A CMOS 1×-16× speed DVD write channel IC

Optical recording demands a meticulous write strategy to control the laser beam power and regulate the phase change layer temperature tightly. The width, height, and delay of a string of short pulses applied to the laser diode need to be adjusted in fine steps, and the writing speed varies widely per applications. A multi-phase phase-locked loop (PLL) tracks a wide range of clock frequencies, and provides a low-jitter time base for write pulses. With two enabling circuit concepts, PLL loop filter voltage folding/unfolding and switch-in of parallel MOS resistors in delay cells, it is possible to operate a PLL to cover a frequency range spanning over three octaves with one VCO. A 10-stage differential VCO is phase-locked to the input channel clock ranging from 26 to 420 MHz (1×-16× DVD speed), and its 20-phase outputs are used to generate write pulses. The pulsewidth and delay are programmed with 120 ± 40 ps time resolution. The prototype chip fabricated in 0.35 μm CMOS occupies 3.5×3.3 mm², and consumes 294 mW at 3.3 V.