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Prof. Hojong Choi
Medical IT Convergence Engineering, Kumoh National University Technology, Gumi, Korea

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0 Electronics
0 Transducers
0 IC
0 Renewable energy devices
0 Ultrasound/photoacoustic systems

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Journal article
Published: 21 August 2021 in Sensors
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This paper introduces an ambient light rejection (ALR) circuit for the autonomous adaptation of a subretinal implant system. The sub-retinal implants, located beneath a bipolar cell layer, are known to have a significant advantage in spatial resolution by integrating more than a thousand pixels, compared to epi-retinal implants. However, challenges remain regarding current dispersion in high-density retinal implants, and ambient light induces pixel saturation. Thus, the technical issues of ambient light associated with a conventional image processing technique, which lead to high power consumption and area occupation, are still unresolved. Thus, it is necessary to develop a novel image-processing unit to handle ambient light, considering constraints related to power and area. In this paper, we present an ALR circuit as an image-processing unit for sub-retinal implants. We first introduced an ALR algorithm to reduce the ambient light in conventional retinal implants; next, we implemented the ALR algorithm as an application-specific integrated chip (ASIC). The ALR circuit was fabricated using a standard 0.35-μm CMOS process along with an image-sensor-based stimulator, a sensor pixel, and digital blocks. As experimental results, the ALR circuit occupies an area of 190 µm2, consumes a power of 3.2 mW and shows a maximum response time of 1.6 s at a light intensity of 20,000 lux. The proposed ALR circuit also has a pixel loss rate of 0.3%. The experimental results show that the ALR circuit leads to a sensor pixel (SP) being autonomously adjusted, depending on the light intensity.

ACS Style

Hosung Kang; Hojong Choi; Jungsuk Kim. Ambient Light Rejection Integrated Circuit for Autonomous Adaptation on a Sub-Retinal Prosthetic System. Sensors 2021, 21, 5638 .

AMA Style

Hosung Kang, Hojong Choi, Jungsuk Kim. Ambient Light Rejection Integrated Circuit for Autonomous Adaptation on a Sub-Retinal Prosthetic System. Sensors. 2021; 21 (16):5638.

Chicago/Turabian Style

Hosung Kang; Hojong Choi; Jungsuk Kim. 2021. "Ambient Light Rejection Integrated Circuit for Autonomous Adaptation on a Sub-Retinal Prosthetic System." Sensors 21, no. 16: 5638.

Communication
Published: 21 August 2021 in Electronics
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On-chip systems are challenging owing to the limited size of the components, such as the capacitor bank in the rectifier. With a small on-chip capacitor, the output voltage of the rectifier might ring if the circuit experiences significant changes in current. The reference circuit is the first block after the rectifier, and the entire system relies on its robustness. A fully integrated dual-voltage reference circuit for bio-implantable applications is presented. The proposed circuit utilizes nonlinear current compensation techniques that significantly decrease supply variations and reject high-supply ripples for various frequencies. The reference circuit was verified using a 0.35 µm complementary metal-oxide semiconductor (CMOS) process. Maximum PSRR values of −112 dB and −128 dB were obtained. With a supply range from 2.8 to 12 V, the proposed design achieves 0.916 and 1.5 mV/V line regulation for the positive and negative reference circuits, respectively.

ACS Style

Ruhaifi Bin Abdullah Zawawi; Hojong Choi; Jungsuk Kim. High PSRR Wide Supply Range Dual-Voltage Reference Circuit for Bio-Implantable Applications. Electronics 2021, 10, 2024 .

AMA Style

Ruhaifi Bin Abdullah Zawawi, Hojong Choi, Jungsuk Kim. High PSRR Wide Supply Range Dual-Voltage Reference Circuit for Bio-Implantable Applications. Electronics. 2021; 10 (16):2024.

Chicago/Turabian Style

Ruhaifi Bin Abdullah Zawawi; Hojong Choi; Jungsuk Kim. 2021. "High PSRR Wide Supply Range Dual-Voltage Reference Circuit for Bio-Implantable Applications." Electronics 10, no. 16: 2024.

Journal article
Published: 21 July 2021 in Sensors
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As technology evolves, more components are integrated into printed circuit boards (PCBs) and the PCB layout increases. Because small defects on signal trace can cause significant damage to the system, PCB surface inspection is one of the most important quality control processes. Owing to the limitations of manual inspection, significant efforts have been made to automate the inspection by utilizing high resolution CCD or CMOS sensors. Despite the advanced sensor technology, setting the pass/fail criteria based on small failure samples has always been challenging in traditional machine vision approaches. To overcome these problems, we propose an advanced PCB inspection system based on a skip-connected convolutional autoencoder. The deep autoencoder model was trained to decode the original non-defect images from the defect images. The decoded images were then compared with the input image to identify the defect location. To overcome the small and imbalanced dataset in the early manufacturing stage, we applied appropriate image augmentation to improve the model training performance. The experimental results reveal that a simple unsupervised autoencoder model delivers promising performance, with a detection rate of up to 98% and a false pass rate below 1.7% for the test data, containing 3900 defect and non-defect images.

ACS Style

Jungsuk Kim; Jungbeom Ko; Hojong Choi; Hyunchul Kim. Printed Circuit Board Defect Detection Using Deep Learning via A Skip-Connected Convolutional Autoencoder. Sensors 2021, 21, 4968 .

AMA Style

Jungsuk Kim, Jungbeom Ko, Hojong Choi, Hyunchul Kim. Printed Circuit Board Defect Detection Using Deep Learning via A Skip-Connected Convolutional Autoencoder. Sensors. 2021; 21 (15):4968.

Chicago/Turabian Style

Jungsuk Kim; Jungbeom Ko; Hojong Choi; Hyunchul Kim. 2021. "Printed Circuit Board Defect Detection Using Deep Learning via A Skip-Connected Convolutional Autoencoder." Sensors 21, no. 15: 4968.

Journal article
Published: 04 July 2021 in Applied Sciences
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Recently released mobile phone cameras are capable of photographing objects at a fairly close distance. In addition, the field angle from the camera has increased. To measure the resolution of a mobile phone camera, the target must be photographed. To measure the resolution according to the object distance change from a mobile phone camera with a wide field angle, the target size must be large, whereas the target position must be moved. However, the target size cannot be changed. A virtual object for the target was created using a collimator. Moving a part of the lens group constituting the collimator also changes the virtual object distance. If the amount of change in the virtual object distance is large, the resolution of the collimator may also change. Therefore, a collimator that maintains the resolution even when the distance of the virtual object changes is designed as a floating type in which two lens groups move. Therefore, we propose a new floating collimator optical system that can inspect the resolution of mobile phone cameras from infinity to a close range to compensate for aberrations caused by object distance changes.

ACS Style

Seonkoo Chee; Jaemyung Ryu; Hojong Choi. New Optical Design Method of Floating Type Collimator for Microscopic Camera Inspection. Applied Sciences 2021, 11, 6203 .

AMA Style

Seonkoo Chee, Jaemyung Ryu, Hojong Choi. New Optical Design Method of Floating Type Collimator for Microscopic Camera Inspection. Applied Sciences. 2021; 11 (13):6203.

Chicago/Turabian Style

Seonkoo Chee; Jaemyung Ryu; Hojong Choi. 2021. "New Optical Design Method of Floating Type Collimator for Microscopic Camera Inspection." Applied Sciences 11, no. 13: 6203.

Journal article
Published: 15 April 2021 in Sensors
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To obtain a high-quality signal from an ultrasound system through the transmitter, it is necessary to achieve an appropriate operating point of the power amplifier in the ultrasonic transmitter by applying high static bias voltage. However, the power amplifier needs to be operated at low bias voltage, because a power amplifier operating at high bias voltage may consume a large amount of power and increase the temperature of the active devices, worsening the signal characteristics of the ultrasound systems. Therefore, we propose a new method of increasing the bias voltage for a specific period to solve this problem by reducing the output signal distortion of the power amplifier and decreasing the load on the active device. To compare the performance of the proposed method, we measured and compared the signals of the amplifier with the proposed technique and the amplifier only. Notably, improvement was achieved with 11.1% of the power added efficiency and 3.23% of the total harmonic distortion (THD). Additionally, the echo signal generated by the ultrasonic transducer was improved by 2.73 dB of amplitude and 0.028% of THD under the conditions of an input signal of 10 mW. Therefore, the proposed method could be useful for improving ultrasonic transmitter performance using the developed technique.

ACS Style

KyeongJin Kim; Hojong Choi. A New Approach to Power Efficiency Improvement of Ultrasonic Transmitters via a Dynamic Bias Technique. Sensors 2021, 21, 2795 .

AMA Style

KyeongJin Kim, Hojong Choi. A New Approach to Power Efficiency Improvement of Ultrasonic Transmitters via a Dynamic Bias Technique. Sensors. 2021; 21 (8):2795.

Chicago/Turabian Style

KyeongJin Kim; Hojong Choi. 2021. "A New Approach to Power Efficiency Improvement of Ultrasonic Transmitters via a Dynamic Bias Technique." Sensors 21, no. 8: 2795.

Journal article
Published: 08 April 2021 in Applied Sciences
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The resolution performance of mobile phone camera optics was previously checked only near an infinite point. However, near-field performance is required because of reduced camera pixel sizes. Traditional optics are measured using a resolution chart located at a hyperfocal distance, which can only measure the resolution at a specific distance but not at close distances. We designed a new collimator system that can change the virtual image of the resolution chart from infinity to a short distance. Hence, some lenses inside the collimator systems must be moved. Currently, if the focusing lens is moved, chromatic aberration and field curvature occur. Additional lenses are required to correct this problem. However, the added lens must not change the characteristics of the proposed collimator. Therefore, an equivalent-lens conversion method was designed to maintain the first-order and Seidel aberrations. The collimator system proposed in this study does not move or change the resolution chart.

ACS Style

Hojong Choi; Se-Woon Choe; Jaemyung Ryu. Optical Design of a Novel Collimator System with a Variable Virtual-Object Distance for an Inspection Instrument of Mobile Phone Camera Optics. Applied Sciences 2021, 11, 3350 .

AMA Style

Hojong Choi, Se-Woon Choe, Jaemyung Ryu. Optical Design of a Novel Collimator System with a Variable Virtual-Object Distance for an Inspection Instrument of Mobile Phone Camera Optics. Applied Sciences. 2021; 11 (8):3350.

Chicago/Turabian Style

Hojong Choi; Se-Woon Choe; Jaemyung Ryu. 2021. "Optical Design of a Novel Collimator System with a Variable Virtual-Object Distance for an Inspection Instrument of Mobile Phone Camera Optics." Applied Sciences 11, no. 8: 3350.

Research article
Published: 29 March 2021 in PLOS ONE
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This paper presents a novel amplifier that satisfies both low distortion and high efficiency for high-frequency wireless ultrasound systems with limited battery life and size. While increasing the amplifier efficiency helps to address the problems for wireless ultrasound systems, it can cause signal distortion owing to harmonic components. Therefore, a new type of class F amplifier is designed to achieve high efficiency and low distortion. In the amplifier, the resonant circuit at each stage controls the harmonic components to reduce distortion and improve efficiency. Transformers with a large shunt resistor are also helpful to reduce the remaining noise in the input signal. The proposed class F amplifier is tested using simulations, and the voltage and current waveforms are analyzed to achieve correct operation with adequate efficiency and distortion. The measured performance of the class F amplifier has a gain of 23.2 dB and a power added efficiency (PAE) of 88.9% at 25 MHz. The measured DC current is 121 mA with a variance of less than 1% when the PA is operating. We measured the received echo signal through the pulse-echo response using a 25-MHz transducer owing to the compatibility of the designed class F amplifier with high- frequency transducers. The measured total harmonic distortion (THD) of the echo signal was obtained as 4.5% with a slightly low ring-down. The results show that the low THD and high PAE of the new high-efficiency and high-voltage amplifier may increase battery life and reduce the cooling fan size, thus providing a suitable environment for high-frequency wireless ultrasound systems.

ACS Style

KyeongJin Kim; Hojong Choi. High-efficiency high-voltage class F amplifier for high-frequency wireless ultrasound systems. PLOS ONE 2021, 16, e0249034 .

AMA Style

KyeongJin Kim, Hojong Choi. High-efficiency high-voltage class F amplifier for high-frequency wireless ultrasound systems. PLOS ONE. 2021; 16 (3):e0249034.

Chicago/Turabian Style

KyeongJin Kim; Hojong Choi. 2021. "High-efficiency high-voltage class F amplifier for high-frequency wireless ultrasound systems." PLOS ONE 16, no. 3: e0249034.

Journal article
Published: 28 March 2021 in Sensors
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Ultrasound transducer devices have their own frequency ranges, depending on the applications and specifications, due to penetration depth, sensitivity, and image resolution. For imaging applications, in particular, the transducer devices are preferable to have a wide bandwidth due to the specific information generated by the tissue or blood vessel structures. To support these ultrasound transducer devices, ultrasound power amplifier hardware with a wide bandwidth can improve the transducer performance. Therefore, we developed a new bandwidth expander circuit using specially designed switching architectures to increase the power amplifier bandwidth. The measured bandwidth of the power amplifier with the help of the bandwidth expander circuit increased by 56.9%. In addition, the measured echo bandwidths of the 15-, 20-, and 25-MHz transducer devices were increased by 8.1%, 6.0%, and 9.8%, respectively, with the help of the designed bandwidth expander circuit. Therefore, the designed architecture could help an ultrasound system hardware with a wider bandwidth, thus supporting the use of different frequency ultrasound transducer devices with a single developed ultrasound system.

ACS Style

KyeongJin Kim; Hojong Choi. Novel Bandwidth Expander Supported Power Amplifier for Wideband Ultrasound Transducer Devices. Sensors 2021, 21, 2356 .

AMA Style

KyeongJin Kim, Hojong Choi. Novel Bandwidth Expander Supported Power Amplifier for Wideband Ultrasound Transducer Devices. Sensors. 2021; 21 (7):2356.

Chicago/Turabian Style

KyeongJin Kim; Hojong Choi. 2021. "Novel Bandwidth Expander Supported Power Amplifier for Wideband Ultrasound Transducer Devices." Sensors 21, no. 7: 2356.

Journal article
Published: 25 March 2021 in Technology and Health Care
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The pulse-echo test is used to evaluate the performance of ultrasonic probes before manufacturing ultrasonic systems. However, commercial alignment instruments are very large and use complex programs with long operation times. To develop a low-cost alignment instrument used in the pulse-echo test for evaluating the performance of various 2D and 3D ultrasonic probes. The developed alignment instrument can be aligned with the X, Y, Z, azimuth, elevation, and tilt axes with manual structure to support mounting fixtures that hold 2D and 3D ultrasonic probes. Each axis has a manual lever and is designed to have no movement when fixed. In particular, tilt and azimuth directions are designed to move more than 5∘ left and right. The probe mounted in the X, Y, and Z axes can move at above 50 mm. The probe mounted in the azimuth, elevation, and tilt axes can move more than 5∘ in the left and right directions. The pulse-echo test using commercial ultrasonic probes showed maximum error rate of less than 5%. Our developed alignment instrument can reduce costs by eliminating the need for shortening inspection times for probe manufacturers.

ACS Style

Jungsuk Kim; Kwang Soo Kim; Hojong Choi. Development of a low-cost six-axis alignment instrument for flexible 2D and 3D ultrasonic probes. Technology and Health Care 2021, 29, 77 -84.

AMA Style

Jungsuk Kim, Kwang Soo Kim, Hojong Choi. Development of a low-cost six-axis alignment instrument for flexible 2D and 3D ultrasonic probes. Technology and Health Care. 2021; 29 (Preprint):77-84.

Chicago/Turabian Style

Jungsuk Kim; Kwang Soo Kim; Hojong Choi. 2021. "Development of a low-cost six-axis alignment instrument for flexible 2D and 3D ultrasonic probes." Technology and Health Care 29, no. Preprint: 77-84.

Communication
Published: 04 February 2021 in Sensors
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We propose an integrated front-end data acquisition circuit for a hybrid ultrasound (US)-gamma probe. The proposed circuit consists of three main parts: (1) a preamplifier for the gamma probe, (2) a preprocessing analog circuit for the US, and (3) a digitally controlled analog switch. By exploiting the long idle time of the US system, an analog switch can be used to acquire data of both systems using a single output channel simultaneously. On the nuclear medicine (NM) gamma probe side, energy resolutions of 18.4% and 17.5% were acquired with the standalone system and with the proposed switching circuit, respectively, when irradiated with a Co-57 radiation source. Similarly, signal-to-noise ratios of 14.89 and 13.12 dB were achieved when US echo signals were acquired with the standalone system and with the proposed switching circuit, respectively. Lastly, a combined US-gamma probe was used to scan a glass target and a sealed radiation source placed in a water tank. The results confirmed that, by using a hybrid US-gamma probe system, it is possible to distinguish between the two objects and acquire structural information (ultrasound) alongside molecular information (gamma radiation source).

ACS Style

Muhammad Ullah; Yuseung Park; Gyeong Kim; Chanho Kim; Chansun Park; Hojong Choi; Jung-Yeol Yeom. Simultaneous Acquisition of Ultrasound and Gamma Signals with a Single-Channel Readout. Sensors 2021, 21, 1048 .

AMA Style

Muhammad Ullah, Yuseung Park, Gyeong Kim, Chanho Kim, Chansun Park, Hojong Choi, Jung-Yeol Yeom. Simultaneous Acquisition of Ultrasound and Gamma Signals with a Single-Channel Readout. Sensors. 2021; 21 (4):1048.

Chicago/Turabian Style

Muhammad Ullah; Yuseung Park; Gyeong Kim; Chanho Kim; Chansun Park; Hojong Choi; Jung-Yeol Yeom. 2021. "Simultaneous Acquisition of Ultrasound and Gamma Signals with a Single-Channel Readout." Sensors 21, no. 4: 1048.

Journal article
Published: 30 November 2020 in Electronics
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This paper presents a fully integrated voltage-reference circuit for implantable devices such as retinal implants. The recently developed retinal prostheses require a stable supply voltage to drive a high-density stimulator array. Accordingly, a voltage-reference circuit plays a critical role in generating a constant reference voltage, which is provided to a low-voltage-drop regulator (LDO), and filtering out the AC ripples in a power-supply rail after rectification. For this purpose, we use a beta-multiplier voltage-reference architecture to which a nonlinear current sink circuit is added, to improve the supply-independent performance drastically. The proposed reference circuit is fabricated using the standard 0.35 µm technology, along with an LDO that adopts an output ringing compensation circuit. The novel reference circuit generates a reference voltage of 1.37 V with a line regulation of 3.45 mV/V and maximum power-supply rejection ratio (PSRR) of −93 dB.

ACS Style

Ruhaifi Bin Abdullah Zawawi; Hojong Choi; Jungsuk Kim. High-PSRR Wide-Range Supply-Independent CMOS Voltage Reference for Retinal Prosthetic Systems. Electronics 2020, 9, 2028 .

AMA Style

Ruhaifi Bin Abdullah Zawawi, Hojong Choi, Jungsuk Kim. High-PSRR Wide-Range Supply-Independent CMOS Voltage Reference for Retinal Prosthetic Systems. Electronics. 2020; 9 (12):2028.

Chicago/Turabian Style

Ruhaifi Bin Abdullah Zawawi; Hojong Choi; Jungsuk Kim. 2020. "High-PSRR Wide-Range Supply-Independent CMOS Voltage Reference for Retinal Prosthetic Systems." Electronics 9, no. 12: 2028.

Journal article
Published: 09 November 2020 in Applied Sciences
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An off-axis system refers to an optical system in which the optical axis and the normal vector at the vertex of each surface do not match. An off-axis optical system can be applied in order to construct a thin and light optical system. In particular, the optical system used for a see-through head-mounted display (HMD) must be designed asymmetrically, with respect to the optical axis. Because the vision of a human is different for each individual, HMD requires focus adjustment. The effective focal length (EFL) of the optical system must be calculated to obtain the focus adjustment. However, the off-axis optical system cannot be calculated by conventional methods. In this study, the EFL was calculated by rotating the coordinates of the rays near the optical axis by the angle of reflection or refraction at the intersection of each surface, with the rays coinciding with the optical axis. The magnitude of movement of the micro-display for focus adjustment was obtained from the calculated EFL, for a see-through type HMD.

ACS Style

So Seo; Jae Ryu; Hojong Choi. Focus-Adjustable Head Mounted Display with Off-Axis System. Applied Sciences 2020, 10, 7931 .

AMA Style

So Seo, Jae Ryu, Hojong Choi. Focus-Adjustable Head Mounted Display with Off-Axis System. Applied Sciences. 2020; 10 (21):7931.

Chicago/Turabian Style

So Seo; Jae Ryu; Hojong Choi. 2020. "Focus-Adjustable Head Mounted Display with Off-Axis System." Applied Sciences 10, no. 21: 7931.

Journal article
Published: 02 November 2020 in Sensors
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Piezoelectric transducers are triggered by the output voltage signal of a transmit voltage amplifier (TVA). In mobile ultrasound instruments, the sensitivity of piezoelectric transducers is a critical parameter under limited power supply from portable batteries. Therefore, the enhancement of the output voltage amplitude of the amplifier under limited power supply could increase the sensitivity of the piezoelectric transducer. Several-stage TVAs are used to increase the voltage amplitude. However, inter-stage design issues between each TVA block may reduce the voltage amplitude and bandwidth because the electronic components of the amplifier are nonlinearly operated at the desired frequency ranges. To compensate for this effect, we propose a novel inter-stage output voltage amplitude improvement (OVAI) circuit integrated with a class-B TVA circuit. We performed fundamental A-mode pulse-echo tests using a 15-MHz immersion-type piezoelectric transducer to verify the design. The echo amplitude and bandwidth when using an inter-stage OVAI circuit integrated with a class-B TVA circuit (696 mVPP and 29.91%, respectively) were higher than those obtained when using only the class-B TVA circuit (576 mVPP and 24.21%, respectively). Therefore, the proposed OVAI circuit could be beneficial for increasing the output amplitude of the class-B TVA circuit for mobile ultrasound machines.

ACS Style

Kiheum You; Hojong Choi. Inter-Stage Output Voltage Amplitude Improvement Circuit Integrated with Class-B Transmit Voltage Amplifier for Mobile Ultrasound Machines. Sensors 2020, 20, 6244 .

AMA Style

Kiheum You, Hojong Choi. Inter-Stage Output Voltage Amplitude Improvement Circuit Integrated with Class-B Transmit Voltage Amplifier for Mobile Ultrasound Machines. Sensors. 2020; 20 (21):6244.

Chicago/Turabian Style

Kiheum You; Hojong Choi. 2020. "Inter-Stage Output Voltage Amplitude Improvement Circuit Integrated with Class-B Transmit Voltage Amplifier for Mobile Ultrasound Machines." Sensors 20, no. 21: 6244.

Journal article
Published: 21 September 2020 in Sensors
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Piezoelectric transducers are important devices that are triggered by amplifier circuits in mobile ultrasound systems. Therefore, amplifier performance is vital because it determines the acoustic piezoelectric transducer performances. Particularly, mobile ultrasound applications have strict battery performance and current consumption requirements; hence, amplifier devices should exhibit good efficiency because the direct current (DC) voltage in the battery are provided to the supply voltages of the amplifier, thus limiting the maximum DC drain voltages of the main transistors in the amplifier. The maximum DC drain voltages are related with maximum output power if the choke inductor in the amplifier is used. Therefore, a need to improve the amplifier performance of piezoelectric transducers exists for mobile ultrasound applications. In this study, a post-voltage-boost circuit-supported class-B amplifier used for mobile ultrasound applications was developed to increase the acoustic performance of piezoelectric transducers. The measured voltage of the post-voltage-boost circuit-supported class-B amplifier (62 VP-P) is higher than that of only a class-B amplifier (50 VP-P) at 15 MHz and 100 mVP-P input. By performing the pulse-echo measurement test, the echo signal with the post-voltage-boost circuit-supported class-B amplifier (10.39 mVP-P) was also noted to be higher than that with only a class-B amplifier (6.15 mVP-P). Therefore, this designed post-voltage-boost circuit can help improve the acoustic amplitude of piezoelectric transducers used for mobile ultrasound applications.

ACS Style

Jungsuk Kim; Kiheum You; Hojong Choi. Post-Voltage-Boost Circuit-Supported Single-Ended Class-B Amplifier for Piezoelectric Transducer Applications. Sensors 2020, 20, 5412 .

AMA Style

Jungsuk Kim, Kiheum You, Hojong Choi. Post-Voltage-Boost Circuit-Supported Single-Ended Class-B Amplifier for Piezoelectric Transducer Applications. Sensors. 2020; 20 (18):5412.

Chicago/Turabian Style

Jungsuk Kim; Kiheum You; Hojong Choi. 2020. "Post-Voltage-Boost Circuit-Supported Single-Ended Class-B Amplifier for Piezoelectric Transducer Applications." Sensors 20, no. 18: 5412.

Journal article
Published: 27 July 2020 in Sensors
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A wireless ultrasound surgical system (WUSS) with battery modules requires efficient power consumption with appropriate cutting effects during surgical operations. Effective cutting performances of the ultrasound transducer (UT) should be produced for ultrasound surgical knives for effective hemostasis performance and efficient dissection time. Therefore, we implemented a custom-made UT with piezoelectric material and re-poling process, which is applied to enhance the battery power consumption and output amplitude performances of the WUSS. After the re-poling process of the UT, the quality factor increased from 1231.1 to 2418 to minimize the unwanted heat generation. To support this UT, we also developed a custom-made generator with a transformer and developed 2nd harmonic termination circuit, control microcontroller with an advanced reduced instruction set computer machine (ARM) controller, and battery management system modules to produce effective WUSS performances. The generator with a matching circuit in the WUSS showed a peak-to-peak output voltage and current amplitude of 166 V and 1.12 A, respectively, at the resonant frequency. The performance with non-contact optical vibrators was also measured. In the experimental data, the developed WUSS reduced power consumption by 3.6% and increased the amplitude by 20% compared to those of the commercial WUSS. Therefore, the improved WUSS performances could be beneficial for hemostatic performance and dissection time during surgical operation because of the developed UT with a piezoelectric material and re-poling process.

ACS Style

Jungsuk Kim; Kiheum You; Sun-Ho Choe; Hojong Choi. Wireless Ultrasound Surgical System with Enhanced Power and Amplitude Performances. Sensors 2020, 20, 4165 .

AMA Style

Jungsuk Kim, Kiheum You, Sun-Ho Choe, Hojong Choi. Wireless Ultrasound Surgical System with Enhanced Power and Amplitude Performances. Sensors. 2020; 20 (15):4165.

Chicago/Turabian Style

Jungsuk Kim; Kiheum You; Sun-Ho Choe; Hojong Choi. 2020. "Wireless Ultrasound Surgical System with Enhanced Power and Amplitude Performances." Sensors 20, no. 15: 4165.

Journal article
Published: 10 June 2020 in Energies
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The robustness of the reference circuit in a wide range of supply voltages is crucial in implanted devices. Conventional reference circuits have demonstrated a weak performance over wide supply ranges. Channel-length modulation in the transistors causes the circuit to be sensitive to power supply variation. To solve this inherent problem, this paper proposes a new output-voltage-line-regulation controller circuit. When a variation occurs in the power supply, the controller promptly responds to the supply deviation and removes unwanted current in the output path of the reference circuit. The proposed circuit was implemented in a 0.35-μm SK Hynix CMOS standard process. The experimental results demonstrated that the proposed reference circuit could generate a reference voltage of 0.895 V under a power supply voltage of 3.3 V, line regulation of 1.85 mV/V in the supply range of 2.3 to 5 V, maximum power supply rejection ratio (PSRR) of −54 dB, and temperature coefficient of 11.9 ppm/°C in the temperature range of 25 to 100 °C.

ACS Style

Ruhaifi Bin Abdullah Zawawi; Wajahat H. Abbasi; Seung-Hwan Kim; Hojong Choi; Jungsuk Kim. Wide-Supply-Voltage-Range CMOS Bandgap Reference for In Vivo Wireless Power Telemetry. Energies 2020, 13, 2986 .

AMA Style

Ruhaifi Bin Abdullah Zawawi, Wajahat H. Abbasi, Seung-Hwan Kim, Hojong Choi, Jungsuk Kim. Wide-Supply-Voltage-Range CMOS Bandgap Reference for In Vivo Wireless Power Telemetry. Energies. 2020; 13 (11):2986.

Chicago/Turabian Style

Ruhaifi Bin Abdullah Zawawi; Wajahat H. Abbasi; Seung-Hwan Kim; Hojong Choi; Jungsuk Kim. 2020. "Wide-Supply-Voltage-Range CMOS Bandgap Reference for In Vivo Wireless Power Telemetry." Energies 13, no. 11: 2986.

Journal article
Published: 28 May 2020 in Sensors
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Our developed wire ultrasound surgical instrument comprises a bolt-clamped Langevin ultrasonic transducer (BLUT) fabricated by PMN-PZT single crystal material due to high mechanical quality factor and electromechanical coupling coefficient, a waveguide in the handheld instrument, and a generator instrument. To ensure high performance of wire ultrasound surgical instruments, the BLUT should vibrate at an accurate frequency because the BLUT’s frequency influences hemostasis and the effects of incisions on blood vessels and tissues. Therefore, we implemented a BLUT with a waveguide in the handheld instrument using a developed assembly jig process with impedance and network analyzers that can accurately control the compression force using a digital torque wrench. A generator instrument having a main control circuit with a low error rate, that is, an output frequency error rate within ±0.5% and an output voltage error rate within ±1.6%, was developed to generate the accurate frequency of the BLUT in the handheld instrument. In addition, a matching circuit between the BLUT and generator instrument with a network analyzer was developed to transfer displacement vibration efficiently from the handheld instrument to the end of the waveguide. Using the matching circuit, the measured S-parameter value of the generator instrument using a network analyzer was −24.3 dB at the resonant frequency. Thus, our proposed scheme can improve the vibration amplitude and accuracy of frequency control of the wire ultrasound surgical instrument due to developed PMN-PZT material and assembly jig process.

ACS Style

Jungsuk Kim; KyeongJin Kim; Sun-Ho Choe; Hojong Choi. Development of an Accurate Resonant Frequency Controlled Wire Ultrasound Surgical Instrument. Sensors 2020, 20, 3059 .

AMA Style

Jungsuk Kim, KyeongJin Kim, Sun-Ho Choe, Hojong Choi. Development of an Accurate Resonant Frequency Controlled Wire Ultrasound Surgical Instrument. Sensors. 2020; 20 (11):3059.

Chicago/Turabian Style

Jungsuk Kim; KyeongJin Kim; Sun-Ho Choe; Hojong Choi. 2020. "Development of an Accurate Resonant Frequency Controlled Wire Ultrasound Surgical Instrument." Sensors 20, no. 11: 3059.

Journal article
Published: 16 April 2020 in Sensors
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In ultrasonic systems, power amplifiers are one of the most important electronic components used to supply output voltages to ultrasonic devices. If ultrasonic devices have low sensitivity and limited maximum allowable voltages, it can be quite challenging to detect the echo signal in the ultrasonic system itself. Therefore, the class-J power amplifier, which can generate high output power with high efficiency, is proposed for such ultrasonic device applications. The class-J power amplifier developed has a power efficiency of 63.91% and a gain of 28.16 dB at 25 MHz and 13.52 dBm input. The pulse-echo measurement method was used to verify the performance of the electronic components used in the ultrasonic system. The echo signal appearing with the discharged high voltage signal was measured. The amplitude of the first echo signal in the measured echo signal spectrum was 4.4 V and the total-harmonic-distortion (THD), including the fundamental signal and the second harmonic, was 22.35%. The amplitude of the second echo signal was 1.08 V, and the THD, including the fundamental signal and the second harmonic, was 12.45%. These results confirm that a class-J power amplifier can supply a very high output echo signal to an ultrasonic device.

ACS Style

Kiheum You; Seung-Hwan Kim; Hojong Choi. A Class-J Power Amplifier Implementation for Ultrasound Device Applications. Sensors 2020, 20, 2273 .

AMA Style

Kiheum You, Seung-Hwan Kim, Hojong Choi. A Class-J Power Amplifier Implementation for Ultrasound Device Applications. Sensors. 2020; 20 (8):2273.

Chicago/Turabian Style

Kiheum You; Seung-Hwan Kim; Hojong Choi. 2020. "A Class-J Power Amplifier Implementation for Ultrasound Device Applications." Sensors 20, no. 8: 2273.

Journal article
Published: 14 April 2020 in Mathematics
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When the number of lens groups is large, the zoom locus becomes complicated and thus cannot be determined by analytical means. By the conventional calculation method, it is possible to calculate the zoom locus only when a specific lens group is fixed or the number of lens groups is small. To solve this problem, we employed the Padé approximation to find the locus of each group of zoom lenses as an analytic form of a rational function consisting of the ratio of polynomials, programmed in MATLAB. The Padé approximation is obtained from the initial data of the locus of each lens group. Subsequently, we verify that the obtained locus of lens groups satisfies the effective focal length (EFL) and the back focal length (BFL). Afterwards, the Padé approximation was applied again to confirm that the error of BFL is within the depth of focus for all zoom positions. In this way, the zoom locus for each lens group of the optical system with many moving lens groups was obtained as an analytical rational function. The practicality of this method was verified by application to a complicated zoom lens system with five or more lens groups using preset patents.

ACS Style

Kang Min Kim; Sun-Ho Choe; Jae-Myung Ryu; Hojong Choi. Computation of Analytical Zoom Locus Using Padé Approximation. Mathematics 2020, 8, 581 .

AMA Style

Kang Min Kim, Sun-Ho Choe, Jae-Myung Ryu, Hojong Choi. Computation of Analytical Zoom Locus Using Padé Approximation. Mathematics. 2020; 8 (4):581.

Chicago/Turabian Style

Kang Min Kim; Sun-Ho Choe; Jae-Myung Ryu; Hojong Choi. 2020. "Computation of Analytical Zoom Locus Using Padé Approximation." Mathematics 8, no. 4: 581.

Journal article
Published: 04 January 2020 in Sensors
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Wide bandwidth ultrasonic devices are a necessity in high-resolution ultrasonic systems. Therefore, constant output voltages need to be produced across the wide bandwidths of a power amplifier. We present the first design of a wide bandwidth class-S power amplifier for ultrasonic devices. The −6 dB bandwidth of the developed class-S power amplifier was measured at 125.07% at 20 MHz, thus, offering a wide bandwidth for ultrasonic devices. Pulse-echo measurement is a performance measurement method used to evaluate the performance of ultrasonic transducers, components, or systems. The pulse-echo signals were obtained using an ultrasonic transducer with designed power amplifiers. In the pulse-echo measurements, time and frequency analyses were conducted to evaluate the bandwidth flatness of the power amplifiers. The frequency range of the ultrasonic transducer was measured and compared when using the developed class-S and commercial class-A power amplifiers with the same output voltages. The class-S power amplifiers had a relatively flat bandwidth (109.7 mV at 17 MHz, 112.0 mV at 20 MHz, and 109.5 mV at 23 MHz). When the commercial class-A power amplifier was evaluated under the same conditions, an uneven bandwidth was recorded (110.6 mV at 17 MHz, 111.5 mV at 20 MHz, and 85.0 mV at 23 MHz). Thus, we demonstrated that the designed class-S power amplifiers could prove useful for ultrasonic devices with a wide frequency range.

ACS Style

Kiheum You; Hojong Choi. Wide Bandwidth Class-S Power Amplifiers for Ultrasonic Devices. Sensors 2020, 20, 290 .

AMA Style

Kiheum You, Hojong Choi. Wide Bandwidth Class-S Power Amplifiers for Ultrasonic Devices. Sensors. 2020; 20 (1):290.

Chicago/Turabian Style

Kiheum You; Hojong Choi. 2020. "Wide Bandwidth Class-S Power Amplifiers for Ultrasonic Devices." Sensors 20, no. 1: 290.