ICS85408 Datasheet, PDF (7/12 Pages) Integrated Circuit Systems – LOW SKEW, 1-TO-8 DIFFERENTIAL-TO-LVDS CLOCK DISTRIBUTION CHIP

Integrated
Circuit
Systems, Inc.
ICS85408
LOW SKEW, 1-TO-8
DIFFERENTIAL-TO-LVDS CLOCK DISTRIBUTION CHIP
APPLICATION INFORMATION
WIRING THE DIFFERENTIAL INPUT TO ACCEPT SINGLE ENDED LEVELS
Figure 1 shows how the differential input can be wired to accept of R1 and R2 might need to be adjusted to position the V_REF in
single ended levels. The reference voltage V_REF = V_DD/2 is
generated by the bias resistors R1, R2 and C1. This bias circuit
should be located as close as possible to the input pin. The ratio
the center of the input voltage swing. For example, if the input
clock swing is only 2.5V and V_DD = 3.3V, V_REF should be 1.25V
and R2/R1 = 0.609.
VDD
Single Ended Clock Input
V_REF
C1
0.1u
R1
1K
CLK
nCLK
R2
1K
FIGURE 1. SINGLE ENDED SIGNAL DRIVING DIFFERENTIAL INPUT
LVDS DRIVER TERMINATION
A general LVDS interface is shown in Figure 2. In a 100Ω differ-
ential transmission line environment, LVDS drivers require a
matched load termination of 100Ω across near the receiver in-
put. For a multiple LVDS outputs buffer, if only partial outputs
are used, it is recommended to terminate the un-used outputs.
3.3V
Zo = 50 Ohm
3.3V
LVDS_DRIVER
R1
100
Zo = 50 Ohm
CLK
nCLK
HiPerClockS
85408BG
FIGURE 2. TYPICAL LVDS DRIVER TERMINATION
www.icst.com/products/hiperclocks.html
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REV. A APRIL 25, 2005