JPH064966U - RF amplifier for optical disk playback device - Google Patents

Abstract

(57) [Abstract] [Purpose] EFM when playing a disc with many scratches.
Reduce signal read errors. [Structure] A resistor R4 and a field effect transistor Q are used as feedback impedance of an operational amplifier 3 which constitutes an RF amplifier 9.
1 series circuit is added in parallel. The gate of the field effect transistor Q1 is connected via a resistor R5 to a connection point of a series circuit of a digital transistor Q2 and a resistor R6 connected between a + 5V power source and a -5V power source. The base of the digital transistor Q2 is connected to the ground via the switch SW1.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an optical disk reproducing apparatus, and more particularly to an RF amplifier for an optical disk reproducing apparatus that improves the reproduction state of an optical disk having scratches on its surface.

[0002]

[Prior art]

 FIG. 3 shows an example of an RF amplifier of a conventional optical disc reproducing apparatus. The output signal of the optical pickup 1 for reproducing the recorded information on the optical disc is input to the RF amplifier 8 after the high-pass components other than the audio E FM signal are removed by the low-pass filter 2.

The RF amplifier 8 includes an operational amplifier 3, an input resistor R1, a resistor R2, a resistor R3, and a feedback impedance of a series-parallel circuit of a capacitor C1. The gain of the RF amplifier 8 is an impedance ratio between the feedback impedance and the input resistance R1, and its frequency characteristic is designed to correct the frequency characteristic of the light receiving element of the optical pickup 1 and the current-voltage conversion circuit. The EFM signal is taken out from such an RF amplifier.

[0004]

[Problems to be solved by the device]

 The RF amplifier of the above-mentioned conventional optical disc reproducing apparatus can obtain an EFM signal with less jitter by emphasizing and amplifying the low frequency component of the EFM signal according to its frequency characteristic when reproducing an optical disc without scratches. .

However, when an optical disc with scratches is reproduced, the frequency band of the disturbance component due to the scratches coincides with the emphasized band, so that EFM data reading error occurs and noise occurs in the voice. It had the drawback of being easy.

The present invention has been made in view of the above points, and an object thereof is an optical disk reproducing apparatus capable of reproducing audio with less noise even when reproducing an optical disk with many scratches. To provide the RF amplifier of.

[0007]

[Means for Solving the Problems]

 The RF amplifier of the optical disk reproducing apparatus of the present invention is an RF amplifier that amplifies an audio EFM signal read from an optical disk and corrects the frequency characteristic, and the frequency characteristic can be switched.

Further, in the RF amplifier of the optical disc reproducing apparatus, the frequency characteristic is switched by an external switch.

Further, in the RF amplifier of the optical disc reproducing apparatus, the frequency characteristic is switched by a signal indicating an error detection of audio data obtained from the audio EFM signal.

[0010]

[Action]

 According to the RF amplifier of the optical disk reproducing apparatus of the present invention, its frequency characteristic can be switched by an external switch or an audio data error detection signal. If the switched frequency characteristics are designed so that the gain in the disturbance band due to scratches is low, the data reading error due to the disturbance is reduced and it is possible to reproduce voice with less noise.

[0011]

【Example】

 An RF amplifier of an optical disk reproducing apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing an RF amplifier of an optical disk reproducing apparatus according to an embodiment of the present invention.

In the RF amplifier 9 shown in FIG. 3, a series circuit of a resistor R4 and a field effect transistor Q1 is added in parallel as a feedback impedance of an operational amplifier in the RF amplifier shown in FIG. Other configurations are the same as those shown in FIG.

The gate of the field effect transistor Q1 is connected via a resistor R5 to a connection point of a series circuit of a digital transistor Q2 and a resistor R6 connected between a + 5V power source and a −5V power source. The base of the digital transistor Q2 is connected to the ground via the switch SW1.

In the above structure, during reproduction of a normal optical disk, the switch SW1 is turned off, the digital transistor Q2 is turned off, and the gate of the field effect transistor Q1 becomes -5V.

Therefore, the field effect transistor Q1 is in the cutoff state, and the feedback impedance of the operational amplifier 3 is the impedance of the series-parallel circuit of the resistors R2, R3 and the capacitor C1. E Amplify the FM signal as the best jitter condition.

When reproducing an optical disc with many scratches, the switch SW1 is turned on, the digital transistor Q2 becomes conductive, and the gate of the field effect transistor Q1 becomes + 5V.

Therefore, The field effect transistor Q1 becomes conductive, and a resistor R4 is added in parallel as a feedback impedance of the operational amplifier 3. Therefore, the feedback impedance in the low frequency range becomes small, and the gain proportional to the feedback impedance also becomes small. Therefore, the disturbance component due to scratches is suppressed and the jitter is slightly worsened, but the read error is reduced.

FIG. 2 shows a modification of the above embodiment. In this case, the base of the digital transistor Q2 of FIG. 1 is connected to the output terminal of the inverter 7. The EFM signal is demodulated into a voice signal by the EFM decoder 4 and the error detection circuit 5, but if the EFM data has an error, the error detection circuit 5 outputs an error detection signal.

The error detection signal is input to the trigger input terminal of the retriggerable monostable multivibrator 6, and the output signal of the retriggerable monostable multivibrator 6 is output to the input terminal of the inverter 7.

When the error detection signal is output from the error detection circuit 5, the output of the retriggerable monostable multivibrator 6 is at a high level for a certain period, and the field effect transistor Q1 is conductive during that period. As described above, the reading error of the EFM signal is reduced. In this case, the state of the optical disk is automatically judged and the frequency characteristic of the RF amplifier is switched.

[0021]

[Effect of device]

 According to the RF amplifier of the optical disk reproducing apparatus of the present invention, the reading error of the EFM signal can be reduced when reproducing a disk with many scratches, and moreover, the jitter is in the best state when reproducing an optical disk without scratches. Is possible.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an RF amplifier of an optical disk reproducing apparatus according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a modified part of the embodiment.

FIG. 3 is a circuit diagram showing an example of an RF amplifier of a conventional optical disc reproducing apparatus.

[Explanation of symbols]

 1 Optical Pickup 2 Low Pass Filter 3 Operational Amplifier 4 EFM Decoder 5 Error Detection Circuit 6 Retriggerable Monostable Multivibrator 7 Inverter 8 RF Amplifier 9 RF Amplifier

Claims (3)

[Scope of utility model registration request] 1. An RF amplifier for an optical disk reproducing apparatus, wherein an RF amplifier for amplifying an audio EFM signal read from an optical disk and correcting the frequency characteristic is capable of switching the frequency characteristic. 2. An RF amplifier for an optical disk reproducing apparatus according to claim 1, wherein the frequency characteristic is switched by an external switch. 3. The RF amplifier for an optical disk reproducing apparatus according to claim 1, wherein the frequency characteristic is switched by a signal indicating error detection of audio data obtained from the audio EFM signal.