A laser power monitor circuit for monitoring the power of a laser used in a magneto-optical disk device and other related devices. In order to provide marks in the recording medium, a write power of the laser is required, and in between the marks, the laser is to have a pedestal power. During recording on the magneto-optical disk, recording corrections are performed at the start of the pedestal power and write power of the laser to provide marks in the recording medium which are properly shaped. The laser power monitor circuit accurately monitors the power of the laser light on a recording medium and includes a reverse correction circuit to provide reverse correction of the recording corrected values among the monitored values of laser power to bring the laser to the appropriate write power or pedestal power.
Provided are a source follower circuit having a current source having its improved current characteristics, laser driving apparatus, semiconductor laser apparatus, current-voltage conversion circuit, and light receiving circuit. Each of the laser driving apparatus, semiconductor laser apparatus, current-voltage conversion circuit, and light receiving circuit comprises the source follower circuit. The source follower circuit 10 comprises a source follower stage 12 and a bias stage 14. The source follower stage has III-V compound semiconductor transistors 16, 18 and 20. The bias stage 14 has a first node 22 for providing a first bias voltage and a second node 24 for providing a second biasing voltage different from the first biasing voltage. The gate of transistor 16 is coupled to input 26 and a source thereof is coupled to output 28. The gate of transistor 18 is connected to the second node 24. The gate of transistor 20 is connected to the first node 24. The transistor 20 is arranged between the source of the transistor 16 and the drain of the transistor 18.
There is provided a semiconductor laser driving circuit. The circuit has: an amplifier for receiving an emission level setting voltage, and outputting a first driving signal on the basis of the emission level setting voltage; a driving signal generation circuit for receiving a control signal for instructing a light-emission period of a semiconductor laser, and the first driving signal output from said amplifier, and outputting a second driving signal corresponding to a level of the first driving signal in accordance with a light-emission or extinction period; a driving circuit for receiving the second driving signal output from said driving signal generation circuit, and generating and outputting a driving current to be supplied to the semiconductor laser; and a control circuit for receiving the emission level setting voltage, and adjusting a level of the second driving signal during the extinction period in correspondence with the emission level setting voltage.
Optical pick-up units and laser drivers are disclosed, which can be used in various types of information recording/reproducing apparatuses, such as, but not limited to, DVD and CD drives, DVD camcorders, and DVD video recorders. A laser driver integrated circuit (LDIC) includes an automatic power controller, a running optical power controller, and a write strategy generator. The LDIC can be part of a chip-set, to be located on an optical pick-up unit (OPU). The chip-set can also include a power monitor integrated circuit (PMIC) to monitor the laser diode, and a photo-detector integrated circuit (PDIC) to detect light produced by the laser diode. The PMIC and the PDIC each include their own offset, gain and sample-and-hold circuitry.
