Laser Diode Driver with Waveform Generator

The EL6938 is a highly integrated laser diode driver designed to support multi-standard writable optical drives. It accomplishes this by incorporating a waveform generator wherein the diode currents and timing details can be programmed before operation. The data input circuitry inspects the NRZ serial data waveform and generates programmed waveforms in recognition of 3, 4, 5, or 6 or more clock periods of space changing to 3, 4, 5, or 6 or more clock periods of mark, and vice versa.

The architecture allows reprogramming of the timers to support different media, Blue, DVD, or CD standards, and different speeds. The programming is accomplished through a serial interface port. Two outputs are provided to support dual-laser multi-standard optical heads. The clock and NRZ inputs can be either standard CMOS or LVDS, selectable through a program bit.

The EL6938 requires 2.5V and 5V supplies, with all the logical interface operating on the 2.5V supply.

Features

• Complete programmable laser diode driver

• 500mA maximum total output

• 10-bit x 10-bit multiplying DAC output provides 10-bit full

scale adjustment and 10-bit resolution at any full scale

output

• 54 psec timer resolution

• Two laser outputs allows read/write DVD and CD

combinations

• Programmable waveform values support CD-R, CD-RW,

DVD-RAM, DVD-R, DVD-RW, DVD+R, DVD+RW, and

Blue

• Two analog inputs support slope and read APC

• HFM oscillator programmable to 100mAP-P from 100MHz

to 500MHz

• PLL allows reduced-frequency clock on flex cable

• Separate serial input works up to 100MHz

• Programmable HFM offset when HFM is off

• Pb-free available

Applications

• Combination DVD writable and CD writable drives

• DVD camcorders

• DVD video recorders