Differential and Common Mode Signals
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- เผยแพร่เมื่อ 10 มิ.ย. 2018
- / edmundsj
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In this video, I explain what differential and common-mode signals are, and how students often get tripped up between these two and DC + small signals. I also discuss why we use these: fundamentally it is because it creates symmetry and allows for easy analysis of circuits that are otherwise extremely difficult.
Hope you found this video helpful, please post in the comments below anything I can do to improve future videos, or suggestions you have for future videos.
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You're awesome! I feel like I can just become an engineer by watching all your videos.
I was thinking about making a video about the CMRR
After watching this video, I decided to pick a different direction for when I make a video for the first time
This video was so professional, it made me change my mind!
Thankful that you are spending effort on these, its not always that someone who knows these topics and can view them in this particular way, is able and successful in making them into videos
Excellent. Very basic thing but much needed concept for circuit designers.
Very nice video on common mode and differential mode. If you’ve not already done so, I would enjoy a video on voltage mode sensors versus current mode sensors and the advantages/disadvantages of each. Thank you!
Instructive video. Thank you for posting !
Really enjoyed... thank you for sharing the video
Great explanation!
Thanks!
Differential-mode and common-mode signals are important to understand in the design of complex signal-conditioning circuits which use operational amplifiers in medical diagnostic, industrial control and military applications.
Operational amplifiers mainly excel in performance to provide a high common-mode rejection ratio and high gain. By using negative feedback, its overall gain, input impedance and bandwidth are determined by external components without these parameters being affected by the op-amp’s parameter variations due to external influences like temperature and so on.
Most amplifiers built using discrete transistors will not be able to match the performance characteristics of an operational amplifier like CMRR, low drift, high input impedance and stability of gain.
Engineers are so used to thinking and visualising currents as differential-mode in circuit analysis that they find it hard to switch their thinking to common-mode currents and their effects in say, amplifying circuits.
It will be instructive to understand and visualise Current at its most fundamental level in the presence of electric fields in ordinary conductors.
Electrostatics and circuits belong to one science not two. To learn the operation of circuits, Current and the conduction process, resistors and how discussing these topics makes it easier to understand the operation of capacitors, inductors, diodes and their operation in amplifier circuits and circuit theory watch these two videos
i. th-cam.com/video/TTtt28b1dYo/w-d-xo.html and
ii. th-cam.com/video/8BQM_xw2Rfo/w-d-xo.html
Most common-mode signals originate because of sources external to the system, and the energy in them circulates annoyingly until it is dissipated in resistive portions. They can be generated internally if proper cables are not used for coupling signals at the frequencies of the signals they carry.
Therefore the need arises for amplifiers to amplify only the useful differential signal and reject the common-mode component which does not belong to the signal conditioning system. Such an amplifier is used as the first stage of an operational amplifier which opens the door to allow a signal from a sensor ‘in’, so to say and so the importance given to this stage.
Topics related to these aspects are discussed in chapters 3 and 5 of textbook 4 (see last frame References in video #1) and a power point presentation with animations “Basic Action of a Differential Amplifer-Heart of the Opamp” which explains differential amplifier with a U-tube manometer analogy of differential- and common- mode signals is included in the CD alongwith this book.
Thanks for the context :)
This really helps thanks
Hi.I like your video very much. It's really great. I'll keep an eye on your channel. I am your fan and I will support you.
Thank you sir,giod explanation
Very good explanation! Which drawing program did you use for the presentation?
great video
Thank u Sir
So we’ll explained
God Bless
Good explanation....
How does this differ from the common mode voltage reported on the data sheets? My understanding is that input/output common mode voltage refers to the range of voltages that the input or output can support with respect to the supply voltage, lest the device stop working properly. What your describing seems to be completely different from this op amp characteristic
Are we biasing the circuit with vcm pls explain the difference in ac current and dc in this circuit
Excellent! Can you tell why V1 biased at 1V with amplitude of 0.4v in the plot but your equation is V1= 1V + 0.5V sin wt? Thank you.
Excellent catch, thanks! It should be 0.5V on the graph as well.
Good Job, Go to front of the class.
Sloppy
can you explain maximum and minimum Vcm? i can't wrap my head around that
Can you please tell any example of practical situation, or practical circuit using diff amp pair.
Hello Sir, what is a differential probe in Oscilloscopes?
Thanks a lot! nice.
Unfortunately I didn't understand your explanation about the application.
I use the Common Mode Rejection (CMR) in signal sensing, to reduce the error (higher SNR).
Common-mode rejection doesn't strictly-speaking improve your SNR. Any *differential* noise at the input is still amplified just like your signal. It is only if your noise is *common* to both inputs and the signal you are trying to record is differential that a high common-mode rejection can help alleviate noise. This is often the case with things like 60Hz noise. If both your "signal" and "noise" are common-mode signals, however, then CMRR also doesn't help.
So in make use of symmetry in circuit analysis, you mean that every symmetric signal (both signal are same) we can get rid off or don't have to account these anymore?
Interesting ! thanks for the explanation. So how is V1 and V2 measured on an actual circuit ? is it by probing +IN and VCC to get V1 and probing (-)IN and V(-) to get V2.
Hello Mr. Edmunds, could you add video about solving complex MOS circuit which may includes current mirrors, current source, cascode stages, differential pairs.. Such as solving width over length each MOS.
@JordanEdmunds
yes we really appreciate it...
I am a chemistry graduate student recently trying to build or optimizing an electrical machine and I am figuring out something related with noise issue. I am studying potential or current signaling stuff now.
Cool! Welcome to EE :)
what is negative feedback in bjt op amp ?
Hi, I looked up for the differential mode voltage, and it seems that the equation is: Vdm=V1-V2 (not divided by 2). Is this equation applying to different situation than showed in the video? Thank you.
Hey, I have the same question. My prof in my Semiconductor Class also did not devide the Vdm by two. Have you come upon an answer since you asked the question or are you also still wondering?
@@AndersAlsDieAnderen9 I think that differential mode is difference between two signals, so the equality should be V1-V2.
thanks
Hello sir i am using stm32 f401 black pill but ADC value of microcontroller fluctuate a lot even on dc input, how to improve it thanks
hello Jordan can you please make a video about the small signal analysis of the Differential mode please
All info seems to be very new to me.
Can you add video about CMRR and PSRR for diff amp with explaination?
Sir what book are you refered in this topic
So nice
awsome...
Polarity and phase are two different things!
Internal circuit working of 741 ic
But why use current source at bottom
Misuse of symbols, looks like its supposed to represent the output
this could use a demo
we would expect VCM to be 1V! lol i love it. Why would you "expect" VCM to be one volt. This is the problem with youtube. assumptions and more assumptions. You do not explain in the slightest why you would "expect" VCM to be 1 V
A better choice of words might be "suppose it's 1V". Integrated circuits almost always operate off voltages between 1V and ~20V, so 1V is an at-least-not-implausible guess. It also just makes it easy to talk about, it's the simplest number.
"in engineering we almost always drop the axis" I dont know what crazy ass engineering you practice but in REAL engineering we never drop the axis or the units. You are just off in lala land man
Ah, sure, clarification: When explaining things qualitatively we often drop the labels on the axis, as they aren't relevant to the general point being made (i.e. it doesn't matter if a sinewave is at 1kHz or 10GHz, the graph will look exactly the same when scaled and the conclusions are the same).
Poor explanation