AN1568/D

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5

termination should be used and placed as close as possible

to the coupling capacitors. (Figure 7)

Figure 7. Capacitive Coupling ECL to LVDS Using

Z = 50

W

Z = 50

W

ECL

1 k

W

1 k

W

100 k

W

1.2 V

10 pF

10 pF

3.3 V

50

W

50

W

LVDS

Direct Interfacing

Interfacing from 2.5 V LVPECL to LVDS

Provided that the LVDS receiver can tolerate large input

voltage peak to peak amplitude, 2.5 V LVPECL can be

directly interfaced to LVDS receiver using proper ECL

termination. 2.5 V LVPECL will be able to drive LVDS

receiver with and without internal 100

W termination

resistor. (See Figures 8, 9 and 10).

Figure 8. Interfacing 2.5 V LVPECL to LVDS with

External 100

W Termination Resistor

100

W

LVPECL

2.5 V

LVDS

Figure 9. Interfacing 2.5 V LVPECL to LVDS with

Internal 100

W Termination Resistor

100

W

LVPECL

2.5 V

LVDS

Figure 10. PSPICE Simulation Levels of 2.5V LVPECL

to LVDS Interface with Example Resistor Values

1.50 V

0.78 V

720 mV

LVDS

Input

2.5 V LVPECL

Output

Furthermore, sreies termination can be used to reduce the

amplitude of the signal as described in AND8020

and the transmission line. (See Figures 11, 12 and 13).

Figure 11. Interfacing 2.5 V LVPECL to LVDS with

100

W

LVPECL

2.5 V

LVDS