European Simulation Multiconference, 1994, Barcleona. [12] Tektronix Inc., XYZs of Oscilloscopes, Tektronix Inc, 2001, published online www.tektronix.com.
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Automated Testing of Power Semiconductor Devices Sven Tschirley and Steffen Bernet
I. I NTRODUCTION
I
N the production process of power semiconductors, factory testers are used to ensure the quality of the devices produced. On the one hand, the devices being produced achieve a higher level of quality, on the other hand, the technical documentation given to the customer has to meet the need for higher quality [4]. High-power semiconductors like IGCTs are individually tested, the measurement results are filed in reports. Common factory testers are specifically designed for a certain product or product family. There is neither the flexibility to change the test circuit nor to use different packages. Factory testers today are highly automated test units, but are very costly. During characterisation of prototypes of new devices [1], a lot of tests are made with different versions of the device. These tests of prototypes are made, before an expensive factory tester is implemented. The new devices are characterised by manual testing different prototypes under different testing conditions, e. g. operating points, temperatures, attached snubber circuitry [2]. Comparing the total cost of testing, automated testing enables a more efficient testing procedure by reducing the time taken for the tests. The customer designing a new product using new power semiconductor available in the market qualifies the devices for his own development and production process. In this step, devices of different manufacturers are compared and datasheet specifications are verified. These tests are done at operating points used in the product, which may differ from those specified in the data sheets. This has to be done to ensure a correct function of the devices in the new product. The quality management makes a type test indispensable when using new semiconductors or even new driving circuitry in a new product. This testing usually is not done by the manufacturer of semiconductors. So, a portion of the process of testing power semiconductors has passed from the semiconductor manufacturer to the customer. For a company designing voltage source inverters, it is not convenient to buy factory testers. Manual testing is the accepted way for type test, validating new devices and modifying e. g. gate drivers.
Another point of interest is parameter extraction for device simulation. Modeling the semiconductor requires a good model of the device and parameters being extracted from measurement data of the device under test [10]. Especially macro modeling based on look-up tables, which treats the semiconductor and its driving circuitry as a system, depends on a large number of measurements in different operating points [11] . By comparing the costs of the test methods, a break even point can be found where the cost of manual testing becomes higher than automated testing, see Fig. 1. Assuming a certain volume of tests to be done, it is a reduction of cost to invest in the development of a test system. As the break-even point was reached durning a single run of tests, each additional testing means further reduction of cost [3]. cost of using existing manual procedure
Cost
Abstract— Testing power semiconductor devices for a new product design or a qualification in the development process is nescessary to ensure a good device utilization. Benchmarking devices and verification of datasheet specifications cause high cost in the pre-design phase of new products. This paper describes the design of a test system that enables automated testing of modern power semiconductor devices. Examples are given by measuring and calculating the turn-off losses of the 10 kV IGCT.
Cost of using automated test system
Time Taken for Measurement
Fig. 1.
Cost of manual vs. system test methods [3]
This paper describes a test setup allowing an automated testing of power semiconductor devices. Benchmarking of devices in the pre-production process is as well considered as the testing of prototypes. The automated measurements of the turn-off losses of modern 10 kV IGCTs in the robust press pack housing and a modern medium power coolMOS transistor are discussed. II. R EQUIREMENTS FOR A S EMICONDUCTOR T EST S YSTEM The test system to be designed has to fill the gap between manual testing, which is expensive if often repeated, and a factory tester, which requires a high investment. Factory testers are designed to cope with large numbers of parts being tested. In contrary, the test system being described here must offer the flexibility to cover testing in different operating points and environmental conditions. The architecture of the system has to use open standards such as IEEE 488 or TCP/IP. The dependency on a single supplier of a certain component should
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be avoided wherever it is possible. This assures, that system maintenance and upgrades are possible without causing further cost. To get the most benefit of the investment, the software solution has to allow an easy exchange of measurement devices and test circuits. The test system must allow manual testing as well as autmatically repeated testing. All data and reports being generated have to be stored on a fileserver. Modern communication technologies should allow sharing the measurement results over the internet and enable remote control of the test system [8].
Lcl
IL
Dcl VDC
Df
LH
CDC-link Rcl
Ccl
DUT Rshunt
Fig. 3.
Schematic for the power part
III. T EST S YSTEM D ESIGN A test system for testing power semiconductor devices consists of a power part, measurement devices, pulse generators and security related devices for the power part and the test setup itself, see Fig. 2. Communication Bus System
Control PC
Test Setup Security
Measurement
Pulse Generation
Power Part
tasks such as turn-on, turn-off, static blocking and short circuit behaviour. Mechanical interfacing the device under test depends on the semiconductor package being used. Todays IGCTs are manufactured in the reliable press pack housing. The test circuit is realised in a power stack, see Fig. 4, where the devices are loaded with the recommended pressure to ensure the contact over the full wafer surface. The clamp circuitry is attached nearby the stack assuring a low stray inductance in the clamp circuit. When testing IGBTs, which are mostly available in a module package, the low inductance of the connection to the DC link becomes important.
Power Part Security
Fig. 2.
Test System for power semiconductor devices DUT HV Probe
The power part realises the desired test circuit. To measure the desired voltages and currents, appropriate probes and current transducers are attached to the test circuit. The measurements are usually done with digital storage oscilloscopes. The semiconductors are switched using a pulse or function generator. With regard to security, it has to be assured that the power part is shortened while the operator is working at the test setup. In the case of an automated measurement, a control computer running the test system’s software is connected via a communication bus system to each of these devices. This computer or an additional machine in the network is then occupied with the analysis and storage of the measurement data. The control computer has no galvanic connection to the test setup, all connections are realized by fibre optic connections. Thus, several media converter are used. A. Power part Within the power part of the test system, the desired test circuit is implemented. In the case of the analysis of the switching behaviour, the power part contains a buck converter and a DC link, as shown in Fig. 3. Depending on the device to be characterised, the DC link can operate at voltages from VDC = 600 V for small Power MOSFETs up to V DC = 10 kV for high-power semiconductors. The DC link needs to be charged up to the desired voltage by a controlled charging device. The hardware for testing high-power semiconductors allows the realization of all static and dynamic measurement
DC link
GU Supply
Fig. 4.
Photo of a power stack for testing 10 kV IGCTs
Since the devices should be tested with different junction temperatures, the device under test can be heated using a controlled heating. Unlike in factory testers, the mechanical interfacing is realised manually. This makes sense, since the high number of parts being tested by a factory tester is not the focus of this test system. B. Security Security planning is an key part of any test system design. Since the voltages in case of testing are high, the requirements for the security of the operating personnel and the test setup are high. In case of testing high power semiconductors at voltages up to several kilovolts, it has to be assured that the operator has no access to the parts carrying voltage. This is realised
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using a door electrical locking the test setup when starting the measurement. When the measurements are completed, the DC link capacitor has to be discharged. The discharging unit has to be very reliable, it has to work properly even if the grid fails to assure safe working conditions for the operator. To make the status of the DC link in high-power test systems visible, at least one digital voltmeter has to monitor the voltage over all DC link capacitors. If a door lock is applied, the digital voltmeter has to be able to transmit the actual voltage measurement to the control computer. Safety and cutoff switches as well as isolation of parts where necessary increase the safety for the system operators. C. Pulse Generation To measure the turn-on and turn-off behaviour, the device under test is driven by a double pulse in a single shot operation [1]. The shortest pulse length which the pulse generation has to realise depends on the semiconductor being tested. In case of IGCTs, the charge carrier distribution becomes stationary after 10 − 30 µs. magnetizing
DUT off
DUT on
freewheeling
gateIGCT1 ∆t ~ ~10ns
tmag ~ ~100µs
gateIGCT2 gateIGCT3
... Trigger Scope 1 Trigger 1 Trigger Scope 2 Trigger 2
t0
Fig. 5.
time
Example of a complex pulsepattern for turn off measurement
When characterizing series or parallel connections of devices, the gate signals sometimes have to be shifted against each other. The time resolution for shifting usually is in the range of nanoseconds. Beside this, one or more trigger signals are also needed to start the measurement done by the data acquisition systems. So the requirements for the pulse generation are in the scope of high speed digital pattern generation. The pulse pattern is programmed before the measurement and then sequenced once a measurement. One possible solution is a programmable digital pattern generator. This allows arbitrary digital patterns to be written to an output port at user defined time steps. The clock base of this generator directly defines the resolution of the time axis. D. Measurement Devices Measurement of transient behaviour of power semiconductors is equivalent with the demand for a high sampling rate in the data acquisition system and a high bandwidth of the analogue frontend. Since most of the tests are done in single shot operations, the transients have to be recorded. A turn-off
transient of an IGCT lasting 10 µs that has to be recorded with 1000 Samples requires a theoretical sampling rate of at least 100 M S/s. If any frequency analysis is made, Nyquist’s theorem has to to be taken into account. 1) Data Acquisition System: Digital Storage Oscilloscopes (DSO) allow to capture transient signals. The waveform information exists in digital form in the systems memory and can be analyzes, archived or otherwise processed within the oscilloscope or by an external computer. Common DSOs meet the need for sampling rates up to 1GS/s. The analogue bandwidth determines an oscilloscope’s capability to measure a signal. It is usually limited by the design of the analogue filters and the adjustable vertical amplifiers for the voltage signals. Signals above this bandwidth will be distorted, edges will vanish [12]. Data acquisition cards for computer systems today realize sampling rates up to 10 M S/s per channel. The analog frontend concising of the adjustable vertical gain amplifiers and attenuators is usually not included with the card and has to be built externally. Beside this, grounding of a card installed in the computer is a problem. Galvanic isolation of the channels and working with different timebases is impossible. 2) Voltage Probes: A probe functions in conjunction with an oscilloscope as part of the measurement system. When measuring the voltage across a high-power semiconductor in the range of several kilovolt, the probe needs an attenuation factor of 100 or 1000, depending on the voltage being measured. The attenuator is realised as a complex voltage divider which has to be adjusted using an external calibration generator. Using probes directly affects the analogue bandwidth of the system [9], [13]. The right probe matching to the oscilloscope will bring the signal cleanly to the oscilloscope and preserves the signal for integrity and measurement accuracy. Another important requirement is the isolation of high voltage probes. When working with high power semiconductors, an isolation voltages of up to 40 kV from probe tip to probe ground is adequate, since in case of failure overvoltages can occur. 3) Current Probes: Transient currents can be measured using different types of current probes. Inductive probes like rogowski coils allow the measurement of currents without the high current flowing through the probe as shown in Fig. 6(a). Therefore, a good isolation is provided. The current flowing through the coils causes a signal u M = c · di/dt proportional to the derivation of the current. The necessity of an integration of the signal limits the the upper cut-off frequency to several 100 kHz. The integrator as a part of the test system has to be set to zero before the measurement. Furthermore, it introduces a delay of about 40 ns due to the slew rate of the internal operational amplifier to the system. Using a low inductance coaxial shunt resistor (Fig. 6(b)) significantly increases the bandwidth. The current to be measured causes a voltage across the shunt which is brought to the oscilloscope. An isolation is not provided, so the shunt has to be applied near the ground potential of the circuit. Especially in the case of an automated measurement, the type of the probe used should be stored for each channel in a logfile. This makes
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ROGOWSKI COIL
I C1 RO
I
VOUT
e
INTEGRATOR
sufficient not to slow down the test system. To enable the galvanic isolation of the test setup, media converters are used to convert the electrical signal to fibre optic. These are available for IEE488.2, RS232 as well as for ethernet. The fibre optic connection behaves transparent, i. e. it is not seen by the controlling computer or the measurement devices. IV. S OFTWARE D ESIGN
(a) Rogowski Coil
Imeas
U
(b) Coaxial Shunt Fig. 6.
Principle of current probes
Designing an automated test system includes software to run the system. As shown in Fig. 7, several measurement devices, power supplies and signal generators have to function in a good interconnection. It is the approach to maintain the modularity of the power part and the measurement equipment in the test systems’s software [3]. Unlike a factory tester, which usually has one firmware for all operation methods, the system described here consists of building blocks, similar to a toolkit. After writing a solid basis of software building blocks to interface the measurement equipment, the overlaying test software is adaptable to different measurement setups (e. g. turn off, turn on, leakage current). Off line Analysis
the measurement repeatable. 4) Interface Busses: The devices in the automated test system are connected to a controlling computer using different interface busses. Most common and widely available are RS232 interfaces. The data rate is limited to 115 kBit/s, so an RS232 connection is not convenient to transfer high data volumes. The communication bus IEEE 488.2, also known as GPIB (General Purpose Interface Bus) offers higher data bandwidth up to 1 M Byte/s and is well supported by manufacturer of measurement devices. Since IEEE 488.2 is no standard computer interface, additional hardware is necessary. IEEE 488.2 is a bus system with a distinct controller, i. e. the controlling personal computer. The system is not vulnerable to any malfunction in the network. New oscilloscopes use ethernet running TCP/IP (Transmission Control Protocol/Internet Protocol) as standard communication interface. This means, that the oscilloscope is plugged into the local network, where any disturbance in the network will affect the test system. For security reasons, a separation of the local network and the measurement network is appropriate. This can easily be achieved using common available office network switches, which seperate the office’s network traffic form the measurement network (Fig. 7). The benefit of running TCP/IP is that no special hardware is necessary to communicate with the instruments. In case of an automated test system, the bandwidth for the measurement data is an important point of interest. The transmission of data from an oscilloscope takes usually more time than the measurement itself. So a high data bandwidth is desirable when interfacing an oscilloscope. The data transmission of other devices like digital voltmeters, controllable power supply units or temperature controllers is not time critical, since the data volumes being transferred are small. For these devices, a connection using IEEE488.2, RS232 or RS422 is
Fileserver
Control Computer
Measurement Network IEEE 488.2 RS232
Digital I/O
IEEE 488.2
Pulse Generation
Media Converter Fibre Optic Connections Media Converter
Trigger
IEEE 488.2
RS232
Power Supply Gate Units DUT Gate Units RS232
Power Supply DC link RS232
Temperature Controller
Security Control
Isolated power part
Fig. 7.
Test System for power semiconductor devices
When operating a test system with different possible test scenarios, the test software has several demands to meet. Since several measurement devices are used in the system, it is useful to store the initial setups for all devices. This includes most of all the settings for the oscilloscopes (i. e. timebase, vertical settings, trigger level and source), which then can be set up
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automatically at startup. The settings can be stored in a logfile or in the operating system’s registry database. In the process of testing semiconductor devices, some steps are repeatedly performed. When all the measurement devices are set up, a measurement is triggered. After a successful measurement, the waveform should be validated. The digital storage oscilloscope captures the relevant waveforms, which are then transferred to the computer. It is checked, if the measurement was successful, if clipping in one of the signals occurs and if the whole vertical range of the oscilloscope is used. Hereafter, some post processing like the calculation of power and energy in case of a switching transient is performed. Thinking about characterizing several similar semiconductor devices it is clear, that these steps are repeated for each operating point, for each temperature and for each sample of the devices to be tested [2]. The manual measurement takes a lot of time and so causes high cost. It is reasonable to use the help of software to automatise these steps.
measurement complies with the expected turn off transient. If clipping of a signal occurs, the integrated autoranging functionality adapts the vertical settings of the oscilloscope channel being affected.
8
allowed area for voltage signal
6
4
forbidden area for voltage signal
2
0
0
A. Requirements To realise the automatising software, a framework is created, see Fig. 8. Within this framework, the measurements are summarised in a single state, which symbolises all possible subsets of automated measurements. It is useful to combine a series of measurements in a test script, so a whole test sequence is repeatable for several devices [3]. In case of the measurement of the turn off behaviour shown in Fig. 13, all the valid voltages and currents are stored in the scriptfile. The test sequencer as shown in Fig. 10 will then process the test script. When changing a parameter e. g. a gate resistor or validating a new device, the script is used repeatedly.
Init END Button pressed
Stop finished
idle loop Go Button pressed
stop measurement
finished
initialise measurement
execute measurement
is safe
tInitReady
ensure safety Fatal Error
Fig. 8.
State Flow Diagram – Main framework of test system software
To decide if a measurement is successful or not, some post processing has to be included. In case of failure of a device under test, the processing of the test script has to be abandoned. Fig. 9 shows a possible tolerance scheme for the voltage of a turn off measurement, which detects of the
5
10
15
20
25
Time in µs
Fig. 9.
Tolerance scheme for the voltage during a turn off transient
Since the software is able to perform a lot of measurements generating lots of data, an automated reporting tool has to be in included. The measurement data has to be stored in the local computers filesystem or on a fileserver. The filenames are automatically generated by the test script. If the public folder of a webserver is accessable, the measurement can be made available on the internet. Beside the measurement software, some external tools are necessary. To assure safety for the test setup and the operating personnel, the maximum values for the power part have to be stored on the control computer. This usually affects the maximal DC link voltage and the maximum value for the load current. These values are stored in the operating system’s registry database (e. g. the Windows registry) taking into consideration that modification is only allowed to authorised operators for security reasons. During commissioning of a new test setup, the correct function of all the measurement devices and the security related device has to be proved. Therefore a tool detecting a short circuit in a test setup has to be prepared. This is realised by charging the DC link to a small value and monitoring the charging current, which has to become zero after some time. The status of any safety-relevant measurement device, e. g. battery powered digital voltmeters, has to be checked before every measurement. During the processing of test scripts, vertical settings of oscilloscopes are changed step by step. A complete remote control for all the settings of the oscilloscope is realised as an external application to keep the automation software concise and free of unautomated features. B. Using LabVIEW LabVIEW is a graphical programming tool for measurement and instrumentation needs. Development environments like LabVIEW allow quickly to generate functioning code [3]. The
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usage of plug-and-play drivers for measurement devices and libraries ease the development of new applications. Instead of writing codelines, a virtual instrument (VI) with a front panel, a user interface and underlaying graphical code is built. The front panel may contain numeric displays as well as advanced graphs [5], [8]. Each VI itself is executable and can be used as a subVI in another VI. This enables the VIs being well tested before integrating in an application. This integrated modularity is the basis for the software toolkit of the automated test system. To use several interfaces, LabVIEW uses a unified virtual instrumentation system architecture (VISA) to communicate with the instruments connected to the system. This unified basis means, that the developer has not to cope with the specific interfaces transport protocol [6]. LabVIEWs VISAServer allows to share the devices interfaced to a computer over the local network or the internet. This enables a test system easily to be split on several computers. Existing drivers for modern measurement devices are based on VISA and can be easily integrated in a new system. To make VIs accessable over the network, the LabVIEW Internet Developer Toolkit can be used. An integrated HTTPserver make a VIs front panel viewable from a regular web browser by the means of CGI scripts. This provides additional flexibility in the transmission of measurement data. Different formats like HTML, XML and JavaScript are permitted. The functionality of the LabVIEW Report Generation Toolkit is a library of flexible, easy to use VIs for programmatically creating and editing Microsoft Word and Excel reports. The reports are generated by using a template, which is then completed using the measurement data. The State Diagram Toolkit assists in providing a framework in which state machines can be built. The state diagram editor
V. E XAMPLE M EASUREMENTS
start measurement Finish measurement script select list entry
finished
store data
Measurement is acceptable
Validate measureme nt data
settling
adapt settings for measurement finished devices running running
Measurement not acceptable
trigger measureme nt
fetch data data transmission finished
set DC link voltage
DC link voltage set
program pulse generator
programming finished
finished
Fig. 10.
uses the notation used in Fig. 8 and 10 to create robust and easily-maintainable code. Using the State Diagram Toolkit, the framework for the test system can be created and tested. All the error handling is integrated an an be tested safely without a complex generation of test scenarios [6]. With version 7, LabVIEW introduces ExpressVIs to the developer. The usage of expressVIs simplifies the development of test, measurement and control applications by providing an interactive, easily-configurable tool. In spite of complex programming, an ExpressVI is configured by a context menu in the block diagram. The need for complex programming is eliminated. Creating new ExpressVIs is supported by the ExpressVI Development Toolkit. For the post-processing of the measurement data, MATLAB script code can be integrated into a VI using a script-node. MATLAB itself is run in the background, processing the script. The embedding of existing MATLAB scripts allow the reuse of post-processing tools, which are intended to be used off line. Communication between two running VIs, which are not sequentially executed, is possible using global variables or socket layer connections. This allows security task running in the background to pass information to the test sequencer in case of a system failure, e. g. in case of a major failure in the power part. Both communicating via global variables or socket connection requires to handle the event in the test software, Fig. 10 shows the state diagram of processing a test script for the measurement of switching transients. The measurement application is built using the state machine as shown in Fig. 10 in combination with subVIS for each state. These are individually tested and then integrated in the measurement-VI, which is called by the framework VI according to Fig. 8. The handling of major errors is realised in the framework.
Software State Flow Diagram – Processing a measurement script
Figure 11 shows the turn-off losses of a 10 kV IGCT prototype [2] for a junction temperature of T j = 85◦ C. The test circuit is shown in Fig. 3. The measurement of the turnoff behaviour is performed at different DC link voltages and different load currents automatically. When performing these measurements manually, the time taken for a single measurement is about 1.5 minutes. Time for the postprocessing has to be added. Using the test system described in section IV, the time for the whole measurements displayed in Fig. 11 can be reduced about 80%. The prototype devices are not stressed for a long time with the DC-link voltage. This is important when the SOA of prototypes is the main focus of the turn off measurements [1]. Using the scripting functionality, the measurement is completely repeatable. Using the same approach for a test system, measurements of the turn-off behaviour of the CoolMOS SPW47N60 are carried out in its whole SOA. The test circuit is shown in Fig. 12. The software is based on the same framework being shown in Fig. 8 and 10. The measurement data are processed online using both MATLAB scripts and LabVIEWs facility of
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SPW47N60 using RG = 20Ω 4 3.5
Turn Off Switching Losses Eoff [mWs]
Eoff,rel [WS/kV/kA]
3 2.5 2 1.5 1 0.5 0 6.8 6.5 6.2 5.9 5.6 5.4 5.0 4.5 4.0
8 7 6 5 4 3 2 1
0 800
200
300
500
400
600
700
800
50
600
DC Link Voltage VDC [V]
Fig. 11. Relative turn-off switching energy of a 10 kV IGCT ( VAC = 4-7.0 kV, Tj = 85◦ C,Lcl = 13.6µH, Ccl = 1µF , Rcl = 2.3 Ω)
Df
30 200
IA[A]
VAC[kV]
40
400 20 0
10
Current Isw [A]
Fig. 13. Turn off losses of CoolMOS SPW47N60 in its SOA ( VDS = 80 − 650 V , IDS = 10 − 47 A, RG = 20 Ω Tj = 25◦ C)
LH
R EFERENCES HFBR2528 RG
Light Trigger Fibre ICL7667
DUT
CDC
VDC
VDS Rshunt
VShunt
Fig. 12. Test circuit for measurement of turn off losses of CoolMOS SPW47N60
pulse transition measurement. All the measurements shown in Fig. 13 are performed within 30 minutes including the calculation of the power and energy. In the process of optimizing a gate unit for a new product or validating new devices in the pre-production process, this automated measurement can drastically reduce the cost of measurement. VI. C ONCLUSION This paper analyses the requirements for an automated testing of semiconductor devices beside the factory testers. Upon these requirements, a modular system in hardware and software is described, that meets the need of a freely configurable and open system for automated testing of power semiconductor devices in research and development. Results of testing high-power devices as well as smaller devices are presented. These results are measured using different test systems that are designed according to the guidelines presented in this paper. It is shown, that the measurements are performed faster than manual testing. The quality of testing is increased by making tests repeatable and adding automatic documentation functionality.
[1] S. Bernet, E. Carroll, P. Streit, O. Apeldoorn, P. Steimer, and S. Tschirley, Design, Test And Characteristics of 10 kV IGCTs, IEEE IAS Annual Meeting 2003, Salt Lake City [2] S. Tschirley, S. Bernet, E. Carroll, P. Streit, and P. Steimer, Design and Characteristics of Low On-state Voltage and Fast Switching 10 kV IGCTs, PCIM, 2004, Nuremberg [3] C. Tursky, R. Gordon, and S. Cowie Test System Design - A Systematic Approach, Prentice Hall Inc. PTR, 2001, New Jersey [4] R. Lappe, F. Fischer, Leistungselektronik Messtechnik, 2nd Edition, Verlag Technik Berlin, 1993 [5] R. Jamal, H. Pichlik, LabVIEW - Das Anwenderbuch, Prentice Hall, 1999, Munich [6] D. Bell, I. Morrey, and J. Pugh, The Essece of Program Design, Prentic Hall Europe, 1997 [7] G. E. Thaller, Der Individuelle Software Prozess bhv Verlags GmbH, 1997, Kaarst [8] J. O. Strandman, R. Berntzen, T. A. Fjeldly, T. Ytterdal, and M. S. Shur, LAB-on-WEB: Performing Device Characterization via Internet Using Modern Web Technology, 4th IEEE Conference on Devices, Circuits and Systems, Caracas, 2002 [9] H. Johnson, M. Graham, High-Speed Digital Design, Prentice Hall Inc , 1993, New Jersey [10] X. Wang, J. L. Hudgins, E. Santi, and P. R. Palmer, Destruction-free Parameter Extraction for a Physics-based Circuit Simulator IGCT Model, IEEE IAS Annual Meeting 2004, Seattle [11] D. Warning, O. Manck, Look-Up Tables and Various Approximation Methods in Device- and Macromodeling for Precise Circuit Simulation, European Simulation Multiconference, 1994, Barcleona [12] Tektronix Inc., XYZs of Oscilloscopes, Tektronix Inc, 2001, published online www.tektronix.com [13] Tektronix Inc., ABCs of Probes, Tektronix Inc, 2001, published online www.tektronix.com
