raja.cedt wrote on Sep 22nd, 2009, 2:37am:hi,
answer seems very clear because according to sampling theorem noise will be aliased with sampling frequency rate, and fortunately additional noise is uncorrelated so you will get white spectrum
Thanks,
Rajasekhar.
Hi Rajasekhar,
This is about correct. However the bandlimited noise is not totally white: a low pass filtered noise has some degree of correlation, as opposed to an infinite bandwidth noise, which is an idealization we call "white noise" (I´m assuming a flat spectrum).
The aliased noise will then have an about flat spectrum but that does not convert it into white noise, since it will also have a degree of correlation due to the low pass filtering. This correlation will be stronger if after sampling such noise is further filtered.
Concerning the noise aliasing ratio, there is a correction factor that should be considered. For a 1-pole like noise spectrum the equivalent noise BW is 1.57 time the pole frequency. Therefore for the 1MHz case you should consider 1.57MHZ instead (again, assuming 1 pole BW). Therefore the ratio is more like 7.85 times.
Regards
Tosei