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Encoding Data for Transmissions Over Link with Limited Low Frequency Bandwidth

IP.com Disclosure Number: IPCOM000113822D
Original Publication Date: 1994-Oct-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 59K

Publishing Venue

IBM

Related People

Newman, EL: AUTHOR

Abstract

Low frequency bandwidth often limits the effectiveness of a link in transmitting data, for example digital data having a DC component. Encoding such data into a series of impulses can reduce this problem, and is particularly effective when used with fibre optical communication links.

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This is the abbreviated version, containing approximately 74% of the total text.

Encoding Data for Transmissions Over Link with Limited Low Frequency
Bandwidth

      Low frequency bandwidth often limits the effectiveness of a
link in transmitting data, for example digital data having a DC
component.  Encoding such data into a series of impulses can reduce
this problem, and is particularly effective when used with fibre
optical communication links.

      The basic arrangement is shown in Fig. 1.  Input digital data 1
is encoded into a series of impulses 2 in a differentiator/rectifier
3.  The impulses are transmitted into the transmission medium by a
transmitting device 4, which, for an optical fibre medium, will
typically be a laser diode.

      The impulses are received by a receiving device 5, typically a
PIN diode for an optical fibre system, and converted into digital
data 7 in an integrator/switch circuit 6.

      Details are shown in Fig. 2, with associated waveforms.  A
differentiating amplifier 8 has both non-inverting and inverting
outputs connected to drive the laser diode 4.  The resulting impulses
are received by the PIN diode 5, the output of which is amplified,
applied to a filter 9 to remove noise and after shaping by a logic
shaper applied to a divide by two circuit to produce the output data.

      Such a system is adequate where the digital data is not sign
sensitive.  The system may be adapted to deal with sign sensitive
data by amplitude modulating the impulses, for example by causing
positive transition...