No matter how many bits an analog-to-digital converter (ADC)
provides, the digital output can only approximate the original
signal. This approximation gives rise to quantization errors, or
quantization "noise." The error values fall between ±1/2 the
voltage represented by the ADC's least-significant bit (LSB) and
they have a fairly uniform distribution within this range.
Although ADCs with higher resolution reduce the quantization
errors, they always remain within ±1/2 LSB. You can think of the
quantization error as adding white noise to the digitized
information. By definition, white noise has a "flat" power
spectrum over the fsample/2 bandwidth. So how can a data-
acquisition system reduce quantization errors? Because these
errors depend only on an ADCs resolution, sampling at a much
higher rate than you would normally spreads the quantization
noise over a larger bandwidth. And thus the power density for a
fixed bandwidth decreases as fsample increases. In practice, a
higher sample rate decreases the quantiz