Temperature Considerations

The MAX3263 output currents are programmed by cur-

so these changes largely cancel, resulting in output cur-

rents that are very stable with respect to temperature (see

Typical Operating Characteristics).

__________________Design Procedure

Interfacing Suggestions

Use high-frequency design techniques for the board

layout of the MAX3263 laser driver. Adding some damp-

ing resistance in series with the laser raises the load

impedance and helps reduce power consumption (see

Reducing Power Consumption section). Minimize any

series inductance to the laser, and place a bypass

capacitor as close to the laser’s anode as possible.

Power connections labeled VCCA are used to supply the

laser modulation and laser bias circuits. VCCB connec-

tions supply the bias-generator and automatic-power

control circuits. For optimum operation, isolate these sup-

plies from each other by independent bypass filtering.

GNDA and GNDB have multiple pins. Connect all pins

to optimize the MAX3263’s high-frequency perfor-

mance. Ground connections between signal lines

(VIN+, VIN-, OUT+, OUT-) improve the quality of the

signal path by reducing the impedance of the intercon-

nect. Multiple connections, in general, reduce induc-

tance in the signal path and improve the high-speed

signal quality. GND pins should be tied to the ground

plane with short runs and multiple vias. Avoid ground

loops, since they are a source of high-frequency inter-

ference.

The MAX3263 data inputs accept PECL input signals,

which require 50

shows alternative termination techniques. When a ter-

mination voltage is not available, use the Thevenin-

equivalent termination. When interfacing with a

non-PECL signal source, use one of the other alterna-

tive termination methods shown in Figure 4.

Bias Network Compensation

For best laser transmitter performance, add a filter to the

circuit. Most laser packages (TO-46 or DIL) have a sig-

nificant amount of package inductance (4nH to 20nH),

which limits their usable data rate. The MAX3263 OUT

pin has about 1pF of capacitance. These two parasitic

components can cause high-frequency ringing and

aberrations on the output signal.

If ringing is present on the transmitter output, try

adding a shunt RC filter to the laser cathode. This

limits the bandwidth of the transmitter to usable levels

and reduces ringing dramatically (Figure 5).

L = Laser inductance

C = Shunt filter capacitance

R = Shunt filter resistance

A good starting point is R = 25

Ω and C = L / 4R.

Increase C until aberrations are reduced.

The IBIASOUT pin has about 4pF of parasitic capaci-

tance. When operating at bias levels over 50mA, the

impedance of the bias output may be low enough to

decrease the rise time of the transmitter. If this occurs,

the impedance of the IBIASOUT pin can be increased by

adding a large inductor in series with the pin.

Reducing Power Consumption

The laser driver typically consumes 40mA of current for

internal functions. Typical load currents, such as 12mA of

modulation current and 20mA of bias current, bring the

total current requirement to 72mA. If this were dissipated

entirely in the laser driver, it would generate 360mW of

Single +5V, Fully Integrated,

155Mbps Laser Diode Driver

_______________________________________________________________________________________

7

Table 1. MAX3263 Truth Table

ENB-

ENB+

0

0

0

1

1

0

1

1

VREF

Off

On

Off

Off

ENB+

DATA OUT

(LOAD = 1300nm

LASER AT OUT-)

2

µs/div

Figure 3. Enable/Disable Operation