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Laser Control Circuit

IP.com Disclosure Number: IPCOM000119215D
Original Publication Date: 1991-Jan-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 2 page(s) / 62K

Publishing Venue

IBM

Related People

Bletscher, WL: AUTHOR [+4]

Abstract

A laser control circuit is shown for providing multiple levels of drive current to a diode laser in the grounded cathode configuration. It is preferred that a photodiode PIN receive light from the laser for controlling the laser current. Switching circuits are shown for switching between the two levels with the laser control being both feedforward and feedback.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 60% of the total text.

Laser Control Circuit

      A laser control circuit is shown for providing multiple
levels of drive current to a diode laser in the grounded cathode
configuration.  It is preferred that a photodiode PIN receive light
from the laser for controlling the laser current.  Switching circuits
are shown for switching between the two levels with the laser control
being both feedforward and feedback.

      The diode laser has its anode connected to a current diversion
circuit which diverts current from a voltage regulator (VR) which
supplies normal current to the laser. The anode of the photodiode PIN
supplies its received current to a read laser control circuit
(operational amplifier which has filter circuits associated
therewith) which, in turn, controls VR as calibrated by the
adjustable resistor Ar during read operation.  The data differential
amplifier is switched such that no current flows from the laser diode
to the write NPN tran sistor.  The write NPN transistor is also
turned off.  This means that the electrical current controlling the
laser drive current flows through the reference transistor controlled
by the reference voltage (VR) to the read current source (RCS).  The
current determines a control voltage to the write laser control
amplifier which is adjusted by the adjustable resistor CAL.  The
output of the write laser control goes to the input of VR accordingly
during read operation.  Not only is the output of the photodiode PIN
supplied to the voltag...