My customer received the evaluation board at the beginning of the week and he performed several measures on it with the AD8065 mounted on the evaluation board and with the ADA4841.
Here are the results:
Fe = 384 kHz
F = 95 kHz
1) AD5452 + ADA4841, RLoad = 1 kOhms :
F = 95 kHz, +10.3 dBm
(Fe - 3F) = 99 kHz ---> - 45 dBc
(Fe - 5F) = 91 kHz ---> - 85 dBc
2) AD5452 + AD8065, RLoad = 1 kOhms :
(Fe - 3F) = 99 kHz ---> - 75 dBc
(Fe - 5F) = 91 kHz ---> - 82 dBc
How would you explain that the 3rd harmonic is so high with the ADA4841 compared to the AD8065?
The slew rate of the op-amp affects the third harmonics amplitude. So if you look at the AD8065, the slew rate is 180V/us whereas the ADA4841-1 has a slew rate of 12V/us. This difference in Slew Rate is more than likely causing the problem.