What is the input frequency range of AD9643 Evaluation board ?


I bought a AD9643 evaluation board and its data capture board for my experiment related to RF.

I read a datasheet of AD9643 dozens of times, but I do not know about the input frequency range of AD9643.

In my experiment with AD9643 with evlauation board and its data capture board, there were some distortions when frequency of input signals is very low( e.g. input signal is rect(squre) function and its frequency range is in 0~5MHz).

In other words, I just trying to obtain a raw data according as a input analog signal using AD9643 evaluation board and capture board.

But, in my experiment, output data is not correspond to input signal. It operates same as a high-pass filter.

Also, by the datasheet(e.g. AD6643/AD6649/AD9613/AD9643 Schematics), there are some RF Transmission Line Transformer(e.g. ETC 1-1-13).

However, the ETC 1-1-13(RF transmission line transformer) is operated in range of 4.5MHz~3000MHz by its datasheet.

Thus, I'm very confused what is the input frequency range of AD9643. I think there is no document which tells accurate frequency range.

Please tell me a guaranteed input frequency range of AD9643 or related documents ( especially, lower limit of input frequency)

  • 0
    •  Analog Employees 
    on Oct 31, 2011 9:21 PM

    Hi Terry, the input frequency range of the AD9643 is approximately 0-400MHz.  The ADC is capable of having DC content in the input waveform.  The evaluation board for the AD9643 however is not DC-coupled, but instead is AC-coupled.  This is done for ease of testing and evaluating the ADC with a signal generator as an analog input signal.  Most signal generators cannot accept DC voltage at their input terminals so the board is AC-coupled to avoid this dilemna.  The effect you are seeing is that the ETC1-1-13 along with the series blocking capacitors in the input network are limiting your low frequency performance and creating a high pass filter.  The upper bounds of the frequency range is governed by the ADC, which is stated in Table 2 of the data sheet as 400 MHz (states the input bandwidth specification of the AD9643).  You can actually input a signal higher than 400 MHz, but above 400 MHz you will begin to see performance degradation of the ADC.  To get back to the low frequency performance, you would need to remove the DC blocking capacitors and remove the baluns and use the footprint available for the transformer instead.  This allows you to keep DC from getting back to the signal generator.

  • Thank you for your prompt reply.

    I have a few questions regarding the accurate lower bound of the input frequency range.

    There are some RF transformers on input path of AD9643 Evaluation Board, e.g. ETC-1-1-13(4.5~3000MHz) on passive path and TC3-1T+(5~300MHz) on active path.

    Am I right in thinking that these two transformers are greatly affecting the lower bound of the input frequency range?

    If yes, should I input a signal higher than 5MHz to avert a distortion in respect of low freqeuncy signal?

    Please tell me a guaranteed lower bound of the input frequency range, if I just use a AD9643 Evaluation Board without additional works.


    Thank you.

  • 0
    •  Analog Employees 
    on Nov 1, 2011 5:53 PM

    Hi Terry, you are correct in that the baluns and transformers on the eval board are what is limiting the lower frequency response of the eval board.  If you input a signal of higher frequency (5-10MHz or above) you should see the signal response look much better.  The baluns that are on the passive network have a stated response on their data sheets of 4.5MHz to 3GHz.  So in the 5-10MHz range and above you should see much better signal response.  If you were to remove the baluns and drive the ADC differentially, the ADC is capable of passing DC content (thus complex signals) - so there isn't really a lower bound, the ADC supports down to 0Hz and into the complex frequency domain.  However, the eval board does not have a second SMA connector to allow for driving the ADC differentially without a balun or transformer unless you modify the board in some way to add another SMA or some other means to allow for driving the ADC differentially.

  • 0
    •  Analog Employees 
    on Aug 2, 2018 4:30 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