[FAQ] ADC Noise: What is ENBW and why is it important?

In general signal-processing terms, a filter’s effective noise bandwidth (ENBW) is the cutoff frequency, f_C, of an ideal brick-wall filter whose noise power is approximately equivalent to the noise power of the original filter, H(f).

As an analogy, consider your home on a cold night. To reduce energy costs and save money, you need to keep your doors and windows closed as much as possible in order to limit the amount of cold air coming in. In this case, your home is the system, your doors and windows are the filter, the cold air is noise, and the ENBW is a measurement of how open (or closed) your doors and windows are. The larger the gap (ENBW), the more cold air (noise) gets into your home (system) and vice versa, as shown in Figure 3.

Figure 3: Wide ENBW leads to more noise (left); narrow ENBW leads to less noise (right)

What system components contribute to ENBW? Read part 4 to learn more.