EKG ECG Amplifier with Right Leg Drive Explained
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- Опубликовано: 6 апр 2024
- An Electrocardiogram or ECG Amplifier with Right Leg Drive is explained in this video which is the 209th example in my Analog Circuit Playlist. The first stage of a differential instrumentation amplifier is designed to provide a programmable gain using a number of 1% precision resistors and a 10k Ohm potentiometer that can adjust the differential gain between 6x to 201x for the desired ECG or EKG signal. The third op amp is designed to operate as a low pass inverting amplifier driving the right leg of the patient with 3dc cut off frequency of bandwidth of 125 Hz to amplify the unwanted common mode interference (for example 60 Hz main power interference). The feedback amplifier has a voltage gain of -20x in this design resulting in overall gain of 1/21 or basically an attenuation of 21x for the unwanted common interference.
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Very cool, I will definitely build this circuit!
Glad that this video is interesting. And nice to hear that you are planning to experiment with his design. For more sensor videos pls see the Sensors Amplifiers playlist ruclips.net/p/PLrwXF7N522y7Ut9bm8TXAOhIWqL__FGlj
I like your videos which explain how its work.
Thank you, Glad that you like my videos. For more sensor videos please see the Sensors Amplifiers playlist ruclips.net/p/PLrwXF7N522y7Ut9bm8TXAOhIWqL__FGlj
Hope it is interesting as well 🙋♂️
Common mode noise is captured and returned (re-injected) into the body but by a phase shift of 180° sort of speak to cancel out. Is it that? And then I guess the times 20 gain is to overcome various losses so it is approximately the same amplitude as the 0° original noise signal when it is in the body.
Yes, well-said. Common mode noise like 60Hz main power sinusoidal interference picked up by the body of patients can be further attenuated by as much additional 30 dB (basically improving CMRR or Common Mode Rejection Ratio) via the negative feedback applied to the leg in this example. The voltage gain of 20x in the feedback path is to attenuate the common mode interference or noise by 1/(1+20) in this system from input to the output.
I always wondered how they do it. Seeing the 3rd wire is what tickled me.
Glad that this video is helpful. More sensors related video are posted in ruclips.net/p/PLrwXF7N522y7Ut9bm8TXAOhIWqL__FGlj Playlist.
that is interesting, thanks 💯🎉
You are welcome, Glad that you like this video. For more sensor videos please see the Sensors Amplifiers playlist ruclips.net/p/PLrwXF7N522y7Ut9bm8TXAOhIWqL__FGlj
Thank you 🙋♂️
Great!
Thank you! Glad that this video is interesting. For more sensor videos pls see the Sensors Amplifiers playlist ruclips.net/p/PLrwXF7N522y7Ut9bm8TXAOhIWqL__FGlj
I remember my brother hooking up the leads to my wrists and ankle when he was playing with his first EKG device fresh from med school. Is it too different to the one used to measure brain waves?
Thanks for another great video!
You're welcome. Glad that you liked this ECG video and it brings back good memories. The one used to measure brain waves is the Electroencephalogram (EEG) used to measure the electrical activity of the brain, via electrodes applied to patient's scalp. More sensor videos are posted in ruclips.net/p/PLrwXF7N522y7Ut9bm8TXAOhIWqL__FGlj which is the the new Sensors Amplifiers playlist.
Is it true that this circuit is used as the central part of industrial ECG machines?
Thanks for the video! It's very informative
My pleasure, you're welcome! Glad that this video is useful. Yes, while signal conditioning and interfacing analog circuitry in commercial ECG devices are more complex with more components depending on the number of supported channels, at the core they have a similar instrumentation-like differential amplifier with negative feedback scheme in place to further improve CMRR from nominal -60 dB to -90 or -100 dB. The ECG signal is then digitized via A/D for further digital post processing and filtering in computer or dedicated signal processor. More sensor videos are posted in the Sensors Amplifiers playlist ruclips.net/p/PLrwXF7N522y7Ut9bm8TXAOhIWqL__FGlj
I see, thank you :)
Really good video sir, but I still have a hard time understanding why VO1=-VO2 , It implies that the potentials are always symmetrical, I've been looking for an explanation everywhere without success 😔
Thanks for watching and your good question. Starting my explanation at 13:01 in this video, I should've clearly mentioned that the virtual short of third op amp (feedback op amp) will enforce that its negative terminal (mid point between Vo1 and Vo2) have the same zero voltage as its grounded positive terminal as seen in the video. This results in mid point between Vo1 and Vo2 to be grounded and therefore in differential mode will result in Vo1 = -Vo2 since current flows from one Voltage to the other voltage through the resistors there are in between. I hope this further explanation answers your question. Here is another instrumentation amplifier video ruclips.net/video/9-MLqyewXW8/видео.html which explains a programmable Switched-Gain Instrumentation Amplifier.
@@STEMprof Thanks for your reply, I thought so, and also found that if we have the differential inputs v1 and v2 we would have vcm = (v1+v2)/2 and vd= v2 - v1, and by rearranging the 2 equations we have v1 = vcm - vd/2 and v2 = vcm + vd/2 which also leads us to the same conclusion.
You're welcome! Glad that the explanation was helpful.
An Electrocardiogram or ECG Amplifier with Right Leg Drive is explained in this video. For more sensor amplifiers see ruclips.net/p/PLrwXF7N522y7Ut9bm8TXAOhIWqL__FGlj and the following videos
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For more analog circuits and signal processing examples see: ruclips.net/p/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt
I hope these sensors and thermometer circuits videos are interesting. 🙂
What happens if driving left leg?)
@@user-ui6xt4fd1f That's a good question. Generally speaking it is possible but with extra care because relative placement of ECG electrodes on arms and legs do matter to achieve proper measurement. So, it is important to follow specific procedure to make adjustments to the placement of the rest of electrodes if left leg drive is desired. For more sensor videos pls see the Sensors Amplifiers playlist ruclips.net/p/PLrwXF7N522y7Ut9bm8TXAOhIWqL__FGlj