JP2001144366A - Ld drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an LD drive circuit which can deal with LD-modulation of GHz order by utilizing the structure of a conventional LD-stem and without newly having to increase its cost. SOLUTION: On the top surface of a flexible board 11, a wiring pattern 12 is formed to form a ground conductor 16 on its rear surface. An LD-stem 14 is mounted adhesively on the side of the grounded conductor 16 of the flexible board 11, and a lead 13 is passed through the flexible board 11 to be connected with the wiring pattern 12. A glass-sealed portion 17 of the LD-stem 14 has a similar cylindrical structure to a coaxial line. Moreover, portion of the grounded conductor 16 corresponding to the glass-sealed portion 17 is removed in advance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an LD driving circuit for mounting an LD stem on a microstrip line formed on a flexible substrate.
It can be applied to an optical pickup used for D, DVD, and the like.

[0002]

2. Description of the Related Art A semiconductor laser (LD) used for an optical pickup such as a CD or a DVD is generally mounted in a metal hermetic container called an LD stem. This L
The D stem and the LD driving IC are electrically connected by a wiring pattern formed on a flexible substrate made of polyimide or the like.

FIG. 4 is a schematic perspective view of a main part showing an LD stem mounted on a conventional flexible substrate. A wiring pattern 12 is formed on a flexible substrate 11. LD
The stem 14 is connected to the wiring pattern 12 by a lead 13, and the light of the LD is emitted from the window 15. Here, the wiring pattern 12 is connected to an LD driving IC (not shown).

[0004] Further, an LD used for picking up a CD or DVD is driven by superimposing a high frequency of several hundred MHz on an LD drive current in order to suppress noise due to return light from the disk. Conventionally, the value of several hundred MHz, which is a high frequency superimposed frequency, is a frequency sufficiently higher than the reading or transfer speed of a signal from a CD or a DVD. Did not.

However, in recent years, the reading and transferring speeds of CD and DVD signals have increased dramatically, and have been increasing to several hundred MHz.
Is approaching the high frequency superimposed frequency. For these reasons, it is necessary to further increase the high frequency superimposed frequency of the LD in the future. However, a new problem arises in the simple mounting method conventionally performed as shown in FIG. This is because when the high frequency superimposed frequency of the LD increases to the GHz order, the flexible substrate 1
This is because problems such as the emission of electromagnetic waves from the wiring pattern 12 formed on the substrate 1 and an increase in reflected waves due to impedance mismatching of the wiring become significant.

It is known that a high frequency transmission line such as a microstrip line or a triplate line with impedance matching can be used to efficiently transmit such a high frequency on the order of GHz. G
Such a configuration corresponding to modulation on the order of Hz has already been realized by an LD module for optical communication or the like. For example, Japanese Patent Application Laid-Open No. Hei 10-270748 discloses an example of an LD module connected by a microstrip line with impedance matching.

[0007]

As described above, LD is converted to G
Many module structures for modulating in the order of Hz have already been proposed for LD modules for optical communication, etc.
The use of these for pickup of CDs and DVDs has the following problems. In other words, since the LD module for optical communication is mainly used for a trunk communication infrastructure,
Although high performance is required and it may cost a little,
It is designed to provide maximum performance, despite its size. On the other hand, LDs used for picking up consumer CDs and DVDs have strict cost and size requirements, and it is very difficult to change to a structure that is significantly different from the current LD stem structure. However, conventional LD
Until now, there has been no proposal of an LD drive circuit that can cope with the modulation on the order of GHz using the structure of the stem.

The present invention has been made in view of the above circumstances, that is, an LD drive circuit capable of coping with modulation on the order of GHz without newly increasing the cost by using the structure of a conventional LD stem. It was made for the purpose of realizing.

[0009]

According to a first aspect of the present invention, there is provided an LD
An LD drive circuit in which a stem and an LD driving IC are connected by a microstrip line fabricated on a flexible substrate, and the LD stem is mounted on the microstrip line ground conductor side of the flexible substrate in a state of being in close contact with the flexible substrate. Thus, an LD driving circuit capable of coping with modulation on the order of GHz without newly increasing the cost is realized.

According to a second aspect of the present invention, in the LD driving circuit of the first aspect, the ground conductor of the microstrip line in a portion in contact with the LD stem is penetrated into the shape of the stem, and the microstrip line ground conductor in this portion is provided. Is replaced by a conductor of the stem, which makes it possible to mount the LD stem more easily.

According to a third aspect of the present invention, in the LD drive circuit of the first aspect, the impedance of the glass sealing portion of the LD stem as the coaxial line is made the same as that of the connected microstrip line. Eliminate the impedance discontinuity between the microstrip line and the coaxial line of the glass sealing part of the LD stem,
This realizes an LD drive circuit that does not cause reflection in a high frequency band.

According to a fourth aspect of the present invention, in the LD drive circuit of the first aspect, since a matching circuit is formed by the coaxial line and the microstrip line in the glass sealing portion of the LD stem, a small LD stem is thereby provided. , A matching circuit can be manufactured with distributed constants, and an efficient LD
A drive circuit can be realized.

According to a fifth aspect of the present invention, in the LD driving circuit of the first aspect, a matching circuit is formed by the coaxial line and the triplate line of the glass sealing portion of the LD stem. Thus, an LD drive circuit capable of realizing a low-impedance line without expanding the range and realizing high-density mounting can be realized.

The invention according to claim 6 is the invention according to claim 4 or 5,
In the D drive circuit, the matching circuit is matched to the high frequency superimposed frequency of the LD, so that an optimum matching circuit can be obtained and an efficient LD drive circuit can be realized. Things.

According to a seventh aspect of the present invention, in the LD driving circuit according to the sixth aspect, the matching circuit is a quarter-wave transformer, so that even if a matching circuit is provided, L can be mounted at a high density.
This is to realize a D drive circuit.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a conventional LD drive circuit,
By changing the line from a simple wiring structure to a transmission line such as a microstrip line, it is possible to reduce a loss in the line portion due to radiation or the like. FIG. 5 is a diagram showing an example of this, in which a ground conductor is provided on the back surface of the flexible substrate to form a microstrip line. As shown in FIG. A ground conductor 16 is formed. The LD stem 14 is connected to the wiring pattern 12 by a lead 13. Further, since the glass sealing portion of the LD stem 14 has the same shape as the coaxial line, high-frequency transmission characteristics are good. However, in such a structure, a microstrip line and an LD
Since the lead 13 serving as a connection portion of the stem is not a high-frequency transmission line, a large loss occurs in this portion and the high-frequency characteristics are degraded, but the length of this connection portion is simply shortened. If this is done, the signal line will come into contact with the metal LD stem.

According to the first aspect of the present invention, there is provided an LD driving circuit in which an LD stem and an LD driving IC are connected by a microstrip line formed on a flexible substrate. The LD stem is mounted on the microstrip line ground conductor side in a state in which the LD stem is in close contact with the flexible substrate. When such mounting is performed, the microstrip line of the flexible substrate and the coaxial line of the glass sealing portion of the LD stem are directly connected in a state where the transmission mode is not hindered, so that the high-frequency characteristics are not deteriorated. As a result, it is possible to realize an LD drive circuit capable of coping with the modulation on the order of GHz without increasing the cost, with the same structure as the conventional LD stem.

To properly match the transmission mode of the microstrip line with the transmission mode of the coaxial line, it is sufficient to make a hole in the ground conductor of the microstrip in accordance with the ground conductor of the coaxial line. In an LD system having such a structure, the work of mounting them with these positions aligned becomes very complicated. As a method for avoiding this, the ground conductor of the microstrip line may be substituted for the LD stem itself made of metal.

(Invention of Claim 2) Therefore, in the invention of Claim 2, in the LD drive circuit of Claim 1, the ground conductor of the microstrip line in contact with the LD stem is penetrated into the shape of the stem. The microstrip line ground conductor in this portion is replaced by a stem conductor.
Thus, the mounting of the LD system can be performed more easily.

The glass sealing portion of the LD stem has the same shape as the coaxial line, but the impedance of this portion is
If it is aligned with the microstrip line, reflection at the connection can be reduced.

According to a third aspect of the present invention, in the LD drive circuit of the first aspect, the impedance of the glass sealing portion of the LD stem as a coaxial line is equal to that of the connected microstrip line. The impedance is the same. As a result, since there is no impedance discontinuity between the microstrip line and the coaxial line of the glass sealing portion of the LD stem, it is possible to realize an LD drive circuit that does not cause reflection in a high frequency band.

Since the impedance during the operation of the LD is very small, on the order of several ohms, many conventional LD modules have a matching circuit using a resistor inside the module. A matching circuit using such a resistor is originally not very desirable because the power use efficiency is low.However, if a matching circuit is manufactured with a distributed constant, the matching circuit becomes too large to fit within the module. That's why. However, this idea is a bad effect because the development of the conventional LD module was performed alone, and by properly connecting the high-frequency transmission lines, it is possible to share the matching circuit to the outside of the module (wiring portion).
That is, by appropriately selecting the impedance of the coaxial line and the microstrip line in the glass sealing portion and connecting them in the arrangement as in the first aspect of the present invention, the wiring portion can function as a matching circuit.

(Invention of Claim 4) Therefore, in the invention of Claim 4, in the LD drive circuit of Claim 1, a matching circuit is formed by the coaxial line and the microstrip line of the glass sealing portion of the LD stem. . As a result, even if a small LD stem is used, a matching circuit can be manufactured with a distributed constant, so that an efficient LD drive circuit can be realized.

The characteristic impedance of the microstrip line formed on the flexible substrate is determined by the width of the upper electrode when the thickness and the material of the substrate are constant. In this case, in order to realize a low impedance line, the line width must be widened. In particular, when matching with an LD whose operating impedance is as low as several Ω, the width of the upper electrode is required to be about twice, but increasing the line width is not preferable for high-density mounting. The triplate line has a structure like a microstrip line having upper and lower ground conductors, and its characteristic impedance is about half that of the microstrip line. That is, by providing a triplate line by providing a dielectric and a ground conductor on the microstrip line, the characteristic impedance can be reduced to about half without increasing the width of the upper electrode.

(Invention of claim 5) Therefore, in the invention of claim 5, in the LD drive circuit of claim 1, a matching circuit comprising a coaxial line and a triplate line in the glass sealing portion of the LD stem. As a result, a low impedance line can be realized without increasing the width of the upper electrode.
An LD drive circuit capable of high-density mounting can be realized.

When a matching circuit is manufactured using distributed constant lines,
Impedance matching cannot be achieved for all frequencies. In other words, the characteristic of the entire system depends on which frequency the impedance matching is performed. L
In the case of the D drive circuit, the high frequency superimposed frequency, which is the highest frequency, is most susceptible to the impedance mismatch.

(Invention of claim 6) Therefore, in the invention of claim 6, in the LD drive circuit of claim 4 or 5, the matching circuit is matched to the high frequency superimposed frequency of the LD. Thus, an optimum matching circuit can be obtained, and an efficient LD driving circuit can be realized.

Although a matching circuit using a distributed constant line can take various circuit systems, in the case of an LD drive circuit, it is preferable that the mounting area be as small as possible. 1/4
A matching circuit using a wavelength transformer does not require a stub or the like, and can be configured simply by changing the impedance of the transmission line.

According to a seventh aspect of the present invention, in the LD drive circuit according to the sixth aspect, the matching circuit comprises a 1/4 wavelength transformer. This makes it possible to realize an LD drive circuit that can be mounted at a high density even if a matching circuit is provided.

(Embodiment) FIG.
FIGS. 1A and 1B are diagrams for explaining an embodiment of an LD drive circuit to which the inventions of FIGS. 6 and 7 are applied, and FIG. 1A is a side view of an LD stem mounted on a flexible substrate. The flexible substrate 11 has a wiring pattern 12 and a ground conductor 16 formed on the back surface. The LD stem 14 is mounted in close contact with the ground conductor 16 side of the flexible substrate 11,
Are connected to the wiring pattern 12 through the flexible substrate 11. FIG. 1B is a cross-sectional view of FIG.
The enlarged cross-sectional view of the part surrounded by
Are the same as those in FIG. The glass sealing portion 17 of the LD stem 14 has a columnar structure like the coaxial line. The ground conductor 16 corresponding to the glass sealing portion 17 has been removed in advance.

In this embodiment, the high frequency superimposed frequency is 2 GHz,
A matching circuit is formed for the operating impedance of the LD of 10Ω. The diameter of the glass sealing portion 17 is 0.98 mm, the diameter of the lead is 0.5 mm, the impedance of the coaxial line is 22Ω, and the length of the coaxial line is 1Ω. .5 mm,
The electrical length is 6.5 deg. The dimensions of the microstrip line connected thereto are a polyimide film having a thickness of 50 μm, an upper electrode width of 347 μm (characteristic impedance: 22Ω), and a length of 20 mm (electric length: 83.5 deg). After that, LD with a microstrip line with an upper electrode width of 107 μm (characteristic impedance 50Ω)
It is connected to the driving IC. By adopting such a configuration, 22 Ω is added to the end of the 50 Ω microstrip line.
Transmission lines are connected together for 1/4 wavelength, and 10Ω
Can be impedance-matched.

FIG. 2 is a diagram for explaining an embodiment of an LD drive circuit to which the invention of claims 1, 2, 3, 4, 6, and 7 is applied. FIG. It is a side view of the mounted LD stem. The wiring pattern 12 is formed on the front surface of the flexible substrate 11, and the ground conductor 16 is formed on the back surface. LD stem 14 is flexible substrate 11
Of the lead 1
3 is a wiring pattern 12 penetrating the flexible substrate 11
It is connected to the. The ground conductor 16 corresponding to the LD stem 14 is not shown, and the ground conductor in this portion is L
Substituted with D stem. Further, FIG.
FIG. 3A is an enlarged sectional view of a portion surrounded by B in FIG.
Symbols 1 to 14 are the same as those in FIG. The glass sealing portion 17 of the LD stem 14 has a columnar structure like the coaxial line.

In this embodiment, the high frequency superposition frequency is 2 GHz,
A matching circuit is formed for the operating impedance of the LD of 10Ω. The diameter of the glass sealing portion 17 is 0.98 mm, the diameter of the lead is 0.5 mm, the impedance of the coaxial line is 22Ω, and the length of the coaxial line is 1Ω. .5 mm,
The electrical length is 6.5 deg. The dimensions of the microstrip line connected thereto are a polyimide film having a thickness of 50 μm, an upper electrode width of 347 μm (characteristic impedance: 22Ω), and a length of 20 mm (electric length: 83.5 deg). After that, LD with a microstrip line with an upper electrode width of 107 μm (characteristic impedance 50Ω)
It is connected to the driving IC. By adopting such a configuration, 22 Ω is added to the end of the 50 Ω microstrip line.
Transmission lines are connected together for 1/4 wavelength, and 10Ω
Can be impedance-matched.

FIG. 3 is a view for explaining an embodiment of an LD drive circuit to which the invention of claims 1, 2, 3, 5, 6, and 7 is applied. FIG. It is a side view of the mounted LD stem. A wiring pattern 12 and ground conductors 16 and 18 above and below the wiring pattern 12 are formed on the flexible substrate 11. LD stem 14 is flexible substrate 1
The lead 13 is connected to the wiring pattern 12 through a part of the flexible substrate 11. The ground conductor 16 corresponding to the LD stem 14 is not shown, and the lower ground conductor of this portion is substituted by the LD stem. FIG.
FIG. 3B is an enlarged cross-sectional view of a portion surrounded by B in FIG. 3A, and symbols 11 to 18 are the same as those in FIG. 3A. The glass sealing portion 17 of the LD stem 14 has a columnar structure like the coaxial line. In order to smoothly connect the transmission mode of the triplate line to the coaxial line, it is preferable to provide a structure for connecting the upper ground conductor and the ground conductor of the coaxial line using a through hole as shown in FIG.

In this embodiment, the high frequency superimposed frequency 2GH
z, operating impedance of LD: 5Ω, dimensions of glass sealing portion: 0.98 mm, lead: 0.5 mm, 22Ω, length: 1.
5mm, electrical length 2.7mm, dimensions of triplate line,
A polyimide film with a thickness of 50 μm above and below the signal line, a microstrip with a signal line width of 176 μm (characteristic impedance: 22Ω), a length of 18.6 mm (electrical length: 83.5 deg), and thereafter an upper electrode width of 107 μm (characteristic impedance: 50Ω) The line is connected to the LD driving IC. By adopting such a configuration, a 22Ω transmission line (a triplate line and a coaxial line) is connected to the end of the 50Ω microstrip line for a quarter wavelength, and
Impedance matching can be achieved for a 10Ω LD.

[0036]

According to the first aspect of the present invention, there is provided an LD driving circuit in which an LD stem and an LD driving IC are connected by a microstrip line formed on a flexible substrate.
Since the LD stem is mounted in close contact with the flexible substrate, it is possible to realize an LD drive circuit capable of coping with modulation on the order of GHz without newly increasing the cost.

According to a second aspect of the present invention, in the LD driving circuit of the first aspect, the ground conductor of the microstrip line in a portion in contact with the LD stem is penetrated into the shape of the stem, and the microstrip line ground conductor in this portion is provided. Is replaced by the conductor of the stem, which makes it easier to mount the LD stem.

According to a third aspect of the present invention, in the LD driving circuit of the first aspect, the impedance of the glass sealing portion of the LD stem as the coaxial line is the same as that of the connected microstrip line. Since there is no impedance discontinuity between the line and the coaxial line in the glass-sealed portion of the LD stem, an LD drive circuit that does not generate reflection in a high frequency band can be realized.

According to a fourth aspect of the present invention, in the LD drive circuit of the first aspect, a matching circuit comprising a coaxial line and a microstrip line in a glass sealing portion of the LD stem is provided.
As a result, even if a small LD stem is used, a matching circuit can be manufactured with a distributed constant, so that an efficient LD drive circuit can be realized.

According to a fifth aspect of the present invention, in the LD driving circuit of the first aspect, a matching circuit comprising a coaxial line and a triplate line in a glass-sealed portion of the LD stem is used, so that the width of the upper electrode is not increased. Since a low impedance line can be realized, an LD drive circuit capable of high-density mounting can be realized.

The invention according to claim 6 is the invention according to claim 4 or 5,
In the D drive circuit, the matching circuit is matched to the high frequency superimposed frequency of the LD, whereby an optimum matching circuit can be obtained, and an efficient LD drive circuit can be realized.

According to a seventh aspect of the present invention, in the LD driving circuit of the sixth aspect, the matching circuit is a quarter-wave transformer, which enables high-density mounting even if a matching circuit is provided.
A D drive circuit can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a first embodiment to which the present invention is applied.

FIG. 2 is a diagram illustrating a second embodiment to which the present invention is applied.

FIG. 3 is a diagram illustrating a third embodiment to which the present invention is applied.

FIG. 4 is a diagram showing a state where an LD stem is mounted on a flexible substrate in a conventional LD drive circuit.

FIG. 5 is a diagram illustrating a microstrip line in which a ground conductor is provided on the back surface of a flexible substrate in an LD drive circuit.

[Explanation of symbols]

11: Flexible board, 12: Wiring pattern, 13:
Lead, 14 LD stem, 15 window, 16, 18, ...
Ground conductor, 17: glass sealing portion, 19: through hole.

Claims (7)

[Claims] In an LD driving circuit in which an LD stem and an LD driving IC are connected by a microstrip line formed on a flexible substrate, the LD stem is connected to the microstrip line ground conductor side of the flexible substrate. An LD drive circuit, wherein the LD drive circuit is mounted in close contact with a substrate. 2. The LD driving circuit according to claim 1, wherein a ground conductor of the microstrip line in a portion in contact with the LD stem is penetrated into the shape of the LD stem, and the microstrip line ground conductor in the portion is the ground conductor. An LD drive circuit characterized by using a conductor of an LD stem. 3. The LD driving circuit according to claim 1, wherein the impedance of the glass sealing portion of the LD stem as a coaxial line is the same as the connected microstrip line. circuit. 4. The LD driving circuit according to claim 1, further comprising a matching circuit including a coaxial line and a microstrip line in a glass sealing portion of the LD stem. 5. The LD driving circuit according to claim 1, further comprising a matching circuit including a coaxial line and a triplate line in a glass sealing portion of the LD stem. 6. The LD drive circuit according to claim 4, wherein the matching circuit is matched with respect to a high frequency superimposed frequency of the LD. 7. The LD driving circuit according to claim 6, wherein said matching circuit comprises a quarter-wave transformer.