HP 8753D - Page 392

Figure
6-66.
Low
P
ass
Step
Measurements
of
Common
Cable
F
aults
(Real
F
ormat)
Transmission
Measurements
In
Time
Domain
Low
Pass
Measuring
small
signal
transient
response
using
low pass
step.
Use the
low
pass
mode
to
analyze
the
test
device's
small
signal
transient response
.The
transmission response
of a
device
to
a
step
input
is
often
measured at
lower frequencies
, using
a function
generator
(to
provide
the step
to the
test device)
and a
sampling oscilloscope
(to
analyze
the
test
device
output
response). The low pass step mode extends the frequency range of
this type of measurement to
3 GHz (6 GHz with an analyzer Option 006).
The step input shown in Figure 6-67 is the inverse F
ourier transform
of the frequency domain
response of a thru measured at calibration. The step rise time is proportional to
the highest
frequency in the frequency domain sweep; the higher the frequency
, the faster the rise time
.
The frequency sweep in Figure 6-67 is from 10 MHz to 1 GHz.
Figure 6-67 also illustrates the time domain low pass response of an amplier under test. The
average group delay over the measurement frequency range is the dierence in time between
the step and the amplier response. This time domain response simulates an oscilloscope
measurement of the amplier's small signal transient response. Note the ringing in the
amplier response that indicates an under-damped design.
Application and Operation Concepts 6-125