AD9914 Reference clock polarity swapping.

Application and Circuit Description

We are using the AD9914 (DDS) to generate a 900MHz frequency modulated signal. The reference to the AD9914 can be either a 2.4GHz or a 3.25GHz LVPECL signal. A differential 2:1 LVPECL multiplexer, SY58018U from Microchip, is used to switch between the two references. A block diagram of the above application circuit is attached.

The PCB layout is currently underway and the LVPECL differential signals from the multiplexer to the AD9914 are crossing over as shown in the layout block diagram.

Engineer Zone Question

In order to facilitate the layout can I swap the AD9914 reference clock inputs?

That is can I apply the “Complementary Reference Clock Input Signal” from the Mux to the “Non-Complementary Reference Clock Input” of the AD9914 and simultaneously apply the “Non-Complementary Reference Clock Input Signal” from the Mux to “Complementary Reference Clock Input” of the AD9914.

In general can the “Complementary and Non-Complementary” signals of a differential interface can be interchanged.

I am fairly certain that it can be done but want to confirm.

Please refer the attached documents for more details.

Block diagram – AD9914_LVPECL_Reference_Clock_Mux_Block_Diagram.pdf