Hi Sheldon,
Thanks for your replying. The analog input source should be ok. The clock may have a risk to be not so clean.
Single-ended clock from equipment is converted to differential one by a balun, and is converted to single-ended clock again using a comparator on PCB, and then goes into the chip through analog IO. Actually, the on-chip clock is treated as pure digital signal with analog power supply driving standard cells.
If the clock is the problem, why does the spur always locate besides the signal for inputs with different frequency?
Regards,
cchen
sheldon wrote on May 29th, 2014, 4:48am:CChen,
Not sure what it could be, have you looked at the clock to see
how clean it is and at the input source to see how clean it is?
Sheldon