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ADC Sampling Rate

Varaprasad Rayudu
Prodigy 150 points

Other Parts Discussed in Thread: ADS5400, ADC12J4000

Hello,

We would like to implement the oscilloscope function in our ATE system to measure rise time,fall time,duty cycle,VOH,VOL by capturing input signal with ADC sampling using microcontroller.

Our frequency range for input square wave signal is from 10MHz to 100MHz with Tr,Tf specification of <5nsec.

Could please suggest selection ADC part # based on above requirements w.r.t sampling rate and what will be the relation between ADC sampling rate  and input signal bandwidth.

Thanks,

Varaprasad

  • 0
    TI__Mastermind 18095 points

    Varaprasad:

    A 100 MHz signal corresponds to a 10 ns period.  For a square wave, the rise/fall time would be less than 5 ns.  Another way to look at it is to determine how accurately you need or want to represent the square wave.  A true square wave has infinite harmonics.  A 100 MHz square wave with a 5 ns rise/fall time would look more like a triangle wave.

    So, the more you want to capture a square wave the faster the ADC sampling rate and the larger the BW is needed.  I would say a reasonable rule of thumb is to select the ADC with 10x sampling/BW capability as the highest input signal.  For a 100 MHz signal, look for an ADC with 1GSPS or higher.

    TI has several options in this space.  One option is the ADS5400 (1 GSPS, 2.1GHz BW).  You can opt to go even higher with a JESD interface with a device like the ADC12J4000 (4 GSPS, 3.2 GHz BW).  Check out TI's web page if you want to explore other GSPS ADC options.

    --RJH