I'm using AD9680-1000 on my board, but I find it can't work when my sample clock set to 1GHz. I read the register , all of them are 0xff. My LMF= 421,and I have set the register 0x56E to 0x10.And I test it at other frequency ,it can work at 500MHz and can't work at 800MHz. And I really sure the 1GHz clock have on problem.There are two AD9680-1000 on my board,and the other one is test ok at 1GHz，I give them the same program and their circuit are same. So if the chip is broken? I can't believe it.