Subthreshold amplifiers suffer from the limited voltage headroom which leaves little space for conventional analog techniques to enhance performance and efficiency. This paper presents an evolution process of implementing conventional structures with inverters, allowing ultralow-voltage operation with increased flexibility in adopting traditional circuit techniques. Based on the proposed inverter-based elementary structure and CMFB, both the Miller-compensated (MC) operational transconductance amplifier (OTA) and the feedforward-compensated (FFC) OTA achieve significantly improved performance as compared to previous works. The proposed amplifier techniques are verified in modulator (DSM) design, with MC-OTA for a DT-DSM and FFC-OTA for a CT-DSM, both fabricated in a 0.13-μm CMOS. The 0.3-V DT-DSM achieves 74.1-dB SNDR, 83.4-dB SFDR and 20-kHz bandwidth with 79.3-μW power, resulting in a Schreier figure of merit (FoM) of 158 dB. The 0.3-V CT-DSM achieves 68.5-dB SNDR, 82.6-dB SFDR, and 50-kHz bandwidth with 26.3-μW power, leading to a Schreier FoM of 161 dB. Both DSMs exhibit highly competitive performance among sub-0.5-V designs, validating the proposed subthreshold amplifier techniques.
Interface circuits for capacitive MEMS accelerometers are conventionally based on charge-based approaches. A promising alternative to these is provided by frequency-based readout techniques that have some unique advantages as well as a few challenges associated with them. This paper addresses these techniques and presents a derivation of the fundamental resolution limits that are imposed on them by phase noise. Starting with an overview of basic operating principles, associated properties and challenges, the discussions then focus on the fundamental trade-offs between noise, power dissipation and signal bandwidth (BW) for the LC-oscillator-based frequency readout and for the conventional charge-based switched-capacitor (SC) readout. Closed-form analytical formulas are derived to facilitate a fair comparison between the two approaches. Benchmarking results indicate that, with the same bandwidth requirement, charge-based readout circuits are more suitable when optimizing for noise performance, while there is still some room for frequency-based techniques when optimizing for power consumption, especially when flicker phase noise can be mitigated.
This paper presents a high-resolution ΔΣ modulator which is capable of operation under supply voltage as low as 250mV. A novel subthreshold inverter-based OTA is proposed and exploited in the switched-capacitor (SC) integrators, permitting a satisfied noise-shaping performance in the 4 th -order feedforward topology. With each stage's coefficient optimized, the integrators' internal swings and the distortion power stemming from OTAs' gain nonlinearity are minimized. Implemented in a 0.13μm CMOS with an OSR of 64 and a sampling frequency (f s ) of 1.28MHz, this design achieves a measured DR of 77.0dB, SNDR of 73.3dB, and SFDR of 85.0dB over a 10kHz bandwidth. To the best of authors' knowledge, it appears to be the converter with highest SNDR observed among sub-0.5V designs.I.
An ultra-low-voltage switched-capacitor (SC) ΔΣ modulator operating at mere 0.25V supply voltage is presented. To facilitate noise shaping in subthreshold region, a novel twostage inverter-based OTA with DC gain of 43dB is proposed. Also ultra-low-voltage switches and subthreshold comparator are exploited. The transistor-level simulation results show that with an oversampling ratio (OSR) of 64 and a sampling frequency (f s ) of 1.28MHz under a 0.25V supply, the converter achieves 86.5dB SNDR over 10kHz bandwidth while consuming a total power of 33.8µW and yielding a figure of merit (FoM) of 97.8fJ/conversion-step.I.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.