EXFO PSO-100 Series Optical Sampling Oscilloscopes - Manual (Page 54)

Setting up and Using the Optical Sampling Oscilloscope
46 PSO-100
Using the Clock Input
To use the external clock input:
1. Connect an external electrical clock to the front panel.
The clock should have a peak-to-peak voltage between 0.8 and 2 volts
for clock frequencies up to 12.5 GHz. It will work also for lower
voltages, but with a slightly worse timing jitter. For clock frequencies up
to 25 GHz, higher voltages are required, between 1.5 and 3 V.
2. Select External from the Clock menu (constant time scale is
recommended for a high quality clock with low timing jitter). The
figure below shows an example using a 10 GHz sub-rate clock and a
40 Gb/s NRZ data signal, that is a ¼ clock sub-rate.
The clock signal itself is shown above the data signal.
Note: If the clock signal on the sample screen turns red, this indicates that the
clock signal is too low, and should be increased; or it may happen in a
measurement situation with frequency holes. It goes away after a while
(read more about frequency holes in Frequency Holes on page 120).