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ADS5553: Anti-aliasing filter for an ADC

xyz xyz
Intellectual 1000 points
Part Number: ADS5553
Other Parts Discussed in Thread: TINA-TI, ADS5560, LMH6552,

Hello

I have an AD5553 ADC. I don't have any anti-aliasing filter so I need to put an first order RC filter at the input of AD5553.

I've studied below document to design anti-aliasing filter.

/cfs-file/__key/communityserver-discussions-components-files/73/8468.4478.PA_2D00_001--Optimize_5F00_SAR_5F00_converter_5F00_design-REV-b.pdf

But I couldn't calculate the t_acq (acquisition time) for AD5553.

the sampling rate is 65MHz and on the other side I should have the first nyquist zone (DC to 32.5MHz).

How should I calculate the amount of R and C? from above document I got that I should be aware of settling time and other parameters.

Regards

  • 0
    TI__Genius 9675 points
    Hi,

    We are looking into this now.

    Jalen
  • 0 in reply to Jalen Tate89
    TI__Guru* 91947 points

    User,

    This is a legacy Burr Brown part and the only information we have available is the data sheet. Regarding your filter design; see if the attached document helps. I would also suggest using a filter design tool which specifies for the type of filter, and the bandwidth of interest. You can then order an ADS5553EVM and try this out with actual components.You can also look into using TI's TINA-TI software download, for simulation.

    Regards,

    Jim

    ADC theory.pdf

  • 0 in reply to jim s
    Intellectual 1000 points

    ADC theory is good

    But...

    page 46 of the ADS5560 datasheet is very useful bcoz I'm using LMH6552. ADS5560 is a 80MSPS so the designer put a Anti-aliasing filter with 40MHz bandwidth. (at the end of page 39):

    on the other side in the page 28 we have: we can consider Rin and Cin is approximately 10K and 7pF repectively.

    But I think for simpler ADCs I can put a first order RC with fs/2 cut off frequency at the input of ADC.

    do you have any idea?

    thanks

  • 0 in reply to xyz xyz
    TI__Guru* 91947 points
    User,

    I suggest you simulate it then try it with evaluation hardware. I have also forwarded this post to our amplifier team which are very knowledgeable with filter design.

    Regards,

    Jim
  • 0 in reply to jim s
    TI__Genius 15975 points

    Hi,

    It is possible to use a simple RC as an anti-aliasing filter between the LMH6552 and the ADS5553. However, the simple RC would not provide a steep roll-off beyond fs/2 Nyquist band and thus, impact system performance in-terms of noise and spurs. Instead, I would recommend to stay with the filter configuration shown below with modified values for 32.5MHz cut-off. You can always tweak values on the bench after implementation to get a flat-band response.

    Best Regards,

    Rohit

  • 0 in reply to Rohit Bhat
    Intellectual 1000 points

    it's notable:
    1-when I have an over-sample the aliasing will not take place. for example when I have a 1MHz signal and the sampling frequency is 10MHz the aliasing will not take place. here OV=5. (first Nyquist zone is 2MHz so OV=fs/Nyquist)
    even the over-sampling improves the SNR and other parameters.
    2- my application is baseband that's meaning the input signal below 50MHz.
    3- RFI filters at the output of FDA is to get rid of high frequency noise. in such application we can use a RFI filter with fc=80MHz or more. it depends on the application.
    4- it's better to use a LPF before the amplifiers stages to limit the noise.
    the below documents are very informative:
    www.analog.com/.../wideband-adc-design-considerations-2.html
    cds.linear.com/.../dn1031.pdf

    Regards