9397 750 14437 © Koninklijke Philips Electronics N.V. 2005. All rights reserved.
Product data sheet Rev. 06 — 20 January 2005 19 of 30
Philips Semiconductors
TZA3011A; TZA3011B
30 Mbit/s up to 3.2 Gbit/s A-rate laser drivers
12.1.3 Dual-loop control
The dual-loop control measures the monitor current (I
MON
) corresponding with an optical
‘one’ level and the I
MON
corresponding with the optical ‘zero’ level. The measured I
MON(one)
and I
MON(zero)
are compared with the average monitor current setting and the extinction
ratio setting according to:
The dual-loop controls the bias and the modulation current for obtaining the I
MON(one)
and
I
MON(zero)
current levels which correspond with the programmed AVR and ER settings.
Performance of the dual-loop for high data-rate is linked to the quality of the incoming
IMON signal: a high performance interconnection between monitor photodiode and MON
input is requested for maximum data rate applications (2.7 Gbit/s).
The operational area of the dual-loop and the control area of the monitor input current
must respect the following equations:
Stability of ER and AVR settings are guaranteed over a range of temperature and supply
voltage variations.
12.1.4 Alarm operating current
The alarm threshold I
oper(alarm)
on the operating current is determined by the source
current I
MAXOP
of the MAXOP pin. The current range for I
MAXOP
is from 10 µA to 200 µA
which corresponds with an I
oper(alarm)
from 7.5 mA to 150 mA. The I
MAXOP
current can be
sunk by an external current source or by connecting R
MAXOP
to ground:
The operating current equals the bias current for an AC-coupled laser application and
equals the bias current plus half of the modulation current for the DC-coupled laser
application:
I
av MON()
I
MON one()
I
MON zero()
+
2
---------------------------------------------------------
=
ER
I
MON one()
I
MON zero()
--------------------------
=
50 µAI
MON zero()
500 µA<<
250 µAI
MON one()
2500 µA<<
I
oper alarm()
N
MAXOP
V
MAXOP
R
MAXOP
---------------------
×=
I
oper TZA3011A()
I
BIAS
=
I
oper TZA3011B()
I
BIAS
I
mod
2
-----------
+=
