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Pop corn noise in INA2128U?

Maximiliano Guzman
Prodigy 220 points
Other Parts Discussed in Thread: INA2128, INA333, INA128, INA111

Hello, I am getting the signal that you can see in the attached pdf5545.INA2128U noise.pdf from a bio-amplifier  input stage made around one INA2128U. Bursts reach 120µVpp while the EEG machine used to see the signal has an input noise  below 1µVpp in the band 0.08-90Hz 3dB. Both input positive and negative are  bootstrapped through the INA2128 Rgain in/out pins, while the INA inputs are biased through a total 3.2Mohm. Input gain is 1X -no Rgain fitted-. It happens more or less the same with bias resistances tested up to 44Mohm (ground noise gets up, but not the 'bursts' or spikes shown). I have tested three different chips, soldered with hot air at a maximun temperature of 280Cº and all of them do the same. Any help?

  • 0
    TI__Genius 12325 points

    Maximiliano,

    All bipolar semiconductor processes are susceptible to popcorn noise with the amplitude and occurance rate varying greatly between wafer lots. Because popcorn noise is a step change in the beta of a transistor, popcorn issues are often exacerbated in bipolar applications with a high source impedance such as yours. My best recommendation would be to switch the design to employ a FET-type of instrumentation amplifier such as the INA111 as the occurance of popcorn noise issues in these designs are much much lower. You will also see the benefit of reduced noise as the input current noise of the INA128 family is most likely dominating the output noise through its interaction with the source impedance. Another possibility is to use a zero drift type of instrumentation amplifier such as the INA333 which is completely free of popcorn phenomenon due to the amplifier's chopping.

    For further information on popcorn noise, Art Kay has written a very good article on the topic that can be found here: http://www.en-genius.net/site/zones/audiovideoZONE/technical_notes/avt_022508#