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Fujitsu Develops 4:1 Multiplexer Circuit for 43 Gbps Optic Communications Systems
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Fujitsu Laboratories Ltd

Fujitsu Develops 4:1 Multiplexer Circuit for 43 Gbps Optic
Communications Systems

Tokyo, February 7, 2002 -- Fujitsu Laboratories Ltd. today announced that it has succeeded in developing a four-to-one multiplexer integrated circuit that will enable 43 Gbps communications over optical fiber links. The new circuit is expected to become a key component in wavelength division multiplexing optical communications systems operating at 40 Gbps, which are near the stage of implementation. This technology was presented in greater detail this month at the ISSCC2002 (2002 IEEE International Solid-State Circuits Conference).

The explosive growth of the Internet has sparked research and development worldwide in high-speed, high-capacity communications systems operating at terabit-grade speeds, particularly in such technologies as wavelength division multiplexing and dense wavelength division multiplexing*1. Once signal transmission speeds reach the 40Gbps level, however, transmitted pulse waveforms deteriorate due to losses of interconnections within the circuit. To solve this problem, a waveform retiming circuit is usually employed at the final output stage. Since the conventional retiming circuit provides only a fixed timing margin between the clock and data signal, it is very difficult to adapt to the timing drift-and the resultant transfer-rate variation-caused by temperature and supply-voltage fluctuations. There has been, therefore, a pressing need for a multiplexing circuit that includes a waveform retiming circuit that can be adjusted relative to the clock when operating at transmission speeds as high as 40 Gbps.

About the Technology
The new 43 Gbps 4:1 multiplexer is an ultra high-speed circuit that employs 0.13 µm InP-HEMT*2 technology and includes a retiming function, enabling it to operate at its full rate clock speed. Noteworthy features include:
  1. A waveform retiming circuit with flip-flop architecture built into the final stage of the multiplexing unit to improve signal quality.
    Using falling-edges of the 43 GHz clock, the waveform retiming circuit*3 is built into the final stage of the multiplexing unit to restore the multiplexed data signal. This feature completely eliminates all jitters in the data signal to improve signal quality.
  2. Integration of a phase shifter with basic functionality.
    The integration of a phase shifter*4 with simplified circuit architecture yields four times the previous operating margin, and also realizes enhanced tolerance and stability to withstand fluctuations in temperatures or power-supply voltages.
In addition, the circuit incorporates transistors and interconnections allocation technology to minimize signal interference, and uses microwave and millimeter-wave technology to obtain high gains for the internal amplifier.

These technologies combine to create a circuit that further enhances the signal quality of 43 Gbps signal processing as well as prevents performance loss caused by temperature and voltage deviations between the clock and data timing, enabling a four-fold improvement in the operating margin.

*1: Wavelength division multiplexing, dense wavelength division multiplexing
This is a multiplexing technique that allows multiple optic signals to be carried over one fiber-optic cable by changing the wavelength of the carrier waves. Using light beams with good properties-wavelengths that don't interfere with one another-permits many such beams to be multiplexed together and vastly more data to be carried over the fiber-optic cable. The number of waves that can be multiplexed together this way has recently reached 40; this process is known as dense wave-division multiplexing.
*2: High electron-mobility transistor (HEMT)
HEMTs are field-effect transistors that take advantage of the fact that electrons created from the hetero-interface of different kinds of semiconductor material (such as GaAs and AlGaAs) operate at higher speeds than those within conventional silicon (Si) semiconductors. Fujitsu pioneered the development of these devices in 1980, and today they are used in nearly all satellite transceivers.
*3: Waveform retiming circuit
A circuit that restores a signal's degraded waveform to a high quality waveform, designed using a flip-flop architecture.
*4: Phase shifter
An electronic circuit that alters a signal's phase in line with an external voltage or current.

Trademark notice
All product names and proper names mentioned in this document are trademarks or registered trademarks of their respective firms.

About Fujitsu Laboratories Ltd.
Founded in 1968 as a wholly owned subsidiary of Fujitsu Limited, Fujitsu Laboratories Limited is one of the premier research centers in the world. With a global network of laboratories in Japan, China, the United States and Europe, the organization conducts a wide range of basic and applied research in the areas of Multimedia, Personal Systems, Networks, Peripherals, Advanced Materials and Electronic Devices. Internet:
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[Press Contacts]
Minoru Sekiguchi, Nancy Ikehara
Fujitsu Limited, Public Relations
Tel: +81-3-3215-5259 (Tokyo)
Fax: +81-3-3216-9365
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[Technical Contact:]
Fujitsu Laboratories
High-Speed Devices Division, G-Project Department
Tel: +81-46-250-8244 (Kawasaki)

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