Oscilloscope problem or noise or what

Discussion in 'Test & Measurement Forum' started by majd-ghadab, Aug 19, 2018.

  1. majd-ghadab

    Thread Starter Member

    Dec 25, 2012
    18
    0
    Hello everyone,
    i bought a couple of weeks ago Rigol oscilloscope 300 Mhz 2Gsa/s because i would like to work with low rf frequencies.. anyway.
    i work also with microcontrollers .. the problem is when i see the Spi data bus 5.5 Mhz the speed of Spi as set in Cubemx the output looks like the picture.
    the circuit is working that means the square wave is correct but why it looks like this . please help
    is there a problem with my oscilloscope?
    i know i need a lot of samples to see squarewave more than sine but is this not enough 300mhz 2gsa/s !!
     
  2. Hymie

    Member

    Mar 30, 2018
    469
    97
    Try an alternative scope probe, make sure that the circuit 0V is connected to the scope chassis.
     
  3. MrChips

    Moderator

    Oct 2, 2009
    16,740
    5,132
    Is your oscillator probe set to 10X attenuation?
    How and where is the grounding clip of the oscillator probe connected?
    Make sure that you connect the grounding clip to a GND location close to the SPI signal source.
     
  4. crutschow

    Expert

    Mar 14, 2008
    19,542
    5,445
    More likely with the oscilloscope user. :D
    It looks like a ground connection problem with the oscilloscope probe as MrChips noted.
    You should be using a 10:1 probe.
     
  5. majd-ghadab

    Thread Starter Member

    Dec 25, 2012
    18
    0
    thank you all for your replies
    i am waiting for the probes and they shipped to me..
    i am using a cheap connector !!
    when the probes come i will post whay will happened. Thanks
     
  6. danadak

    Well-Known Member

    Mar 10, 2018
    1,459
    297
  7. Wuerstchenhund

    Member

    Aug 31, 2017
    101
    29
    Well, I really hope you got this scope really really cheap (i.e. <$200) because the Rigol DS1302CA has been out of production for over 5 years now. Also, it's specs are pretty poor (only 10kpts memory which is laughable, shitty low-res screen, very low update rate, no serial decoders).

    As the others said probably user error. You didn't provide any details as to how you probed the signal so it's hard to tell what you did wrong.

    300Mhz BW and 2GSa/s are generally more than enough to capture all relevant parts of a 5.5MHz SPI signal, however because your scope has so little memory the sample rate may drop quickly to become insufficient for resolving the actual signal (i.e. with single ch mode anything longer than a 5us segment means your sample rate and with that your usable BW will drop). However, the image shows as timebase setting of 50ns/div which at 12 divisions is a time span of 600ns so the sample rate should not be a problem here.

    Tell us a bit more about your probing technique.
     
  8. rsjsouza

    Member

    Apr 21, 2014
    40
    16
    Wuerstchenhund, it could well be the much newer DS2302A.
     
  9. Wuerstchenhund

    Member

    Aug 31, 2017
    101
    29
    You are right, from his description it could be a DS2302A, however the picture clearly shows a DS1302CA ;)
     
    rsjsouza likes this.
  10. rsjsouza

    Member

    Apr 21, 2014
    40
    16
    Duh! I didn't see the picture... :confused:
     
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