Tool/software:
Hello,
We are working on a very sensitive amplifier to interface with a high impedance sensor.
I discovered that the datasheet and the simulation model doesn't include the current 1/f noise.
We need to make sure that the 1/f current noise doesn't cause issues in our application. Is there any test data on 1/f current noise?
Thanks!
Generally, the plot of current noise versus frequency is given only for devices where current noise is large in magnitude and has a flicker (1/f) region like in the case of bipolar input transistor op amps. The flicker noise is believed to be caused by charge carriers that are randomly trapped and released between the interfaces of two materials like p-n junction and since in the case of CMOS and JFET input transistor op amps, the low frequency current noise is from the shot noise of the input leakage current of the ESD structures, or any other semiconductor junction, for this reason it does not increase at low frequency - see below. Therefore, the low frequency current noise in CMOS and JFET input op amps (like OPA140) is flat and may be calculated using following equation: Inoise=sq-rt(2qIb).
The very low current noises do not impact overall noise performance unless the source impedance is very large. In the case of a 1fA/√Hz current noise, the source resistance needs to be greater than 16.5 GΩ for current noise to make a significant contribution to overall noise. For CMOS and JFET devices, it is common for current noise to increase at higher frequencies. This increase in current noise is called f-squared noise. However, circuits where the source impedance is high limits the bandwidth below the frequency where current noise begins to increase. This bandwidth limitation tends to counterbalance the impact of the f-squared noise so that the total RMS noise is not impacted significantly by the f-squared noise. For more information regarding this topic, please review the application note under following link:
