VITESSE

SEMICONDUCTOR CORPORATION

G52028-0, Rev 4.1

Page 9

05/25/01

© VITESSE SEMICONDUCTOR CORPORATION • 741 Calle Plano • Camarillo, CA 93012

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

Internet: www.vitesse.com

Data Sheet

VSC8021/VSC8022

8-Bit MUX/DEMUX Chipset

2.5Gb/s SONET-Compatible

Figure 5: SONET Frame Structure

High-Speed Inputs

In the past, the high-speed inputs, which are typically used for serial data and high-speed clock inputs with

frequencies greater than 1GHz, were specified with absolute minimum and maximum voltage values. Since

these inputs are intended for AC-coupled applications, they have been re-specified in terms of a voltage swing

(

∆V

High-speed clocks are intended for AC-coupled operation. In most situations high-speed serial data will

have high transition density and contain no DC offsets, making them candidates for AC-coupling as well. How-

ever, it is possible to employ DC-Pcoupling when the serial input data contains a DC component.

The structure of the high-speed input circuit is shown in Figure 6. DC-coupled circuits may be used to oper-

ate this input provided that the input swing is centered around the reference voltage. It is recommended that, in

single-ended DC-coupling situations, the user provide an external reference which has better temperature and

power supply rejection than the simple on-chip voltage divider. This external reference should have a nominal

value of -3.5V and can be connected to the complementary input. This complication can be avoided in DC-cou-

pled situations by using differential signals.

Figure 6: High-Speed Input Circuit Structure

3 x 3 Bytes

Transport

Overhead

STS-3 Envelope

Capacity

125

µs

STS-3 Frame

3 x 90 Bytes

A1s and A2s: SONET Framing Sequence

C1s: STS Frame ID

DATA

3 A1s

9 Rows

3 A2s

3 C1s

3 x 48 Bytes

Transport

Overhead

STS-48 Envelope

Capacity

125

µs

STS-48 Frame

48 x 90 Bytes

DATA

48 A1s

9 Rows

48 A2s

48 C1s

50•

Chip Boundary

-3.5 V

-3.5 V

150 pF

R

• 1k•

150 pF

Ω