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Fibre Optic Receiver

IP.com Disclosure Number: IPCOM000113848D
Original Publication Date: 1994-Oct-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 44K

Publishing Venue

IBM

Related People

Newman, EL: AUTHOR

Abstract

In a typical fibre optic receiver, the current from a photo diode is converted to a voltage by a transimpedance amplifier. The voltage is conditioned and then processed by a decoder to recover the original transmitted data. If a link detection indication is required, this is derived from the transimpedance amplifier output levels, perhaps in conjunction with detected timing information. In high speed data links, these signals are often small and distorted. The receiver is usually optimised for data recovery and link detectors based on the data path transimpedance amplifier often do not perform well.

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Fibre Optic Receiver

      In a typical fibre optic receiver, the current from a photo
diode is converted to a voltage by a transimpedance amplifier.  The
voltage is conditioned and then processed by a decoder to recover the
original transmitted data.  If a link detection indication is
required, this is derived from the transimpedance amplifier output
levels, perhaps in conjunction with detected timing information.  In
high speed data links, these signals are often small and distorted.
The receiver is usually optimised for data recovery and link
detectors based on the data path transimpedance amplifier often do
not perform well.

      Fig. 1 shows an improved receiver in which both terminals of
the photo diode are connected to active circuitry.  One terminal of
the diode is connected to a conventional receiver, while the other
terminal is connected to a current comparator which is optimised to
detect average light level.  The comparator impedance Z2 is such that
it does not interfere with the transimpedance amplifier, yet the
voltage developed across the impedance will indicate the presence of
an optical connection to an active transmitter.

      The impedance Z2 could be a capacitor to the transimpedance
reference voltage and, if a voltage comparator is used, a resistance
to the comparator reference.  The capacitor is taken to the
transimpedance reference simply to avoid induced power supply noise
being falsely detected as data.  (Photo diode capacitan...