76-dB DR, 48 fJ/Step Second-Order VCO-Based Current-to-Digital Converter

Low-Voltage, Low-Area, nW-Power CMOS Digital-Based Biosignal Amplifier

“…Given the above limitations, there has been an increas-ing research interest towards the implementation of traditional analog blocks by low-cost CMOS digital-based replacements. This concept has been previously proposed in all-digital phase-locked loops (PLLs) [17]- [19], Analogto-Digital-Converters (ADCs) [20]- [34], Digital-to-Analog Converters (DACs) [20], [35]- [38], Low-Dropout Regulators (LDOs) [39]- [44], switching-mode power converters [45], [46], filters [47], [48], voltage references [49]- [51], temperature sensors [52], oscillators [53] and Operational Transconductance Amplifiers (OTAs) [54]- [63]. Most of these solutions achieve relevant area reduction and power savings compared to traditional analog solutions with similar performance, as shown in Fig.…”

A 77.8-dB DR, 114.2 fJ/Step Amplifier-Less Current-to-Digital Converter

“…Current-to-Digital converters (CDCs) are widely utilized in various domains, that includes biosensors, imaging and IoT devices [1]- [3]. Biosensors are diagnostic means, used to uncover chemical affluence which syndicates a biological element.…”

“…To facilitate measuring of amalgamated chemical absorptions, a low-energy and high dynamic range (DR) design is required to support a multitude of applications. Multiple approaches have been adopted for CDC including current to voltage conversion using a Transimpedance amplification (TIA) [3]- [5], current to frequency (C2F) transformation [2], Voltage Controlled Oscillator (VCO) [1], [7], and ƩΔ-based CDC [8], [9] as shown in Fig. 1.…”

“…Similarly, the VCO technique utilizes a VCO to convert the input current to digital. VCO-based digitization is an area-efficient technique because of the utilization of all-digital realization with intrinsic anti-aliasing filtering and noise shaping [1], [7]. However, the non-linearity associated with the VCO's voltage-to-frequency should be carefully minimized not to limit the performance of these converters [1].…”

“…VCO-based digitization is an area-efficient technique because of the utilization of all-digital realization with intrinsic anti-aliasing filtering and noise shaping [1], [7]. However, the non-linearity associated with the VCO's voltage-to-frequency should be carefully minimized not to limit the performance of these converters [1]. The ΣΔ-based CDC is power and noise efficient technique but the design process is complex.…”