OQ2545BHP Philips Semiconductors, OQ2545BHP Datasheet - Page 8

• Manufacturer Part Number: OQ2545BHP
• Description: SDH/SONET STM16/OC48 laser drivers
• Manufacturer: Philips Semiconductors

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Philips Semiconductors
FUNCTIONAL DESCRIPTION
The OQ2545(B)HP can be divided into two functional
blocks (see Fig.1):
The data input buffers present an impedance of 50
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 V
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).
1999 Aug 24
A digital section on the input side
An analog section on the output side.
SDH/SONET STM16/OC48 laser drivers
DIN, DLOOP
CIN, CLOOP
EE1
.
V EE1
Fig.5 Schematic for CML differential inputs.
50
to
8
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
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.
MGL731
50
DINQ, DLOOPQ,
CINQ, CLOOPQ
OQ2545HP; OQ2545BHP
outputs (pins MON
Product specification