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ADA2200 Program filter setting and Output waveform calculation

Hi,

There are two questions about use ADA2200.

1. Regarding to the ADA2200 Program filter function, Could you please help to provide some reference data for the Program filter setting. The datasheet doesn't tell too much about it.

2. Regarding to the output waveform, the datasheet says -

In the default configuration, there are eight output sample periods during each RCLK cycle. There are four updated output samples while the RCLK signal is high. While RCLK is low, the fourth updated sample is held constant for four additional output sample periods.  (Page 13, Mixer section)

Does it means only half cycle waveform will be present (As below figure) ??  How to calculate the input waveform value?

Hear from you soon and thanks!

  • Hi Brent,

    I already contacted the product owner of the ADA2200 regarding your query. I'll get back to you as soon as I heard anything from him.

    Best regards,

    Emman

  • Hi Brent,

    We have a tutorial, MT-234, on using the programmable filter of the ADA2200 at this link. I hope that will answer your first question.

    Regarding your second question...the ADA2200 mixing function produces a sampled output that is in between a 1/2 wave rectification and a full-wave rectification. To measure the input waveform value you can do one of the following:

         - Low pass filter the output and measure value

         - Calculate the cycle mean. This is done by sampling 8 consecutive output values (5 unique values+3 hold values) and taking the average value.

    Regards,

    Brian

  • Hi Brian,

    Still have question about output waveform calculation,

    As you mentioned : Calculate the cycle mean, the output waveform is done by sampling 8 consecutive output values (5 unique values+3 hold values)  >>  This should have accuracy concern if calculate the mean including these 3 hold values (These 3 hold value may have very big difference with the real waveform).


    Or, is it ok to calculate the mean for 4 unique vales (Calculate it as full-wave rectification) ??



  • Hi Brent,

    The value of interest is the average value of the waveform.  While the output samples from the ADA2200 will not closely resemble the instantaneous input waveform, this is does not impact the accuracy of the average value. The datasheet accuracy specs were determined using the 8 sample method I suggested.

    Using 8 samples per cycle versus 4 samples for cycle will lower the noise floor due to the higher number of samples. You could use 4 samples instead of 8 per cycle, but unless you are trying to reduce the computational load on your micro, I would use 8 samples.

    Brian

  • Hi

    A question about values:

    Calculate the cycle mean. This is done by sampling 8 consecutive output values (5 unique values+3 hold values) and taking the average value.

    The ADA2200 only give out 4 unique values+4 hold values ( value of the 4th unique value), as I can see in the datasheet page 6 (sample 0, 1, 2 and 3+4 hold samples)

     

    So where does the 5 unique values+3 hold values come from ?

     

    /Steffen

  • Hi Steffen,  

    You are correct.  The cycle mean is the average of 8 samples. 4 of which are unique, and 4 of which are hold values.

    Brian

  • Hi Brian

    I have an other question:

    In the MT-324 the BP1 and BP2 filter that I tried to use, but they has Corner/center frequency at Fsi/32 (Hz/Nyquist = 0.5) and I need to use them with Fsi/64 (Hz/Nyquist = 0.25), so that they have corner at my RLCK frequency as the default filter (this filter has a wide filter responce, wish does not filter noise very well, out of the signal.

    I have tried to change the 0x0024 for 4F to E0 , but this does not work, something else goes wrong - so is it possibly to get BP1 and/or BP2 with Fsi/64 and not Fsi/32 ?

    With mixer on.

    /Steffen

  • Unfortunately we do not have any bandpass filters with a center frequency of Fsi/64.

  • Is it possibly to get one ?, since the filter in MT-324 have different Corner frequency, so they are diffucult to use in a application.