| 摘要 |
A problem with the known laser driving circuit is that the laser driving circuit needs a relatively high operating voltage. This problem becomes more severe in the current type of lasers such as DVD or Blu-Ray type of lasers. Therefore, it is an object of the invention to provide a laser diode circuit that is able to drive a laser diode with a relatively low operating voltage. This object is achieved according to the invention with a laser diode circuit comprising a laser diode having an anode and a cathode, and a laser current driver for controlling a current through the laser diode, the laser current driver comprising a current sinking element, characterized in that the anode of the laser diode is connected to a laser supply voltage which is positive with respect to ground, and in that the cathode of the laser diode is connected to the current sinking element, and wherein the current through the laser diode is controllable by the current sinking element. The laser current driver in the laser diode circuit according to the invention only "sees" the voltage at the bottom of the cathode of the laser diode instead of seeing the full laser supply voltage. The highest voltage placed on the laser current driver is the laser supply voltage minus the voltage drop over the laser which varies between the threshold voltage and the operating voltage. Hence, the voltage on the laser current driver lies between the laser supply voltage minus the laser threshold voltage and the laser supply voltage minus the laser operating voltage. Thus, the laser current driver can be made with the lower voltage type of technology which has several advantages. For instance, the power dissipation is reduced. This is due to the fact that internal circuitry and particularly logic can be designed for and run off lower voltages than in the prior art systems. |
