Divider output noise floor is worse than rfout and noise floor values for different frequencies are given below.
Adc nose floor.
Adc noise performance trends.
Over the last three posts it was seen that the overall state of the art with respect to absolute noise power sampling jitter and relative total noise floor has not improved during the last 5 10 years it is therefore concluded that all significant aspects of adc noise performance appear to have reached saturation.
Adisimadc the fft output can be used like an analog spectrum analyzer to measure the amplitude of the.
In practice however the noise floor will always be higher than this due to electronic noise.
In this case the noise floor of the fft would be equal to the noise spectral density of the adc but the total noise power still has never changed.
When sampling very low power signals the adc works as expected.
This noise floor corresponds to overall adc performance and if plotted in the amplitude frequency spectrum it offers a quick comparison with the common noise floor.
For small analog input signals on the order of 35dbfs the thermal quantization noise power dominate the adc noise floor which is used to approximate the adc s effective noise figure nf.
Calculate the input noise of the converter which is the theoretical thermal noise floor limit ktb 174dbm at room temperature.
Rfout has the best noise floor as would be expected 160dbc hz pdivout 8 ghz 8 ghz div by 1 153 dbc hz due to noise floor of the mux.
But when sampling signals closer to the full scale the noise floor raises significantly together with the harmonics.
Effectively we have at most 8 bits worth of signal and snr close to 50 db instead of the 74 db specified in the datasheet.
The same noise power is only spread across finer frequency bin widths as seen in figure 1.
The ratio of the signal to noise level is defined as the signal to noise ratio snr.
Fft output for an ideal 12 bit adc input 2 111mhz f s 82msps average of 5 ffts m 8192 data generated from.
Pdivout 14 6 ghz 14 6 ghz div by 1 152 dbc hz.
For example the noise floor of a 16 bit measurement system can never be better than 96db and for a 24 bit system the lower limit is limited to 144 db.
For a large level analog input signal closer to full scale the adc noise floor level increases mainly due to clock jitter.
Measure the snr of the adc in nyquist bandwidth usually 0 5db or 1db below fullscale normalize the converter s noise power to a 1hz bandwidth by simply subtracting 10log fs 2 from the snr value.
Fft noise floor 110db rms quantization noise level data generated using adisimadc figure 2.
The noise floor of a measurement system is also limited by the resolution of the adc system.
