Understanding Circuits - ECE topics #4 (part 1)

This episode continues our journey through circuit theory and beyond. The goal is to illuminate the key aspects of circuit analysis that practicing engineers use to understand circuits. Linearity and Thevenin's theorem are introduced, but the main focus is on how these can be used to parse analog schematics into block diagrams that show the functions of different parts of the circuit.

[@robballantyne3]

Thank you again for another great explanation!

[@Homer19521]

Great stuff 👍

[@TekCroach]

Very intuitive.

[@TekCroach]

❤❤❤ Excellent

[@kamleshchavan7451]

Simply great video , nicely explained , even a dumb beginners like is able to understand electronics Humble request please make another part of this video , and much more , please excuse my English knowledge , hope u understood what I want to say

[@MegawattKS]

Thank you. And your English is very good. There is another part of this video coming, but I'm slow these days. Still refining the slides for Part 2 before recording the narration. Maybe in a week or so. Thanks for the comment. It is very encouraging and helpful.

[@TekCroach]

When I think about the J1,J2 phone jack inputs, its working is very exciting. Those phone jacks employed in the circuit are TS with Normally Connected tip switch type. When no phone plugs are connected, the tips of the jacks are grounded. If you connect the plug to j1, it open its NC switch, and the signal goes through both R1 and R2. R1,R2 are in parallel now, so they become 11k ohms effectively. When the plug is connected to j2, the signal is potentially divided as you explained. There is a 6dB reduction in the input signal. That fact is mentioned near the jacks as well. So, it’s an input with an attenuation. When you plug to both jacks, those 2 input signals are fed independently without any attenuation (no voltage divider met).

[@MegawattKS]

They definitely created an interesting input circuit here (timestamp 1:22) ! I agree on all points, except the last one. I would argue that when two instruments are plugged in at the same time, each is attenuated by 1/2. This follows from using superposition in the analysis. Even though J1 plug disconnects the path to ground, superposition says, for the signal plugged into J2, that we "turn off the J1 signal" (meaning set its voltage source to zero) when finding the response to the J2 signal. So there's a zero-valued V source there now, which is a connection to ground :-) (The case for the signal applied through J1 is symmetric - so it is divided by 2 also).

[@TekCroach]

@@MegawattKS Yes. Summing amp using the non-inverting configuration is different than that of using the inverting configuration. Inputs are not isolated from one another. So, the input current flowing through one particular input is also going through or shared among the other inputs. As a result, all the input voltages are averaged. For example, if v1, v2, v3 are three inputs, the non-inverting input is presented with the (v1+v2+v3)/3. Anyway what I tried to point out is that this averaging effect is not obtained simply by voltage division.

[@TekCroach]

This simple average is obtained if the input impedances are all the same of course. :)

[@lattehour]

i really like thiis type of learning where you explain the blocks what devices are used and why and how they interact and all , thanks alot

[@MegawattKS]

Thanks for letting me know ! This will help as I work on part 2 of this video (and others to follow). Its always hard to decide what people will find most useful and to know how much prior knowledge to assume. Doing videos for KZbin is different from the classroom where that is known from the pre-requisites. Your comment helps me know that at least some of what I'm doing is working :-) Thank you.

[@lattehour]

@@MegawattKS i am intersted in RF design and amplifiers (all types) what i liked was the RF 101 if you can do another course on transmitters with various architectures analog and digital modulation based on the classroom pre-requisites because the 101 was magnificent there is nothing on that level on ytube actually i have just seen steven elingson channel but it`s not as practical as yours altough he has some very practical videos , presenting the fundamental structure and interactions in the system then going with the modern applied approach using various IC`s and commercial products is perfect it gives me a tangibile sense and a sense that designing one is actually posibille because when i learned the maths calc 3 dif eq and all that i was thinking i would need 3 brains to make something for real , in summary another series will do just fine at least for me

[@lattehour]

​@@MegawattKS btw dont skip on maths if it`s required to give a full understanding on the design , let`s say it requires heavy use of network analysis like say Design a circuit to realize the following transfer h= whatever function and using only resistors, capacitors, opams/transistors at least for me math is not problematic and for those intersted in radio design it shouldn`t be that in general should make your audience

[@MegawattKS]

@@lattehour The level of math to use in the videos has been limited to algebra to avoid problems for those that don't have experience with complex numbers or interpretation of complicated expressions. That said, there is plenty of math at the companion website pages. Here is one page with links to the entire senior-level university course. The "notes" are somewhat rough, but they're appropriate for those at a senior or graduate level :-) ecefiles.org/rf-circuits-course-notes/ (They're rough because these are just my personal-use notes for when I was lecturing in the class. But they're reasonably complete at least :-)

[@lattehour]

@@MegawattKS what books do you recommend for vhf uhf with a more practical approach both from the systems perspectives that are designed at this frequencies and device level

[@babeimichen3891]

Hi it's a great video. But why is the Ri of the gain stage equivalent circuit equals to 270K? Or is it the approximation of 270k+1.5k since they are both connected to the ground?

[@MegawattKS]

Hi. Looking at slide 19, the short answer is that R3 on the + input of the opamp is in parallel with the impedance seen looking into the + input (pin 3). But the impedance seen looking into that pin is close to infinity. So there's just R3 (270K) to ground loading the source. It is true that we sometimes talk about the opamp as having a "virtual short circuit" between it's inputs since when it's in a typical negative-feedback amp such as this, the voltages on the + and - pins are the same. But that's a "virtual" short circuit and is only a useful construct when solving for the voltages and gain in the circuit. There is no actual connection inside the opamp from pin 3 to pin 2 where the 1.5K is. So the 1.5K is not seen by the source. Bottom line, looking into pin 3 (the + input) we see an open circuit, since no current enters that pin. So the only thing loading the source is the 270K (R3) to ground - at low frequencies where we ignore the 100pF C2. Does that help?