8732-01 Datasheet, PDF (8/17 Pages) Integrated Device Technology – Low Voltage, Low Skew 3.3V LVPECL Clock Generator

8732-01 Data Sheet
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
single ended levels. The reference voltage V_REF = V_CC/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
in the center of the input voltage swing. For example, if the input
clock swing is only 2.5V and V_CC = 3.3V, V_REF should be 1.25V
and R2/R1 = 0.609.
VCC
Single Ended Clock Input
V_REF
C1
0.1u
R1
1K
CLK
nCLK
R2
1K
FIGURE 1. SINGLE ENDED SIGNAL DRIVING DIFFERENTIAL INPUT
TERMINATION FOR LVPECL OUTPUTS
The clock layout topology shown below is a typical termination
for LVPECL outputs. The two different layouts mentioned are
recommended only as guidelines.
FOUT and nFOUT are low impedance follower outputs that
generate ECL/LVPECL compatible outputs. Therefore, termi-
nating resistors (DC current path to ground) or current sources
must be used for functionality. These outputs are designed to
drive 50Ω transmission lines. Matched impedance techniques
should be used to maximize operating frequency and minimize
signal distortion. Figures 2A and 2B show two different layouts
which are recommended only as guidelines. Other suitable clock
layouts may exist and it would be recommended that the board
designers simulate to guarantee compatibility across all printed
circuit and clock component process variations.
FIGURE 2A. LVPECL OUTPUT TERMINATION
FIGURE 2B. LVPECL OUTPUT TERMINATION
©2016 Integrated Device Technology, Inc
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Revision E January 22, 2016