Design of low power, low noise instrumentation amplifiers for MEMS sensor interfacing

La presente tesi di dottorato tratta del progetto di amplificatori da strumentazione in tecnologia CMOS atti ad interfacciare sensori MEMS resistivi. Il progetto di un amplificatore da strumentazione integrato in tecnologia CMOS a basso offset e basso rumore, utilizzato per la lettura di sensori di flusso di tipo MEMS, viene ampliamente discusso. Per raggiungere l'elevata risoluzione richiesta, nell'ordine dei microvolt, sono state utilizzate tecniche dinamiche, come ad esempio la modulazione chopper e il matching dinamico delle porte di ingresso. La stretta banda di frequenze richiesta dall'applicazione viene ottenuta introducendo nell'amplificatore stesso un filtraggio passa-basso del secondo ordine. Sono inoltre stati forniti dei criteri per la progettazione ottima di filtri a bassa frequenza. Infine, viene presentato il progetto di un amplificatore da strumentazione per sensori magnetici integrati, sviluppato presso NXP Semiconductors (NL), durante una internship di 8 mesi, svolta all'interno del Programma di Dottorato

Low-Power Wireless Medical Systems and Circuits for Invasive and Non-Invasive Applications

Approximately 75% of the health care yearly budget of public health systems around the world is spent on the treatment of patients with chronic diseases. This, along with advances on the medical and technological fields has given rise to the use of preventive medicine, resulting on a high demand of wireless medical systems (WMS) for patient monitoring and drug safety research. In this dissertation, the main design challenges and solutions for designing a WMS are addressed from system-level, using off-the-shell components, to circuit implementation. Two low-power oriented WMS aiming to monitor blood pressure of small laboratory animals (implantable) and cardiac-activity (12-lead electrocardiogram) of patients with chronic diseases (wearable) are presented. A power consumption vs. lifetime analysis to estimate the monitoring unit lifetime for each application is included. For the invasive/non-invasive WMS, in-vitro test benches are used to verify their functionality showing successful communication up to 2.1 m/35 m with the monitoring unit consuming 0.572 mA/33 mA from a 3 V/4.5 V power supply, allowing a two-year/ 88-hour lifetime in periodic/continuous operation. This results in an improvement of more than 50% compared with the lifetime commercial products. Additionally, this dissertation proposes transistor-level implementations of an ultra-low-noise/low-power biopotential amplifier and the baseband section of a wireless receiver, consisting of a channel selection filter (CSF) and a variable gain amplifier (VGA). The proposed biopotential amplifier is intended for electrocardiogram (ECG)/ electroencephalogram (EEG)/ electromyogram (EMG) monitoring applications and its architecture was designed focused on improving its noise/power efficiency. It was implemented using the ON-SEMI 0.5 µm standard process with an effective area of 360 µm2. Experimental results show a pass-band gain of 40.2 dB (240 mHz - 170 Hz), input referred noise of 0.47 Vrms, minimum CMRR of 84.3 dBm, NEF of 1.88 and a power dissipation of 3.5 µW. The CSF was implemented using an active-RC 4th order inverse-chebyshev topology. The VGA provides 30 gain steps and includes a DC-cancellation loop to avoid saturation on the sub-sequent analog-to-digital converter block. Measurement results show a power consumption of 18.75 mW, IIP3 of 27.1 dBm, channel rejection better than 50 dB, gain variation of 0-60dB, cut-off frequency tuning of 1.1-2.29 MHz and noise figure of 33.25 dB. The circuit was implemented in the standard IBM 0.18 µm CMOS process with a total area of 1.45 x 1.4 mm^(2). The presented WMS can integrate the proposed biopotential amplifier and baseband section with small modifications depending on the target signal while using the low-power-oriented algorithm to obtain further power optimization

MICRO-ELECTRO-MECHANICAL SYSTEM OSCILLATING ACCELERAMETERS WITH CMOS READOUT CIRCUITS

Ph.DDOCTOR OF PHILOSOPH