Service manual

11
Swept-Sine Measurements (Option 1D2)
Logarithmic sweep
Test devices over more than six
decades of frequency range using
logarithmic sweep. In this mode, the
frequency is automatically adjusted
to provide the same resolution over
each decade of frequency range. With
FFT-network analysis, resolution is
constant—not a problem when mea-
suring over narrow frequency ranges.
Flexible
Make the measurement your way.
Independently select logarithmic or
linear sweep, sweep up or down,
automatic or manual sweep, and
autoresolution.
Automatic frequency resolution
Use autoresolution to obtain the fast-
est sweep possible without sacrific-
ing accuracy. With autoresolution, the
35670A automatically adjusts the fre-
quency step according to the device
re sponse. High rates of amplitude and
phase change are matched with small
frequency steps. Low rate-of -change
regions are quickly measured with
larger frequency steps.
The stability of
a control loop is
quickly char ac ter ized
using the gain and
phase margin marker
function.
130 dB dynamic range
Logarithmic or linear sweeps
“Auto” frequency resolution
While FFT-based network analysis
is fast and accurate, swept-sine
mea sure ments are a better choice
when the device under test has a
wide dynamic range or covers several
decades of frequency range. Use
swept- sine measurements to extend
the network measurement ca pa bil i-
ties of the 35670A.
Network analysis over a
130 dB range
With traditional swept-sine, the
35670A is optimally configured to
measure each individual point in the
frequency response. The result is
a 130 dB dynamic range. With FFT-
based network analysis, all fre quen cy
points are stimulated simultaneously
and the instrument configures itself
to measure the highest amplitude
response—thereby limiting the
dynamic range.
Characterize nonlinear net works
Use the auto-level feature to hold the
input or output amplitude constant
during a sweep. This provides the
device response for a specific signal
amplitude. With FFT-based network
analysis using random noise, the ran-
dom am pli tudes of the stimulus tend
to “average out” the non-linearities
and therefore does not capture the
dependency of the response on the
stimulus amplitude.
Test multiple devices
simultaneously
Increase throughput in production.
Swept-sine measurements up to
25.6 kHz can be made on three devic-
es simultaneously using swept-sine
on a four-channel 35670A. Channel
one is the common reference channel
for these measurements.
Alternatively, channels one and
three can be designated as in de pen-
dent reference channels for two
totally independent swept-sine
mea sure ments.