JP2005303684A - Gain variable amplifier circuit and optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gain variable amplifier circuit capable of executing the switching of a gain among a large number of gains with a simple circuit constitution, and also, capable of obtaining optimum phase characteristics and frequency characteristics, and an optical pickup device. <P>SOLUTION: A light-receiving amplifier circuit is provided with an amplifier 2, switches 4-1 to 4-L for selecting and using any one of a plurality of feedback loops including feedback circuits 3-1 to 3-L with mutually different resistance values as a feedback loop for feeding back the output of the amplifier 2 to the input of the amplifier 2, and in addition to them, a plurality of amplifiers 7-1 to 7-M connected in parallel and having different gains each other, and a switch 8 for selecting and using any one of the amplifiers 7-1 to 7-M. The gain of the entire circuit can be switched by the combination of the switching of the switches 4-1 to 4-L and that of the switch 8. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an amplifying circuit (variable gain amplifying circuit) having a variable gain (gain) by switching the feedback rate of a feedback loop in order to process various signals, and in particular, receives reflected light from an optical disc. The present invention relates to a light receiving amplifier circuit that amplifies a signal from a light receiving element that performs a variable gain. The present invention also relates to an optical pickup device provided with the light receiving amplifier circuit, and more particularly to an optical pickup device suitable for reproducing a writable optical disc such as a CD-R (Compact Disc Recordable).

  In an optical pickup device for reproducing an optical disk, a light receiving element that receives reflected light from the optical disk and converts it into a signal, and an amplifier circuit (light receiving amplifier circuit) that amplifies the output signal of the light receiving element are used. (See Patent Document 1). In an optical pickup device for reproducing one type of read-only optical disc, for example, a CD, an amplifier circuit having a fixed gain is used as the amplifier circuit.

  Thereafter, with the advent of writable optical discs such as CD-Rs, gain switching has been demanded of optical amplifier circuits for reproducing optical discs. This is for the following reason. That is, first, in a writable optical disc, at the time of writing, the laser beam for writing is irradiated and reflected on the optical disc, and the laser beam incident on the light receiving element is detected as a signal. At this time, since the writing laser beam is a stronger laser beam than the reproducing laser beam, it is necessary to reduce the gain of the light receiving amplifier circuit in order to detect without saturating the signal. . In addition, the writable optical disc differs from the read-only optical disc in the difference in reflectivity between the high reflectivity portion and the low reflectivity portion due to structural differences. For this reason, when the reproduction-only optical disk and the writable optical disk are reproduced using a common light receiving amplifier circuit, the amplitude of the output signal differs between the reproduction. The difference in the amplitude of the output signal may lead to a phenomenon that the signal is saturated because the amplitude of the output signal is too large, or a phenomenon that the signal cannot be reproduced accurately because the amplitude of the output signal is too small. Therefore, the light receiving amplifier circuit is required to be able to switch the gain between a gain suitable for reproduction of a read-only optical disc and a gain suitable for reproduction of a writable optical disc.

  Further, in a writable optical disc such as a DVD-R (Digital Versatile Disc Recordable) which is generally written at a higher speed than a CD family writable optical disc such as a CD-R, an average value servo is employed at the time of writing. As a result, the difference in the amplitude of the output signal also occurs due to the difference in the writing speed. Therefore, there is a demand for a light receiving amplifier circuit that the gain can be switched between a plurality of different gains corresponding to a large number (three or more types) of writing speed.

  At present, a wide variety of optical discs have appeared, and in order to support a wide variety of optical discs, the light receiving amplifier circuit can switch gains among a large number (three or more types) of different gains. It is requested to be.

  Therefore, a variable gain amplifier circuit has been proposed as an amplifier circuit (light receiving amplifier circuit) that amplifies the output signal of the light receiving element. An example of a conventional variable gain type light receiving amplifier circuit is shown in FIG.

  As shown in FIG. 5, the variable gain type light receiving amplifier circuit 100 includes an amplifier 102 for amplifying a signal from a light receiving element 101 such as a photodiode using a reference voltage Vref, and an output of the amplifier 102 of the amplifier 102. Two feedback circuits 104 and 105 for feeding back to the input are provided. These feedback circuits 104 and 105 are connected in parallel between the output and input of the amplifier 102 and can be selected by the corresponding switches 108 and 109. That is, conduction / cutoff of the feedback loop through the feedback circuits 104 and 105 is controlled by the switches 108 and 109. Buffer amplifiers 106 and 107 for selecting the feedback circuits 104 and 105 are provided between the output of the amplifier 102 and the feedback circuits 104 and 105, respectively.

  As shown in FIG. 6, each of the feedback circuits 104 and 105 includes a gain resistor 17 for adjusting the gain of the light receiving amplifier circuit 100 by adjusting the feedback factor of the feedback loop, and a phase compensation (light receiving amplifier). The phase compensation capacitor 18 for adjusting the phase so that the circuit 100 does not oscillate) is connected in parallel. The feedback circuit 104 and the feedback circuit 105 are configured with gain resistors 17 having different resistance values so that the feedback rates of the feedback loops through the feedback circuit 104 and the feedback circuit 105 are different (attenuation rates are different from each other).

  In the light receiving amplifier circuit 100, for example, according to the type of the optical disc, an instruction signal for instructing to turn on either of the switches 108 and 109 is input to the switches 108 and 109 from a control circuit (not shown). As a result, one of the switches 108 and 109 is turned on, and either the first feedback loop through the buffer amplifier 106 and the feedback circuit 104 or the second feedback loop through the buffer amplifier 107 and the feedback circuit 105 is turned on. . Here, the resistance value of the gain resistor 17 constituting the feedback circuit 105 is larger than the resistance value of the gain resistor 17 constituting the feedback circuit 104, that is, the feedback rate of the second feedback loop is that of the first feedback loop. It is assumed that the return rate is lower. In this case, when the switch 109 is turned on, only the second feedback loop having a lower feedback rate is used, and the gain of the light receiving amplifier circuit 100 becomes higher. On the contrary, when the switch 108 is turned on, only the first feedback loop having a higher feedback rate is used, and the gain of the light receiving amplifier circuit 100 becomes lower. In this manner, in the light receiving amplifier circuit 100, the gain is switched by the switches 108 and 109.

The phase characteristics of the light receiving amplifier circuit 100 when the first feedback loop is used and when the second feedback loop is used are the adjustments of the time constants of the feedback circuits 104 and 105, that is, the feedback circuits 104 and 105. By adjusting the capacitance of the phase compensation capacitor 18, adjustment is made to obtain optimum characteristics.
JP 2001-202646 (released July 27, 2001)

  As the writing speed of writable optical discs such as DVD-R increases, the amount of incident light to the optical amplifier for reproducing optical discs has increased, and the range of desired gains has become wide. Therefore, there is a demand for a light receiving amplifier for reproducing an optical disc that can switch the gain between more gains.

  However, in the conventional configuration, when the number of gains to be switched increases, it is necessary to increase the number of feedback circuits according to the number, and the circuit configuration becomes complicated. Further, in the method of adjusting the gain by changing the feedback factor of the feedback loop as described above, if the feedback factor of the feedback loop is changed too much, the optimum phase characteristics (response speed and stability) and frequency characteristics are obtained. It becomes difficult to obtain.

  The present invention has been made in view of the above problems, and an object of the present invention is to switch gains between a large number of gains with a simple circuit configuration, and to achieve optimum phase characteristics. Another object of the present invention is to provide a variable gain amplifier circuit and an optical pickup device that can obtain frequency characteristics.

  In order to solve the above problems, a variable gain amplifier circuit according to the present invention switches a feedback ratio of a first amplifier, a feedback loop that feeds back an output of the first amplifier to an input of the first amplifier, and a feedback loop. Thus, in a variable gain amplifier circuit comprising a first gain switching means for switching the gain of the first amplifier, a plurality of second amplifiers connected in parallel and having different gains and a second amplifier to be used are switched. And a second gain switching means for switching the gain of the entire circuit.

  Further, according to the above configuration, the gain of the variable gain amplifying circuit can be set to a large number of values with a simple circuit configuration by combining the gain switching by the first gain switching unit and the gain switching by the second gain switching unit. Can be adjusted.

  This point will be described in more detail. First, from the viewpoint of only characteristics such as S / N ratio and output offset voltage, it is desirable to switch the gain by switching the feedback loop as in the first amplifier. However, as shown in FIG. 5, if the gain is only variable by switching the feedback loop, the feedback circuit that is not selected becomes a parasitic component with respect to the feedback circuit that is selected. In addition, the wiring between elements becomes redundant, and the resistance component and capacitance component of the wiring also increase. Therefore, in the configuration shown in FIG. 5, when the variable number of gains by switching the feedback loop is increased, these parasitic components increase, and the response characteristics of the variable gain amplifier circuit that greatly depends on the characteristics of the amplifier deteriorate. On the other hand, according to the configuration of the present invention, the total gain variable number is the sum of the gain switching number by the first gain switching unit and the gain switching number by the second gain switching unit. Even when the overall gain variable number is increased, the gain switching number (gain variable number) by switching the feedback loop can be reduced. As a result, parasitic components can be reduced and response characteristics can be improved.

  In addition, since the object (variable gain amplifier circuit) of the present invention is a consumer product, it is necessary to keep in mind the miniaturization and cost reduction of the circuit when designing the circuit. In the conventional variable gain amplifier circuit, particularly in the configuration in which the feedback circuit is selected by a non-saturated switch circuit as shown in FIG. 5, the increase in the circuit scale accompanying the increase in the variable gain number is significant. For example, when the variable gain number of the entire variable gain amplifier circuit is 9, in the light receiving amplifier circuit 100 shown in FIG. 5, the number of feedback circuits is nine, and the circuit scale becomes large. On the other hand, in the configuration of the present invention, when the gain of the entire variable gain amplifier circuit is set to 9, the number of gain switching by the first gain switching means is 3, and the number of gain switching by the second gain switching means is 3. Therefore, the circuit scale can be reduced.

  Further, according to the above configuration, since the second gain switching means is provided, it is not necessary to change the feedback rate of the feedback loop so much in the first gain switching means. Characteristics) and frequency characteristics.

  In the variable gain amplifier circuit of the present invention, the feedback loop is a plurality of feedback loops connected in parallel between the output of the first amplifier and the input of the first amplifier. Preferably, feedback resistors having different resistance values are provided, and the first gain switching means switches the gain of the first amplifier by switching a feedback loop to be used.

  According to the above configuration, not only the gain but also the phase characteristics can be switched simultaneously by switching the feedback loop to be used.

  The variable gain amplifier circuit of the present invention preferably further comprises characteristic control means for controlling the characteristics (phase characteristics and frequency characteristics) of the first amplifier.

  According to the above configuration, the response speed, stability, frequency characteristics, and the like can be optimized by controlling the characteristics.

  The characteristic control means preferably includes a plurality of bias means for applying different bias currents to the first amplifier, and bias control means for controlling the bias current supplied to the first amplifier.

  According to the above configuration, response speed and stability can be optimized.

  The bias control means preferably controls the bias current applied to the first amplifier in accordance with the switching of the feedback loop by the first gain switching means.

  According to the above configuration, sufficient response speed and stability can be obtained by compensating for changes in response speed and stability due to switching of the feedback loop.

  The bias control means may reduce the bias current applied to the first amplifier as the amplitude of the input signal increases.

  The plurality of bias means may apply a bias current having the same polarity to the first amplifier.

  According to the above configuration, since a large bias current can be easily applied to the first amplifier, the response speed can be easily increased.

  At least one of the plurality of bias means may supply a bias current having a polarity opposite to that of the other to the first amplifier.

  According to the above configuration, since a small bias current can be easily applied to the first amplifier, stability can be easily increased.

  The variable gain amplifier circuit of the present invention is preferably used for amplifying an output signal of a light receiving element in an optical pickup device for reproducing an optical recording medium.

  According to the above configuration, the light receiving amplifier circuit for an optical pickup device that can switch the gain among a large number of gains with a simple circuit configuration and can obtain an optimum phase characteristic and frequency characteristic ( An amplification circuit used to amplify the output signal of the light receiving element in an optical pickup device for reproducing an optical recording medium can be provided.

  In order to solve the above-described problems, an optical pickup device of the present invention is an optical pickup device for reproducing an optical recording medium. In the optical pickup device, a light receiving element for detecting reflected light from the optical recording medium, and an output of the light receiving element A variable gain amplifying circuit according to claim 1 for amplifying a signal.

  According to the above configuration, since the variable gain amplifier circuit is provided, the gain of the variable gain amplifier circuit can be adjusted to a large number of values with a simple circuit configuration, and the optimum phase characteristics (response speed and stability) An optical pickup device having frequency characteristics can be provided.

  As described above, the variable gain amplifier circuit and the optical pickup device according to the present invention include a plurality of gains having different gains in addition to the first gain switching means for switching the gain of the first amplifier by switching the feedback factor of the feedback loop. Since the second gain switching means for switching the gain of the entire circuit by switching the second amplifier is provided, the gain of the variable gain amplifier circuit can be adjusted to a large number of values with a simple circuit configuration. In addition, since it is not necessary to change the feedback rate of the feedback loop so much, it is possible to obtain optimum phase characteristics and frequency characteristics. Therefore, the present invention provides a variable gain amplifier circuit and an optical pickup capable of switching gains between a large number of gains with a simple circuit configuration and capable of obtaining optimum phase characteristics and frequency characteristics. There exists an effect that an apparatus can be provided.

[Embodiment 1]
One embodiment of the present invention will be described below with reference to FIGS.
As shown in FIG. 1, a light receiving amplifier circuit as an embodiment of a variable gain amplifier circuit according to the present invention is a first amplifier that amplifies a signal from a light receiving element 1 such as a photodiode that converts incident light into an electric signal. A variable gain amplification stage (preamplifier) 11, a second variable gain amplification stage 12 that receives the output signal of the first variable gain amplification stage 11 and further amplifies this signal, and a second variable gain amplification stage 12 And a third variable gain amplification stage 13 for further amplifying the output signal and outputting it as an output voltage Vout to the outside.

  The first variable gain amplification stage 11 has selectable L (L is an integer of 2 or more) feedback circuits 3-1 to 3-L, similarly to the conventional light receiving amplifier circuit 100 shown in FIG. That is, the first variable gain amplification stage 11 includes an amplifier (first amplifier) 2 and L feedback circuits 3 (L is an integer of 2 or more) for feeding back the output of the amplifier 2 to the input of the amplifier 2. -1 to 3-L and a buffer amplifier 6 for outputting the output signal of the amplifier 2. These feedback circuits 3-1 to 3-L are connected in parallel between the output and input of the amplifier 2, and can be selected by the corresponding switches 4-1 to 4-L. That is, conduction / cutoff of the feedback loop via the feedback circuits 3-1 to 3-L is controlled by the switches 4-1 to 4-L. Buffer amplifiers 5-1 to 5-L are provided between the output of the amplifier 2 and the feedback circuits 3-1 to 3-L, respectively.

  As shown in FIG. 6, each of the feedback circuits 3-1 to 3 -L has a gain resistor for adjusting the gain of the first variable gain amplification stage 11 by adjusting the feedback rate of the feedback loop. 17 and a phase compensation capacitor 18 for performing phase compensation are connected in parallel. The feedback circuits 3-1 to 3 -L are configured by gain resistors 17 having different resistance values so that the feedback loops through the feedback circuits have different feedback rates (different attenuation rates).

  In the first variable gain amplification stage 11, for example, a signal indicating an operation mode corresponding to the type of the optical disk to be reproduced is input from the outside of the light receiving amplifier circuit, and based on this signal, the switch control circuit 14 switches to the switch 4-1. An instruction signal for instructing any one of ˜4-L to be conducted is input to the switches 4-1 to 4-L. As a result, any one of the switches 4-1 to 4-L becomes conductive based on the instruction signal, and the first feedback loop through the buffer amplifier 5-1 and the feedback circuit 3-1, the buffer amplifier 5-2, and the feedback. Any one of the second feedback loop via the circuit 3-2 and the Lth feedback loop via the buffer amplifier 5-L and the feedback circuit 3-L is conducted. Here, the resistance value of the gain resistor 17 constituting the feedback circuit 3-2 is larger than the resistance value of the gain resistor 17 constituting the feedback circuit 3-1, that is, the feedback rate of the second feedback loop is the first. Is assumed to be lower than the feedback rate of the feedback loop. In this case, when the switch 4-2 is turned on, only the second feedback loop having a lower feedback rate is used, and the gain of the first variable gain amplification stage 11 becomes higher. On the contrary, when the switch 4-1 is turned on, only the first feedback loop having a higher feedback rate is used, and the gain of the first variable gain amplification stage 11 becomes lower. In this manner, in the first variable gain amplification stage 11, the gain is switched at the L stage by the switches 4-1 to 4-L. Therefore, in this case, the first gain switching means for switching the gain of the amplifier 2 is configured by the switches 4-1 to 4 -L and the switch control circuit 14.

  The output signal of the first variable gain amplification stage 11 is input to the second variable gain amplification stage 12. The second variable gain amplification stage 12 includes a switch 8 that receives the output of the first variable gain amplification stage 11, and M (M is an integer of 2 or more) amplifiers (second amplifiers) that can be selected by the switch 8. 7-1 to 7-M. The amplifiers 7-1 to 7-M have different gains. According to the operation mode, the switch 8 receives an instruction signal for instructing one of the amplifiers 7-1 to 7-M to be connected to the output of the first variable gain amplification stage 11 from the switch control circuit 14. Is done. The switch 8 connects any one of the amplifiers 7-1 to 7-M to the output of the first variable gain amplification stage 11 based on this instruction signal. As a result, the output signal of the first variable gain amplification stage 11 is input to one of the amplifiers 7-1 to 7-M and amplified. In this way, in the second variable gain amplification stage 12, the gain is switched in M stages by the switch 8. Therefore, in this case, the second gain switching means is constituted by the switch 8 and the switch control circuit 14.

  An output signal of the second variable gain amplification stage 12 is input to the third variable gain amplification stage 13. The third variable gain amplification stage 13 includes a switch 10 that receives the output of the second variable gain amplification stage 12, and N amplifiers 9-1 to 9- that can be selected by the switch 10 (N is an integer of 2 or more). N. The amplifiers 9-1 to 9-N have different gains. The switch 10 receives an instruction signal for instructing to connect any one of the amplifiers 9-1 to 9-N to the output of the second variable gain amplification stage 12 from the switch control circuit 14 in accordance with the operation mode. Is done. The switch 10 connects one of the amplifiers 9-1 to 9-N to the output of the second variable gain amplification stage 12 based on this instruction signal. As a result, the output signal of the second variable gain amplification stage 12 is input to any of the amplifiers 9-1 to 9-N and amplified. Thus, in the third variable gain amplification stage 13, the gain is switched by the switch 10 in N stages. The switch 10 and the switch control circuit 14 also constitute second gain switching means.

  As described above, in the light receiving amplifier circuit according to the present embodiment, the first variable gain amplification stage 11 is the L stage, the second variable gain amplification stage 12 is the M stage, and the third gain is the next stage. Since the variable amplification stage 13 has N stages of gain, it is possible to have L × M × N types of gains. That is, the light receiving amplifier circuit according to the present embodiment can adjust the gain in (L × M × N) stages. In addition, when the conventional light receiving amplifier circuit shown in FIG. 5 is to have L × M × N types of gains, (L × M × N) feedback circuits, switches, and buffer amplifiers are required. Although the circuit configuration is complicated, the light receiving amplifier circuit according to the present embodiment has a simple circuit configuration as compared with it. In order to minimize the circuit scale, the variable gain number L of the first variable gain amplification stage, the variable gain number M of the second variable gain amplification stage 12, and the gain of the third variable gain amplification stage 13 are described. The variable number N is preferably set so that the desired gain variable number L × M × N becomes the desired gain variable number, and the total of the gain variable numbers (L + M + N) is minimized.

  In the light receiving amplifier circuit according to the present embodiment, the second variable gain amplification stage 12 and the third variable gain amplification stage 13 are provided, so that the feedback rate of the feedback loop does not have to be changed so much. Phase characteristics and frequency characteristics can be obtained.

[Embodiment 2]
Another embodiment of the present invention will be described below with reference to FIG. For convenience of explanation, members having the same functions as those shown in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  The light receiving amplifier circuit according to the present embodiment has the same configuration as the light receiving amplifier circuit according to the first embodiment, except that the first variable gain amplification stage 21 is provided instead of the first variable gain amplification stage 11. Yes. The first variable gain amplification stage 21 includes an amplifier (first amplifier) 22 instead of the amplifier 2 and further includes a variable bias current supply circuit (characteristic control means) 23. The gain variable amplification stage 11 has the same configuration.

  Light incident on the light receiving element 1 is converted into an electric signal by the light receiving element 1, and this electric signal is input to the amplifier 22 and amplified. The amplifier 22 includes a transistor 24 that amplifies a signal from the light receiving element 1 and a transistor 25 that serves as an active load. The transistor 24 is an npn transistor, and has a base connected to the light receiving element 1 and an emitter connected to the ground. The transistor 25 is a pnp transistor, and has an emitter connected to a power supply line for supplying the power supply voltage Vcc and a collector connected to the collector of the transistor 24. The amplifier 22 outputs a signal from a wiring connecting the collectors of the transistor 24 and the transistor 25.

  The variable bias current supply circuit 23 supplies a variable bias current to the amplifier 22, that is, supplies a variable bias current to the transistor 24. The variable bias current supply circuit 23 includes transistors 26 and 27-1 to 27 -L, voltage sources 28-1 to 28 -L, switches 29-1 to 29 -L, and a switch control circuit 30. . The transistors 26 and 27-1 to 27-L and the voltage sources 28-1 to 28-L constitute a plurality of bias means. The switches 29-1 to 29 -L and the switch control circuit 30 constitute a bias control means.

  The transistor 26 is a pnp transistor, and has a base connected to the base of the transistor 25 and an emitter connected to a power supply line that supplies the power supply voltage Vcc. The base of the transistor 25 and the base and collector of the transistor 26 are connected to the ground via collectors and emitters of L transistors 27-1 to 27-L connected in parallel. That is, the transistors 27-1 to 27 -L are npn transistors, the collectors are connected to the bases of the transistors 25 and 26, and the emitters are connected to the ground. The bases of the transistors 27-1 to 27 -L are connected to voltage sources 28-1 to 28 -L via switches 29-1 to 29 -L controlled by the switch control circuit 30. The voltage sources 28-1 to 28-L output voltages Vbias1 to VbiasL having the same polarity and different from each other. The currents Vbias1 to VbiasL output from the voltage sources 28-1 to 28-L are respectively supplied to the transistor 24 by positive (or negative) bias currents corresponding to the feedback amounts of the corresponding feedback circuits 3-1 to 3-L. Is set to be given.

  As shown in FIG. 7, the voltage sources 28-1 to 28-L are formed of a current mirror circuit, and a diode of the current mirror circuit is connected to the bases of the transistors 27-1 to 27-L. .

  Next, the operation of the first variable gain amplification stage 21 will be described. The bias to amplifier 22 is determined by the current flowing through transistor 26. The value of the bias to this amplifier 22 is switched by selectable transistors 27-1 to 27-L. That is, first, the switch control circuit 30 returns the feedback amount of the feedback circuit (any one of 3-1 to 3-L) selected by the switches 4-1 to 4-L among the switches 29-1 to 29-L. Only one switch connected to the voltage source (any one of 28-1 to 28-L) corresponding to is made conductive. As a result, a bias current corresponding to the feedback amount of the feedback circuit (any of 3-1 to 3-L) selected by the switches 4-1 to 4-L is given to the transistor 24. In this way, the switch control circuit 30 and the switches 29-1 to 29 -L control the bias current applied to the amplifier 22 in accordance with the switching of the feedback loop by the switches 4-1 to 4 -L. . Thereby, the bias state of the amplifier 22 can be switched according to the feedback amount of the selected feedback circuit (any one of 3-1 to 3-L). That is, for example, the bias current to the amplifier 22 can be increased as the feedback rate of the feedback loop decreases. As a result, it is possible to ensure a sufficient response speed and stability by compensating for a decrease in response speed and stability due to a reduction in the feedback rate of the feedback loop.

[Embodiment 3]
Another embodiment of the present invention is described below with reference to FIG. For convenience of explanation, members having the same functions as those shown in the first or second embodiment are denoted by the same reference numerals, and description thereof is omitted.

  The light receiving amplifier circuit according to the present embodiment has the same configuration as that of the light receiving amplifier circuit according to the second embodiment except that the first variable gain amplifying stage 31 is provided instead of the first variable gain amplifying stage 21. Yes. The first variable gain amplification stage 31 has a basic configuration similar to that of the first variable gain amplification stage 21 in the second embodiment, but instead of the variable bias current supply circuit 23, a variable bias current supply circuit (characteristic control means). ) 33 is different from the first variable gain amplification stage 21 only in that it is further provided.

  The variable bias current supply circuit 33 supplies a variable bias current to the amplifier 22, that is, supplies a variable bias current to the transistor 24. The variable bias current supply circuit 33 includes transistors 26, 27, 34, 35, 36, a voltage source 37, a voltage source 38, and a switch control circuit (bias control means) 39. The transistors 26, 27, 34, 35, and 36, the voltage source 37, and the voltage source 38 constitute a plurality of bias means.

  The transistor 26 is a pnp transistor, and has a base connected to the base of the transistor 25 and an emitter connected to a power supply line that supplies the power supply voltage Vcc. The base of the transistor 25 and the base and collector of the transistor 26 are connected to the ground via the collector-emitter of the transistor 27. That is, the transistor 27 is an npn-type transistor, the collector is connected to the bases of the transistors 25 and 26, and the emitter is connected to the ground. The base of the transistor 27 is connected to the voltage source 37. The voltage source 37 outputs a constant voltage Vbias12 so that a predetermined bias current is applied to the transistor 24. The transistor 34 is a pnp transistor, and has an emitter connected to a power supply line that supplies a power supply voltage Vcc, and a collector connected to the collector of the transistor 26. The transistor 35 is a pnp transistor, and has a base connected to the base of the transistor 34 and an emitter connected to a power supply line that supplies the power supply voltage Vcc. The base of the transistor 34 and the base and collector of the transistor 35 are connected to the ground via the collector-emitter of the transistor 36. That is, the transistor 36 is an npn-type transistor, the collector is connected to the bases of the transistors 34 and 35, and the emitter is connected to the ground. The base of the transistor 36 is connected to a voltage source 38 via a switch 58 controlled by a switch control circuit 39. The voltage source 38 outputs a constant current Vbias11 so that a bias current having a polarity opposite to that of the bias current given by the voltage source 37 is given to the transistor 24. The current Vbias11 is set to a value slightly smaller than, for example, Vbias12.

  The bias current to the transistor 24 performing the amplifying function is determined by the transistor 27. The value of the bias current is reduced by the current value when the transistor 36 operates. This makes it possible to easily switch the bias only during a specific operation when the feedback circuits 3-1 to 3-L are selected. In these switching operations, when the gain is large (when the feedback is shallow), the bias current is increased due to high-speed response, but when the gain is small (when the feedback is deep), the bias current is decreased to ensure the stability of the amplifier. .

  Next, the operation of the first variable gain amplification stage 31 will be described in detail. That is, first, the amount of bias current applied to the transistor 24 by the current control circuit 30 changes according to a change in gain (change in the feedback rate of the feedback loop) due to switching of the feedback loop by the switches 4-1 to 4-L. Thus, the output voltage Vbias11 of the voltage source 38 is changed. Specifically, when the gain of the amplifier 22 is large (when the feedback rate of the feedback loop is small), the switch 58 is turned off by the switch control circuit 39, and the base current of the transistor 36 is set to zero. As a result, the bias current to the transistor 24 is increased and the response speed is improved. Therefore, it is possible to compensate for a decrease in the response speed due to a reduction in the feedback rate of the feedback loop. When the gain of the amplifier 22 is small (when the feedback factor of the feedback loop is large), the switch 58 is turned on by the switch control circuit 39, and the output voltage Vbias11 of the voltage source 38 is supplied to the base of the transistor 36. As a result, the bias current to the transistor 24 is reduced and the stability of the amplifier 22 is improved. Therefore, it is possible to compensate for a decrease in stability due to an increase in the feedback rate of the feedback loop. In this way, by increasing the bias current as the feedback ratio of the feedback loop decreases, the response speed and stability decrease due to the decrease of the feedback ratio of the feedback loop are compensated, and sufficient response speed and stability are achieved. Sex can be secured.

  In the present embodiment, the gain of the first variable gain amplification stage 31 is changed from gain G1 (gain when the feedback circuit 3-1 is selected) to gain G (L-1) (feedback circuit 3- ( The desired characteristics are realized in each gain without switching the voltage source until the gain when L-1) is selected), but the gain of the first variable gain amplification stage 31 is Only when the minimum gain GL (gain when the feedback circuit 3-L is selected) is reached, it is suitable when the feedback rate is large and the stability of the light receiving amplifier cannot be secured. According to the configuration of the present embodiment, in such a case, when the gain of the first variable gain amplification stage 31 is the minimum gain GL, the current can be reduced to ensure the stability of the light receiving amplifier. it can.

[Embodiment 4]
Next, as a fourth embodiment, FIG. 4 shows a configuration example of an optical pickup device using any of the light receiving amplifier circuits of the first to third embodiments. The optical pickup device according to this embodiment is compatible with CD, CD-R, DVD, and DVD-R. As shown in FIG. 4, the optical pickup device according to the present embodiment includes a laser diode 43C for irradiating a CD or CD-R with a light beam a when a CD or CD-R is used as the optical disc 45, and an optical disc 45. A laser diode 43D for irradiating the DVD or DVD-R with the light beam b when a DVD or DVD-R is used, and a reflection mirror for guiding the light beams a and b from the laser diodes 43C and 43D to the optical disk 45 44. Furthermore, the optical pickup device according to the present embodiment includes a light receiving element 1 such as a photodiode for detecting reflected light a ′ and b ′ from a CD, CD-R, DVD or DVD-R, And a light receiving amplifier circuit 42 for amplifying the output signal. The light guide unit that guides the light beam from the laser diodes 43C and 43D onto the optical disk 45 is adjusted so that the incident point on the light receiving element 1 is the same for the laser beam for CD and the laser beam for DVD. Has been.

  When reproducing a CD or CD-R as the optical disk 45, the reflected light from the CD or CD-R is received by the light receiving element 1 and converted into an electrical signal. A signal from the light receiving element 1 is input to the light receiving amplifier circuit 42. The light receiving amplifier circuit 42 amplifies the signal with a relatively low gain when reproducing the CD and with a relatively high gain when reproducing the CD-R, and outputs the amplified signal to the outside. Further, the light receiving amplifier circuit 42 amplifies the signal at a gain lower than that at the time of reproducing the CD when the CD-R is written.

  When a DVD or DVD-R is reproduced as the optical disk 45, the reflected light from the DVD or DVD-R is received by the light receiving element 1 and converted into an electrical signal. A signal from the light receiving element 1 is input to the light receiving amplifier circuit 42 through the switching circuit 41. The light receiving amplifier circuit 42 amplifies the signal with a relatively low gain when reproducing the DVD and with a relatively high gain when reproducing the DVD-R, and outputs the amplified signal to the outside. Further, the light receiving amplifier circuit 42 amplifies the signal with a lower gain when writing to the DVD-R than when reproducing the DVD. Further, the gain of the light receiving amplifier circuit 42 is adjusted to a gain different from that at the time of reproduction of CD and CD-R when reproducing DVD and DVD-R. Therefore, in this case, the gain of the light receiving amplifier circuit 42 is adjusted in six steps.

  Here, the optical pickup device corresponding to CD, CD-R, DVD, and DVD-R has been described. However, the optical pickup device of the present invention can be applied only to one type of writable optical disc, for example, CD-R. An optical pickup device used in a corresponding optical recording / reproducing device may be used. Further, here, the gain of the light receiving amplifier circuit 42 is adjusted depending on the type of the optical disc and whether it is during reproduction or recording. However, the gain may be adjusted for other purposes. For example, if the intensity of the writing laser beam is changed, the gain of the light receiving amplifier circuit 42 may be adjusted in accordance with the change in the intensity of the writing laser beam.

  In the above description, the case where the gain of the amplifier 11 is switched by switching a plurality of feedback loops having feedback resistors having different resistance values has been described. However, the amplifier 2 has a feedback loop that feeds back its output to its input. It is only necessary to be provided and to be able to switch the feedback rate of the feedback loop. Therefore, for example, the feedback loop itself has only one feedback loop that does not include a switch, and a plurality of resistance elements having different resistance values are connected in parallel between the light receiving element 1 and the amplifier 2, and these are switched by the switch. The feedback rate of the feedback loop may be changed by using it.

  In the above description, there are provided two variable gain amplification stages in which the gain is switched by using a plurality of amplifiers having different gains. However, the number of variable gain amplification stages is particularly limited. Instead, it may be one stage.

  In the second and third embodiments, the configuration in which the phase characteristic of the first variable gain amplification stage (21, 31) is optimized by controlling the bias current applied to the amplifier 22 has been described. The configuration may be such that the phase characteristics of the first variable gain amplification stage (21 · 31) are controlled, or the frequency characteristics and the like of the first variable gain amplification stage (21 · 31) may be controlled.

  In the fourth embodiment, the case where the present invention is applied to an optical pickup device for reproducing a plurality of types of optical recording media has been described. However, the present invention is not limited to this. For example, even if the present invention is applied to an optical pickup device for reproducing an optical recording medium written at a different writing speed, substantially the same effect as in the present embodiment can be obtained.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and the technical means disclosed in different embodiments can be appropriately combined. Embodiments are also included in the technical scope of the present invention.

  In the light receiving amplifier circuit according to the present invention, a plurality of feedback resistors are provided for the amplifier unit, and the gain is switched by switching the feedback loop. It may be configured to have.

  According to the above configuration, a light receiving amplifier element having a large number of modes can be realized by a combination of amplifiers having a plurality of gains and switching of the characteristics of the amplifier unit.

  The light receiving amplifier circuit according to the present invention preferably has a configuration in which switching means for switching the characteristics of the amplifier unit is provided in the above configuration.

  Further, the light receiving amplifier circuit according to the present invention is preferably configured such that, in the above configuration, the switching means is composed of a plurality of bias means.

  When the gain ratio is large, the feedback amount to the amplifier is also greatly different, but the optimized characteristic is realized by switching the bias means of the amplifier.

  Further, the light receiving amplifier circuit according to the present invention is preferably configured such that independent switching means is provided for each operation mode in the configuration in which the switching means is composed of a plurality of biasing means.

  The light receiving amplifier circuit according to the present invention is preferably configured such that, in the configuration in which the switching means is composed of a plurality of bias means, the characteristics of the amplifier section are switched by a combination of bias means having the same polarity.

  The light receiving amplifier circuit according to the present invention is preferably configured such that, in the configuration in which the switching means is composed of a plurality of bias means, the characteristics of the amplifier section are switched by a combination of reverse polarity bias means.

  In the light receiving amplifier circuit according to the present invention, preferably, in the configuration in which the switching means is composed of a plurality of bias means, the bias current is reduced when the amount of received light is large, and the bias current is increased when the amount of received light is small. It is a configuration.

  Further, the pickup device according to the present invention has a configuration using the light receiving amplifier circuit having any one of the above configurations.

  The variable gain amplifier circuit of the present invention is an amplifier circuit having a variable gain (gain) by switching the feedback factor of the feedback loop in order to process various signals. In particular, it receives light reflected from a plurality of types of optical disks. It can be suitably used as a light receiving amplifier circuit that amplifies a signal from the element with a variable gain.

It is a block diagram which shows the structure of the light reception amplifier circuit as one Embodiment of the variable gain amplifier circuit of this invention. It is a block diagram which shows the structure of the light reception amplifier circuit as other Embodiment of the variable gain amplifier circuit of this invention. It is a block diagram which shows the structure of the light reception amplifier circuit as another Embodiment of the variable gain amplifier circuit of this invention. It is a block diagram which shows the structure of the optical pick-up apparatus which concerns on one Embodiment of this invention. It is a figure which shows an example of the light reception amplifier circuit provided with the conventional several feedback loop. It is a circuit diagram which shows an example of a feedback circuit. FIG. 3 is a circuit diagram illustrating a configuration of a voltage supply unit in the light receiving amplifier circuit of FIG. 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light receiving element 1C Light receiving element 1D Light receiving element 2 Amplifier (1st amplifier)
3-1 to 3-L feedback circuit 4-1 to 4-L switch 7-1 to 7-M amplifier (second amplifier)
8 switch 9-1 to 9-N amplifier (second amplifier)
DESCRIPTION OF SYMBOLS 10 Switch 11 1st gain variable amplification stage 12 2nd gain variable amplification stage 13 3rd gain variable amplification stage 14 Switch control circuit 17 Gain resistance (feedback resistance)
21 First gain variable amplification stage 22 Amplifier (first amplifier)
23 variable bias current supply circuit 28-1 to 28-L voltage source 29-1 to 29-L switch 30 switch control circuit 31 first gain variable amplification stage 33 variable bias current supply circuit 37 voltage source 38 voltage source 39 switch control Circuit 42 Light receiving amplifier circuit (gain variable amplification circuit)
45 Optical disk 58 switch

Claims (9)

A first amplifier;
A feedback loop for feeding back the output of the first amplifier to the input of the first amplifier;
In a variable gain amplifier circuit comprising first gain switching means for switching a gain of the first amplifier by switching a feedback factor of a feedback loop,
A plurality of second amplifiers connected in parallel and having different gains;
And a second gain switching means for switching a gain of the entire circuit by switching a second amplifier to be used. The feedback loop is a plurality of feedback loops connected in parallel between the output of the first amplifier and the input of the first amplifier;
The plurality of feedback loops are provided with feedback resistors having different resistance values, respectively.
2. The variable gain amplifier circuit according to claim 1, wherein the first gain switching means switches the gain of the first amplifier by switching a feedback loop to be used.   2. The variable gain amplifier circuit according to claim 1, further comprising characteristic control means for controlling characteristics of the first amplifier. The characteristic control means includes a plurality of bias means for applying different bias currents to the first amplifier,
4. The variable gain amplifier circuit according to claim 3, further comprising bias control means for controlling a bias current applied to the first amplifier.   5. The variable gain amplifier circuit according to claim 4, wherein the bias control means controls a bias current applied to the first amplifier in response to switching of the feedback loop by the first gain switching means.   5. The variable gain amplifier circuit according to claim 4, wherein the plurality of bias means supply a bias current having the same polarity to the first amplifier.   5. The variable gain amplifier circuit according to claim 4, wherein at least one of the plurality of bias means supplies a bias current having a polarity opposite to that of the other to the first amplifier.   2. The variable gain amplifier circuit according to claim 1, wherein the variable gain amplifier circuit is used for amplifying an output signal of a light receiving element in an optical pickup device for reproducing an optical recording medium. In an optical pickup device for reproducing an optical recording medium,
A light receiving element for detecting reflected light from the optical recording medium;
9. An optical pickup device comprising: the variable gain amplifier circuit according to claim 1 for amplifying an output signal of a light receiving element.

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