Service Manuals, User Guides, Schematic Diagrams or docs for : Keithley Appnotes 2636 Low Level
<< Back | HomeMost service manuals and schematics are PDF files, so You will need Adobre Acrobat Reader to view : Acrobat Download Some of the files are DjVu format. Readers and resources available here : DjVu Resources
For the compressed files, most common are zip and rar. Please, extract files with Your favorite compression software ( WinZip, WinRAR ... ) before viewing. If a document has multiple parts, You should download all, before extracting.
Good luck. Repair on Your own risk. Make sure You know what You are doing.
Image preview - the first page of the document
>> Download 2636 Low Level documenatation <<
Text preview - extract from the document
A G R E AT E R M E A S U R E O F C O N F I D E N C E offsets and drift in voltage readings. In the
past, it would have been possible to simply
increase the test current until the DUT's re-
sponse voltage was much larger than these
errors, but with today's smaller devices this
is no longer an option. Increased test cur-
rent can cause device heating, changing the
device's resistance, or even destroy the de-
vice. The key to obtaining accurate, consis-
tent measurements is eliminating the error.
For low-voltage measurement applications,
such error is composed largely of white noise
(random noise across all frequencies) and 1/f
noise. Thermoelectric voltages (typically
Low-Voltage
having 1/f distribution) are generated from
temperature differences in the circuit.
Resistance is calculated using Ohm's
Measurement
Law; that is, the DC voltage measured
across the device divided by the DC stimu-
lus current yields the resistance. The voltage
Techniques readings will be a sum of the induced volt-
age across the device (VR), lead and contact
resistance (Vlead res), other 1/f noise contribu-
tions (V1/f noise), and white noise (Vwhite noise),
and thermoelectric voltages (Vt). Using
Adam Daire, Product Marketer four separate leads to connect the voltmeter
Keithley Instruments, Inc. and current source to the device eliminates
lead resistance, because the voltmeter won't
Introduction This article discusses techniques to elim- measure the voltage drop across the source
Electronics are continuing to shrink as inate thermoelectric voltages to allow more leads. Implementing filtering may reduce
consumers demand faster, more feature-rich accurate resistance measurements, including white noise but will not reduce 1/f noise sig-
products in ever-smaller form factors. Be- a three-step delta measurement method for nificantly, which often sets the measurement
cause of their small sizes, these electronic low-power/low-voltage applications. In addi- noise floor.
components usually have limited power han- tion, it also presents a method for accurately Thermoelectric voltages normally have a
dling capability. As a result, when electri- making differential conductance measure- 1/f characteristic. This means there can be
cally characterizing these components, the ments. significant offset, and the more measure-
test signals need to be kept small to prevent ments that are made the more drift. Taken
component breakdown or other damage. Low-Level Voltage Measurements together, the offset and drift may even ex-
Testing these devices and materials often There are many factors that make low- ceed VR, the voltage across the DUT induced
includes making low-voltage measurements. voltage measurements difficult. For instance, by the applied current. It's possible to reduce
This involves sourcing a known current, various noise sources can hinder resolving thermoelectric voltages using techniques
measuring the resulting voltage, and calcu- the actual voltage, and thermoelectric volt- such as all-copper circuit construction, ther-
lating resistance. If the device has a low re- ages (thermoelectric EMFs) can cause error mal isolation, precise temperature control,
sistance, that resulting voltage will be very
small and great care needs to be taken to Multimeter/Ohmmeter Rlead
Rlead
reduce offset voltage and noise, which can
normally be ignored when measuring higher
Vmeasured = Vmeasured =
signal levels. Current
Voltmeter Vlead res + Vt + R
Current
Voltmeter
VR + Vt +
R
Source Vwhite noise + V1/f noise Source Vwhite noise +
Even if the resistance is far from zero, the V1/f noise
voltage to be measured is often very small
due to the need to source only a small current Rlead
in order to avoid damaging the device. This Rlead
power limitation often makes characterizing
Figure 1: The schematic on the left shows a standard DC resistance measurement setup. Changing
the resistance of modern devices and materi- the standard measurement setup to the schematic on the right by using four leads eliminates errors
als very challenging. due to lead resistance.
Low-Voltage Measurement Techniques October2005
4.00E◦ Jabse Service Manual Search 2024 ◦ Jabse Pravopis ◦ onTap.bg ◦ Other service manual resources online : Fixya ◦ eServiceinfo