ad8369: Very low input voltage

Document created by analog-archivist Employee on Feb 23, 2016
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Can I use the AD8369 to amplify 1µV ?


The AD8369 should be able to amplify a 1uV signal very well. I think the key
spec here for such a small signal is the noise figure, which for the AD8369 is
7.0dB. Since this is 7.0dB relative to the thermal noise floor of -174dBm/Hz,
which is about 0.45nV/RtHz into 50 ohms, there should be an insignificant
amount of noise degradation due to the thermal noise of the AD8369. The only
thing to be careful of is the bandwidth of the signal being amplified. If the
bandwidth of the signal is very wide, then the thermal noise from the
amplifier, within the signal bandwidth, may cause the SNR of the signal to be

My only other thought on this is that in a typical RF VGAs, there is a small
amount of dc offset shift for each gain code. However, in this case, with the
outputs ac coupled, this dc shift will not be an issue. Of course there will be
a small glitch on the output every time the gain is changed, so the system will
need to be designed to take this settling time into account.