Atec Keithley-6220-6221 - Manual (Page 3)

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A Greater Measure of Confidence
www.keithley.com
1.888.KEITHLEY
(U.S. only)
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The delta mode enables measuring low voltages and resistances accurately . Once the Model 622X and
the Model 2182A are connected properly, the user simply presses the current source’s Delta button,
followed by the Trigger button, which starts the test . The Model 622X and the Model 2182A work
together seamlessly and can be controlled via the GPIB interface (GPIB or Ethernet with the Model
6221) . The free example control software available for the Model 622X includes a tutorial that “walks”
users through the delta mode setup process .
Pulsed Tests
Even small amounts of heat introduced by the measurement process itself can raise the DUT’s tem-
perature, skewing test results or even destroying the device . The Model 6221’s pulse measurement
capability minimizes the amount of power dissipated into a DUT by offering maximum flexibility
when making pulsed measurements, allowing users to program the optimal pulse current amplitude,
pulse interval, pulse width, and other pulse parameters .
The Model 6221 makes short pulses (and reductions in heat dissipation) possible with microsecond
rise times on all ranges . The Model 6221/2182A combination synchronizes the pulse and measure-
ment—a measurement can begin as soon as 16µs after the Model 6221 applies the pulse . The entire
pulse, including a complete nanovolt measurement, can be as short as 50µs . Line synchronization
between the Model 6221 and Model 2182A eliminates power line related noise .
standard and arbitrary Waveform Generator
The Model 6221 is the only low current AC source on the market . It can be programmed to gen-
erate both basic waveforms (sine, square, triangle, and ramp) and customizable waveforms with
an arbitrary waveform generator (ARB) that supports defining waveforms point by point . It can
generate waveforms at frequencies ranging from 1mHz to 100kHz at an output update rate of
10 megasamples/ second .
Performance superior to aC resistance bridges and lock-In amplifiers
The Model 622X/2182A combination provides many advantages over AC resistance bridges and lock-in
amplifiers, including lower noise, lower current sourcing, lower voltage measurements, less power
dissipation into DUTs, and lower cost . It also eliminates the need for a current pre-amplifier .
Models 6220 and 6221 vs.
Homemade Current sources
Many researchers and engineers who need a
current source attempt to get by with a volt-
age source and series resistor instead . This is
often the case when an AC current is needed .
This is because, until the introduction of the
Model 6220/6221, no AC current sources were
available on the market . However, homemade
current sources have several disadvantages vs .
true current sources:
• Homemade Current Sources Don’t Have
Voltage Compliance. You may want to be
sure the voltage at the terminals of your
homemade “current source” never exceeds
a certain limit (for example, 1–2V in the
case of many optoelectronic devices) . The
most straightforward way to accomplish
this is to reduce the voltage source to that
level . This requires the series resistor to
be reduced to attain the desired current . If
you want to program a different current,
you must change the resistor while the
voltage is held constant! Another possibility
is to place a protection circuit in parallel
with the DUT . These do not have precise
voltage control and always act as a parallel
device, stealing some of the programmed
current intended for the DUT .
• Homemade Current Sources Can’t Have
Predictable Output. With a homemade
“current source” made of a voltage source
and series resistor, the impedance of the
DUT forms a voltage divider . If the DUT
resistance is entirely predictable, the
current can be known, but if the DUT
resistance is unknown or changes, as most
devices do, then the current isn’t a simple
function of the voltage applied . The best
way to make the source predictable is to
use a very high value series resistor (and
accordingly high voltage source), which
is in direct contradiction with the need
for compliance .
• While it’s possible to know (if not control)
the actual current coming from such an
unpredictable source, this also comes at a
cost . This can be done with a supplemental
measurement of the current, such as using
a voltmeter to measure the voltage drop
across the series resistor . This measurement
can be used as feedback to alter the voltage
source or simply recorded . Either way,
it requires additional equipment, which
adds complexity or error . To make matters
worse, if the homemade current source
is made to be moderately predictable by
using a large series resistor, this readback
would require using an electrometer to
ensure accuracy .
DC
Measurement
Delta Mode
Measurement
4 µV
5nV
figure 2. Delta mode offers 1000-to-1 noise reduction.
6220
6221
DC Current Source
AC and DC Current Source