Higher-order VCO-based ADCs for Sensor Interfaces

The rapid proliferation of Internet of Things (IoT) devices has revolutionized the technological landscape, permeating various domains and significantly impacting how we interact with the digital and physical realms. As everyday objects become imbued with the capability to collect, manipulate, and acquire data autonomously. Smart distributed sensor networks are formed and are expected to allow transformative changes in sectors such as healthcare, industrial production, and agriculture by allowing continuous monitoring and data-supported decision-making, improving outcomes and efficiency.The design of these highly advanced sensor nodes presents challenges as they must be extremely power efficient to allow for continuous long-term monitoring with a small battery or energy harvester to ensure unobtrusive form factors. A key component to reducing the power consumption and allowing large-scale deployment of IoT sensors is the use of on-device data processing, which reduces the data-transmission bandwidth, latency, and power consumption. This digital heavy preprocessing drives the system design towards selecting highly integrated system-on-chip (SoC) solutions that rely on the advanced process nodes for highly efficient operation of the digital core in charge of data processing at the sensor nodes. However, these advanced technologies do not scale as well for analog front-ends in charge of acquiring the sensor data as they do for digital signal processing with second-order effects significantly degrading key analog transistor parameters (gain, gate leakage, mismatches, etc.), making the design of high-performance analog circuits increasingly difficult. A lot of research has been dedicated to developing alternative architectures that are more resilient or even benefit from technology scaling. Among these architectures, voltage-controlled oscillator (VCO) based analog-to-digital converters (ADC) leverage digital-friendly ring oscillators to perform signal processing and quantization, providing highly scalable analog-to-digital interfaces. These VCO-based ADCs have been mostly designed for high-speed applications with MHz of bandwidth but have started showing their potential for lower bandwidth sensor nodes thanks to their supply insensitivity, infinite DC gain, and compact area. However, many challenges are associated with designing high dynamic range (DR) ADCs using VCO-based integrators as they have limited intrinsic linearity and require a large oversampling ratio due to being limited to 1st-order noise shaping. This dissertation presents several innovations at the circuit and architecture level that can increase the noise-shaping order of VCO-based ADCs and achieve outstanding linearity. These techniques were integrated into two prototype chips: 1) an ADC for the direct-digitization of biopotential signals and 2) a purpose sensor front-end ADC for ultra-low-power IoT nodes. The first prototype is intended to be used for wearable continuous health monitoring. It was designed to interface directly with high-impedance recording electrodes and provide a wide dynamic range and linearity to absorb motion artifacts and correct them in the digital domain. The prototype ADC achieves 2nd-order noise-shaping with high linearity and power efficiency using a novel Gated-inverted-ring-oscillator(GIIRO)-based time-to-digital converter and a multi-quantizer scheme. The ADC achieves a dynamic range greater than 90 dB and above 110 dB of linearity while consuming only 5.4 µW of power. This corresponds to a Schreier Figure of Merit (FoM) of 174.7 dB, which was state-of-the-art for VCO-based ADCs at the time of publication. The second prototype was developed by building upon the feedforwarding techniques commonly used in the standard voltage domain ADC architectures and applying them to capacitively coupled VCO-based ADCs. Using the pseudo-virtual ground (PVG) at the input of the VCO integrator and feeding it further down the loop, we showed that high linearity and higher-order noise-shaping shaping could be achieved extremely power-efficiently. The prototype achieved 3rd-order noise-shaping with a 92.1 dB SNDR and a peak linearity of 123 dB while consuming only 4.4 µW. This led to a Schreier FoM of 179.6 dB, indicating how efficient the proposed structure is and showing comparable performance to standard voltage domain architectures. These VCO-based ADCs have been mostly designed for high-speed applications with MHz bandwidth but have started showing their potential for lower bandwidth sensor nodes thanks to their supply insensitivity, infinite DC gain, and compact area. However, many challenges are associated with designing high dynamic range (DR) ADCs using VCO-based integrators as they have limited intrinsic linearity and require a large oversampling ratio due to being limited to 1st-order noise shaping.This dissertation presents several innovations at the circuit and architecture level that can increase the noise-shaping order of VCO-based ADC and achieve outstanding linearity. These techniques were integrated into two prototype chips: 1) an ADC for the direct-digitization of biopotential signals and 2) a purpose sensor front-end ADC for ultra-low-power IoT nodes. The first prototype is intended to be used for wearable continuous health monitoring. It was designed to interface directly with high-impedance recording electrodes and provide a wide dynamic range and linearity to absorb motion artifacts and correct them in the digital domain. The prototype ADC achieves 2nd-order noise-shaping with high linearity and power efficiency using a novel GIRO-based time-to-digital converter and a multi-quantizer scheme. The ADC achieves a dynamic range greater than 90 dB and above 110 dB of linearity while consuming only 5.4 μW of power. This corresponds to a Schreier Figure of Merit (FoM) of 174.7 dB, which was state-of-the-art for VCO-based ADCs at the time of publication. The second prototype was developed by building upon the feedforwarding techniques commonly used in the standard voltage domain ADC architectures and applying them to capacitively coupled VCO-based ADCs. Using the pseudo-virtual ground (PVG) at the input of the VCO integrator and feeding it further down the loop, we showed that high linearity and higher-order noise-shaping shaping could be achieved extremely power-efficiently. The prototype achieved 3rd-order noise-shaping with a 92.1 dB SNDR and a peak linearity of 123 dB while consuming only 4.4 μW. This led to a Schreier FoM of 179.6 dB, indicating how efficient the proposed structure is and showing comparable performance to standard voltage domain architectures

Hexadentate N,N,N’,N’-tetrapyrazolyl alkyl diamine metal complexes as scaffolds for bimetallic systems

Multielectron transformations are essential in the catalytic activity of many rare transition metals such as palladium-based catalysts. However, transposing this chemistry to more accessible and sustainable metals remains challenging as such elements tend to favor single-electron transfer. To overcome this limitation, placing two redox-active metal partners in close proximity can promote cooperative two-electron processes. Cooperativity is a key concept in chemistry, whereby multiple components work together to achieve a specific function. In particular, redox cooperativity refers to the facilitated transfer of multiple electrons involving several redox-active partners, i.e., multielectron transformations. Tetrapyrazole-based ligands represents a new class of ditopic hexadentate scaffolds, offering a tunable second coordination sphere through accessible N–H protons. Their ability to reversibly switch from pyrazole to pyrazolate donors allows control over metal redox properties and binding modes, paving the way for the formation of bimetallic complexes and the investigation of metal-metal redox cooperativity.(SC - Sciences) -- UCL, 202

Towards the synthesis of ligands scaffold for cooperative bimetallic systems

Areas ranging from fine chemical synthesis to sustainable energy development rely on highly efficient metal-based catalysts to perform key chemical transformations [1]. Then metals such as Pd, Pt, Rh, Ir or Ru are used because they are proficient at mediating the multi-electron transfer steps required for these applications. In contrast to synthetic chemistry, biological systems do not use noble metals but rather employ cooperative reactivity between multiple redox sites [2]. These sites store and provide additional electrons to avoid unfavorable oxidation states at the reactive centers. Replicating this strategy of redox cooperativity in synthetic complexes could offer a valuable way to enhance the reactivity of base metal catalysts like iron, copper, etc. Such kind of systems have already been developed by Rauchfuss et al. to mimic Fe-Fe hydrogenase [3] and Bosnich and co-workers placed the basics for understanding bimetallic systems [4]. However, increase the comprehension of incorporating and controlling the additional redox centers is still a major challenge. Here, we planned to develop new bimetallic complexes where the two metals will be in a close proximity thanks to a ditopic ligand and then, to better understand the cooperativity between the metal centers and highlight the importance of the ligands design. Reference

Towards the synthesis of ligand scaffold for bimetallic systems

Areas ranging from fine chemical synthesis to sustainable energy development rely on highly efficient metal-based catalysts to perform key chemical transformations [1]. Then metals such as Pd, Pt, Rh, Ir or Ru are used because they are proficient at mediating the multi-electron transfer steps required for these applications. In contrast to synthetic chemistry, biological systems do not use noble metals but rather employ cooperative reactivity between multiple redox sites [2]. These sites store and provide additional electrons to avoid unfavorable oxidation states at the reactive centers. However, these cooperative processes remain not well-known, specifically in multi-metallic systems [3]. Then, replicating this strategy of redox cooperativity in synthetic complexes could offer a valuable way to enhance the reactivity of first-row transition metals like iron, copper, etc. To address this challenge, our project seeks to develop and study the biomimetic strategy of incorporating metal-based electron reservoirs within the periphery of reactive metal centers. Thus, ditopic ligands able to interact with two metallic centers have been developed based on N,N,N’,N’-tetra(heterocyclic)propylene- and ethylene-diamines. Modifying the substituents on the heterocycles and the Bite angle may provide interesting properties to our bimetallic systems. For now, their monometallic counterparts have been synthesized and characterized through spectroscopic and electrochemical technics that brought promising results

Biocatalytic synthesis of planar chiral macrocycles

Enzymes lock in planar chirality Molecules with very large rings—macrocycles—are often conformationally constrained, and some exhibit planar chirality when substituents of the ring cannot rotate freely. Restricted rotation is generally valued in macrocycles because it can hold the molecule in functional conformations. Using a well-established lipase enzyme, Gagnon et al. developed a synthesis of planar chiral macrocycles with handles that can be easily functionalized. Computational docking suggests how using an enzyme as the catalyst for sequential acylation reactions can impart the observed stereochemistry. Science , this issue p. 917 </jats:p

Spinal cord compression caused by metastasis of a non-seminomatous testicular tumour with a predominant Yolk sac component in a 26-year-old man

Background: Pure testicular yolk sac tumours are extremely rare among adults, and there is no prior report of spinal cord compression syndrome due to yolk sac testis tumour metastasis in an adult. Case presentation: Here we describe the case of a 26-year-old male with a testicular yolk sac tumour that was found when a vertebral metastasis caused spinal cord compression. Symptoms included lower back pain and a growing painless testicular mass. Treatment comprised emergency surgical spinal cord decompression and orchidectomy, followed by 3 cycles of bleomycin, etoposide, and platinum (BEP) chemotherapy, and then 3 cycles of etoposide and platinum and 40 Gy vertebral radiotherapy. One year later, cement leaked into the spinal duct, prompting a return of compression syndrome. Corporectomy was performed, followed by osteosynthesis. The patient’s treatment was consolidated with 34 months and zoledronic acid administration. Although spinal metastasis from a yolk sac tumour is extremely rare, it must be considered in young adults with a testicular mass who exhibit pain or limb numbness. Such cases warrant rapid surgical decompression and radical orchidectomy, followed by adjuvant chemotherapy. Conclusion: Our case is atypical due to the patient’s age and the disease presentation. Spinal cord compression syndrome caused by yolk sac tumor metastasis is extremely rare in adulthood, and usually has a bad prognosis when diagnosed late