Understanding AD9364 Direct Conversion RFIC

Started by cogwsn 4 years ago5 replieslatest reply 4 years ago302 views

Hi all, New year wishes :) 

I am going through the specs of AD9364 which has direct conversion receiver architecture.

When I see the block diagram, I notice there is an RF Local Oscialltor before the ADC. This confuses me. If it is direct conversion, what is the LO doing there before ADC. Shouldn't that be a phase splitter instead ? 



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Reply by brutorJanuary 1, 2019

See perhaps the following article for an explanation :

Happy New Year

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Reply by cogwsnJanuary 1, 2019

Got it! Thanks :) 

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Reply by Rick LyonsJanuary 2, 2019

Hi. Here's 'Part 2' of the article that brutor referenced:

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Reply by cogwsnJanuary 2, 2019

Thank you very much. 

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Reply by fred_harrisJanuary 2, 2019
The signal presented to the mixer is presented to two mixers, with quadrature versions of the local oscillator. There is an in-phase and quadrature version of the down conversion to baseband. If the mixers, the analog filters, and the ADCs are perfectly balanced the spectrum of the signal will be found at baseband being carried by the complex (ordered pairs) baseband time series. I-Q imbalances, Self mixing, and truncating ADCs cause imaging terms from negative frequency to overlay the desired terms from positive frequency. Positive and negative frequency terms are no longer orthogonal. The self mixing also injects a DC line in the center of the down converted spectrum. The local oscillator also gets to see the input antenna and contributes to local interference. Cell phones use the zero IF to control costs. High performance, wide dynamic range receivers avoid the homo-dyne option. have a look at attached papers