audio/videoZONE Products for the week of January 28, 2002
Analog Devices Says . . .
Analog Devices Delivers ADN2843 10.7 Gbps, 3.3 V Laser
Diode Driver With Dual-Loop Control For Fiber Optic Applications
New laser diode driver optimizes performance in direct-coupled
metro/access applications
Analog Devices, Inc., a global leader in high-performance semiconductors
for signal processing applications, announced the first 10.7 gigabit per
second (Gbps) Laser Diode Driver (LDD) with dual-loop control. The dual-loop
control of both average power and extinction ratio provides consistent optical
performance by compensating for temperature variations and aging effects
in the laser diode. Operating at a 3.3 V supply voltage, the ADN2843 also
augments the power, integration and cost advantages of directly-coupled
applications-those where the laser and laser driver are packaged together
for maximum space and power benefits, such as small form factor (SFF) modules-without
sacrificing driver performance.
"Together, our unique dual-loop architecture and proprietary driver topology enable designers to quickly and cost-effectively implement a high-performance solution at significant space and power savings," said Peter Real, product line director, High Speed Networking Group, Analog Devices. "These benefits are essential for the metro/access arena, especially for 10 GbE modules, where cost, size and power are at a premium, and an accelerated time-to-market is fundamental for success."
Dual Loop Control
The ADN2843 is the first OC-192/SDH-64 and 10 GbE-compatible laser diode
driver with closed loop control of both average power and extinction ratio.
The ADN2843 actively maintains consistent laser diode performance by continuously
sensing the optical output and correcting it for variations caused by changes
in operating temperature and laser diode degradation. Overall transmitter
performance is improved with reduced design time, board real-estate, component
and manufacturing cost. This feature is especially important in uncooled
applications, and those that require long-term stability and reliability.
Direct-Coupling at 3.3 Volts
The ADN2843 is optimized for applications where a laser driver and laser
diode are co-packaged. The ADN2843 couples directly to the laser diode,
providing the benefits of decreased cost, size, and power while significantly
reducing pattern-dependent jitter that occurs in standard ac-coupled designs.
The proprietary driver topology of the ADN2843 offers the added benefit
of operation from a 3.3 V power supply while maintaining key driver parameters
such as high-modulation current. The ADN2843 features modulation and bias
currents of up to 80 mA. Additional capabilities include laser fail and
degrade alarms, automatic laser shutdown (ALS), bias current monitors and
modulation current monitors.
analogZone Says . . .
The story of the ADN2843 is speed: The first 10.7-GBit/s laser diode driver. It is actually two devices; the ADN2844 Control IC provides the bias and modulation controls to the ADN2845 driver. Optimally, both parts would be used in die format -- to optimize layout -- but the ADN2844 is also available in a LFCSP-32 (with an exposed paddle.)
The 3.3-V chipset can provide a laser bias current from 3 to 80 mA, and a modulation current range from 5 to 80 mA. An external monitoring photo-diode measures the laser diode's output and feeds a current back to the control IC in a range from 50 to 1100 uA, giving a closed-loop control of both the average optical power and the extinction ratio. A second monitoring photo-diode can be added for wavelength control. That on-board control of power and extinction ratio reduces the external component count to three preset pots (power set, extinction ratio set, and alarm level set), a handful of capacitors and an inductor.
A laser degrade alarm is provided to indicate a pending failure, and a laser full-fail alarm is also provided. There is also an automatic laser shutdown applied from the control chip to the driver. Data terminations are made on-chip. The total supply current of the two parts is a typical 80 mA.
The ADN2843 will gain easy acceptance in OC-192 and 10-Gbit Ethernet, especially in small form-factor modules, and particularly from designers who have used earlier devices in the family while they were working on slower systems.
The ADN2843 is in production and is priced at $130.00 in 1000-piece lots