JPH0198164A - Characteristic switching device for amplifier circuit used for digital reproducing system - Google Patents

Abstract

PURPOSE:To obtain accurate reproducing signals at the time of reproducing at standard speed and high speed by switching the characteristic of an amplifying circuit in interlocking with the switching of a reproducing speed. CONSTITUTION:The output of a four division type optical detector 15 in a pickup 15 passes through I/V conversion amplifying circuits 17 and 18, is added, is inputted to the negative terminal of a wide band amplifier 19, and the output is fed back in a circuit 20, whereby a positive terminal is earthed. The feedback circuit 20 consists of a resistance R, a capacity C and a transistor Q. When the signal of an H level is fed to the base 49 of an element Q from a reproducing speed control circuit 43 at the standard speed for reproduction, the element Q is turned on, and the frequency characteristic of the amplifier 19 attenuates more than 700kHz. When the signal of an L level is inputted to the terminal 49 at the twofold speed of the standard one for reproduction, the element Q is turned off, and the frequency characteristics of the amplifier 19 are decided in R3-R5, C1 and C2, and they attenuate more than 1,400kHz, whereby the optimum characteristics can be obtained. With such a constitution, the accurate signals can be obtained at either speeds.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a digital playback system capable of switching the playback speed, and in particular, to change the characteristics of an amplifier circuit that amplifies a playback signal depending on the playback speed. The present invention relates to a characteristic switching device for switching characteristics.

(Prior Art) As is well known, in a digital playback system such as a compact disc player, the recording time is determined in consideration of recording the played analog audio signal on another recording medium such as a tape. In order to shorten the time, some devices have been added with a function that allows playback to be performed at twice the standard speed.

However, this type of digital playback system is still in the development stage, and there are two types of playback: playback at standard speed and playback at twice the standard speed.
There is still much room for improvement in terms of configuration and performance so that optimal playback operations can be performed.

(Problems to be solved by the invention) As mentioned above, the conventional digital playback system, which has the function of playing at twice the standard speed, is still not able to fully meet the needs of users. I have a problem.

Therefore, this invention was made in consideration of the above circumstances, and by switching the characteristics of the amplifier circuit that amplifies the reproduced signal according to the reproduction speed, it is possible to perform reproduction at standard speed and at a speed faster than the standard. It is an object of the present invention to provide an extremely good characteristic switching device for an amplifier circuit used in a digital reproduction system, which allows accurate reproduction signals to be obtained at any time.

[Configuration 1 of the Invention (Means for Solving the Problems) That is, the characteristics switching device of the amplifier circuit used in the digital reproduction system according to the present invention drives the recording medium and changes the digital information recorded on the recording medium. This device reads the signal and leads it to the amplifier circuit, and is intended for digital playback systems that can switch the playback speed by changing the drive speed of the recording medium, and is configured to switch the characteristics of the amplifier circuit by driving when the playback speed is changed. It is something.

(Function) According to the above configuration, since the characteristics of the amplifier circuit are switched by driving when switching the playback speed, it is possible to change the characteristics of the amplifier circuit when playing at the standard speed and when playing at a speed faster than the standard. This also makes it possible to obtain accurate reproduction signals.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings. FIG. 3 shows the overall structure of a compact disc player to which the present invention is applied and whose playback speed can be switched.

That is, numeral 11 in the figure denotes a separate disc playback section, which includes a disc table 14 on which a disc 12 is placed and rotated by the action of a disc motor 13, an optical pickup 15 that reads digital data recorded on the disc 12,
It is comprised of a pickup feed motor 16 that moves this optical pickup 15 in the radial direction of the disk 120.

Then, the reproduction R output from the optical pickup 15
The F signal is transmitted to an analog amplifier circuit 21 consisting of a current-voltage conversion amplifier circuit 17.1g, a wideband RF amplifier circuit 19, and a feedback circuit 20 that determines the characteristics of the wideband RF amplifier circuit 19.
After being amplified, the signal is supplied to the servo control circuit 22.

This servo control circuit 22 controls the reproduction R performed by a person.
The F signal is level-sliced at a predetermined slice level and converted into digital data, and a disk motor control signal and a pickup feed motor control signal are generated based on this digital data.

Of these, the disk motor control signal is supplied to the disk motor 13 via a drive circuit 25 consisting of an amplifier circuit 23 and a feedback circuit 24, and its rotational speed is controlled. Further, the pickup feed motor control signal is supplied to the pickup feed motor 16 via the drive circuit 26, and the optical pickup 1
The moving speed of 5 is controlled.

Note that within the analog amplifier circuit 21, a tracking error signal and a focus error signal are generated. Of these, the tracking error signal is supplied to the optical pickup 15 via a drive circuit 29 consisting of an amplifier circuit 27 and a feedback circuit 28, and tracking servo is performed for an objective lens (not shown). Further, the focus error signal is supplied to the optical pickup 15 via a drive circuit 32 consisting of an amplifier circuit 30 and a feedback circuit 31, and focus servo for the objective lens is performed. .

Here, the servo control circuit 22 uses a phase locked loop circuit (PLL) based on the generated digital data.
) 33 to generate a bit synchronization clock.

Then, the servo control circuit 22 generates a data extraction clock based on the bit synchronization clock and outputs it to the digital signal processing circuit 34 together with the digital data.

This digital signal processing circuit 34 synchronizes with a system clock outputted from a clock generation circuit 36 equipped with a crystal oscillator 35,
1 is used to absorb jitter components, correct errors, and perform correction processing on digital data. The digital data output from this digital signal processing circuit 34 is then transferred to a D/A (digital/analog) conversion circuit 38.
The signals are converted into R-channel analog signals and supplied to an audio reproduction system (not shown) via amplifier circuits 39 and 40 and output terminals 41 and 42, respectively.

Here, this compact disc player has:
A reproduction speed control circuit 43 is provided.

When the disc 12 is required to be played back at twice the standard playback speed, the playback speed control circuit 43 controls the crystal oscillator 35 and the phase-locked loop circuit 33 to use a system clock at twice the standard frequency. and control to generate a bit synchronized clock, and each feedback circuit 2
Wideband RF amplifier circuit 19 for 0.24.28.31
．． This functions to switch the characteristics of the drive circuits 25, 29, and 32 so that they are optimal for reproduction at twice the standard speed.

The playback speed control circuit 43 also has the function of causing the display circuit 44 to display the operating status, time, etc. of the compact disc player.

Here, the system clock output from the clock generation circuit 36 is supplied to the cassette tape recorder 46 via the digital signal processing circuit 34 and the synchronization control circuit 45. This cassette tape recorder 46 is of a type in which the tape running speed during recording and reproduction changes in synchronization with the system clock, that is, the recording and reproduction speed changes.

Therefore, when the disc 12 is being played back at the standard speed, the system clock is also at the standard frequency, so when the cassette tape recorder 46 is set to the recording state, its recording speed is also standard, and the output terminals 4.1. The acoustic signal output from 42 is recorded on the tape at standard speed. Furthermore, when the disc 12 is being played back at twice the standard speed, the system clock is also at twice the standard frequency, so if the cassette tape recorder 46 is set to recording mode, the recording speed will also be twice the standard speed. Therefore, the acoustic signal output from the output terminals 41° and 42 is recorded on the tape as standard 2.
Records will be recorded at twice the speed.

FIG. 1 shows details of the analog amplifier circuit 21. As shown in FIG. That is, 47 in the figure is the optical pickup 15.
Four light-receiving areas A are installed inside the photodetector.
-D. Then, the output currents from the light receiving areas A and C are added together and supplied to the current-voltage conversion amplifier circuit 17.
The output currents from B and D are added together and supplied to a current-voltage conversion amplifier circuit 18.

Here, the outputs of the current-voltage conversion amplifier circuits 17 and 18 are added together via resistors R1 and R2, and then supplied to the negative input terminal of the wideband RF amplifier circuit 19. Further, the positive input terminal + of this broadband RF amplifier circuit 19 is grounded, and the output terminal is connected to the servo control circuit 22 via the output terminal 48.

Furthermore, resistors R3 to R5, capacitors CI,
A feedback circuit 20 consisting of C2 and transistor Q is interposed. The base of the transistor Q is connected to a connection terminal 49. This connection terminal 49 is supplied with a signal from the playback speed control circuit 43 that is at the H level when the disc 12 is played back at the standard speed, and is at the L level when the disc 12 is played back at twice the standard speed. It is done like this.

Therefore, when the disc 12 is being played back at the standard speed, an H level signal is supplied to the connection terminal 49, so the transistor Q is in the on state, so the frequency characteristics of the wideband RF amplifier circuit 19 are is the resistance R3 to R5
and a feedback circuit 20 consisting of capacitors C1 and C2.

That is, during standard speed playback, the wideband RF amplifier circuit 19
The frequency characteristics are similar to those of conventional compact disc players that play only standard speed, and as shown in Figure 2A, they are approximately flat, rise around 700 kHz, and then attenuate as the frequency increases, i.e., standard speed. The characteristics are set to be optimal for the frequency of the reproduced RF signal to be reproduced.

On the other hand, when the disc 12 is being played back at twice the standard speed, an L level signal is supplied to the connection terminal 49, so the transistor Q is in the off state, so the broadband RF amplifier circuit 19 The frequency characteristics of resistor R3~
It will be determined by the feedback circuit 20 consisting of R5 and capacitor C1.

In this case, as shown in Figure 2B, the frequency characteristics of the wideband RF1 [circuit 19] are approximately flat, rising around 1400 kllz, which is twice 700 kHz, and then attenuating as the frequency increases, i.e., the standard The characteristics are set to be optimal for the frequency of the reproduced RF signal that is reproduced at twice the speed.

Therefore, according to the configuration of the above embodiment, the frequency characteristics of the wideband RF amplifier circuit 19 that amplifies the reproduced RF signal are adjusted to be optimal for the obtained reproduced RF signal according to the reproduction speed of the disc 12. Since the speed is switched, accurate reproduction signals can be obtained both when playing back at the standard speed and when playing back at twice the standard speed.

Regarding this point, if the frequency characteristics of the wideband RF amplifier circuit 19 remain compatible with standard speed playback as shown in FIG. Since the phase characteristics do not match the signal, a problem arises in that jitter increases and the amount of error correction increases significantly, making it impossible to obtain a good reproduced signal.

Furthermore, if the frequency characteristics of the wideband RF amplifier circuit 19 are fixed in advance to those corresponding to playback at twice the standard speed, as shown in FIG.
k) Since the characteristics are flat near lx, it is not possible to obtain a good reproduction signal, so it is necessary to change the frequency characteristics of the wideband RF amplifier circuit 19 between standard speed reproduction and double speed reproduction. occurs.

Here, the optical pickup 15 is of an ideal type in which the response to the frequency of the reproduced RF signal during reproduction at twice the standard speed is shifted as is from the response to the frequency of the reproduced RF signal during reproduction at the standard speed. Therefore, when playing at twice the standard speed, we created a frequency characteristic that compensates for the deviation.
It is also possible to set the constant of the feedback circuit 20.

It should be noted that the present invention is not limited to the above-mentioned embodiments, and can be implemented with various modifications without departing from the gist thereof.

[Effects of the Invention] Therefore, as detailed above, according to the present invention, the characteristics of the amplifier circuit that amplifies the reproduced signal are switched according to the reproduction speed, so that the reproduction speed is higher than the standard speed and when the reproduction signal is reproduced at the standard speed. It is possible to provide a characteristic switching device for an amplifier circuit used in an extremely good digital playback system that can obtain accurate playback signals even when playing back at high speeds.

[Brief explanation of the drawing]

FIG. 1 is a block circuit configuration diagram showing an embodiment of a characteristic switching device for an amplifier circuit used in a digital reproduction system according to the present invention, FIG. 2 is a characteristic diagram showing frequency characteristics of the same embodiment, and FIG. 1 is a block configuration diagram showing the overall configuration of a compact disc player to which the present invention is applied. 11... Disk playback mechanism section, 12... Disk,
13... Disc motor, 14... Disc table, 15... Optical pickup, 16... Pickup feed motor, 17.18... Current-voltage conversion amplifier circuit, 19... Broadband RF amplification Circuit, 20... Feedback circuit, 21... Analog amplifier circuit, 22... Servo control circuit, 23... Amplifier circuit, 24...
Feedback circuit, 25.26 drive circuit, 27... amplifier circuit,
28...Feedback circuit, 29...Drive circuit, 30...
Amplifying circuit, 31... Feedback circuit, 32... Drive circuit,
33... Phase locked loop circuit, 34... Digital signal processing circuit, 35... Crystal oscillator, 36... Clock generation circuit, 37... RAM138... D/A conversion circuit, 39.40 ...Amplification circuit, 41.42...Output terminal, 43...Playback speed control circuit, 44 River display circuit, 45...Synchronization control circuit, 46...Cassette tape recorder, 47...Photodetector , 48...output terminal, 49...connection terminal. Applicant's agent Patent attorney Takehiko Suzue

Claims (1)

[Claims] In a digital playback system that drives a recording medium to read and guide digital information recorded on the recording medium to an amplification circuit, the playback speed can be switched by switching the drive speed of the recording medium, wherein the playback speed is switched. 1. A characteristic switching device for an amplifier circuit used in a digital playback system, characterized in that the device is provided with a switching means for driving to switch the characteristics of the amplifier circuit.