14
for small—on the order of 100 pF or less—capac-
itive loads and large voltages), the current limit
(dominates for large—on the order of tens of
nanofarads—capacitive loads) and the RC filter
(dominates for large capacitive loads and very
small peak voltages). The smallest of the 1-MHz
closed loop bandwidth, the calculated slew-rate
limited bandwidth, the calculated current-limited-
bandwidth, and the calculated RC bandwidth
determines the maximum bandwidth of the
Model 3211. Four examples illustrating how to
determine the maximum bandwidth follow.
Example 1 (slew-rate-limited case)
Peak voltage=200 V
Load capacitance=10 pF
1. Slew-rate-limited bandwidth:
111 MHz/200=555 kHz
2. Current-limited bandwidth:
0.0191/(10x10
-12
×
200)=9.55 MHz
3. Closed-loop bandwidth: 1 MHz
4. RC bandwidth: 1/(2
π×
25
×
10x10
-12
)=637 MHz
Therefore, the maximum bandwidth is the small-
est of the four, or 555 kHz.
Example 2 (current-limited case)
Peak voltage=200 V
Load capacitance=100 nF
1. Slew-rate-limited bandwidth:
111 MHz/200=555 kHz
2. Current-limited bandwidth:
0.0191/(100x10
-9
×
200)=955 Hz
