On-Chip Sinusoidal Signal Generators for Electrical Impedance Spectroscopy: Methodological Review

Abstract

This paper reviews architectures and circuit implementations of on-chip sinusoidal signal generators (SSGs) for electrical impedance spectroscopy (EIS) applications. In recent years, there have been increasing interests in on-chip EIS systems, which measure a target material's impedance spectrum over a frequency range. The on-chip implementation allows EIS systems to have low power and small form factor, enabling various biomedical applications. One of the key building blocks of on-chip EIS systems is on-chip SSG, which determines the frequency range and the analysis precision of the whole EIS system. On-chip SSGs are generally required to have high linearity, wide frequency range, and high power and area efficiency. They are typically composed of three stages in general: waveform generation, linearity enhancement, and current injection. First, a sinusoidal waveform should be generated in SSGs. The generated waveform's frequency should be accurately adjustable over a wide range. The firstly generated waveform may not be perfectly linear, including unwanted harmonics. In the following linearity-enhancement step, these harmonics are attenuated by using filters typically. As the linearity of the waveform is improved, the precision of the EIS system gets ensured. Lastly, the filtered voltage waveform is now converted to a current by a current driver. Then, the current sinusoidal signal is injected into the target impedance. This review discusses the principles, advantages, and disadvantages of various techniques applied to each step in state-of-the-art on-chip SSGs. In addition, state-of-the-art designs are compared and summarized.

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

“…In practice, however, the injected sinusoidal current might have considerable harmonic content, which will fold into the bio-Z bandwidth during the demodulation process, degrading the accuracy. 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].…”

“…Consequently, bio-Z spectroscopy systems require readouts with low noise (Z n,rms < 10 mΩ rms ) and large signal-to-noise ratio (SNR > 100 dB) to detect the baseline bio-Z signal and its fluctuations over the entire frequency range. Moreover, to diagnose neuromuscular disorders, bio-Z errors below 1% are typically required [18]. Furthermore, it has been demonstrated that muscle contractions, which happen in the 0.1 Hz to 2-10 Hz bandwidth [19], [20], can be detected in two ways: i) single-frequency multi-channel EIM, by measuring relative bio-Z magnitude and phase changes of all channels [10], [21], ii) multi-frequency single-channel EIM, by measuring phase shifts in the bio-Z spectrum [11].…”

Development of a Tetherless Bioimpedance Device That Uses Morphologic Changes to Predict Blood Flow Restrictions Mimicking Peripheral Artery Disease Progression

“…Existing bioimpedance pulse devices allow measurements from various locations, but the signal processing (either analog or digital) typically needs to be customized for each specific vessel investigated due to the different morphological features of the pulse [ 25 , 26 , 27 , 28 , 29 , 30 ]. The result of this is that, even though it is not difficult to extract signals from various arteries using existing commercial devices, it is challenging to quantitatively compare waveforms from different areas due to the need to adjust settings for each specific artery [ 31 ].…”

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

“…Consequently, bioimpedance spectroscopy systems require programmable sinusoidal signal generators (SSGs) which can cover a wide range of frequencies and output currents. Moreover, the aforementioned applications also impose accurate impedance measurements (typically, errors bellow 1%), which can only be achieved by minimizing the SSG's distortions [10].…”