可视激光驱动器有数字控制功率调制-Visible-Laser

2011-04-21 22:30:43来源: 互联网
Many laser diodes include a photodiode that generates a current proportional to the intensity (optical power) of the laser beam. Most of these photodiodes, however, have relatively slow response times and cannot track the peak optical power of a typical modulated laser diode. Instead, the driver circuits for these devices control the laser by monitoring a relative average optical power.

The circuit in the figure below includes a 10-bit digital-to-analog converter (DAC) with 3-wire serial input that operates and maintains a visible-light laser diode at constant average optical output power. A separate digital input line (MOD) enables a comparator with open-drain output (IC4) to implement digital communications by pulsing the laser-diode through Q1. Circuit components were chosen to minimize the layout are and cost.


For Larger Image
This circuit provides digital control of the modulation and power output of a visible-light laser diode.

Resistor R6 converts the photodiode current to a usable voltage, which is applied to the inverting input of a "leaky" integrator based on the high-speed op amp IC3. The integrator smoothes out variations in the modulation and prevents the feedback loop from trying to regulate the laser pulses. The integrator is made leaky (by R10) to ensure compensation of downward as well as upward variations in the average power.

Thus, the integrator creates an error signal and base drive for Q1 by monitoring the voltage across R6 and comparing it to the DAC's preset voltage. The DAC's reference voltage (from IC1) is 2.5V, but its output-voltage buffer has a gain of 2V/V, giving the DAC output an adjustment range of 0 to 5V. With its nominal base voltage set by the DAC output, Q1 controls the optical power by regulating current through the laser diode.

R9 provides isolation and helps to stabilize IC3 when the base of Q1 is being shorted and released by a signal from the MOD input. By maintaining a small laser-diode current during the "off" periods of digital modulation, R1 preempts another problem: Startup time for a laser diode increases tremendously if the forward current goes to zero. R1 ensures that the laser current is below the threshold for lasing, but high enough to allow an acceptable turn-on time for communication and modulation.

A similar version of this article appeared in the March 23, 1998 issue of Electronic Design magazine.

关键字:可视  数字控制  功率

编辑:神话 引用地址:http://www.eeworld.com.cn/mndz/2011/0421/article_7462.html
本网站转载的所有的文章、图片、音频视频文件等资料的版权归版权所有人所有,本站采用的非本站原创文章及图片等内容无法一一联系确认版权者。如果本网所选内容的文章作者及编辑认为其作品不宜公开自由传播,或不应无偿使用,请及时通过电子邮件或电话通知我们,以迅速采取适当措施,避免给双方造成不必要的经济损失。
论坛活动 E手掌握
微信扫一扫加关注
论坛活动 E手掌握
芯片资讯 锐利解读
微信扫一扫加关注
芯片资讯 锐利解读
推荐阅读
全部
可视
数字控制
功率

小广播

独家专题更多

富士通铁电随机存储器FRAM主题展馆
富士通铁电随机存储器FRAM主题展馆
馆内包含了 纵览FRAM、独立FRAM存储器专区、FRAM内置LSI专区三大部分内容。 
走,跟Molex一起去看《中国电子消费品趋势》!
走,跟Molex一起去看《中国电子消费品趋势》!
 
带你走进LED王国——Microchip LED应用专题
带你走进LED王国——Microchip LED应用专题
 
电子工程世界版权所有 京ICP证060456号 京ICP备10001474号 电信业务审批[2006]字第258号函 京公海网安备110108001534 Copyright © 2005-2016 EEWORLD.com.cn, Inc. All rights reserved