JPH06275014A - Information reproducing device - Google Patents

Abstract

PURPOSE:To improve a reproducing error rate by changing the filter characteristics of a reproducing signal system in accordance with a recording zone. CONSTITUTION:The cutoff frequency of a low pass filter 10 is inversely proportional to an equivalent internal resistor Rt of a transistor Tr1. Thus, the cutoff frequency of the filter 10 is controlled in accordance with the frequency of a master clock. Namely, the master clock frequency becomes higher as it goes to the outer side zone of an optical disk, the resistor Rt of the Tr1 becomes smaller as a current IB of a current source 22 increases and the cutoff frequency of the filter 10 shifts to a higher frequency side. Since the master clock frequency corresponds to the position of a recording zone, the cutoff frequency is automatically changed in accordance with the position. Moreover, the cutoff frequency of the filter 10 is continuously varied without an increase in parts number and various media are accommodated. Note that the amount of an output current E26 of a frequency/current converter 26 is programmable by digital data.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for reproducing recorded information from a disc adopting, for example, a zone bit recording system, and more particularly, by changing a filter characteristic of a reproduction signal system according to a recording zone, a reproduction error rate can be improved. The present invention relates to an improved information reproducing device.

[0002]

2. Description of the Related Art The zone bit recording method is a disk in which a data recording area is divided into a plurality of concentric annular zones, and each zone records data at a constant angular velocity (CAV). A recording method that increases the For example, in the optical disc shown in FIG.
The data area is divided into n zones, and the number of sectors in 1 to n zones is m1 to mn (m1 <m2 <... <m, respectively).
n).

In a disk having a constant number of rotations adopting such a zone bit recording method, since the number of sectors per one rotation of each zone is different and the reproduction signal frequency is different for each zone, it is unnecessary from the reproduction signal of the disk. It is necessary to change the frequency characteristic of the filter that removes the signal component (cutoff frequency of the low-pass filter) for each zone.

The variable frequency characteristic filter can be realized by, for example, as shown in FIG. 6, an active filter in which a plurality of capacitors C1 to Cn are switched according to the reproduction system master clock frequency.

[0005]

The active filter of FIG. 6 has various recording media (CDROM, MO) even if the type / standard of the recording media is fixed.
If it is applied to a reproducing system such as a disc, it is necessary to prepare a plurality of capacitor sets having different values for each medium, resulting in an extremely complicated and costly filter. This problem also occurs when disks having different numbers of zones are used together even if there is only one kind of recording medium. Further, even when the type / standard of the recording medium is fixed, the active filter in FIG. 6 requires a high-speed operational amplifier, which results in a large circuit scale and high power consumption and component cost.

An object of the present invention is to provide an information reproducing apparatus provided with a filter capable of realizing a programmable variable frequency characteristic without increasing the number of parts of a filter circuit according to the increase in the types of media to be supported. It is to be.

[0007]

A frequency characteristic of a reproducing system filter is continuously changed corresponding to a frequency of a master clock which changes depending on which recording zone of an optical disk adopting a zone bit recording system from which data is reproduced. Means for doing so.

[0008]

The frequency characteristic of the filter is determined by the product of the internal resistance of the variable resistance element whose internal resistance changes in response to a predetermined bias signal and the predetermined reactance, and by controlling the bias signal, The frequency characteristics of the filter are made variable (programmable).

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 3 shows the essential parts of an information reproducing apparatus including a variable frequency characteristic low pass filter of the present invention. The information recorded in each zone of the data area of the optical disc of FIG. 5 is reproduced by an optical pickup (not shown). This reproduction signal Vi is input to the filter circuit 100 of the reproduction device.

The filter circuit 100 has a bias signal IB.
Low-pass filter 1 whose cutoff frequency changes with
0 and a cutoff frequency switching circuit 20 for generating a bias signal IB having a magnitude proportional to the frequency of the master clock of the reproducing apparatus. Here, the frequency of the master clock is the outer zone (zone n
Side) becomes higher.

The unnecessary high frequency component (noise) of the reproduction signal Vi is cut off by the filter 10, and the analog signal Vout mainly containing the information recorded on the optical disk is filtered by the filter 1.
Input from 0 to the binarization circuit 30. The binarization circuit 30 binarizes the input signal Vout at a predetermined level (threshold value). The binarized pulse signal is sent to a demodulation circuit (not shown) via a phase locked loop (PLL) circuit 40. In this demodulation circuit, the information recorded on the optical disc is converted into a signal of a predetermined format.

FIG. 1 shows a specific example of the low-pass filter 10 and the cutoff frequency switching circuit 20 shown in FIG. The voltage amplitude of the reproduction signal Vi from the optical pickup (not shown) is converted by the voltage / current converter 12 into the input current Iin having the corresponding current amplitude.

The current Iin is input to the bases of bipolar transistors Tr1 and Tr2 which form a current mirror circuit. The base of the transistor Tr1 is connected to its collector, and the capacitor C is connected in parallel between its collector / emitter. Transistors Tr1 and Tr2
Their emitters are grounded and their collectors have a current source 2
2, 24 are connected.

The current sources 22 and 24 are supplied with a power source voltage + Vc, and a constant current I proportional to the magnitude of the IB control signal E26.
B is the transistors Tr1 and Tr of the current mirror circuit
Supply to 2. The IB control signal E26 is obtained by converting the frequency of the master clock into a current by the frequency / current converter 26 and has a DC value proportional to the master clock frequency.

A voltage / is applied to the collector of the transistor Tr1.
Since the current converter 12 is connected, the sum of the DC value of the constant current IB from the current source 22 and the DC value of the output current Iin of the converter 12 becomes the collector current of the transistor Tr1. Further, since the current / voltage converter 14 is connected to the collector of the transistor Tr2, the sum of the DC value of the constant current IB from the current source 24 and the DC value of the input current I14 of the converter 14 is the sum of the transistor Tr2. It becomes the collector current. Since the transistors Tr1 and Tr2 form a current mirror circuit, their collector currents match.
Therefore, the following relationship holds: Iin + IB = I14 + IB (1)

Equation (1) shows that the input current I14 of the converter 14 is equal to the output current Iin of the converter 12, regardless of the value of the constant current IB. Therefore,
If the transfer function (gain) of the converters 12 and 14 is 1, then the input signal Vi = the output signal Vout. That is, in a frequency band (frequency region lower than the cutoff frequency of the low-pass filter 10) where the reactance component of the capacitor C does not affect, the input signal Vi passes through the filter 10 as it is and becomes the output signal Vout.

In the frequency region around the cutoff frequency of the low pass filter 10 and above the cutoff frequency, the reactance component of the capacitor C has an influence. That is, since the AC component of the output current Iin of the converter 12 is also shunted to the capacitor C, the current I flowing into the current mirror circuit is increased.
The AC component of in decreases as the frequency increases. When the cutoff frequency fc is defined as the frequency at which the alternating current component flowing into the current mirror circuit has a magnitude of −3 db (about 70%) with respect to the direct current value, fc = 1 / 2πCRt (2)

[0018] Here, Rt represents the equivalent internal resistance of the diode-connected transistor Tr1. Equation (2) shows that if the internal resistance Rt is changed, the low-pass filter 1
It shows that the cutoff frequency fc of 0 also changes.

FIG. 2 is a graph illustrating the characteristics of the diode-connected transistor Tr1 (variable resistance element). In this graph, the horizontal axis represents the base-emitter voltage VBE of the transistor Tr1 and the vertical axis represents the emitter current IE thereof. If the current amplification factor (hFE) of the transistor Tr1 is sufficiently large, the emitter current IE becomes substantially equal to the collector current (corresponding to the left side of Expression (1)). In FIG. 2, when the base-emitter voltage VBE is Vt, the emitter current IE flows It, and the internal resistance Rt of the transistor Tr1 at that time is Rt = (dVBE / dIE) (3) (d is a differential symbol) ). Generally, the voltage / current characteristic between the base and the emitter of a bipolar transistor is an exponential function as shown in FIG. 2, and this characteristic can be expressed by the following equation: IE = Is [exp (q.VBE) / kT-1] (4) Here, Is represents the saturation current of the transistor Tr1,
q represents the charge of the electron, k represents the Boltzmann constant, T
Represents absolute temperature. By transforming the equation (4), the following equation is obtained: VBE = kT / q [ln (IE / Is-1)] (5) Equations (4) and (5) hold even in a minute region. Therefore, when these are applied to the equation (3), Rt = (kT / Is · q) [1 / (IE / Is-1)] ... (6). Formula (6) is the internal resistance R of the transistor Tr1.
It shows that t changes according to the emitter current IE.

As described above, the emitter current IE of the transistor Tr1 is substantially equal to its collector current, and its magnitude is Iin + IB. Therefore, the internal resistance Rt of the transistor Tr1 changes according to the current IB of the current source 22. Since the current IB can be controlled by the IB control signal E26, the internal resistance Rt of the transistor Tr1 can be controlled according to the frequency of the master clock which is the input of the frequency / current converter 26.

Since the cutoff frequency of the lowpass filter 10 is inversely proportional to the internal resistance Rt as shown in the equation (2), the cutoff frequency of the lowpass filter 10 can be controlled according to the frequency of the master clock.
That is, the master clock frequency becomes higher in the outer zone of the optical disk, and accordingly, the current IB of the current source 22 increases.
Is increased, the internal resistance Rt of the transistor TR1 is decreased, and the cutoff frequency of the low pass filter 10 is shifted to the high frequency side.

According to the circuit configuration of FIG. 1, since the master clock frequency corresponds to the positions of the recording zones (1 to n) of FIG. 5, the low-pass filter 10 corresponds to the positions of the recording zones (1 to n). The cutoff frequency of can be changed automatically. Moreover, since the cutoff frequency of the low-pass filter 10 can be continuously varied without increasing the number of parts, it is possible to automatically obtain the filter characteristics corresponding to various recording media without increasing the cost of parts. At this time, the output current of the frequency / current converter 26 (I
The magnitude of the B control signal E26) can be made variable (programmable) by digital data.

FIG. 4 exemplifies a case where a frequency characteristic variable high-pass filter is constructed using the frequency characteristic variable low-pass filter of FIG. That is, the subtractor 16 subtracts the transfer function of the low-pass filter from the transmission system of the transfer function 1 to equivalently obtain the high-pass filter 18 whose cutoff frequency is automatically variable.

Since the internal resistance between the source / drain of the field effect transistor (FET) can be changed by the gate potential thereof, the FET can be used as a variable resistance element instead of the bipolar transistor Tr1. In this case, the converter 26 is a frequency / voltage converter, and a voltage output corresponding to the master clock frequency is added to the gate of the FET as a variable resistance element. Then, from the drain of this FET, through a buffer circuit (emitter follower or the like), a filter output V corresponding to the input signal Vi
out can be obtained.

[0025]

According to the present invention, even if the types of media to be supported increase, the filter circuit does not become complicated correspondingly, and a filter having a programmable variable frequency characteristic with a wide adaptation range is provided. An information reproducing device is obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a low-pass filter having a variable frequency characteristic applied to an information reproducing apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating characteristics of a bipolar transistor used as a variable resistance element in the filter of FIG.

FIG. 3 is a block diagram showing a main part of an information reproducing apparatus including the frequency characteristic variable low pass filter of FIG.

FIG. 4 is a block diagram illustrating a case where a frequency characteristic variable high-pass filter is configured using the frequency characteristic variable low-pass filter of FIG. 1.

FIG. 5 is a diagram illustrating a configuration of an optical disc that employs a zone bit recording method.

FIG. 6 is a circuit diagram illustrating a low-pass filter whose frequency characteristic is variable according to the present invention.

[Explanation of symbols]

100 ... Filter circuit, 10 ... Low pass filter (variable cutoff frequency), 20 ... Cutoff frequency switching circuit (frequency characteristic changing means), 30 ... Binarization circuit, 40 ... Phase Locked loop (PL
L), 12 ... voltage / current converter, 14 ... current /
Voltage converter, 16 ... Subtractor, 18 ... High-pass filter (cutoff frequency variable), 22, 24 ... Variable current source, 26 ... Frequency / current converter, Tr1 ...
・ Bipolar transistor (variable resistance element), Rt ・ ・
・ Internal resistance, IB ... Bias signal, E26 ... I
B control signal.

Claims (2)

[Claims] 1. An apparatus for reproducing data from an information recording medium having a plurality of concentrically arranged annular areas as a data recording area, using a master clock having a frequency proportional to a required frequency band of a data reproducing system. A filter for extracting a predetermined signal frequency component from a signal extracted from the information recording medium, and means for reproducing data recorded in each annular area of the information recording medium from the signal frequency component extracted by the filter, Frequency characteristic changing means for changing the frequency characteristic of the filter corresponding to the frequency of the master clock that changes depending on where in the annular region data reproduction is performed, and the frequency characteristic of the filter is set to a predetermined bias signal. The internal resistance of the variable resistance element whose internal resistance changes according to Wherein by controlling the bias signal, the information reproducing apparatus characterized by being configured the frequency characteristic of the filter so as to variably. 2. The predetermined reactance includes a capacitor, and the frequency characteristic changing means includes means for reducing the internal resistance of the variable resistance element in proportion to the frequency of the master clock. The information reproducing apparatus described in.