Ultra-Low-Power Subthreshold Teager Energy Operator Circuits for Sleep Spindle and K -Complex Detection

The paper presents subthreshold circuits for the realization of an ultra-low-power subthreshold Teager Energy Operator (TEO) implementation. The TEO is designed using an exponential cell-based multiplier and a 2nd order Butterworth Lowpass Filter (LPFs) biased in the weak inversion region. The supply voltage used is 0.6 V for the multipliers and ±0.6 V for the LPFs in order to gain the optimum performance at their best configurations. The proposed TEO circuit is optimized through the removal of the subtraction block; where instead the subtraction is carried out through current addition at the differential output stage of the multiplier. Further., the LPF is programmable in its gain and bandwidth which allows tunability of TEO”s delay by the designer according to the intended application. The final TEO circuit was tested using LTSpice and 90nm CMOS model BSIM4v4.3. Simulation results show that the multiplier and LPF designed perform successfully to result in a TEO circuit of dynamic range ±40 mV. When programmed to have a cut-off frequency of 110Hz., the resulting TEO circuit had a 2 ms sample delay of 1 % variation. The proposed circuits achieve the lowest static power consumption reported thus far at 53.59 nW.