Op Amp Design Basics - Non-Inverting Amplifier Video

A series of videos on the operational amplifier. You can think of this as a buffer with gain. For questions on these and other videos, contact Professor Santiago at john@e-liteworks.com or vist the above website. Distributed by Tubemogul.
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Male Speaker: Here we are going to introduce op amp circuit analysis using examples that are building blocks for analog signal processing systems. And we discussed this earlier when we talked about the non-inverting amplifier itself. Now, some of the other basic circuit blocks include the voltage follower, the inverting amplifier, the summer and the last one we will discuss is the subtractor. Now in order to do a basic building block approach to designing circuits using op amps is to recognize the feedback pattern and then once you do that you need to isolate the basic circuit as a building block and we will illustrate this with an example. Let's analyze this op amp. Here we partition the circuit as a source recognize that this feedback configuration with this op amp is a non-inverting amplifier and the load and we are asked to find the relationship between the output voltage that's across this load and the input voltage Vs, this voltage source. So, you want to find the relationship and mathematical relationship between Vo or output over our input Vs. First we recognized that this is voltage divider since we know that Ip the current going into the non-inverting input is equal to zero since it has infinite input impedance. So all of the current going through R1 is going to R2, so we can use the voltage divider to find Vp. Once we know Vp we can find the relationship between Vo and Vs. So, here Vp using voltage divider is equal to our input source Vs multiplied by a scale factor of R2 divided by R1 plus R2. Okay, so Vp divided by Vs is equal to R2 all over R1 plus R2. Now whats the relationship between Vp and Vo. Well, we have recognized that this configuration is non-inverting amplifier and we know that Vo divided by Vp is equal to one plus the feedback resistor R3 all over R4 in this example. Now we note we want Vo over Vs, where we can manipulate this saying that we already found the relationship between Vo over Vp and Vp over Vs as shown here and we see that Vps canceled and we get Vo over Vs but we have this relationship and we highlight that Vp over Vs for this ratio and then Vo over Vp is found using this relationship. Now if you take these two expressions that I just highlighted and just multiplied together and get a relationship between the output voltage and the input voltage vice versa voltage here. In that case we have Vo over Vs so we have a ratio of Vo over Vp that's governed by one plus R3 over R4 and then we have Vp over Vs which is governed by this relation in which we used the voltage divider R2 over R1 plus R2 and that's our relationship between our output voltage and our input voltage and notice we had two factors concerning the product of what we call Ks using the voltage divider. So here that's just Ks and then this relationship we have identified as Kamp. So, we replace this circuit with this block diagram here Kamp or non-inverting amplifier as Kamp and our voltage divider network here as Ks and then to get the relationship between Vs and Vo, we multiplied these two diagrams here, these block diagrams Ks times Kamp. In other words, Vo over Vs is just simply the product, this is Kamp in this case and then this term is Ks to get the relationship between Vo over Vs. So, hopefully this example illustrates the process to using the building a block approach to first recognize the feedback pattern and then isolate the basic circuit as a building block as we did here.

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