JPH0352391A - Magnetic recording and reproducing circuit - Google Patents

Abstract

PURPOSE:To make after-image in one preceding field inconspicuous on the screen with simple constitution by using a filter with a shallow comb-line characteristic to eliminate crosstalk from adjacent tracks and mixed in a demodulated luminance signal. CONSTITUTION:In the case of reproducing a signal recorded with a step difference of 1/2fH, a CCD(Charge Coupled Device) element 41 is adopted for a comb- line filter 28 reducing crosstalk from adjacent tracks. Then the comb-line filter 28 whose frequency characteristic is nearly flat over the signal band of a luminance signal and having a prescribed attenuation is made of the CCD element 41 to omit a 1/2fH step difference compensation circuit. Thus, a crosstalk signal mixed in a reproducing signal is eliminated and a DC V step difference mainly comprising low frequency components is sufficiently made inconspicuous.

Description

[Detailed Description of the Invention] [Industrial Application Field 1] This invention records video signals using a helical scan method,
The present invention relates to a magnetic recording and reproducing circuit for reproducing data, and particularly relates to a comb-shaped filter inserted in the reproducing circuit.

[Summary of the Invention] The magnetic recording/reproducing circuit of the present invention converts a luminance signal separated from a video signal into an FM signal, supplies this to two rotating heads for each field, and records the signal in an oblique direction on a magnetic tape. When sequentially recording on the formed tracks, 1/2 f. In a recording and reproducing circuit that aims to reduce crosstalk during reproduction by adding a frequency step, a comb-shaped filter whose pass characteristic matches a shallow wi-type attenuation characteristic at fHru'l intervals is used in the reproduction circuit. is provided, thereby making it possible to omit the DC V-step return that was conventionally performed.

[Prior Art] Tape is diagonally moved by two rotating heads? A helical scan type magnetic recording/reproducing circuit that sequentially records video signals in units of fields on a track created by the system usually converts the separated luminance signal into a low carrier FM signal, and adds a carrier color signal converted to a low frequency to this signal. The signals are superimposed and recorded.

In this case, by lowering the running speed of the magnetic tape, the recording density of the tape can be increased and a long-time recording mode can be achieved, but during playback, FM signals recorded on adjacent tracks may cause crosstalk. Since they are simultaneously reproduced as signals, the image quality generally deteriorates.

Therefore, in the long-time recording mode, when recording by FM modulating the luminance signal, 1/2f. ．． (f. is the horizontal frequency) is recorded with a frequency difference, and at the time of playback, a comb-shaped filter that suppresses crosstalk reproduced from adjacent tracks is inserted into the playback system circuit, and at the same time, the crosstalk component is removed. A rectangular shape is applied to the demodulated output to compensate for the V step difference caused by the frequency shift of 1/2t'■. A V-step return circuit for adding a signal is known. (Japanese Unexamined Patent Publication No. 53-6012) Figure 5 shows a block diagram of such a recording/reproducing system, in which the luminance signal of the recording system is transmitted from the human power terminal 11 to the AGC amble l2 to the sync tip clamp circuit l3 to It is supplied to the FM modulator l6 via the bias circuit l4 → W/B (white/dark) clip circuit l5, and the low carrier wave F
It is converted into an M signal. Although not shown, the two rotating heads 18A. 18B is switched and supplied field by field to track A.18B of the tape. The data are recorded sequentially in H.

In the FM modulator l6, the sync chip of the luminance signal is, for example, 3.
．． 5M}{■, white level is 4'. Frequency modulation is applied so that the frequency becomes 8MH2, but in this type of recording/reproducing circuit, the FM modulator l6 has, for example,
As shown in FIG. 6, a rectangular wave signal S having a different level is supplied from a control circuit (not shown) for each field. Therefore, as shown in Figure 6, the frequency deviation of the FM signal obtained by frequency modulating the luminance signal is 3.58 to 4.5 MHz in track A, but that frequency deviation in track B is is 1/2 f. compared to that of track A. It is converted into a shifted FM signal and recorded.

Therefore, the frequency spectrum of the FM signals recorded on track A and track B occurs at the seed cotton and at the position shown by the dotted line as shown in FIG. 7, and 1/2 f.
It becomes something that has shifted.

If the FM signal spectrum is recorded with a level difference of 1/2fH between adjacent tracks A and B in this way, the crosstalk signal components mixed in from the adjacent tracks during playback will be absorbed by the comb as shown in Figure 8. It can be removed by passing it through a filter using a glass retardation element with type attenuation characteristics.

[Problem to be Solved by the Invention J] However, in the above method, since a comb-shaped filter is formed by the glass delay element r, it is difficult to remove DC level crosstalk that exists in the low frequency range. The reproduction system circuit includes the above-mentioned comb filter and a rectangular wave signal SF.
It is necessary to place a V-level difference return circuit that adds up the FM modulator at the subsequent stage of the FM modulator to eliminate the level difference.

Therefore, the reproduction circuit requires a modulation circuit to form a comb filter using a glass delay element and a circuit to supply a rectangular wave signal and perform V step return, making the circuit configuration complicated. was there. [1,000 Steps to Solve the Problems The present invention has been made in view of these problems.
l/2 f. LI that reduces crosstalk from adjacent tracks when playing back signals recorded with steps.
CCD (Charge Couple) is used as a type filter.
dDevice) element, and this CCD element allows the luminance signal to be almost flat over the signal band,
In addition, a comb-shaped filter is formed to provide a predetermined amount of attenuation, and the 1/2 ts step return circuit is omitted.

[Action J A comb filter consisting of a CCD delay element has a f. It is easy to flatten the attenuation characteristic of the frequency spectrum in the interval within the signal bandwidth of the luminance signal, so if the attenuation amount is set appropriately, the crosstalk signal mixed in the reproduced signal can be removed, and at the same time the main It becomes possible to make the DC V level difference consisting of low frequency components sufficiently inconspicuous.

Embodiment J FIG. 1 is a block diagram of a reproducing system circuit in a magnetic recording/reproducing circuit of the present invention.

In this figure, reference numeral 20 indicates a tape that is played back by rotary heads 21A and 21B.As explained in the conventional example above, on this tape 20, a luminance signal as a low carrier FM signal is transmitted to track A, track A, track It is recorded in B.

Then, track A is played back by the rotating head 2LA,
A frequency difference of 1/2 f's is added to the frequency spectrum of track B reproduced by the rotary head 21B.

Adjacent truck A. The reproduced RF signal reproduced by scanning B is sent to amplifier 22AJ5 and amplifier 22B.
The signal is supplied to the rotary switch SW via the signal generator and is converted into a continuous reproduction signal by a compliment signal (not shown).

23 is a Y/C separation circuit, and this Y/C separation circuit 23
The luminance signal (FM signal) separated by the FM signal passes through the limiter 24 and is limited to a constant amplitude. 25 is an FM demodulator, and the demodulated output is extracted by a low-pass filter 26 as a luminance signal within a predetermined bandwidth. 27 is a de-emphasis circuit that corrects the frequency characteristics of the demodulated luminance signal, and 28 also serves as a noise canceller. A comb filter is shown.

This comb-shaped filter 28 uses a CCD delay element as an IF-1 delay circuit, and this CCD delay element forms a filter having a comb-shaped passage characteristic as described later. This i-type filter 28 suppresses crosstalk signals mixed in from adjacent tracks during playback and eliminates beat interference.
The steps are eliminated to reduce flicker or line crawling.

The color signal separated by the Y/C separation circuit 23 is converted into a carrier color signal with a carry frequency of 3.58 MHz in the color signal processing circuit 30. The signal-processed luminance signals are combined in an adder circuit 29 and supplied as a color composite video signal from the output amplifier 3l to a monitor television or the like.

Figure 2 shows 4! of the present invention! This shows an example of the i-type filter 28, where 4l is formed by a CCD delay element driven by the clock CLK. In the IH delay circuit, 42 is a coefficient multiplier, and 43 is an adder.

As is well known, this circuit has nfs spacing (n=1
．． 2, 3, 4, etc.), it does not attenuate the frequency vector spectrum generated. n-1/
Attenuation determined by the coefficient k (1>k>0) of the coefficient multiplier 42 is given to the frequency spectrum occurring at intervals of 2 f n, and its frequency characteristics are f′■ as shown in FIG. The damping position increases with the interval, so-called
It has a comb-shaped passage characteristic.

In addition, in the embodiment of the present invention, the coefficient k is set to 1 or less,
As shown in FIG. 3, the characteristic is that the attenuation amount is shallow and has a comb-shaped characteristic.

In the case of the magnetic recording/reproducing circuit of the present invention, as described above, the horizontal filter 28 having shallow attenuation characteristics, which is embodied by a CCD delay element, is disposed in the reproducing circuit, and this i4-shaped filter characteristic is By removing the crosstalk of frequencies around 2 Mif, which indicate the fine parts of the video signal, ，It's not noticeable on the screen.

In addition, the V level difference (frame level difference) that occurs due to the l/2f■ shift during recording can be solved by shallowly removing the signal component with low crosstalk mixed in the demodulated luminance signal, that is, as described above. By removing the signal corresponding to the frequency spectrum component of the rectangular wave signal, the occurrence of step differences is prevented and line crawling is suppressed.

Note that if you only want to remove crosstalk, you can deepen the attenuation characteristic of the horizontal filter, but if you deepen the attenuation characteristic, the video signal V (h) before IH will be affected by the next scanning line as shown in Figure 4. The afterimage image signal V (h+1) is projected on the screen:. , the vertical resolution will be degraded.

Therefore, in the case of the present invention, the attenuation characteristics of the #III type filter 28 are set to be flat and shallow by using a CCD element, and at the same time, the circuit is simplified, and at the same time, the image quality due to crosstalk is improved in practice. This is done to make the deterioration less noticeable.

“Effects of the Invention J As explained above, the magnetic recording bpi generation circuit of the present invention has the following features:
During recording, the brightness signal is 1/1 between each track A and B.
When recording with FM modulation that shifts the amount by 2fH, when playing back... In order to remove crosstalk from adjacent tracks mixed in the demodulated luminance I8, a filter with shallow S-type characteristics is used, so a simple configuration can be used to remove lFil 1: Previous afterimage. This has the effect of making it less noticeable on the screen, and also reducing line crawling due to step differences.

Furthermore, a shallow comb filter can be constructed at low cost using a CCD. (2) Since the step return circuit can be omitted, there is an advantage that the cost of the VTR can be reduced.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the reproducing circuit of the magnetic recording/reproducing circuit of the present invention, Fig. 2 is a block diagram showing a specific example of a comb filter, Fig. 3 is a characteristic diagram of the comb filter, and Fig. 4 is an afterimage. FIG. 5 is an explanatory diagram of the l/
2 f'. A block diagram of the recording circuit for performing the shift,
Figure 6 is a waveform diagram showing the frequency deviation of the FM signal during recording.
FIG. 7 is a diagram showing the frequency spectrum of tracks A and H, and FIG. 8 is a characteristic diagram of a comb filter using a glass delay line. In the figure, 21A and 121B are rotary heads, 25 is an FM demodulator, and 26 is a comb filter.

Claims (1)

[Claims] A magnetic recording/reproduction method in which a luminance signal is modulated into an FM signal with a frequency difference of 1/2 f_H in each field unit, and the FM signal is sequentially recorded and reproduced in a field unit on a track inclined with respect to the running direction of a magnetic tape. In the circuit, a comb-type filter using a CCD is adopted as a circuit for reproducing and demodulating the FM signal recorded on the magnetic tape,
A magnetic recording/reproducing circuit characterized in that the pass characteristic of the comb filter is set to be substantially flat within the signal band of the luminance signal and to provide a predetermined amount of attenuation.