JP2008109489A - Signal processing circuit, and optical disk device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a characteristic difference between two RF signals when generating the signals whose phases are mutually inverted from a plurality of signals outputted from a photodiode. <P>SOLUTION: This signal processing circuit is provided with: a differential amplifier 41 having a first node T1 and a second node T2 for respectively receiving voltage and reference voltage Vc of an input signal obtained by synthesizing a plurality of signals SigA to SigD and differentially outputting current Ia corresponding to a difference between the voltages; a first voltage source 42 connected to the first node T1 through a resistor R15 to output first voltage V1; a second voltage source 43 connected to the second node T2 through a resistor R16 to output second voltage V2; and an outputing stage 44 for respectively driving the voltage of the first node T1 and the second node T2. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a signal processing circuit and an optical disc apparatus including the signal processing circuit.

  2. Description of the Related Art Conventionally, optical disc apparatuses that reproduce data recorded on an optical disc such as a CD (Compact Disc) and a DVD (Digital Versatile Disk) are widely known.

  In this optical disk apparatus, data recorded on the optical disk is read as follows by a photodetector (PD) having a photoelectric conversion circuit and a signal processing circuit.

  First, a light beam emitted from a laser light source is irradiated onto the recording surface as a beam spot. The photoelectric conversion circuit of the photodetector receives the reflected light of the irradiated light beam from the optical disk and outputs a voltage corresponding to the received light intensity. Note that the photoelectric conversion circuit has a light receiving surface divided into a plurality of parts, receives reflected light from the optical disc, and outputs a plurality of signals corresponding to the number of divisions of the light receiving surface.

  The signal processing circuit performs various types of signal processing on the output signal of the photoelectric conversion circuit to perform various servo controls such as focus servo and tracking servo, and reproduces data recorded on the optical disc (for example, patents) Reference 1).

  Here, an example of a configuration in which a conventional signal processing circuit generates an RF signal based on a plurality of signals output from a photoelectric conversion circuit will be described with reference to the drawings. FIG. 6 is a diagram showing a configuration for generating an RF signal in the conventional signal processing circuit 100. The signal processing circuit 100 is a voltage signal generated in the photoelectric conversion circuit, and receives voltage signals (SigA to SigD) corresponding to the incident light corresponding to each of the four divided light receiving surfaces, and is phase-shifted with each other. The RF + signal and the RF− signal are generated by inverting. These SigA to SigD are signals based on the reference voltage Vc.

  As shown in FIG. 6, the signal processing circuit 100 includes a first RF circuit 101 that generates and outputs an RF + signal, and a second RF circuit 102 that generates and outputs an RF− signal.

  The first RF circuit 101 includes input resistors R100 to R103 for synthesizing SigA to SigD output from the photoelectric conversion circuit, a differential amplifier AMP100 for non-inverting amplification of the synthesized signal, and an amplification factor of the differential amplifier AMP100. And resistors R108 and R110 for adjusting the DC operating point of the RF + signal, and an amplifier AMP101.

  The second RF circuit 102 includes input resistors R104 to R107 for synthesizing SigA to SigD output from the photoelectric conversion circuit, a differential amplifier AMP102 for inverting and amplifying the synthesized signal, and amplification of the differential amplifier AMP102. Resistors R112 and R113 for adjusting the rate, and a resistor R111 and an amplifier AMP103 for adjusting the DC operating point of the RF-signal are provided.

  The first RF circuit 101 and the second RF circuit 102 configured as described above synthesize SigA to SigD output from the photoelectric conversion circuit via input resistors R100 to R107, and the first RF circuit 101 uses a non-inverting differential amplifier. The RF + signal is amplified by the AMP 100 and the RF− signal is output by the inverting differential amplifier AMP 102 in the second RF circuit 102. The input resistors R100 to R107 have the same resistance value, the resistance values of the resistors R109 and R112 are 1/4 of the resistance value of R100, the resistors R108 and R110 have the same resistance value, and the resistors R111 and R113 have the same resistance value. .

If the RF + signal and the RF− signal are generated with reference to the reference voltage Vc, the dynamic range of these signals cannot be taken sufficiently. Therefore, in order to adjust the DC operating point of these signals, the voltage V2 is output via the resistor R108 by the amplifier AMP101 constituting the voltage follower, and the voltage V1 is outputted via the resistor R110 by the amplifier AMP103 constituting the voltage follower. The RF + signal is output with the voltage V2 as a reference, and the RF− signal is output with the voltage V1 as a reference.
JP 2000-269762 A

  However, in the conventional signal processing circuit, since the first RF circuit 101 and the second RF circuit 102 have different differential amplifiers AMP100 and AMP102, due to variations in characteristics of these differential amplifiers AMP100 and AMP102, As shown in FIG. 7, there is a slight difference in signal quality between the RF + signal output from the first RF circuit 101 and the RF− signal output from the second RF circuit 102 in terms of frequency characteristics and group delay characteristics. Come. Due to this subtle difference in signal quality, there is a problem that the frequency band that can be used as data becomes low.

  In addition, since the first RF circuit 101 and the second RF circuit 102 use different differential amplifiers AMP100 and AMP102, a layout area equivalent to two differential amplifiers is required.

  In order to solve the above-mentioned problems, the invention according to claim 1 inputs a voltage of an input signal obtained by synthesizing a plurality of signals and a reference voltage, and outputs a current corresponding to a difference between these voltages as a differential output. A differential amplifier having a first node and a second node, a first voltage source for outputting a first voltage connected to the first node via a first load, and a second load on the second node. And a signal processing circuit including a second voltage source that outputs a second voltage connected via the first voltage source, and an output stage that drives the voltages of the first node and the second node, respectively.

  According to a second aspect of the present invention, in the first aspect of the invention, the differential amplifier is connected to a pair of transistors each including a first transistor and a second transistor, and to the emitters of these transistors. A first constant current source and a second constant current source; a resistor connected between the emitters of the pair of transistors; a third constant current source and a fourth constant current source respectively connected to collectors of the pair of transistors; The input signal voltage is input to the base of the first transistor, the reference voltage is input to the base of the second transistor, the collector of the first transistor is the first node, and the first node The collector of the two transistors is the second node.

  According to a third aspect of the present invention, in the optical disc apparatus for reproducing data recorded on the optical disc, the light receiving surface is divided into a plurality of portions, and the reflected light from the optical disc is received to correspond to the number of divisions of the light receiving surface. A first node that outputs a current corresponding to a difference between the photoelectric conversion unit that outputs the plurality of signals, and a voltage of an input signal obtained by synthesizing the plurality of signals and a reference voltage. And a differential amplifier having a second node; a first voltage source for outputting a first voltage connected to the first node via a first load; and a second voltage connected to the second node via a second load. An optical disc apparatus comprising: a second voltage source that outputs a second voltage, and an output stage that drives the voltages of the first node and the second node, respectively.

  According to the present invention, it is possible to generate the RF + signal and the RF− signal whose phases are inverted with each other using the same differential amplifier while adjusting their DC operating points. Accordingly, differences in AC (alternating current) characteristics such as frequency characteristics and group delay characteristics of the RF + signal and the RF− signal can be reduced. Furthermore, according to the present invention, since the differential amplifier is shared, the layout area can be reduced.

 The optical disk apparatus according to the present embodiment includes a photoelectric conversion circuit and a signal processing circuit. The photoelectric conversion circuit has a light receiving surface divided into a plurality of parts, receives reflected light from the optical disk, and corresponds to the number of divided light receiving surfaces. Output multiple signals.

  The signal processing circuit inputs a voltage of an input signal obtained by synthesizing a plurality of signals output from the photoelectric conversion circuit and a reference voltage, and differentially outputs a current corresponding to a difference between these voltages. A differential amplifier having a node and a second node; a first voltage source for outputting a first voltage connected to the first node via a first load; and a second voltage connected to the second node via a second load. A second voltage source that outputs a second voltage; and an output stage that drives the voltages of the first node and the second node to output RF + and RF− signals whose phases are inverted.

  As described above, the RF + signal and the RF− signal can be output while adjusting their DC operating points without using separate differential amplifiers for the RF + signal and the RF− signal. Differences in AC characteristics such as frequency characteristics and group delay characteristics of signals and RF-signals can be reduced, and the layout area can be further reduced.

  As the differential amplifier, for example, a pair of transistors composed of a first transistor and a second transistor, a first constant current source and a second constant current source respectively connected to the emitters of these transistors, and an emitter of the pair of transistors And a third constant current source and a fourth constant current source connected to the collectors of the pair of transistors, respectively, and the voltage of the input signal is input to the base of the first transistor, and the second transistor The reference voltage is input to the base of the first transistor, the collector of the first transistor is used as the first node, and the collector of the second transistor is used as the second node.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram of an optical disc apparatus 1 of the present embodiment.

  As shown in FIG. 1, an optical disc apparatus 1 according to this embodiment includes a CD laser diode 2 that emits a laser beam that is an optical signal for CD, and a DVD laser that emits a laser beam that is an optical signal for DVD. A diode 3, an optical system 4, a photodetector circuit 5 that receives laser light reflected from an optical disk 6 such as a CD or a DVD and converts it into an electrical signal, a servo motor 7 for controlling the rotation of the optical disk 6, and an optical system Front monitor photodetector circuit 10 for converting the laser beam dispersed through 4 into an electrical signal, control signal generation processing for emitting the laser beam from each laser diode 2, 3, from each of the photodetector circuits 5, 10 The DSP 11 that performs various signal processing such as output signal processing and control signal generation processing for the servo motor 7 and the entire optical disc apparatus 1 Gosuru and the like controller 12. The optical system 4 includes lenses 20, 21, 25 to 27, a prism 22, a splitter 23, and a reflection mirror 24.

  In the optical disc apparatus 1, when the recording data is received by the controller 12 via the interface, the controller 12 controls the DSP 11 to modulate the laser light modulated according to the data to be recorded for the CD laser diode 2 or the DVD. The light is emitted from the laser diode 3.

  Laser light emitted from the CD laser diode 2 enters the splitter 23 via the lens 21 and the prism 22. Similarly, the laser beam emitted from the DVD laser diode 3 enters the splitter 23 via the lens 20 and the prism 22.

  The laser light incident on the splitter 23 is split by the splitter 23 in the direction of the reflection mirror 24 and the direction of the front monitor photodetector circuit 10. The direction of the laser light dispersed in the direction of the reflection mirror 24 is changed by reflection by the reflection mirror 24, collimated by the lens 25, condensed by the lens 27, and irradiated onto the optical disk 6.

  The laser light irradiated to the optical disk 6 and reflected by the optical disk 6 is received by the photodetector circuit 5 through the lenses 25 and 26, the reflection mirror 24, the splitter 23, and the lens 27. Further, when reading data written on the optical disk 6, laser light for reading is emitted from the laser diode 2 for CD or the laser diode 3 for DVD. Thereafter, the split laser beam is received by the front monitor photodetector circuit 10 and the laser beam reflected by the optical disc 6 is received by the photodetector circuit 5 through the same path as described above.

  The laser beam received by the photodetector circuit 5 is converted into an electrical signal by the photodetector circuit 5 and transmitted to the DSP 11. The DSP 11 performs control such as focus servo and tracking servo based on the electrical signal transmitted from the photodetector circuit 5. The laser light received by the front monitor photodetector circuit 10 is converted into an electrical signal by the front monitor photodetector circuit 10 and transmitted to the DSP 11. The DSP 11 detects the intensity of the laser light emitted from each of the laser diodes 2 and 3 based on the electrical signal transmitted from the front monitor photodetector circuit 10 and determines the intensity of the laser light emitted from each of the laser diodes 2 and 3. adjust.

  Next, the photoelectric conversion circuit 30 and the signal processing circuit 40 constituting the photodetector circuit 5 will be specifically described with reference to the drawings. The photodetector circuit 5 is housed in a COB (chip on board) package. Note that a transparent mold package or the like can be used instead of the COB package as the package. 2 is a diagram showing a four-divided light receiving surface of the photodetector circuit 5 in the present embodiment, FIG. 3 is a diagram showing a configuration of the photoelectric conversion circuit 30 in the present embodiment, and FIG. 4 is a configuration of the signal processing circuit 40 in the present embodiment. FIG.

  First, the configuration of the photoelectric conversion circuit 30 will be described with reference to FIGS.

  As shown in FIG. 2, the photoelectric conversion circuit 30 is divided into four light receiving surfaces A, B, C, and D, and photodiodes PD1a provided on the light receiving surfaces A, B, C, and D, respectively. Photoelectric conversion blocks 31A to 31D for outputting voltage signals SigA to SigD corresponding to the reflected light received by PD1d, respectively.

  The photoelectric conversion block 31A includes differential amplifiers AMP1a and AMP2a and resistors R1a to R5a. The current signal Ipd1a flowing through the photodiode PD1a is converted into a voltage signal Viv by the differential amplifier AMP1a, and further the differential amplifier AMP2a. To output a signal SigA amplified at a predetermined amplification factor (= 1 + R5a / R4a). Note that R1a = R2a and R3a = R4a // R5a. Also, the photoelectric conversion blocks 31B to 31D have the same configuration as the photoelectric conversion block 31A, and output signals SigB to SigD, respectively.

  As described above, in the photoelectric conversion circuit 30, the light receiving surface is divided into four, receives the reflected light from the optical disc 6, and outputs a plurality of electrical signals SigA to SigD corresponding to the divided light receiving surfaces. Thus, the magnitudes of the signals SigA to SigD are determined by the intensity of the incident reflected light.

  Next, the configuration of the signal processing circuit 40 will be described with reference to FIG.

  The signal processing circuit 40 inputs a voltage of an input signal obtained by synthesizing a plurality of signals SigA to SigD output from the photoelectric conversion circuit 30 and a reference voltage, and differentially outputs a current Ia corresponding to the difference between these voltages. A differential amplifier 41 having a first node T1 and a second node T2 for outputting, and a first voltage V1 connected to the first node T1 via a resistor R15 (corresponding to an example of a first load). A voltage source 42; a second voltage source 43 that outputs a second voltage V2 connected to the second node T2 via a resistor R16 (corresponding to an example of a second load); a first node T1 and a second node T2. And an output stage 44 for driving (current amplification) the respective voltages, and the RF + signal and the RF− signal can be generated by the same differential amplifier 41.

  The differential amplifier 41 includes a pair of transistors including a first transistor Q1 and a second transistor Q2, and a first constant current source I1 and a second transistor connected between the emitters of these transistors Q1 and Q2 and the ground GND, respectively. A constant current source I2, a resistor R13 connected between the emitters of the transistors Q1 and Q2, and a third constant current source I3 connected between the collectors of the first and second transistors Q1 and Q2 and the power supply voltage Vdd, respectively. And a fourth constant current source I4, and a fifth constant current source I5 and a sixth constant current source I6 connected between the collectors of the first and second transistors Q1 and Q2 and the ground GND, respectively.

  Further, the differential amplifier 41 has input resistors R6 to R9 for inputting signals SigA to SigD, respectively, connected to the base of the first transistor Q1, whereby the voltage of the input signal is applied to the base of the first transistor Q1. Is entered. Further, the reference voltage Vc is input to the base of the second transistor Q2 via the resistor R14, the collector of the first transistor Q1 is the first node T1, and the collector of the second transistor Q2 is the second node T2. .

  The first voltage source 42 has a configuration in which the first voltage V1 is connected to the input of the amplifier AMP7 that constitutes the voltage follower, and the second voltage source 43 has the second voltage V2 at the input of the amplifier AMP8 that constitutes the voltage follower. Is connected.

  The output stage 44 includes transistors Q3 to Q6 and constant current sources I8 to I11, drives the voltage of the first node T1, amplifies the current, and outputs it as an RF + signal. Further, the voltage of the second node T2 is driven to amplify the current and output as an RF-signal. The output stage 44 is configured as follows.

  The base of the transistor Q3 is connected to the first node T1, and the base of the transistor Q4 is connected to the second node T2. The emitter of transistor Q3 is connected to one end of constant current source I8 and to the base of transistor Q5. The emitter of the transistor Q4 is connected to one end of the constant current source I9 and to the base of the transistor Q6. The emitter of the transistor Q5 is connected to one end of the constant current source I10, and the emitter of the transistor Q6 is connected to one end of the constant current source I11. The collectors of the transistors Q3 and Q4 and the other ends of the constant current sources I10 and I11 are connected to the ground GND, and the collectors of the transistors Q5 and Q6 and the other ends of the constant current sources I8 and I9 are connected to the power supply voltage Vdd.

  Here, the current value of the third constant current source I3 is a value obtained by adding the current values of the first constant current source I1 and the fifth constant current source I5 (I3 = I1 + I5), and the current value of the fourth constant current source I4 is The current value is a value obtained by adding the current values of the second constant current source I2 and the sixth constant current source I6 (I4 = I2 + I6). The resistors R6 to R9 have the same resistance value, and the resistor R14 has a resistance value obtained by dividing the resistor R6 by 4 (R14 = R6 / 4).

  As described above, the differential amplifier 41 in the present embodiment inputs the combined signal of the signals SigA to SigD to one input and the reference voltage Vc that is the same voltage as the DC operating point of the signals SigA to SigD to the other input. The voltage difference between the two inputs is converted into a current having a current value Ia by the resistor R13. Since I3 = I1 + I5 and I4 = I3 + I6 as described above, a current of Ib = Ic (= Ia) is generated as shown in FIG. These currents Ib and Ic generate voltages at the resistors R15 and R16, and the voltages at the first node T1 and the second node T2 change. The output stage 44 drives the voltages of the first node T1 and the second node T2 and outputs them as RF + signals and RF- signals.

  Further, if the signals SigA to SigD are not input, the current Ia is not generated, so that the currents Ib and Ic are not generated, and the voltages V1 and V2 become the RF + signal voltage and the RF− signal voltage, respectively.

  Thus, since the first voltage V1 is applied to the first node T1 via the resistor R15 and the second voltage V2 is applied to the second node T2 via the resistor R16, the voltage V1 , V2 can set different DC operating points for the RF + signal and the RF− signal, and the dynamic range of the RF + signal and the RF− signal can be expanded.

  Further, the resistors R15 and R16 and the resistor R13 determine the gain of the RF + signal and the RF− signal. The gain equation of the differential amplifier 41 is shown below.

また、信号処理回路40におけるゲイン式は、信号ＳｉｇＡ〜ＳｉｇＤの４入力のため、以下のように差動アンプ41のゲインの１／４倍となる。

Further, the gain expression in the signal processing circuit 40 is ¼ times the gain of the differential amplifier 41 as follows because of the four inputs of the signals SigA to SigD.

以上のように構成された信号処理回路40の周波数特性（入力信号の周波数と入出力ゲインとの関係を示す特性）を図５に示す。このように本実施形態における信号処理回路40は、同一の差動アンプ41を用いてＲＦ＋信号とＲＦ-信号とを生成しているために、これらの信号は周波数特性や群遅延特性などのＡＣ特性のずれを抑制することができる。

FIG. 5 shows the frequency characteristics (characteristics indicating the relationship between the frequency of the input signal and the input / output gain) of the signal processing circuit 40 configured as described above. Thus, since the signal processing circuit 40 in this embodiment generates the RF + signal and the RF− signal using the same differential amplifier 41, these signals are AC signals such as frequency characteristics and group delay characteristics. A deviation in characteristics can be suppressed.

  Moreover, since the conventional circuit has different differential amplifiers for the RF + circuit and the RF- circuit, a layout area equivalent to two differential amplifiers is required. Since the amplifier is shared, the layout area can be reduced.

  Furthermore, since the DC operating point can be different between the RF + signal and the RF− signal by setting the voltages V <b> 1 and V <b> 2, the dynamic range of the RF + signal and the RF− signal can be expanded.

  As mentioned above, some of the embodiments of the present invention have been described in detail with reference to the drawings. However, these are merely examples, and the present invention is variously modified and improved based on the knowledge of those skilled in the art. It is possible to carry out the invention.

  For example, although the constant current sources I5 and I6 are provided in the present embodiment, the constant current sources I1 and I3 are set to the same current value, and the constant current sources I2 and I4 are set to the same current value. The sources I5 and I6 may be deleted.

1 is a diagram illustrating an overall configuration of an optical disc apparatus according to an embodiment of the present invention. It is a figure which shows the 4 division | segmentation light-receiving surface of the photodetector circuit which concerns on one Embodiment of this invention. It is a figure which shows the structure of the photodetector which concerns on one Embodiment of this invention. It is a figure which shows the structure of the signal processing circuit which concerns on one Embodiment of this invention. It is a figure which shows the frequency characteristic of the signal processing circuit which concerns on one Embodiment of this invention. It is a figure which shows the structure of the conventional figure signal processing circuit. It is a figure which shows the frequency characteristic of the signal processing circuit of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical disk apparatus 30 Photoelectric conversion circuit 40 Signal processing circuit 41 Differential amplifier 42 1st voltage source 43 2nd voltage source 44 Output stage Q1 1st transistor Q2 2nd transistor I1 1st constant current source I2 2nd constant current source I3 1st 3 constant current source I4 4th constant current source R6 to R9, R13, R15, R16 Resistance

Claims (3)

A differential amplifier having a first node and a second node for inputting a voltage of an input signal obtained by synthesizing a plurality of signals and a reference voltage, and differentially outputting a current corresponding to a difference between the voltages;
A first voltage source for outputting a first voltage connected to the first node via a first load;
A second voltage source for outputting a second voltage connected to the second node via a second load;
An output stage for driving the voltages of the first node and the second node, respectively.
A signal processing circuit comprising: The differential amplifier includes a pair of transistors including a first transistor and a second transistor, a first constant current source and a second constant current source respectively connected to emitters of the transistors, and an emitter between the pair of transistors. And a third constant current source and a fourth constant current source respectively connected to the collectors of the pair of transistors.
The voltage of the input signal is input to the base of the first transistor, the reference voltage is input to the base of the second transistor, the collector of the first transistor is a first node, and the collector of the second transistor is The signal processing circuit according to claim 1, wherein the signal processing circuit is a second node. In an optical disc apparatus for reproducing data recorded on an optical disc,
A light receiving surface is divided into a plurality of portions, a photoelectric conversion unit that receives reflected light from the optical disc and outputs a plurality of signals corresponding to the number of divisions of the light receiving surface;
A differential amplifier having a first node and a second node that respectively input a voltage of an input signal obtained by synthesizing the plurality of signals and a reference voltage, and differentially output a current corresponding to a difference between the voltages;
A first voltage source for outputting a first voltage connected to the first node via a first load;
A second voltage source for outputting a second voltage connected to the second node via a second load;
An output stage for driving the voltages of the first node and the second node, respectively.
An optical disc apparatus comprising:

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