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ICS85411AM

LOW SKEW, 1-TO-2 DIFFERENTIAL-TO-LVDS FANOUT BUFFER

Integrated Circuit Systems 

Integrated

Circuit

Systems, Inc.

ICS85411

LOW SKEW, 1-TO-2

DIFFERENTIAL-TO-LVDS FANOUT BUFFER

APPLICATION INFORMATION

WIRING THE DIFFERENTIAL INPUT TO ACCEPT SINGLE ENDED LEVELS

Figure 1 shows how the differential input can be wired to accept

single ended levels. The reference voltage V_REF = VDD/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

of R1 and R2 might need to be adjusted to position the V_REF in

the center of the input voltage swing. For example, if the input

clock swing is only 2.5V and VDD = 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

differential transmission line environment, LVDS drivers

require a matched load termination of 100Ω across near the

receiver input. For a multiple LVDS outputs buffer, if only

partial outputs are used, it is recommended to terminate

the un-used outputs.

3.3V

LVDS

R1

100

100 Ohm Differential Transmission Line

3.3V

+

-

85411AM

FIGURE 2. TYPICAL LVDS DRIVER TERMINATION

www.icst.com/products/hiperclocks.html

8

REV. B JUNE 16, 2004

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