CMOS Ultralow Power Brain Signal Acquisition Front-Ends: Design and Human Testing

Two brain signal acquisition (BSA) front-ends incorporating two CMOS ultralow power, low-noise amplifier arrays and serializers operating in mosfet weak inversion region are presented. To boost the amplifier's gain for a given current budget, cross-coupled-pair active load topology is used in the first stages of these two amplifiers. These two BSA front-ends are fabricated in 130 and 180 nm CMOS processes, occupying 5.45 mm $^{2}$ and 0.352 mm $^{2}$ of die areas, respectively (excluding pad rings). The CMOS 130-nm amplifier array is comprised of 64 elements, where each amplifier element consumes 0.216 $\mu$ W from 0.4 V supply, has input-referred noise voltage (IRNoise) of 2.19 $\mu$ V $_{\text{RMS}}$ corresponding to a power efficiency factor (PEF) of 11.7, and occupies 0.044 mm $^{2}$ of die area. The CMOS 180 nm amplifier array employs 4 elements, where each element consumes 0.69 $\mu$ W from 0.6 V supply with IRNoise of 2.3 $\mu$ V $_{\text{RMS}}$ (corresponding to a PEF of 31.3) and 0.051 mm $^{2}$ of die area. Noninvasive electroencephalographic and invasive electrocorticographic signals were recorded real time directly on able-bodied human subjects, showing feasibility of using these analog front-ends for future fully implantable BSA and brain– computer interface systems.