12

VOICE

It’s been five years since I first

started designing laser driver ICs,

and by now I have a good idea of

what is required in laser driver ICs.

I strongly recommend that you

look into the CXA2680ER, which

was developed based on this ac-

cumulated know-how.

Five-Channel Dual CD/DVD Laser Driver for Ultra Combo Drives

CXA2680ER

Sony developed the CXA2680ER as a dedicated laser driver

IC that increases the number of channels to five to support

increased bit depth recording strategies. The CXA2680ER

also adds a DVD modulator amplitude switching function

to the CXA2640ER for use in dual drive systems and fea-

tures high linear velocity to follow the actuators used in

conventional CD-R/RW drives.

I

CD system total maximum drive current: 370 mA

I

DVD system total maximum drive current: 320 mA

I

Rise/fall time: 1 ns

I

Support for strategy in all 5 channels

I

Read channel low noise: 1.5 nA/

√Hz

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High-frequency modulator frequency accuracy:

<

±10%

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Built-in DVD modulator amplitude switching func-

tion

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Support for a variety of timing signals

Achieving both Higher

Output and Higher Speed

While both an increased output transient

waveform speed and an increased maxi-

mum output drive current are required to

achieve increased linear velocities,

increasing the maximum output drive

current required increasing the size of the

output transistors. However, increasing the

size of the output transistors leads to

delays in the output transient waveform.

Despite this tradeoff relationship, the

CXA2680ER achieves both of the follow-

ing output current performance levels.

• CD system total maximum drive current:

370 mA (figure 1)

°C)

• DVD system total maximum drive

current: 320 mA (figure 2)

°C)

Thus this device can supply the required

maximum output drive current even

under severe operating conditions for both

CD and DVD. Furthermore, in the

CXA2680ER, Sony optimized the output

transient waveforms to have both higher

speed and a minimal amount of overshoot

by including a built-in waveform shaping

circuit. This allows this device to support

×8-speed DVD recording.

Read Channel Low Noise

Sony’s painstaking low-noise design

efforts to achieve the signal-to-noise

ratio required for higher linear speeds

achieved a noise level of 1.5 nA/

√Hz (at

20 MHz, 35 mA, 20 mA p-p).

High-Frequency Modulator

Frequency Accuracy

In high-frequency modulator, which is

used to reduce noise during playback,

interference between the return light from

the disc and the laser beam due to varia-

tions in frequency causes noise to be

aggravated. The CXA2680ER cancels

frequency variations depending on the

internal resistance caused by VCO that has

the emitter junction multivibrator, thus

allowing noise to reduce.

DVD System Modulator

Amplitude Switching

Function

This function allows applications to set a

modulator amplitude value that is

optimal for the DVD media used.

Support for a Variety of

Timing Signals

The CXA2680ER provides both differen-

tial inputs (LVDS/LVPECL) for higher

speeds and single-ended inputs (3.3 V

CMOS/TTL).

Small Package with Improved

Heat Dissipation

The CXA2680ER is provided in a 32-pin

VQFN (4.8

× 4.8 mm) miniature package

that can contribute to pickup miniaturiza-

tion through reductions in the mounting

area.

Not only is the package size noteworthy,

but this package can also increase the

efficiency with which heat is dissipated,

since it allows the heat sink to be con-

nected with silicon grease to the die pads,

which are exposed at the package surface.

Since this prevents heat from escaping

through the PWB to the laser diode, PWBs

using this device are easy on the laser

diode. This also allows the IC to be con-

nected at the rear surface.