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Using the bandpass sigma delta ADC in AD9874?

Our application is a narrow band I/Q signal at around 2.6MHz, that seems to fall on the input range of the IF2 signal in AD9874.

Can we bypass the LNA and mixer front end of the AD9874 and just use the bandpass sigma delta ADC in AD9874 by directly feeding the signal to the IF2 port? 

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  • Yes it is possible if you operate the ADC clock at 20.8 MSPS such that the IF2 is centered at 2.6 MHz.  Also you can refer to page 38 of the datasheet that describes such an application where the mixer's LO port is fixed to a DC bias voltage such that one can still use the LNA input path for the 2.6 MHz IF signal.  Lastly, you may want to refer to the recently updated AD9864 datasheet (sister product of the AD9874) for an updated (more robust) SPI  initialization procedure. 

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  • Yes it is possible if you operate the ADC clock at 20.8 MSPS such that the IF2 is centered at 2.6 MHz.  Also you can refer to page 38 of the datasheet that describes such an application where the mixer's LO port is fixed to a DC bias voltage such that one can still use the LNA input path for the 2.6 MHz IF signal.  Lastly, you may want to refer to the recently updated AD9864 datasheet (sister product of the AD9874) for an updated (more robust) SPI  initialization procedure. 

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