In this paper, fully-synthesizable Successive Approximation Register (SAR) Analog-to-Digital Converters (ADCs) suitable for low-cost integrated systems are proposed both for voltage and current input. The proposed ADCs are digital in nature and are based on the Dyadic Digital Pulse Modulation (DDPM) Digital-to-Analog (DAC), instead of a traditional capacitive DAC. The proposed fully-digital ADC architectures enable low-effort design, silicon area reduction, and voltage scaling down to the near-threshold region. Compared to traditional analog-intensive designs, their digital nature allows easy technology and design porting, digital-like area shrinking across CMOS technology generations, and also drastically reduced system integration effort through immersed-in-logic ADC design. The voltage-input ADC architecture is demonstrated with a 40-nm testchip showing 3,000-µm 2 area, 6.4-bit ENOB, 2.8kS/s sampling rate, 40.4dB SNDR, 49.7dB SFDR, and 3.1µW power at 1V. A current-input ADC is also demonstrated for direct current readout without requiring a trans-resistance stage. 40-nm testchip measurements show a 5-nA to 1-µA input range, 4,970µm 2 area, 6.7-bit ENOB and 2.2-kS/s sample rate, at 0.94-µW power. Compared to the state of the art, the proposed ADC architecture exhibits the highest level of design automation (standard cell), lowest area, and the unique ability to cover direct acquisition of both voltage and current inputs, suppressing the need for transresistance amplifier in current readout. INDEX TERMS Analog-to-digital converter (ADC), fully-digital, fully-synthesizable, standard cell design, low design effort, low area, analog sensing Analog-to-digital converter (ADC), current sensing.

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This paper proposes topological enhancements to increase voltage gain of ultra-low-voltage (ULV) inverter-based OTAs. The two proposed improvements rely on adoption of composite transistors and forward-body-biasing. The impact of the proposed techniques on performance figures is demonstrated through simulations of two OTAs. The first OTA achieves a 39 dB voltage gain, with a power consumption of 600 pW and an active area of 447 μm2. The latter allies the forward-body-bias approach with the benefit of the independently biased composite transistors. By combining both solutions, voltage gain is raised to 51 dB, consuming less power (500 pW) at the cost of an increased area of 727 μm2. The validation has been performed through post-layout simulations with the Cadence Analog Design Environment and the TSMC 180 nm design kit, with the supply voltage ranging from 0.3 V to 0.6 V.

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