Single +5V, Fully Integrated,
155Mbps Laser Diode Driver
MAX3263
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 50Ω termination to (V
CC
- 2V). Figure 4
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.
ENB+
DATA OUT
(LOAD = 1300nm
LASER AT OUT-)
2µs/div
Figure 3. Enable/Disable Operation
Table 1. MAX3263 Truth Table
ENB-
0
0
1
1
ENB+
0
1
0
1
VREF
Off
On
Off
Off
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 = 25Ω 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.
Temperature Considerations
The MAX3263 output currents are programmed by cur-
rent mirrors. These mirrors each have a 2V
BE
temperature
coefficient. The reference voltage (V
REF
) is adjusted 2V
BE
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
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
7
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