VITESSE
SEMICONDUCTOR CORPORATION
Preliminary Data Sheet
VSC7940
Features
SONET/SDH 3.125Gb/s
Laser Diode Driver with Automatic Power Control
Applications
• SONET/SDH at 622Mb/s, 1.244Gb/s,
2.488Gb/s, 3.125Gb/s
• Full-Speed Fibre Channel (1.062Gb/s)
• Power Supply: 5V
±
5%
• DC-Coupled to Laser Diode
• Programmable Modulation Current: 5mA to 100mA
• Programmable Bias Current: 1mA to 100mA
• Enable/Disable Control
• Automatic Optical Average Power Control
• Modulation and Bias Current Monitors
General Description
The VSC7940 is a single 5V supply laser diode driver specially designed for SONET/SDH applications up
to 3.125Gb/s. External resistors set a wide range of bias and modulation currents for driving the laser. Data and
clock inputs accept differential PECL signals. The Automatic Power Control (APC) loop maintains a constant
average optical power over temperature and lifetime. The dominant pole of the APC loop can be controlled with
an external capacitor. Other features include enable/disable control, programmable slow-start circuit to set laser
turn-on delay, and failure-monitor output to indicate when the APC loop is unable to maintain the average opti-
cal power. The VSC7940 is available in die form or in a 32-pin TQFP package.
Block Diagram
V
CC
L AT C H
IOUT+
IOUT-
MUX
DATA+
DATA-
CLK+
CLK-
CLR
Q
BIAS
SET
Q
C
F
R
F
V
CC
D
V
CC
ENABLE
DISABLE
V
CC
MODMON
BIASMON
APC
MD
FAIL
1nF
MODSET
BIASMAX
CAPC
APCSET
G52357-0, Rev 3.2
05/11/01
©
VITESSE
SEMICONDUCTOR CORPORATION
• 741 Calle Plano • Camarillo, CA 93012
Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: prodinfo@vitesse.com
Internet: www.vitesse.com
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