AD8347 Baseband Frequency Limitiation?

Using the AD8347 in a direct down conversion (Zero IF) application.

2.4 GHz to basband with a 9600 bps data rate.

Not seeing output as expected. Is there a frequency limitation to the baseband output (some minimum ?)?

Thanks

  • 0
    •  Analog Employees 
    on Mar 16, 2010 8:04 PM

    The Baseband output frequency will go down to DC. The part is meant for direct conversion applications where the there is a zero IF.  You may want to enable the DC offset compensation loop, if not done so already, to mop up offsets that may plague the desired signals.

  • 0
    •  Analog Employees 
    on Mar 16, 2010 9:33 PM

    Thanks,

    Actually I am implementing it already - set to default 400 Hz via the equation for .1uF on page 22.

    This failed to work, yet is significantly under the data rate (DR is 9600).

    If the offset compensation circuits are tied IOFS and QOFS to VREF to disable them, the data works properly, but I then have to deal with the offset.

    The datasheet says (page 22),  "The corner frequency must be set to a frequency that is much lower than the symbol rate of the demodulated data."

    What is the ratio between the corner frequency to the symbol rate for this to work reliably? It seems 400/9600 is not wide enough - or do you think it is something else?

    Thanks

  • 0
    •  Analog Employees 
    on Mar 17, 2010 12:17 AM

    9600bps is a not a large BW. Therefore, the high pass corner introduced by AC coupling should not "eat into" too much of the DC energy. I'd suggest trying setting the cap to 1uF or 10uF cap so that the the Fc is much more smaller and the relative BW is much more smaller. Currently 400 Hz corner is way too high for a 9600 bps signal.

  • 0
    •  Analog Employees 
    on Aug 2, 2018 4:10 PM
    This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

    Thank you,
    EZ Admin