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Universal Research Publications. All rights reserved
ISSN 2320 –3927
Abilash
Lecturer, B.T.T.I, Pilani, e-mail: abhi716va_kal@yahoo.co.in
Received 06 November 2015; accepted 16 November 2015
Abstract
Simulation is the imitation of the operation of a real process over time. It is an important feature in engineering which helps an engineer in many ways. A low-pass filter circuit is a filter circuit which passes the signals which have lower frequency and attenuates the signals which have frequencies higher than the cutoff frequency which is determined by the
RC time constant. It has a wide application in audio amplifiers, radio transmitters and digital circuits
© 2015 Universal Research Publications. All rights reserved
Key words : Simulation, voltage source, RC low pass filter circuit.
1. INTRODUCTION: Simulation can be used to show the real effects of various conditions. LT Spice IV is an analogue circuit simulator with integrated schematic capture and waveform viewer, which is most widely used.
In a RC low-pass filter circuit the reactance of a capacitor varies inversely with the frequency, but the value of the resistor remains constant as the frequency changes. At lower frequency the capacitive reactance of the capacitor will be more compared to the resistive value of the resistor.
The voltage potential across the capacitor will be much larger than the voltage drop developed across the resistor.
1.1 LT Spice IV: LT spice IV is a simulator which is used for simulation of electronic circuits, produced by semiconductor manufacturer Linear Technology (LTC).
It has two modes for driving the simulation. The simulator can be used as a general purpose schematic capture with an integrated simulator or the simulator can be feed with a handcrafted net list or a net list generated with a different schematic capture tool. Circuit simulations can be done on transient, AC, DC, and analysis can be plotted. More ever it can be used to calculate and generate efficiency reports of the heat dissipation of components. LT Spice IV has a large database of components including resistors, inductors, capacitors, diodes and transistors.
The main simulation tools are:-
.OP- used to calculate the operating point of a circuit.
.DC- used to calculate the operating point of a circuit for various value of voltage or current source. The output will be in the form of graph.
.TRAN- used to view the timing diagram of various signals.
.AC- used to find the frequency response of a circuit.
.MEAS- used to perform measurement on the result of analysis.
2. SCOPE OF APPROACH: This article gives the overview that simulating a circuit helps a great before designing the hardware. Without changing the hard ware by the help of simulation, the effects of various components can be verified. A low-pass filter circuit has a wide application in audio amplifiers, radio transmitters, digital circuits, DSL splitters and image blurring.
3. METHOD: A new sheet is created and the schematic is drawn. The components are placed after selecting it from the database and wiring is made. The ground terminal is connected to the circuit. In/Out labels are marked at the nodes as shown in figure 1. The label keys can be accessed by clicking the F4 key. The value of resistor is selected at 1 kilo ohm and capacitor at 100 nano farad.
The voltage source is selected to provide a square wave.
For this the voltage source is right clicked and the function is set to pulse. PULSE is used for a transient simulation of a circuit. LT spice IV calculates it is in the time domain. V initial represents the value when the pulse is not on. V on represents the value when the pulse is turned on. T delay is the time delay in seconds. It can be set to zero, but it cannot be negative at any instance.
T rise is the rise time of the pulse in seconds. T fall is the fall time of the pulse in seconds.
T on is the pulse width in seconds. It is the time when the pulse is fully on.
T period is the time period in seconds of the pulse.
N cycles are the number of cycles of the required for the pulse.
Figure 2 shows the Value of independent voltage source used at pulse input mode. The V initial [V] is kept at -5, V on [V] at 5, T delay [S] at 0, T rise [S] at 0.01m, T fall [S] at 0.01m, T on [S] at 0.49 and T period [S] at 1m.
Advanced Engineering and Applied Sciences: An International Journal 2015; 5(4): 104-106 104

Fig. 1. RC Low pass filter
Now the simulation is run by selecting input and output voltage. The input pulse at the given value can be seen. The effect of given pulse to the RC low pass circuit can be seen as shown in figure 4. On clicking the V (in) and V (out) the average and RMS value can be measured as shown in figure 5.
Fig. 4: Input and output
When the source is set the transient analysis is then selected as shown in figure 3. The transient analysis depends on time. DC component of the source is applied to the circuit during transient analysis. This analysis is very important because it almost shows a real situation. It saves the node voltage and current in branches at each time point in the analysis. Convergence failure might occur if the stated initial conditions are not very close to the real DC operating point values. In this to perform a nonlinear time domain simulation the stop time is set 10ms, time to start saving data at 0 and maximum time step at 0.01m.
Fig. 5: V in and V out
The FFT analysis converts the signal from its real domain to a representation in the frequency domain. It is a powerful tool in the analysis and observation of circuit in electronics.
LT spice IV uses a proprietary FFT algorithm, which allows an arbitrary number of data points. To see the spectrum of signal, FFT is clicked as shown in figure 6 and the fast Fourier transform can be seen.
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Fig. 6: FFT
3. RESULT & CONCLUSION: On simulating the RC low pass filter with square wave input the V out is received which have an RMS value of 3.8884 Vand average value of
-755.68 micro V. The various effects on output can be seen by changing the value of resistor and capacitor and the desired output can be achieved. The circuit can be modified as desired for passing the low frequency signals to sub woofers in audio amplifier.
REFERENCES
1 Miklos Herpy, Berka. Studies in Electrical and Electronic
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Fig. 3: Transient analysis
Advanced Engineering and Applied Sciences: An International Journal 2015; 5(4): 104-106

2 Arthur Williams, Fred Taylor. Electronic Filter Design
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AUTHOR
Mr. Abilash is working as lecturer in the department of
Digital electronics in B.T.T.I, Pilani. His stream in MTech is VLSI. He worked as system engineer in GAM IT, Dubai and as project engineer in Indutech, Dubai. He has an experience of more than 13 years. He is the author of a book published in Digital electronics. He has published various papers in international journals in advances in polymer science and technology, nanoscience and nanotechnology. He is an associate member of I.E.T.E and
I.E. His areas of interest are digital systems and sound engineering.
106 Advanced Engineering and Applied Sciences: An International Journal 2015; 5(4): 104-106