VITESSE
SEMICONDUCTOR CORPORATION
Data Sheet
2.5Gb/s 16-Bit
Multiplexer/Demultiplexer Chipset
VSC8061/VSC8062
Coupling for Inputs
Figure 7: AC-Coupling for DCLK, DCLKN Inputs
Chip Boundary
VCC = GND
DCLK
ZO
CIN
-1.32V
-1.32V
RT = ZO
R| | = 1kW
VTT
DCLKN
CSE
VTT
VTT = -2V
C
C
typ = 0.1mF
IN
typ = 0.1mF for single-ended applications
SE
(Capacitor values are selected for DCLK = 155Mb/s.)
DCLK, DCLKN Inputs
Internal biasing will position the reference voltage of approximately -1.32V on both the true and comple-
ment inputs. This input can either be DC-coupled or AC-coupled; it can also be driven single-ended or differen-
tially. Figure 7 shows the configuration for a single-ended, AC-coupling operation. In the case of direct
coupling and single-ended input, it is recommended that a stable V
mentary input.
for ECL levels be used for the comple-
REF
High-Speed Clock and Serial Data Inputs
It is recommended that all high-speed clock and serial data inputs (CLK/CLKN for the VSC8061; DI/DIN
and CLK/CLKN for the VSC8062) be AC-coupled. Figure 8 shows the configuration for a single-ended AC-
coupling operation.
In most situations, these inputs will have high transition density and little DC offset. However, in cases
where this does not hold, direct DC connection is possible. The following is to assist in this application.
All serial data and clock inputs have the same circuit topology, as shown in Figure 8. The reference voltage
is created by a resistor divider as shown. If the input signal is driven differentially and DC-coupled to the part,
the mid-point of the input signal swing should be centered about this reference voltage and not exceed the max-
imum allowable amplitude. For single-ended, DC-coupling operations, it is recommended the user provide an
external reference voltage which has better temperature and power supply noise rejection than the on-chip resis-
tor divider. The external reference should have a nominal value as indicated in the table and can be connected to
either side of the differential gate.
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Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: prodinfo@vitesse.com
Internet: www.vitesse.com
Page 8
G52069-0, Rev 4.3
05/11/01
VITESSE [ VITESSE SEMICONDUCTOR CORPORATION ]
