Page 1
6220 DC Current Source
6221 AC and DC Current Source
6220 and 6221
• Source and sink (programmable
load) 100fA to 100mA
14
• 10
Ω output impedance ensures
stable current sourcing into
variable loads
• 65000-point source memory
allows executing comprehensive
test current sweeps directly from
the current source
• Built-in RS-232, GPIB, Trigger
Link, and digital I/O interfaces
• Reconfigurable triax output
simplifies matching the
application's guarding
requirements
• Model 220 emulation mode
eliminates need to reprogram
existing applications
• Instrument control software
available for both Macintosh
and PC controllers
6221 Only
• Source AC currents from 1pA to
100mA for AC characterization
of components and materials.
The 6221’s 10MHz output
update rate generates smooth
sine waves up to 100kHz
• Built-in standard and arbitrary
waveform generators with 1mHz
to 100kHz frequency range.
Applications include use as a
complex programmable load or
sensor signal and for noise
emulation
• Programmable pulse widths as
short as 5µs, limiting power
dissipation in delicate components. Supports pulsed I-V
measurements down to 50µs
when used with Model 2182A
Nanovoltmeter
• Built-in Ethernet interface for
easy remote control without a
GPIB controller card
The Model 6220 DC Current Source and Model 6221 AC and DC Current Source combine ease of
use with exceptionally low current noise. Low current sourcing is critical to applications in test environments ranging from R&D to production, especially in the semiconductor, nanotechnology, and
superconductor industries. High sourcing accuracy and built-in control functions make the Models
6220 and 6221 ideal for applications like Hall measurements, resistance measurements using delta
mode, pulsed measurements, and differential conductance measurements.
The need for precision, low current sourcing.
Device testing and characterization for today's very
small and power-efficient electronics requires sourcing low current levels, which demands the use of
a precision, low current source. Lower stimulus currents produce lower—and harder to measure—
voltages across the device. Combining the Model 6220 or 6221 with a Model 2182A Nanovoltmeter
makes it possible to address both of these challenges.
AC current source and current source waveform generator. The Model 6221 is the only AC current source on the market. Before its introduction, researchers and engineers were forced to build
their own AC current sources. This cost-effective source provides better accuracy, consistency, reliability, and robustness than “home-made” solutions. The Model 6221 is also the only commercially available current source waveform generator, which greatly simplifies creating and outputting complex
waveforms.
Simple programming. Both current sources are fully programmable via the front panel controls or
from an external controller via RS-232 or GPIB interfaces; the Model 6221 also features an Ethernet
interface for remote control from anywhere there’s an Ethernet connection. Both instruments can
source DC currents from 100fA to 105mA; the Model 6221 can also source AC currents from 1pA to
100mA. The output voltage compliance of either
source can be set from 0.1V to 105V in 10mV
steps. Voltage compliance (which limits the
amount of voltage applied when sourcing a current) is critical for applications in which overvoltages could damage the device under test
(DUT).
Drop-in replacement for the Model 220
current source. These instruments build upon
Keithley’s popular Model 220 Programmable
Current Source; a Model 220 emulation mode
makes it easy to replace a Model 220 with a
Model 6220/6221 in an existing application without rewriting the control code.
Define and execute current ramps easily.
Both the Models 6220 and 6221 offer tools for
defining current ramps and stepping through
predefined sequences of up to 65,536 output
TYPICAL APPLICATIONS
• Nanotechnology
- Differential conductance
- Pulsed sourcing and resistance
• Optoelectronics
- Pulsed I-V
• Replacement for AC resistance
bridges (when used with Model
2182A)
- Measuring resistance with low
• Replacement for lock-in amplifiers (when used with Model
2182A)
- Measuring resistance with low
values using a trigger or a timer. Both sources
Precision low current sourcing
power
noise
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201
Page 2
6220 DC Current Source
6221 AC and DC Current Source
Ordering Information
6220 DC Precision Current
6221 AC and DC Current
6220/2182A
6221/2182A
Extended warranty, service, and
calibration contracts are available.
Precision low current sourcing
Accessories Supplied
237-ALG-2
8501-2 6.6 ft (2m) Trigger Link
CA-180-3A
CA-351A
CS-1195-2
Instruction manual on CD
Getting Started manual (hardcopy)
Software
7078-TRX-5 5ft (1.5m), Low Noise, Triax-to-Triax Cable
7006-* GPIB Cable with Straight-On Connector
Source
Source
Complete Delta Mode
System, w/DC Current
Source, Nanovoltmeter,
and all necessary cables
(GPIB cables not
included)
Complete Delta Mode
System, w/AC and DC
Current Source, Nanovoltmeter, and all necessary cables (GPIB cables
not included)
6.6 ft (2m), Low Noise,
Input Cable with Triaxto-Alligator Clips
Cable to connect 622x to
2182A
Ethernet Crossover
Cable (6221 only)
Communication Cable
between 2182A and
622x
Safety Interlock
Connector
ACCESSORIES AVAILABLE
(Male on Both Ends)
support linear, logarithmic, and custom sweeps. The Model 6221’s combination of high source resolution and megahertz update rates makes it capable of emulating high fidelity current signals that are
indistinguishable from analog current ramps.
Free Instrument Control Start-up Software
The instrument control software provided with the sources simplifies both performing basic sourcing
tasks and coordinating complex measurement functions with the Keithley Model 2182A. Both
Macintosh- and PC-compatible versions of the software are supplied. The software, developed in the
™
LabVIEW
programming environment, includes a step-by-step measurement guide that helps users
set up their instruments and make proper connections, as well as program basic sourcing functions.
The advanced tools in the package support delta mode, differential conductance, and pulse mode
measurements. From this package, users can print out the instrument commands for any of the preprogrammed functions, which provides a starting point for incorporating these functions into customized applications.
Differential Conductance
Differential conductance measurements are among the most important and critical measurements
made on non-linear tunneling devices and on low temperature devices. Mathematically, differential
conductance is the derivative of a device’s I-V curve. The Model 6220 or 6221, combined with the
Model 2182A Nanovoltmeter, is the industry’s most complete solution for differential conductance
measurements. Together, these instruments are also the fastest solution available, providing 10× the
speed and significantly lower noise than other options. Data can be obtained in a single measurement pass, rather than by averaging the result of multiple sweeps, which is both time-consuming and
prone to error. The Model 622X and Model 2182A are also easy to use because the combination can
be treated as a single instrument. Their simple connections eliminate the isolation and noise current
problems that plague other solutions.
Figure 1. Perform, analyze, and display differential conductance measurements.
Delta Mode
Keithley originally developed the delta mode method for making low noise measurements of voltages
and resistances for use with the Model 2182 Nanovoltmeter and a triggerable external current
source. Essentially, the delta mode automatically triggers the current source to alternate the signal
polarity, then triggers a nanovoltmeter reading at each polarity. This current reversal technique cancels out any constant thermoelectric offsets, ensuring the results reflect the true value of the voltage.
This same basic technique has been incorporated into the Model 622X and Model 2182A delta mode,
but its implementation has been dramatically enhanced and simplified. The technique can now
cancel thermoelectric offsets that drift over time, produce results in half the time of the previous
technique, and allow the source to control and configure the nanovoltmeter, so setting up the
202
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Page 3
6220
DC
Measurement
Delta Mode
Measurement
4µV
5nV
DC Current Source
6221
Figure 2. Delta mode offers 1000-to-1 noise reduction.
measurement takes just two key presses. The improved cancellation and higher reading rate reduces
measurement noise to as little as 1nV.
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 control software provided with the Model 622X includes a tutorial that
“walks” users through the delta mode set-up process.
Pulsed Tests
Even small amounts of heat introduced by the measurement process itself can raise the DUT’s temperature, 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 measurement—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 current source waveform generator on the market. It can be programmed to generate 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.
AC and DC Current Source
Models 6220 and 6221 vs.
Homemade Current Sources
Many researchers and engineers who need a
current source attempt to get by with a voltage 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.
Precision low current sourcing
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Page 4
6220
Source Current
1/60 second (1/50 when operating off 50Hz power)
Programmable: 50µs to 12ms
Measurement integration period
Measuring difference voltage eliminates
line frequency noise, DC offsets
Voltage measurement noise at line frequency
Measured response voltage
Pulsed measurement without line sync Line synchronized pulse measurements
DC Current Source
6221
AC and DC Current Source
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.
The Model 6221 can also expand the capabilities
of lock-in amplifiers in applications that already
employ them. For example, its clean signals and
its output synchronization signal make it an
ideal output source for lock-in applications such
as measuring second and third harmonic device
response.
Model 2182A Nanovoltmeter
Figure 4. The Model 6221 and the free start-up
control software supplied make it easy to create complex waveforms by adding, multiplying,
stringing together, or applying filters to standard wave shapes.
The Model 2182A expands upon the capabilities
of Keithley’s original Model 2182 Nanovoltmeter. Although the Model 6220 and 6221 are
compatible with the Model 2182, delta mode
Precision low current sourcing
and differential conductance measurements
require approximately twice as long to complete
with the Model 2182 as with the Model 2182A.
Unlike the Model 2182A, the Model 2182 does
not support pulse mode measurements.
Figure 3. Measurements are line synchronized to minimize 50/60Hz interference.
APPLICATIONS OF 622X/2182A
COMBINATION:
• Easy instrument coordination and
intuitive example software
simplifies setup and operation in
many applications.
• Measure resistances from 10nΩ to
100MΩ. One measurement system
for wide ranging devices.
• Low noise alternative to AC
resistance bridges and lock-in
amplifiers for measuring
resistances.
• Coordinates pulsing and
measurement with pulse widths as
short as 50µs (6221 only).
• Measures differential conductance
up to 10x faster and with lower
noise than earlier solutions allow.
Differential conductance is an
important parameter in semiconductor research for describing
density of states in bulk material.
• Delta mode reduces noise in low
resistance measurements by a
factor of 1000.
• For low impedance Hall measurements, the delta mode operation of
the Model 622X/2182A combination
provides industry-leading noise
performance and rejection of
contact potentials. For higher
impedance Hall measurements
(greater than 100MΩ), the Model
4200-SCS can replace the current
source, switching, and multiple high
impedance voltage measurement
channels. This provides a complete
solution with pre-programmed test
projects.
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Page 5
6220
DC Current Source
6221
AC and DC Current Source
SOURCE SPECIFICATIONS
6221 ONLY
RANGE
(+5% over
range)
2nA 0.4 % + 2 pA 100 fA 0.02 % + 100 fA 400 / 80 fA 250 / 50 pA 10 kHz 90 µs 100 µs
20 nA 0.3 % + 10 pA 1pA 0.02 % + 200 fA 4 / 0.8 pA 250 / 50 pA 10 kHz 90 µs 100 µs
200 nA 0.3 % + 100 pA 10 pA 0.02 % + 2 pA 20 / 4 pA 2.5 / 0.5 nA 100 kHz 30 µs 100 µs
2µA 0.1 % + 1 nA 100 pA 0.01 % + 20 pA 200 / 40 pA 25 / 5.0 nA 1 MHz 4 µs 100 µs
20 µA 0.05%+ 10 nA 1nA 0.005% + 200 pA 2 / 0.4 nA 500 /100 nA 1 MHz 2 µs 100 µs
200 µA 0.05%+ 100 nA 10 nA 0.005% + 2 nA 20 / 4 nA 1.0 / 0.2 µA 1 MHz 2 µs 100 µs
2mA 0.05% + 1 µA 100 nA 0.005% + 20 nA 200 / 40 nA 5.0 / 1 µA 1 MHz 2 µs 100 µs
20 mA 0.05%+ 10 µA 1µA 0.005% + 200 nA 2 / 0.4 µA 20 / 4.0 µA 1 MHz 2 µs 100 µs
100 mA 0.1 % + 50 µA 10 µA 0.01 % + 2 µA 10 / 2 µA 100 / 20 µA 1 MHz 3 µs 100 µs
ACCURACY
(1 Year)
23°C ±5°C
±(% rdg. + amps)
PROGRAMMING
RESOLUTION
ADDITIONAL SOURCE SPECIFICATIONS
OUTPUT RESISTANCE: >1014Ω (2nA/20nA range).
OUTPUT CAPACITANCE: <10pF, <100pF Filter ON (2nA/20nA
range).
LOAD IMPEDANCE: Stable into 10µH typical, 100µH for 6220, or
for 6221 with Output Response SLOW.
VOLTAGE LIMIT (Compliance): Bipolar voltage limit set with
single value. 0.1V to 105V in 0.01V programmable steps.
MAX. OUTPUT POWER: 11W, four quadrant source or sink oper-
ation.
GUARD OUTPUT ACCURACY: ±1mV for output currents <2mA
(excluding output lead voltage drop).
PROGRAM MEMORY: Number of Locations: 64K. Offers point-
by-point control and triggering, e.g. sweeps.
MAX. TRIGGER RATE: 1000/s.
RMS NOISE 10Hz–20MHz (2nA–20mA Range): Less than
1mVrms, 5mVp-p (into 50Ω load).
SOURCE NOTES
1. Settling times are specified into a resistive load, with a maximum resistance equal to 2V/ I
2. Settling times to 0.1% of final value are typically <2× of 1% settling times.
3. Typical values are non warranted, apply at 23°C, represent the 50th percentile, and are provided solely as useful information.
of range. See manual for other load conditions.
full scale
2182 MEASUREMENT FUNCTIONS
DUT RESISTANCE: Up to 1GΩ (1ns) (100MΩ limit for pulse
mode).
DELTA MODE RESISTANCE MEASUREMENTS AND DIFFEREN-
TIAL CONDUCTANCE: Controls Keithley Model 2182A
Nanovoltmeter at up to 24Hz reversal rate (2182 at up to
12Hz).
PULSE MEASUREMENTS (6221 ONLY):
Pulse Widths: 50µs to 12ms, 1pA to 100mA.
Repetition Interval: 83.3ms to 5s.
TEMPERATURE
COEFFICIENT/°C
0°–18°C &
28°–50°C
TYPICAL NOISE
(peak-peak)/rms
0.1Hz–10Hz
TYPICAL NOISE
3
(peak-peak)/rms
10Hz–(BW)
ARBITRARY FUNCTION GENERATOR
(6221 only)
WAVEFORMS: Sine, Square, Ramp, and 4 user defined arbitrary
waveforms.
FREQUENCY RANGE: 1mHz to 100kHz.
FREQUENCY ACCURACY4: ±100ppm (1 year).
SAMPLE RATE: 10 MSPS.
AMPLITUDE: 2pA to 210mA peak-peak into loads up to 10
AMPLITUDE RESOLUTION: 16 bits (including sign).
AMPLITUDE ACCURACY (<10kHz):
Magnitude: ±(1% rdg + 0.2% range).
Offset: ±(0.2% rdg + 0.2% range).
SINE WAVE CHARACTERISTICS:
Amplitude Flatness: Less than 1dB up to 100kHz.
SQUARE WAVE CHARACTERISTICS:
Overshoot: 2.5% max.
Variable Duty Cycle:4Settable to 1µs min. pulse duration,
0.01% programming resolution.
Jitter (RMS): 100ns + 0.1% of period.
RAMP WAVE CHARACTERISTICS:
Linearity: <0.1% of peak output up to 10kHz.
ARBITRARY WAVE CHARACTERISTICS:
Waveform Length: 2 to 64K points.
Jitter (RMS): 100ns + 0.1% of period.
6
5
5
6
6
6
6
WAVEFORM NOTES
4. Minimum realizable duty cycle is limited by current range
response and load impedance.
5. Amplitude accuracy is applicable into a maximum resistive load
of 2V/I
higher frequencies dependent upon current range and load
impedance.
6. These specifications are only valid for the 20mA range and a
50Ω load.
of range. Amplitude attenuation will occur at
full scale
12
Ω.
OUTPUT
RESPONSE
BANDWIDTH
3
(BW) INTO
SHORT
COMMON MODE VOLTAGE: 250V rms, DC.
COMMON MODE ISOLATION: >10
REMOTE INTERFACE: SCPI (Standard Commands for
Programmable Instruments).
DIGITAL I/O: 1 trigger input, 4 TTL/relay drive outputs.
OUTPUT CONNECTIONS:
Teflon insulated 3-lug triax connector for output.
Banana safety jack for GUARD, OUTPUT LO.
Screw Terminal for CHASSIS.
DB-9 connector for EXTERNAL TRIGGER INPUT, OUTPUT,
and DIGITAL I/O.
Two position screw terminal for INTERLOCK.
WARRANTY: 1 year.
ENVIRONMENT: Operating: 0°–50°C, 70%R.H. up to 35°C.
Derate 3% R.H./°C, 35°–50°C. Storage: –25°C to 65°C,
guaranteed by design.
EMC: Conforms to European Union Directive 89/336/EEC,
EN 61326-1.
SAFETY: Conforms to European Union Directive 73/23/EEC,
EN61010-1.
VIBRATION: MIL-PRF-28800F Class 3, Random.
WARMUP: 1 hour to rated accuracies.
PASSIVE COOLING: No fan.
SETTLING TIME
(1% of final value)
OUTPUT
RESPONSE
FAST (Typical
(6221 Only)
GENERAL
3
)
9
Ω, <2nF.
SLOW (Max.)
1, 2
6220, 6221
WITH
OUTPUT
RESPONSE
Model 6220 and 6221 Specifications
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