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OQ2545HP

SDH/SONET STM16/OC48 laser drivers

Philips Electronics 

Philips Semiconductors

SDH/SONET STM16/OC48 laser drivers

Product specification

OQ2545HP; OQ2545BHP

RF connections

A coupled stripline or microstrip with an odd mode

characteristic impedance of 50 Ω (nominal value) should

be used for the differential RF connections on the PCB.

This applies to the CML differential line pairs on pins CIN

and CINQ, DIN and DINQ, CLOOP and CLOOPQ,

DLOOP and DLOOPQ, and MON and MONQ.

In addition, the following lines should not differ in length by

more than 10 mm:

• Lines to pins DIN, DINQ, CIN and CINQ

• Lines to pins CLOOP, CLOOPQ, DLOOP

and DLOOPQ.

ESD protection

In order to achieve high frequency performance, it has

been necessary to make adjustments to the standard ESD

protection scheme. Inputs on pins DIN, DINQ, CIN, CINQ,

DLOOP, DLOOPQ, CLOOP and CLOOPQ and outputs on

pins MON and MONQ are protected by a reduced ESD

structure. The outputs on pins LA and LAQ have no

protection against ESD, so extra care should be taken

with these pins.

Power consumption

The total power consumption of the OQ2545(B)HP

depends strongly on the application. A rough guideline is

given to estimate the power consumption for a specific

application.

The total power dissipation (Ptot) consists of the following

terms:

Ptot = PVEE1 + PVCC + PVEE2 − (PLA + PLAQ + PIBIAS)

where

1. PVEE1 and PVCC represent the power consumption

terms corresponding with the supplies VEE1 and VCC,

required for the digital section and the TTL interfaces.

These 2 terms are application independent and only

depend on the process spread and supply voltages.

Values can be found in Chapter “Characteristics”.

2. PVEE2 = IEE2 × VEE2 represents the power

consumption of the analog section, including the

modulation current and bias current. It is mainly

determined by the magnitude of the modulation

current and bias current and the additional biasing

currents of the preamplifier and emitter followers.

The supply current is the summation:

IEE2 = 55 mA + 1.5 × Imod + IIBIAS + 3 × IAMPADJ

+ 55 × IEFADJ

where IAMPADJ and IEFADJ are the currents through

pins AMPADJ and EFADJ, respectively.

These figures are valid for nominal supply voltage and

temperature and are given for rough indication only.

3. PLA, PLAQ and PIBIAS represent the dissipation in the

external load (laser or EAM), caused by the

modulation and bias current. The expressions are:

PLA = 0.5 × ILA(ext) × VLA,

PLAQ = 0.5 × ILAQ(ext) × VLAQ and

PIBIAS = IIBIAS × VIBIAS.

The factor 0.5 represents the fact that, for a

(scrambled) random data pattern, the modulation

switch will be switched to either side 50% of the time

integrated over many cycles.

VLA and VLAQ are the voltages on pins LA and LAQ

when the modulation current flows through pins LA

and LAQ, respectively and the values depend on the

external laser or EAM supply voltage, the forward

diode voltage drop and additional loads.

To increase the dissipation in the external load and

thereby decreasing the dissipation in the IC, the values

of VLA or VLAQ can be increased by adding

additional external resistors. A minimum value of VLA

and VLAQ is required for proper operation of the IC.

A similar argument is valid for power consumption due

to the bias current. It should be noted that this is

important, because it provides an easy way to lower

the power dissipation of the IC.

Example

Consider the following example to illustrate the calculation

of Ptot. A laser diode operates at 0.3 mW (optical low) and

3 mW (optical high), i.e. an extinction ratio of 10 dB.

For this laser type this requires IBIAS = 20 mA and

ILA(ext) = 40 mA (see Fig.8).

The series resistance of the laser is 30 Ω. Therefore the

ratio is: I-I-L-L--A-A---((-e-i-n-x--t-t-)) = 1--3--0--0-0--

Consequently, a total Imod = (130/100) × 40 = 52 mA will

be generated by the IC.

The impedance connected to pin LAQ is 30 Ω as well.

As a result also ILAQ(ext) = 40 mA and ILAQ(int) = 12 mA

(see Fig.9).

In first instance the eye pattern is of adequate quality and

the preamplifier and emitter follower do not need additional

bias current, i.e. pins AMPADJ and EFADJ can be left

open-circuit.

1999 Aug 24

11

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