I am working on a EMG sensor. I am using INA 126 in first stage to amplify the EMG signals with gain 5. Then an amplifier( inverting ) using IC LM358 with gain 1000 is used as second stage. I am using a 5 volts dual supply for the circuit by stepping down two 9V batteries.I m using SMD components but still getting noise of around 100mV RMS. plz help me to reduce noise.
I did a quick calculation and I estimate that you should get about 53mV p-p at the output of your amplifier. (see attachment). So you are reading higher noise that I estimate but the difference is not huge. The difference could be accounted for by noise from your sensor which was not included in my analysis. Based on your measurements I think the circuit is working as expected.
There are two main ways that you can reduce the noise. 1) You can further limit the bandwidth. 2) You can use a different instrumentation amplifier that has lower noise. Also you may want to repartition the gain so that the instrumentation amplifier has higher gain. More gain on the input stage takes advantage of the high end input stage.
I have a book and article series on this subject. See links below.
Book: Operational Amplifier Noise
Article Series: Intrinsic Noise
Art Kay Senior Applications Engineer High Performance Linear
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