Applicability of phase-locked loop to tracking the rhythmic activity in EEGS

Conventional methods of spectral analysis are based on mathematical or numerical algorithms applied to digitized signals. This paper discusses the applicability of the phase-locked loop (PLL) approach for tracking electroencephalogram (EEG) rhythmic bands (delta, theta, alpha, or beta). The use of the PLL for frequency tracking should also aid the development of online EEG interpretation and screening based on frequency characteristics when the PLL is realized by hardware. As a result, two factors in the applicability of the PLL are: (1) translation of the EEG spectrum to a higher-frequency band by a single-sideband (SSB) modulation scheme, and (2) the narrowband spectral feature of the EEG—a small difference between two major frequencies. The PLL output is further quantized according to the EEG rhythmic bands. Our analysis shows that the integrated system is capable of tracking the EEG rhythmic patterns.