EMG - Instrumentation Amplifier

Discussion in 'The Projects Forum' started by ObezBalet, Jul 31, 2014.

  1. ObezBalet

    Thread Starter New Member

    Jul 31, 2014
    3
    0
    Hello everyone,

    I'm working on a EMG circuit and I have already ordered my components.

    I've ordered INA826AIDR for the pre-amp part of my design. It seems a good instrumentation amplifier

    http://www.ti.com/product/ina826

    But when I compare it with INA128 which is also highly recommended for medical signal acquisition, I noticed that INA826 has a very high input bias current like 65nA whereas INA128 has only 5nA.

    Do you think I should order a new instrumentation amplifier before it's too late or it doesn't matter that much and I worry myself needlessly ?

    By the way, INA128 costs nearly as much as the rest of the design with delivery costs.

    Or do you have another point to tell me that I should pay attention?
     
  2. DickCappels

    Moderator

    Aug 21, 2008
    2,647
    632
    If you cannot tell ahead of time, try the INA826AIDR and see if it meets your specifications.
     
  3. AlphaDesign888

    New Member

    Jul 27, 2014
    189
    10
    Try some Tsingtaeo Chinese beer. Buy a case of it. Money better spent.
     
  4. crutschow

    Expert

    Mar 14, 2008
    12,991
    3,227
    The input bias current causes input voltage offset due to this current flowing through impedance seen by the inputs. So whether it's a problem depends upon your input impedances and the input signal levels.
     
  5. ObezBalet

    Thread Starter New Member

    Jul 31, 2014
    3
    0
    Thank you guys for the answer,

    As I don't know the magnitude of the signal I'm trying to acquire yet, I'm not sure 65nA would be a problem or not. I expect something around 100uV and guess I would not be a problem.

    @AlphaDesign888
    Great tip :)
     
  6. crutschow

    Expert

    Mar 14, 2008
    12,991
    3,227
    What is the signal source impedance?
     
  7. ObezBalet

    Thread Starter New Member

    Jul 31, 2014
    3
    0
    As I use surface electrodes on human skin, say it is 50k ohm.
    From a medical instrumentation book, these are basic requirements for pre-amp part.


    By the way, I've just received my order: INA826AIDR. Such a fool I am, I didn't pay attention when ordering, it is SOIC size. I cannot use it on my breadbord. I just ordered INA128PA therefore.

    http://www.ti.com/product/INA128/description
     
    Last edited: Aug 1, 2014
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