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Re: INA333 EMG Instrumentation Amplifier

Jacek Urbanowicz
Prodigy 10 points
Other Parts Discussed in Thread: INA333

Hi!

I am confused about using INA333 in EMG application, because of huge input bias current, which is typical +-70pA and max 200pA.

I found in "Handbook of biomechanics and human movement science" on p. 217 that max input bias current should be max +-50pA or in some paper of Delsys Ib is in range of few fA.

 

What you think about that?

Sources would be appreciated.
  • Guru 21975 points

    Jacek,

    Low input bias current is desirable because it reacts with electrode contact resistance to create an input voltage that is not related to muscle activity. It is generally the variation in contact resistance with motion or movement that creates undesirable artifacts. The guideline you cite calling for an input bias current less than +/-50pA may or may not be appropriate in your application. It depends on the impedance of your electrodes and how much movement might be expected that would create undesirable artifacts. There is no absolute rule for suitable input bias currents, however, currents in the range of bipolar technology amplifiers (nanoamps and greater) are much more likely to give you problems.

    The INA333 has very low 1/f noise for its low quiescent current. The advantages of this low noise may outweigh the disadvantage of somewhat higher input bias current in your application. This is a trade-off that only you can evaluate.

    Regards, Bruce.