1. Introducing Noise Floor The noise floor of a measurement
device is the measured noise level with its inputs grounded. You
will usually see it expressed either as a noise density function
with units of , or as a single number representing the total
noise, expressed in Vrms. To convert from a noise density
function to Vrms, you must integrate the noise density function
over your bandwidth of interest. In the case of wide band (flat)
noise, this integration breaks down into simple multiplication
where In general, you can derive the RMS noise of a device from
the noise density function, but you cannot get the shape of a
graph from a single number. The figure below illustrates a
typical measurement device's noise density curve at low
frequencies. This curve consists of the two sections in the
figure. The steeply sloping portion to the left of the point,
known as the corner is referred to as noise. To the right of the
corner, the noise level flattens out and is known as wide band
noise. Figure 1. Noise Spectral