INTERNATIONAL JOURNAL OF ELECTRONICS AND COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET)

Transcription

1 INTERNATIONAL JOURNAL OF ELECTRONICS AND COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET) International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 ISSN (Print) ISSN (Online) Volume 5, Issue 2, February (2014), pp IAEME: Journal Impact Factor (2014): (Calculated by GISI) IJECET I A E M E A VERSATILE MICROCONTROLLER BASED SEMICONDUCTOR DEVICE TESTER Kanade Jyoti Suresh 1, Kulkarni Vishwashri Amrut 2 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 (V F ) and forward current (I F ) for diode, current gain (H FE ) for BJT, saturation current with the gate shorted to the source (I DSS ), cut-off voltage (V GS(OFF) ) and drain source on resistance (R DS(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 42

2 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 V GS(OFF) and drain source on resistance R DS(ON) [6]. In proposed module the values of V GS(OFF) and R DS(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). 43

3 B. Resistor Bank Resistor bank consists of 3 resistors of values 1KΩ, 100Ω and 150KΩ. 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 150KΩ resistors. Basic purpose behind designing a variable power supply is to calculate gate to source cut off voltage (V GS (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 1KΩ resistor. The lead of diode connected to test terminal three is grounded through same resistor value that is 1KΩ. Microcontroller measures voltage across 1KΩ 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. Voltage applied to test terminal (TT) through 1KΩ resistor in terms of logic levels 0 and 1 TABLE I: Logic of detecting anode and cathode leads of diode Voltage Voltage applied Voltage measured to test terminal measured across 1 KΩ (TT) through across 1 KΩ resistor 1KΩ resistor in resistor connected to terms of logic connected to TT3 levels 0 and 1 TT1 Remarks TT1 TT3 TT1 TT TT1-Anode, TT3-Cathode TT1- Cathode, TT3-Anode 44

4 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 100Ω resistance and other two leads are connected to ground potential through 1KΩ 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 1KΩ. 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 V F and I F for diode, current gain for NPN and PNP type of BJT and I DSS and R DS(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 45

5 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 R SWITCH represents internal resistance of each switch of the analog mux/demux74hc4052. Its value is approximately 65Ω. 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 (I DSS ) as well as drain source on resistance (R DS(ON) ) is calculated for V GS =0V. To calculate cut-off voltage (V GS(OFF) ) gate to source reverse bias voltage is gradually increased and drain voltage is measured; for certain value of gate to source voltage (V GS ) 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 V GS(OFF) and R DS(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. 46

6 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 H FE. Second line of display indicates it s lead arrangement and collector current. 47

7 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 (I DSS ) and second line of the display represents drain source on resistance (R DS(ON) ) for JFET. Fig. 5 Test results for diode. The tester s Fig. 6 Test results for bipolar transistor. display indicates DIODE; I f = 1.7mA; The tester s display indicates BJT; PNP; 1-A 3-K; V f = 0.62V. h fe = 163; EBC; I c = 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 I DSS =3.35mA; R DS(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 V GS(OFF) for JFET and also as a further provision for calculation of threshold voltage (V TH ) 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. 48

8 REFERENCES [1] I. Lita, M. Jurian, D. A. Visan, S. Opera, and I. B. Cioc, Microcontroller based tester for semiconductor Devices, Electronics Technology, 31st International Spring Seminar, ISSE 08, pp , May 7-11, [2] R. L. Boylestad and L. Nasheisky, Electronic Devices and Circuit Theory, 10th ed., Pearson Education South Asia, India, [3] T. L. Floyd, Electronic Devices, 7th ed., Pearson Education South Asia, India, [4] R. Gaonkar, Fundamentals of Microcontrollers and Applications in Embedded Systems (with the PIC18 Microcontroller Family), Penram International India, [5] A. S. Sedra and K. C. Smith, Microelectronic Circuits, 5th ed., Oxford University Press. [6] [7] Microcontroller datasheet. [online]. Available: [8] 74HC4052 datasheet. [online]. Available: [9] MCP4822 datasheet. [online]. Available: [10] LM741 datasheet. [online]. Available: 49