Increase the resolution of a counter

Discussion in 'General Electronics Chat' started by bug13, Apr 30, 2015.

  1. bug13

    Thread Starter Senior Member

    Feb 13, 2012
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    Hi guys

    I am looking at the datasheet here: (DS00VQ100 chip, laser range finder chip)
    http://forums.parallax.com/attachment.php?attachmentid=84096&d=1313511811

    The chip is only running at 12.8MHz, by my calculation, it has a resolution of 156.25ns. So how does it get 60ps - 400ps resolution? (Counter is used to measure time of flight of the laser pulse)

    I am guessing something like over sampling uses in ADC. so if I am right, what this technique calls, I want to find out more about it.

    Thanks guys!
     
  2. Papabravo

    Expert

    Feb 24, 2006
    11,063
    2,150
    This is just a guess, but what you are seeing is just the reference frequency. It may be part of a phase locked loop in which an oscillator with a much higher frequency is divided down and compared to the reference frequency. Then using a control voltage the higher frequency (VCO) is adjusted up or down in order lock it to the reference frequency.
     
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  3. bug13

    Thread Starter Senior Member

    Feb 13, 2012
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    Hi,

    I found this: (ref: http://forum.arduino.cc/index.php?topic=110549.30)
    But I still don't understand, any more guess?
     
  4. bug13

    Thread Starter Senior Member

    Feb 13, 2012
    1,257
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    Hi,

    I think it explains (sort of) how to get a higher resolution in the datasheet from page 12, but I still don't get it. Any thoughts?
     
  5. RichardO

    Well-Known Member

    May 4, 2013
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    I agree with you that the data sheet doesn't tell us how the part works.

    I am just guessing here but I think they are dithering the crystal oscillator frequency. This is why they need a crystal that can be pulled in frequency. By varying the oscillator frequency they can do a lot of averaging of the received signal timing and get improved time resolution. They also seem to be comparing the frequency of the varying oscillator frequency to a stable oscillator by mixing (down converting). The source of the signal that varies the frequency may be controlled the Noise register.

    Here is a newer version of the data sheet.
     
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  6. bug13

    Thread Starter Senior Member

    Feb 13, 2012
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    Thanks for the new datasheet, it gives me a bit more info, which is good. It looks like some sort of DSP happening in that FPGA, I guess I need more googling.
     
  7. RichardO

    Well-Known Member

    May 4, 2013
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    You are very welcome. Please let us know what you find out. :)
     
  8. bug13

    Thread Starter Senior Member

    Feb 13, 2012
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    RichardO likes this.
  9. bug13

    Thread Starter Senior Member

    Feb 13, 2012
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