 Welcome to the session of AC analysis using the LTSpy software learning outcome of the session. Before proceeding, let me ask you one question. What are the applications of the low pass filter and the high pass filter? You can pause the video, write down your answer in your notebook. You can resume the review to see the answer. Now let me give you the answer. The low pass filters are basically used in audio amplifiers, equalizers or the speaker systems in order to direct the low frequency which is a bus signal to the larger bus speakers or to reduce the any high frequency noise component which is present in the audio. This type of the noise is also called as a hiss type distortion. The high pass filters are used in audio amplifiers, equalizers, speakers, systems to direct the high frequency signal to the smaller tweeter speakers or to reduce any low frequency noise signal. These low frequency noise signals are called as a rumble type distortion. Now let us see the AC analysis of passive low pass filter in the LTSpy software. So as we have seen in a circuit, let us build the circuit in the schematic environment of the LTSpy software. So here is the resistor. So let us add the resistor component, let us rotate the component. Then we will add the capacitor, then we will add the input voltage source. So search for voltage, you will see the symbol of voltage source then click ok, then add the voltage source at the input. Now let us add the ground at the input as well as at the output. Let us connect this component together by using the wire. Now we have built the circuit, let us give the value of the resistance, move your cursor over that resistor and right click your mouse, give the value of 1 kilo ohm, then give the value to the capacitor, right click it, I will give the value of 1 micro faraday. And this is the voltage source, click on right click, right click on and go to the advance, then I will give the AC amplitude as 1, then click ok. Since the cutoff frequency of the above circuit is 1 upon 2 pi fc. So let us see what is the cutoff frequency practically. So run the circuit, after that first go to the simulate option, then edit simulation command. Now since we have to do the AC analysis, there is a second tab which is representing the AC analysis, click on that AC analysis. So the type of analysis will be the decayed, then I will take the number of decayed points for the decayed, 20 points per decayed. Starting frequency let us take 1 hertz and ending frequency let us take 2 kilo hertz and click on ok. So this transient response will present at this, the characteristics will be represented by this text. Now go to the run option, there is an option of run, so simulate that circuit. So you can see the output here, there is no output right now because we have not connected the probe to the output, let us connect the probe to the output. So this if when you move your cursor over that wire, it will show you the one probe terminal, click on that. As you can see we have the output available here, this is at 0 dB, below that we have the output response. As you can see this dotted line represents the phase angle and this represents the gain. So let us see the frequency, what we need we have to observe the cutoff frequency at minus 3 dB point. So in order to see that move your cursor over, as you can see that if I if you move this cursor, here there are changes, here you will see the magnitude and here you will see the frequency and here you will see the change in the phase. So let us move to the 3 dB point, now we are at the minus 3 dB point which will show you the cutoff frequency and the cutoff frequency is 159.08 hertz which is nearly equal to the 160 hertz. So for this circuit passive filter circuit we are getting the cutoff frequency as 160 hertz. Let us see the AC analysis of active low pass filter. So this is the active low pass filter, as you can see it consists of one opamp circuit, it consists of the opamp circuit, the capacitor is connected at the feedback. So the cutoff frequency of the above circuit is given by fc will be equal to 1 upon 2 pi r 2 into c. So let us simulate this circuit in LTC spice, go to the option of component. Now we will need the opamp circuit. So go to the option search for the component LTC 6240. So I will use this LTC 6240 opamp as a circuit, the opamp need the two differential voltages. So go to the symbol component and search for the voltage and click on ok. Then rotate this component at the another voltage source. So I will make this, connect this component together in order to produce the two voltage sources, connect the ground at this terminal. Next is this I will connect to the positive terminal here and this I will connect to the negative terminal. Now let us add the resistor at the input, one resistor at the feedback and one capacitor at the feedback, connect this together as per the circuit diagram. Let us add the voltage at the input, this is the voltage source at the input and let us add the ground. Let us give the value to the resistor, go to the option right click, I will give the value of 1 k and similarly for the capacitor I will give the value of 1 micro faraday, at the input I will give the value of 1 k. So the feedback consists of the resistance 1 of 1 k and 1 micro faraday capacitor. So the cutoff frequency will be of nearly 160 hertz. So let us observe that cutoff frequency. Again select the voltage, right click on that voltage source, go to the setting advance and give the AC amplitude of 1 because we are going to see the AC as analysis and go to the option of simulate and then go to the edit simulation command option. Here we have to select the option of AC analysis, the type of the sweep will be again decayed, number of points I will take 20, starting frequency is 1 hertz, ending frequency will be 2 kilo hertz, click on ok. Now let us run the simulation circuit. Let us add the resistance at the output. Now give the value to the voltage source of say 15 volt and for this we will add the value of 15 volt. So this will have terminal will receive positive supply and this will receive the negative supply. So here we have completed the circuit diagram. So let us simulate that circuit diagram, go to the option simulate edit simulation command. Now I have added the type of the sweep as a decayed and number of points 20, starting frequency of 1 and stop frequency of 2 kilo hertz as earlier, click on ok and run the circuit. Now here we have to observe the output. So again as you can see we have a output like this, so this is the phase angle. So you get the cutoff frequency here by setting the db point here. So we have to set it to the minus 3 db cutoff frequency. So at minus 3 db you can have the cutoff frequency of 160 hertz. So this is the simulation of the active low pass filter in LT SPICE. So these are the references of the session, thank you.