José Luis Ausín

Wearable bioimpedance spectroscopy within Internet of Medical Things ecosystems requires energy-efficient analog front-ends (AFEs) capable of processing small impedance-dependent signals over a wide excitation-frequency range. This paper presents a preliminary study of an automated g_m/I_D-based framework for the co-design of wideband CMOS instrumentation amplifiers, jointly considering power, noise, bandwidth, and frequency-dependent common-mode rejection. The proposed flow combines technology-characterized device data, Verilog-A behavioral modeling, Python-based optimization, and SKILL-assisted transistor-level verification. The methodology is applied to a wideband CMOS current-feedback instrumentation amplifier (CFIA) designed in a 180-nm CMOS technology. Operating from a 1.8-V supply, the amplifier provides a nominal gain of 30 V/V over the 1-kHz to 2-MHz signal band. Particular attention is given to the coupling between transistor sizing, parasitic capacitance, and high-frequency CMRR in a local current-feedback topology. The paper establishes the BIS readout requirements, describes the selected CFIA architecture, and formulates the main design variables and optimization targets. The presented results constitute the initial stage of a broader design framework; complete optimization, statistical robustness, and experimental validation are reserved for the subsequent full study.

A bandpass filter (BPF), with high quality factor ( Q ) and wide tuning range of the centre frequency ( $f_0$ ), for signal separation in simultaneous multi-sine bioimpedance analysis, is presented. The cell follows the $G_m$ - C approach, where a multiple-output transconductor has been incorporated, for the sake of compactness, and a fully-differential structure has been selected, to enhance the general performance of the solution. The linearized transconductors ( $G_m$ ) are based on a double asymmetric differential pair and the integrated capacitors ( C ) are implemented in such a way that the required transfer function for the differential-mode signal is achieved and the stability of the common-mode component is granted. The BPF has been designed and fabricated in 180 nm CMOS technology to operate with a 1.8-V supply and feature a nominal gain at $f_0$ of 0 dB and a Q equal to 20, whereas $f_0$ is programmed by modifying the biasing current of the transconductors. Experimental results, measured on 8 samples of the silicon prototype, show that the BPF centre frequency can be continuously swept from 102 Hz to 2.06 MHz with a supply current ranging between 981 nA and 686 $\mu$ A. Besides, the maximum output voltage range of the filter, determined according to the –40 dB THD criterion, varies between around 31.5 mV and 64 mV within the frequency range indicated, thus leading to a dynamic range between 42.3 dB and 48.6 dB, which illustrates its suitability for the target application.

Noninvasive remote monitoring of hemodynamic variables is essential in optimizing treatment opportunities and predicting rehospitalization in patients with congestive heart failure. The objective of this study is to develop a wearable bioimpedance-based device, which can provide continuous measurement of cardiac output and stroke volume, as well as other physiological parameters for a greater prognosis and prevention of congestive heart failure. The bioimpedance system, which is based on a robust and cost-effective measuring principle, was implemented in a CMOS application specific integrated circuit, and operates as the analog front-end of the device, which has been provided with a radio-frequency section for wireless communication. The operating parameters of the proposed wearable device are remotely configured through a graphical user interface to measure the magnitude and the phase of complex impedances over a bandwidth of 1 kHz to 1 MHz. As a result of this study, a cardiac activity monitor was implemented, and its accuracy was evaluated in 33 patients with different heart diseases, ages, and genders. The proposed device was compared with a well-established technique such as Doppler echocardiography, and the results showed that the two instruments are clinically equivalent.

Two techniques to design a low-transconductance (G m ) widely-tunable transconductor are described. The operation principle consists in both cases in the subtraction of two nominally equal transconductances, one of which can be electronically tuned. The circuit implementation differs, being one solution based on the use of source followers (SF), a linearization resistor, and a tunable current mirror, and consisting the other approach of differential pairs (DP) with resistive source degeneration, and an electronically programmable current biasing. Both transconductors have been designed in 180 nm CMOS technology to operate with 1.8 V. The SF and DP solutions achieve a minimum G m nominal value of 1.38 nA/V and 6.03 nA/V, respectively, with a simulated transconductance tuning range of 729.6× and 7129.4×, also respectively, obtained from a Montecarlo analysis. The application of the transconductors to the design of a second-order G m − C bandpass filter for signals separation in multi-sine bioimpedance spectroscopy is also addressed.

An instrumentation amplifier (IA) with continuous tuning of the voltage gain, suitable for operation over a wide frequency range, and aimed to electrical bioimpedance spectroscopy, is proposed. The operation principle of the IA is based on indirect current feedback (ICF), which leads to an almost-constant bandwidth regardless of the value of the programmed voltage gain. The use of improved voltage followers in the transconductors required in the ICF technique allows achieving a compact implementation with a bandwidth compatible with bioimpedance spectroscopy applications. The tuning strategy relies on a continuously programmable current mirror that can be electronically adjusted by means of a control current. The IA has been designed and fabricated in 180 nm CMOS technology to operate with a 1.8-V single supply. The experimental characterization of the silicon prototypes showed a gain programmability range higher than 45 dB, between −4.6 dB and 41.2 dB, a BW around 3 MHz, and a maximum CMRR at DC higher than 86 dB, all this with a minimum current consumption of $144.8~\mu \text{A}$ and an area occupation of 0.0196 mm2.