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Differential Fiber-Optics Receiver

IP.com Disclosure Number: IPCOM000119338D
Original Publication Date: 1991-Jan-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 3 page(s) / 95K

Publishing Venue

IBM

Related People

Ippolito, PM: AUTHOR

Abstract

This article describes the operation of a differential fiber-optics receiver circuit. The purpose of this circuit is to amplify and convert the relatively weak electrical currents produced by a device known as a 'photo-diode' into electrical signals that are appropriate for interfacing to digital logic circuits. Electrically, this function is accomplished by a current-to-voltage converter and by subsequent stages which amplify the electrical signal to appropriate levels.

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This is the abbreviated version, containing approximately 52% of the total text.

Differential Fiber-Optics Receiver

      This article describes the operation of a differential
fiber-optics receiver circuit.  The purpose of this circuit is to
amplify and convert the relatively weak electrical currents produced
by a device known as a 'photo-diode' into electrical signals that are
appropriate for interfacing to digital logic circuits.  Electrically,
this function is accomplished by a current-to-voltage converter and
by subsequent stages which amplify the electrical signal to
appropriate levels.

      The figure shows a schematic of the circuit described. The
overall circuit is realized by the combination of five sub-stages:
      1)  the photodiode bias
      2)  gain stage 1
      3)  gain stage 2
      4)  gain stage 3
      5)  the DC feedback buffer

      A differential approach has been used in the design of gain
stages 1-3 and for the DC feedback buffer.  This approach has the
advantage of providing good gain characteristics while maintaining a
high degree of immunity to both power supply and EMF-induced noise.
Thus, the signal-to-noise ratio of the amplifier is optimized.
      The circuit operates as follows:

      The series combination of R1, R2, R3, and R4 establish the
electrical bias for photodiode PD1 from the voltage source Vpd.  The
value of Vpd is chosen so as to provide appropriate bias for PD1.  C1
and C2 are used to filter high frequency noise which may be present
at nodes Vpd or Gnd.

      The photo-current-generated PD1 is coupled into gain stage 1 by
C3 and C4.  Gain stage 1 is configured as a balanced transimpedance
amplifier with the transimpedance determined by the value of R7 and
R8.  C5 and C6 are used to tune the frequency response of gain stage
1.

      The output of gain stage 1 is amplified by gain stage 2 which
is configu...