Keithley 6221/2182A/E Digital-Multimeter, DMM, 6221/2182/A/E Data Sheet

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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 .

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