JPS631649B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical recording device for optically recording and reproducing information such as video and audio onto an information medium using an FM modulation method.

Conventionally, in this type of device, as shown in Figure 1, the duty of the recording pit (hole) decreases in the high frequency range, so the playback output decreases and accurate information cannot be detected, and the video and audio after demodulation decreases. The SNR of such a signal decreases as shown in FIG.
For this reason, when recording color video in analog form using the FM modulation method, a method has been used in which the color subcarrier is reduced and converted. However, this low-frequency conversion method had the disadvantage that characteristics such as SNR, resolution, and moiré were insufficient in order to obtain broadcast-standard image quality.

In order to eliminate these drawbacks, the present invention suppresses the decrease in the duty of the recording pit (hole) on the information medium by increasing the duty of the signal in advance in the high recording frequency area and performing optical recording. It improves the frequency characteristics and the SNR of the video signal after demodulation, and will be explained in detail below with reference to the drawings.

FIG. 3 shows the frequency characteristics of the duty of the optical pulse. 1 means that the duty is almost constant with respect to the signal frequency, 2 means that the duty is increased in proportion to the frequency (hereinafter referred to as duty emphasis in the present invention), and 3 means that the amount of duty emphasis is greater than 2. It's big. 4, 5, and 6 in FIG. 4 are schematic diagrams of optical pulse waveforms corresponding to frequency characteristics 1, 2, and 3 in FIG. 3, respectively. Six of them have waveforms in which the DC component is further biased in addition to the duty emphasis for the signal component.

FIG. 5 shows the frequency characteristics when optical recording is performed using such optical pulses on a disk-shaped medium of equal radius under the condition that the output peak value of the optical pulses is constant. In the figure, frequency characteristics 7, 8, and 9 correspond to optical pulse waveforms 4, 5, and 6 in FIG. 4, respectively. The recording frequency on the vertical axis is the frequency at which the reproduced signal output is half the value at low frequency (-6 dB), and the horizontal axis is the recording power normalized by the recording sensitivity (threshold) of the medium.

The following effects are clear from this experimental result.

(1) In the conventional recording method shown in 7 of FIG. 5, in which neither duty emphasis nor DC bias is used, the recording frequency increases with recording power and eventually saturates to a constant value.

(2) The frequency characteristic indicated by 8 in FIG. 5 using duty emphasis has an improved recording frequency and is less dependent on recording power than the conventional frequency characteristic indicated by 7 in FIG. In other words, when the recording power normalized by the recording threshold is 1.5, the recording frequency at which the output decreases by -6 dB increases by 28%, and when the recording power normalized by the recording threshold is 1.2, the recording frequency decreases by -6 dB.
The recording frequency where the output decreases is increased by 69%.

(3) By adding a DC bias in addition to duty emphasis, the recording frequency improves in the region of low recording power, but conversely decreases in the region of high recording power, resulting in significant recording power dependence.

An embodiment of a semiconductor laser drive circuit according to the present invention for obtaining effects based on each frequency characteristic as described above will be described. Figure 6 10 shows the video
This is an FM signal input such as audio, and the duty conversion circuit 11 modulates the FM signal into a highly modulated optical pulse having a high frequency component. The signal modulated with a high duty causes the semiconductor laser 13 to emit light for a time proportional to the duty by the switching circuit 12.
At this time, in order to record one screen of video per disk rotation, the gate circuit 16 is controlled by the motor rotation synchronization pulse 14 and the recording start pulse 15.
The switching circuit 12 is driven only for one TV frame. Also, if necessary, the DC bias circuit 17
It is possible to add a DC component to the signal component.

Next, the configuration of the duty conversion circuit will be explained.

FIG. 7 is a block diagram of one embodiment of the duty conversion circuit. 10 is an FM signal input, and 11 is a duty conversion circuit. The duty conversion circuit 11 includes a bias circuit 18, an amplifier circuit 19, and a shaping circuit 20. The operation of the duty circuit will be explained with reference to the principle diagram of duty emphasis shown in FIG. In the figure, 10 is the waveform of the FM signal input, 21 is the biased FM signal waveform, and 22 is the amplified output of the FM signal output, which is shaped by the shaping circuit 20 to obtain a duty-emphasized signal 23. In this example, the duty increases by increasing the amplification factor of the amplifier circuit 19 and keeping the limiter level of the shaping circuit 20 constant for high frequency components.

As explained above, optical recording using a signal whose duty is increased in proportion to the frequency has the effect of improving the duty of pits (holes) on the information medium and increasing the recording frequency. Furthermore, in the case of unsaturated recording where the optical power is insufficient for the sensitivity of the information medium, the recording frequency can be improved by further biasing the DC component.

Therefore, when recording video information in analog form using the FM modulation method, direct FM modulation is possible without depending on the low-frequency conversion method of the color subcarrier.
Also, among the direct FM modulation methods, a high-band method with a high carrier frequency (7.9MHz) and a high degree of modulation is possible. According to experiments, the high-band method improved SNR by 7 dB compared to the low-band method.

[Brief explanation of the drawing]

Figure 1 shows that the duty of the optical recording pit decreases at high frequencies, and Figure 2 shows that the duty of the optical recording pit decreases at high frequencies.
Figure 3 shows the relationship between the SNR of the video signal after FM demodulation, Figure 3 shows the frequency characteristics of the duty of the optical pulse, Figure 4 shows the waveform of the optical pulse, Figure 5 shows the relationship between recording frequency and recording power, and Figure 6 shows the relationship between the recording frequency and recording power. 7 is a block diagram of a semiconductor laser drive circuit for optical recording, FIG. 7 is a block diagram of a duty conversion circuit, and FIG. 8 is a diagram of the principle of duty emphasis. 10...FM signal input, 11...Duty conversion circuit, 12...Switching circuit, 13...Semiconductor laser, 14...Motor rotation synchronization pulse, 15
...recording start pulse, 16...gate circuit,
17... DC bias circuit, 18... Bias circuit, 19... Amplification circuit, 20... Shaping circuit.

Claims (1)

[Claims] 1. An optical recording device that optically records information such as video and audio on an information medium using an FM modulation method and optically reproduces the information, comprising: an FM signal recorded on the information medium; 1. An optical recording device, characterized in that the input section is equipped with duty conversion means for increasing the duty of an FM signal for recording in proportion to the recording frequency.