Please someone correct me if I am wrong, but is the noise of the 5444 about five to ten times higher than the noise from the cheap Chinese scopes from the first page?
This makes little sense to me, since it has modes up to 16 bit resolution.
Well, these tests have been with just 8 bits resolution.
We need to be cautious to not compare apples with oranges. I have used the best of the “cheap Chinese scopes” and tried hard to resemble the test scenario for the PicoScope 5444 as close as possible, i.e. 1GSa/s, 1.4Mpts, 100µs/div and 2mV/div:
Siglent SDS1104X-E_100µs_2mV_100MHz_T50
Yes we get lower noise (63µV), but bandwidth is only 110MHz for this scope. The average noise density over the full bandwidth is about 6nV/sqrt(Hz) and I cannot see how this could be 5-10 times better than the ~9nV/sqrt(Hz) of the Pico 5444.
For the true high resolution models, like the 4262, we get much lower noise (4.33µV) because of the limited bandwidth, but also a lower noise density of <2nV/sqrt(Hz) at 2mV/div (zoomed to 100µV/div):
Pico 4262_Noise_10ms_2mV_5MHz_T50_Z100µV
The noise spectrum of the 4262 from 5Hz – 5MHz captured at a RBW of 14Hz looks like this:
Pico 4262_Noise_10ms_2mV_5MHz_T50_FFT
1/f noise is not very pronounced down to 50kHz and noise floor is below -156dBV (16nV) at 50kHz and even lower above. The strongest spurious signal measures -149.5dBV (32nV).
A closer look at the low frequency spectrum finally shows 1/f noise quite clearly:
Pico 4262_Noise_10ms_2mV_5MHz_T50_FFT_Z50kHz
We can see -156.5dBv (15nV) at 50kHz and -135.7dBV (164nV) at 100Hz. Given the FFT bin width of 4.768Hz and the flat-top window, we can expect a noise bandwidth of some 14Hz for the measurement.
This would result in 4nV/sqrt(Hz) at 50kHz and 44nV/ sqrt(Hz) at 100Hz, yet all these figures have to be taken with a grain of salt, because even at 5MHz, where we get -160dBV (10nV) the calculated noise density would still be ~2. 4nV/sqrt(Hz), which does not conform to the total noise density of <2nV/sqrt(Hz) as calculated earlier. I would tend to rather trust the FFT and believe that the RMS measurement in y-t mode might have given a slightly low reading.