminance signal etc. while circulating for each track as shown in Figure 1O. and recorded. Furthermore, the frequencies of these pilot signals f1 to f4 are 6.5 f, 7.5 f, 10.5 f, as shown in FIG.
9, 5 f, (f is the horizontal synchronization frequency), respectively.

2.3 rotates while obliquely contacting this magnetic tape I.
The first one. The second rotating magnetic head, 4, responds to the head switching pulse to the first rotating magnetic head. This is a head amplifier that alternately amplifies and outputs the output of the second rotating magnetic head 2.3.

The video tape recorder of this embodiment includes a beat signal forming circuit 5 that forms two types of first and second beat signals based on the reproduced PYW signal reproduced from the magnetic tape 1 and four types of reference pilot signals; Beat signal forming circuit 5 for each field in response to head switching pulses
The first and second beat signals are alternately switched to produce two types of beat signals. A switching circuit 6 outputs a second error signal, and a first switching circuit 6 detects both error signals from the switching circuit 6. Comparison circuit 9 that compares the output levels of the second detection circuits 7, 8 and both transverse wave circuits 7.8
It is equipped with

The beat signal forming circuit 5 has a low-pass filter 16, a mixer 17, and a band frequency f. , 3f.

1st. Second bandpass filter 18, 19 and 11
It consists of a reference pilot signal generating means 20 that forms reference pilot signals f, -f having the same frequency as the fourth pilot signals f1 to f, and outputs them in this order. The reference pilot signal generating means 20 generates the first to fourth pilot signals "
1 to “Same frequency as 4 6.5r, 7.5r, .
A reference pilot signal generation circuit 21 that sequentially outputs four types of reference pilot signals: l 0.5 "., 9, 5 ", (r, horizontal synchronization frequency), and this generation circuit 2.
A selection circuit 22 selectively outputs the output of I in response to a head switching pulse.

In the present invention, in the odd-numbered speed video search described later, the reference pilot signals are sequentially output in the same order as in the normal playback mode, that is, in the order of f and -f4.

This beat signal forming circuit 5 generates a frequency difference f between the reference pilot signal and the reproduced pilot signal. , 3r.

1st. It forms and outputs a second beat signal, and in the normal playback mode, as in the conventional example, the first or second rotating magnetic heads 2 and 3 form and output the pilot signal recorded on the video track on which they run, and the pilot signal. A beat signal having a frequency difference with each pilot signal recorded on adjacent video tracks on both sides of the video track is formed and output.

Since the two types of first and second beat signals from the beat signal forming circuit 5 have opposite phase leads and lag polarities for each field, the switching circuit 6 switches between the two types of beat signals in response to the head switching pulse. The polarity is switched each time, and there are two types of 1st. It is output as a second error signal. Both error signals are
1st. The signals are detected by the second detection circuits 7 and 8 and provided to the comparison circuit 9. This configuration is similar to the conventional example shown in FIG. 8 described above.

The video tape recorder of this embodiment further includes a phase comparator circuit IO that compares the phase of the output of the comparator circuit 9 with the phase of a reference signal of 30 Hz, which has the same frequency as the head switching pulse, and a phase comparator circuit IO that compares the phase of the output of the comparator circuit 9 with the phase of a reference signal of 30 Hz, which is the same frequency as the head switching pulse, and Normally plays the tracking control signal.

It is provided with a changeover switch 11 that can be changed according to each mode of video search.

The phase comparison circuit 10 includes a trapezoidal wave shaping circuit 12 that shapes a trapezoidal wave as a reference slope wave from the reference signal, and a waveform shaping circuit 13 that shapes the output of the comparison circuit 9 into a rectangular wave.
A frequency dividing circuit 14 for matching the frequency of this rectangular wave with the frequency of the reference signal, a sampling pulse generating circuit 15 for forming and outputting a sampling pulse based on the rectangular wave from the frequency dividing circuit 14, and a sampling pulse generating circuit 15 for forming and outputting a sampling pulse based on the square wave from the frequency dividing circuit 14, It consists of a sample and hold circuit 23 that samples and holds waves.

The changeover switch 11 is connected to a first individual contact 11a to which the output of the comparison circuit 9 is applied, a second individual contact 11b to which the output of the phase comparison circuit IO is applied, and a servo circuit, and is connected between each individual contact 11a and fib. Common contact 11 that switches and moves
It consists of c. Common contact 11c of this changeover switch 11
is located on the first individual contact 11a side in the normal playback mode, and is configured to be switched to the second individual contact ttb side during odd-numbered speed video search.

In the video tape recorder of the present invention, in the normal playback mode, the output of the comparator circuit 9 is applied to the servo circuit as a tracking control signal via the changeover switch II, thereby performing tracking control in the same manner as in the conventional example,
On the other hand, when performing an odd-numbered speed video search, the output of the phase comparator circuit 10 is applied to the servo circuit as a tracking control signal via the changeover switch 11 as described later, thereby performing tracking control and fixing the noise bar. It is.

Next, the operation of the video tape recorder of the present invention in odd-numbered speed video search will be explained.

First, the case of triple speed fast forward search will be explained based on FIGS. 2 and 3.

FIG. 2 (A) is a diagram showing the positional relationship between the magnetic tape I and the rotating magnetic head, FIG. 2 (B) is a head switching pulse, and FIG. 2 (C) is a diagram showing the positional relationship between the magnetic tape I and the rotating magnetic head. Reference pilot signal to be output, Figure 2 (DXE)
are two types of first and second bandpass filters 18 and 19 of the beat signal forming circuit 5, respectively.
The second beat signal, FIG. 2 (F Second error signal, Figure 2 (■
() is a diagram showing the output waveform of the comparator circuit 9. In addition, in FIG. 2(A), the running directions of the first to fourth pilot signals r, to r, the rotating magnetic heads and the magnetic tape recorded on each video track are also shown.

In the case of a 3x fast forward search, the rotating magnetic head traces across three video tracks for each field ad, as shown in FIG. 2(A). As shown in FIG. 2(C), the HQ pilot signal is output from the reference pilot signal generating means 20 in the same manner as in the normal reproduction mode, in the order of 1st to 4th ", ~r4" for each field.
are output sequentially.

In the beat signal forming circuit 5, a mixer 17 mixes the reproduced pilot signal from the head amplifier 4 and the reference pilot signal shown in FIG. 2nd bandpass filter! After 8.19, Figure 2 (D
), two types of first and second beat signals are output. Both beat signals are alternately switched for each field by the switching circuit 6 and output as two types of first and second error signals shown in FIG. 2 (F XG ), respectively. From the comparison circuit 9 based on both error signals, FIG. 2 (H)
The comparison output shown in is given to the waveform shaping circuit 13 of the phase comparison circuit 10.

Figure 3 (A) shows the head switching pulse, Figure 3 (B)
) is a reference signal with the same frequency as the head switching pulse, FIG. 3(C) is a trapezoidal wave output from the trapezoidal wave shaping circuit 12, FIG.
E) shows the output of the frequency dividing circuit 14, FIG. 3 (1?) shows the sampling pulse output from the sampling pulse generation circuit 15, and FIG. In addition, Fig. 3 (A) (D
) respectively show the head switching pulses and the output of the comparator circuit 9 in FIGS. 2(B) and 2(H) for convenience of explanation.

The trapezoidal wave shaping circuit 12 of the phase comparator circuit 10 has a configuration shown in FIG.
A reference signal of B) is given, and from this reference signal, Fig. 3 (
The trapezoidal wave shown in C) is shaped and output to the sample hold circuit 23. On the other hand, the waveform shaping circuit I3 of the phase comparison circuit 10 is given the output of the comparison circuit 9 shown in FIG. 3(D), and based on this, it shapes the rectangular wave shown in FIG. 3(E). It is applied to the frequency dividing circuit 14. In the case of this triple-speed fast-forward search, since the frequency of the rectangular wave is equal to the frequency of the reference signal, the frequency of the rectangular wave is directly transmitted to the frequency dividing circuit 14 without being divided.
from the sampling pulse generating circuit 15. The sampling pulse generation circuit 15 forms a sampling pulse shown in FIG. 3 (F') from this rectangular wave and supplies it to the sample hold circuit 23. The sample and hold circuit 23 samples and holds the trapezoidal wave shown in FIG. 3(C) using a sampling pulse, and provides the output shown in FIG. 3(G) to the servo circuit via the changeover switch 11.

When the tracking state shown in FIG. 2(A) shifts,
Since the phase of the output of the frequency dividing circuit I4 is shifted, the phase of the sampling pulse is shifted, and the sample and hold voltage shown in FIG. 3(G) changes. Therefore, tracking control can be performed based on this sample and hold voltage, and the noise bar can be fixed.

FIG. 4 is a diagram corresponding to FIG. 2 in the case of triple speed rewind search. Figures 4 (A) to (H) are shown in Figures 2 (A) to (H).
), and FIG. 4(I) shows the waveform shaping circuit 13.
FIG. 4 (J) shows the output waveform of the frequency dividing circuit 11, respectively. In this triple speed rewind search, the rotating magnetic head traces across five video tracks for each field. The reference pilot signal generation means 20 outputs reference pilot signals in the first to fourth orders f1 to r4, as in the normal reproduction mode.

During this triple speed rewind search, two types of first . The output waveform of the second beat signal is as shown in FIG. 4 (D
．． The waveform of the second error signal is as shown in FIG. 4 (F XG ). The two membrane difference signals are applied to a comparison circuit 9 for comparison, and a comparison output shown in FIG. 4(H) is applied to a phase comparison circuit IO.

The waveform shaping circuit I3 of the phase comparison circuit IO shapes the comparison output from the comparison circuit 9 into a rectangular wave shown in FIG. In the case of this triple speed rewind search, the frequency of the output of the waveform shaping circuit 13 is 6
01 (z), in order to match the frequency of the reference signal and enable phase comparison, the frequency is divided by I/2 by the frequency divider circuit 14 and the sampling pulse is converted into a rectangular wave as shown in FIG. 4 (J). This sampling pulse generating circuit I5 forms a sampling pulse in the same manner as described above based on this rectangular wave, samples and holds the trapezoidal wave shown in FIG. 3(C) using this sampling pulse, and
Tracking control is performed using this sample and hold output.

FIGS. 5 and 6 are waveform diagrams corresponding to FIG. 4 for 5x fast forward and rewind searches, and tracking control is performed in the same manner as in the 3x search. In addition, 5
During the double-speed fast-forward search, the output of the waveform shaping circuit I3 has a frequency of 601-(z as shown in FIG. 5(I)), so the frequency dividing circuit 14 outputs the output as shown in FIG. 5(J). When the frequency is divided by 1/2 and the 5x speed rewind search is performed, the output of the waveform shaping circuit 13 has a frequency of 90 Hz as shown in FIG.
Divide the frequency by 1/3 as shown in J).

In this way, a phase comparison circuit IO is provided which compares the phase of the comparison output of the comparison circuit 9 and the reference signal, and when performing an odd-numbered speed video search, a sampling pulse is formed based on the comparison output of the comparison circuit 9, Sample and hold a trapezoidal wave formed from the reference signal using this sampling pulse,
Since tracking control is performed using this sample and hold output, the noise bar on the screen during odd-numbered speed search can be fixed, resulting in an easy-to-read screen. Moreover, in the present invention, by adding the phase comparator circuit IO to the conventional configuration, it is possible to perform tracking control for odd-numbered speed video search with the same circuit operation as in the normal playback mode.

In the present invention, tracking control is performed in odd-numbered speed video searches to fix the noise bars on the screen, but the number of noise bars changes depending on the azimuth of the rotating magnetic head used for reproduction. For example, 5
In the case of double speed fast forward search, as shown in FIG. 7(A), video tracks TRI, TR3, TR5...
. is recorded with a +azimuth rotating magnetic head (R head), and video tracks TR2, TR4, . . . are recorded with a -azimuth rotating magnetic head (L head). In this case, when playing back with the R head, as shown in Figure 7 (
As shown in C), there are two points where the playback output is minimum, and these appear as noise bars on the screen. on the other hand,
When the playback head is used for playback, there are three points where the playback output is minimum as shown in FIG. 7(D), and points a and b
does not appear on the screen because it is a vertical blanking period.

Note that FIG. 7(B) shows the head switching pulse.

Therefore, in the tracking control of the present invention, by selecting the rotating magnetic head for reproduction and controlling the phase so that the point at which the reproduction output is minimum is within the vertical retrace period as shown in FIG. 7(D). , it is possible to fix the noise bars on the screen to the smallest number in odd-numbered multiple speed searches.

In the above-described embodiment, the case of video search at 3x speed and 5x speed was explained, but it goes without saying that the present invention can also be applied to video search at odd-numbered speeds higher than that.

<Effects of the Invention> As described above, according to the present invention, two types of beat signals are formed based on the reproduced pilot signal reproduced from the magnetic tape and the reference pilot signal, and these two heat signals are combined into one.
In a video tape recorder that alternately switches each field to form two types of error signals and performs tracking control by comparing these two types of error signals, the phase of the comparison output of both error signals and the head switching pulse are determined. A phase comparison circuit is provided to compare the phase of a reference signal of the same frequency, and when performing an odd-numbered multiple speed video search, a sampling pulse is formed from the comparison output of both error signals, and a reference slope wave formed from the reference signal is formed. is sampled and held using the sampling pulse, and tracking control is performed based on this sampled and held output, so that the noise bar on the screen during odd-numbered speed search can be fixed, resulting in an easy-to-read screen.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIGS. 2 and 3 are signal waveform diagrams for triple-speed fast-forward search, and FIG.
Signal waveform diagram for double speed rewind search, Figure 5 is a signal waveform diagram for 5x fast forward search, Figure 6 is a signal waveform diagram for 5x speed rewind search, Figure 7 is a signal waveform diagram for 5x fast forward search,
FIG. 8 is a block diagram of the conventional example, FIG. 9 is a diagram showing the frequency distribution of recording signals on the magnetic tape, FIG. 10 is an explanatory diagram of the magnetization pattern, and FIG. 11 is the first to fourth pilot signals r, .
FIG. 12 is a diagram showing the frequency distribution of r4, and FIG. 12 is a diagram showing the trace state of the rotating magnetic head. 5... Beat signal forming circuit, 6... Switching circuit, 9...
... Comparison circuit, 10... Phase comparison circuit, 12... Trapezoidal wave shaping circuit, 13... Waveform shaping circuit, 14... Frequency dividing circuit, 15... Sampling pulse generation circuit, 23...
... Zumble hold circuit.

Claims (1)

[Claims] (1) A helical azimuth recording method in which four types of pilot signals with different frequencies are synthesized into an FM luminance signal, etc., which is sequentially switched for each field and recorded on a magnetic tape, and which performs tracking control using the pilot signals during playback. In a scan type video tape recorder, a reproduced pilot signal reproduced from the magnetic tape and 4
a beat signal forming circuit that forms two types of beat signals based on different reference pilot signals; and a beat signal forming circuit that alternately switches both beat signals from the beat signal forming circuit for each field in response to a head switching pulse. a switching circuit that outputs an error signal, a comparison circuit that compares these two types of error signals, and a phase comparison circuit that compares the phase of the output of this comparison circuit with the phase of a reference signal having the same frequency as the head switching pulse. This phase comparison circuit includes a reference slope wave shaping circuit that shapes a reference slope wave from the reference signal, a waveform shaping circuit that shapes the output of the comparison circuit into a rectangular wave, and a sampling pulse based on the rectangular wave. and a sample hold circuit that samples and holds the reference slope wave using the sampling pulse, and performs tracking control based on the output of the sample hold circuit when performing an odd speed video search. A videotape recorder characterized by a fixed noise bar on the screen.