34
DSOX4USBSQ USB 2.0 Signal Quality Analysis Application Electrical Testing Notes
2
Device Signal Quality Testing
On 4- channel oscilloscopes, you are forced to use different channel
pairs for the D+ and D- signals. This provides the maximum sample
rate. (Channels 1 and 2 are one pair and channels 3 and 4 are the
other pair.)
c
Press the
Adj D- Source
softkey and select the analog input source
channel connected to the adjacent D- signal (channel 1 in the
previous connection instructions).
7
Press the
Auto Setup
softkey to automatically set up the oscilloscope for
the selected test.
For optimal test results, you can make adjustments to the auto setup.
Generally, you want one packet of data, plus the time of one bit on
each end, across the oscilloscope's display. Also, vertical scale and
offset should be adjusted so that the signals take six vertical divisions
without being clipped.
You should see the transmitted test packet on the oscilloscope as below.
8
Press the
Run Test
softkey to run the selected signal quality test.
When tests are run, the oscilloscope stops acquisitions if they are
running, analyzes the data on screen, and then displays the results.
N O T E
Tests can take several minutes to run and cannot be cancelled once started.
