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

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MAX3273
(Rev.:2002)

+3.3V, 2.5Gbps Low-Power Laser Driver

Maxim Integrated 

+3.3V, 2.5Gbps Low-Power Laser Driver

Table 1. Optical Power Relations

PARAMETER

Average Power

SYMBOL

PAVG

RELATION

PAVG = (P0 + P1) / 2

Extinction Ratio

re

re = P1 / P0

Optical Power of a 1

P1

P1 = 2PAVGre / (re + 1)

Optical Power of a 0

P0

P0 = 2PAVG / (re + 1)

Optical Amplitude

PP-P

PP-P = P1 - P0 = 2PAVG(re - 1) / (re + 1)

Laser Slope Efficiency

η

η = PP-P / IMOD

Modulation Current

IMOD

IMOD = PP-P / η

Threshold Current

ITH

P0 at 1 ≥ ITH

Bias Current

IBIAS

IBIAS ≥ ITH + IMOD / 2

Laser-to-Monitor Transfer

ρMON

IMD / PAVG

Note: Assuming a 50% average input duty cycle and mark density.

Applications Information

An example of how to set up the MAX3273 follows.

Select Laser

A communication-grade laser should be selected for

2.5Gbps/2.7Gbps applications. Assume the laser out-

put average power is PAVG = 0, the minimum extinction

ratio is re = 6.6 (8.2dB), the operating temperature is

-40°C to +85°C, and the laser diode has the following

characteristics:

• Wavelength: λ = 1310nm

• Threshold Current: ITH = 22mA at +25°C

• Threshold Temperature Coefficient: βTH = 1.3%/°C

• Laser-to-Monitor Transfer: ρMON = 0.2A/W

• Laser Slope Efficiency: η = 0.05mW/mA at +25°C

Determine RAPCSET

The desired monitor diode current is estimated by IMD

= PAVG × ρMON = 200µA. The IMD vs. RAPCSET graph

in the Typical Operating Characteristics shows that

RAPCSET should be 7.5kΩ.

Determine RMODSET

To achieve a minimum extinction ratio (re) of 6.6 over

temperature and lifetime, calculate the required extinc-

tion ratio at +25°C. Assuming re = 20, the peak-to-peak

optical power PP-P = 1.81mW, according to Table 1.

The required modulation current is 1.81mW/

(0.05mW/mA) = 36.2mA. The IMOD vs. RMODSET graph

in the Typical Operating Characteristics shows that

RMODSET should be 5kΩ.

Determine RBIASMAX

Calculate the maximum threshold current (ITH(MAX)) at

TA = +85°C and end of life. Assuming ITH(MAX) =

50mA, the maximum bias current should be: IBIASMAX

= ITH(MAX) + (IMOD / 2). In this example, IBIASMAX =

68.1mA. The IBIASMAX vs. RBIASMAX graph in the

Typical Operating Characteristics shows that RBIASMAX

should be 3.5kΩ.

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