LT1016
APPLICATIO S I FOR ATIO
U
problem in high speed circuits and can be quite confusing.
It is not due to suspension of natural law, but is traceable
to a grossly miscompensated or improperly selected
oscilloscope probe.
Use probes that match your
oscilloscope’s input characteristics and compensate them
properly.
Figure 6 shows another probe-induced problem.
Here, the amplitude seems correct but the 10ns response
time LT1016 appears to have 50ns edges! In this case, the
probe used is too heavily compensated or slow for the
oscilloscope. Never use 1¥ or “straight” probes. Their
bandwidth is 20MHz or less and capacitive loading is high.
Check probe bandwidth to ensure it is adequate for
the measurement. Similarly, use an oscilloscope with
adequate bandwidth.
100ns/DIV
1016 F04
In Figure 4 the LT1016’s supplies are bypassed, but it still
oscillates. In this case, the bypass units are either too far
from the device or are lossy capacitors.
Use capacitors
with good high frequency characteristics and mount them
as close as possible to the LT1016. An inch of wire
between the capacitor and the LT1016 can cause prob-
lems. If operation in the linear region is desired, the
LT1016 must be over a ground plate with good RF bypass
capacitors (
≥
0.01
m
F) having lead lengths less than 0.2
inches. Do not use sockets.
In Figure 5 the device is properly bypassed but a new
problem pops up. This photo shows both outputs of the
comparator. Trace A appears normal, but Trace B shows
an excursion of almost 8V—quite a trick for a device
running from a 5V supply. This is a commonly reported
TRACE A
2V/DIV
TRACE B
2V/DIV
10ns/DIV
1016 F05
Figure 5. Improper Probe Compensation Causes
Seemingly Unexplainable Amplitude Error
W
U U
2V/DIV
Figure 4. LT1016 Response with Poor Bypassing
1V/DIV
50ns/DIV
1016 F06
Figure 6. Overcompensated or Slow Probes
Make Edges Look Too Slow
9
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