9397 750 14437 © Koninklijke Philips Electronics N.V. 2005. All rights reserved.
Product data sheet Rev. 06 — 20 January 2005 9 of 30
Philips Semiconductors
TZA3011A; TZA3011B
30 Mbit/s up to 3.2 Gbit/s A-rate laser drivers
The circuit generates an internal common mode voltage for AC-coupled data and clock
inputs and for single-ended applications.
If V
DIN
>V
DINQ
, the modulation current is sunk by the LA pins and corresponds to an
optical ‘one’ level of the laser.
7.2 Retiming
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 before the first rising edge of the
clock input.
7.3 Pulse width adjustment
The on-duration of the laser current can be adjusted from −100 ps to +100 ps. The
adjustment time is set by resistor R
PWA
. The maximum allowable capacitive load on pin
PWA is 100 pF. Pulse width adjustment is disabled when pin PWA is short-circuited to
ground.
7.4 Modulator output stage
The output stage is a high-speed bipolar differential pair with typical rise and fall times of
80 ps and with a modulation current source of up to 100 mA when the LA pins are
connected to V
CCO
.
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 allowing a 2 V dynamic range and a 1.2 V
minimum voltage. The LAQ output is optimized for the dummy load.
The output stage of the TZA3011A is optimized for AC-coupled lasers and the output
stage of the TZA3011B is optimized for DC-coupled lasers.
The BIAS output is optimized for low voltage requirements (0.4 V minimum for a 3.3 V
laser supply; 0.8 V minimum for a 5 V laser supply).
7.5 Dual-loop control
The TZA3011 incorporates a dual-loop control for a constant, accurate and
temperature-independent control of the optical average power level and the extinction
ratio. The dual-loop guarantees constant optical ‘one’ and ‘zero’ levels which are
independent of the laser temperature and the laser age.
The dual-loop operates by monitoring the current of the monitor photodiode which is
directly proportional to the laser emission. The ‘one’ and ‘zero’ current levels of the
monitor diode are captured by the detector of the dual-loop control. The pin MON for the
monitor photodiode current is an RF input.
The average monitor current is programmable over a wide current range from 150 µA
to 1300 µA for both the dual-loop control and the average loop control. The extinction ratio
is programmable from 5 to 15.
