JP2001352229A - Filter circuit and reproduction signal processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain consumption power when a cut-off frequency is set in a high region, without decreasing setting precision of a signal expansion current when a cut-off frequency is set in a low region. SOLUTION: A capacitor 24 is installed on an output end of a mutual conductance amplifier 23 having mutual conductance gm proportional to a current ratio of a signal compression current Ia or (1/2)Ia to the signal expansion current Icnt. A current control circuit 22 is installed, the signal expansion current Icnt flowing in the amplifier 23 is adjusted, the mutual conductance gm is changed, and the cut-off frequency determined by the mutual conductance gm and a capacitance C is changed. A current changeover switch 31 is installed, the signal compression current flowing in the amplifier 13 is switched over to the value la or (1/2)Ia, and the change gradient of mutual conductance gm due to the signal expansion current Icnt is switched over.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter circuit for optimally performing signal processing (for example, equalization processing) particularly in an optical disk system and the like, and a reproduced signal processing apparatus using the same.

[0002]

2. Description of the Related Art A general structure of an optical disk system is shown in FIG. In this optical disk system, an optical disk medium 11 as a recording medium is rotated by a motor 17 driven by a motor driver 16. The laser beam emitted from the optical pickup 12 driven by the actuator driver 18 is
1 and the reflected light returns to the optical pickup 12. Then, the reflected light is photoelectrically converted by the optical pickup 12 to become a reproduction signal, which is input to the reproduction signal processing system (reproduction signal processing device) 13. In the reproduction signal processing system 13, waveform equalization is performed, and the waveform-equalized signal is input to the disk controller 14, and then data is processed by the CPU 15. The waveform equalization is performed by the disk controller to binarize the data without fail, and the high frequency component of the reproduction signal is removed. In the CAV method, the frequency of the signal is 2.5 times the inner circumference on the outer circumference of the disk, so that the reproduction is performed by changing the setting of the cutoff frequency of the filter.

[0003] The reproduction speed of the optical disk medium 11 is changed by the recording medium. Therefore, stable reproduction is enabled by setting a filter so as to extract a required frequency corresponding to the reproduction speed. The reason why the reproduction speed is changed is, for example, to reproduce the optical disk medium at a reduced reproduction speed when necessary data cannot be taken.

A conventional filter circuit for equalization processing of a reproduction signal processing system can set a cutoff frequency (720 kHz to 36 MHz) corresponding to a reproduction speed of CD × 1 to DVD × 8. Note that CD × 1 means CD × 1 speed, and DVD × 8 means DVD × 8 speed.

The motor driver 16 and the actuator driver 18 are controlled by a servo controller 20 according to the operation of a servo signal processing system 19.

The disk controller 14 has a function of performing data processing of a reproduction signal and controlling the entire operation of the disk. Further, the CPU 15 issues various commands, and the servo controller 20 performs arithmetic processing on the commands issued from the CPU 15 and outputs control signals. In addition, the servo signal processing system 19 has a function of a focus servo that focuses the laser light irradiated on the disk medium 11 and a function of a tracking servo that focuses the center of the laser light on the middle point of the track.

Next, FIG. 3 shows the configuration of a conventional reproduction signal processing system. The reproduction signal processing system includes a gain control amplifier 21 for amplifying an input signal, that is, an output signal of an optical pickup, with a variable gain, and a filter circuit having a variable cutoff frequency that receives an output of the gain control amplifier 21 as an input and passes only a required frequency band. 25, a fixed-gain output amplifier 28 for amplifying the output of the filter circuit 25,
A fixed-gain feedback amplifier 26 for amplifying the output of the filter circuit 25, and an amplitude detector 27 for detecting the output amplitude of the feedback amplifier 26 and changing the gain of the gain control amplifier 21 so that the output amplitude of the feedback amplifier 26 becomes constant. And

The above-described filter circuit 25 is, specifically,
A transconductance amplifier 23 having a transconductance gm proportional to the current ratio between the signal compression current Ia and the signal expansion current Icnt;
8 and a signal expansion current Icn flowing through the transconductance amplifier 28.
By adjusting t, the transconductance amplifier 28
The current control circuit 22 changes the mutual conductance gm to change the cutoff frequency fc determined by the mutual conductance gm and the capacitance value C.

FIG. 8 shows a specific example of the transconductance amplifier 23. In FIG. 8, D1 and D2 are diodes,
Q1 to Q8 are transistors, R1 to R3 are resistors, IS1
ＩＳIS5 is a current source. IN is an input signal, OUT is an output signal, Vbias1 and Vbias2 are bias voltages,
Vcc is a power supply voltage. And current sources IS1, IS
2 is the signal compression current Ia, and the current source IS3
Is the signal expansion current Icnt.

In the circuit shown in FIG. 3, the amplitude in the filter can be expressed by the following equation using the gain G of the feedback amplifier 26, where the output amplitude of the feedback amplifier 26 is a constant value A.

[0011]

## EQU1 ## In-filter amplitude = A / G The cutoff frequency fc of the filter circuit 25 is expressed by the following equation 2 using the mutual conductance gm and the capacitance value C.

[0012]

Fc = gm / 2πC Here, the signal expansion current Icnt and the signal compression current Ia indicate a current value flowing through the transconductance amplifier 23, and R indicates a resistance value in the transconductance amplifier 23. At this time, the transconductance gm is equal to the signal extension current Icn.
Using t, the signal compression current Ia, and the resistance value R,
It is represented by Here, the resistance value R is the resistance value of the resistor R1 in FIG.

[0013]

Gm = Icnt / IaR The input dynamic range is expressed by the following equation 4 using the signal compression current Ia and the resistance value R.

[0014]

Input dynamic range = 2IaR As described above, the transconductance gm of the transconductance amplifier 23 is determined by Expression 3. Further, the input dynamic range of the filter circuit 25 is determined from Equation 4.

Conventionally, in order to secure an input dynamic range, the resistance value R and the value of the signal compression current Ia are fixed. Then, by making the signal expansion current Icnt variable, the mutual conductance gm is made variable, and a wide range of cutoff frequency of the filter circuit 25 can be set.

Since the signal compression current Ia can be set to a cut-off frequency extending to a high frequency band by the filter circuit 25, setting the value to a small value sets the signal expansion current Icnt at the time of setting the low range. The accuracy cannot be set small because the accuracy is lowered and the setting accuracy of the cutoff frequency fc is lowered.

[0017]

In recent years, the speed of disc reproduction has been increased (DVD × 16), and the cut-off frequency setting range of the filter circuit 25 of the reproduction signal processing system has been extended to a frequency band higher than before. (Broadbanding) is required (CD × 1 to DVD × 16, 720 kHz to 72
MHz). As a result, since the transconductance gm needs to be further increased, a large current is required for the signal extension current Icnt. Therefore, when setting the cutoff frequency of the DVD × 16, as shown in FIG.
The problem is that the power consumption at the airport rapidly increases.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and does not reduce the setting accuracy of the signal extension current when setting the cut-off frequency to a low range, and reduces the consumption when setting the cut-off frequency to a high range. It is an object to provide a filter circuit capable of suppressing power.

[0019]

In order to achieve this object, a filter circuit according to the present invention comprises a transconductance amplifier having a transconductance proportional to a current ratio between a signal compression current and a signal expansion current. That is, the configuration is such that the value of the signal compression current that determines the mutual conductance is switched between when the cutoff frequency is set to a low frequency and when the high speed reproduction is performed, that is, when the cutoff frequency is set to a high frequency. And

Specifically, the filter circuit of the present invention comprises a transconductance amplifier having a transconductance proportional to a current ratio between a signal compression current and a signal expansion current, and a capacitor provided at an output terminal of the transconductance amplifier. A current control circuit that changes the cutoff frequency determined by the mutual conductance and the capacitance value by changing the mutual conductance of the mutual conductance amplifier by adjusting a signal expansion current flowing through the mutual conductance amplifier; and a signal that flows through the mutual conductance amplifier. Current switching means for switching the gradient of the transconductance due to the signal expansion current by switching the value of the compression current.

According to this configuration, at the time of high-speed reproduction, that is,
When the cutoff frequency is set to be high, the signal compression current is smaller than that at the time of low-speed reproduction (for example, 1
/ 2 times), it is possible to increase the transconductance without increasing the signal expansion current. As a result, the power consumption of the filter circuit when the cutoff frequency is set high can be suppressed.

On the other hand, at the time of low-speed reproduction, that is, when the cut-off frequency is set low, the signal compression current is increased (for example, twice that at the time of high-speed reproduction) as compared with high-speed reproduction. Does not decrease the setting accuracy of the signal expansion current.

Further, the reproduction signal processing apparatus of the present invention comprises a gain control amplifier for amplifying an input signal with variable gain, a filter circuit having an output of the gain control amplifier as an input, and an output amplifier for amplifying an output signal of the filter circuit. And a feedback amplifier for amplifying the output signal of the filter circuit, and an amplitude detector for detecting the output amplitude of the feedback amplifier and changing the gain of the gain control amplifier so that the output amplitude of the feedback amplifier becomes constant. .

The above-mentioned filter circuit is constituted by the above-described transconductance amplifier, capacitance, current control circuit, and current switching means.

According to this configuration, an operation similar to that of the above-described filter circuit is provided.

Further, another reproduction signal processing apparatus of the present invention comprises:
A gain control amplifier that amplifies the input signal with variable gain, a filter circuit that receives the output of the gain control amplifier as an input, an output amplifier that amplifies the output signal of the filter circuit, a feedback amplifier that amplifies the output signal of the filter circuit, An amplitude detector for detecting the output amplitude of the feedback amplifier and changing the gain of the gain control amplifier so that the output amplitude of the feedback amplifier becomes constant.

[0027] The above-mentioned filter circuit comprises the above-mentioned transconductance amplifier, capacitance, current control circuit, and current switching means. Further, the output amplifier and the feedback amplifier are provided with gain switching means for switching the gains of the output amplifier and the feedback amplifier in response to the switching of the value of the signal compression current, and switching the magnitude of the switching between the values of the signal compression current in reverse. Here, the switching ratio of the gain by the gain switching unit is set to, for example, the reciprocal of the switching ratio of the signal compression current by the current switching unit.

According to this configuration, in addition to having the same operation as that of the above-described filter circuit, the gain of the output amplifier and the feedback amplifier is changed by switching the value of the signal compression current in conjunction with the switching of the value of the signal compression current. Since the relationship is reversed,
The amplitude in the filter at the time of low-speed reproduction can be set large, so that the SN ratio at the time of low-speed reproduction can be increased, and low noise output can be achieved in combination with the small gain of the output amplifier.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] A first embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a configuration of a reproduction signal processing device including a filter circuit. The difference from the configuration of the conventional example (FIG. 3) is that the signal compression current Ia is supplied to a filter circuit 25 having a variable cutoff frequency which is composed of a transconductance amplifier 23 having a variable transconductance gm and a capacitor 24 by a current control circuit 22. For example, a signal compression current switch 31 for switching between two levels, large and small, is added.

As a result, the change gradient of the transconductance gm due to the signal expansion current Icnt is switched. The number of switching stages is not limited to two, and may be three or more. The above-described signal compression current switch 31
Corresponds to the current switching means in the claims.

At the time of high-speed reproduction, the signal compression current is set to (1/1 /
2) By setting Ia, the transconductance gm can be increased even with the same signal expansion current Icnt, that is, the cutoff frequency can be doubled. However, the input dynamic range of the filter circuit 25 is determined by Equation 4, and the input dynamic range is also reduced to に よ り by setting the signal compression current to (１ ／) Ia.

In this case, if the amplitude within the dynamic range is not passed through the filter circuit 25, the signal will be distorted.
By setting it in a), there is no particular problem.

With such a configuration, it is possible to suppress power consumption during high-speed reproduction. Switching of the signal compression current switch 31 selects Ia at the time of low-speed playback at a certain playback speed, and selects (1/1) at the time of high-speed playback.
2) It is divided to select Ia.

When the signal compression current is switched to, for example, three stages, Ia, (2/3) Ia, (1/3) I
a, or Ia, (1/2) Ia, (1 /
4) What is necessary is just like Ia.

FIG. 6 shows the power consumption of the filter circuit 25 corresponding to the reproduction speed in this embodiment. In FIG. 6, at the time of low-speed reproduction (CD × 1 to DVD × 2)
Select Ia as the signal compression current, and at high speed reproduction (D
In VD × 4 to DVD × 16, the signal compression current is (1
/ 2) The case where Ia is selected is shown. Compared with FIG. 5, it is clear that the power consumption of the filter circuit 25 during high-speed reproduction (DVD × 4 to DVD × 16) is reduced by half.

[Second Embodiment] Hereinafter, a second embodiment of the present invention will be described.
An embodiment will be described with reference to the drawings.

The second embodiment of the present invention reduces noise at the time of low-speed reproduction of the first embodiment.

FIG. 2 is a block diagram showing a configuration of a reproduction signal processing device including a filter circuit. The difference from the reproduction signal processing apparatus of FIG. 1 is that, for example, a feedback amplifier 42 having a gain set to 1 is provided in addition to a feedback amplifier 26 having a gain set to 2 times, and the output signal of the filter circuit 25 is fed back. An amplifier switch 41 for selectively supplying one of the amplifiers 26 and 42 is provided. Further, for example, an output amplifier 44 having a gain set to 1 is provided in addition to an output amplifier 28 having a gain set to 2 times. In addition, an amplifier changeover switch 43 for selectively supplying the output signal of the filter circuit 25 to one of the output amplifiers 28 and 44 is provided, and the amplifier changeover switches 41 and 43 are linked with the signal compression current changeover switch 31. That is the point.

In this case, the signal compression current switch 31
Is switched to the a side, that is, when Ia is selected as the signal compression current, the amplifier changeover switch 41,
43 is switched to the a side, and the gain is small (the gain is 1
X) The feedback amplifier 42 and the output amplifier 44 are selected.

On the other hand, the signal compression current switch 31
Side, that is, when (1/2) Ia is selected as the signal compression current, the amplifier changeover switches 41 and 43 are switched to the b side, and the feedback amplifier 26 having a large gain (gain is twice) and the output are output. Each of the amplifiers 28 is selected.

In FIG. 2, two feedback amplifiers 26 and 42 having different gains are provided, and the output signal of the filter circuit 25 is supplied to the feedback amplifier 26 and 42 by an amplifier changeover switch 41.
42 is selectively supplied to one of them.
The number of feedback amplifiers may be configured to be switchable, and the gain of the feedback amplifier may be switched by a gain switch.

Further, two output amplifiers 2 having different gains are used.
8 and 44 are provided, and the output signal of the filter circuit 25 is selectively supplied to one of the output amplifiers 28 and 44 by the amplifier changeover switch 43. However, one output amplifier is configured such that the gain can be switched. Alternatively, the gain of the output amplifier may be switched by a gain switch.

In the case of the configuration shown in FIG.
Reference numerals 6 and 42 correspond to feedback amplifiers capable of switching gains, and the amplifier switch 41 corresponds to gain switching means. Further, the two output amplifiers 28 and 44 correspond to output amplifiers capable of switching gain, and the amplifier switch 43 corresponds to gain switching means. Note that the gains of the feedback amplifier and the output amplifier may be switched in three or more stages in accordance with the switching of the signal compression current. In this case, the gain is switched to the reciprocal of the current switching ratio.

With the above configuration, the signal compression current Ia at the time of low-speed reproduction is equal to the signal compression current (1/2) Ia at the time of high-speed reproduction.
Using the fact that the input dynamic range is twice (Equation 4), the feedback amplifiers 26 and 42
And the gain setting of the output amplifiers 28 and 44 are set smaller at low speed setting than at high speed setting (for example, 1/2).
Thus, the amplitude in the filter can be increased (Equation 1).

As an example, if the input of the amplitude detector 27 is 500
Assuming that feedback is applied at mVpp, during high-speed playback,
When the signal compression current changeover switch 31 is on the b side and the amplifier changeover switches 41 and 43 are on the b side, the feedback amplifier 26
By doubling the gain of the output amplifier 28 and doubling the gain of the output amplifier 28, the amplitude in the filter can be made 250 mVpp (Equation 1).

Also, at the time of low-speed reproduction, when the signal compression current changeover switch 31 is on the a side and the amplifier changeover switches 41 and 43 are on the a side, the gain of the feedback amplifier 42 is set to 1 and the gain of the output amplifier 44 is set to 1. Thus, the amplitude in the filter can be set to 500 mVpp (Equation 1).

FIG. 4A shows that the amplitude in the filter is 250 mV.
It is a figure showing the SN ratio at the time of pp. FIG. 4B is a diagram illustrating the SN ratio when the amplitude in the filter is 500 mVpp. In FIG. 4B, since the amplitude in the filter is larger than that in FIG. 4A, only the amplitude in the filter changes without changing the noise value. And by increasing the amplitude in the filter,
The SN ratio of the filter circuit 25 is improved. Further, since the gain of the output amplifier 43 is 1, the noise can be reduced by half compared to the normal time, that is, low noise output at the time of low-speed reproduction is possible.

In the second embodiment, during high-speed reproduction of an optical disk (DVD × 4 to DVD × 16), the signal compression current selector switch 31 is set to the b side, and the amplifier selector switches 41 and 43 are set.
Can be reproduced only on the b side, and during low-speed reproduction of an optical disc (CD × 1 to DVD × 2), the signal compression current changeover switch 31 can output low noise on the a side, and the amplifier changeover switches 41 and 43 can output low noise on the b side. And

[0050]

As described above, according to the present invention, at the time of high-speed reproduction, that is, when the cutoff frequency is set high, the signal compression current is made smaller than at the time of low-speed reproduction.
It is possible to increase the transconductance without increasing the signal extension current. As a result, the power consumption of the filter circuit when the cutoff frequency is set high can be suppressed. Also, at low speed reproduction, that is, when the cut-off frequency is set low, the signal compression current is made larger than during high-speed reproduction, so the setting accuracy of the signal expansion current when setting the cut-off frequency to a low range is reduced. I won't let you.

Further, since the magnitudes of the output amplifier and the feedback amplifier are switched in a magnitude relationship opposite to the switching of the value of the signal compression current in conjunction with the switching of the value of the signal compression current, the amplitude in the filter during low-speed reproduction is increased. Can be set, so that the SN ratio at the time of low-speed reproduction can be increased, and in combination with the small gain of the output amplifier,
Low noise output is possible.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a reproduction signal processing device according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a reproduction signal processing device according to a second embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of a conventional reproduction signal processing system.

FIG. 4 is a characteristic diagram showing a difference in S / N ratio due to a difference in filter amplitude; FIG.
The output amplitude characteristic with respect to the input frequency at the time of pp,
(B) shows the characteristic of the output amplitude with respect to the input frequency when the amplitude in the filter is 500 mVpp.

FIG. 5 is a characteristic diagram showing power consumption of a filter circuit according to a reproduction speed in a conventional example.

FIG. 6 is a characteristic diagram showing power consumption of a filter circuit according to a reproduction speed in the first embodiment.

FIG. 7 is a block diagram showing the configuration of a conventional optical disk system.

FIG. 8 is a circuit diagram showing a specific example of a transconductance amplifier.

[Explanation of symbols]

 Reference Signs List 11 optical disk medium 12 optical pickup 13 reproduction signal processing system 14 disk controller 15 CPU 16 motor driver 17 motor 18 actuator driver 19 servo signal processing system 20 servo controller 21 gain control amplifier 22 current control circuit 23 mutual conductance amplifier 24 capacity 25 filter circuit 26 Feedback amplifier 27 Amplitude detector 28 Output amplifier 31 Signal compression current selector switch 41 Amplifier selector switch 42 Feedback amplifier 43 Amplifier selector switch 44 Output amplifier

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H03H 11/04 H03H 11/04 GF term (Reference) 5D044 AB05 AB07 BC03 CC06 FG01 FG05 FG24 FG30 5J030 AA01 AB05 AC02 AC04 AC09 AC11 AC19 AC26 5J098 AB02 AB03 AB08 AB13 AC02 AC20 AC22 AD11 AD24 CA02 CB03 CB09 5J100 AA26 BA01 BC01 CA00 CA11 CA18 DA06 EA02 FA00 JA01 LA00 LA10 QA01 SA00

Claims (4)

[Claims] 1. A transconductance amplifier having a transconductance proportional to a current ratio between a signal compression current and a signal expansion current, a capacitor provided at an output terminal of the transconductance amplifier, and the signal flowing through the transconductance amplifier. A current control circuit for changing a transconductance of the transconductance amplifier by adjusting an expansion current to change a cutoff frequency determined by the transconductance and the capacitance value; and a value of the signal compression current flowing through the transconductance amplifier. And a current switching means for switching a change gradient of the mutual conductance due to the signal expansion current by switching the current. 2. A gain control amplifier that amplifies an input signal with a variable gain, a filter circuit that receives an output of the gain control amplifier as an input, an output amplifier that amplifies an output signal of the filter circuit, and an output of the filter circuit. A feedback amplifier that amplifies a signal; and an amplitude detector that detects the output amplitude of the feedback amplifier and changes the gain of the gain control amplifier so that the output amplitude of the feedback amplifier becomes constant. A transconductance amplifier having a transconductance proportional to a current ratio between the signal compression current and the signal expansion current, a capacitor provided at an output terminal of the transconductance amplifier, and the signal expansion current flowing through the transconductance amplifier are adjusted. The mutual conductance of the transconductance amplifier It said transconductance and the capacitance value by varying the Nsu and the current control circuit for changing the cutoff frequency determined by,
A reproduction signal processing device comprising: a current switching unit that switches a gradient of a mutual conductance caused by the signal expansion current by switching a value of the signal compression current flowing through the mutual conductance amplifier. 3. A gain control amplifier that amplifies an input signal with a variable gain, a filter circuit that receives an output of the gain control amplifier as an input, an output amplifier that amplifies an output signal of the filter circuit, and an output of the filter circuit. A feedback amplifier that amplifies a signal, and an amplitude detector that detects the output amplitude of the feedback amplifier and changes the gain of the gain control amplifier so that the output amplitude of the feedback amplifier becomes constant. A transconductance amplifier having a transconductance proportional to a current ratio between the signal compression current and the signal expansion current, a capacitor provided at an output terminal of the transconductance amplifier, and the signal expansion current flowing through the transconductance amplifier are adjusted. The mutual conductance of the transconductance amplifier It said transconductance and the capacitance value by varying the Nsu and the current control circuit for changing the cutoff frequency determined by,
Current switching means for switching the value of the signal compression current flowing through the transconductance amplifier to change the gradient of the transconductance due to the signal expansion current, wherein the gain of the output amplifier and the feedback amplifier is reduced by the signal compression current. A reproduction signal processing apparatus, wherein gain switching means for switching the magnitude of the signal compression current in reverse of the magnitude of the signal compression current in conjunction with the value switching is provided in the output amplifier and the feedback amplifier. 4. The reproduction signal processing device according to claim 3, wherein a switching ratio of the gain by the gain switching unit is set to a reciprocal of a switching ratio of the signal compression current by the current switching unit.