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Optical Receiver Balancing Circuit

IP.com Disclosure Number: IPCOM000112601D
Original Publication Date: 1994-Jun-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 4 page(s) / 131K

Publishing Venue

IBM

Related People

Murfet, P: AUTHOR [+2]

Abstract

Disclosed is a transmission line optical balancing circuit which is applied to the receiving circuit that translates an optical signal to an electrical signal and removes not only timing distortion of the receiving circuit but also distortion that may have occurred further up the line. The circuit could be used with a standard copper link to extend range or for repeater technology.

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This is the abbreviated version, containing approximately 48% of the total text.

Optical Receiver Balancing Circuit

      Disclosed is a transmission line optical balancing circuit
which is applied to the receiving circuit that translates an optical
signal to an electrical signal and removes not only timing distortion
of the receiving circuit but also distortion that may have occurred
further up the line.  The circuit could be used with a standard
copper link to extend range or for repeater technology.

      With high speed serial links such as SSA, the ability to decode
the electrical signal on the link back into data is often close to
the limit of technology.  Extending the range of a link is often
impossible without introducing some specialized extender technology.
One such often chosen is the fiber-optical link which involves
turning on and off a light source under the control of a serialized
logic signal, and at the far end of the fiber, converting and
deserializing it via some photo-sensitive device and electronics.
Unfortunately, such a system can distort the serialized signal
unacceptably, mainly because of differences in various turn-on and
turn-off times along the path which can accumulate to degrade the
original time shape of the signal.  Described is how this new circuit
causes the time shape of a distorted logical signal to be restored
when a DC balanced code such as the SSA code is used.  The following
description is for a fiber-optic link, but the method is relevant to
any media such as copper or modulated carrier.

      A serial optical link can be designed such that an electrical
logic signal can be translated by a photo-transmitter into a
two-level light signal (bright and dim).  The light signal is
transmitted down an optical fiber and detected by a photo-receiver
and electronics.  Change in timing of the electrical and optical
transitions will affect the ability of the link to transfer
error-free data.

      Refer to Fig. 1 which is a block diagram of an optical link.
The "source" system output "A" is some point where the data has been
serialised.  The "driver electronics" takes this signal and processes
it so that it can drive the photo-transmitter device.  At this point
the signal "B" has become single-ended.  The output of the
"transmitter" is a light signal "C", and this comes out of the
optical fiber as signal "D".  The optical signal is detected by the
photo "receiver" as signal "E" which is amplified and converted by
the "receiver electronics" to signal "F" which is delivered to the
"target" system.  Signal "G" is a signal within the receiver
electronics that is operated upon to restore the DC "balance" of the
output signal "F".  Standard optical links do not have the "balancer"
block.  This invention deals with this added block.

      The distorting effect that deteriorates the time shape of the
signal is the difference between the turn-on and turn-off time of a
particular block.  The rise times and fall times of the signals are
unimportant, providing that...