VSC7940 datasheet(13/16 Pages) VITESSE

13 / 16 page

VITESSE

SEMICONDUCTOR CORPORATION

Preliminary Data Sheet

VSC7940

SONET/SDH 3.125Gb/s

Laser Diode Driver with Automatic Power Control

G52357-0, Rev 3.2

Page 13

05/11/01

Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: prodinfo@vitesse.com

Internet: www.vitesse.com

Select Resistors for MODMON and BIASMON

Assuming the modulation and bias currents never exceed 120mA, the following equations provide values

for the resistor at MODMON, RMODMON, and the resistor at BIASMON, RBIASMON:

RMODMON = 1V * 28 / 120mA = 233Ω

RBIASMON = 1.6V * 35 / 120mA = 467Ω

Standard values for these values are RMODMON = 232Ω and RBIASMON = 464Ω. A voltage of 4.8V at

MODMON would indicate a modulation current of:

IMOD = (5.2V - 4.8V) * 28 / 232mA = 48mA

Wire Bonding

For best performance, gold ball-bonding techniques are recommended. Wedge bonding is not recom-

mended. For best performance and to minimize inductance keep wire bond lengths short.

PCB Layout Guidelines

Use high frequency PCB layout techniques with solid ground planes to minimize crosstalk and EMI. Keep

high speed traces as short as possible for signal integrity. The output traces to the laser diode must be short to

minimize inductance. Short output traces will provide best performance.

VSC7940 Datasheet(PDF) 13 Page - Vitesse Semiconductor Corporation