The acceptable level of adc noise power in any particular application is calculated for the case when both a.
Adc nose floor.
Adisimadc the fft output can be used like an analog spectrum analyzer to measure the amplitude of the.
If the effective noise floor is noticeably above the common noise floor the overall adc performance is considerably limited also by spurious and or harmonic components.
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.
Fft output for an ideal 12 bit adc input 2 111mhz f s 82msps average of 5 ffts m 8192 data generated from.
The same noise power is only spread across finer frequency bin widths as seen in figure 1.
The noise floor of a measurement system is also limited by the resolution of the adc system.
For a large level analog input signal closer to full scale the adc noise floor level increases mainly due to clock jitter.
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.
When sampling very low power signals the adc works as expected.
Calculate the input noise of the converter which is the theoretical thermal noise floor limit ktb 174dbm at room temperature.
Adc noise performance trends.
Pdivout 14 6 ghz 14 6 ghz div by 1 152 dbc hz.
The ratio of the signal to noise level is defined as the signal to noise ratio snr.
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.
Divider output noise floor is worse than rfout and noise floor values for different frequencies are given below.
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.
Fft noise floor 110db rms quantization noise level data generated using adisimadc figure 2.
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.
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.
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.
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.
