JPS61142532A - Rf signal amplifier circuit of optical disk reproducing device - Google Patents

Abstract

PURPOSE:To prevent the output waveform of an RF signal from being saturated with the dispersion of the output current of an optical pickup even if a driving voltage is low by changing the operation reference voltage level of an adder by an RF signal peak detecting output outputted from the adder. CONSTITUTION:In the RF signal amplifier circuit, a peak detecting circuit 16 detects the peak level of an RF signal Vout extracted from the adder 13, a comparator 17 compares a peak detecting signal level Vp with a reference voltage Vo and generates a control signal corresponding to the difference voltage to control an output current to be outputted from a variable current source 15. Consequently, the current value I can be changed in accordance with the change of the peak level of the RF signal Vout independently of the adjustment of a variable resistor VR.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] This invention is applicable to, for example, CDs (compact discs), VDs (
It relates to an optical disc playback device that plays back optical discs such as video discs, and particularly relates to an improved RF signal amplification circuit so that the RF multiplied signal output waveform does not saturate due to variations in the output current of the optical pickup. .

[Technical background of the invention and its problems] Conventionally, for example, in a CD-type optical disc playback device, a light beam is irradiated onto one side of a disc to detect the presence or absence of pits formed on the disc surface. The information signal recorded on the disk is read using an optical pickup that receives reflected light that has undergone changes corresponding to the changes in the optical pickup. When such a device is used, an RF signal amplification circuit as shown in FIG. 3 is used to extract an RF multiplied signal corresponding to the presence or absence of the pits.

That is, the reference numeral 11 in FIG. 3 is a four-part photodetector in the optical pickup, and the signals obtained by photoelectric conversion at A and C of each of the light-receiving areas A to D of this detector 11 are subjected to current addition, and then First current-voltage conversion circuit 12
The first voltage signal -1 is converted at a, and the signals taken out through photoelectric conversion at B and D are subjected to current addition in the same manner, and then converted into a second voltage signal -1 at the second current-voltage conversion circuit 12b. ■Converted to 2. These voltage signals -Vl and -V2 are used, for example, as signals for focus servo, as is well known. Then, these first and second voltage signals -Vl,
-V2 are resistors R1 to R3 and operational amplifier circuit A, respectively
The signals are added in an adder circuit 13 consisting of the following, and taken out as an RF multiplied signal out corresponding to the presence or absence of pits. Here, if the power supply voltage supplied to the adder circuit 13 is Vcc, and the reference voltage is vrer, the RF signal can be expressed as follows. The output waveform becomes as shown in FIG. 5(a), and reaches its maximum value at the total reflection level.

Note that since the current output from each light receiving area A to D of the detector 11 is only in one direction (the direction indicated by the arrow in the figure),
Output voltage -V of each current-voltage conversion circuit 12a, 12b
l, -V2 are lower than the reference voltage V ref, and the output voltage VOUT of the adder circuit 13 is lower than the reference voltage V ref.
It can only swing upwards.

The RF signal amplification circuit of the conventional optical disc playback device as described above has no problem when the power supply voltage Vcc is high, but when lowering the voltage for application to a portable type playback device, the following problems occur. There's a problem.

(1) If the power supply voltage Vcc is lowered as it is, as shown in Fig. 5(b)
), the upper side clips.

To prevent this clipping, the gain must be lowered.

(2) If the gain is lowered as in (1), the next stage data slice circuit (EFM signal generation circuit) cannot perform slice processing.

In order to improve this problem, an RF signal amplification circuit as shown in FIG. 4 has been considered. That is, in this RF signal amplification circuit, the inverting input terminal (-) of the operational amplifier A of the adder circuit 13 is connected to the level shift current source 1.
4, and a variable resistor VR is connected in place of the resistor R3. In other words, from the current source 14 to the inverting input terminal (-) of the operational amplifier A
A current of 0 is supplied to the output D as shown in Figure 5(C).
The above problem can be solved by shifting the C level downward. Then, by adjusting the variable resistor VR, R
The F signal amplitude can be made constant. however,
RF multiplied signal o extracted by this RF signal amplification circuit
If the resistance value of the variable resistor VR is Ra, ut can be expressed as -I -Ra +Vref (2), so if the resistance value Ra of the variable resistor VR is decreased when the input signal is large, the level shift amount will also be small. It will become.

[Object of the Invention] This invention was made to improve the above-mentioned problem, and the RF signal output waveform does not saturate due to variations in the output current of the optical pickup even if the driving voltage is low. An object of the present invention is to provide an RF signal amplification circuit for an optical disc playback device that can perform the following steps.

[Summary of the Invention J That is, R of the optical disc playback device according to the present invention.
The F signal amplification circuit irradiates an optical disk with a light beam, receives reflected light that changes depending on the presence or absence of pits formed on the disk surface, and receives the reflected light with a multi-segment photodetector. In an optical disc playback device that extracts an RF multiplied signal corresponding to the presence or absence of pits by adding signals photoelectrically converted in a light receiving area in an adder circuit, a peak detection circuit detects a peak level change in the output of the adder circuit; , a comparison circuit that compares the output voltage of this beep detection circuit with a reference voltage and outputs the difference voltage; and a variable that is controlled by the difference voltage output from this comparison circuit and level-shifts the operating reference voltage of the adder circuit. a current source, and R output from the adding circuit.
The present invention is characterized in that the operating reference voltage level of the adder circuit is changed by the F-fold signal peak detection output.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described in detail with reference to FIGS. 1 and 2. However, in FIG. 1, the same parts as in FIGS. 3 and 4 are designated by the same reference numerals, and only the different parts will be described here.

FIG. 1 shows its configuration. In this RF signal amplification circuit, the inverting input terminal (
-) is connected to the VCC power supply via a variable current source 15 for level shifting, and the variable resistor VR is used as a feedback resistor, and the output of this adder circuit 13 (RF multiplied signal This peak detection circuit 16 has a time constant circuit consisting of a detection capacitor C1 and a discharge resistor R4, and the time constant is designed to prevent RF multiplied signal dropout due to scratches, vibrations, etc. is set to a sufficiently long value.The output of this peak detection circuit 16 is supplied to one input terminal of a comparison circuit 17.This comparison circuit 17 is connected to the peak detection circuit 16.
Peak detection signal level ■p detected by p and reference voltage 11
It compares the reference voltage 0 from Eo and outputs a control signal according to the level difference, and this control signal is supplied to the control input terminal of the variable current source 15.

That is, this RF signal amplification circuit includes the addition circuit 13
A peak detection circuit 16 detects the peak level of the RF multiplied signal OUT extracted from the RF signal OUT, and a comparison circuit 17 compares the peak detection signal level Vp with a reference voltage 0 to generate a control signal according to the difference voltage. The output current amount of the variable current source 15 is controlled by this control signal, and the current amount I can be changed according to the change in the peak level of the RF multiplied signal out, regardless of the adjustment of the variable resistor VR. It is something.

FIG. 2 is a circuit diagram showing a specific configuration of the RF signal amplification circuit, in which the portions surrounded by dotted lines indicate the circuit configurations of the addition circuit 13, peak detection circuit 16, and comparison circuit 11.

First, in the adder circuit 13, Ql and Q2 are NPN transistors that constitute a differential amplifier circuit, ■1 is a first current source that determines the amount of operating current of transistors Q1 and Q2, and ■2
is a second current source for equalizing the collector currents of transistors Ql and Q2, and is set to 1/2 of the first current source 11. In addition, Q3 is an NPN transistor that constitutes the output stage of the emitter follower, and I3 is a transistor Q3.
This is the third current source that determines the amount of operating current. Here, Q4 and R5 in the figure are a PNP transistor and a resistor that constitute the level shifting variable current source 15, and the transistor Q
The collector of the transistor Q2 is connected to the base of the transistor Q2, and the base of the transistor Q8 is connected to the base of a PNP transistor Q8, which will be described later.

Next, in the peak detection circuit 16, Q5 is an NPN transistor for beep detection, and its base is connected to the base of the transistor Q3 at the output stage of the adder circuit 13. R6 is a resistor that determines the amount of charging current for the capacitor C1.

In the comparison circuit 17, Q6 and Q7 are NPN transistors forming a differential circuit, and the transistor Q6
The base of the transistor Q7 is connected to the reference voltage source EO, and the base of the transistor Q7 is connected to the output terminal of the peak detection circuit 16. 1, R7, and R8 reduce the collector current change width with respect to the input differential voltage, and the current source 15
Transistors Q6 and Q7 to widen the control range of
4 is a current source that determines the amount of operating current of transistors Q6 and Q7, Q8 is a diode-connected PNP transistor, and the resistances of transistors Q8 and R9 are the same as transistor Q4 of current source 15 and resistor R5.
and constitutes a current mirror circuit.

Here, in the above circuit configuration, if the peak level of the RF multiplied signal out is larger than the reference voltage ■0 (base voltage of Q6 < base voltage of 07), the collector current of Q6 < Q
7, and the output current 0 of the level shifting variable current source 15 increases due to the current mirror circuit. In this way, feedback is applied so that the base voltage of Q6 and the base voltage of 07 become equal, and the peak level of the RF doubler output vout becomes equal to the reference voltage 0. In other words, since the output current value IO of the level shift variable current source 15 changes so that the peak level of the RF doubler ■out and the reference voltage (set voltage) VO are equal, the reference voltage ■0 is set to be lower than the lowest power supply voltage. If you set it lower, the output waveform will not become saturated.

Therefore, since the RF signal amplification circuit configured as described above changes the amount of DC level shift of the RF output by the RF multiplied signal peak detection output, it can be used even when the detector output current of the pickup is large and the power supply voltage is low. However, the voltage range can be used effectively without the output waveform becoming saturated. Furthermore, since there is no AC feedback, there is no effect on the high frequency characteristics of RF amplification. moreover,
Since it can be realized with a relatively small number of elements, it is suitable for integrated circuit implementation.

[Effects of the Invention] As detailed above, according to the present invention, even if the driving voltage is low, the RF signal output waveform can be prevented from becoming saturated due to variations in the output current of the optical pickup. An RF signal amplification circuit for an optical disc playback device can be provided.

[Brief explanation of the drawing]

FIG. 1 shows the RF of the optical disc playback device according to the present invention.
FIG. 2 is a block circuit configuration diagram showing an embodiment of the signal amplification circuit, FIG. 2 is a circuit diagram showing a specific configuration of the same embodiment, and FIGS. 3 and 4 are R diagrams of a conventional optical disc playback device.
FIG. 5 is a block circuit diagram showing the configuration of the F signal amplification circuit. FIG. 5 is a waveform diagram showing the output waveform of each RF signal amplification circuit shown in FIGS. 3 and 4. 11...4-segment photodetector, 12a,''・12
b... Current voltage conversion circuit, 13... Addition circuit, 14
... Level shift current source, 15... Level shift variable current source, 16... Peak detection circuit, 17...
Comparison circuit. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 2

Claims (1)

[Claims] A light beam is irradiated onto an optical disk, and a multi-segment photodetector receives the reflected light, which changes depending on the presence or absence of pits formed on the disk surface, and is photoelectrically converted in each light-receiving area of this photodetector. In an optical disc playback device that extracts an RF signal corresponding to the presence or absence of pits by adding together signals in an adder circuit, the optical disc playback device includes a peak detection circuit that detects a peak level change in the output of the adder circuit; A comparison circuit that compares an output voltage and a reference voltage and outputs the difference voltage, and a variable current source that is controlled by the difference voltage output from the comparison circuit and level-shifts the operating reference voltage of the adder circuit, An RF signal amplification circuit for an optical disc reproducing apparatus, characterized in that an operating reference voltage level of the adder circuit is changed by a peak detection output of the RF signal output from the adder circuit.