I have designed an EMG amplifier circuit using the instrumentation amplifier INA128 and opamps TL072.
Here is my circuit

I have tried it on DSO but didn't found any EMG wave there was only noise in the DSO. If there is any error then please suggest me changes.Please help me.

 

I see several problems:

1. I believe your precision rectifier circuit is incorrect; the cathode of D2 should be connected to the anode of D1, not the cathode of D1. As it is now, the output of U5 will saturate negative when the signal coming from U4 is positive; this is not desirable.

2. Your circuit has a lot of end-to end voltage gain, making the TL072 a poor choice for an op amp because of its very large worst-case input offset voltage (± 10 mV). This offset voltage gets amplified along with your signal and could result in as much as several volts of offset on the output of your X220 gain stage. This offset very likely will render your precision rectifier circuit inoperative.

3. You've configured the INA128 to have a differential voltage gain of only 6, which is why you've had to put so much voltage gain downstream in the signal chain. You'd be better off putting as much gain as possible up front in the INA128, and reducing the gain of subsequent stages correspondingly. This should improve the noise performance.

4. Remember that you need a reference electrode connection to your test subject to keep your inputs from floating relative to circuit ground and to minimize common-mode interference. (This isn't necessary for simulation, of course, but in actual use you will need one.)

This paper, Surface EMG Signal Amplification and Filtering, gives a lot of good information on EMG amplifier design.

Hope this helps a bit...

 

I see several problems:

1. I believe your precision rectifier circuit is incorrect; the cathode of D2 should be connected to the anode of D1, not the cathode of D1. As it is now, the output of U5 will saturate negative when the signal coming from U4 is positive; this is not desirable.

2. Your circuit has a lot of end-to end voltage gain, making the TL072 a poor choice for an op amp because of its very large worst-case input offset voltage (± 10 mV). This offset voltage gets amplified along with your signal and could result in as much as several volts of offset on the output of your X220 gain stage. This offset very likely will render your precision rectifier circuit inoperative.

3. You've configured the INA128 to have a differential voltage gain of only 6, which is why you've had to put so much voltage gain downstream in the signal chain. You'd be better off putting as much gain as possible up front in the INA128, and reducing the gain of subsequent stages correspondingly. This should improve the noise performance.

4. Remember that you need a reference electrode connection to your test subject to keep your inputs from floating relative to circuit ground. (This isn't necessary for simulation, of course, but in actual use you will need one.)

This paper, Surface EMG Signal Amplification and Filtering, gives a lot of good information on EMG amplifier design.

Hope this helps a bit...

Thank you for your answer.
Problem 1 I will check and manage.
Problem 2 Will it work if i use TL072 but with a gain of around 100?
Problem 3 I will increase the gain of instrumentation amplifier by 10.
Problem 4 is the main issue. I will be connecting the output from the precision rectifier to the arduino. Hence i will use arduino ground as my ground. So do i still need this reference electrode? If yes than will it work if i will directly connect it to ground?
Please reply soon.

 

You will need some way of clipping/limiting the final stage output so that it doesn't go beyond the Arduino supply rail voltages.

 

Problem 2 Will it work if i use TL072 but with a gain of around 100?

Maybe. Maybe not. I don't know. My own choice would be to discard the TL072 and use a much better op amp with lower input offset voltage.

Problem 3 I will increase the gain of instrumentation amplifier by 10.

My choice would be to increase the gain of the INA to over 100.

Problem 4 is the main issue. I will be connecting the output from the precision rectifier to the arduino. Hence i will use arduino ground as my ground. So do i still need this reference electrode? If yes than will it work if i will directly connect it to ground?

Read the paper I linked to; it shows how to make a proper reference electrode connection. Remember, the reference electrode is needed to establish your subject's potential relative to circuit ground; it has nothing to do with the connection between your circuit and the Arduino.

 

This paper, Surface EMG Signal Amplification and Filtering, gives a lot of good information on EMG amplifier design.

That paper is very well written -- how refreshing.
Thanks for the link.

 

Maybe. Maybe not. I don't know. My own choice would be to discard the TL072 and use a much better op amp with lower input offset voltage.


My choice would be to increase the gain of the INA to over 100.


Read the paper I linked to; it shows how to make a proper reference electrode connection. Remember, the reference electrode is needed to establish your subject's potential relative to circuit ground; it has nothing to do with the connection between your circuit and the Arduino.

Is it will be good to use opa2131 in place of tl072. It has an offset voltage of 750 micro volts

 

That would probably work well enough.

 

can someone suggest me the best op amp for emg signal extraction with less noise??

 

can someone suggest me the best op amp for emg signal extraction with less noise??

There is no "best" op amp for that job, since many factors are involved (noise voltage, noise current, input offset voltage, input bias current, etc., etc., etc.) in determining how well a particular part will work in any given application.

All of the major op amp manufacturers have some sort of "selector guide" on their web site which allows you to view their various op amp products and sort them by selected characteristics; I suggest you make use of those to pick an op amp for your application.

In my own work, when I've needed a part for precision applications I've usually turned to three op amps: the OP177, the LT1007 and the MAX44246. It's possible that one or all of these would work well for you; but there are many others available.

EDIT: you might find this thread helpful.