tza3050 NXP Semiconductors, tza3050 Datasheet - Page 6

• Manufacturer Part Number: tza3050
• Description: Tza3050 30 Mbits/s Up To 1.25 Gbits/s Burst Mode Laser Driver
• Manufacturer: NXP Semiconductors

Philips Semiconductors
9397 750 14806
Product data sheet
7.2 Retiming
7.3 Pulse width adjustment
7.4 Modulator output stage
7.5 Average loop control
7.6 Direct current setting
7.7 Soft start
The retiming function synchronizes the data with the clock to improve the jitter
performance. The data latch switches on the rising edge of the clock input. The retiming
function is disabled when both clock inputs are below 0.3 V.
At start-up the initial polarity of the laser is unknown until the first rising edge of the clock
input appears.
The on-duration of the laser current can be adjusted with a guaranteed range from 50 ps
to +50 ps. The adjustment time is set by connecting a resistor, R
maximum allowable capacitive load on pin PWA is 100 pF. Pulse width adjustment is
disabled when pin PWA is short-circuited to ground.
The output stage is a high-speed bipolar differential pair with typical rise and fall times of
120 ps and with a modulation current source of up to 100 mA. The output stage of the
TZA3050 is optimized for DC-coupled lasers.
The modulation current switches between the LA and LAQ outputs. For a good RF
performance the inactive branch carries a small amount of the modulation current.
The LA output is optimized for the laser, the LAQ output is optimized for the dummy load.
The BIAS output is optimized for low voltage requirements (1.25 V minimum).
The average power control loop maintains a constant average power level of the monitor
current over temperature and lifetime of the laser. The average monitor current is
programmable over a wide current range, from 150 A to 1300 A typical, by tuning the
setting resistor R
is 100 pF.
The TZA3050 can also operate in open-loop mode with direct setting of the bias and
modulation currents. The bias and modulation current sources are transconductance
amplifiers and the output currents are determined by the BIASIN and MODIN voltages
respectively. The bias current source has a bipolar output stage with minimum output
capacitance for optimum RF performance.
At power-up the bias and modulation current sources are released when V
reference voltage has reached the correct value of 1.2 V and the voltage on pin ENABLE
is HIGH.
The control loop starts with minimum bias and modulation current at power-up provided
the device is enabled. The current levels increase until the input current on pin MON
matches the programmed average level.
AVR
. The maximum allowable capacitive load on pins AVR and BIASOUT
Rev. 03 — 7 April 2005
30 Mbits/s up to 1.25 Gbits/s burst mode laser driver
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
PWA
, to pin PWA. The
TZA3050
CCA
> 2.7 V, the
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