Kang-Ho Lee

A 40 mV Transformer-Reuse Self-Startup Boost Converter With MPPT Control for Thermoelectric Energy Harvesting

This paper presents transformer-based self-starting boost converter architecture with low-power maximum power point tracking (MPPT) control for low-voltage thermoelectric generator applications. The minimum working voltage of the proposed boost converter is 40 mV with oscillation through a positive feedback loop formed by a native MOS and transformer. The oscillation autonomously starts up by thermal noise and VOUT is charged up to 1.2 V by the oscillation so that the control block can operate. After that, the transformer for start-up is reused as an inductor, and the normal boost converter mode is enabled for better energy transfer efficiency. An improved MPPT sensing method is also proposed to simplify the circuit. The prototype chip is implemented in a 0.13-μm CMOS process. It operates with an input voltage range of 40 mV to 300 mV and provides a maximum output power of 2.7 mW with a maximum efficiency of 61% at an output voltage of 2 V.

One-chip electronic detection of DNA hybridization using precision impedance-based CMOS array sensor

This paper describes a label-free and fully electronic detection method of DNA hybridization, which is achieved through the use of a 16×8 microarray sensor in conjunction with a new type of impedance spectroscopy constructed with standard complementary metal-oxide-semiconductor (CMOS) technology. The impedance-based method is based on changes in the reactive capacitance and the charge-transfer resistance after hybridization with complementary DNA targets. In previously published label-free techniques, the measured capacitance presented unstable capacitive properties due to the parallel resistance that is not infinite and can cause a leakage by discharging the charge on the capacitor. This paper presents an impedance extraction method that uses excitation by triangular wave voltage, which enables a reliable measurement of both C and R producing a highly sensitive sensor with a stable operation independent of external variables. The system was fabricated in an industrial 0.35-μm 4-metal 2-poly CMOS process, integrating working electrodes and readout electronics into one chip. The integrated readout, which uses a parasitic insensitive integrator, achieves an enlarged detection range and improved noise performance. The maximum average relative variations of C and R are 31.5% and 68.6%, respectively, after hybridization with a 1 μM target DNA. The proposed sensor allows quantitative evaluation of the molecule densities on the chip with distinguishable variation in the impedance. This fully electronic microsystem has great potential for use with bioanalytical tools and point-of-care diagnosis.

A CMOS label-free DNA sensor using electrostatic induction of molecular charges.

This paper reports a label-free biosensor for the detection of DNA hybridization. The proposed biosensor measures the surface potential on oligonucleotide modified electrodes using a direct charge accumulation method. The sensor directly and repeatedly measures the charges induced in the working electrode, which correspond to intrinsic negative charges in immobilized molecules. The sensor achieves an improved signal-to-noise ratio (SNR), through the oversampling effect of accumulation for charges and the differential architecture. The sensor also shows stable, robust, and reproducible measurement independent of slight changes in the reference voltage, unlike previous ion-sensitive field effect transistors (ISFETs), providing the benefits of choosing a wide variety of reference electrode materials. The proposed device is integrated with working electrodes, a reference electrode and readout circuits into one package via a 0.35 μm complementary metal-oxide-semiconductor (CMOS) process. The sensor achieves a detectable range of 88.3 dB and a detection limit of 36 μV for surface potential. It is demonstrated that the sensor successfully achieves specific detection of oligonucleotide sequences derived from the H5N1 avian influenza virus. The experiments show a limit of detection of 100 pM and include a single-base mismatch test in 18-mer oligonucleotides.

CMOS capacitive biosensor with enhanced sensitivity for label-free DNA detection

Silicon devices based on impedance measurements offer label-free and direct electrical detection when used to quantify the hybridization of DNA molecules. They show rapid, robust, and inexpensive measurement and compatibility with commercial microfabrication technology. The real-time measurement of the impedance does not require the use of labeling molecules attached to the target DNA in optical and magnetic technology [1,2]. It also has the advantage of miniaturization for point-of-care (PoC) or on-site sensing applications, unlike the 3-electrode topology in electrochemical sensors [3]. Several studies have proposed capacitive biosensors that utilize a nonfaradaic process, which refers to transient currents charging a geometrical capacitor in an electrolyte-electrode interface [4]. Conventional capacitive biosensors using the excitation of the bidirectional current [5,6] can be implemented with a compact design, but they have several issues that degrade the sensitivity of the sensor, such as DC drift in the electrode caused by a charge imbalance, the electrolysis generated by DC voltage across the electrodes, the offset generated by pre-charged initial values, and weakness against common-mode noise. As a solution, we report a fully integrated capacitance-based biosensor that locates two electrodes differentially in a single current source.

A Direct-Type Fast Feedback Current Driver for Medium-to Large-Size AMOLED Displays

The current or voltage driving schemes are employed for pulse-amplitude modulation (PAM) in AMOLED displays. Current driving methods have advantages over voltage driving schemes including improvement of luminance uniformity at display panels and compensation of TFT characteristics at pixels. degrade the driving accuracy. This paper introduces a direct-type fast feedback current (DFFC) driver that offers fast settling time with good accuracy by comparing the data with the pixel current directly. An optimum compensation method for the feedback loop is suggested as well.

Power-efficient series-charge parallel-discharge charge pump circuit for LED drive

A charge pump drive circuit for LED lighting is proposed. This circuit is realized with repeated use of a compact unit module consisted of a capacitor and diodes. The series-charge and parallel-discharge operation gives the efficiency better than the conventional converters with AC line input. This paper also shows how to minimize the number of modules for a given number of LEDs. A prototype implemented the charge pump drive circuit shows a maximum efficiency of 95% for 22 LEDs in series with the AC line voltage of 220 Vrms.

An autonomous CMOS hysteretic sensor for the detection of desorption-free DNA hybridization

This paper describes a sensor for label-free, fully electrical detection of DNA hybridization based on capacitive changes in the electrode-electrolyte interface. The sensor measures capacitive changes in real time according to a charging-discharging principle that is limited by the hysteresis window. In addition, a novel autonomous searching technique, which exclusively monitors desorption-free hybridized electrodes among electrode arrays, enhances the performance of the sensor compared with conventional capacitive measurement. The sensor system achieves a detection range of 80 dB. The integrated circuit sensor is fabricated with a 0.35 μm CMOS process. The proposed sensor offers rapid, robust and inexpensive measurement of capacitance with highly integrated detection circuitry. It also facilitates quantitative evaluations of molecular densities on a chip with distinctive impedance variations by monitoring desorption-free hybridized electrodes. Our electrical biosensor has great potential for use with bio analytical tools and point-of-care diagnosis.

An electronic DNA sensor chip using integrated capacitive read-out circuit

This paper presents fully integrated label-free DNA recognition circuit based on capacitance measurement. A CMOS-based DNA sensor is implemented for the electrical detection of DNA hybridization. The proposed architecture detects the difference of capacitance through the integration of current mismatch of capacitance between reference electrodes functionalized with only single-stranded DNA and sensing electrodes bound with complementary DNA strands specifically. In addition, to minimize the effects of parallel resistance between electrodes and DNA layers, the compensation technique of leakage current through the use of constant current charging and discharging is implemented in the proposed detection circuit. The chip was fabricated in 0.35um 4-metal 2-poly CMOS process, and 16×8 sensing electrode arrays were fabricated by post-processing steps.

Fast switching charge dump assisted Class-D audio amplifier with high fidelity and high efficiency

A fast switching charge dump assisted class-D audio amplifier is presented in this paper. To achieve high efficiency and high linearity, the Class-K* audio amplifier consists of the class D amplifier with high efficiency and the proposed charge dump amplifier with high linearity. The charge pump amplifier works at faster switching frequency than class D amplifier so as to compensate the distortion caused by switching of the class-D amplifier. The class-K* audio amplifier implemented in 0.35mum CMOS process shows -71.8 dB THD+N at 1 KHz and a maximum efficiency of 81% at an output power of 257 mW for 4.1Omega load.

A High-Performance Fast Switching Charge Dump Assisted Class-

A new Class-K* audio amplifier with high-power efficiency and high fidelity is integrated in a 0.35-μm CMOS process. It proposes a new topology connected Class-D amplifier with fast-switching charge-dump (FSCD) amplifier in parallel. The integration of the amplifier requires neither analog buffer amplifier nor a complex compensation circuit needed in hybrid audio amplifier (Class-K). The FSCD amplifier composed of comparators and switches works at a high-switching frequency in order to absorb the distortion caused by Class-D amplifier switching. Thus, this assists the audio amplifier to have good linearity under switching operation. With the proposed topology, the audio amplifier has a flat frequency response with - 3-dB bandwidth of 60 KHz and is capable of delivering up to 257 mW into 4.1-Ω load with maximum efficiency of 81%. A typical total harmonic distortion plus noise (THD+N) is less than 0.1% at the power level over 25 mW within the audio frequency range (20 Hz-20 kHz), and the minimum THD+N is 0.025% with the audio input frequency of 1 kHz at the output power of 114 mW.