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I'm looking to understand how to read the noise spec of the INA103 (and others). It's expressed as e.g. 1 nV/√Hz. Does this signify that at 1MHz, I would expect as much as 1uV (1nV * √1000000) of noise? If so, I'd appreciate recommendations of alternative differential amplifiers I could use with lower noise in the band 0.2-5MHz?
INA103 input refered noise, Vn_RTI, is a function of gain and expressed as:
The input noise spectral density of 1nV/rt-Hz is extremely low and the only way to further lower the total integrated noise is to lower the effective bandwidth by adding a low-pass filter at the output. Keep in mind that placing the INA103 in gain of 100 will require RG=60ohm, which itself generates 1nV/rt-Hz noise. Thus, even if the noise of INA103 itself is zero (Vn_input=0 and Vn_output=0), you cannot get lower than the resistor, RG, thermal noise.
Having said that, considering that the input voltage offset of INA103 is as much as (250+ 5000/G) [uV], why do you consider 1uV noise to be a problem?
Marek,
We of course expect to need to do some averaging and filtering. However, measuring this signal will enable a new class of medical imaging technologies. I'm at this point open to any suggestions as to how to capture the signal that has the lowest possible noise levels before any averaging, etc. If the quiescent current needs to be high to achieve this, that should not be a major issue. If you'd be willing to have an offline conversation about this, I would be most grateful.
Thanks,
Pierre