Hello,
I am using a MSO54 O-scope and a Siglent SDG6000X to test for an application where a small amplitude signal is buried in a large amplitude signal. The MSO54 has 8-bit, 12-bit, and up to 16-bit acquisition.
Considering I have the range of a channel on the O-scope set to +/- 5 Volts, then at 8-bits - the smallest digitized increment should be 10*2^-8 = 0.0390625 volts, about 40mV correct? - (I'm not considering ENOB here)
So I send two sinusoidal signals from the SDG6000X ARB in one channel of the MSO54 terminated at 50Ohm. Signal 1 is 5 Vpp and signal 2 is under 40mVpp. Because signal 2 is under the smallest digitized increment, I thought I shouldn't be able to see signal 2.
And yet when I used the FFT on the MSO54 I can still see signal 2 in the FFT, even down to 1mVpp. I'm confused as to why. Does the FFT on the MSO54 do something similar to a signal analyzer? I wouldn't think it did.
Perhaps it might have something to do with isolation of the channels on the SDG6000X? I tried many different configurations, but the small signal is still seen in the FFT. I'm not understanding why I see it there. Perhaps my knowledge of test equipment needs a bit of help.
If anyone knows why I might be seeing this, I'd love to know why.
Thanks.