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AD9958 internal reference clock with 25MHz Crystal

Question asked by jonasz on Jan 17, 2014
Latest reply on Jan 19, 2014 by LouijieC



I am using an AD9958 DDS on its evaluation board and tried to replace the external frequency reference source (25MHz) with an onboard crystal I bought ( which is also 25MHz.

I followed the guidance of the evaluation board and put 0Ohm resistors on positions R52 and R53 as well as 33pF capacitors on C66 and C67. Later I added in parallel 6.8pF capacitors to get closer to the desired 39pF.

Additionally I soldered 0Ohm Resistors to positions R44 to R49.


While the DDS works fine with jumper W11 set on external reference clock, it does not when I try to use the supplied crystal. The clock signal was monitored on J13 (SYNC CLK) and with the crystal no signal could be observed.

What am I doing wrong?