AD9517 LVPECL output interface to a fanout buffer

Question

Hello everyone: 
 I am using one AD9517-0 LVPECL output to drive a fanout buffer to convert the signal to two LDVS signals. 
 In the AD9517-0 datasheet I can see this figure to interface LVPECL stages: 
 
 On the other hand, in the datasheet of the fanout buffer, I can see this other configuration: 
 
 My dessign follows the AD recomendation (first schematic) and incorporates R1 to R4 of the second schematic. 
 Question : Should I keep the 100 Ohn resistor at the imput of the receiver (as proposed in the AD schematic)? 
 Thanks in advance 
 Regards 
 GuiX

ADIApproved · Accepted Answer

Dear GuiX, 
 Kyle is correct. The 100ohm resistor marked with the red "X" is not needed and if you include it, you'll cut the amplitude in half. 
 For Question 2, the max frequency isn't a simple number. The max speed is governed by the amplitude you require. The LVPECL outputs will toggle at 3 GHz, but waveform will be sinusoidal and the amplitude will be small. Refer to Figure 25 in the datasheet to see the amplitude vs frequency plot. The reason we spec 1.6 GHz is that it's max frequency at which there is enough amplitude so that nearly all LVPECL receivers will still function with good performance. 
 The neat part about following my suggestion for driving an LVDS input using an LVPECL output is that you have four amplitude settings to choose from, and it's easy to increase the output driver amplitude in the event that you need to. LVPECL is much better at driving long traces at high frequency than LVDS. 
 -Paul)

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AD9517 LVPECL output interface to a fanout buffer