... And with full scale amplitude...I apply sin signal at the frequency of interest
It's the only way to get the input referred noise.what is the purpose of measuring the output referred noise
If 100mV is about -80dB ....I made the test as you suggested with small input signal (100mVp-p),
"Analog to Digital" in the menue is not what I meant. That option is to convert for example analog waveforms into their digital (0 and 1) representation. For example, if you have a bus with pulses between 0V and 2V, this option can convert it to digital representation in either binary, hex, decimal formats.
When I asked you about the ADC, I really meant analog to digital converter, and you are not using it in your simulations. So, basically you don't have thermal, flicker or quantization noise in your simulation, so you can't really talk about noise there. The noise floor you see in the spectrum comes from the accuracy/rounding errors of the simulator. Unfortunately, it looks like the harmonic distortion is quite real. In your previous plots the 3rd harmonic is at about 40db below fundamental and it is still at 40db below when you used my setup. The only difference is that now, with my setup you force the simulator to be more accurate and its "noise" floor is very much lower compared to your earlier simulations and that's why you can see more harmonics popping up in your spectrum. Before they were below the accuracy noise floor.
.
Hi,
If 100mV is about -80dB ....
Then the FS signal amplitude is about 1000V. ;-)
It rather looks like you reduced the amplitude by 25dB only..
*****
The new diagram shows that the whole problem is not related to noise, but it's a problem of the measurement setup.
Or better say: the frequencies...
Try to rectify the frequencies...
Or use a windowing function as workaround.
Klaus
The effective bits are apparently including THD which isn't noise. The noise floor should be reevaluated with appropriate windowing, it doesn't look trustworthy.
Not sure if the amplifier non-linearity is that high, I would like to see THD versus signal level or IP2 and IP3 figures.
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