OQ2545HP Ver la hoja de datos (PDF) - Philips Electronics

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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

FUNCTIONAL DESCRIPTION

The OQ2545(B)HP can be divided into two functional

blocks (see Fig.1):

• A digital section on the input side

• An analog section on the output side.

The data input buffers present an impedance of 50 Ω to

the data stream on the differential data inputs (see Fig.5).

The input data is then fed to a multiplexer where normal

mode (pin ENL = HIGH-level) or loop mode

(pin ENL = LOW-level) inputs are selected. For driving an

EAM, a second multiplexer inverts the input signals when

pin SMOD is connected to VEE1.

An external clock (OQ2545HP only) connected to a

master-slave flip-flop is then used to retime the data. This

reduces jitter on the data signal to a minimum.

The preamplifier boosts the signal to a suitable level for the

modulation driver. Two emitter followers provide the

necessary signal isolation between the preamplifier and

the high current modulation driver. The bias currents for

the preamplifier and the emitter followers contain an output

level dependent component, along with an independent

component. The output level dependent component is

controlled via the signal on pin SIMOD and the operational

amplifier, which also sets the modulation driver level.

The independent component is adjusted by means of the

signal on pin AMPADJ (preamplifier) and pin EFADJ

(emitter followers).

The signal on pin AMPADJ also controls the shape of the

output signal on pins LA and LAQ.

An independent adjustable on-chip bias current source is

provided to drive directly a modulated laser diode.

Pin SIBIAS is used to set the bias current level. The output

current at pin IBIAS will be approximately 106 times the

input current at pin SIBIAS. A similar arrangement is used

to control the modulation current at pins LA and LAQ.

The output current at pins LA and LAQ is proportional to

the input current at pin SIMOD. The coefficient depends

on the load impedance on pins LA and LAQ and on the

voltage setting of pin SMOD (see section ‘Modulation

current setting’).

Pin ALS is a TTL compatible input and at HIGH-level it can

be used to switch off all current sources. This function

makes it possible to implement safety measures that will

switch off the circuit in the event of an optical system

malfunction.

The buffered differential 50 Ω outputs (pins MON

and MONQ) can be used to monitor the optically

modulated data.

Loop mode

The loop mode is provided for system testing. A LOW-level

on pin ENL selects the loop mode. When pin ENL is left

open-circuit, it is pulled to a HIGH-level (TTL) by an

internal pull-up resistor.

handbook, full pagewidth

DIN, DLOOP

CIN, CLOOP

50 Ω

50 Ω

DINQ, DLOOPQ,

CINQ, CLOOPQ

1999 Aug 24

VEE1

MGL731

Fig.5 Schematic for CML differential inputs.

8

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