Parasitic spectral component AD6636

In case of chip utilization of AD6636 there was the following problem:
at a zero spectral bin there is always a parasitic spectral component of which existence it is possible to get rid changing values of the register CIC scale factor. But at the same time the one-signal dynamic range of a receiving path makes 60 dB that is unacceptable for our product. Absolute level of a parasitic spectral component doesn't depend on value of the register CIC scale factor, therefore she is born or in CIC5, or after it.
Whether this problem is standard for a chip of AD6636 or there is a method will get rid of a parasitic spectral component in a zero bin?
  • 0
    •  Analog Employees 
    on Nov 1, 2016 11:36 PM


    The AD6636 is a product that we still manufacture, but do not recommend  or provide support for new designs.  Most new designs that require a DDC require a faster data rate than the AD6636 can provide.  They are generally either integrated into the ADC or implemented in an FPGA or ASIC.  

    I was able to find this information that I hope will be helpful for you: 

    The AD6636 DDC internal databus is actually 22-bits (not 24-bits) prior to the AGC with 16bits available as output for the user. If the AGC is bypassed, the 16 MSB justified bits are available as output and the lower 6-bits are truncated. This will typically result in a noticeable DC spur component in the output. If AGC is enabled, even with zero gain attributes, the lower 6-bits get rounded by the AGC which will typically result in a much lower DC spur component in the output.



  • Many thanks for the response David
    Let's try to realize your idea, I will report about results later.