Ryota Sekimoto

A 0.5 V 1.1 MS/sec 6.3 fJ/Conversion-Step SAR-ADC With Tri-Level Comparator in 40 nm CMOS

This paper presents an extremely low-voltage operation and power efficient successive-approximation-register (SAR) analog-to-digital converter (ADC). Tri-level comparator is proposed to relax the speed requirement of the comparator and decrease the resolution of internal Digital-to-Analog Converter (DAC) by 1-bit. The internal charge redistribution DAC employs unit capacitance of 0.5 fF and ADC operates at nearly thermal noise limitation. To deal with the problem of capacitor mismatch, reconfigurable capacitor array and calibration procedure were developed. The prototype ADC fabricated using 40 nm CMOS process achieves 46.8 dB SNDR and 58.2 dB SFDR with 1.1 MS/sec at 0.5 V power supply. The FoM is 6.3-fJ/conversion step and the chip die area is only 160 μm × 70 μm.

A 0.5-V 5.2-fJ/Conversion-Step Full Asynchronous SAR ADC With Leakage Power Reduction Down to 650 pW by Boosted Self-Power Gating in 40-nm CMOS

This paper presents an ultralow-power and ultralow-voltage SAR ADC. Full asynchronous operation and boosted self-power gating are proposed to improve conversion accuracy and reduce static leakage power. By designing with MOSFET of high threshold voltage (HVt) and low threshold voltage (LVt), the leakage power is reduced without decrease of maximum sampling frequency. The test chip in 40-nm CMOS process has successfully reduced leakage power by 98%, and it achieves 8.2-bit ENOB and while consuming only 650 pW at 0.1 kS/s from 0.5-V power supply. The power consumption is scalable up to 4 MS/s and power supply range from 0.4 to 0.7 V. The best figure of merit at 0.5 V is 5.2 fJ/conversion-step at 20 kS/s.

A 40nm 50S/s–8MS/s ultra low voltage SAR ADC with timing optimized asynchronous clock generator

This paper presents an ultra low power and low voltage successive-approximation-register (SAR) analog-to-digital converter (ADC) that uses an adaptive timing optimized asynchronous clock generator. Compared to asynchronous converters that use the conventional clock generator, the frequency range is expanded by 50% at 0.4V analog and 0.7V digital power supply voltage. By calibrating the delay time of the clock generator, the DAC settling time is optimized to counter the device mismatch. Test chip has been fabricated in 40nm standard CMOS process and achieved figure of merit (FoM) of 8.75-fJ/conversion-step with 2.048MS/s at 0.6V analog and 0.7V digital power supply voltage. The ADC operates from 50S/s to 8MS/s performing over 7.5-ENOB.

A power scalable SAR-ADC in 0.18µm-CMOS with 0.5V nano-watt operation

This paper presents an extremely low-power and low-voltage Analog-to-Digital Converter (ADC) for wireless sensor networks or medical implantable devices. Top plate sampling and bootstrap switch are used to realize ultra low-voltage (0.5V) operation. Configuration of capacitor array which can decrease the number of control bus lines are proposed to reduce the circuit area and power consumption. To further reduce the power consumption, optimal power supply voltages are determined independently for analog blocks and digital blocks considering the tradeoff between the speed and power. Test ADC chip fabricated in 0.18µm-CMOS process has achieved 0.5V, 6nW operation at sampling frequency of 0.4kS/s. The achieved effective number of bit (ENOB) is 7.19-bit. When the supply voltage is increased to 1V, the ADC operates at 820kS/s with power consumption of 30.9µW and ENOB of 7.41-bit.

An 8bit 0.35–0.8V 0.5–30MS/s 2bit/step SAR ADC with wide range threshold configuring comparator

An extremely low-voltage operating high speed and low power 2bit/step asynchronous SAR ADC is presented. Wide range dynamic threshold configuring comparator is proposed to enable power and area efficient 2bit/step operation. By configuring the comparator threshold by simple Vcm biased current sources, the ADC holds immunity against 10% power supply variation. The prototype ADC fabricated in 40nm CMOS achieved 44.3 dB SNDR with 6.14 MS/s at a single supply voltage of 0.5 V. The ADC achieved a peak FoM of 5.9fJ/conv-step at 0.4V and operates down to 0.35V.

A 0.5V 65nm-CMOS single phase clocked bootstrapped switch with rise time accelerator

This paper presents a twice the supply voltage bootstrapped switch with the proposed rise time accelerator that has high linearity and fast rising with single phase clock input at low voltage. The proposed rise time accelerator improves rising time and ensures circuit operation at extremely low supply voltage without any complex timing generation circuit. The prototype switch is designed in 65nm CMOS process and the simulation results show that the power consumption of quasi differential bootstrapped switch is less than 11nW/MHz at a supply voltage of 0.5V with 10MS/sec. The third order harmonic distortion (HD3) is −104dB with sampling capacitor of 1.28pF.

An 8b extremely area efficient threshold configuring SAR ADC with source voltage shifting technique

An extremely low power and area efficient threshold configuring ADC (TC-ADC) for time interleaved ADC is proposed. The threshold configuring comparator (TCC) performs a binary search. 5b conversion is carried out by TCC with source voltage shifting technique. Additional 2b resolution is achieved by the proposed threshold interpolation (TI) technique with only 15% power overhead. Prototype ADC in 40nm CMOS occupies a core area of only 0.0038mm2 and when calibration circuit included, 0.0058 mm2. With a supply voltage of 0.7V, the ADC achieves 7.0 ENOB with 24MS/s. Peak FoM of 9.8fJ/conv. is obtained at 0.5V supply, which is over 15x improvement compared with conventional TC-ADC.

A 40nm CMOS full asynchronous nano-watt SAR ADC with 98% leakage power reduction by boosted self power gating

This paper presents an ultra low power and ultra low voltage SAR ADC. Full asynchronous operation and boosted self power gating are proposed to improve conversion accuracy and reduce static leakage power. Test chip fabricated in 40nm CMOS process has successfully reduced leakage power by 98% and it performs ENOB of 8.2bit and consumes only 0.65nW with 0.1kS/s at 0.5V. The power consumption is scalable up to 4MS/s and power supply range from 0.4 to 0.7V. The best figure of merit (FoM) of 5.2fJ/conversion-step was obtained with 20kS/s at 0.5V.

A 0.35-0.8V 8b 0.5-35MS/s 2bit/step extremely-low power SAR ADC

An extremely low-voltage operating high speed and low power 2bit/step asynchronous SAR ADC is presented. Wide range dynamic threshold configuring comparator is proposed to enable power and area efficient 2bit/step operation. By configuring the comparator threshold by simple Vcm biased current sources, the ADC holds immunity against 10% power supply variation. The prototype ADC fabricated in 40nm CMOS achieved 44.3 dB SNDR with 6.14 MS/s at a single supply voltage of 0.5 V. The ADC achieved a peak FoM of 5.9fJ/conv-step at 0.4V and operates down to 0.35V.