Section 4: Theory of operation Model 2657A High Power System SourceMeter® Instrument Reference Manual
4-26 2657A-901-01 Rev. B/December 2012
Pulse rise and fall times
Although the Model 2657A can create pulses, it is not a pulse generator (pulse rise times are not
programmable).
The pulse rise time is the time it takes a pulse to go from 10% to 90% of the pulse's maximum value.
Pulse fall time is similar but on the pulse's trailing edge. For the Model 2657A, pulse rise and fall
times can vary depending on the following factors:
• Cable specifications and connection configuration (on page 4-26)
• Range and pulse settling (on page 4-26)
• Load and operating mode (on page 4-27)
• Compliance limit settings (for details, see Compliance limits on page 2-18)
Refer to the Model 2657A specifications for details on source settling times. For latest specifications,
go to the Keithley Instruments website
(http://www.keithley.com).
Figure 91: Pulse rise and fall times
Cable specifications and connection configuration
Cable length, as well as capacitance and inductance in both the cabling and the test fixture, can
affect pulse performance. See Output connection considerations
(on page 4-25) for pulse related
considerations that may affect your connection scheme.
Range and pulse settling
Each range has different specifications for source settling times. This causes different rise and fall
time characteristics depending on the set range.
In addition, pulse performance is dependent on the pulse setting as a percent of full scale. For
example, a 0.1 mA pulse on the 1 mA range (which is 10%) will perform differently than a 1 mA pulse
on the same range (which is full scale). Refer to the Model 2657A specifications for details. For latest
specifications, go to the Keithley Instruments website
(http://www.keithley.com).
NOTE
Pulse level
Bias level
Start t
on
Start t
off
90%
10%
t
Latency
on
t
off
10%
Rise
time
Trigger
Pulse
Period
Fall
time
(Pulse width)
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