In recent years, integrated circuits (ICs) for biosignal acquisitions have gained popularity in both academia and the industry due to the rising demands in medical applications. Biosignals such as brain signals monitored during electroencephalography (EEG) tests can have very low signal levels down to a few microvolts. Therefore, a biosignal measurement system usually requires multiple stages of amplification and filtering to extract the signal of interest from noise and interference. The need to improve the quality of the signal after processing in the analog front-end leads to circuit design challenges that are addressed in this thesis.
The focus of this research is on the design of a low-pass notch filter (LPNF) and a variable gain amplifier (VGA), which are both integrated into a Self-Calibrated Analog Front-End for Long Acquisitions of Biosignals (SCAFELAB) system. The circuits were designed, simulated and fabricated in 0.13-µm complementary metal-oxide semiconductor (CMOS) technology. Post-layout simulations of the LPNF show a passband attenuation of 2.08 dB, a bandwidth of 47.2 Hz, and a 60.9 dB notch depth at 60 Hz to reject powerline interference. The filter’s total input-referred noise integrated from 0.1 Hz to 47.2 Hz is 138.6 μV. Its simulated third-order harmonic distortion (HD3) with the highest anticipated input amplitude is 61.1 dB. The post-layout simulations of the VGA demonstrate a gain range of 32.2-51.3 dB with seven steps. The VGA’s total input-referred noise integrated from 0.1 Hz to 47.2 Hz is 30.8 μV. Its HD3 is 86.7 dB with the lowest gain setting and a 1 Vpk-pk output swing. Measurements of the complete analog front-end chip (signal path blocks: instrumentation amplifier, LPNF and VGA) reveal a differential gain range of 66-93 dB with a total power consumption of 41.26 µW. The front-end bandwidth covers 0.5-40 Hz for EEG target applications, and its integrated input-referred noise over the bandwidth is 3.75 µVrms. The measured third-order harmonic distortion component is at least 57 dB below the fundamental signal level. A common-mode rejection ratio (CMRR) of 77.6 dB and a power supply rejection ratio (PSRR) of 74 dB were measured at 10 Hz.
Advisor: Professor Marvin Onabajo
Professor Marvin Onabajo
Professor Nian Sun
Professor Mark Niedre