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Optical Detector Circuit

IP.com Disclosure Number: IPCOM000118423D
Original Publication Date: 1997-Feb-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 2 page(s) / 59K

Publishing Venue

IBM

Related People

Kijanski, R: AUTHOR

Abstract

In data communication channels using optical fibers, a linear transimpedance amplifier is typically incorporated with a Positive, Intrinsic, Negative (PIN) diode to convert the optical power into an electrical signal for further processing. The circuit described obviates the use of a closed loop amplifier with feedback, so eliminating problems such as possible instability, bandwidth limitations, and output slew rates.

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Optical Detector Circuit

      In data communication channels using optical fibers, a linear
transimpedance amplifier is typically incorporated with a Positive,
Intrinsic, Negative (PIN) diode to convert the optical power into an
electrical signal for further processing.  The circuit described
obviates the use of a closed loop amplifier with feedback, so
eliminating problems  such as possible instability, bandwidth
limitations, and output slew rates.

      The circuit is designed for operation at a data transfer rate
of 100 Mhz using 62.5/125 micron optical fiber and a PIN diode with a
wavelength of nominally 1310 nanometers.  Optical power in the fiber
is designed to be typically 1.4 milliwatt (1.461 dBm).

      TU9-2 and TU9-4 form a current switch pair with R39 and R40
providing the output loads.  R5 and C7 are used to provide the pseudo
supply needed by subsequent stages.  The current source transistor,
U9-12, is controlled by a bandgap voltage reference, U5, and
transistor U9-9 provides temperature tracking.  R36 defines the
current available  for the current switch pair.  U2-5 generates a DC
logic low output when  optical power is present in the fiber.

Principle of Operation

      PIN diode sensitivity selected for this design is nominally
0.9A/Watt.  With 1.4 mW of power in the fiber, the light current as
defined by the PIN will be 1.26 mA.  The dark current is specified to
be less than 1 nA.  An important aspect of this design is the
c...