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adf4351 spur at the output

Question asked by kalupen on Jun 20, 2018


I am using adf4351 custom board  with evaluation board loop filter components and it is designed for generating 2780MHz with 10 MHz as ref input and ref doubler enabled.At the output of 2780Mhz at 21.4Mhz away(2758.6@-60dBc) a spur is seen and it is not controllable. May i know the reason for that spur generation.I had changed the reference from 10MHz to 25MHz  but the spur is appearing at same place i.e 21.4 MHz.Please help me to remove the spur.My register settings and output signal pics are uploaded. Thankyou.Best Regards.