6
\$\begingroup\$

I'm trying to understand how I can figure out the minimum requirements of an oscilloscope in order to measure for example USB 2 full speed signals at 12mbps.

I know it's not safe or correct to say that 12mbps = 12MHz. So how do I determine the adequate frequency requirement, if I wanted to buy a scope.

\$\endgroup\$
  • \$\begingroup\$ The same answers as for USB3 apply, just scaled down by whatever factor: electronics.stackexchange.com/questions/206578/… \$\endgroup\$ – PlasmaHH Apr 12 '16 at 14:23
  • \$\begingroup\$ Cheap and powerful Rigol DS oscilloscopes have analogue bandwidth up to 50Mhz (100Mhz after some crappy tweaking) which should be enough, just buy it, connect and enjoy! \$\endgroup\$ – Jakub Rakus Apr 12 '16 at 14:25
  • 1
    \$\begingroup\$ A bandwidth of 50MHz might not be enough for sampling 12MHz square waves, as they are composed with much higher frequency components. The signal will be very distorted. Don't mix the sampling rate with the bandwidth, these are different beasts. \$\endgroup\$ – Eugene Sh. Apr 12 '16 at 14:36
2
\$\begingroup\$

12 Mbps is equivalent to a square wave of 6 MHz when the bits are toggling at maximum rate.

However, if you are wanting to measure rise times and fall times to any degree of accuracy you are going to have to dig deeper and put more info in your question.

If you are not too fussed about rise times and fall times and just want to capture streams of data for logical analysis then a 100 MHz sampling scope is good enough and you might get away with decent results at 50 MHz sampling.

\$\endgroup\$
  • \$\begingroup\$ Is the question here about sampling rate or the bandwidth? The bandwidth should be few orders higher.. \$\endgroup\$ – Eugene Sh. Apr 12 '16 at 14:33
  • \$\begingroup\$ @EugeneSh. most o-scopes these days are digital so sampling rate is probably the most important consideration. \$\endgroup\$ – Andy aka Apr 12 '16 at 14:40
  • 1
    \$\begingroup\$ the input circuitry is still analog, and if it will filter out some harmonics , the sampling rate won't help much... \$\endgroup\$ – Eugene Sh. Apr 12 '16 at 14:41
  • \$\begingroup\$ There will be an anti-alias filter in a digital scope. It's frequency will be related to the sample rate but I don't intend to go into details about how this filter will "purify" the signal to make it compatible with the sampling. Maybe you should make an answer of this detail. \$\endgroup\$ – Andy aka Apr 12 '16 at 14:45

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.