Design of Sub-10-μW Sub-0.1% THD Sinusoidal Current Generator IC for Bio-Impedance Sensing

This article presents a low-power, low-distortion, and compact mixed-signal sinusoidal current generator (CG) IC for bio-impedance (Bio-Z) sensing applications. By utilizing the digital
$\Delta \Sigma $
modulation to bridge the digitally synthesized sinewave data and the analog-domain voltage output, implementation of a low-distortion sinewave lookup table (LUT) is significantly simplified. Not only does this approach lead to the reduced number of routing wires, pin allocation, and output registers after logic synthesis but also, it allows the use of dynamic element matching (DEM) with a low-cost, before interfacing with the digital-to-analog converter (DAC). In addition, 0.5 V of low-supply voltage exploits a highly power-efficient operation for both synthesized digital logic and its subsequent analog circuit chain. To suppress the noise-floor increase that is induced from the reset signal of capacitor-DAC, a half-period reset scheme is introduced. The prototype chip is fabricated in 65-nm CMOS technology and it outputs
$2~\mu \text{A}_{\text {PP}}$
of amplitude with 20 kHz of sinusoidal frequency. It records the first sinusoidal CG IC that achieves sub-
$10~\mu \text{W}$
(
$6.2~\mu \text{W}$
) of power consumption and sub-0.1% (0.088%) of total harmonic distortion (THD) at the same time which has not been demonstrated ever in the prior arts. Furthermore, 0.059 mm
²
of its compact area facilitates the low-cost production of Bio-Z sensor systems.