I made the circuit in singlesupply mode and measured the output noise by shorting and grounding the inputs.calculated the noise refered to input.gain of my circuit is 40db.I got only 24nv/root hz instead of 14.why
I have some questions regarding your methods on how you are measuring the noise.
What is your test setup looks like? Are you using spectrum analyzer? What is your measurement bandwidth? Do you have post amplifier after the AD8220?
Also what is the voltage level at the reference pin when you do the measurements? Make sure that the inamp is operating in a linear region by sourcing the Ref pin preferably at mid supply. Please use clean dc source or better yet a battery for biasing the Ref pin so that it will not add noise on the measurements.
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