JP2007018640A - Dpd signal generator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the degradation of signal quality of a DPD signal even when regenerating the point where reflectivity falls off due to the adhesion of a smudge etc. <P>SOLUTION: The apparatus includes gain variable amplifiers 1A to 1D which correspond respectively to four regions of a photodetector 5, binarization circuits 2A to 2B which binarize the outputs of the gain variable amplifiers 1A to 1D. a first phase comparison circuit 11 which detects the phase difference between the outputs of the binarization circuits 2C to 2D, a second phase comparison circuit 12 which detects the phase difference between the outputs of the binarization circuits 2C to 2D, and an adder circuit 13. The apparatus in the above described configuration is equipped with a gain controller 4 which increases the gain of the gain variable amplifiers 1A to 1D when the signal level inputted to the gain variable amplifiers 1A to 1D gets small. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  In the present invention, the amplifier that amplifies the output of the light receiving element and sends it to the binarization circuit is a variable gain amplifier with variable gain, and when the signal level input to the variable gain amplifier decreases, the gain of the variable gain amplifier is increased. The present invention relates to a DPD signal generating apparatus.

  One of the methods for generating a tracking error signal required when reproducing an optical disc such as a DVD is a DPD (Differential Phase Detection) method (referred to as a first conventional technology). In this method, as shown in FIG. 8, the binarization circuit is obtained after amplifying the outputs of the areas A to D of the light receiving element (PDIC) 5 using equalizers 91A to 91D having predetermined pass characteristics. Binarization is performed using 2A to 2D. The phase comparison circuit 11 is used to detect the phase difference between the signal obtained by binarizing the output of the region A and the signal obtained by binarizing the output of the region B. Further, a phase difference between a signal obtained by binarizing the output of the region C and a signal obtained by binarizing the output of the region D is detected by using the phase comparison circuit 12. A DPD signal, which is a signal obtained by removing unnecessary high-frequency components from the signal obtained by adding the output of the phase comparison circuit 11 and the output of the phase comparison circuit 12, using a low-pass filter 14, is used as a tracking error. A signal indicating the amount is output to a servo control circuit (not shown) (see, for example, Patent Document 1).

Patent Document 1 also proposes the following technique (referred to as a second conventional technique). That is, in this technique, as shown in FIG. 9, the AGC circuit (level detection) that maintains the amplitude constant even when the output level of the regions A to D changes with respect to the outputs of the regions A to D. Circuit and a variable gain amplifier). Further, a DC component is removed from the output of the AGC circuit using a high-pass filter. The output of region A and the output of region C are multiplied among the four outputs from which the amplitude is constant and the DC component is removed. Also, the output of region B and the output of region D are multiplied. Then, an unnecessary high frequency component is obtained by using a low-pass filter from a signal obtained by adding the multiplication result of the output of region A and the output of region C and the multiplication result of the output of region B and the output of region D. The DPD signal is obtained by removing.
JP 2004-87046 A

  However, when the first prior art is used, the following problems have occurred. That is, in a portion where the reflectance is low due to dirt such as fingerprints attached, the intensity of the reflected light is weakened, the output level of the light receiving element is lowered, and the level of the signal input to the binarization circuits 2A to 2D Becomes smaller. On the other hand, as the characteristics of the binarization circuits 2A to 2D, when the level of the input signal becomes small, a symmetry shift or the like occurs, the slice level is not properly maintained, and the level change timing in binarization is disturbed. Occurs. That is, the signal quality of the binarized signal is deteriorated. Accordingly, when a DVD with dirt such as fingerprints attached to the information recording surface is a reproduction target, the output level of the equalizer is reduced and the signal of the DPD signal (tracking error signal) is obtained when the reproduction position becomes a spot with dirt. Quality deteriorates. For this reason, it is easy for the track to come off at the spot where the dirt adheres. In addition, when seeking the place where dirt is attached, there may be a situation where the seek performance is deteriorated.

  Note that the equalizer has a variable gain, and in the initial setting when the DVD is replaced, the equalizer gain is set to an optimum value for the reflectance of the information recording surface based on the output level of the light receiving element. In this configuration, the gain of the equalizer is maintained at the initial setting. For this reason, when the spot where the dirt is attached is reproduced, the output level of the equalizer is reduced, so that the signal quality of the DPD signal is lowered and the off-track is likely to occur as described above. Moreover, the situation where the seek performance deteriorated sometimes occurred.

  The calculation used in the second prior art is a calculation method on the assumption that the amplitude of the signal input to the multiplier is always maintained at the same amplitude, and the signal amplitude input to the multiplier is Immediately appears as an error in the DPD signal. That is, the AGC circuit including the level detection circuit and the variable gain amplifier functions as one of arithmetic circuits in the arithmetic operation. That is, the second prior art is a technique in which the presupposed configuration is different when viewed from a configuration in which a DPD signal is obtained by performing phase comparison. For this reason, in the case of using the configuration that obtains the DPD signal by phase comparison, that is, the problem that occurred in the first prior art, the accuracy of the DPD signal is lowered and the off-track occurs when reproducing the contaminated portion. From the viewpoint of solving the problem of facilitating, this technique is difficult to apply.

  The present invention was devised to solve the above problems, and its purpose is to improve the signal quality of the DPD signal even when reproducing a portion where the reflectance is reduced due to the adhesion of dirt or the like. DPD signal generation device capable of preventing a decrease in the circuit scale and also preventing a decrease in the signal quality of the DPD signal when reproducing a portion where the reflectance is reduced Is to provide.

  Another object of the present invention is to make the amplifier that amplifies the output of the light receiving element and sends it to the binarization circuit a variable gain amplifier with a variable gain, and when the signal level input to the variable gain amplifier becomes small, To provide a DPD signal generation device capable of preventing a decrease in signal quality of a DPD signal even when reproducing a portion where the reflectance is reduced due to adhesion of dirt or the like by increasing the gain It is in.

  In addition to the above purpose, controlling the gain of each variable gain amplifier based on the signal level input to each causes a shift of the objective lens, which causes the beam spot to deviate from the track. Another object of the present invention is to provide a DPD signal generation device capable of preventing a decrease in signal quality of a DPD signal even when an output level of an area located on one side with respect to a track axis is reduced.

  In order to solve the above problems, a DPD signal generation device according to the present invention is a light receiving element in which a light receiving region is divided into four regions by a track direction axis indicating the track direction of the optical disc and an axis orthogonal to the track direction axis. And an amplifier that amplifies the output signal of each of the four areas, and is provided corresponding to each of the four areas, and is obtained by binarizing the output of the amplifier. A binarization circuit that outputs the binarized signal obtained, and a first that detects a phase difference between the binarized signals of two regions located on one side of the track direction axis among the four regions A phase comparison circuit, a second phase comparison circuit for detecting a phase difference between binarized signals of two regions located on the other side of the track direction axis among the four regions, and a first phase comparison Circuit detection result and second It is applied to the DPD signal generator with a summing circuit for outputting a signal obtained by adding the detection result of the phase comparator circuit as a tracking error signal. The amplifier is a variable gain amplifier having a variable gain, and includes a gain control unit that increases the gain of the variable gain amplifier when the level of the RF signal obtained by adding the outputs of the four regions decreases.

  That is, when the reproduction position on the optical disk is a portion having a low reflectance, the output level of the light receiving element is small, so that the signal level input to the gain variable amplifier is small. However, at this time, since the level of the RF signal is also reduced, the gain of the variable gain amplifier is increased. Therefore, the signal sent from the gain variable amplifier to the binarization circuit is a signal of a level necessary for the binarization circuit to perform binarization with high accuracy. The gain control unit can perform the above-described control only by detecting the level of the RF signal.

  The DPD signal generation device according to the present invention includes a light receiving element that is divided into four regions by a track direction axis indicating the track direction of the optical disc and an axis orthogonal to the track direction axis, and each of the four regions. An amplifier that amplifies the output signal of each of the four regions and a binarized signal that is provided corresponding to each of the four regions and obtained by binarizing the output of the amplifier. An output binarization circuit, a first phase comparison circuit for detecting a phase difference between binarization signals of two regions located on one side of the track direction axis among the four regions, and four Among the regions, a second phase comparison circuit that detects the phase difference between the binarized signals of two regions located on the other side with respect to the track direction axis, the detection result of the first phase comparison circuit, and the second Detection result of phase comparison circuit It is applied to the DPD signal generator with a summing circuit for outputting a signal obtained by adding the as the tracking error signal. The amplifier is a variable gain amplifier having a variable gain, and includes a gain control unit that increases the gain of the variable gain amplifier when the signal level input to the variable gain amplifier decreases.

  That is, when the reproduction position on the optical disk is a portion having a low reflectance, the output level of the light receiving element is small, and the signal level input to the variable gain amplifier is small. Accordingly, at this time, the gain control unit increases the gain of the variable gain amplifier. For this reason, the signal sent from the variable gain amplifier to the binarization circuit is a signal of a level necessary for the binarization circuit to perform binarization with high accuracy.

  In addition to the above configuration, the gain control unit controls each gain of the variable gain amplifier based on a signal level input to each variable gain amplifier. That is, when the output level of the area located on one side of the track axis is reduced due to the shift of the objective lens and the beam spot being deviated from the track, this corresponds to the area. The gain of the variable gain amplifier is controlled to be high. Therefore, in the binarization circuit that binarizes the output of the variable gain amplifier, accurate binarization is performed.

  According to the present invention, when the portion of the optical disk having a low reflectance is reproduced, the level of the RF signal is reduced, so that the gain of the variable gain amplifier is increased. Therefore, the signal sent from the gain variable amplifier to the binarization circuit is a signal of a level necessary for the binarization circuit to perform binarization with high accuracy. The gain control unit can perform the above-described control only by detecting the level of one signal called an RF signal. For this reason, it is possible to prevent the signal quality of the DPD signal from being deteriorated even when reproducing a portion where the reflectance is reduced due to adhesion of dirt or the like. In addition, it is possible to suppress an increase in circuit scale when preventing a decrease in signal quality of the DPD signal when reproducing a portion where the reflectance is reduced.

  Further, according to the present invention, when reproducing a portion of the optical disk having a low reflectance, the level of the signal input to the variable gain amplifier is reduced, so that the variable gain amplifier is controlled so as to increase the gain. Therefore, the signal sent from the gain variable amplifier to the binarization circuit is a signal of a level necessary for the binarization circuit to perform binarization with high accuracy. For this reason, it is possible to prevent the signal quality of the DPD signal from being deteriorated even when reproducing a portion where the reflectance is reduced due to adhesion of dirt or the like.

  Further, when the output level of the area located on one side across the track axis decreases due to the shift of the objective lens and the beam spot deviating from the track, The gain of the corresponding variable gain amplifier is controlled to be high. For this reason, even when the output level of the region located on one side of the track axis is reduced due to the shift of the objective lens and the deviation of the beam spot from the track, the signal of the DPD signal Quality degradation can be prevented.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 2 is an explanatory diagram showing the configuration of the optical system of the optical pickup.

  In the figure, the laser light emitted from the laser diode 41 is guided to the half mirror 44 through the optical element 42 and reflected. The laser light reflected by the half mirror 44 is guided to the launch mirror 46 through the optical element 45 and reflected upward. The laser beam reflected upward is guided to the objective lens 48 through the optical element 47 and condensed on the information recording surface of the DVD (optical disk) 49.

  The laser light reflected by the information recording surface is guided to the light receiving element (PDIC) 5 through the objective lens 48, the optical element 47, the launch mirror 46, the optical element 45, the half mirror 44, and the optical element 43. An arrow 51 indicates the track direction, and an arrow 52 indicates a direction orthogonal to the track direction.

  FIG. 1 is a block diagram showing an electrical configuration of a first embodiment of a DPD signal generating apparatus according to the present invention, which is used for a DVD player.

  The light receiving element 5 includes a region A, a region B, a region C, a region in which a light receiving region indicates a track direction axis indicating the track direction of the optical disc (an arrow Tr indicates the track direction) and an axis orthogonal to the track direction axis. The region D is divided into four regions. The gain variable amplifiers 1A to 1D amplify the output signals of the regions A to D with the gains instructed by the gain control unit 4 and output the amplified signals to the binarization circuits 2A to 2D. The binarization circuits 2A to 2D generate and output a binarized signal obtained by binarizing the signals output from the variable gain amplifiers 1A to 1D.

  The first phase comparison circuit 11 (same as the phase comparison circuit 11 shown in FIG. 8) detects the phase difference between the binarized signal corresponding to the region A and the binarized signal corresponding to the region B. . That is, the phase difference between the binarized signal output from the binarizing circuit 2A and the binarized signal output from the binarizing circuit 2B is detected. Then, the detection result is sent to the adding circuit 13. The second phase comparison circuit 12 (same as the phase comparison circuit 12 shown in FIG. 8) detects the phase difference between the binarized signal corresponding to the region C and the binarized signal corresponding to the region D. . That is, the phase difference between the binarized signal output from the binarization circuit 2C and the binarized signal output from the binarization circuit 2D is detected. Then, the detection result is sent to the adding circuit 13.

  The adder circuit 13 adds the detection result of the first phase comparison circuit 11 and the detection result of the second phase comparison circuit 12 and outputs the addition result to the low-pass filter 14. The low-pass filter 14 sends a DPD signal obtained by removing high frequency components from the output of the adder circuit 13 to a servo control unit (not shown) as a tracking error signal.

  The adder 3 generates an RF signal by adding all the outputs of the areas A to D, and sends the RF signal to a signal processing unit (not shown). Also, the generated RF signal is sent to the gain control unit 4. The gain control unit 4 controls the gains of the variable gain amplifiers 1A to 1D based on the level of the RF signal. Specifically, when the level of the RF signal decreases, the gains of the variable gain amplifiers 1A to 1D are increased by assuming that the signal level input to the variable gain amplifiers 1A to 1D is small. More specifically, when the level of the RF signal is N, the gains of the variable gain amplifiers 1A to 1D are controlled so that the gains of the variable gain amplifiers 1A to 1D are G1 / N (G1 is a constant).

  The operation of the embodiment having the above configuration will be described.

  When reproducing the DVD 49, the gain control unit 4 sets the gains of the gain variable amplifiers 1A to 1D to a gain (G1 / N) determined in accordance with the level N of the RF signal. Therefore, as shown by 71 in FIG. 3, when the reflectivity of the information recording surface of the DVD 49 is high and the output level from the areas A to D of the light receiving element 5 is large, the level of the RF signal becomes large. The gains of the variable gain amplifiers 1A to 1D are set low. For this reason, the level of the signal guided to the binarization circuits 2A to 2D becomes a level L at which the binarization circuits 2A to 2D can perform binarization with the highest accuracy.

  As shown in 72, since the reflectivity of the information recording surface of the DVD 49 is medium, when the output level from the areas A to D of the light receiving element 5 is medium, the level of the RF signal is also medium. It will be about. For this reason, the gains of the variable gain amplifiers 1A to 1D are set to a medium level. As a result, the level of the signal guided to the binarization circuits 2A to 2D becomes a level L at which the binarization circuits 2A to 2D can perform binarization with the highest accuracy.

  Further, as shown in 73, when the reflectivity of the information recording surface of the DVD 49 is low and the output level from the areas A to D of the light receiving element 5 is small, the level of the RF signal is also small. The gains 1A to 1D are set high. For this reason, the level of the signal guided to the binarization circuits 2A to 2D becomes a level L at which the binarization circuits 2A to 2D can perform binarization with the highest accuracy.

  That is, even when the reflectivity of the information recording surface of the DVD 49 changes, the gains of the variable gain amplifiers 1A to 1D change corresponding to the change in reflectivity, so that they are input to the binarization circuits 2A to 2D. The signal level is maintained at a level L at which the binarization circuits 2A to 2D can perform binarization with the highest accuracy.

  Now, assume that the fingerprint is attached to a part of the information recording surface of the DVD 49, so that the reflectance of the portion where the fingerprint is attached is lowered. When reproducing such a DVD 49, as shown in FIG. 4, when reproducing a portion where the fingerprint is attached and the reflectance is low (indicated by a period t1), the level of the RF signal becomes small. On the other hand, when the level of the RF signal decreases, the gains of the variable gain amplifiers 1A to 1D increase by the reciprocal of the decreased ratio. Therefore, even when reproducing a portion having a low reflectance due to the fingerprint attached (indicated by the period t1), the signal levels input to the binarization circuits 2A to 2D are the highest in the binarization circuits 2A to 2D. It is maintained at a level L at which binarization can be performed with high accuracy. For this reason, stable tracking is performed even at a spot where dirt is attached.

  Next, a second embodiment of the present invention will be described.

  FIG. 5 is a block diagram showing the electrical configuration of the second embodiment. The same reference numerals as those in FIG. 1 are given to the same blocks as those shown in FIG. An adder 3 for generating an RF signal is also provided, but is not shown in FIG.

  The level detection circuits 6A to 6D detect the levels of the signals input to the variable gain amplifiers 1A to 1D, and set the gains of the variable gain amplifiers 1A to 1D based on the detection results. That is, the gain control unit described in the claims is composed of the block 7 constituted by the level detection circuits 6A to 6D, and the variable gain amplifiers 1A to 1D based on the signal levels input to the variable gain amplifiers 1A to 1D, respectively. Control each gain of.

  Specifically, the level detection circuit 6A increases the gain of the variable gain amplifier 1A when the signal level output from the region A decreases and the signal level input to the variable gain amplifier 1A decreases. Similarly, in the level detection circuits 6B to 6D, when the signal level output from the regions B to D decreases and the signal level input to the gain variable amplifiers 1B to 1D decreases, the level detection circuits 6B to 6D Increase the gain.

  More specifically, the level detection circuits 6A to 6D set the gains of the variable gain amplifiers 1A to 1D to G2 / M (G2 is a constant) when the signal level output from the areas A to D is M.

  The operation of the second embodiment having the above configuration will be described.

  The level detection circuits 6A to 6D decrease the gains of the variable gain amplifiers 1A to 1D as indicated by 81 in FIG. 6 when the output signal levels of the corresponding regions A to D are large. For this reason, the signal level input to the binarization circuits 2A to 2D becomes a level L at which the binarization circuits 2A to 2D can perform binarization with the highest accuracy.

  When the output signal levels of the corresponding areas A to D are medium, as shown at 82, the gains of the variable gain amplifiers 1A to 1D are medium. For this reason, the signal level input to the binarization circuits 2A to 2D becomes a level L at which the binarization circuits 2A to 2D can perform binarization with the highest accuracy. Further, when the signal level of the output of the corresponding region A to D decreases, as shown at 83, the gain of the gain variable amplifiers 1A to 1D is increased. For this reason, the signal level input to the binarization circuits 2A to 2D becomes a level L at which the binarization circuits 2A to 2D can perform binarization with the highest accuracy.

  Now, it is assumed that the DVD 49 with information such as fingerprints attached to the information recording surface is reproduced. At this time, as shown in FIG. 7, when the reproduction position is a place where a fingerprint is attached (indicated by a period t2), the signal level output from each of the regions A to D becomes small. Therefore, the gains of the variable gain amplifiers 1A to 1D are increased. Accordingly, the signal levels input to the binarization circuits 2A to 2D are binarized by the binarization circuits 2A to 2D with the highest accuracy even when the portion where the fingerprint is attached and the reflectance is low is reproduced. It is maintained at a level L that can be performed. For this reason, stable tracking is performed even in a portion where dirt is attached.

  Further, it is assumed that the objective lens 48 is shifted and the spot is shifted from the center of the track. At this time, the output level of the regions A and B (or regions C and D) decreases, and the output level of the regions C and D (or regions A and B) increases (the RF signal when such a situation occurs) This level is substantially the same as the level of the RF signal when the spot does not deviate from the center of the track).

  When the above situation occurs, the gain of the variable gain amplifier 1A that amplifies the output of the region A and the gain of the variable gain amplifier 1B that amplifies the output of the region B are set to be large, and the output of the region C is amplified. The gain of the variable gain amplifier 1C to be set and the gain of the variable gain amplifier 1D to amplify the output of the region D are set to be small.

  Accordingly, the level of the RF signal is substantially constant and does not change, the output level of the regions A and B (or regions C and D) is reduced, and the output level of the regions C and D (or regions A and B) is increased. Even in this case, the signal level input to each of the binarization circuits 2A to 2D is maintained at the level L at which the binarization circuits 2A to 2D can perform binarization with the highest accuracy. For this reason, stable tracking is performed even when the objective lens 48 shifts and the spot deviates from the track center.

  The present invention is not limited to the above embodiment, and the gain control units 4 and 7 are output from the variable gain amplifiers 1A to 1D even when the signal level input to the variable gain amplifiers 1A to 1D changes. The signal output from the variable gain amplifiers 1A to 1D is also described when the signal level input to the variable gain amplifiers 1A to 1D changes. It is not necessary to control the level to be constant, and even when the reflectivity of the information recording surface of the DVD 49 becomes low due to dirt or the like and the output level of the light receiving element 5 becomes low, the signals are input to the binarization circuits 2A to 2D. It is only necessary to maintain the signal level at which the binarization circuits 2A to 2D can perform binarization with high accuracy. For this reason, the gain control units 4 and 7 are configured so that the rate of change of the signal level output from the variable gain amplifiers 1A to 1D is suppressed to about a fraction of the rate of change of the input signal level. It can also be set as the structure controlled.

  Moreover, although the case where it applied to a DVD player was demonstrated, it can apply similarly also in the case of the apparatus which has the function to record information on optical disks, such as DVD.

It is a block diagram which shows the electric constitution of 1st Embodiment of the DPD signal generation apparatus which concerns on this invention. It is explanatory drawing which shows the structure of the optical system of an optical pick-up. It is explanatory drawing which shows the relationship between the reflectance of an information recording surface, the gain of a gain variable amplifier, and the input level of a binarization circuit. It is explanatory drawing which shows the relationship between the reflectance of an information recording surface, the gain of a gain variable amplifier, and the input level of a binarization circuit when reproducing the location where dirt adhered. It is a block diagram which shows the electric constitution of 2nd Embodiment. It is explanatory drawing which shows the relationship between the reflectance of an information recording surface, the gain of a gain variable amplifier, and the input level of a binarization circuit. It is explanatory drawing which shows the relationship between the reflectance of an information recording surface, the gain of a gain variable amplifier, and the input level of a binarization circuit when reproducing the location where dirt adhered. It is a block diagram which shows the electrical structure of a prior art. It is a block diagram which shows the electrical structure of a prior art.

Explanation of symbols

1A to 1D Variable gain amplifiers 2A to 2D Binary circuit 3 Adders 4 and 7 Gain control unit 5 Light receiving element 11 First phase comparison circuit 12 Second phase comparison circuit 13 Addition circuit 49 DVD (optical disk)
Tr Track direction

Claims (3)

A light receiving element that is divided into four regions by a track direction axis indicating a track direction of the optical disc and an axis orthogonal to the track direction axis;
An amplifier that is provided corresponding to each of the four regions and amplifies the output signal of each of the four regions;
A binarization circuit that is provided corresponding to each of the four regions and outputs a binarized signal obtained by binarizing the output of the amplifier;
A first phase comparison circuit that detects a phase difference between binarized signals of two regions located on one side of the track direction axis among the four regions;
A second phase comparison circuit that detects a phase difference between binarized signals of two regions located on the other side of the track direction axis among the four regions;
In a DPD signal generation device including an addition circuit that outputs a signal obtained by adding the detection result of the first phase comparison circuit and the detection result of the second phase comparison circuit as a tracking error signal,
The amplifier is a gain variable amplifier with variable gain,
A DPD signal generation device comprising a gain control unit that increases a gain of a variable gain amplifier when the level of an RF signal obtained by adding the outputs of four regions decreases. A light receiving element that is divided into four regions by a track direction axis indicating a track direction of the optical disc and an axis orthogonal to the track direction axis;
An amplifier that is provided corresponding to each of the four regions and amplifies the output signal of each of the four regions;
A binarization circuit that is provided corresponding to each of the four regions and outputs a binarized signal obtained by binarizing the output of the amplifier;
A first phase comparison circuit that detects a phase difference between binarized signals of two regions located on one side of the track direction axis among the four regions;
A second phase comparison circuit that detects a phase difference between binarized signals of two regions located on the other side of the track direction axis among the four regions;
In a DPD signal generation device including an addition circuit that outputs a signal obtained by adding the detection result of the first phase comparison circuit and the detection result of the second phase comparison circuit as a tracking error signal,
The amplifier is a gain variable amplifier with variable gain,
A DPD signal generation apparatus comprising a gain control unit that increases a gain of a variable gain amplifier when a signal level input to the variable gain amplifier decreases.   The DPD signal generation device according to claim 2, wherein the gain control unit controls each gain of the variable gain amplifier based on a signal level input to each of the variable gain amplifiers.

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