tza3041ahl NXP Semiconductors, tza3041ahl Datasheet - Page 7

• Manufacturer Part Number: tza3041ahl
• Description: Gigabit Ethernet/fibre Channel Laser Drivers
• Manufacturer: NXP Semiconductors

Philips Semiconductors
For ECL signals (negative and referenced to ground), the
inputs should be AC-coupled to the signal source.
If AC-coupling is applied, a constant input signal (either
LOW or HIGH) will cause the device to be in an undefined
state. To avoid this, it is recommended to apply a slight
offset to the input stage. The applied offset must be higher
than the specified value in Chapter “Characteristics”, but
much lower than the applied input voltage swing.
The RF path is fully differential and contains a differential
preamplifier and a main amplifier. The main amplifier is
able to operate at the large peak currents required at the
output laser driver stage and is insensitive to supply
voltage variations. The output signal from the main
amplifier drives a current switch which supplies a
guaranteed maximum modulation current of 60 mA to
pins LA and LAQ (see Fig.6). The BIAS pin outputs a
guaranteed maximum DC bias current of up to 90 mA for
adjusting the optical laser output to a level above its light
emitting threshold (see Fig.7).
2002 Aug 13
handbook, halfpage
handbook, halfpage
Gigabit Ethernet/Fibre Channel laser
drivers
Fig.7 Laser driver bias current output circuit.
ALS
ALS
Fig.6 LA and LAQ outputs.
TR
TR
GND
GND
TR n
TR n
LA
BIAS
LAQ
MGS906
MGS907
7
Automatic laser control
A laser with a Monitor PhotoDiode (MPD) is required for
the laser control circuit (see application diagrams
Figs 18 and 19).
The MPD current is proportional to the laser emission and
is applied to pin MONIN. The MPD current range is
100 to 1000 A (p-p). The input buffer is optimized to cope
with an MPD capacitance of up to 50 pF. To prevent the
input buffer from oscillating if the MPD capacitance is low,
the capacitance should be increased to the minimum value
specified in Chapter “Characteristics”, by connecting a
capacitor between pin MONIN and V
DC reference currents are applied to pins ONE and ZERO
to set the MPD reference levels for laser HIGH and laser
LOW respectively. This is adequately achieved by using
resistors to connect V
(see Fig.8), however, current DACs can also be used. The
voltages on pins ONE and ZERO are held at a constant
level of 1.5 V below V
to pin ONE is internally multiplied by 16 and the reference
current flowing into pin ZERO is internally multiplied by 4.
The accuracy of the V
and ZERO is described in Section “Accuracy of voltage on
inputs: ONE, ZERO, ALARMLO, ALARMHI”.
handbook, halfpage
Fig.8
ONE, ZERO, ALARMLO and ALARMHI
inputs.
TZA3041AHL; TZA3041BHL;
30 k
V CC(R)
50 A
CC(R)
CC(R)
CC(R)
ONE, ZERO, ALARMLO, ALARMHI
. The reference current applied
to pins ONE and ZERO
1.5 V voltage at pins ONE
Product specification
CC(G)
TZA3041U
MGS908
.
GND