Data Sheet
September 1999
1241/1243/1245-Type Uncooled Laser
Functional Overview
(continued)
V
CC
LASER
BACK-FACET
DETECTOR
(2)
(+)
LASER BIAS MONITOR VOLTAGE
(4)
(–)
15 k•
(+)
(19)
15 k•
15 k•
FIBER PIGTAIL
LASER BACK-FACET MONITOR VOLTAGE
(17)
(–)
15 k•
BAND GAP
REFERENCE
AUTOMATIC POWER
CONTROL CIRCUITRY
I
BF
10 •
(16)
DATA
30 k•
V
CC
– 1.3 V
INPUT DATA
COMPARATOR
t
TEMPERATURE
SENSOR
MODULATION
CIRCUITRY
I
BIAS
I
MOD
30 k•
(15)
DATA
TRANSMITTER
DISABLE
(7)
1-868(C).h
Figure 1. Simplified Transmitter Schematic Input Data
Input Data
Data enters the transmitter through a comparator.
These inputs have internal pull-down resistors to a volt-
age reference that is 1.3 V below V
CC
. This configura-
tion allows the transmitter to be driven from either a
single-ended or a differential input signal. Since the
input is a comparator instead of a gate, the absolute
input signal levels are not important when the inputs
are driven differentially. When driven single-ended,
however, the input signal voltage should be centered
around V
CC
– 1.3 V to eliminate pulse-width distortion.
With a single-ended input, either input can be used and
the unused input can be left as an open circuit due to
the internal reference shown in Figure 1. The optical
output signal will be in the same sense as the input
data—an input logic high turns the laser diode on and
an input logic low turns the laser diode off. However, if
the negative input is used with a single-ended data
Agere Systems Inc.
input signal, the optical signal will be the complement
of the data input signal.
The differental inputs of the 1241 Gbit versions are ter-
minated internally with 100
Ω
between the DATA and
DATA inputs.
Minimum Data Rate
Because the modulation and bias control circuitry are
influenced by the input data pattern, the standard
transmitter cannot be used in burst-mode type applica-
tions. For burst-mode applications, please contact your
Agere Account Manager. The minimum data rate
(pseudorandom data, 50% average duty cycle) for the
1241/1243/1245-Type Transmitters is approximately
1 Mbit/s.
3
AGERE [ AGERE SYSTEMS ]
