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opa129

DEEPAK SREEDHARAN
Prodigy 150 points


hai

     i have designed a circuit using opa129. the circuit works as an electrometer to detect ions. the input to the circuit is of the order 1pA. 

I want to know how to measure the overall noise of this circuit. what instruments are used to meaure the noise. how to make high frequency and low frequency noise measurements?

please help

  • 0
    TI__Guru 68541 points

    Sreedharan,

    The simplest way to measure the noise is to ground the inputs and use scope to determine output noise peak-to peak value.  However, typically this method requires circuit configuration in a high close-loop gain so that the magnitude of the measurement is significantly above scope’s noise floor.  A more sophisticated method requires use of spectrum analyzer which measures the noise over desired frequency range and displays the results in terms of noise spectrum density in units of nV/rt-Hz.  The noise spectrum density can then be converted to rms noise by integrated it across a given frequency range which then can also be expressed as peak-to-peak value by multiplying it by 6 (+/-3-sigma distribution or 99.7% confidence level).

    If you need complete information about the diffferent type of operational amplifiier noise, measurement techniques and ways to reduce it, please check the textbook under link below:

    http://www.amazon.com/Operational-Amplifier-Noise-Techniques-Analyzing/dp/0750685255/ref=sr_1_1?s=books&ie=UTF8&qid=1398891599&sr=1-1&keywords=noise+kay