ECG amplifier

[yiyi1987]

i think opamp TL074 connected to A is a buffering amp just to buffer the ref point A of the human body
AMP02 connected to B and C seems to be an instrumentation amp that hv a large gain to amplify the small ECG signal with respect to the ref point/signal of A
Then, the last stage is a second amplifier stage and filtering stage before get the ECG signal
the separate opamp should be used to stabilize the virtual ground

I am not sure my explanation is correct or not
Maybe there is someone else can help u out more
My advise is to get the opamp datasheet to understand all the pins description

 

[audioguru]

Your circuit does not make sense:
1) U5 is not an opamp. It is an intrumentation amp.
2) U2 does not do anything.
3) R5 does not do anything.
4) R6 does not do anything.
5) U1 is missing an input resistor.

U3 is a high gain amplifier and a very simple lowpass filter.

You should make the ECG circuit that is shown on the datasheets of instrumentation amps.

 

[Roff]

Post deleted - essentially a duplication of Audioguru's.

EDIT: U3 is also missing an input bias resistor. I suspect R5 is supposed to be connected to ground, from the junction of C1 and U3 + input.

 

[ke5frf]

One approach would be to not reply about subjects that are not in your area of expertise.
I try to live by that rule, and I still wind up with my foot in my mouth on occasion.

I agree with that comment to a certain degree, with a caveat. I absolutely LOVE discussing subjects outside of my expertise. In all honesty, my only areas of electronics expertise would be RF and antenna circuits and industrial control instrumentation, but fortunately these areas are broad enough to have familiarity with many aspects of electronics, enough to "speak intelligently" so to speak. By discussing them, I reinforce and often deepen my comprehension, and sometimes correct misconceptions.

So I think it is fully appropriate to comment, but be prepared to concede mistakes or else defend your position with supported facts, and most importantly clearly state your gaps of knowledge to avoid confusion. The last part is usually the most difficult to do.

 

[Roff]

I agree with that comment to a certain degree, with a caveat. I absolutely LOVE discussing subjects outside of my expertise. In all honesty, my only areas of electronics expertise would be RF and antenna circuits and industrial control instrumentation, but fortunately these areas are broad enough to have familiarity with many aspects of electronics, enough to "speak intelligently" so to speak. By discussing them, I reinforce and often deepen my comprehension, and sometimes correct misconceptions.

So I think it is fully appropriate to comment, but be prepared to concede mistakes or else defend your position with supported facts, and most importantly clearly state your gaps of knowledge to avoid confusion. The last part is usually the most difficult to do.

I agree with that. The problem with offering "expertise" when you are lacking it is that, gone uncontested, it may lead the OP (and others) down the garden path.
I probably should have replaced "reply" with "offer advice".

 

[manoj443]

I connected the circuit and it is working fine but i m not able to understand the working of leg driver circuit(U1 and U2 blocks)...How does it work??can somebody explain in detail watz goin in the circuit in the block U1 and U2....and why one terminal of R2 is connected to the input and the other to the output of the opamp as this thing does not happen with regular opamp

https://www.electro-tech-online.com/attachments/ecgopamp1-jpg.35113/

 

[Roff]

I connected the circuit and it is working fine but i m not able to understand the working of leg driver circuit(U1 and U2 blocks)...How does it work??can somebody explain in detail watz goin in the circuit in the block U1 and U2....and why one terminal of R2 is connected to the input and the other to the output of the opamp as this thing does not happen with regular opamp

Since we can't read your mind, you need to post the schematic you are referring to. The previous one had errors.

 

[manoj443]

I connected the circuit and it is working fine but i m not able to understand the working of leg driver circuit(U1 and U2 blocks)...How does it work??can somebody explain in detail watz goin in the circuit in the block U1 and U2....and why one terminal of R2 is connected to the input and the other to the output of the opamp as this thing does not happen with regular opamp

 

[Roff]

I connected the circuit and it is working fine but i m not able to understand the working of leg driver circuit(U1 and U2 blocks)...How does it work??can somebody explain in detail watz goin in the circuit in the block U1 and U2....and why one terminal of R2 is connected to the input and the other to the output of the opamp as this thing does not happen with regular opamp

Your link doesn't work.

 

[manoj443]

It was working when i posted it....i m posting it again....I connected the circuit and it is working fine but i m not able to understand the working of leg driver circuit(U1 and U2 blocks)...How does it work??can somebody explain in detail watz goin in the circuit in the block U1 and U2....and why one terminal of R2 is connected to the input and the other to the output of the opamp as this thing does not happen with regular opamp

https://www.electro-tech-online.com/attachments/ecgopamp1-jpg.35113/

 

[audioguru]

Your schematic is missing important parts and has some useless extra parts and will not work.

The right leg driver is like a ground but it has the common-mode signals out-of phase with the common-mode signals picked up from the patient's arms.

The common-mode signals are DC and low frequency AC including mains hum pickup. Since they are out of phase then they cancel the common mode signals that are picked up. if the common mode signals are not cancelled then the instrumentation amplifier might be saturated and not work.

 

[manoj443]

Hii...thanks for all your suggestions.....what is the purpose C1 and R5 in the circuit??

 

[audioguru]

C1 couples the audio and blocks the DC.
R5 does nothing like many other parts in that defective circuit.

 

[manoj443]

I dont see any baseline wandering in my output. What part of my circuit removes baseline wandering??

 

[audioguru]

Your circuit is incomplete and has many useless parts.
You should make the circuit shown in the datasheet of an instrumentation amplifier.

 

[baratang]

im also designing an ecg amplifier and the one with the ad620 has to much noise...even with the filters the wave is not clear to be descriped ... can someone send me a working ecg circuit please

 

[audioguru]

The ECG circuit in the datasheet for the AD620 works well. It uses feedback (common-mode DC shifts and hum) out-of-phase to the patient's right leg so they get cancelled. Maybe you are using unshielded cables that are acting like antennas and are picking up noise.

 

[AndreyMiller]

corner frequency

When the capacitive reactance of the 1.5nF capacitor equals 1M at 106Hz then the gain of the opamp is reduced -3dB.

Hi Audioguru!

please do not offend if question is to simple but I just cannot understand

Would not it be if the "1.5nF capacitor equals 1M resistance" (1M=1/(2pi*f*C)) it would decrease common resistance of C and R parallel connection by 2 ?

But how I understand -3db is about 0.707 or 1.41 times less.

I have same circuit (a bit newer version of it from TI home page) and there is written F0=100Hz near A3 OP. So it seems to be right value of frequency. Still I cannot understand from where such number is taken

 

[masoud vahaby]

Hello
help the circuit for ad620a , shematic for input dif

 

[masoud vahaby]

Can"t speack english