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ADSxx54, PGA281 & antialiasing

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Replies: 1

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Hello,

Can you recommend antialiasing filter between PGA281 and ADSxx54, cutoff ~2kHz. Traditionally with another diff amp or?

I assume ADSxx54 converters can be daisy-chained but want to be absolutely sure?

Best Regards,

risto

  •  Hello Risto,

    The circuit driving the SAR ADC (differential amplifier + antialiasing filter) must be able to drive the ADC sampling capacitor and settle to the target voltage within the required resolution during the allowed acquisition period. Designing the RC filter requires knowledge about the signal being converted as well as details of the driver amplifier.  The ADSxx54 datasheet applications section provides some examples of ADSxx54 driving circuits on page 48. In addition, the articles and app notes below provide good background info:

    http://www.planetanalog.com/author.asp?section_id=483&doc_id=563628

    http://www.ti.com/tool/TIPD168?DCMP=contrib-en&HQS=tlead-dconv-pdc-hpa-pa-sar-smallads-contrib-050-tipd168-tidesigns-en

    http://www.ti.com/tool/TIPD117

    In order to answer the question, we need to know details of the application:

    -Which ADSxx54 device are you planning to use: ADS8354, ADS7854 or ADS7254? What is the sampling rate required?

    - Details about the sensor or signal measured: If this is a DC signal, what is the differential and common mode voltage? If AC signals, what are the frequency range, common-mode voltage and amplitude? Single-ended or differential signal?

    - Details about the driving amplifier used in the application: if using the PGA281 (IA typically used in DC applications) please provide the details of supply connections, the gain setting (s) required, etc. If a preliminary schematic is available, please post.

    - Unfortunately, the ADSxx54 does not support daisy chain option. We have other devices that support daisy chain: ADS868x (8ch/4ch 16B SAR ADC with programmable input ranges), ADS886x (16B, 1MSPS miniature SAR), ADS888x, ADS8556 (16B 6ch +/-12Vsimultaneous sampling), etc.  Please let us know the requirements: single-ended or differential ADC input, resolution, sampling rate, input voltage range, # of channels and we could suggest other devices. Also, let us know if simultaneous sampling is required.

    Thank you and Best Regards,

    Luis

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