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TZA3047B

30 Mbits/s up to 1.25 Gbits/s laser drivers

Philips Electronics 

Philips Semiconductors

30 Mbits/s up to 1.25 Gbits/s laser drivers

Product specification

TZA3047A; TZA3047B

7.5 Dual-loop control

The TZA3047 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. Pin MON for the monitor photodiode current is an

RF input.

The average monitor current is programmable over a wide

current range from 150 to 1300 µA for both the dual-loop

control and the average loop control. The extinction ratio is

programmable from 5 to 15.

The maximum allowable capacitive load on pins AVR, ER,

BIASOUT and MODOUT is 100 pF.

7.6 Average loop control

The average power control loop maintains a constant

average power level of the monitor current over

temperature and lifetime of the laser. The average loop

control is activated by short-circuiting pin ER to ground.

7.7 Direct current setting

The TZA3047 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.

7.9 Alarm functions

The TZA3047 features two alarm functions for the

detection of excessive laser operating current and monitor

diode current due to laser ageing, laser malfunctioning or

a too high laser temperature. The alarm threshold levels

are programmed by a resistor or a current source. In the

TZA3047A, for the AC-coupled application, the operating

current is equal to the bias current. In the TZA3047B, for

the DC-coupled application, the operating current equals

the bias current plus half of the modulation current.

7.10 Enable

A LOW level on the enable input disables the bias and

modulation current sources: the laser is off. A HIGH level

on the enable input or an open enable input switches both

current sources on: the laser is operational.

7.11 Reference block

The reference voltage is derived from a band gap circuit

and is available at pin RREF. An accurate (1%) 10 kΩ

resistor has to be connected to pin RREF to provide the

internal reference current. The maximum capacitive load

on pin RREF is 100 pF.

The reference voltage on the setting pins (MAXOP,

MAXMON, PWA, ER and AVR) is buffered and derived

from the band gap voltage.

The output voltage on pin VTEMP reflects the junction

temperature of the TZA3047, the temperature coefficient

of VVTEMP equals −2.2 mV/K.

7.8 Soft start

At power-up the bias and modulation current sources are

released when VCCA > 2.7 V and the reference voltage has

reached the correct value of 1.2 V.

The control loop starts with minimum bias and modulation

current at power-up and when the device is enabled. The

current levels increase until the MON input current

matches the programmed average level and, in the case

of dual-loop control, the extinction ratio.

2003 Jun 05

8

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