When reading from a GPIO pin, at what frequency do the crests and troughs of a wave begin to blend together to the point that the CPU can no longer distinguish between them?

I assume the answer depends on the CPU and implementation, so to keep this simple, let's assume I'm using a BeagleBone Black (because I am).

If I have a 1Ghz sine wave, ranging from 0V - 3.3V, will be BeagleBone Black still be able to read it as anything other than a blur of ~1.65V?

Edit: Ok, I'm not worried about 1GHz specifically. I'm just wondering at what frequency the GPIO pin can no longer discern between the crests and troughs of the wave. The 1GHz example was just meant to be an extreme case.

  • \$\begingroup\$ Analog or digital IO? \$\endgroup\$
    – pjc50
    Feb 10, 2014 at 8:32
  • \$\begingroup\$ The GPIO pins on a BBB are digital IO. \$\endgroup\$
    – Soviero
    Feb 10, 2014 at 21:18

1 Answer 1


At 1GHz, any kind of single-ended measurement will be 100% rubbish. Be it digital or analog.


It may not be rubbish, if you had taken care of specific voodoo things.

  1. Termination - high frequency signals need termination resistance to preserve integrity.
  2. Shielding - a 1GHz signal becomes very sensitive to noise. You need to keep it out.
  3. Tons of other things I can't think of right now.

Anyway, these boards are made for signals to 30-50 MHz tops.

  • \$\begingroup\$ See edit above. \$\endgroup\$
    – Soviero
    Feb 10, 2014 at 21:21
  • \$\begingroup\$ Get your hands on the datasheet of the IC that takes care of the IO function. Probably one of the processors? \$\endgroup\$
    – Dzarda
    Feb 10, 2014 at 22:31

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