1. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 –
INTERNATIONAL JOURNAL OF ELECTRONICS AND
6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 2, February (2014), pp. 42-49 © IAEME
COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET)
ISSN 0976 – 6464(Print)
ISSN 0976 – 6472(Online)
Volume 5, Issue 2, February (2014), pp. 42-49
© IAEME: www.iaeme.com/ijecet.asp
Journal Impact Factor (2014): 3.7215 (Calculated by GISI)
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IJECET
©IAEME
A VERSATILE MICROCONTROLLER BASED SEMICONDUCTOR DEVICE
TESTER
Kanade Jyoti Suresh1,
Kulkarni Vishwashri Amrut2
1, 2
Electronics and Telecommunication Dept.
Jawaharlal Nehru Engineering College, Aurangabad, (M.S.) INDIA
ABSTRACT
This paper proposes the design and development of a simple, low cost tester system for
diode, bipolar junction transistor (BJT), and junction field effect transistor (JFET). The basic
building blocks for this tester design include PIC 18F452 microcontroller, analog
multiplexer/demultiplexer 74HC4052, 12 bit digital to analog converter (DAC) MCP4822,
operational amplifier LM741 and liquid crystal display (LCD). The tester system discussed in this
paper provides accurate identification of semiconductor device under test (diode, BJT, JFET), types
of bipolar transistor (NPN, PNP), types of junction field effect transistor (N channel JFET, P channel
JFET). The proposed system also detects leads of diode, bipolar junction transistor (BJT), and
junction field effect transistor (JFET). Apart from this the tester also measures various parameters of
above mentioned semiconductor devices such as forward voltage (VF) and forward current (IF) for
diode, current gain (HFE) for BJT, saturation current with the gate shorted to the source (IDSS), cut-off
voltage (VGS(OFF)) and drain source on resistance (RDS(ON)) for JFET. All measurement and test
results are clearly represented on LCD. Low cost, low power consumption, simple hardware, user
friendly design and compact size are salient features of this semiconductor device tester.
Keywords: Bipolar Junction Transistor (BJT), Cut-Off Voltage, Diode, Junction Field Effect
Transistor (JFET), Microcontroller.
I. INTRODUCTION
Semiconductor devices are used in all the current electrical or electronics products on the
market. As a result of the increasing demand for semiconductors, the semiconductor industry has
experienced significant growth over the past 8 to 10 years. The semiconductor industry is one of the
most productive and dynamic industries in the world. It introduces continuous and rapid
advancement in technology, new devices and integrated circuits. Challenges that the industry is
facing are to continuously improve product and service quality and reliability, achieve greater
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2. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 –
6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 2, February (2014), pp. 42-49 © IAEME
functionality, higher performance and zero defects. In order to meet all these challenges electronic
products and integrated circuits need to be highly testable. Testing is a very critical component of the
product development and production process. It can improve product’s performance, increase quality
and reliability, and lower return rates. The rising cost of electronics product testing is now one of the
main challenges to manufacturers. Sometimes cost of testing can be even greater than the cost of
product manufacturing itself. To make a significant impact on the cost of test may require a change
in test strategy which may result in bringing a new, lower cost test platform. It is estimated that the
cost of failure decreases ten times when an error is caught during production instead of the field, and
decreases ten times again if it is caught in design instead of production. Hence to reduce
manufacturing cost and improve yield semiconductor devices should be tested after being fabricated.
Thus by taking into account practical importance of above mentioned fact valuable work has been
accomplished in designing new versatile testing scheme for semiconductor devices. A few design
methodology of semiconductor device tester has been adopted in recent days [1]-[6]. Some of them
have made use of a mathematical model for the calculation of gate to source cut off voltage VGS(OFF)
and drain source on resistance RDS(ON) [6]. In proposed module the values of VGS(OFF) and RDS(ON) are
actually measured and for this a variable bipolar power supply of 5V has been designed. The
software coding part is done using MPLAB IDE.
II. GENERAL OVERVIEW OF PROPOSED DESIGN
Block diagram of semiconductor device tester is as shown in Fig.1. It consist of 6 blocks as
PIC18F452 microcontroller, resistor bank, analog multiplexer 74HC4052, variable bipolar power
supply and device under test which interact with each other as follows : microcontroller applies
necessary potential values to the leads of unknown device through suitable resistor in the resistor
bank and also performs required voltage measurements for further tests and parameter calculations.
S1, S2 represents select lines for mux1, S3, S4 for mux2 and S5, S6 for mux3. The purpose of select
lines is to make proper choice of resistor values in resistor bank with the help of analog multiplexer.
All measurement and test results for the device under test are clearly represented on liquid crystal
display unit. Detailed description of each block is given below.
Fig. 1 Block diagram of semiconductor device tester
A. Microcontroller
Microcontroller employed is Microchip’s PIC18F452. Few of its built in features are as
follows: It has linear program memory addressing to 32 Kbytes, linear data memory addressing to
1.5 Kbytes, 5 I/O ports, 10 bit analog to digital converter (ADC) module having 8 input channels,
parallel slave port (PSP), analog comparator (AC).
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3. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 –
6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 2, February (2014), pp. 42-49 © IAEME
B. Resistor Bank
Resistor bank consists of 3 resistors of values 1K , 100 and 150K . Suitable resistor values
are selected on the basis of type of test procedure to be carried out on a device under test.
C. Analog Switch 74HC4052
It is dual 4 channel analog multiplexer/demultiplexer with common select logic. It plays very
important role in making design of semiconductor device tester more user friendly.
D. Liquid Crystal Display
In this system 16x2 character liquid crystal display is used to print test and measurement results
for transistor and diode.
E. Variable Bipolar Power Supply
DAC MCP4822 and operational amplifier LM741 together forms a variable bipolar power
supply of 5V. It supplies power to the device under test through the array of 150K resistors. Basic
purpose behind designing a variable power supply is to calculate gate to source cut off voltage (VGS
(OFF)) for JFET.
III. MEASUREMENT TECHNIQUE AND ELECTRONIC HARDWARE OF THE TESTER
Microcontroller starts its test schedule by performing very first test to determine whether
device under test is two lead device that is diode. Diode can be connected between test terminals one
and three. The test is based on the basic concept that is PN junction conducts current in only one
direction [3]. In this test Microcontroller applies 5V to the lead of diode connected to test terminal 1
via 1K resistor. The lead of diode connected to test terminal three is grounded through same
resistor value that is 1K . Microcontroller measures voltage across 1K resistor connected to test
terminal 3 through switch and stores measured value. One more measurement of this sort is made
with different lead sequence. Microcontroller performs some logical operations on these two
measured values to get final result. Now there are two ways in which diode can be connected
between test terminals one and three that is cathode facing towards terminal three and cathode facing
towards terminal one. Same test sequence is repeated for diode connected in another way to get one
more final result. Thus based on these two result microcontroller determines whether device under
test is diode or any other device. This test is also sufficient to locate anode and cathode leads of
diode. After identification of diode leads its forward voltage is calculated by making necessary
analog voltage measurements and calculations. Table I represents theoretical logic to locate anode
and cathode leads for diode. In this table potential values applied and measured at test terminals 1
and 3 are represented in terms of logic levels 1 and 0.
TABLE I: Logic of detecting anode and cathode leads of diode
Voltage
Voltage applied
Voltage
Remarks
Voltage applied
to test terminal
measured
to test terminal
measured
(TT) through
across 1 K
(TT) through
across 1 K
1K resistor in
resistor
1K resistor in
resistor
terms of logic
connected to
terms of logic
connected to
levels 0 and 1
TT3
levels 0 and 1
TT1
TT1
TT3
TT1
TT3
1
0
1
0
1
0
TT1-Anode,
TT3-Cathode
1
0
0
0
1
1
TT1Cathode,
TT3-Anode
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4. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 –
6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 2, February (2014), pp. 42-49 © IAEME
In two conditions microcontroller executes programme for testing 3 lead devices that are
transistor. The first condition is that if the test for diode fails and the second condition is that if the
test for diode is positive and voltage of test terminal (TT) 2 is not zero. Microcontroller checks the
second condition to avoid wrong identification of device under test. In case of transistor
microcontroller conducts first test by performing voltage measurement to determine whether
connected device is bipolar junction transistor or junction field effect transistor. The same logic for
testing diode can be extended to test transistor; as transistor also consist of PN junctions which
conduct current in only one direction; thus by considering the direction of current conduction one
can determine whether the transistor under test is bipolar transistor or junction field effect transistor.
This test is realised by connecting one of the three leads of transistor to 5V through 100 resistance
and other two leads are connected to ground potential through 1K resistance; their voltages are
then digitally read in the form of logic levels 0 and 1. This process can be repeated for other two lead
sequences.
Each time microcontroller stores measured voltage values and performs some logical
operations on them. Now transistor can be connected in between three test terminals in six ways, so
the test sequence is repeated for that many times. The analysis shows a unique hex data
corresponding to NPN BJT and N channel JFET; while the data corresponding to PNP BJT and P
channel JFET is same therefore once it is recognized that the device under test is PNP BJT or P
channel JFET it is further subjected to a test that differentiates PNP BJT from P channel JFET. The
first test is also sufficient to determine base lead of BJT and gate lead of JFET. After identification of
base lead the task remained is to identify the other two leads of BJT that are collector and emitter. In
a properly biased transistor the current gain from base to collector is much higher than base to
emitter. This property can be used to identify the actual collector lead of transistor. For this circuit is
connected in common emitter configuration, base current is applied and the assumed collector is
connected to supply through a lead resistor of 1K . If it is real collector the current gain will be
high, collector current will be high and collector voltage will be low. Repeating this process for other
lead and comparing the collector voltages one can decide the actual collector lead. Configurations
used for measurement of VF and IF for diode, current gain for NPN and PNP type of BJT and IDSS and
RDS(ON) for N channel JFET are shown in Fig. 2.
Fig. 2 Measurement configurations
Once the collector lead is identified a proper biasing is applied choosing suitable collector
and base resistors through the mux. The analog voltages at collector and base terminals are measured
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5. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 –
6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 2, February (2014), pp. 42-49 © IAEME
using analog to digital converters. The collector current and base current are calculated by measuring
voltages across the collector and base resistances and current gain is calculated.
Resistor RSWITCH represents internal resistance of each switch of the analog
mux/demux74HC4052. Its value is approximately 65 . Most of JFETs are symmetrical in nature
that is their source and drain terminals can be interchanged hence the tester can identify only gate
lead of JFET and other two leads can be assumed as source and drain without altering the results
related to the calculation of its parameters [5]. Once the gate lead is identified JFET is properly
biased and saturation current with the gate shorted to the source (IDSS) as well as drain source on
resistance (RDS(ON)) is calculated for VGS=0V. To calculate cut-off voltage (VGS(OFF)) gate to source
reverse bias voltage is gradually increased and drain voltage is measured; for certain value of gate to
source voltage (VGS) the drain voltage becomes maximum as drain current falls to zero in N channel
JFET and drain voltage becomes zero as drain current falls to zero in P channel JFET and this value
of gate to source voltage is taken as cut off voltage. Operational flow of semiconductor device tester
is given in Fig. 3.
Fig. 3 Operation flowchart of semiconductor device tester
Fig. 4 shows the circuit diagram of the semiconductor device tester. The external crystal of
12MHz is used as clock source. In the proposed module device under test is subjected to large no of
permutations and combinations of logic levels in perfect sequence through suitable resistor values.
Without removing device under test this is possible if and only if analog switches are used for proper
routing of signal. Three analog to digital converter input channels are used to make necessary analog
voltage measurements. The LCD panel communicates with the microcontroller in 8 bit mode. In the
presented work the values of VGS(OFF) and RDS(ON) are actually measured by applying necessary
potential values to the gate lead of JFET in order to force the device to work in a cut off region for
this a variable bipolar power supply of 5V has been designed using DAC and operational amplifier.
DAC is controlled through microcontroller for generating suitable voltage values. Current flowing
through device terminal has to pass through the selected series resistance and internal resistance of
analog switch. The current is calculated by measuring the potential difference across series
resistance; therefore second analog switch of 74HC4052 is used to connect potential of other lead of
series resistor to analog input of microcontroller. Input impedance of analog input of microcontroller
is always extremely high hence no current flows through the internal resistance of second switch and
all the voltage at desired point is coupled to analog input of microcontroller. Thus the effect of
internal resistance of analog switch can be compensated to some extent while making current
measurements.
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6. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 –
6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 2, February (2014), pp. 42-49 © IAEME
Fig. 4 Circuit diagram of semiconductor device tester
IV. TEST RESULTS OF THE SEMICONDUCTOR DEVICE TESTER
Fig. 5, Fig. 6, Fig. 7 and Fig. 8 illustrate results displayed on LCD panel while testing
semiconductor devices. Fig. 5 shows test results for diode. First line of display indicates forward
current for diode and second line of display indicates lead arrangement and forward voltage for
diode. Fig. 6 shows test results for bipolar junction transistor. First line of the display indicates the
type of BJT and it’s current gain HFE. Second line of display indicates it’s lead arrangement and
collector current.
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7. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 –
6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 2, February (2014), pp. 42-49 © IAEME
Fig. 7 and Fig. 8 illustrate test results for junction field effect transistor. In Fig.7 first line of
the display indicates the type of JFET and second line of the display indicates it’s lead arrangement.
In Fig. 8 first line of the display represents saturation current with the gate shorted to the source
(IDSS) and second line of the display represents drain source on resistance (RDS(ON)) for JFET.
Fig. 5 Test results for diode. The tester’s
display indicates DIODE; If = 1.7mA;
1-A 3-K; Vf = 0.62V.
Fig. 6 Test results for bipolar transistor.
The tester’s display indicates BJT; PNP;
hfe = 163; EBC; Ic = 3.27mA.
Fig. 7 Test results for junction field
effect transistor. The tester’s display
indicates N-CHANNEL JFET; G-S-D.
Fig. 8 Test results for junction field
effect transistor. The tester’s display
indicates IDSS=3.35mA; RDS(ON)=54ohm.
V. CONCLUSION AND FUTURE WORK
By taking into account immense practical importance of testing semiconductor devices
especially diode, bipolar junction transistor and junction field effect transistor a low cost, high
performance testing scheme is presented in this paper. A variable bipolar power supply of 5V has
been designed to calculate VGS(OFF) for JFET and also as a further provision for calculation of
threshold voltage (VTH) for metal oxide semiconductor field effect transistor (MOSFET). The
proposed module can further be developed to test MOSFET and calculate it’s parameters with few
modifications in software.
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8. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 –
6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 2, February (2014), pp. 42-49 © IAEME
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