Design of Low-Cost Multi- Waveforms Signal Generator Using Operational Amplifier

Transcription

1 Ali S. Aziz Al-Hussain University College, Karbala Province, IRAQ Design of Low-Cost Multi- Waveforms Signal Generator Using Operational Amplifier Function signal generator has a wide range of applications in electronic measurement and teaching. Yet, many of the trading tests signal generators are bulky and expensive. Furthermore, many types of them are in a fixed operating mode with limited utilized signals. The aim of this research paper is to design a multi-functional, multiwaveform with high accuracy economic signal generator based on operational amplifier, which is able to provide waveforms that are commonly used in electronics experiments. The circuit is simulated in Multisim software, and the hardware circuit is validated. The results show that using Multisim simulation results are basically consistent with the hardware circuit. The output value of the waveforms of the signal generator are square, triangle, sine wave with voltage range of (0-14 V) and output frequency range of (50 Hz-3.1 khz). The signal generator has simple, practical, low cost features and the important application value. Keywords: Signal generator, Waveforms, Operational amplifier, Frequency, Amplitude Received: 4 September 2017; Revised: 9 November 2017; Accepted: 16 November Introduction Waveforms are electrical signals that provide information about the attributes or behaviors of certain phenomenon [1]. Square, triangle, and sine wave signals generated by function signal generators are commonly utilized in a wide applications range, generally as a standard signal in the testing of electronic circuits, demonstration in experimental courses, and measurement of parameters [2,3]. However, because of the fixed operating mode, high cost, and poor extensibility combine the programmable functions for producing arbitrary waveforms and other functions that cannot be fully played out in the teaching experiments of common signal generator, there is a need for a small and costcompetitive waveforms generator which is capable of meeting commonly used functions and be appropriate for many experimental courses. Studies have been performed to design different types of function generator. In reference [1] the authors designed a simple waveform generator. The device is able to produce different waveform shapes but they have not equal amplitude and frequency. Design and analysis of a cheap signal generator based on DDS technology is discussed in reference [2]. The signal generator is able to produce output square and sine waves only. The authors in reference [4] have designed a sinusoidal, triangular and square wave generator using second generation current conveyor (CCII). The simulation results showed that the proposed function generator has better linearity and range of frequency as compared with existing reported configurations. Operational amplifier IC usually called Op amp is the most commonly utilized IC between many general purpose linear Integrated circuits. Op amp is a high gain differential amplifier which is able to amplify signal right down to DC because of the using of DC coupling in the internal architecture of the circuit. Because of the distinctive characteristics the operational amplifier such as the high bandwidth, high input impedance, high differential gain, low output impedance (high current gain), and many other desired features, operational amplifiers suitable for most thinkable circuit applications ranging from active filters to regulators, amplifiers to oscillators, and computational building blocks to data conversion circuits [5,6]. The most common type of operational amplifier is ua741 op amp. The internal circuit of the amplifier is composed of resistors, transistors, diodes, and a single 30 pf capacitor as shown in Fig. (1) [7]. In the present research paper a very costeffective, simple and multi used waveforms generator based on operational amplifiers is both simulated and implemented. Cost-effective since the whole components of the design are cheap, simple because the design of circuit operation is not complex and fabricate using easily obtainable components, and multi used since it is able to produce different waveforms with suitable range of amplitude and frequency. 2. Materials and Methods 2.1 Square and Triangular Waves Generator The circuit of the square and triangle waveforms generator consists of a non-inverting Schmitt trigger and an integrator as shown in Fig. 2. The integrator is driven by the rectangular wave output of the schmitt trigger. The output of the integrator is a a triangular wave, which is also fed back and utilized for driving the Schmitt trigger. In other words, the first part of the circuit drives the second part, and the second drives the first [8, 9]. The square and triangle All Rights Reserved ISSN (printed) , (online) Printed in IRAQ 13

2 waveforms generators parts of the circuit are explained in details in this section. When the power supply is connected to the schmitt trigger for the first time, the Schmitt trigger output must be either at high state or at low state [10]. The integrator output will be a raising ramp when the Schmitt trigger output is low. Whilst, for Schmitt trigger of high output, a faling ramp will be produced by the integrator. Either way, the triangular signal will initiate to generate, and the feedback to the Schmitt trigger positive input keeps it going. In other words, the triangular wave produced by the integrator is capable of driving the Schmitt trigger. Fig. (2) Design concept for a basic square & triangular wave generator 2.2 Sine Wave Generator Production of the sine wave is acheived by applying proper circuit and using triangle wave input. As mentioned in the previous part, the triangular signal is generating by employing a Schmitt trigger circuit and an integrator. Then, by using the diode loading circuit, this triangular wave is converted to a sine wave as shown in Fig. (3). circuit, the output voltage increses less sharply and it falls lower than the value of V1 and the diode stops conducting, as it is in reverse-bias [11]. As shown in Fig. (4), by utilizing a six-level diode loading circuit, the approximation can be further improved. The connection of the all diodes to different bias voltage levels is done by using suitable values of resistors. There will be three positive- and three negative-bias voltage levels since there are six diodes. Therefore, the slope changes six times at each half-cycle of the output voltage, and the shape of output wave will give a better approximation of the sine wave. The conversion of triangular to sine wave is carried out by using an amplifier in which the amplitude of the output voltage varies inversely with the gain. R1 and R3 set the slope of the output voltage at low amplitude near the zero crossing. when the output voltage rises, the voltage across R3 increases to begin forward biasing D1 and D3 for positive outputs or D2 and D4 for negative output. As the the conduction of these diodes is taken place, they shunt feedback resistance R3 lowering the gain which leads to convert the shape of the signal from triangular to sine wave. Furthermor, R2 is adjusted in order to make the gain of the amplifier approach zero at the peak so as to get the rounded tops for the sine wave [11]. Figure 5 shows the generation of sine wave using op amp. In order to get more accuracy waveform, a capacitor can be added at the positive terminal of the amplifier. Furthermore, it is possible to connect the output of the first amplifier to another amplifier to increase the amplitude of the waeform. Fig. (4) Six level diode loading circuit Fig. (3) Two level diode loading circuit Resistors R1 and R2 operate as the voltage divider. The diode D1 becomes forward-biased when the voltage across R2 is higher than V1. The behaviour of the circuit is a simple voltage-divider. This is also applies to the negative half-cycle of the input voltage. If R3 and R4 are accurately selected to be equal, the positive and the negative cycles of the output voltage will be also the same. The shape of the output signal is approximately sine wave. There is more attenuation in the levels of the output voltage bove V1 than levels below V1. Because of the existence of the resistor R 3 and diode D 1 in the Fig. (5) Sine wave generator using operational amplifier 14 Iraqi Society for Alternative and Renewable Energy Sources and Techniques (I.S.A.R.E.S.T.)

3 2.3. Design of Proposed Waveform Generator The signal generator, that is capable of generating various waveforms shapes, is designed and developed by using the schematic diagram shown in Fig 6. The main components of the circuit are ua741 IC operational amplifiers, resistors, capacitors, diodes, switches, Furthermore, operational amplifiers operate on a dual power supply which consists of two DC supply voltages. The typical commercially used power supply voltages for ua741 IC are ± 5 V to ± 18 V [12]. The batteries used in this research paper have a value of ± 15 V. 3. Results and Discussions From the results, it is clean that the circuit is able to produce square, triangular, and sine waves each of them has the same amplitude and frequency equal to the others which is not achieved in most of the other researches. It is found that the the amplitude can be varried between 0 and 14 V by using the potensiometer. Furthermore, the output waveform of the circuit has a frequency range between 50 Hz and khz which can be modified by changing the value of the variable capacitor. Figure (7) shows the output waveforms with output voltage of 7.7 V and frequency of 62 Hz. A much higher ranges of frequencies for about 1 MHz can be produce using the same same circuit whith some modifications. If higher frequencies are required, R 1 and R 2, R 3, and C 4 have to be replaced by another values according to the following frequency equation: F = 1 = 1 T 4 R 1 C 1 ( R (1) 2 R3 ) get a perfect sine waves at a certain frequencies, It is possible to use appropriate capacitors at those frequencies. The output waves after connecting capacitor to the positive terminal of amplifier (A3) in parallel mode is shown in Fig. 8. Fig. (8) The output waves after connecting capacitor to the amplifier (A3) In many cases, the comparison between the simulation and practical results shows a very large differences. In order to validate the simulation results, a practical experiment on a bread board has been done for the circuit as shown in Fig. (9). Fig. (9) Laboratory setup of the hardware model Fig. (7) The output waveforms with output voltage of 7.7 V and frequency of 62 Hz It is found that both triangle and rectangular waves have a significantly higher accuracy than the sinewave. Furthermore, Improvement of the sine wave shape at any particular frequency can be done by using filters components. However, Utilizing of filters will result in a loss of amplitude at higher frequencies and distortion at lower frequencies. To The results which are presented on the oscilloscope show that the actual (measured) minimum and maximum frequencies are respectively 46 Hz and 3.04 khz against 50 khz and khz, the designed frequencies. Furthermore, the range of the output voltage is found to be between 0 and 13.6 V. This is due to the losses in the real circuit. However, the comparison shows good agreement between experimental and simulation results. Figures (10), (11) and (12) show the output regtangular, triangular, and sine waves respectively. Some development can be made for the design to make it with better features. Additional waveforms types can be introduced by adding some components, for example in order to get cosine wave the output of the operational amplifier (A4) is connected to a differential circuit which is shown in Fig. (13) [13]. The mathematical operation of Differentiation is performed by using this All Rights Reserved ISSN (printed) , (online) Printed in IRAQ 15

4 operational amplifier circuit which generates an output voltage that is directly proportional to the rate-of-change of the input voltage with respect to time. Further waveforms types can be produced such as sawtooth and spike waveforms by adding suitable circuits. Furthermore, Pule width modulation (PWM) can be generated by using comparator operational amplifier which is usually used in the communications laboratories [14]. Fig. (13) Circuit diagram of differentiator operational amplifier Fig. (10) Sine wave output waveform Fig. (11) Regtangular output waveform Fig. (12) Triangular output wave 4. Conclusion Acompetitive cost, muliwaveforms function generator based on operational amplifier is simulated and implemented in this research paper. It can produce square wave, sine wave and triangle wave signals to satisfy the requirements of laboratories in colleges and other organizations. At the same time, some rarely used functions have been removed to reduce costs. The simulated design is validated by making practical design of the circuit on a bread board. It is found that both simulation and practical results are almost the same with negligible difference. The proposed functions generator can be modified to produce a another range of frequency by changing some of the components in the circuit. Moreover with some improvement, it is possible to get other waveforms such as cosine, spike, and sawtooth waveforms. Furthermore, PWM (pulse width modulator) circuit can be added which produces new dimensions for the proposed signal generator. References [1] A. P. Manandhar and V. Gupta, "Design and Fabrication of a Simple Waveform Generator", Int. J. Electron. Comm. Tech., 6(6) (2015) [2] J. Qi, Q. Sun, X. Wu, C. Wang and L. Chen, "Design and Analysis of a Low Cost Wave Generator Based on Direct Digital Synthesis", J. Elec. Comp. Eng., (2015) [3] P. O. Olabisi and B. J. Olufeagba, "Step-Wise Approximation Technique in the Design of a Function Generator", Int. J. Eng. Tech., 4(6) (2014) [4] D. K. Patel and R. Khatri, "Function Generator using Current Conveyor (CCII)", Int. J. Comp. Appl., 147(7) (2016) 1-4. [5] M.M. Abrar, "Design and Implementation of Op amp based Relaxation Oscillator", Int. Res. J. Adv. Eng. Sci., 2(1) (2017) [6] K.A. Humood, A.H. Saleh and W.Q. Mohamed, "Design and Implementation of Op-Amp-RC Sine Wave Oscillator", Diyala J. Eng. Sci., 8(1) (2015) Iraqi Society for Alternative and Renewable Energy Sources and Techniques (I.S.A.R.E.S.T.)

5 [7] U.A. Bakshi and A.P. Godse, "Power Electronics II", Technical Publications (Pune, India) (2009), Ch. 4, p. 47. [8] S. Fuada and F.T. Aquari, "Square Wave Generator Circuit Analysis Using Matlab Approach", Int. J. Eng. Sci. Res. Tech., 2(2) (2013) [9] A.P. Godse and U.A. Bakshi, "Linear ICs and Applications", Technical Publications (Pune, India) (2009), Ch. 6, p. 3. [10] M.M. Abrar, "Design and Implementation of Schmitt Trigger using Operational Amplifier", Int. J. Eng. Res. Appl., 7(1) (2017) 5-9. [11] D. De and K.P. Ghatak, "Basic Electronics", Pearson Education India (India) (2010), Ch. 14, p [12] H.L.F. Canque, "Analog Electronics Applications: Fundamentals of Design and Analysis", CRC Press (United States) (2016), Ch. 14, p. 75. [13] M.S.P. Rao, "Pulse and Digital Circuits", Tata McGraw Hill Education (United States) (2009), Ch. 2, p. 64. [14] A. Yadav, "Analog Communication System", University Science Press (New Delhi, India) (2008), Ch. 10, p Fig. (1) Internal circuit of 741 operational amplifier IC All Rights Reserved ISSN (printed) , (online) Printed in IRAQ 17

6 C1 R2 220 n F Key=A 50 % 60. 5k R1 23kΩ A1 Vout 1 (triangle) R3 60kΩ A2 Vout 2 (square) R10 R4 20kΩ D5 R5 1.1kΩ 2kΩ D6 A3 R k Key = Space A4 R % 10kΩ R11 Key = Space Key=A R7 5kΩ R8 5kΩ 1kΩ Vout 3 (sine) R9 D1 D3 Key = Space 1.5kΩ D2 D4 Fig. (6) Circuit diagram of the designed signal generator 18 Iraqi Society for Alternative and Renewable Energy Sources and Techniques (I.S.A.R.E.S.T.)