JPH0311025B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording/reproducing device, and more particularly to a signal processing circuit for improving the S/N ratio when reproducing a video signal.

Taking a VTR as an example of a magnetic recording/reproducing device,
The level of the reproduced FM signal read from the tape is proportional to the track width, and the S/N ratio is proportional to the square root of the track width. By the way, in recent years VTR
As the length of time increases, the track width on the tape surface gradually becomes narrower, and compared to the standard mode (track width 58 μm for VHS), the track width becomes 19 μm in 3x mode (long time). The influence of a decrease in track width on the reproduced signal level, especially on the S/N ratio, is becoming more and more significant. Therefore, in the long-time 3x mode, as a conventional means of improving the S/N ratio, it is possible to apply non-linear emphasis or FM interleaving, which automatically changes the amount of emphasis according to the level of the input video signal. It is being done.
However, this is to prevent the reversal phenomenon and improve the S/N ratio deterioration, and the playback in each mode
This is not a correction for variations in FM signal level. Even in each mode itself, there are variations in the level of the reproduced FM signal due to differences in the characteristics and type of tape (soft tape, tape demagnetized by repeated use, etc.), which causes S/N
There is a considerable difference in the ratio. Such a difference in S/N ratio has the drawback of making video playback extremely unstable.

Therefore, the main object of the present invention is to provide a magnetic recording and reproducing device that can improve the S/N ratio of a reproduced video signal regardless of the track width for recording provided on a magnetic recording medium. It is.

The above objects and other objects and features of the present invention will become more apparent from the following description with reference to the drawings.

To summarize the invention, the level of a reproduced FM signal is detected, the impedance is varied by an impedance variable means according to the detected level, and the video is demodulated by a demodulator according to the varied impedance. The S/N ratio is improved by changing the frequency characteristics of the signal.

The drawing is a block diagram showing the configuration of an embodiment of the present invention. In the figure, the reproduced FM signal extracted by the tape video head system (not shown) is
As conventionally done in this type of device, the signal is applied to input terminal 1, amplified by head AMP 2, phase and frequency corrected by FM equalizer 3, and passed through limiter 4 and FM demodulator 5. and demodulated into a video signal. This video signal is further passed through a de-emphasis circuit 6 to form a video signal in which noise in the high frequency range is suppressed.
A frequency correction circuit 7 is provided at the next stage of the de-emphasis circuit 6, and the frequency correction amount is controlled by receiving the output of the impedance variable means, which will be described next. The output terminal 8 is reached. The signal delivered to the output terminal 8 is mixed with a chroma signal processed in another processing circuit and supplied as a composite video signal to a video output terminal (not shown) and an RF converter (not shown).

In the reproduced FM signal processing circuit having the above configuration, the present invention is provided with an AM detector 9 to which the reproduced FM signal X outputted from the FM equalization circuit 3 is input, and in which the reproduced FM signal Detect the magnitude of the level. At the next stage of the AM detector 9, an impedance variable means 10 is provided whose output signal Y is given to the frequency correction circuit 7 in the reproduced FM signal processing circuit system, and the reproduced FM signal detected by the AM detector 9 is An output signal Y formed by variable impedance based on the level of X is output.
Since this signal Y is given to the frequency correction circuit 7, the frequency correction circuit 7
The frequency characteristic correction amount is controlled to apply frequency characteristic correction corresponding to the level of the FM signal to the reproduced video signal output from the de-emphasis circuit 6, and the video signal with the frequency characteristic corrected is output to the terminal 8. be done.

For example, when the level of a reproduced FM signal read from a magnetic recording medium with a narrow track width is low, the AM detector 9 detects that the signal level is low.
This level detection signal increases the impedance of the variable impedance means 10, and the signal from the variable means 10 having this large impedance causes the frequency correction circuit 7 to operate in the direction of decreasing the amount of correction. In other words, the amount of correction in the frequency correction circuit 7 is controlled by the level of the reproduced FM signal, and the input reproduced FM
A video signal that has been corrected according to the signal level is derived from the output terminal 8.

Level detection is performed in the above configuration.
Although the output of the FM equalization circuit 3 is given as the input to the AM detector 9, the output of the head AMP 2 can also be used in the same manner.

The present invention is not limited to the VTR of the above embodiment, but can be applied to magnetic recording devices in general.

As described above, according to the present invention, the level of the reproduced FM signal is detected, the impedance is varied by the impedance variable means according to the detected level of the reproduced FM signal, and the impedance is demodulated according to the varied impedance. playback by changing the frequency characteristics of the video signal demodulated by
It is possible to set the frequency correction amount according to the FM signal. Therefore, the difference in S/N ratio can be significantly reduced, and a stable reproduced signal can be formed, regardless of the characteristics or types of tapes that cause variations in the level of the reproduced FM signal.

[Brief explanation of drawings]

The figure is a block diagram of one embodiment of the present invention. In the figure, 2 is a head AMP, 3 is an FM equivalent circuit, 7 is a frequency correction circuit, 9 is an AM detector, 1
0 indicates impedance variable means.

Claims (1)

[Claims] 1. A magnetic recording and reproducing device that processes a reproduced FM signal read from a magnetic recording medium, comprising: demodulating means for demodulating the reproduced FM signal into a video signal; and a level detection unit for detecting the level of the reproduced FM signal. means, impedance variable means for varying impedance according to the level detected by the level detecting means, and impedance variable means demodulated by the demodulating means according to the impedance varied by the impedance variable means. A magnetic recording and reproducing device equipped with a frequency control means for controlling the frequency characteristics of a video signal.