# Residual phase noise of ADL5569 or any other fast differential amplifier

I am going to use the most resent and the fastest ADL5569 differential amplifier as a buffer at the output of DDS. Naturally my aim is to impose as lower as possible phase noise on the DDS output signal. But the ADL5569 datasheet does not contain any information about its residual phase noise and it is the case for other similar amplifiers.

I can suggest that the phase noise is low enough since such an amplifier utilizes SiGe process, but I do not have enough time to check that by myself.

Perhaps somebody could provide  me and the community with measured or simulated data related to phase noise performance of  ADL5569 or similar DA.

Thanks in advance.

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• Hello.

I am not sure if I understand your question, but I try to answer.

Non-linear operation devices like transistor in oscillator or PA End-Stage working in any class (B, AB, F...) influence the phase of the signal in large signal condition. So we can speak about phase noise (or AM-PM conversion) in these cases.

Usually diff. amplifier are used under linear operation. I hope it is also your case. The output noise density of DDS and noise contribution of diff. amplifier are simply added here from power point of view. The graph of noise figure vs. frequency is on the figure 8 in the datasheet of ADL5569. Of course you need to calculate with flicker noise at low frequencies (N*1kHz).

Reply
• Hello.

I am not sure if I understand your question, but I try to answer.

Non-linear operation devices like transistor in oscillator or PA End-Stage working in any class (B, AB, F...) influence the phase of the signal in large signal condition. So we can speak about phase noise (or AM-PM conversion) in these cases.

Usually diff. amplifier are used under linear operation. I hope it is also your case. The output noise density of DDS and noise contribution of diff. amplifier are simply added here from power point of view. The graph of noise figure vs. frequency is on the figure 8 in the datasheet of ADL5569. Of course you need to calculate with flicker noise at low frequencies (N*1kHz).

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