A Low-Distortion Current-Mode Signal Generator for Wide-Range Bioimpedance Spectroscopy

Abstract

This paper presents a low-distortion current-mode sinusoidal signal generator for bioimpedance spectroscopy measurements. The proposed full current-mode operation enables linearity enhancement and potential savings in silicon area and power consumption. Programmability in the low-pass filter and current driver enables impedance measurements from 0.2 Ω to 10 kΩ over a wide frequency range from 1 kHz to 1 MHz. The current generator, designed in a 0.18 µm CMOS process, consumes between 736 µW at the lowest frequency and gain, and 1.70 mW at the highest frequency and gain, and occupies 1.76 mm 2 silicon area. Post-layout simulation results show a spuriousfree dynamic range larger than 40 dBc over the entire frequency range, which enables bioimpedance measurements with errors below 1%, as it is required for wearable devices evaluating neuromuscular disorders.

A Bioimpedance Spectroscopy Interface for EIM Based on IF-Sampling and Pseudo 2-Path SC Bandpass ΔΣ ADC

“…State-of-the-art SSGs generate sinusoidal waveforms via direct digital synthesis (DDS), as it provides a good compromise between power consumption, linearity, and flexibility [18]. In DDS, a sinusoidal signal at f SG , is generated by oversampling in digital domain at f s , and converting the signal via a digital-to-analog converter (DAC), with N DAC bits [28]. The choice of oversampling ratio (OSR SG =f s /f SG ) and N DAC determines the achievable signal-tonoise ratio (SNR SG = 1.76 + 6.02N DAC + 10 log (OSR SG )) and spurious-free dynamic range (SFDR SG ) of the SSG, which is given by [29]:…”

“…Additionally, the limited SNR SG and non-linearities in the SSG's IDAC will cause odd harmonics at frequencies below 63f SG , which will also be down-converted. Nonetheless, the amplitude of these harmonics can be estimated to be 20 dB lower (∼ 55.94 dBc) than the one at 63f SG due to the chosen SNR SG and applied DEM [28], [29]. Therefore, they will introduce errors below 0.017 %, which should not significantly degrade the system accuracy either.…”