Spurious Free Dynamic Range

Spurious free dynamic range (SFDR) is the usable dynamic range before spurious noise interferes with or distorts the fundamental signal. The amplitude of the fundamental signal is usually -1 dBFS. SFDR is the measure of the ratio in amplitude between the fundamental signal and the largest harmonically or non-harmonically related spur from DC to the full Nyquist bandwidth (half the sampling rate). A spur is any frequency bin on a spectrum analyzer, or from a Fourier transform, of the analog signal. SFDR is expressed in dBc.

The following figure illustrates how SFDR is measured.