Yonsei University · Engineering
Professor Youngcheol Chae's research lab specializes in low-power, high-efficiency analog and mixed-signal integrated circuits, with a focus on energy-constrained applications such as implantable medical devices, image sensors, and wearable health systems. The lab develops innovative circuit architectures—including inverter-based switched-capacitor circuits and zoom ADCs—enabling ultra-low power operation in scaled CMOS technologies. It also explores emerging 2D materials like MoS₂ for extended-spectrum photodetection and integrates advanced materials such as graphene into flexible, wearable sensors for real-time physiological monitoring. The lab's work bridges cutting-edge semiconductor design with practical biomedical and environmental sensing applications.
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An operational transconductance amplifier (OTA) is a major building block and consumes most of the power in switched-capacitor (SC) circuits, but it is difficult to design low-voltage OTAs in scaled CMOS technologies. Instead of using an OTA, this paper proposes an inverter-based SC circuit and its application to low-voltage, low-power delta-sigma (DeltaSigma) modulators. Detailed analysis and design optimizations are also provided. Three inverter-based DeltaSigma modulators are implemented for
A 20-bit incremental ADC for battery-powered sensor applications is presented. It is based on an energy-efficient zoom ADC architecture, which employs a coarse 6-bit SAR conversion followed by a fine 15-bit ΔΣ conversion. To further improve its energy efficiency, the ADC employs integrators based on cascoded dynamic inverters for extra gain and PVT tolerance. Dynamic error correction techniques such as auto-zeroing, chopping and dynamic element matching are used to achieve both low offset and hi
This paper presents a 2.1 M pixel, 120 frame/s CMOS image sensor with column-parallel delta-sigma (ΔΣ) ADC architecture. The use of a second-order ΔΣ ADC improves the conversion speed while reducing the random noise (RN) level as well. The ΔΣ ADC employing an inverter-based ΔΣ modulator and a compact decimation filter is accommodated within a fine pixel pitch of 2.25-μm and improves energy efficiency while providing a high frame-rate of 120 frame/s. A prototype image sensor has been fabricated w
A 2.1 Mpixel 120 frame/s CMOS image sensor with column-parallel ΔΣ ADCs is realized in a 0.13 μm CMOS process. Column-parallel ΔΣ ADC architectures improve the conversion speed while reducing the random noise level as well. Inverter-based SC circuits maximize the power efficiency. This sensor achieves a measured noise floor of 1.9e-, while dissipating 180 mW.
MoS<sub>2</sub>, an emerging material in the field of optoelectronics, has attracted the attention of researchers owing to its high light absorption efficiency, even as an atomically thin layer. However, the covered spectra of the reported MoS<sub>2</sub>-based photodetectors are restricted to the visible range owing to their electronic bandgap (∼1.9 eV). Strain engineering, which modulates the bandgap of a semiconductor, can extend the application coverage of MoS<sub>2</sub> to the infrared spe
Thermal imaging provides information regarding the general condition of the human body and facilitates the diagnosis of various diseases. Heat therapy or thermotherapy can help in the treatment of injuries to the skin tissue. Here, we report a wearable thermal patch with dual functions of continuous skin temperature sensing and thermotherapy for effective self-care treatment. This system consists of a graphene-based capacitive sensor, a graphene thermal pad, and a flexible readout board with a w
This paper presents an improved low-power DeltaSigma modulator, exploiting the class-C inverter and the feedforward topology. The measurement results show 14b dynamic range for a 20kHz bandwidth with 36muW power consumption from a 0.7V supply.
In switched capacitor sigma-delta (ΣΔ) analog-to-digital converters (ADCs), an operational transconductance amplifier (OTA) is the main building block and consumes most of power. This paper proposes that the OTAs can be replaced with class-C inverters for low-power consumption without sacrificing the performance. A second order ΣΔ modulator using class-C inverter technique is fabricated with a 0.35-μm CMOS process, occupies 3024 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink=
The inverter circuit has been adopted to welding machines to improve welding performance. As the conventional inverter welding machine has a diode rectifier, there are many problems such as input current harmonics generation and low power factor, which can be solved by the high power factor inverter arc welding machine proposed. The characteristics of new type noise cut transformer is investigated, which could prevent switching devices from being destroyed by electrical noise generated from arc
According to the adoption of inverter circuit topology for welding machine area, the improvement of welding performance con be achieved. However conventional CO/sub 2/ inverter arc welding machine uses the constant voltage characteristics. So the metal transfer is performed under nonoptimum conditions in view of spatter generation. In this paper the new control algorithm is proposed for welding machine, which is the instantaneous output current control method using single chip microprocessor. Bu
The ultrafast bouncing motion of a liquid droplet has been investigated for droplet manipulation with a single droplet actuator using an electrostatic force for the first time.
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