JPS6011378B2 - Optical recording signal reproducing device - Google Patents

Description

[Detailed description of the invention]

The present invention provides an apparatus for optically recording and reproducing information.
The present invention relates to a device that reduces the influence of noise contained in a reproduced signal and effectively demodulates the reproduced signal. Generally, an optically high-density audio signal or image signal is FM-modulated using a carrier having a frequency set to an appropriate value, and then recorded on a high-density recording medium. In the reproduction of this recorded signal, a minute spot of a size corresponding to the maximum unit on the recording medium of the recorded information is irradiated,
A recorded signal is reproduced by the reflected light, scattered light, or transmitted light. In these devices, the frequency shift of the FM signal is generally wide compared to the carrier frequency. This is done in order to effectively utilize the recording medium and the maximum recording/reproducing disassembly for recording and reproducing for as long as possible, and to improve the S/N of the recording medium itself by converting it into an FM signal. In order to record and reproduce signals over a long period of time, the carrier frequency is generally made as low as possible, and the frequency shift is made as large as possible in order to improve the S/N ratio of the demodulated signal. Furthermore, when optically reproducing information by irradiating a minute light spot onto a high-density recording medium as described above, the reproduction signal may be affected by blocking or transparent noise caused by dust, scratches, or pinholes on the recording medium. necessarily accompanies. Such a noise section often does not contain signal components of the reproduced signal, resulting in dropout, and when demodulated by a secondary FM demodulator, becomes a large noise. Currently, a common method for reducing this type of noise is to use a phase-locked loop (PLL) to compensate for the dropout portion. In Figure 1, waveform [1] is the FM signal reproduced from the recording medium.
In the waveform [1], A indicates the above-mentioned blocking noise, and B indicates the transparent noise. When blocking noise A and transparent noise B occur in this way,
No signal is included in that part, resulting in a dropout, and when this is FM demodulated, it is output as a large noise as shown in C of waveform [m]. A PLL is used to reduce this noise. Waveform

[0] is an example of the PLL output waveform,
In the dropout portion, a signal is inserted so that the frequency is closer to the FM modulation carrier frequency than the frequency before the dropout. Therefore, the noise is reduced as shown by D in the waveform [m]. Waveform [m] E is a waveform diagram of the demodulated signal when there is no dropout. However, if the width of the dropout is noise outside the lock range of the PLL, it deviates from the lock range of the PLL and generates abnormal noise. Similarly to waveform [1], waveform [W] is a reproduced signal waveform, and even if there is no noise like that shown in A and B of waveform [1], when the signal at the time of recording is overmodulated, the PLL may deviate from the lock range and generate abnormal noise as shown in F' of the waveform [V]. When using PLL in this way,
In order to avoid generating abnormal noise, it is desirable to perform recording and reproduction within the lock range of the PLL as much as possible. However, when the modulation carrier is low and a broadband frequency shift is required, such as in an optical recording/reproducing device, there is no PLL with a wide lock range that can be used for this purpose, and most of them are used within the lock range of the PLL. Also, methods of expanding the lock range have been considered. However, if the frequency deviation of the FM signal is narrowed to fit within the lock range of the PLL, no improvement in FM can be obtained, and various methods have been proposed to expand the lock range, but the circuit There were problems such as increased complexity. FIG. 2 shows an example of a conventional optical recording/reproducing device. Terminal 1 is an input terminal for audio signals, image signals, etc. 2
is an FM modulation circuit for converting the signal input from terminal 1 into the FM signal required for recording, 3 is a light source such as a laser, and 4 is an FM signal.
This is an optical modulator for converting the FM signal from the M modulation circuit 2 into an optical information signal. 5 is a recording medium; 6 is a photodetector for reproducing the FM signal recorded on the recording medium 5; the detected signal is converted into an electric signal and is applied to the reproducing amplifier 7; 8 is a band pass filter for removing noise outside the signal band, and 9 is a PLL circuit, whose purpose is to fill in areas where there is no signal such as dropouts and to reduce noise. 1M limiter circuit 11 is an FM modulation circuit, which demodulates the reproduced FM signal into an audio signal or image signal inputted to input terminal 1 and outputs it from terminal 12. FIG. 3 shows the frequency band range at the time of recording and reproducing in the optical recording and reproducing apparatus shown in FIG. 2. As an example, a case will be described in which a high-speed audio signal such as a current FM broadcast is recorded. 3A shows the frequency band range of the ×h audio signal inputted from the terminal 1 in FIG.
0 plate HZ, and FM modulation is performed by the FM modulation circuit 2 using the audio signal shown in A. However, as mentioned in the previous section, in order to perform long-time recording and playback and high-quality recording and playback, wideband (as an example, frequency shift , FM modulation is performed at 400KHZ±200KHZ). C indicates the frequency band of the FM signal reproduced from the recording medium 5, and : indicates the frequency band of the audio signal obtained by FM demodulating the reproduced signal C. In the above case, dropout occurs in the reproduced signal C due to dust or scratches adhering to the recording medium 5, and noise occurs in the demodulated audio signal II.
In order to reduce this noise, PLL9 is used as shown in Figure 2.
However, as mentioned above, the PLL lock range is narrow, so the recording signal band is limited.
The improvement effect of using FM cannot be sufficiently obtained, and overmodulation causes the PLL to go out of lock range, causing abnormal noise. The present invention relates to an improvement over the prior art described above. The details of the present invention will be explained below along with examples. In FIG. 4, since the recording system circuit can be performed in the same manner as in FIG. 2, it will be omitted, and only the reproduction system will be explained. In FIG. 4, reference numeral 13 denotes a photodetector for obtaining a reproduced signal, which converts optical information into an electrical signal and inputs it to a regenerative amplifier 14. A bandpass filter 15 removes noise and harmonic components outside the signal band. 16 is a balanced modulation circuit, and 17 is an oscillator that generates an arbitrary constant frequency, and performs balanced modulation of the modulated carrier from the oscillator 17, which may be a crystal oscillator, for example. Reference numeral 18 denotes a bandpass filter that detects a necessary band among the double-side bands generated by the balanced modulation circuit 16. Next, a broken line 28 constitutes a PLL, 19 a phase comparator,
21 is a voltage controlled oscillator (V
CO). 22 is a low pass filter, VC0
The harmonic components of the output signal of No. 21 are removed. A balanced modulation circuit 23 performs balanced modulation of the modulation carrier generated from the oscillator 17 with a signal from the low-pass filter 22. Reference numeral 24 denotes a low-pass filter, which detects only the necessary double-side band that is the output of the balanced modulation circuit 23. A limiter circuit 25 shapes the waveform of the signal from the low-pass filter 24 and sends it to the FM demodulation circuit 26. In the FM demodulation circuit 26, the FM signal, which is a reproduced signal,
Convert to audio signal. FIG. 5 shows the frequency bands of the block diagram of the optical recording/reproducing apparatus shown in FIG. The operation and effects will be described in detail below with reference to FIG. E indicates the frequency band of the 2ch audio signal in the same way as shown in FIG. 3A. is an FM signal required for recording on and reproducing from a recording medium. [As an example, modulation carrier fc=400KH
2. Frequency deviation (fc±△f) 400KH2±200
KH2]. The photodetector 13 and the regenerative amplifier 14 produce a regenerated signal a in a frequency band as shown in FIG. The bandpass filter 15 removes recordings outside the band and also removes harmonic components of the signal. H indicates the frequency band of the output of the balanced modulation circuit 16, and as an example, the oscillator 17
When the modulated carrier frequency h from 2.4 MHZ is set, the output of the balanced modulation circuit 16 is hfc±(fc±△f)
Therefore, hfc-(fc Δf) should be 2MHZ±
200KHZb and hfc ten (fc soil △f) should be 2. Both sides of the main MHZ ± 200 KHZc are obtained, and the lower side band (2 MHZ ± 200
Take out only KH2). By frequency-converting the reproduction signal a to Takagi in this way, the frequency deviation Δf of the FM signal does not change, but the frequency deviation ratio becomes smaller. For example, as mentioned above, the ratio of frequency deviation to 400KHZ for the modulation carrier is 200KH23600KHZ.
In other words, the ratio is 1:3. Also, modulation carrier hfc=2MH
The ratio of frequency deviation to Z is 1.8MHZ:2.2MH
Z, that is, 1:1.22. If the frequency shift is small in such a high frequency band, it can be sufficiently within the lock range of the PLL 28. In other words, the lock range of the PLL 28 has been expanded with respect to the playback signal a. The signal thus converted into a high frequency band by the balanced modulation circuit 16 is input to the PLL circuit 28. In the PLL circuit 28, the phase comparison 19 compares the signal 29 from the bandpass filter 18 and the signal 3 from the VC021.
By comparing the phases of 0 and passing through the low-pass filter 20, an error voltage 3 corresponding to the frequency and phase difference of both signals is generated.
Generates 1. This error voltage 31 is added to the VCO,
Generates a corresponding frequency. In this way, the error voltage 31 changes the frequency of VC021 in a direction that reduces the frequency difference between the input signal 29 and the output frequency 30 of VC021. On the other hand, the output signal of VC021 is low pass filter 2.
In addition to 2, high frequency components are removed, and in the balanced modulation circuit 23, the modulation carrier h from the oscillator 17 has a frequency of 2.4 MHz.
If we perform balanced modulation, we get fox fc-(fo±△f), 4.4
MHZ soil 200KHZ, e of Fig. 5 and (fo±△f
), 400KH2 Sat 200KHZ, the signal d in Figure 5 is obtained, and the same Obijo signal as a in Figure 6 is obtained.
A low-pass filter 24 extracts the signal d. The FM signal d, which has been balanced modulated and converted to the same band as a, is sent to the limiter 2.
5, and demodulated into an audio signal shown in FIG. 5 in an FM demodulation circuit 26. As described above, in the present invention, the signal reproduced from the recording medium is converted into a frequency band range that is sufficiently within the lock range of the PLL, and the frequency band range at the time of recording is not limited by the PLL, and wide band recording and playback is possible. This makes it possible to improve S/N by using FM. Also, the dropout that causes noise when demodulating is P.
Since it is within the lock range of LL, sufficient compensation can be made and noise can be reduced. In addition, in FIG. 4, VC0 of PLL28
The output 30 of the PLL 22 is also balanced modulated to obtain the low-frequency FM band d in Figure 5, and FM demodulation is performed in the low-frequency band.
The control voltage 31 of VC021, which is the output of 0, is also the same signal as the audio signal shown in FIG. It is also possible to do so. In FIG. 6, flocks 13-21 and lines 28-31
is the same as in FIG. 4, so it will be omitted. However, demodulating low-frequency FM signals is better than demodulating high-frequency FM signals.
A larger amplitude can be obtained than the characteristics of the FM modulation circuit,
This is effective by improving the S/N, and therefore, in the present invention, after balanced modulation of the PLL output to the low frequency band, the FM
It demodulates the signal.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of signal waveforms in a conventional optical recording signal reproducing device, Fig. 2 is a circuit diagram of an embodiment of a conventional optical recording signal reproducing device, and Fig. 3 is an explanation of the operation of Fig. 2. A waveform diagram, FIG. 4 is a configuration diagram of an optical recording signal reproducing device according to an embodiment of the present invention, FIG. 5 is an operation explanatory diagram of FIG. 4, and FIG. 6 is a circuit configuration diagram of a different embodiment of the present invention. It is. 13...Photodetector, 14...Amplifier,
15, 18...Band pass filter, 16, 2
3... Balanced modulator, 17... Oscillator, 19
... Phase comparator, 20, 24 ... Low pass filter, 21 ... VC○, 22. ．． ．． ．． ．． ．． LPF, 2
5...Limiter, 2 6...FM demodulation circuit. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] 1 a first filter that removes out-of-band noise from a reproduced electrical signal obtained by optically reproducing an optically recorded signal by FM modulation; an oscillator that generates a constant frequency; and an oscillator that generates a constant frequency; a first balanced modulation circuit that performs balanced modulation using the output of the first balanced modulation circuit; and a second balanced modulation circuit that obtains a sideband in a higher frequency band than one of the double sidebands that is the output of the first balanced modulation circuit. 2 filter and this second filter.
a phase-locked loop circuit that uses the output of the filter as an input signal to approximate a noise section; and a second balanced modulation circuit that balance-modulates an arbitrary constant frequency with the output signal of the phase-locked loop circuit. An optical recording signal reproducing apparatus characterized in that one sideband of a frequency band lower than the output of the phase-locked loop circuit is taken out of the double-sideband output from the second balanced modulation circuit and subjected to FM demodulation.