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searching solution for differential inputs for 14/16 ADC

Harshad Chirutkar
Prodigy 180 points
Other Parts Discussed in Thread: ADS8412, ADS8318, THS4520, THS4521, THS4131, THS4524, THS4522, THS4509

Sir,

I have differential Inputs

VS - 2 to 2.7V

VR - 2 to 1.3V

I want to design ADC Card with differential amplifiler.for 14/16 bit ADC

can you suggest and solution.

thanks,

  • 0
    TI__Mastermind 33340 points

    Harshad,

    There are several options we can consider, but before we start narrowing them down, it would be good to know:

    1. Available power supplies.
    2. ADC part number and input common-mode input (if this is known).
    3. Frequency range of desired signal
    4. Required amplifier gain
    5. Overall peformance targets for amp+ADC (SNR, SFDR if this is known).
    6. Desired input characteristics of card such as: 
           - AC coupled or DC-coupled
           - Input impedance

     

    Best Regards,

    John

  • 0
    TI__Expert 4115 points

    I read your previous posts on "Finding 14/16-bit differential input ADC" along with reply from Chris Opoczynski. If you choose to use the ADS8318 or the ADS8412, the THS4521 fully differential amplifier will provide for full performance with single 5V supply to about 100kHz input signal frequency with mininmal degradation of THD to about 1MHz. The THS4520 with single 5V supply will provide full THD performance to 1MHz  and higher.

    If you opt to find a differential input ADC that will take 0 to 5V on each input (10V differential) the drive amplifier will need to have supply voltage higher than this range. The THS4131 is used quite a lot in this situation with +/-8V supplies. I think the +/-8V supplies are used because they are symetrical and common, at least in the past. The +8V posistive supply is a good choice, but a negative supply below -3V does not really improve performance. So  +8/-3, +8/-3.3, +8/-5, or +8/-8 can be considered.

  • 0
    TI__Mastermind 33340 points

    Fully differential amplifiers make effcient ADC drivers and there are a few choices depending on the speed and the power requirements.

    The THS4521, THS4522, and THS4524 are a low-power family of fully differential amplfiers in single, dual and quad packages respectively. They draw about 1ma of current per channel from a 5V power supply, and can operate from 2.5V to 5.5V. They will offer 14b/16b of performance at frequencies less than 1MHz.

    The THS4520 is a little faster than the THS4521 and it draws about 14ma of current from a 5V power supply. It offers 14b/16b of performance for frequencies less than 5MHz.

    The THS4509 is our fastest fully differential amplifier. It draws 34ma of current from a 5V power supply and can serve as an effective 14b ADC driver for frequencies less than 50Mhz.

    There are several application notes available on the TI web site that cover many aspects of circuit design and performance with fully differential amplifiers. I checked a few moments ago and there doesn't seem to an easy way to find a dedicated list on this topic. A work-around is to go to the link below and search the browser page with the key word "fully". That seemed to identify the major app notes on this topic.

    http://focus.ti.com/analog/docs/analogtechdoc_hh.tsp?familyId=57&docCategoryId=1&contentType=8&viewType=mostuseful&rootFamilyId=57