DDC All-bypass real output ?

There is insufficiant information in the AD6636 DDC datasheet to interrpret what output should be produced when all filter and NCO elements are set to "bypassed" mode. My goal is to see the RAW ADC input to this chip being passed through to the output port.

Setup: Observation of my data output from PORT A OUTPUT ( driven by a single activated channel) from a single portA INPUT ( set to "real input only" ) in fact produces output from BOTH INPUTS PORT A and PORT B. ( A input appears on "I" 16 bit word, while B input appears on "Q" word).

This is despite not 'allocating' Port B input to any DDC channel.

Is this correct behaviour? and If I do nothing else now expect turn on NCO with zero hertz, will the "B" real input still appear on the "Q" word output?

Thanks for any replies.

Dave

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  • 0
    •  Analog Employees 
    on May 4, 2012 10:19 PM

    The AD6636 does not support a mode where the ADC input data is passed directly to the output port.  For proper operation you will need to enable at least one block and decimate by at least 2 - it's really intended for IF sampling with the NCO and filters enabled.  The specific supported modes depend on your input clock rate, PCLK rate, and PLL settings.  The output block expects to get and output I/Q data from one or more channels.

    Regarding the specific case you mention above I'm not sure I can comment except to state that I would not expect to see data on a single output from two different ADC inputs unless you have multiple channels enabled.

    Regards,

    Michael

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  • 0
    •  Analog Employees 
    on May 4, 2012 10:19 PM

    The AD6636 does not support a mode where the ADC input data is passed directly to the output port.  For proper operation you will need to enable at least one block and decimate by at least 2 - it's really intended for IF sampling with the NCO and filters enabled.  The specific supported modes depend on your input clock rate, PCLK rate, and PLL settings.  The output block expects to get and output I/Q data from one or more channels.

    Regarding the specific case you mention above I'm not sure I can comment except to state that I would not expect to see data on a single output from two different ADC inputs unless you have multiple channels enabled.

    Regards,

    Michael

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