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High-Speed Modulator with Variable Pre-Drive for Multi-Gbit/s Fiber-Optic Links

IP.com Disclosure Number: IPCOM000108874D
Original Publication Date: 1992-Jun-01
Included in the Prior Art Database: 2005-Mar-23
Document File: 1 page(s) / 45K

Publishing Venue

IBM

Related People

Nicoletta, C: AUTHOR [+2]

Abstract

This article describes a high-speed modulator with variable pre-drive and sub-nanosecond current pulses for multi-Gbit/s fiber-optic links.

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High-Speed Modulator with Variable Pre-Drive for Multi-Gbit/s Fiber-Optic Links

      This article describes a high-speed modulator with variable
pre-drive and sub-nanosecond current pulses for multi-Gbit/s
fiber-optic links.

      The detailed circuit is shown in the figure.  The modulation
section uses emitter degeneration, Re, and the pre-drive stage is
shown.  The differential output levels, nodes 3 and 4, are
proportional to the current in Q5, which tracks the current in Q6 and
Q7.  This variable drive scheme provides adequate drive to Q3 and Q4
when large modulation currents are needed, while preventing Q3 and Q4
from being overdriven.  This provides optimal pulse fidelity to
control the laser light output.

      The presence of the emitter degeneration resistance (Re)
significantly extends the linear range of Q3 and Q4. This allows the
differential stage to behave linearly for a wider range of
differential input signals, providing consistent rise and fall times
over the 1-to-32 milli amp current range.

      The advantages:
.    Variable pre-drive to accommodate a wide range of modulation
current (1:32 mA).
.    Optimum variable pre-drive for producing good fidelity pulses.
.    Simple design allows multi Gbit/sec operation.
.    Implementable using standard high-speed bipolar process.

      Disclosed anonymously.