Considering AD7606B but need more PGA ranges (down to +-20mV)

Hi,

I'm considering an AD7606B for its channel count, oversampling capability and ease of synchronisation.

I am trying to digitise a modulated 5kHz sine wave carrier (from 4, 8 or more sources) and need to acquire 8 samples per cycle (40ksps) for a lock-in correlating demodulator. Demodulated bandwidth is about 1 to 2kHz. I intend to clock the ADC at 640kHz and use the oversampling function to achieve 40ksps. 16 bits of resolution is sufficient but 18 would be better (limited by Johnson noise).

A range of signals are to be connected, hence the need for 10V to ~20mV range. Can you suggest an appropriate additional PGA?

I also need to allow some future-proofing by perhaps increasing the data rate (by reducing the oversampling). This is a nice-to-have for product specmanship.

Is this an appropriate ADC? I have also considered AD7771 and AD7768 (and ADS8688).

FYI, I am considering using and AD9542 to derive the 640kHz clock from a distributed 5kHz system clock (covered in another post)

Am I on the right track?

Thanks in advance,

Steve



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[edited by: Lluis at 8:41 AM (GMT 0) on 20 Apr 2020]
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  • 0
    •  Analog Employees 
    on Apr 20, 2020 8:39 AM

    Hi Steve,

    Is you input range fixed at +/-20mV, or should it cover from a variety of input ranges, including +/-20mV?

    For the AD7606B, I do not have a recommended (tested) front-end amplifier as of today, but we can help review your signal chain design. For the AD7771, it has gains up to 8, that would allow you to get closer to the +/-Vref input range. However, note they are at different level of performance (16b SAR vs 24b SD), not sure what the requirements are.

    Regards,

    Lluis.

  • Hi Lluis, thank you for your reply.

    Our current system uses multiple SD ADS1672 ADCs with our own AFE. We only use the top 16 bits and only sample at 40ksps (!).

    I am looking to save cost by moving to a multi-channel ADC with simplified AFE. I want to make incremental improvements in sampling rates and resolution - where practicable (i.e. nice to haves). I do like the oversampling capability of the AD7606B and can push the anti-alias filter from 20kHz to 160kHz or so and I'll sample at 640kHz.

    I am investigating the use of PGA280 as an AFE - does Analog have an equivalent that could help me build a 10V to 10mV system?

    Steve 

  • 0
    •  Analog Employees 
    on Apr 21, 2020 10:10 AM in reply to squirest

    Hi Steve,

    How about  ADA4254? Although I haven´t looked your signal chain to know if that would match with AD7606B inputs. I´d suggest looking at the model we have on AD7606B´s product page. You can learn its frequency response, configure front end RC filter, and learn how it works in general: oversampling performance, interface, calibration, CRC, etc.

    https://www.analog.com/media/en/engineering-tools/design-tools/AD7606X-Software-Model-2-0-1.zip

    Regards,

    Lluis.

  • Thanks Lluis - I downloaded and ran the AD7606B software model the other week - it really helps with understanding and comparing functionality. Great tool!

    I have ordered the AD7606B Eval Board so will see how it looks. 

    I'll take a look at the AD4254 too.

    Thanks,

    Steve

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