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Laser Diode Control Circuits

IP.com Disclosure Number: IPCOM000039515D
Original Publication Date: 1987-Jun-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 2 page(s) / 47K

Publishing Venue

IBM

Related People

Benedict, MK: AUTHOR [+2]

Abstract

Laser diodes are controlled for multiple power levels of emitted radiation. These circuits provide rapid transitions between power levels. Two versions of the circuit are shown, one being an all-NPN version. The first version shows a laser in the grounded cathode configuration. A set of reference diodes in the grounded anode configuration provides a reference voltage to the laser control circuit. PIN (photo diodes) can replace the reference diodes, as is well known. In the laser control, transistor Q4 transfers the laser diode's current to a current source of any design. When transistor Q3 is activated to the current conduction state, transistor Q4 is forced to the current non- conduction state. As a result, laser diode is driven by a write data amplitude current through source Q5 .

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Laser Diode Control Circuits

Laser diodes are controlled for multiple power levels of emitted radiation. These circuits provide rapid transitions between power levels. Two versions of the circuit are shown, one being an all-NPN version. The first version shows a laser in the grounded cathode configuration. A set of reference diodes in the grounded anode configuration provides a reference voltage to the laser control circuit. PIN (photo diodes) can replace the reference diodes, as is well known. In the laser control, transistor Q4 transfers the laser diode's current to a current source of any design. When transistor Q3 is activated to the current conduction state, transistor Q4 is forced to the current non- conduction state. As a result, laser diode is driven by a write data amplitude current through source Q5 . Switching Q3 to the current non- conduction state switches the laser current to the read back or lower value since Q4 diverts some of the Q5 current to the current source. The reference diodes are connected between plus voltage (+V) and ground reference potential. A separate read and write current control circuit are provided for controlling the laser's diodes. Again, the reference diodes may be photo diodes as is well known. The NPN version can be extendable to more than two current levels. DAC 1 and DAC 2 (digital-to-analog converters), respectively, provide reference current levels for read and write current through the differential actions of a differe...