M318264 八、新型說明： 【新型所屬之技術領域】 本新型是有關於一種驅動電路，且特別是有關於一種 用於雷射二極體驅動電路。 【先前技術】 目前雷射二極體（Laser Diode ; LD)由於具有體積小、 饧格低廉、使用方便的優點，已被廣泛地應用在資訊的光 儲存與光讀取、光通信和距離量測等眾多領域中。 但依據用途的不同，對雷射二極體之驅動電路的要 求，也相對的有所改變。 參照第1圖，係為習知雷射二極體於不同溫度下，順 向電流（mA)與光輸出功率（mA)之關係曲線。 只有在驅動電流大於臨界電流Ith時，雷射二極體LD 所發出的才是有效的雷射光，並且溫度對雷射二極體ld 輸出的光功率有很大影響，在同樣的驅動電流之下，溫度 越高，輸出的光功率越小。 然而，大多數的應用（如CD、DVD，或是長距、中距 和短距離量測）皆要求雷射二極體LD能夠輸出穩定的雷射 光。換言之，雷射二極體LD皆需要一適當之驅動電路， 以能提供恰當的驅動電流，使其能夠工作在輪出有效雷射 光的狀態。 【新型内容】 5 M318264 因此本新型的目的就是在提供一種雷射二極體驅動 電路’藉由控制雷射二極體（LD)的驅動電流值，以期獲得 輸出功率穩定的雷射光。 根據本新型之上述目的，提出一種雷射二極體驅動電 路，包含一光發射元件、一偏壓電路、一光接收元件，以 及一自動控制系統。 該光發射元件，用以產生光信號。 該偏壓電路，耦接於該光發射元件，用以產生一驅動 電信號’致使該光發射元件操作於一工作區間。 該光接收元件，用以感測該光發射元件之光輸出功 率，並產生一對應之電信號。 該自動控制系統，耦接於該光接收元件與該偏壓電路 之間’用以根據該光接收元件輸出的電信號，調整該光發 射元件之驅動電流值，該自動控制系統包括一第一控制信 號、一分壓電路，以及一積分迴路。該第一控制信號與該 分壓電路’用以調制該光發射元件之一偏壓。該積分迴 路，耦接於該分壓電路的輸出端。 本新型藉由光接收元件、自動控制系統與偏壓電路， 根據所採集到之光輸出功率的大小，自動地調整光發射元 件之驅動電信號的大小，使光發射元件輸出之光功率等於 (趨近）一預定值。而且，由於已限制了雷射二極體（LD)的 最大驅動電流和最小驅動電流，基於已做最大程度上減少 因調製失真所造成的測量誤差，所以，可使不同頻率的調 製信號，對光信號的調製幅度達到一致的目的與功效。 6 M318264 【實施方式】 隨著電子技術和半導體雷射器的發展，掌上型雷射相位 測距儀已經商品化，且廣泛地應用在建築、交通、地形勘測 與室内裝潢等方面。 一般而言，此種相位式測距儀係配備有一光發射器，用 以發出雷射光束，以便能夠對準一量測點（目標物）。由於對準 一被測物體之光束會散射，並且被内建之一接收器所記錄下 來，藉由相較於發射器所發出之光束，與所接收到之光束間 的相位變化量，即可求出與被測物之間的距離。 一般而言，相位式測距儀中之偵測器，係使用PIN光二 極體或崩潰光二極體（Avalanche Photo Diode ; APD)，將所反 射回來之光束，轉換成電性信號。 常見的相位式測距儀，係藉由測量相位作為判定距離的 標準，在這種裝置中，所接收到的電性信號會疊加上一混波 頻率，以產生一個低頻量測信號，量測此低頻量測信號之相 位，再與一參考信號之相位作比較。藉由低頻量測信號之相 位與參考信號之相位間之相位差，即可作為被測物之距離的 量測。 參照第2圖，係為本新型一實施例之用於雷射相位測 距的雷射二極體驅動裝置的電路方塊圖。 參照第3圖，係為第2圖的詳細電路圖。 參照第2圖與第3圖，本新型之雷射二極體驅動電 7 M318264 路，包含一光發射元件100、一光接收元件200、一偏壓 電路300、一自動控制系統400，以及一交流通路500。 該光發射元件1〇〇為一雷射二極體（Laser Diode ; LD)，用以產生光信號。 該光接收元件200，用以感測該光發射元件100之光 輸出功率的大小，並產生一相應之電信號。一般而言，光 信號的接收裝置常使用光電轉換元件作為接收端，特別是 使用崩潰光二極體（Avalanche Photo Diode ; APD)或光二極 體（Photo Diode ; PD)，並根據所接收之光信號強度，產生 對應之電輸出信號。 該偏壓電路300，用以產生一驅動電信號，致使該光 發射元件1〇〇操作於適當的工作範圍中。於本實施例中， 此偏壓電路300係產生一驅動電信號，使光發射元件100 操作於預定的一工作區間中。此偏壓電路300至少包括有 一個開關元件（Q3)301、一第六電阻（R6)302、一第七電阻 (R7)303以及一第一電感（Ll)304。該第七電阻（R7)303係 耦接於該開關元件（Q3)301之一第一端（集極）與一電源電 壓（Vcc)之間；該第六電阻（Q6)302係耦接於該開關元件 (Q3)301之一第二端（基極）與該電源電壓（Vcc)之間；該第 一電感（Ll)304係耦接於該開關元件（Q3)301之一第三端 (射極）與該光發射元件100之間，且該光發射元件100是 以正向偏壓的形式耦接於該第一電感（Ll)304與接地端。 在此，該開關元件（Q3)301可為NPN型之雙載子電晶 體或功率電晶體，主要是為該光發射元件1〇〇提供驅動電 M318264 流；該第六、七電阻（R6、R7)302、303為開關元件（Q3)301 提供適當的工作點，並防止通過光該發射元件1〇〇的電流 過大；該第一電感（Ll)304為一隔離電感，是用以將交流 信號限制於交流通路500;且所述電源電壓（Vcc)須大於 3.3V(伏特），但不限定於此。 該自動控制系統400,用以根據來自該光接收元件200 輸出的電信號，控制該偏壓電路300以調整驅動電信號， 使得該光發射元件1〇〇之光輸出功率穩定於一預定值。於 是，該自動控制系統400與該偏壓電路300共同組成了此 雷射二極體驅動裝置中的直流驅動部分。 該自動控制系統400包括一第一控制信號（Ctrl)401、 一分壓電路（至少包括第一電阻R1、第二電阻R2、第三電 阻R3)402、一第一阻抗403、一第一可變電壓（Vrl)404、 一積分迴路（至少包括運算放大器OP1、第一電容Cl)405、 一第二控制信號（Crt2)406以及一達靈頓迴路（至少包括第 一電晶體Q1、第二電晶體Q2)407。 於此電路中，是藉由改變該第一控制信號（Crtl)401的 電壓值以控制該光發射元件100之啟閉。其中，A點之一 第一電壓VA是由此第一控制信號（Crtl)401與此分壓電路 (即第一電阻R1、第二電阻R2與第三電阻R3)402所產生， 且經由該第一阻抗（R4)403於B點形成一第三電壓VB。M318264 VIII. New description: [New technical field] The present invention relates to a driving circuit, and in particular to a laser diode driving circuit. [Prior Art] At present, Laser Diode (LD) has been widely used in information optical storage and optical reading, optical communication and distance because of its small size, low cost and convenient use. Testing in many fields. However, depending on the application, the requirements for the driving circuit of the laser diode have also changed relatively. Referring to Fig. 1, the forward current (mA) and the light output power (mA) of a conventional laser diode at different temperatures are shown. Only when the driving current is greater than the critical current Ith, the laser diode LD emits effective laser light, and the temperature has a great influence on the optical power of the laser diode ld output, at the same driving current. The higher the temperature, the smaller the output optical power. However, most applications (such as CD, DVD, or long-range, medium-range, and short-range measurements) require the laser diode LD to output stable laser light. In other words, the laser diode LD requires a suitable drive circuit to provide the proper drive current to operate in a state where effective laser light is emitted. [New content] 5 M318264 Therefore, the purpose of the present invention is to provide a laser diode driving circuit 'by controlling the driving current value of the laser diode (LD) in order to obtain laser light with stable output power. According to the above object of the present invention, a laser diode driving circuit comprising a light emitting element, a bias circuit, a light receiving element, and an automatic control system is provided. The light emitting element is configured to generate an optical signal. The biasing circuit is coupled to the light emitting element for generating a driving electrical signal to cause the light emitting element to operate in a working interval. The light receiving component is configured to sense a light output power of the light emitting component and generate a corresponding electrical signal. The automatic control system is coupled between the light receiving component and the biasing circuit to adjust a driving current value of the light emitting component according to an electrical signal output by the light receiving component, the automatic control system including a first A control signal, a voltage divider circuit, and an integration loop. The first control signal and the voltage dividing circuit ' are used to modulate one of the light emitting elements. The integration loop is coupled to the output of the voltage dividing circuit. According to the light receiving component, the automatic control system and the bias circuit, the novel automatically adjusts the size of the driving electrical signal of the light emitting component according to the magnitude of the collected optical output power, so that the optical power outputted by the light emitting component is equal to (Approaching) a predetermined value. Moreover, since the maximum driving current and the minimum driving current of the laser diode (LD) have been limited, based on the measurement error caused by the modulation distortion being minimized, the modulation signals of different frequencies can be made, The modulation amplitude of the optical signal achieves a consistent purpose and efficacy. 6 M318264 [Embodiment] With the development of electronic technology and semiconductor lasers, handheld laser phase range finder has been commercialized and widely used in construction, transportation, terrain survey and interior decoration. In general, such a phase range finder is equipped with a light emitter for emitting a laser beam so as to be able to align a measuring point (target). Since the beam that is aimed at an object to be measured is scattered and recorded by one of the built-in receivers, by comparing the amount of phase change between the beam emitted by the emitter and the received beam, Find the distance from the object to be measured. In general, the detector in a phase range finder uses a PIN photodiode or an Avalanche Photo Diode (APD) to convert the reflected beam into an electrical signal. A common phase range finder is a standard for determining the phase by measuring the phase. In this device, the received electrical signal is superimposed with the previous mixing frequency to generate a low frequency measurement signal, and the measurement is performed. The phase of the low frequency measurement signal is then compared to the phase of a reference signal. By measuring the phase difference between the phase of the low-frequency measurement signal and the phase of the reference signal, it can be measured as the distance of the object to be measured. Referring to Fig. 2, there is shown a circuit block diagram of a laser diode driving apparatus for laser phase ranging according to an embodiment of the present invention. Referring to Fig. 3, it is a detailed circuit diagram of Fig. 2. Referring to FIGS. 2 and 3, the laser diode driving circuit 7 M318264 includes a light emitting element 100, a light receiving element 200, a bias circuit 300, an automatic control system 400, and An AC path 500. The light emitting element 1 is a laser diode (LD) for generating an optical signal. The light receiving component 200 is configured to sense the magnitude of the optical output power of the light emitting component 100 and generate a corresponding electrical signal. In general, a receiving device for an optical signal often uses a photoelectric conversion element as a receiving end, in particular, an Avalanche Photo Diode (APD) or a Photodiode (PD), and according to the received optical signal. Intensity produces a corresponding electrical output signal. The bias circuit 300 is operative to generate a drive electrical signal that causes the light emitting element 1 to operate in an appropriate operating range. In the present embodiment, the bias circuit 300 generates a drive electrical signal to operate the light-emitting component 100 in a predetermined operating interval. The bias circuit 300 includes at least one switching element (Q3) 301, a sixth resistor (R6) 302, a seventh resistor (R7) 303, and a first inductor (L1) 304. The seventh resistor (R7) 303 is coupled between the first end (collector) of the switching element (Q3) 301 and a power supply voltage (Vcc); the sixth resistor (Q6) 302 is coupled to The second end (base) of the switching element (Q3) 301 is coupled to the power supply voltage (Vcc); the first inductor (L1) 304 is coupled to the third end of the switching element (Q3) 301. The (emitter) is coupled to the light emitting element 100, and the light emitting element 100 is coupled to the first inductor (L1) 304 and the ground terminal in a forward biased manner. Here, the switching element (Q3) 301 can be an NPN-type bipolar transistor or a power transistor, mainly for supplying the driving power M318264 to the light emitting element 1〇〇; the sixth and seventh resistors (R6, R7) 302, 303 provide a suitable operating point for the switching element (Q3) 301 and prevent excessive current flow through the transmitting element 1; the first inductor (L1) 304 is an isolated inductor for communicating The signal is limited to the AC path 500; and the power supply voltage (Vcc) must be greater than 3.3 V (volts), but is not limited thereto. The automatic control system 400 is configured to control the bias circuit 300 to adjust the driving electrical signal according to an electrical signal output from the light receiving component 200, so that the optical output power of the light emitting component 1 is stabilized at a predetermined value. . Thus, the automatic control system 400 and the biasing circuit 300 together form the DC drive portion of the laser diode drive. The automatic control system 400 includes a first control signal (Ctrl) 401, a voltage dividing circuit (including at least a first resistor R1, a second resistor R2, and a third resistor R3) 402, a first impedance 403, and a first a variable voltage (Vrl) 404, an integration loop (including at least an operational amplifier OP1, a first capacitor C1) 405, a second control signal (Crt2) 406, and a Darlington circuit (including at least a first transistor Q1, Two transistors Q2) 407. In this circuit, the opening and closing of the light-emitting element 100 is controlled by changing the voltage value of the first control signal (Crtl) 401. The first voltage VA of the point A is generated by the first control signal (Crtl) 401 and the voltage dividing circuit (ie, the first resistor R1, the second resistor R2, and the third resistor R3) 402, and The first impedance (R4) 403 forms a third voltage VB at point B.
該積分迴路405之該運算放大器OP1的正極輸入端電 性地連接於該B點。由於該運算放大器OP1的正極輸入端 與負極輸入端之電壓值應相等（即，B點之第三電壓VB 9 M318264 值與第一可變電壓（Vrl)404值相等），因此，可藉由控制該 .第一可變電壓（Vrl)404間接改變B點之該第三電壓 並且，再由該第一阻抗（r4)403之兩端，a點與b點之電 壓差值（vA-vB)，以及該第一阻抗（R4)403，以獲得提供予 該光發射元件1〇〇的驅動電流。 簡言之，於此自動控制系統中，是藉由該第一控制信 號（ctrl)401調制A點之該第一電壓Va、藉由該第一可變 電壓（Vrl)404調制B點之該第三電壓Vb，並以該第一電 壓vA、該第三電壓Vb，以及該第一阻抗（R4)4〇3決定該光 發射兀件1〇〇的驅動電流。且，於該積分迴路4〇5的輸出 端（亦即該運算放大器OP1的輸出端）c點輸出一 壓vc。 該達靈頓迴路407接設於該積分迴路405的輸出端（第 二電壓c點），是由第一電晶體Q1、第二電晶體Q2所組 成，此第一電晶體Q1、第二電晶體Q2分別是PNp型和 NPN型的雙載子放大電晶體。且，將第一電晶體卩丨的基 極端設置為一第二可變電壓（Vr2)406，因此，可利用調制 該第二可變電壓（Vr2)406來變更該達靈頓迴路4〇7之放大 倍率，並藉此可控制該光發射元件100驅動電流的範圍。 本電路於實際應用的動作情形如下：當該光接收元件 (PD)200接收由該光發射元件（LD)1〇〇所發出的部分光束 時，會產生與上述光束的功率相應之光電流Ai。舉例而 言，當光發射元件（LD)100發出的光束功率越高，該光接 收兀件（PD)200所產生的相應光電流△ i值越大，此時，流 M318264 經第一阻抗（R4) 403的電流值相對提高，從而使得B點之 第三電壓VB電位降低，以至於C點之第二電壓Vc值下 降，進而達到該光發射元件（LD)100的驅動電流值降低、 輸出光束之功率下降的目的。 反之，當該光發射元件（LD)100輸出光功率下降時， 該光接收元件（PD)200所產生的相應光電流△ i值亦降 低，流經第一阻抗（R4)403的電流值將減少、B點之第三 電壓VB電位將提高、C點之第二電壓Vc值亦上升，進而 使得該光發射元件（LD)100的驅動電流值增加、提昇輸出 光束之功率。 據此，當整體系統自身發熱或者環境條件改變等因素 造成光發射元件（LD)100之光束輸出功率發生改變時，本 新型之雷射二極體驅動電路即可藉由光接收元件200、自 動控制系統400與偏壓電路300，根據所採集到之光輸出 功率的大小，自動地調整光發射元件1〇〇之驅動電信號的 大小，使光發射元件100輸出之光功率等於（趨近）一預定 值。 其中，上述偏壓電路300所產生之驅動電信號可為電 流信號或電壓信號。 此外，該交流通路500是耦接於該光發射元件100與 外部信號源之間，用以接收至少一交流調製信號（INH與 INL)，致使該光發射元件100產生至少一已調製之光信 號。於本實施例中，此交流通路500包含有一第二電容 (C2)510、一第三電容（C3)520、一第二電感（L2)530與一第 11 M318264 二阻抗（R8)540，用以接收交流調製信號INH與INL，但 不限定於此。 該第二電容（C2)510與該第三電容（C3)520之一端均 耦接於該光發射元件（LD)IOO與該第一電感（Ll)304之 間。該第二電容（C2)510之另一端與該第二電感（L2)530串 聯，該第二電感（L2)530之另一端用以接收第一交流調製 信號（INH)。該第三電容（C3)520之另一端與該第二阻抗 (R8)540串聯，該第二阻抗（R8)540之另一端用以接收第二 交流調製信號（INL)。其中，該第一交流調製信號（INH)為 高頻信號，且該第二交流調製信號（INL)為低頻信號。 在一般的測距系統中，為了獲得較大的量測距離和較 高的準確度，通常需要多個相位量測信號，因此也就需要 多數個調製頻率，範圍由幾MHz(百萬赫芝）至幾百MHz(百 萬赫芝)不等。所以測距系統中之頻率合成器（未圖示）會根 據處理單元之控制信號，產生對應之交流調製信號（如INH 與INL)，此交流通路500會被耦接至頻率合成器，用以將 頻率合成器所輸出之交流調製信號，載入到光發射元件 100之輸入端（陽極端）。 一般而言，第二電容（C2)510與第二電感（L2)530可用 於將具有較高頻率之第一交流調製信號（INH)載入至光發 射元件100，而第三電容（C3)520與第二阻抗（R8)540可用 於將具有較低頻率之第二交流調製信號（INL)載入至光發 射元件100，於是光發射元件100會根據所載入之交流調 製信號，輸出與調製信號相同頻率之明暗變化的光信號。 12 M318264 在本實施例中，第-交流調製信號（INH)之頻率較第二交流 調製L號（INL)頻率高，且兩個之間約有幾KHz(千赫芝） 之頻率差，但不限定於此。 歸納上述，由於本新型之用於雷射相位測距的雷射二 極體驅動電路’在雷射二極體由於自身發熱或者環境改變 等因素，而造成其光束輸出功率發生改變時，可根據所採 集到之光束輸出功率的大小，自動地調整光發射元件 之驅動電流的大小，使光發射元件丨〇〇輸出之光功率等於 (趨近）穩定值，並同時可藉由交流通路5〇〇載入交流調製 號因此本新型之雷射一極體驅動裝置不僅可應用於距 離里測系統中，亦可應用於資訊的光存儲與讀取和光通信 等眾多領域中。 雖然本新型已以一實施例揭露如上，然其並非用以限 定本新型，任何熟習此技藝者，在不脫離本新型之精神和 範圍内，當可作各種之更動與潤飾，因此本新型之保護範 圍當視後附之申請專利範圍所界定者為準。 【圖式簡單說明】 為讓本新型之上述和其他目的、特徵、優點與實施例 能更明顯易懂，所附圖式之詳細說明如下·· 第1圖係為習知雷射二極體於不同溫度下，順向電流 (mA)與光輸出功率（mA)之關係曲線。 第2圖係為本新型一實施例之雷射二極體驅動電路的 電路方塊圖。 13 M318264 第 3圖係為第2圖之詳細電路圖。 【主要元件符號說明】 10 0 ·· 光發射元件 300 ： 偏壓電路 302 ： 第六電阻（R6) 304 ： 第一電感（R1) 401 ： 第一控制信號（Ctrl) 403 ： 第一阻抗（R4) 405 ： 積分迴路 407 ： 達靈頓迴路 510 ： 第二電容（C2) 530 ： 第二電感（L2) VA · 第一電壓 Vc : 第二電壓 INL : 第二交流調製信號 OP1 ••運算放大器 Q2 ： 第二電晶體 200 ： 光接收元件 301 ： 開關元件（Q1) 303 ： 第七電阻（R7) 400 ： 自動控制系統 402 ： 分壓電路(R卜R2、R3) 404 ： 第一可調電壓（Vrl) 406 ： 第二可調電壓（Vr2) 500 : 交流通路 520 ： 第三電容（C3) 540 ： 第二阻抗（R8) VB : 第三電壓 INH :第一交流調製信號 C1 ： 第一電容 Q1 : 第一電晶體 △ i : 光電流 14The positive input of the operational amplifier OP1 of the integrating circuit 405 is electrically coupled to the point B. Since the voltage values of the positive input terminal and the negative input terminal of the operational amplifier OP1 should be equal (ie, the third voltage VB 9 M318264 value of point B is equal to the first variable voltage (Vrl) 404 value), Controlling the first variable voltage (Vrl) 404 to indirectly change the third voltage of point B and, by the first impedance (r4) 403, the voltage difference between point a and point b (vA-vB) And the first impedance (R4) 403 to obtain a driving current supplied to the light emitting element 1?. In short, in the automatic control system, the first voltage Va of the A point is modulated by the first control signal (ctrl) 401, and the B point is modulated by the first variable voltage (Vrl) 404. The third voltage Vb determines the driving current of the light emitting element 1〇〇 by the first voltage vA, the third voltage Vb, and the first impedance (R4)4〇3. Further, a voltage vc is outputted at the output terminal of the integrating circuit 4〇5 (i.e., the output terminal of the operational amplifier OP1). The Darlington circuit 407 is connected to the output end of the integration circuit 405 (the second voltage c point), and is composed of a first transistor Q1 and a second transistor Q2. The first transistor Q1 and the second transistor The crystal Q2 is a PNp type and an NPN type double carrier amplifying transistor, respectively. Moreover, the base terminal of the first transistor 设置 is set to a second variable voltage (Vr2) 406. Therefore, the Darlington circuit can be changed by modulating the second variable voltage (Vr2) 406. The magnification, and thereby the range of the driving current of the light-emitting element 100 can be controlled. The operation of the circuit in practical use is as follows: when the light receiving element (PD) 200 receives a partial light beam emitted by the light emitting element (LD) 1 , a photocurrent Ai corresponding to the power of the light beam is generated. . For example, when the power of the light emitted by the light emitting element (LD) 100 is higher, the value of the corresponding light current Δ i generated by the light receiving element (PD) 200 is larger, and at this time, the stream M318264 passes through the first impedance ( R4) The current value of 403 is relatively increased, so that the potential of the third voltage VB at point B is lowered, so that the value of the second voltage Vc at point C is decreased, thereby lowering the driving current value of the light-emitting element (LD) 100, and outputting The purpose of the power drop of the beam. On the contrary, when the output optical power of the light emitting element (LD) 100 decreases, the value of the corresponding photocurrent Δ i generated by the light receiving element (PD) 200 also decreases, and the current value flowing through the first impedance (R4) 403 will The decrease, the third voltage VB potential at point B will increase, and the second voltage Vc value at point C also rises, thereby increasing the drive current value of the light-emitting element (LD) 100 and increasing the power of the output beam. Accordingly, when the overall system self-heating or environmental conditions change and other factors cause the beam output power of the light-emitting element (LD) 100 to change, the novel laser diode driving circuit can be automatically received by the light-receiving element 200, The control system 400 and the bias circuit 300 automatically adjust the magnitude of the driving electrical signal of the light emitting element 1 according to the magnitude of the collected optical output power, so that the optical power outputted by the light emitting element 100 is equal to ) a predetermined value. The driving electrical signal generated by the bias circuit 300 may be a current signal or a voltage signal. In addition, the AC path 500 is coupled between the light emitting element 100 and an external signal source for receiving at least one AC modulated signal (INH and INL), such that the light emitting element 100 generates at least one modulated optical signal. . In this embodiment, the AC path 500 includes a second capacitor (C2) 510, a third capacitor (C3) 520, a second inductor (L2) 530, and an 11th M318264 second impedance (R8) 540. The AC modulation signals INH and INL are received, but are not limited thereto. The second capacitor (C2) 510 and one end of the third capacitor (C3) 520 are coupled between the light emitting element (LD) 100 and the first inductor (L1) 304. The other end of the second capacitor (C2) 510 is connected in series with the second inductor (L2) 530, and the other end of the second inductor (L2) 530 is used to receive the first AC modulation signal (INH). The other end of the third capacitor (C3) 520 is connected in series with the second impedance (R8) 540, and the other end of the second impedance (R8) 540 is for receiving a second alternating current modulated signal (INL). The first alternating current modulated signal (INH) is a high frequency signal, and the second alternating current modulated signal (INL) is a low frequency signal. In a general ranging system, in order to obtain a larger measurement distance and higher accuracy, multiple phase measurement signals are usually required, and thus a plurality of modulation frequencies are required, ranging from several MHz (million megahertz). ) to several hundred MHz (million Hz). Therefore, the frequency synthesizer (not shown) in the ranging system generates a corresponding AC modulated signal (such as INH and INL) according to the control signal of the processing unit, and the AC path 500 is coupled to the frequency synthesizer for The AC modulated signal output from the frequency synthesizer is loaded to the input end (anode end) of the light emitting element 100. In general, the second capacitor (C2) 510 and the second inductor (L2) 530 can be used to load a first alternating current modulated signal (INH) having a higher frequency to the light emitting element 100, and the third capacitor (C3) 520 and a second impedance (R8) 540 can be used to load a second alternating current modulated signal (INL) having a lower frequency into the light emitting element 100, and the light emitting element 100 outputs an output according to the loaded alternating current modulated signal. An optical signal that modulates the brightness of the signal at the same frequency. 12 M318264 In this embodiment, the frequency of the first alternating current modulated signal (INH) is higher than the frequency of the second alternating current modulated L number (INL), and the frequency difference between the two is about several KHz (kilogram), but It is not limited to this. In summary, since the laser diode driving circuit for laser phase ranging of the present invention causes the output power of the laser diode to change due to factors such as self-heating or environmental changes, The magnitude of the output power of the collected beam automatically adjusts the magnitude of the driving current of the light-emitting element so that the optical power output from the light-emitting element 等于 is equal to (reaching) a stable value, and at the same time, through the AC path 5〇 〇Loading AC modulation number Therefore, the novel laser-pole driving device can be applied not only to the distance measuring system but also to various fields such as information optical storage and reading and optical communication. Although the present invention has been disclosed in an embodiment of the present invention, it is not intended to limit the present invention. Any one skilled in the art can make various changes and retouchings without departing from the spirit and scope of the present invention. The scope of protection is subject to the definition of the scope of the patent application attached. BRIEF DESCRIPTION OF THE DRAWINGS In order to make the above and other objects, features, advantages and embodiments of the present invention more obvious, the detailed description of the drawings is as follows: Figure 1 is a conventional laser diode The forward current (mA) versus light output power (mA) at different temperatures. Fig. 2 is a circuit block diagram of a laser diode driving circuit of an embodiment of the present invention. 13 M318264 Figure 3 is a detailed circuit diagram of Figure 2. [Main component symbol description] 10 0 ·· Light emitting element 300: Bias circuit 302: Sixth resistor (R6) 304: First inductance (R1) 401: First control signal (Ctrl) 403: First impedance ( R4) 405 : Integral loop 407 : Darlington loop 510 : Second capacitor (C2) 530 : Second inductor (L2) VA · First voltage Vc : Second voltage INL : Second AC modulation signal OP1 • Operational amplifier Q2: Second transistor 200: Light receiving element 301: Switching element (Q1) 303: Seventh resistor (R7) 400: Automatic control system 402: Voltage dividing circuit (Rb R2, R3) 404: First adjustable Voltage (Vrl) 406 : Second adjustable voltage (Vr2) 500 : AC path 520 : Third capacitor (C3) 540 : Second impedance (R8) VB : Third voltage INH : First AC modulation signal C1 : First Capacitor Q1: First transistor Δ i : Photocurrent 14