Electronic Design

Laser-Diode Driver Supports Multiple Standards

A single laser-diode driver from Elantec Semiconductor directly drives both CD and DVD lasers, simplifying the task of combining these optical drives in a single system. Elantec's patented EL629XC series of highly integrated laser-diode drivers supports multistandard writable optical drives, including CD-R, CD-RW, DVD-R, DVD-RW, DVD-RAM, DVD+R, and DVD+RW.

To accomplish this, the driver's timing generator permits the programming of diode currents and laser-timing details prior to operation. Also, unlike previous designs based on a parallel format, the EL629XC driver uses a serial data and control format.

"This architecture eliminates all timing noise and significantly increases accuracy of recording, and speed as well," says Steve Sacarisen, Elantec's director of marketing for optical products. "Plus, the serial interface reduces the total number of signal lines needed to send timing and current values generated by the write-pattern generator."

The laser driver implements a programmable state machine to generate the timing waveform that feeds an 8- by 8-bit multiplying-output digital-to-analog converter (DAC). The output DAC in turn produces the requisite amplitude to directly drive the laser. The state machine reviews the NRZ serial data, which provides the write timing and amplitude information. Using this serial input, it sets all the power levels for the type of formats to be recorded. The on-chip ROM, in conjunction with the state machine, contains all the write strategy timing data. A built-in phase-locked loop (PLL) reduces the external clock required. Maximum output is 200 mA, while the timer resolution is 0.17 ns.

The EL6291C is the first member of this family, which comes in 32-pin LPP and QFN packages for improved thermal performance and reduced footprint. It requires 3.3- and 5-V supplies. In 10,000-unit lots, it costs $4.00 each. Other members of this family include the EL6293C, a programmable dual CD/DVD writer with a built-in sample-and-hold circuit for automatic power control, and the EL6296C, which comes in a 24-pin LPP package.

Elantec Semiconductor, 675 Trade Zone Blvd., Milpitas, CA 95035; (408) 945-1323; www.elantec.com.

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