Aspects of VR-LRC use @

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• Aspects of VR-LRC use _at_ Transilvania University
  in cooperation with Siemens PSE
• - practical guide for remote measurement (real
  and simulated)
• of n-channel junction field effect transistors -
• Florin SANDU
  Szilard CSEREY
• Individualized Learning Enhanced by Virtual
  Reality IDENTITY
• Agreement number 229930-CP-1-2006-1-RO-MINERVA-M
  Contractual Authority EU Education Audiovisual
  and Culture Executive Agency

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• Data sheet for the transistor used

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STEP 1 Selecting NJFET measurement

• Accessing the remote lab

The address for measurements and data
sheets http//vlab.unitbv.ro/velab/
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• STEP 2 Selecting the browser ( /mobile
  alternative )
• For a normal browser one can choose the second
  option ( / the measurement can also be done with
  a JavaScript enabled mobile phone by selecting
  the third option)

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• STEP 3 Selecting the experiment
• The page displays several options for
  measurement,
• from which it was chosen the one for NJFET

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• STEP 4 Entering the stimuli
• After entering the stimuli values in the text
  boxes, if you push the Measure button you will
  obtain the results both from the PSpice
  simulation and the real remote measurement done
  in the Lab.

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• STEP 5 Retrieving experimental data
• After waiting about 15 seconds the result file
  will be printed on the page.

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• The .xls version of the results

UGS UDS U2 ID
-3.00E-01 0.00E00 0.00E00 0
-3.00E-01 9.77E-03 5.00E-01 8.75419E-05
-3.00E-01 1.95E-02 1.00E00 0.000175084
-3.00E-01 2.44E-02 1.50E00 0.000263497
-3.00E-01 3.42E-02 2.00E00 0.000351039
-3.00E-01 4.39E-02 2.50E00 0.000438581
-3.00E-01 5.37E-02 3.00E00 0.000526123
-3.00E-01 6.84E-02 3.50E00 0.000612793
-3.00E-01 7.81E-02 4.00E00 0.000700335
-3.00E-01 9.28E-02 4.50E00 0.000787005
-3.00E-01 1.07E-01 5.00E00 0.000873675
-3.00E-01 1.27E-01 5.50E00 0.000959473
Using .xls file you can make your own XLS charts
from measured data
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• Comparison between the data sheet and the .xls
  sample
• We are going to use this example

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Static Characteristics
DATA SHEET
MEASURED
Obs. Breakdown voltage -0.5V

• UGS -0,3V -0,4V -0,5V -0,6V
• One can notice that closer to UGS -0,3V
  asymptotic trend isn't obvious
• Closer to UGS -0,7V, smaller current values
  are more affected by discretization errors

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This measurement is intended to find the point of
convergence of the ID(UDS) asymptotes (for
constant UGS)
DATA SHEET
MEASURED
UGS -0.4 -0.42 -0.44 and -0.46V  
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• For UGS -0.42 -0.44 and -0.46V, only (three
  sets of) points to the right were chosen and
  "trend lines" determined
• From the equation y mxn, the ration -n/m gave
  3 estimates of the convergence point, approx. (0
  - 43,7V)

UGS -0.42V n 0.000345213316 m
0.000008205356 U(convergence) -n/m
-42.07170487 UGS -0.44V n
0.00024277885 m 0.00000557362
U(convergence) -n/m -43.55855799 UGS
-0.46V n 0.00016389815 m 0.00000373679
U(convergence) -n/m -43.86067989
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Breakdown voltage
Up(aprox.) - 0.0304 / ( 2 0.0287 ) -0.52962
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m 0.1466 n 0.0816
Up -n/m -0.55662
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• Multiple VD measurement with fixed U2 , (max)
  10V (that grants SATURATION)

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Multiple VD measurement with fixed U2 , (max)
10V (that grants SATURATION)
Limit line 10V / 9,8kW 1,02 mA
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Multiple VD measurement with fixed U2 , (max)
10V (that grants SATURATION)
Limit line 10V / 9,8kW 1,02 mA
Parabolic ID, saturated (UGS)
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Multiple VD measurement with fixed U2 , (max)
10V (that grants SATURATION)
Limit line SQRT(1,02)
Linear SQRT( ID, saturated ) (UGS)
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Multiple VD measurement with fixed U2 , (max)
10V (that grants SATURATION)
SQRT( IDSS) 0,072 IDSS 5,1 mA
Parameters check on measured values close to
UGS,bias -0,3V
UP - 0,46 V
SMALL SIGNAL PARAMETER computed in UGS,bias
-0,3V
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• Multiple VD measurement ( VG - 0,1V -
  0,2V - 0,3V - 0,4V ) ( U2 0V 0,5 V
  9,5V )

2nd SMALL SIGNAL PARAMETER measured in UGS,bias
-0,3V rd 56,7 kW

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Multiple VD measurement ( VG - 0,295V -
0,3V - 0,305V ) ( U2 8,5V )
The result , respectively, VD 2,87V
3,225V 3,567V MEASURED gain, Au (
3,567V 2,87V ) / 0,305V ( 0,295V )
69,7
On the SMALL SIGNAL EQUIVALENT CIRCUIT it
results COMPUTED gain, Au 8,44mS . ( 9,8 kW
II 56,7 kW ) 70,5
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• Comparison to PSpice simulation

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Comparison to PSpice simulation
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Comparison to PSpice simulation
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Determining UP and IDSS using graphical methods
(1)

• Comparison to MatLab simulation

• Using continuous current measurements of VD, ID
  can be obtained by a simple calculus
  ID(E-VD)/9.8kO
• IDSS is equal to ID when VG0
• UP represents the gate source cut-off voltage
  (for lower Drain voltages ID0)
• Both IDSS and UP values are determined through
  graphical methods (use of cubic spline
  interpolation)
• The obtained (NOT measured) values are
• UP 0.4998 V and IDSS 1.0179 mA (for
  VSupply10 V)

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Determining UP and IDSS using graphical methods
(2)
Measured UGS values - Interpolation Curve
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Alternating current calculus and measurements

• The alternating current input signal is simulated
  through symmetrical variations of UGS around a
  given value (in this case -0.3 V with 0.05 V
  variation margin)
• VD is measured several times for a more accurate
  value in all three cases (UGS -0.295 V , -0.3 V
  and -0,305 V)
• The first voltage gain is obtained using the
  following formula

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Alternating current calculus and measurements

• In order to be able to calculate the theoretical
  gain, gm must be determined. This is done by
  finding the slope of ID(UGS) using mathematical
  analysis. Thus,

Because ID(UGS) is obtained by measurements
(later points being approximated), it is not
possible to calculate a lime. Therefore
discrete values are given to ?V and then , by
gradually reducing it down to 0.
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Alternating current calculus and measurements
The resulted value of gm is around 6.7 mS.
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Alternating current calculus and measurements

• The theoretical gain is AU2 -gmR -6.7 mS 9.8
  kO -65.66 (rd ? 8)
• Compared to AU1, this value is smaller due to
  approximations in later calculus (like gm).
• Note All the graphical representations have been
  plotted in Matlab 5.2