200529524 九、發明說明： 【發明所屬之技術領域】 本發明係有關用於半導體雷射（稱為雷射二極體）之光傳 送裝置（Optical Transmitter)之雷射二極體之驅動電路。 【先前技術】 近年來，光通信速度更加高速，伴隨於此，供給至雷射 二極體之驅動電路之用以通信而使用之數位信號〇、1所組 成之脈衝信號的速度亦高速化。具體而言，脈衝信號之數 位信號0、1之位元間隔縮短至丨〜⑺奈秒程度。雷射二極體 之驅動電路將此脈衝信號之電性振幅轉換成雷射二極體之 驅動電流之強弱。當此雷射二極體驅動電路之驅動電流存 在雜訊，光信號波形紊亂時，必須將用以去除雜訊之濾波 電路加入電流路徑。 以往，去除雷射二極體之驅動電流之雜訊時，用以使脈 衝電流之振幅安定，同時使其信號成分不致作為雜訊被去 除’將雜訊去除濾波器插入電流變化少的部分。 具體而言，如圖6所示，將鐵氧磁珠（Ferritebead)等之濾 波電路10 ’插入開關脈衝電流之電晶體FET1之源極電極與 接地之間之通常放置電阻之部分。 [專利文獻Π特開平6-164038號公報 然而’將前述濾波電路1〇設在電晶體FET1之源極電極與 接地之間時，如圖7所示，由於濾波電路丨〇之電阻成分，發 生FET1之源極電壓v上升，與閘極電壓之電壓差變小，電 流輸出I之振幅變小的問題。電晶體不是場效型而是雙極型 98239.doc 200529524 之情況亦同。 又，使用市售之雷射二極體驅動ic時，由於内部構造為 非公開，因此亦有無法得知安裝濾波器之端子為何者的情 況。 並且，使用市售之雷射二極體驅動1C時，如圖8所示，亦 有在雷射二極體驅動1C之内部，接地端子b已共同化者。此 時，即使有意以濾波電路10去除雜訊，由於雷射二極體驅 動1C之接地端子b之阻抗低，因此可能無法完全去除流過雷 射二極體驅動1C之雜訊。 【發明内容】 因此，本發明之目的在於提供一種雷射二極體之驅動電 路，其係可不對於雷射二極體之驅動電路之電流放大作用 造成不良影響而確實地去除雜訊，因此可傳送高品質之光 信號者。 本發明之雷射二極體之驅動電路設有：從電源、雷射二 極體電θθ體到接地之電流路徑；對於該電晶體供給輸入 信號，用以分別控制流過前述電流路徑之電流；前述遽波 電路插入於電源與雷射二極體之間。 右根據此構成，由於在電源與雷射：極體之間插入遽波 電路’因此濾波電路之阻抗對於放大作用所造成之影響 少，可防止電流輸出之振幅變動。 本^明之雷射二極體之驅動電路設有：從電源、雷 射一極體、第一電晶體到接地之第一電流路徑；及從電源、 電Ρ第-電Ba體到接地之第二電流路徑；對於前述第一 98239.doc 200529524 及第二電晶體供給互為反相 過前、+、笛d Φ . 之輪入信號，用以分別控制流 過刖述弟一及弟一電流路經之雷 ^ E t 電4 ;前述濾波電路插入於 笔源與雷射二極體及電阻之共同接點之間。 、 若根據此構成，由於流過前述 ^ 弟及弟二電流路徑之電 k之和係無關於輸入信號之狀熊 〜成為固定，濾波電路插 入於電源與雷射二極體及電阻 ^ 之，、冋接點之間，因此流過 濾波電路之電流亦為固定。因 口此濾波電路之阻抗對於放 大作用所造成之影響少，可碰奋 、 ^ J確只地去除雜訊，同時可防止 電流輸出之振幅變動。 又’若為-種電路構成’其設有：第三電流路徑，其係 用以控制流過前述雷射二極體之偏壓電流者；及第四電流 路控’其係用以補償流過前述第三電流路徑之偏壓電流之 :減者；流過前述第三及第四電流路徑之電流和亦為固 定’流過濾波電路之電流不會變動。因此，濾波電路之阻 抗對於放大作用所造成之影響少，可防止電流輸出之振幅 變動。 如以上’若根據本發明，將獲得即使輸人信號以高速變 化i對於雷射二極體之驅動電路之電流輸出之影響少，可 確K地達成雜訊去除的優異效果。 【實施方式】 以下’荟考附圖詳細說明本發明之實施型態。 圖H系表示本發明之雷射二極體（以下稱為「LD」）之驅動 電路1之電路圖。 LD之驅動電路1係具備：由2個電晶體FET1、FET2所組 98239.doc 200529524 成之放大電路；用以控制脈衝調制之振幅之第三電晶體 FET3，用以设定LD之偏壓電流之第四電晶體FET4 ;分別插 入放大電路之負載之電阻R&LD;及共同連接於前述電阻& 和LD之濾波電路2。 從電源、LD、第一電晶體FET1到接地之路徑以稱為第一 電流路徑p 1，從電源、電阻R、第二電晶體FET2到接地之 電流路徑稱為第二電流路徑P2。 用以將W以高速開關之突發信號（Burst signal)係從信號 電路（未圖示）輸入構成放大電路之2個FET1、FET2之閘極。 此突發信號係由施加於FET1之閘極之信號及施加於FET2 之閘極之彳§號等2者所構成，以互相反相位供給此等2個信 號。又，脈衝電流控制信號輸入於調制振幅控制用之FET3 之閘極’偏壓設定信號輸入偏壓設定用之FET4之閘極。 前述濾波電路2係用以去除重疊於LD驅動電流信號之雜 訊所設置之電路，特徵在於共同連接於電源與電阻r和LD 之間。 圖2係表示LD之驅動電流I與時間t之關係之曲線圖。ld 驅動電流I之振幅之寬度以Iw表示，偏壓電流值以IB表示。 振幅之寬度1〜係按照前述脈衝電流控制信號之大小決定， 偏壓電流值IB係按照前述偏壓設定信號之大小決定。 如圖3之「信號輸入」所示，突發信號係以極短週期（例 如：1〜10奈秒）重複1、〇之信號。LD之驅動電路1根據突發 信號，產生用以驅動LD之驅動電流I。以此驅動電流信號， 將LD之輪出光進行強度調制。強度調制後之光入射於傳送 98239.doc 200529524 用光纖（未圖示），並傳搬於此光纖。 圖4係表示濾波電路2之具體構成之電路圖。此濾波電路2 之構成包含：鐵氧磁珠所組成之電感器L，其係串聯地插入 於電阻R和LD之共同接點a與電源之間者；及電阻R1和電容 器C1，其係串聯地連接於前述共同接點&與接地之間者。 說明將此濾波電路2設置於電阻R和LD之共同接點a與電 源之間之效果。 由於流過圖1之FET1及FET2之電流量之合計為固定，因 此藉由將濾波電路2設置於電阻r和LD之共同接點a與電源 之間，即使輸入信號變動，仍可使流於濾波電路2之電流維 持固定。因此，濾波電路2所造成之電壓下降維持固定，可 防止共同接點a之電位變動。故，FET1之源極電壓不會變 動决疋負載電流篁之閘極—源極間電壓亦可保持安定 值。因此，可消除電流增益變動、放大特性不穩定等以往 之缺點。 圖5係表示可按照輸入切換偏壓電流之LD之驅動電路ρ 之電路圖。此電路作為例如：p()N㈣用戶側終端裝置適 用之L D之驅動電路使用。 此電路係於LD之陰極側，設置用以控制流於LDi偏壓電 流之第五電晶體FET5。藉由控制FET5之閘極電壓而控制偏 壓電流。 並且，藉由電阻R，及第六電晶體FET6,構成用以補償LD ，偏壓電流之增減之補償電路。從FET5到接地之路徑稱為 第三電流路徑P3，從FET6到接地之電流路徑稱為第四電流 98239.doc 200529524 路徑P4。 施加於FET6之閘極之閘極電壓正好與FET5之閘極電壓 成為反相位。因此，流過LD之電流量與流過電阻R，之電流 里之合計成為固定，流過濾波電路2之電流保持在固定值。 …果兵圖1之LD之驅動電路相同，fet 1之源極電麼不變 動’可防止電流增益之變動。 以上說明本發明之實施型態，但本發明之實施不限於前 述型態。例如：可使電源之正極及負極互換，使LD之極性 相反而連接。又，濾波電路2不限定為圖4所示之LCR所組 成之倒L型電路，亦可採用一般使用之濾波電路。又，至此 斤使用之電曰曰體係作為切換開關而作用，但亦可藉由適當 設定半導體元件之動作點，使之作為電阻類比性地變化之 可交電阻器而作用。於其他本發明之範圍内，可施行各 變更。 【圖式簡單說明】 圖1係表示本發明之雷射二極體之驅動電路之電路圖。 圖2係表示雷射二極體之驅動電流I之波形之曲線圖。 圖3係表示突發信號波形之曲線圖。 圖4係表示濾波電路2之具體構成例之電路圖。 圖5係表示偏壓電流可變之雷射二極體之驅動電路之、 路圖。 圖6係表示以往之雷射二極體之驅動電路之電路圖。 圖7係用以說明藉由濾波電路10降低電壓之要部電路圖。 圖8係於雷射二極體之驅動1C適用濾波電路時之要^電 98239.doc 200529524 路圖。 【主要元件符號說明】 1、Γ LD之驅動電路 2、10 濾波電路 P1 第一電流路徑 P2 第二電流路徑 P3 第三電流路徑 P4 第四電流路徑 a 共同接點 b 共同端子 98239.doc200529524 IX. Description of the invention: [Technical field to which the invention belongs] The present invention relates to a driving circuit of a laser diode for a semiconductor laser (called a laser diode) optical transmission device (Optical Transmitter). [Prior art] In recent years, the optical communication speed has become faster. With this, the speed of the pulse signal composed of digital signals 0 and 1 supplied to the driving circuit of the laser diode for communication is also increasing. Specifically, the bit interval between the digital signals 0 and 1 of the pulse signal is shortened to about ˜ ~ nanoseconds. The driving circuit of the laser diode converts the electrical amplitude of this pulse signal into the strength of the driving current of the laser diode. When there is noise in the driving current of this laser diode driving circuit and the waveform of the optical signal is disordered, a filter circuit to remove the noise must be added to the current path. In the past, when the noise of the driving current of the laser diode was removed, it was used to stabilize the amplitude of the pulse current and prevent its signal components from being removed as noise. 'The noise removal filter is inserted into the part with less current change. Specifically, as shown in FIG. 6, a filter circuit 10 'such as a ferrite bead (Ferrite Bead) is inserted into a portion where a resistor is usually placed between the source electrode of the transistor FET1 that switches the pulse current and the ground. [Patent Document No. 6-164038] However, when the aforementioned filter circuit 10 is provided between the source electrode of the transistor FET1 and the ground, as shown in FIG. 7, the resistance component of the filter circuit There is a problem that the source voltage v of the FET1 rises, the voltage difference between the source voltage v and the gate voltage becomes small, and the amplitude of the current output I becomes small. The transistor is not a field effect type but a bipolar type. In addition, when a commercially available laser diode drive IC is used, the internal structure is not disclosed, so it may not be possible to know which terminal to install the filter on. In addition, when a commercially available laser diode drive 1C is used, as shown in FIG. 8, there is also a ground terminal b that is common to the inside of the laser diode drive 1C. At this time, even if the noise is intentionally removed by the filter circuit 10, since the impedance of the ground terminal b of the laser diode driving 1C is low, the noise flowing through the laser diode driving 1C may not be completely removed. [Summary of the Invention] Therefore, an object of the present invention is to provide a driving circuit of a laser diode, which can surely remove noise without adversely affecting the current amplifying effect of the driving circuit of the laser diode, so that it can remove noise. Those who transmit high-quality light signals. The driving circuit of the laser diode of the present invention is provided with a current path from the power source, the laser diode electric θθ body to the ground; and an input signal is supplied to the transistor to control the current flowing through the foregoing current path, respectively. The aforementioned chirped wave circuit is inserted between the power source and the laser diode. According to this configuration, since a chirped wave circuit is inserted between the power source and the laser: polar body, the impedance of the filter circuit has little effect on the amplification effect, and the amplitude variation of the current output can be prevented. The driving circuit of the laser diode of the present invention is provided with a first current path from a power source, a laser diode, a first transistor to the ground; and a power path from the power source, the power source, the power source, the power source, and the power source. Two current paths; for the first 98239.doc 200529524 and the second transistor, the in-phase signals of the forward, +, and flute d Φ. Are used to control the current flowing through the first and the second. The path of the lightning ^ E t electric 4; the aforementioned filter circuit is inserted between the pen source and the common junction of the laser diode and the resistor. According to this structure, since the sum of the electric current k flowing through the aforementioned current path of the younger brother and the younger brother is not related to the input signal, it becomes fixed, and the filter circuit is inserted into the power source, the laser diode, and the resistor, And 冋 contacts, so the current of the filter circuit is also fixed. Because the impedance of this filter circuit has little effect on the magnification, you can try to remove noise only, and at the same time prevent the amplitude of the current output from changing. And 'if it is a kind of circuit configuration', it is provided with: a third current path, which is used to control the bias current flowing through the aforementioned laser diode; and a fourth current path control, which is used to compensate the current The bias current passing through the aforementioned third current path: minus; the sum of the current flowing through the aforementioned third and fourth current paths is also fixed and the current of the filter circuit will not change. Therefore, the impedance of the filter circuit has less influence on the amplification effect, and it can prevent the amplitude variation of the current output. As described above, according to the present invention, even if the input signal changes at high speed, i has a small effect on the current output of the driving circuit of the laser diode, and an excellent effect of noise removal can be achieved. [Embodiment] The embodiment of the present invention will be described in detail below with reference to the drawings. Fig. H is a circuit diagram showing a driving circuit 1 of a laser diode (hereinafter referred to as "LD") of the present invention. The drive circuit 1 of LD is equipped with: an amplifier circuit composed of two transistor FET1 and FET2 98239.doc 200529524; a third transistor FET3 for controlling the amplitude of pulse modulation, and used to set the bias current of LD The fourth transistor FET4; a resistor R &LD; which is respectively inserted into the load of the amplifier circuit, and a filter circuit 2 which is commonly connected to the aforementioned resistor & and LD. The path from the power source, LD, and the first transistor FET1 to ground is referred to as a first current path p1, and the current path from the power source, the resistor R, and the second transistor FET2 to ground is referred to as a second current path P2. The burst signal used to switch W at high speed is input from the signal circuit (not shown) to the gates of the two FET1 and FET2 constituting the amplifier circuit. This burst signal is composed of a signal applied to the gate of FET1 and a 彳 § number applied to the gate of FET2, and these two signals are supplied in opposite phases to each other. The pulse current control signal is input to the gate of the FET3 for the modulation amplitude control. The bias setting signal is input to the gate of the FET4 for the bias setting. The aforementioned filter circuit 2 is a circuit provided to remove noise overlapping the LD drive current signal, and is characterized in that it is commonly connected between the power source and the resistors r and LD. FIG. 2 is a graph showing the relationship between the driving current I and time t of the LD. ld The width of the amplitude of the drive current I is represented by Iw, and the value of the bias current is represented by IB. The width of the amplitude 1 to 1 is determined according to the magnitude of the aforementioned pulse current control signal, and the bias current value IB is determined according to the magnitude of the aforementioned bias setting signal. As shown in "Signal Input" in Figure 3, the burst signal is a signal that repeats 1 and 0 in a very short period (for example, 1 to 10 nanoseconds). The driving circuit 1 of the LD generates a driving current I for driving the LD according to the burst signal. This drives the current signal to modulate the intensity of the light emitted by the LD wheel. The intensity-modulated light is incident on an optical fiber (not shown) for transmission of 98239.doc 200529524, and is transmitted to this optical fiber. FIG. 4 is a circuit diagram showing a specific configuration of the filter circuit 2. The structure of this filter circuit 2 includes: an inductor L composed of ferrite beads, which is inserted in series between the common contact a of the resistors R and LD and the power source; and a resistor R1 and a capacitor C1, which are connected in series The ground is connected between the common contact & and the ground. The effect of setting this filter circuit 2 between the common contact point a of the resistors R and LD and the power supply will be described. Since the total amount of current flowing through FET1 and FET2 in FIG. 1 is fixed, by setting the filter circuit 2 between the common contact a of the resistors r and LD and the power source, even if the input signal changes, the The current of the filter circuit 2 remains fixed. Therefore, the voltage drop caused by the filter circuit 2 is kept constant, and the potential variation of the common contact point a can be prevented. Therefore, the source voltage of FET1 will not change, and the gate-source voltage of the load current will also remain stable. Therefore, conventional disadvantages such as fluctuations in current gain and unstable amplification characteristics can be eliminated. FIG. 5 is a circuit diagram showing a LD driving circuit ρ that can switch a bias current according to an input. This circuit is used as, for example, a driving circuit for L (D) suitable for a user-side terminal device. This circuit is on the cathode side of the LD, and a fifth transistor FET5 is provided to control the bias current flowing through the LDi. The bias current is controlled by controlling the gate voltage of the FET5. In addition, a resistor R and a sixth transistor FET6 constitute a compensation circuit for compensating LD and increasing or decreasing the bias current. The path from FET5 to ground is called the third current path P3, and the path from FET6 to ground is called the fourth current 98239.doc 200529524 path P4. The gate voltage applied to the gate of FET6 is exactly out of phase with the gate voltage of FET5. Therefore, the sum of the current flowing through LD and the current flowing through resistor R becomes fixed, and the current flowing through filter circuit 2 is maintained at a fixed value. … The driving circuit of the LD in Fruit Solder Figure 1 is the same. The source of the fet 1 does not change 'to prevent the current gain from changing. The embodiment of the present invention has been described above, but the implementation of the present invention is not limited to the aforementioned embodiment. For example, the positive and negative poles of the power supply can be interchanged, and the polarity of the LD can be reversed and connected. In addition, the filter circuit 2 is not limited to the inverted L-shaped circuit composed of the LCR shown in Fig. 4, and a filter circuit generally used may be used. In addition, the electric power system used so far functions as a changeover switch, but it can also function as a crossable resistor whose resistance is changed analogously by appropriately setting the operating point of the semiconductor element. Various changes can be made within the scope of other inventions. [Brief Description of the Drawings] FIG. 1 is a circuit diagram showing a driving circuit of a laser diode of the present invention. FIG. 2 is a graph showing a waveform of a driving current I of a laser diode. Fig. 3 is a graph showing a burst signal waveform. FIG. 4 is a circuit diagram showing a specific configuration example of the filter circuit 2. FIG. 5 is a circuit diagram showing a driving circuit of a laser diode with a variable bias current. FIG. 6 is a circuit diagram showing a driving circuit of a conventional laser diode. FIG. 7 is a circuit diagram of a main part for explaining a voltage reduction by the filter circuit 10. Fig. 8 is a circuit diagram of the power required when a laser diode driving 1C is applied to a filter circuit. [Description of Symbols of Main Components] 1. Driving circuit of Γ LD 2.10 Filter circuit P1 First current path P2 Second current path P3 Third current path P4 Fourth current path a common contact b common terminal 98239.doc