Renesas Technology

EDGE

Optical disk drive manufacturers want new models to read and write at higher speeds and densities, so they require a driver IC for the laser diode that delivers both a fast through-rate and great precision. To meet this need, Renesas has introduced the M64030FP, a laser diode driver for use in optical pickups for Blu-ray Disks (BDs). The IC drives a blue-violet laser diode and has a new waveform-correction function that enables a high through-rate: 0.8ns or less. Using an internal write-strategy circuit, it achieves high-precision writing.

Through-rate is about 50 percent better than previous Renesas drivers, for stable writing performance

Blu-ray Disks (BDs) illustrate the trend to optical disk drives that can read and write at higher speeds while storing more data. The BD standard specifies a storage capacity of 25GB on single-layer disks, or 50GB on dual-layer disks. The characteristics of the 405nm wavelength blue-violet lasers used in such high-density disks make it more difficult to achieve the required through-rate (the time required for the waveform to rise or fall) than is the case for infrared lasers and red lasers with a wavelength of 780nm. This makes it very hard to increase the speed and precision of the drive.

To solve this problem, Renesas has applied the high withstand voltage technology and high-speed circuit capability accumulated over many years to produce the M64030FP. This laser diode driver for BD drives significantly improves the through-rate of blue-violet laser diodes and has a high drive capacity for handling future double-speed and double-layer disks. The driver incorporates a newly developed waveform-correction function that improves the through-rate to 0.8ns or less, based on Renesas test results. Compared to the performance of previous Renesas models without a waveform correction function, this through-rate is about 50 percent better, for stable writing performance.

A feature of the waveform-correction function is that it permits the through-rate to be controlled flexibly via a serial interface. This makes it relatively easy for engineers to implement methods for suppressing two optical-waveform problems that previously have challenged the development of optical pickups for BD drives:

Waveform overshoot — the waveform temporarily goes past the target level on the rising or falling edge of a pulse. Overshoot causes excessive heating to occur in a specific region. That, in turn, causes a loss of writing precision and deterioration of the write endurance for rewritable disks.

Ringing — a short-duration oscillation in a region of the waveform where a sharp change occurs, such as on the rising or falling edge of a pulse. Like overshoot, ringing causes a loss of write precision.

Multiple functions contribute to high-precision operation

The M64030FP supports a 132MHz data clock and delivers a maximum output current of 350mA. Moreover, it is designed to enable the use of higher speeds and densities in the future. This sophisticated device provides the following function elements for reading and writing:

A high-frequency current-superposition circuit that reduces laser noise during reading in the optical pickups used with single-mode lasers that read BD, DVD, MD, and CD-RW media. This circuit can generate a current output with a frequency of 250MHz to 500MHz for writing.

An automatic power control (APC) driver that compensates for variations in the relationship between the drive current and output power of the laser diode caused by factors such as temperature and time. The APC driver uses feedback to adjust for these changes, ensuring that the output power remains constant. It supplies a stable laser drive current based on the signal from the analog front end IC.

A 32-phase write-strategy function that supports double-speed 132MHz operation for high-precision writing. Because heat is used for recording, this function improves the ability to store a signal on the disk by using multi-pulse modulation of the laser output. Specifically, five drive signals are generated within the M64030FP based on a single input signal. This eliminates need to synchronize input signal delays during system design and saves design time.
(By contrast, a laser diode driver without a write-strategy function mandates that the five pulse currents be output by five drivers in the IC, each of which must be controlled by a signal external to the IC. This complicates system design, due to the need to allow for the delay that occurs in the circuit board for each signal.)

The high-speed laser driver circuit required for accurate writing using the high-precision/high-speed write-strategy waveform. The improved write precision the device achieves is another benefit that helps shorten the development time of optical disk drives.

Other functions that simplify system design, including an input data-compensation function and a superposition amplitude-compensation circuit.

Small package offers good heat dissipation capability

To aid mechanical design and ease system packaging tasks, the M64030FP blue-violet laser diode driver is supplied in a small (5mm x 5mm) 28-pin leadless QFN package with good heat dissipation efficiency. Renesas plans to continue to respond to market needs by developing advanced products that deliver even higher precision and can control yet faster laser diodes.

For more information on this laser diode driver, please contact sales personnel at Renesas. Note that the datasheet and other specification documents for the M64030FP include information from the BD Rewritable Standard, which is published by the Blu-ray Disc Association (BDA). Therefore, Renesas can only supply specifications to customers that have entered into the Blu-ray Disc Information Agreement and have obtained a Blu-ray Disc Rewritable License.

M64030FP Specifications

Item	Specification	Remarks
Name	M64030FP
Power supply voltage	2.5V ± 0.25V, 5V ± 0.5V, 7V to 9V	The 7V to 9V power supply is for the anode voltage of the laser diode and for withstand voltage protection for the laser diode connection terminal.
Supported laser types	Floating type	Connect the laser's cathode to the driver and the anode to the power supply.
Maximum write strategies - Operating frequency - Through-rate	150MHz0.8ns or less (based on Renesas testing)
Laser diode drive current	Write: 200mA, max. Servo: 150mA, max.
Package	28-pin QFN 5mm x 5mm	High-heat-dissipation, leadless package

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