MAX3273(2002) Просмотр технического описания (PDF) - Maxim Integrated

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производитель

MAX3273
(Rev.:2002)

+3.3V, 2.5Gbps Low-Power Laser Driver

Maxim Integrated 

+3.3V, 2.5Gbps Low-Power Laser Driver

LATCH

0

MUX

DATA

D

Q1

CLK

VCC

MAX3273

EN

x160

VBG

x190

VCC

LP1

OUT-

OUT+

IMOD

LP1

25Ω

CD RD

LP2

BIAS VCC

FAILURE

DETECTOR

FAIL

TIA

MD

IMD

IAPCSET

MODSET

RMODSET

BIASMAX

RBIASMAX

APCFILT1

APCFILT2

CAPCFILT

APCSET

RAPCSET

VCC

IBIAS

500pF

Figure 3. Functional Diagram

Detailed Description

The MAX3273 laser driver consists of two main parts: a

high-speed modulation driver and a laser-biasing block

with automatic power control (APC). The circuit design

is optimized for both high-speed and low-voltage

(+3.3V) operation. To minimize the jitter of the input sig-

nal at speeds as high as 2.7Gbps, the device accepts

a differential CML clock signal for data retiming. When

LATCH is high, the input data is synchronized by the

clock signal. When LATCH is low, the input data is

directly applied to the output stage.

The output stage is composed of a high-speed differ-

ential pair and a programmable modulation current

source. Because the modulation output drives a maxi-

mum current of 60mA into the laser with an edge speed

of 59ps, large transient voltage spikes can be generat-

ed (due to the parasitic inductance of the laser). These

transients and the laser-forward voltage leave insuffi-

cient headroom for the proper operation of the laser dri-

ver if the modulation output is DC-coupled to the laser

diode. To solve this problem, the MAX3273’s modula-

tion output is AC-coupled to the cathode of a laser

diode. An external pullup inductor is necessary to DC-

bias the modulation output at VCC. Such a configuration

isolates laser-forward voltage from the output circuitry

and the supply voltage VCC. A simplified functional dia-

gram is shown in Figure 3.

The MAX3273 modulation output is optimized for dri-

ving a 25Ω load. Modulation current swings of 75mA

are possible, but because of minimum power-supply

and jitter requirements at 2.5Gbps, the specified maxi-

mum modulation current is limited to 60mA. To inter-

face with the laser diode, a damping resistor (RD) is

required for impedance matching. An RC-shunt net-

work might also be necessary to compensate for the

laser-diode parasitic inductance, thereby improving the

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