85356AMI

www.icst.com/products/hiperclocks.html

REV. A OCTOBER 7, 2004

6

Integrated

Circuit

Systems, Inc.

ICS85356I

V

50

Ω

50

Ω

RTT

Z

Z

FOUT

FIN

RTT =

Z

o

1

((V

3.3V

125

Ω

125

Ω

84

Ω

84

Ω

Z

Z

FOUT

FIN

The clock layout topology shown below is a typical termina-

tion for LVPECL outputs. The two different layouts mentioned

are recommended only as guidelines.

FOUT and nFOUT are low impedance follower outputs that gen-

erate ECL/LVPECL compatible outputs. Therefore, terminating

resistors (DC current path to ground) or current sources must

be used for functionality. These outputs are designed to drive

50

Ω 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 lay-

outs 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 2 shows how the differential input can be wired to accept

single ended levels. The reference voltage V_REF = V

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 V

and R2/R1 = 0.609.

V_REF

R1

1K

C1

0.1u

R2

1K

Single Ended Clock Input

CLKx

nCLKx

VCC