Host Signal Quality Testing
3
DSOX4USBSQ USB 2.0 Signal Quality Analysis Application Electrical Testing Notes
41
If you are using a single- ended (SMA cables) connection, press the
DP SMA
softkey and select the analog input source channel connected
to the D+ signal. Then, press the
DN SMA
softkey and select the
analog input source channel connected to the D- signal.
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.)
Hi- Speed tests using single- ended SMA cable connections are not
supported on 2- channel oscilloscopes because the sample rate does
not meet the required 5 GSa/s.
c
Press the
Test Type
softkey and select
Near-end
or
Far-end
.
The terms "near- end" and "far- end" are based on which end of the
cable the test fixture is attached in relation to the device being
tested. The point where measurements are made dictates what eye
template is used.
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.
