JPS6260375A - Recording and reproducing device - Google Patents

Abstract

PURPOSE:To securely equalize the characteristic of a recording system to that of a reproducing system and to simplify a circuit by inserting a circuit selectively emphasizing only the component of a signal at a low level in a high frequency band into a recording circuit system in a recording and reproducing device equipped with a high frequency noise canceler in its reproducing circuit system, sharing an HPF and a limiter and installing a circuit switching recording and reproducing at the preceding stage of an HPF circuit. CONSTITUTION:A reproduction signal from a magnetic head 11 is amplified, and high level noises are equalized at the prescribed amplitude by a limiter circuit 13, returned to a video signal by an FM demodulator circuit 14, and inputted to the noise canceler 17 through an LPF circuit 15, a deemphasis circuit 16 and contact points 27 and 28 of a switching circuit 25. A high frequency noise is mixed at the output point E of the deemphasis circuit 16 when the magnetic head 11 reproduces a signal. The signal of a high frequency component at a point B, which passes through the HPF circuit 18, is cut into an amplitude at a low level at a point G through a limiter circuit 19, and a signal of a phase reverse to the signal at a point B can be obtained. A mixing circuit 20 mixes both signals, and weakens a noise at a low level. The signal component of the high frequency previously emphasized by the recording circuit system is weakened, and transmitted to a video output terminal 22 through an output terminal 22.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a recording/reproducing apparatus using a magnetic tape, a magnetic disk, or the like. More specifically, the present invention relates to a recording and reproducing apparatus that improves the characteristics of the entire system by compensating in advance in the recording system for deterioration in low-level high-frequency characteristics caused by a noise canceller provided in the reproducing system.

"Prior Art" First, the recording system will be explained based on Fig. 6.The input terminal (
The video signal input to 1) is sent through an AGC (automatic gain control) circuit (2), an LPF (low pass filter) circuit (3), a clamp circuit (4), and a pre-emphasis circuit (5) that removes high frequencies. Emphasize it appropriately, then clip the white and black signals using the white clip and black clip circuits (6), and
The frequency is modulated by an M (frequency modulation) circuit (7), amplified by a recording amplifier circuit (8), and recorded on a magnetic tape (10) by a recording magnetic head (9).

Next, to explain the reproduction system, the signal recorded on the magnetic tape (10) by the recording circuit is detected by the reproduction magnetic head (11), the preamplifier circuit (12), the limiter circuit (13), and the F
It returns to the original video signal through the M demodulation circuit (14), and further passes through the LPF circuit (15) and the de-emphasis circuit (14).
6), a signal as shown in FIG. 7(a) is output.

In addition to the video signal recorded on the magnetic tape (10), this output signal is mixed with high-frequency noise (n) mainly during reproduction by the magnetic head (11). This noise (n)
is removed by the noise canceller (17). That is, the signal shown in FIG. 7(a) is obtained by a HPF (bypass filter) circuit (18) as a high-frequency component signal as shown in FIG. By cutting with the width (U), a signal as shown in FIG. 7(c) is obtained. The phase of this signal is inverted by 180 degrees and the mixing circuit (
20) and mixed with the signal shown in FIG. 7(a). Then, high-frequency noise (n) appears on the output side as shown in Figure 7(d).
A video signal from which .

"Problems to be Solved by the Invention" Accordingly, the noise canceller provides the effect of removing or reducing high-frequency noise. However, when high-frequency noise is removed, at the same time, low-level high-frequency signal components such as (x) in FIG. 7(a) are lost as shown in (X') in FIG. 7(d). There were problems such as deterioration in image quality and definition.

"Means for Solving the Problems" The present invention has been made in order to solve the above-mentioned problems, and is directed to a recording and reproducing apparatus equipped with a noise canceller for removing high-frequency noise in the reproducing circuit system. , an emphasis circuit for selectively emphasizing only high-frequency low-level signal components is inserted into the recording circuit system, and the emphasis circuit and the noise canceller each consist of an HPF circuit, a limiter circuit, and a mixing circuit. Among them, the HPF circuit and the limiter circuit are shared, and the HP
A recording circuit and a reproducing circuit are connected to each other via a recording/reproducing switching circuit before the F circuit.

"Function" When recording the input signal, switch the switching circuit to the recording side. Then, only the high frequency component signal is extracted from the input signal by the HPF circuit of the emphasis circuit inserted in the recording circuit system, and this is cut to a predetermined amplitude by the limiter circuit. The high-frequency, small-level signal thus obtained is mixed in phase with the original video signal by a mixing circuit.

Then only the high-frequency components are emphasized, and this is recorded on videotape. When reproducing a signal recorded on a videotape, the switching circuit is switched to the reproduction side. Then, the high-frequency noise is removed by the noise canceller, but at this time, some of the high-frequency low-level signal components are also removed or damaged. However, since it is emphasized by the recording circuit system, it is restored to the original video signal. Further, since the noise canceller and emphasis circuit share the HPF circuit and the limiter circuit, the characteristics of the recording system and the reproduction system are reliably matched, and the circuit is also simplified.

“Embodiment” An embodiment of the present invention will be described below based on the drawings. Note that the same parts as in FIG. 6 are given the same reference numerals.

In Figure 1, (1) is a video signal input terminal, and this input terminal (1) is connected to the AGC circuit (2) and the LPF circuit (3).
One switching contact of the regeneration switching circuit (25)
26), and an emphasis circuit (23) inserted according to the invention is coupled to the common contact (28). This emphasis circuit (23) includes an HPF circuit (18) that detects high-frequency components, a limiter circuit (19) that keeps the amplitude constant and outputs in the same phase and opposite phase as the input value, and outputs in the same phase. It consists of a semi-fixed level adjustment resistor (24) connected to the side, and a mixing circuit (29) that mixes the output of the LPF circuit (3) and the output of the limiter circuit (19). The output side of this mixing circuit (29) includes a clamp circuit (4), a pre-emphasis circuit (5), a white clip and black clip circuit (6), and an FM modulation circuit (7).
, and is coupled to a magnetic head (9) for recording on a magnetic tape (10) via a recording amplifier circuit (8).

The playback circuit system is basically the same as the playback circuit shown in Figure 1, but the de-emphasis circuit (16) is a switching circuit (2
5), and among the components of the noise canceller (17), the HPF circuit (1
8) and the limiter circuit (19) are shared in order to match the characteristics of the recording circuit and the reproduction circuit and to simplify the circuit. The mixer circuit (20) is connected to the opposite phase output side of the limiter circuit (19) via a level adjustment semi-fixed resistor (30).
) to connect.

Next, in the above configuration, the operation of the recording circuit system will be explained first.

When the switching circuit (25) is connected to one of the contacts (26), the video signal input to the input terminal (1) is controlled to have a constant gain by the AGC circuit (2), and then sent to the LPF circuit (3) and the switching circuit. It is input to the emphasis circuit (23) via (25). At the output point (A) of the LPF circuit (3), as shown in FIG.
If a video signal as shown in A) is output, this signal is obtained as an output as shown in FIG. 2(B) in which only high-frequency components pass through the output point (B) of the HPF circuit (18). This output is adjusted to a small amplitude (Q) to become a small level signal by a limiter circuit (19), and the in-phase output point (C)
is output in the same phase as the input point (B). The input and output characteristics of this limiter circuit (19) are as shown in Figure 3.
The input level and output level are approximately -25
It is linear when it is smaller than dB, and the amplitude (
Q) is set.

The output shown in FIG. 2 (C) obtained in this way is sent to the mixing circuit (29) and outputted to the output point (A) shown in FIG. 2 (A
), an output in which only the high-frequency low-level signal is selectively emphasized is obtained at the output point (D) as shown in FIG. 2(D). Specifically, as shown in FIG.
At 0 dB, high-frequency signals are greatly emphasized, and -25
As the input level increases from dB to -20 dB to -10 dB, the signal is gradually emphasized. This output is clamped to a constant level by a clamp circuit (4), and a pre-emphasis circuit (5) moderately emphasizes high-frequency components to prevent high-frequency S/N deterioration. ), the white level and black level are clipped to predetermined values, the signal is modulated into an FM signal by an FM modulation circuit (7), amplified by a recording amplifier circuit (8), and sent to a magnetic head (9). Then, the magnetic tape (
10) is recorded with the high frequency low level signal emphasized.

Next, the operation of the reproducing circuit system will be explained. Switching circuit (25)
is connected to the other contact (27) side. A reproduced signal is taken out by a magnetic head (11) from the magnetic tape (10) on which the signal is recorded, amplified by a preamplifier circuit (12), and adjusted to a predetermined amplitude by a limiter circuit (I3) to remove large-level noise. , the FM demodulation circuit (14) demodulates it back to the original video signal, and then the contacts (27) (28) of the LPF circuit (15), de-emphasis circuit (16), and switching circuit (25).
) and then input to the noise canceller (17).

At the output point (E) of the de-emphasis circuit (16),
Since high-frequency, low-level noise is mixed mainly during reproduction by the reproduction magnetic head (11), a signal mixed with high-frequency noise (n) as shown in FIG. 2(E) is output.

When this signal passes through the HPF circuit (18), it passes through the point (F) (
At the same position as point (B), only the high-frequency component signal as shown in FIG. 2(F) is obtained. This signal is connected to the limiter circuit (1
9), the signal is cut to a small level of amplitude (flooding) as shown in Figure 2 (G), and a signal with the opposite phase that is 180 degrees reversed from the signal at point (B) is obtained at the output point (G). By mixing the signal at the point (E) with the signal at the point (E) in the mixing circuit (20), small level noise is removed, and
The high-frequency signal components that had been emphasized in advance by the recording circuit system are weakened and returned to their original level, and the signal shown in Figure 2 (H) appears at point (G).
A signal like this is obtained. This signal is output from the output amplifier circuit (
21) and sent to the video output terminal (22).

In the embodiment described above, the limiter circuit (19) is configured to obtain an output that is in phase with the input side and an output that is in opposite phase.

However, the invention is not limited to this, and as shown in FIG. 5, if the mixing circuit (29) is used for addition and the mixing circuit (20) is used for subtraction, the limiter circuit (19) is in phase with the input side. It may also be one that outputs a signal. Also, a mixed circuit (
29) may be used for subtraction, the mixing circuit (20) may be used for addition, and the limiter circuit (19) may output a signal with a phase opposite to that on the input side.

In the above embodiment, a case has been described where the magnetic recording circuit once records on a magnetic tape and then the reproducing circuit reproduces from the magnetic tape. However, the present invention is not limited to this, and the signal recorded in the recording circuit may be transmitted. It can also be used in cases where high-frequency, small-level noise is mixed in the transmission path in a device that transmits data as is through the receiver and transmission line, and reproduces it with the receiver's regeneration circuit.

In the above embodiment, the case where a magnetic tape was used for recording was explained, but it goes without saying that the present invention can be used as is even if a magnetic disk is used.

In the present invention, the high frequency range refers to video signal components of several hundred KHz or higher, and the input signal level to be emphasized is V.
, S IVp-p (V=0.7Vp-pH, pair L0
．． 07vp-p or below.

"Effects of the Invention" Since the present invention is configured as described above, for example, in the case of recording and reproducing video signals, it is possible to achieve both noise reduction in the reproduced luminance signal and faithful reproduction of the high frequency signal. the result,
It is possible to reproduce subtle details such as the shine on the water surface and the gloss on the face.

In addition, the noise canceller in the playback circuit and the emphasis circuit in the recording circuit share the components HPF circuit and limiter circuit, so the characteristics of both circuits are the same, accurate control is possible, and the circuit configuration is easy and inexpensive. can be provided to

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a recording/reproducing apparatus according to the present invention, and FIG. 2 is an output waveform diagram of each part in FIG.
FIG. 3 is a characteristic diagram between the input and output levels of the limiter circuit, FIG. 4 is a characteristic diagram of the emphasis circuit, FIG. 5 is a block diagram of another embodiment according to the present invention, and FIG. 6 is a block diagram of a conventional device. FIG. 7 is an output waveform diagram of each part in the conventional device. (1)...Input terminal, (9)...Magnetic head for recording, (10)...Magnetic tape, (11)...Magnetic head for reproduction, (17)...Noise canceller, ( 18
)...HPF circuit, (19)...limiter circuit, (
20)...Mixing circuit, (22)...Output terminal, (2
3)... Emphasis circuit, (25)... Switching circuit, (26) (27) (28)... Contact, (29)...
...Mixed circuit.

Claims (4)

[Claims] (1) In a recording/playback device equipped with a noise canceller for removing high-frequency noise in the reproduction circuit system, an emphasis circuit is inserted in the recording circuit system to selectively emphasize only low-level signal components in the high frequency range. However, this emphasis circuit and the noise canceller each include an HPF circuit, a limiter circuit, and a mixing circuit, and among these, the HPF circuit and the limiter circuit are shared, and the
A recording/reproducing device characterized in that a recording circuit and a reproducing circuit are coupled to each other via a recording/reproducing switching circuit at the front stage of the circuit. (2) The mixing circuit of the emphasis circuit is used for addition, and this mixing circuit is connected to the in-phase output terminal of the limiter circuit.The mixing circuit of the noise canceller is used for addition, and this mixing circuit is connected to the negative-phase output terminal of the limiter circuit. A recording and reproducing apparatus according to claim 1, comprising: (3) The record set forth in claim 1, wherein the mixing circuit of the emphasis circuit is used for addition, the mixing circuit of the noise canceller is used for subtraction, and both of these mixing circuits are coupled to the in-phase output terminal of the limiter circuit. playback device. (4) The mixing circuit of the emphasis circuit is used for subtraction, the mixing circuit of the noise canceller is used for addition, and both of these mixing circuits are coupled to the negative phase output terminal of the limiter circuit. Recording and playback device.