JPH0525262Y2 - - Google Patents

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Publication number
JPH0525262Y2
JPH0525262Y2 JP1990093319U JP9331990U JPH0525262Y2 JP H0525262 Y2 JPH0525262 Y2 JP H0525262Y2 JP 1990093319 U JP1990093319 U JP 1990093319U JP 9331990 U JP9331990 U JP 9331990U JP H0525262 Y2 JPH0525262 Y2 JP H0525262Y2
Authority
JP
Japan
Prior art keywords
laser diode
current
circuit
optical output
transistor
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
JP1990093319U
Other languages
Japanese (ja)
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JPH0345674U (en
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Filing date
Publication date
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Priority to JP1990093319U priority Critical patent/JPH0525262Y2/ja
Publication of JPH0345674U publication Critical patent/JPH0345674U/ja
Application granted granted Critical
Publication of JPH0525262Y2 publication Critical patent/JPH0525262Y2/ja
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Description

【考案の詳細な説明】[Detailed explanation of the idea]

考案の技術分野 本考案はレーザダイオードの駆動回路に関し、
一定光出力を実現しまたサージなどによるレーザ
ダイオードの破壊防止を図ろうとするものであ
る。 技術の背景 レーザダイオードは第1図に示す如き回路で駆
動される。この図で10はレーザダイオード、1
2は入力信号VPを受けて駆動電流IPを生じる電流
ドライバ、14はバイアス電流Ibを供給する電
源、16はバイアス電流を所定値内に制限する電
流リミツタ、18はチヨークコイル、20は差動
アンプで、基準電圧発生器22からの基準値と、
ホトダイオード24で検出したレーザダイオード
光出力を示す信号を比較し、この差が0になるよ
うに電源14が出力するバイアス電流Ibを調整す
る。26はホトダイオード24の出力の増幅器で
ある。既知のようにレーザダイオードの駆動電流
対光出力特性は左右を入れ換えたL型特性を示
し、駆動電流が小さい範囲では殆んど光出力はな
く、ある値(閾値)を越えると急激に光出力が生
じ始める。バイアス電流Ibはこの閾値相当の電流
であつて、これを信号電流IPに加えると信号−光
出力特性がリニアになる。閾値は温度によつて変
り、そこでダイオード24で光出力を検出してそ
れが一定になるように(IPは一定として)バイア
ス電流Ibを変える。 抵抗RとコンデンサCの直列回路はサージ吸収
用で、レーザダイオード10に加わる過大高周波
電圧を吸収する。Dは逆電圧防止用で、レーザダ
イオード10に逆方向電圧が加わらないようにす
る。 従来技術と問題点 かゝるレーザダイオード駆動回路でR,Cを除
き、信号電圧VPを第2図に示すように矩形波に
するとレーザダイオード10の光出力Pは同図に
示すように最初大で以後減衰する特性を示す。こ
れは減衰後の光出力がむしろ正常で、最初の大光
出力はいわば休止中の分が加算された結果であ
る。従つてマーク期間に比べてスぺース期間が大
であると、大出力部分は益々大になる。第4図お
よび第5図はこれを示す図で、第4図は発光期間
が短い場合、第5図は発光期間が長い場合であ
る。第4図の場合を想定すると尖頭部分により制
限されてレーザを定格出力以下で動作させざるを
得ない。RCを加えると、一般には第3図に示す
如くなり、光出力Pは最初の部分が小になる。 レーザダイオードをプリンタ等に使用する場
合、必要な周波数は0〜数MHzの範囲に及び、マ
ーク、スペースの割合も大幅に変る。従つてR,
Cがないと光出力の変動が大きくて不具合であ
る。またRCを付加すると先頭部分が欠けるとい
う問題がある。第1図R,C直列回路では第3
図、第4図、および第5図の光出力Pをすべて一
定出力にする即ち矩形波にすることは不可能であ
る。例えば第4図Pを矩形波にするRCにすると
第5図は矩形波にならず、第5図を矩形波にする
RCにするとコンデンサ容量が過大で第4図の波
形はつぶれてしまう。第6図および第7図はこれ
を示すグラフで、第6図はRCを短い発光期間に
合せた例、第7図はRCを長い発光期間に合せた
場合で、前者では長発光期間の場合bの光出力が
減衰し、後者では短い発光期間の場合の光出力が
小になる(レーザダイオードは充分駆動されない
間に駆動期間終了になつてしまう)。 またダイオードDで逆サージを逃がす第1図の
方式では、第8図のようにスペース期間が短い場
合次の発光に対する補正が充分に行なわれず、や
はり光出力先頭部分にピークが生じる。 考案の目的 本考案は上記の点に鑑みて案出しこもので、広
範囲な周波数帯において光出力を一定に保つこと
ができ、また順方向、逆方向サージよりレーザダ
イオードを守ることができるレーザダイオード駆
動回路を提供しようとするものである。 考案の構成 本考案は、入力信号VPに応じてレーザダイオ
ードを駆動する駆動電流を供給する手段を有する
レーザダイオード駆動回路であつて、前記レーザ
ダイオードを駆動する前記駆動電流を調整する補
償回路を備え、該補償回路は、抵抗R1とコンデ
ンサC1を含み、前記入力信号VPの極性を反転し
た信号*Vpに応じて充放電される微分回路と、
該微分回路の充電々圧Bにより駆動されるトラン
ジスタQとよりなり、該トランジスタQによつて
制御される電流によつて、前記駆動電流をバイア
スすることを特徴とするが、次に実施例を参照し
ながらこれを説明する。 考案の実施例 第9図は光出力一定化の原理図で、レーザダイ
オード10に並列に電流源ICを接続し、レーザダ
イオードに流れる電流Ifを If=Ib+IP−IC にしてパルス特性の改善(光出力の一定化)を図
る。Icはこのための補償電流である。Icを第11
図の如く選ぶと光出力は第10図aの点線の如く
なり、一定化が可能である。このような補償電流
Icを発生する回路を第12図に示す。この図でR1
〜R4は抵抗、C1はコンデンサ、Qはトランジス
タであり、抵抗R4、トランジスタQの直列回路
がレーザダイオード10に並列に接続され、抵抗
R1、コンデンサC1を含む微分回路がトランジス
タQのベースを制御する。*Vpは増幅器12に
入力される入力信号Vpの極性を反転した信号で
ある。発光期間が長い場合のこの回路の各部の波
形を第13図に、同短い場合のそれを第14図に
示す。 第13図に示されるように、発光期間が長い場
合はコンデンサC1の充電が充分に行なわれ、非
発光期間になるとB点電位は電源電圧+V以上に
高く上り、放電が始まるが期間が短いので放電は
僅かである。充分放電しないうちに次の発光期間
に入り、負の*Vpの方へ引張られるが残留電荷
があるのでB点電位はそれほど負にならない。結
局B点電位は強く負にはならないが負である期間
が長い図示のような変化をする。これによりトラ
ンジスタQは発光期間の初めから比較的長い時間
オンになつて図示の如き波形の補償電流Icを流
し、発光ダイオード10の駆動電流Ifは前端から
中央部にかけて角がとれ、光出力Pは矩形波状に
なる。発光期間が短い場合コンデンサC1は余り
充電されないうちに充電停止になり、放電は充分
行なわれ、結局B点電位は図示の如く強く負にな
る*Vp類似の波形になる。従つて補償電流Ic,レ
ーザダイオード駆動電流Ifは図示の如くなつて光
出力Pは矩形波状になる。点線は補正前である。 レーザプリンタなどへの応用では光出力は第2
図に示す結果になるが、この実測データを次表
に、オツシロ観測波形を第15図に示す。この表
でP1(nw)は発光開始時の光出力、P2(nw)は発光開始
時の光出力、△PsはP1−P2である。
Technical field of the invention This invention relates to a laser diode drive circuit.
The aim is to achieve a constant optical output and to prevent damage to the laser diode due to surges and the like. Background of the Technology A laser diode is driven by a circuit as shown in FIG. In this figure, 10 is a laser diode, 1
2 is a current driver that receives an input signal V P and generates a drive current I P ; 14 is a power supply that supplies a bias current I b ; 16 is a current limiter that limits the bias current within a predetermined value; 18 is a choke coil; and 20 is a differential a reference value from a reference voltage generator 22, and
The signals indicating the laser diode light output detected by the photodiode 24 are compared, and the bias current I b output by the power supply 14 is adjusted so that the difference becomes zero. 26 is an amplifier for the output of the photodiode 24. As is known, the driving current vs. optical output characteristic of a laser diode exhibits an L-shaped characteristic with the left and right sides reversed.When the driving current is small, there is almost no optical output, and when the driving current exceeds a certain value (threshold), the optical output suddenly decreases. begins to occur. The bias current I b is a current corresponding to this threshold value, and when this is added to the signal current I P , the signal-optical output characteristic becomes linear. The threshold value changes depending on the temperature, so the diode 24 detects the optical output and changes the bias current I b so that it becomes constant (assuming I P is constant). The series circuit of resistor R and capacitor C is for surge absorption, and absorbs excessive high frequency voltage applied to laser diode 10. D is for reverse voltage prevention, and prevents reverse voltage from being applied to the laser diode 10. Prior Art and Problems In such a laser diode drive circuit, if R and C are removed and the signal voltage V P is made into a rectangular wave as shown in Figure 2, the optical output P of the laser diode 10 will initially be as shown in the figure. It exhibits a characteristic of attenuating after a large value. This is because the light output after attenuation is rather normal, and the initial large light output is the result of adding up the rest. Therefore, when the space period is larger than the mark period, the large output portion becomes even larger. FIGS. 4 and 5 are diagrams showing this. FIG. 4 shows the case where the light emission period is short, and FIG. 5 shows the case where the light emission period is long. Assuming the case shown in FIG. 4, the laser has no choice but to operate at less than the rated output due to the limitations of the peak. When RC is added, the optical output P generally becomes smaller in the first part as shown in FIG. When a laser diode is used in a printer or the like, the required frequency ranges from 0 to several MHz, and the ratio of marks and spaces varies considerably. Therefore R,
Without C, the optical output fluctuates greatly, which is a problem. There is also the problem that when RC is added, the beginning part is missing. In Figure 1 R, C series circuit, the third
It is impossible to make all of the optical outputs P in FIGS. 4, 4, and 5 constant, that is, a rectangular wave. For example, if P in Figure 4 is set to RC which makes it a square wave, Figure 5 will not become a rectangular wave, but Figure 5 will become a rectangular wave.
If RC is used, the capacitor capacity will be too large and the waveform in Figure 4 will be distorted. Figures 6 and 7 are graphs showing this. Figure 6 shows an example in which RC is adjusted to a short emission period, and Figure 7 is an example in which RC is adjusted to a long emission period. The optical output of b is attenuated, and in the latter case, the optical output becomes small in the case of a short light emission period (the driving period ends before the laser diode is not sufficiently driven). In addition, in the method shown in FIG. 1 in which the reverse surge is released by diode D, when the space period is short as shown in FIG. 8, the correction for the next light emission is not sufficiently performed, and a peak still occurs at the beginning of the light output. Purpose of the invention The present invention was devised in view of the above points, and is a laser diode drive that can maintain constant optical output over a wide frequency range and protect the laser diode from forward and reverse surges. It is intended to provide a circuit. Structure of the Invention The present invention provides a laser diode drive circuit having means for supplying a drive current for driving a laser diode according to an input signal V P , the invention including a compensation circuit for adjusting the drive current for driving the laser diode. the compensation circuit includes a resistor R1 and a capacitor C1, and a differentiation circuit that is charged and discharged in accordance with a signal * Vp whose polarity is inverted from the input signal VP ;
A transistor Q is driven by the charging voltage B of the differentiating circuit, and the drive current is biased by the current controlled by the transistor Q. This will be explained with reference to Embodiment of the invention Figure 9 is a diagram showing the principle of constant optical output. A current source I C is connected in parallel to the laser diode 10, and the current I f flowing through the laser diode is set to I f = I b + I P - I C. The aim is to improve the pulse characteristics (constant light output). I c is the compensation current for this purpose. I c 11th
When selected as shown in the figure, the optical output becomes as shown by the dotted line in Figure 10a, and can be made constant. Such compensation current
A circuit for generating I c is shown in FIG. In this diagram R 1
~R 4 is a resistor, C 1 is a capacitor, and Q is a transistor. A series circuit of resistor R 4 and transistor Q is connected in parallel to the laser diode 10, and the resistor
A differentiating circuit including R 1 and capacitor C 1 controls the base of transistor Q. *V p is a signal obtained by inverting the polarity of the input signal V p input to the amplifier 12. FIG. 13 shows the waveforms of each part of this circuit when the light emission period is long, and FIG. 14 shows the waveforms when the light emission period is short. As shown in Figure 13, when the light emission period is long, the capacitor C1 is sufficiently charged, and when the non-light emission period begins, the potential at point B rises to a level higher than the power supply voltage +V and discharge begins, but the period is short. Therefore, the discharge is small. Before it is fully discharged, the next light emitting period begins, and it is pulled toward negative *V p , but since there is a residual charge, the potential at point B does not become so negative. In the end, the potential at point B does not become strongly negative, but changes as shown in the figure, with a long negative period. As a result, the transistor Q is turned on for a relatively long time from the beginning of the light emitting period, and a compensation current I c having a waveform as shown in the figure flows. P becomes a rectangular wave. When the light emitting period is short, the capacitor C1 stops charging before it is sufficiently charged, and is sufficiently discharged, so that the potential at point B eventually becomes strongly negative and has a waveform similar to *V p as shown in the figure. Therefore, the compensation current I c and the laser diode drive current If become as shown in the figure, and the optical output P becomes a rectangular wave. The dotted line is before correction. In applications such as laser printers, light output is the second
The results are shown in the figure, and the measured data is shown in the table below, and the observed waveform is shown in Fig. 15. In this table, P 1 (nw) is the light output at the start of light emission, P 2 (nw) is the light output at the start of light emission, and ΔP s is P 1 - P 2 .

【表】 第15図aはNo.1のケースの、同bはNo.4のケ
ースの観測波形である。 考案の効果 以上説明したことから明らかなように本考案で
は入力信号のマーク、スペースに応じて補償電流
を流し、光出力を矩形波入力信号に相似な矩形波
とすることができる。またレーザダイオードに逆
電圧が加わる場合はトランジスタQがオンになつ
て該レーザダイオードを保護することができる。
[Table] Figure 15a shows the observed waveform for the No. 1 case, and Figure 15b shows the observed waveform for the No. 4 case. Effects of the Invention As is clear from the above explanation, in the present invention, a compensation current is caused to flow according to the marks and spaces of the input signal, and the optical output can be made into a rectangular wave similar to the rectangular wave input signal. Further, when a reverse voltage is applied to the laser diode, the transistor Q is turned on to protect the laser diode.

【図面の簡単な説明】[Brief explanation of the drawing]

第1図は従来のレーザダイオードの駆動回路
図、第2図〜第8図、第10図、第11図、第1
3図および第14図は動作説明用波形図、第9図
は本考案の原理図、第12図は本考案の実施例を
示す回路図、第15図は光出力の観測波形例を示
す波形図である。 図面で、10はレーザダイオード、12は信号
電流源、14はバイアス電流源、Ipは信号電流、
Ibはバイアス電流、R1〜R4,C1,Qは補償回路、
Qはトランジスタ、R1,C1は微分回路、*Vp
信号電圧の反転電圧である。
Figure 1 is a conventional laser diode drive circuit diagram, Figures 2 to 8, Figures 10, 11, and 1.
3 and 14 are waveform diagrams for explaining operation, FIG. 9 is a principle diagram of the present invention, FIG. 12 is a circuit diagram showing an embodiment of the present invention, and FIG. 15 is a waveform showing an example of observed waveform of optical output. It is a diagram. In the drawing, 10 is a laser diode, 12 is a signal current source, 14 is a bias current source, I p is a signal current,
I b is the bias current, R 1 to R 4 , C 1 , Q are the compensation circuits,
Q is a transistor, R 1 and C 1 are differentiating circuits, and *V p is the inversion voltage of the signal voltage.

Claims (1)

【実用新案登録請求の範囲】 入力信号VPに応じてレーザダイオード10を
駆動する駆動電流を供給する手段12を有するレ
ーザダイオード駆動回路であつて、 前記レーザダイオード10を駆動する前記駆動
電流を調整する補償回路を備え、該補償回路は、 抵抗R1とコンデンサC1を含み、前記入力信号
VPの極性を反転した信号*VPに応じて充放電さ
れる微分回路と、 該微分回路の充電々圧Bにより駆動されるトラ
ンジスタQとよりなり、 該トランジスタQによつて制御される電流によ
つて、前記駆動電流をバイアスすることを特徴と
するレーザダイオードの駆動回路。
[Claims for Utility Model Registration] A laser diode drive circuit having means 12 for supplying a drive current for driving a laser diode 10 according to an input signal VP , the circuit comprising: adjusting the drive current for driving the laser diode 10; The compensation circuit includes a resistor R1 and a capacitor C1, and the compensation circuit includes a resistor R1 and a capacitor C1, and
It consists of a differentiating circuit that is charged and discharged according to the signal *V P in which the polarity of V P is inverted, and a transistor Q that is driven by the charging voltage B of the differentiating circuit, and the current that is controlled by the transistor Q. A laser diode drive circuit, characterized in that the drive current is biased by.
JP1990093319U 1990-09-05 1990-09-05 Expired - Lifetime JPH0525262Y2 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
JP1990093319U JPH0525262Y2 (en) 1990-09-05 1990-09-05

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP1990093319U JPH0525262Y2 (en) 1990-09-05 1990-09-05

Publications (2)

Publication Number Publication Date
JPH0345674U JPH0345674U (en) 1991-04-26
JPH0525262Y2 true JPH0525262Y2 (en) 1993-06-25

Family

ID=31642710

Family Applications (1)

Application Number Title Priority Date Filing Date
JP1990093319U Expired - Lifetime JPH0525262Y2 (en) 1990-09-05 1990-09-05

Country Status (1)

Country Link
JP (1) JPH0525262Y2 (en)

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5348614A (en) * 1976-10-15 1978-05-02 Toshiba Corp Differentiating device for picture quality control kcircuit
JPS5356985A (en) * 1976-11-02 1978-05-23 Fujitsu Ltd Light emitting element driving circuit

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5348614A (en) * 1976-10-15 1978-05-02 Toshiba Corp Differentiating device for picture quality control kcircuit
JPS5356985A (en) * 1976-11-02 1978-05-23 Fujitsu Ltd Light emitting element driving circuit

Also Published As

Publication number Publication date
JPH0345674U (en) 1991-04-26

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