Output Connection Considerations; Effects Of Load On Current Source Settling Time; Creating Pulses With The Model 2657A - Keithley 2657A Reference Manual

Model 2657A High Power System SourceMeter® Instrument Reference Manual

Output connection considerations

Use care when designing a system that contains the Model 2657A (or any other high voltage source).
There are several specific considerations that should be taken into account when making or
designing connections to the Model 2657A output:
•
Both the HI and LO terminals are high voltage terminals. Use care to prevent operators from
accessing these terminals.
•
The maximum common mode voltage (voltage between LO and chassis ground) is 250 V DC.
•
Neither the HI nor the LO terminal is connected to chassis. When a voltage step is programmed
on the Model 2657A, voltages may develop between HI and chassis and also between LO and
chassis. These voltages can be dangerously high. This requires that you take high voltage
precautions for both the HI and LO terminals. Alternatively, limit hazardous levels by adding
external protection to limit the voltage between LO and chassis.

Effects of load on current source settling time

The settling time of the source-measure unit (SMU) can be influenced by the impedance of the device
under test (DUT) in several ways. One influence is caused by an interaction between the impedances
of the SMU current source feedback element and the DUT. This interaction can cause a reduction in
the bandwidth of the SMU. This reduction causes an increase in the settling time of the current
source.
There is a maximum DUT impedance for each current source range for which the specified current
settling times are maintained. The following table lists the DUT impedances for each of these current
source ranges. For latest specifications, go to the
(http://www.keithley.com). The settling time on a current source range can increase significantly when
measuring DUTs that have an impedance that is higher than the maximum DUT impedance listed
below.
Maximum DUT impedances for specified settling time performance
Range
1 nA
10 nA
100 nA
1 μA
10 μA
100 μA
1 mA
2 mA
20 mA
120 mA

Creating pulses with the Model 2657A

Although the Model 2657A is not a pulse generator, you can create pulses by programming the Model
2657A to output a DC value and then return to an idle level. For information on how to create pulses,
refer to
2657A-901-01 Rev. B/December 2012
SMU feedback
impedance
1 GΩ
33 MΩ
33 MΩ
396 kΩ
396 kΩ
3660 Ω
3660 Ω
166 Ω
166 Ω
32 Ω
Sweep operation (on page 3-19) and
Keithley Instruments website
Maximum DUT impedance
10 GΩ
10 GΩ
10 GΩ
1 GΩ
100 MΩ
10 MΩ
1 MΩ
500 kΩ
50 kΩ
12.5 kΩ
Using the remote trigger model
Section 4: Theory of operation
(on page 3-33).
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