JPH04188434A - Current-voltage conversion circuit for optical recording reproducer - Google Patents

Abstract

PURPOSE:To prevent the deterioration of an MTF by composing the title conversion circuit of a photoelectric conversion means receiving returned light from an optical recording medium and capable of photoelectrically converting returned light and an amplifying means converting currents obtained from the photoelectric conversion means into voltage and having a feedback resistor determining gains and constituting the feedback resistor of at least a plurality of resistors connected in series. CONSTITUTION:An amplifier 3 composed of a detector 2 capable of photoelectrically converting light from an optical recording medium and an amplifier 3 converting photocurrent formed from the detector 2 into voltage is fed back through a feedback resistor 8, in which a resistor 5 having a capacitor 4 as a component and a resistor 7 having a capacitor 6 as a component are connected in series. Photocurrents formed by the detector 2 are converted into voltage by the amplifier 3 and the feedback resistor 8 at that time. Since the resistors 5 and 7 are connected in series, the value of combined resistance is doubled, and the value of combined capacitor is halved. Accordingly, the deterioration of an MTF defined by formula I can be prevented by simply reducing a capacitor component and without changing a resistance value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a current-voltage conversion circuit for an optical recording/reproducing device that can photoelectrically convert optical information from an optical recording medium to obtain voltage information.

[Prior Art] In recent years, optical recording and reproducing technology has been developed, in which information is recorded by forming bits on an optical recording medium using a laser, and information is reproduced and read out based on the bits formed on the optical recording medium. A device is being developed. Optical recording media are disc-shaped,
Alternatively, it has a card-like shape, and the recording surface is divided into a plurality of tracks. Furthermore, the track is divided into sectors, which are recording units in read/write control.

When recording information on an optical recording medium, in order to record efficiently, it is necessary to convert the recording data into a modulation code before recording.

Among these modulation codes, an inter-mark recording method is known in which recording is performed only when the polarity of the signal is reversed. In this method, when a section where the polarity of the signal is frequently reversed is compared with a section where the polarity of the signal is not frequently reversed, a difference occurs in the density of marks.

Therefore, RLL modulation (Run Length Lim
1ted (:□rding) is known.

- As an example, FIG. 3 shows a timing diagram when the shortest mark interval and the longest mark interval are adjacent to each other in the (2.7) RLL modulation code adopted in the continuous servo method for a 130 mm disc according to the ISO standard. (a) is (2,7)R
LL modulation code is shown, (b) shows a mark on the recording medium recorded by this (2,7) RLL modulation code,
(C) shows a reproduction signal reproduced by an optical pickup (hereinafter abbreviated as pickup).

When a mark recorded using a modulation code is reproduced by a pickup, the reproduced signal can clearly identify the mark boundaries because the optical frequency characteristics of the pickup are proportional to (wavelength of light source)/(NA of objective lens). Can not do it. Therefore, the reproduction signal of a mark is affected by the density of marks before and after the mark. This effect is called code amount interference.

In FIG. 3C, the following quantities are defined, where a is the amplitude at the shortest mark interval of the reproduced signal that caused code amount interference, and b is the amplitude at the longest mark interval.

MTF=(a/b)*100 [%]=11) If the value of this MTF becomes too small, it becomes impossible to identify the shortest mark interval. The lower limit of MTF is usually about 30%.

On the other hand, as shown in No. 47, a t-current current positive conversion circuit 30 of an optical recording/reproducing apparatus is well known as a first-stage amplifying circuit for amplifying a reproduced signal. This t current positive conversion circuit 3
0 converts the photocurrent generated in the detector 32 connected to the bias power supply 31 into a voltage.

Here, if the resistance value of the feedback resistor 34 of the amplifier 33 is R, and the capacitor component of this feedback resistor 34 is C, then the transfer function G(S) of this current-voltage conversion circuit 30 is G (s) = E (s) /I (s)=R* (1+
5CR) ・(2), and the frequency characteristic G (f
) becomes G(f)=R/1+(2πfCR)2 (3) with 5=j2πf(j''=-1).

[Problem to be solved by the invention] By the way, in an actual optical recording/reproducing device, (3)
Let's check what value the expression gives.

When playing a IO5 standard 13'Omm disc by rotating it at 3600 rpm, the synchronization frequency f for the shortest mark interval is 7.4 [MHz], and the synchronization frequency f for the longest mark interval is 2.775 [MHz]. becomes.

If R = 20 [KΩ] and C = 0.3 [pF], each amplitude characteristic G (f) is G (f, )
=G (7,4'MHz)=0. 963*20[KΩ
G (f,)=G (2,775MHz)=0. 99
5 * 20 [KΩ], and from equations (4) and (5), when the amplitude of the longest mark is set to 1, the MTF is MTP = (G (f,) /G (f,)) 10
0= (0,96310,995)*100=96.8
[%]. This means that the MTF in the current-voltage conversion circuit is 3.
This means a decrease of 2% (=100-96.8).

Since the actual lower limit of MTF is about 30%, 3.2
% decrease corresponds to a deterioration of about 107% of the lower limit.

That is, the presence of a capacitor component of 0.3 pF in the feedback resistance of the current-voltage conversion circuit degrades the MTF by about 10%.

One way to prevent this is to choose a resistor with a small value for the capacitor component, but since this capacitor component is determined by the structure of the resistor, there are restrictions on reducing the capacitor component due to the structure of the resistor. be. Another option is to lower the resistance value, but in order to obtain the same effect as when the capacitor component is halved, it is necessary to reduce the resistance value by half, and if the resistance value is halved (3
) As can be seen from the equation, there is a problem that the output is also reduced by half, making it vulnerable to noise.

The present invention was made in view of the above circumstances, and utilizes the fact that the value of the capacitor component of a resistor is determined by the structure of the resistor regardless of the resistance value, and connects resistors in series to reduce only the capacitor component. MT without changing the resistance value
It is an object of the present invention to provide a current-voltage conversion circuit for an optical recording/reproducing device that prevents F deterioration.

[Means for Solving the Problems] A current-voltage conversion circuit of an optical recording/reproducing device of the present invention includes a photoelectric conversion means capable of receiving and photoelectrically converting returned light from an optical recording medium, and a current-voltage conversion circuit obtained from the photoelectric conversion means. In the current-voltage conversion circuit, the feedback resistor is composed of at least a plurality of resistors connected in series.

[Function] In the present invention, since the feedback resistor is composed of a plurality of resistors connected in series, a desired resistance value can be obtained and the capacitor component of the feedback resistor can be reduced.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a configuration diagram showing the configuration of a current-voltage conversion circuit according to a first embodiment of the present invention.

A current-voltage conversion circuit 1 (of an optical recording/reproducing device) of the first embodiment includes a detector 2 that can photoelectrically convert light from an optical recording medium (not shown), and a photocurrent generated by this detector 2 that converts it into a voltage. The amplifier 3 is fed back via a feedback resistor 8 in which a resistor 5 having a capacitor 4 as a component and a resistor 7 having a capacitor 6 as a component are connected in series. still,
A bias power supply 9 is connected to the detector 2 . Further, the values of the capacitors 4 and 6 of the feedback resistor 8 are both c [pF], and the resistance values of the resistors 5 and 7 are both r [KΩ].

The operation of the current-voltage conversion circuit 1 configured in this way is such that the photocurrent generated by the detector 2 is transferred to the amplifier 3 and the feedback resistor 8.
is converted to voltage. Since resistors 5 and 7 are connected in series, the value of the combined resistance is doubled and the value of the combined capacitor is 1/2. Here, r=10 [KΩ]
, c=o,, 3 [pF], then the combined resistance value R and combined capacitor value C are R=2*r=20 [KΩ] C= (1/2) c=0.15 [pF] becomes. Further, the amplitude characteristic G (f) is G(f)=R/, /”〽〇〇〇〇゜゜(4).

The synchronization frequencies f0 and fl corresponding to the shortest mark interval and longest mark interval by an optical signal from an optical medium (not shown), for example, an optical signal reproduced by rotating a 130 mm disk of IO5 standard at 3600 rpm, are f, = 7. 4 [MHz] f,=2. 775 [MHz], the amplitude characteristic G (f,) of the shortest mark interval and the amplitude characteristic G (fl) of the longest mark interval are calculated from equation (4) as follows: G (f,) = G (7,4 [MHz )
=o, 990*20[KΩkoG (f,) =G (2,775[MHz
) = 0. 999*20[KΩ, MTF is MTF= (G (fo)/G (f,)) *10
0=99.1[%]. That is, the decrease in MTF of the current-voltage changing circuit 1 is 09%.

As described above, the current-voltage conversion circuit l of the first embodiment has a decrease in MTF of 3.2-0. compared to the conventional current-voltage conversion circuit described above. 9=2. It was an improvement of 3 [%],
The amount of improvement relative to the lower limit of MTF is (2,3/30)*100=7.7 [%].

Therefore, the MTF can be improved with an extremely simple circuit configuration in which a desired combined resistance is constructed by simply dividing the feedback resistor 8 and connecting them in series, so that it can be easily realized with an optical recording/reproducing device.

Although the divided resistors 5 and 7 have the same resistance value, the first embodiment is not limited to this, as long as a desired combined resistance value can be obtained.

FIG. 2 is a configuration diagram showing the configuration of a current-voltage changing circuit according to a second embodiment of the present invention.

The amplifier 3 includes a resistor 13 having a capacitor lO as a component.
is fed back through a feedback resistor 15 which is a series connection of a resistor 14 having the capacitor 11 as a component and a resistor 15 having the capacitor 12 as a component, and the values of the capacitors 10 to 12 of the feedback resistor 15 are both c=0
．． 3 [pF], the values of resistors 13 and 14 are both r = 2
It is 0/3 [KΩ].

Other configurations and operations are the same as in the first embodiment.

Current-voltage conversion circuit 1 of the second embodiment configured in this way
The combined resistance R and combined capacitor C are R=3 pieces r=2
0 [KΩ C= (1/3) *C=0. 1 [pF].

An optical signal from an optical medium (not shown), for example, the amplitude characteristic G (fO
) and the amplitude characteristic of the longest mark interval G (f,) can be calculated from the above equation (4) as G (f,) = G (7,4[MHz
]) = 0.997 lines 20 [KΩ] G (f,) = G (2,775 [MHz] ) =
0. 999*20[KΩ], and the MTF is MTF= (G (f,)/G (f,))*100
=99.8[%]. That is, the decrease in MTF of the current-voltage conversion circuit 1 is 02%.

As described above, the t-current voltage conversion circuit 1 of the second embodiment has a decrease in MTF of 3.2-0. compared to the conventional current-voltage conversion circuit described above. 2=3. The improvement is 0 [%], and the relative improvement amount to the lower limit of MTF is (3, O/30) 100 = 10 0 [%], and the MTF is further improved compared to the first example. be done.

Note that the composite resistance is a composite resistance made up of resistors divided into two or three parts, but this embodiment is not limited to this, and may also be a composite resistance made up of resistors divided into any number of parts, such as four or more. good. Furthermore, although the composite resistor is configured by series connections, it may also be a composite resistor configured by series and interconnect connections as long as the capacitor component of the resistance can be reduced.

The structure and material of the resistor may be any material as long as the effects of this embodiment can be obtained.For example, the structure may be a lead resistor, a chip resistor, etc.
The material may be carbon, metal film, etc.

Further, the detector may be one that can perform photoelectric conversion.

[Effects of the Invention] As explained above, according to the present invention, the current-voltage conversion circuit of the optical recording/reproducing device of the present invention includes a photoelectric conversion means capable of receiving and photoelectrically converting returned light from an optical recording medium; and an amplifying means equipped with a feedback resistor that converts the current obtained from the photoelectric converter into a voltage and determines a gain, the current-voltage conversion circuit comprising at least a plurality of resistors in which the feedback resistor is connected in series. Since the structure is made up of M
Deterioration of TF can be prevented. Moreover, since the configuration is simple, it can be easily realized.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a current-voltage conversion circuit according to a first embodiment of the present invention, and FIG. 2 is a block diagram showing the configuration of a current-voltage changing circuit according to a second embodiment of the present invention. 3 and 4 relate to the conventional example, and FIG. 3 shows (2,7)RL
FIG. 4 is a timing diagram illustrating the MTF in the L modulation code. FIG. 4 is a configuration diagram showing the configuration of the current-voltage changing circuit. 1. Current-voltage conversion circuit 2. Detector 3 Amplifier
8. Return resistance, Z' knee. Do' Figure 1 tuff"t1"1°02 Figure 2 /-・ Figure 3 Otoo too I 00 10000000
1 000000010fa) Figure 4

Claims (1)

[Claims] A current/voltage device comprising a photoelectric conversion means capable of receiving and photoelectrically converting returned light from an optical recording medium, and an amplification means equipped with a feedback resistor that converts the current obtained from the photoelectric conversion means into voltage and determines a gain. 1. A current-voltage conversion circuit for an optical recording/reproducing device, wherein the feedback resistor is comprised of at least a plurality of resistors connected in series.