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LMC6001: Popcorn noise? (the dip on output)

Tao_2199
Genius 5810 points
Part Number: LMC6001


Hello,

 

Regarding to the LMC6001,my customer is asking some question.

They are using this device as I-V amp.

To evaluation their board, they check output with input capacitor (several pF:connecting to between input and GND.) as zero input condition.

The board is sealed by metal casing.

At that time, they confirmed the dip on output and it’s happened at a few times in hour.(Please refer below.)

 


 


 

 

They guess that the dip of output will be occurred by popcorn noise in LMC6001.

I’m asking to them about result of replaced other LMC6001.

What do you thing about that? Is there any other possible causes? (For example, power line(GND), leak current …..)

Could you please tell us any possible causes , comment and advice?

 

Regards,

Tao2199

  • 0
    TI__Guru* 93105 points

    Hello Tao2199,

    Popcorn noise is most commonly observed with some bipolar transistor operational amplifiers, not with devices such as the LMC6001 which use CMOS processing. The ultra-low input bias current is achieved by a novel bootstrap circuit that cancels nearly all leakage current associated with the input amplifier stage and input ESD protection cells. 

    The sudden pop that exhibits the slow, exponential decay, is very likely caused by Ionizing Radiation that randomly enters the input circuit of the ultra-low input current operational amplifier. Here are some of the characteristics of Ionizing Radiation that I gleaned from TI Applications Engineer, Paul Grohe: 

    • Naturally occurring background radiation - sources are terrestrial and extraterrestrial
    • Particles ionize the air in their wake as they zip by
    • Charge deposits on nearby traces, resulting in pops and jumps
    • Random in time and amplitude

    • Alpha particles stopped by paper, Beta stopped by aluminum, but Gamma is only stopped by very thick lead

    Effect - a sudden “pop” with an exponential decay in buffer and transimpedance amplifier circuits.

    Some possible solutions:

    • Use multiple integrations, not just one – ignore the “one that was not like the others”

    • Minimize amount of air between op amp input and any guard circuit 
    • Minimize surface area of input traces and lines
    • Don’t layout your circuit such that it creates an inadvertent Ion Chamber!

    Regards, Thomas

    Precision Amplifiers Applications Engineering