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AD9364 External LO phase noise

Question asked by Olegis on Nov 2, 2014
Latest reply on Nov 11, 2014 by tlili

Hello,

 

I'm using the AD9364 IC for a transceiver application at 2.4GHz. During the receiver evaluation I did a blocking test (injecting both desired signal at 2300MHz and interfering tones at various offsets from that frequency) and got the following results -

 

Blocker @ 5MHz offset -59dBm (which corresponds to phase noise of ~-105dBc/Hz)

Blocker @ 10Mhz offset -46dBm (which corresponds to phase noise of ~-120dBc/Hz)

Blocker @ 20MHz offset -28dBm (which corresponds to phase noise of ~-138dBc/Hz)

 

The test was done with a desired signal level of -95dBm at the Rx balun input of the AD9364. The blocker tone level was increased until the SNR at the receiver output degraded to ~3dB. The receiver gain control was set to maximum gain, manual gain control. The analog BB filter was set to 2MHz.

 

The same test was performed with an External Rx LO, which was configured per "AD9361RFandBBPLLUserGuide2.4.pdf" document. The external LO level was set to 0dBm. I was expecting much better results with the external LO, since blocking performance depends heavily on the LO phase noise - but the results I got were the same as if the internal LO was used.

 

So my question is - maybe one of the dividers in the external LO path limits the phase noise performance ?

 

Thank you in advance,

Oleg C.

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