VITESSE

SEMICONDUCTOR CORPORATION

Data Sheet

VSC8113

ATM/SONET/SDH 622 Mb/s Transceiver Mux/Demux

with Integrated Clock Generation and Clock Recovery

Page 26

© VITESSE SEMICONDUCTOR CORPORATION

G52154-0, Rev 4.2

741 Calle Plano, Camarillo, CA 93012 • 805/388-3700 • FAX: 805/987-5896

3/19/99

Layout of the High Speed Signals

The routing of the High Speed signals should be done using good high speed design practices. This would

include using controlled impedance lines and keeping the distance between components to an absolute mini-

mum. In addition, stubs should be kept at a minimum as well as any routing discontinuities. This will help min-

imize reflections and ringing on the high speed lines and insure the maximum eye opening. In addition the

output pull down resistor should be placed as close to the VSC8113 pin as possible while the AC-coupling

capacitor and the biasing resistors should be placed as close as possible to the optics input pin. The same is true

on the receive circuit side. Using small outline components and minimum pad sizes also helps in reducing dis-

continuities.

Ground Planes

The ground plane for the components used in the High Speed interface should be continuous and not sec-

tioned in an attempt to provide isolation to various components. Sectioning of the ground planes tends to inter-

fere with the ground return currents on the signal lines. In addition, the smaller the ground planes the less

effective they are in reducing ground bounce noise and the more difficult to decouple. Sectioning of the positive

supplies can provide some isolation benefits.

Figure 13: AC Coupled High Speed I/O

Table 19: AC Coupling Component Values

Component

Value

Tolerance

R1

270 ohms

5%

R2

75 ohms

5%

R3

68 ohms

1%

R4

190 ohms

1%

C1, C2, C3, C4

.01uf High Frequency

PC Board Trace

PC Board Trace

DRIVER

(Optics Module)

RECEIVER

(Optics Module)

VSC8113

PECL I/O

R2

R4

C2

C1

R3

Note: Only one side of a differential signal is shown.

R1

GND

+3.3V

+5.0V

GND

GND

GND