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Implantable Medical Devices (IMDs) have been developing in ways to be lighter and lower-power systems. In the view of such developments, the battery recharging capacity to ensure the stable operation of the system is essential. Wireless power transfer (WPT) was proposed as a solution to recharge the battery without complex metallic contacts. However, due to limitations such as threshold voltage of power switches and minimal input power of the multi-stage structure (Rectifier + Regulator/DC-DC converter) of conventional voltage-mode (VM) WPT, there are drawbacks of an input power range above a certain threshold level and limitations due to strict regulations on the human body. These issues make the design of the IMD battery charger much harder and prevent IMDs from being a more viable option for people-in-need. This paper introduces distinguishing characteristics of resonant current-mode (RCM) WPT technology to overcome the aforementioned issues. It also describes the basic theory, conventional circuits of VM/RCM, comparisons, and major challenges of RCM. Finally, advanced and efficiency-enhancing techniques of the-state-of-art works among the RCM topologies will be discussed to follow up the trend of RCM WPT.

Encapsulation of organic light-emitting diodes (OLEDs) is the only way to prevent degradation due to the penetration of moisture and oxygen. However, the upper encapsulation layer, located in the path through which light from the OLED passes, adversely affects light transmission. In this study, we calculated the optical transmittance by using admittance trajectory simulation and compared the data with actual Al2O3/TiO2 multilayer film processed by atomic layer deposition (ALD). By applying the simulated data on to actual encapsulation layer, we can observe the optical transmittance increase of up to 8% compared to the film of Al2O3/TiO2/Al2O3 structure. Over 90% of optical transmittance was achieved for all the visible wavelength ranges while maintaining water vapor transmission rate (WVTR) of the processed multilayer thin film as low as of 5 × 10−5 g/m2/day, which was measured using MOCON Aquatran 2.

This letter proposes a loop-free autocalibration technique for self-balancing of flying capacitors in a three-level dc–dc buck converter. The proposed converter utilizes a dual-path power stage with balancing switches that adaptively short flying capacitors at de-energizing phases. Thus, the dual-path three-level converter ensures that flying capacitor voltages are self-balanced at half the input voltage without using additional feedback calibration loops, leading to robust operation and competitive efficiencies. The prototype was fabricated in the 0.13- μ m CMOS BCD process and adopted two flying capacitors of 4.7 μ F each and an inductor of 10 μ H with a dc resistance of 128 mΩ. When an 8-V input was converted to a 3-V output voltage with a load current of 400 mA, the measured efficiency was 88.6% at 800 kHz switching while flying capacitors are automatically balanced.

This article proposes a bandgap reference (BGR) recursive low-dropout (LDO) regulator chip that achieves a high power supply rejection (PSR) in the low- to mid-frequency range. The presented LDO design enables the total PSR of LDO to be free from the finite ripple-rejection of the BGR circuit, resulting in low design complexity and low power consumption. To improve the PSR further, the gate buffer is modified to provide an additional ripple feedforward cancellation. The modified gate buffer also offers fast transient response and stable operation. Moreover, a light-load stabilizer loop is also suggested to provide high stability over all load conditions. A prototype chip able to supply up to 300 mA output current was implemented by 0.5- μ m 5-V CMOS devices. The PSR was measured to be –102 to –80 dB at frequencies from 100 Hz to 0.1 MHz, which is higher than that of prior LDOs with C OUT ≥ 1 μ F. The proposed LDO consumes only 50 μ A at a load current of 300 mA, and a peak current efficiency of 99.98% was achieved. The line and load regulations were measured as 0.003%/V and 0.28%/A, respectively. This chip shows a figure-of-merit of 11 ps in the transient response.

This article proposes a new boost converter topology called dual-path step-up dc–dc converter (DPUC). Unlike the conventional boost converter (CBC), the DPUC has a hybrid structure using one inductor and one flying capacitor to make dual current delivery paths. This allows continuous current delivering to the output, reducing both the dc level of the inductor current and the output voltage ripple. Therefore, the DPUC has higher efficiency and smaller output voltage ripple than those of the CBC. In addition, the feedforward characteristic of the flying capacitor can alleviate the effect of right-half-plane zero that degrades the transient response. Even with the inductor dc resistance of 200 mΩ, the DPUC achieves a high efficiency of 95.2% and a small ripple of up to 15 mV.

By simply adding a few components to a previous type-II voltage compensator, a single path inner feedback loop type-III voltage compensator is proposed. With the proposed compensator, a dc-dc converter achieves over / undershoot of 165/220 mV and 1% settling time of 8.5/8 μs when load current changes between 20 mA-1 A within 100 ns. Also, a seamless mode transition technique enables the converter to smoothly change the operation mode between continuous conduction mode and discontinuous conduction mode, without deterioration of the transient response. The measured efficiency reaches 95.3% and the size of integrated circuit is 0.46 mm 2 .

This article proposes a resonant voltage mode receiver (RVM-Rx) as a new topology of a wireless power receiver for battery charging. With a resonant capacitor interleaving scheme, an LC tank in the receiver can always be configured and isolated from the output, leading to optimal power transfer regardless of the operation phase. Thus, the power transfer efficiency is not sensitive to load conditions, such as battery voltage variation. In the RVM-Rx, a diode-based voltage peak time detection (VPTD) technique enables the system operation at a high resonant frequency. Also, a delay-based control scheme with a minimum diode time tracking loop (MDTL) and an optimum duty tracking loop (ODTL) leads to efficient power conversion by adaptively adjusting the operation state. The RVM-Rx prototype in a 0.18- $\mu \text{m}$ CMOS process can operate at a high resonant frequency of 13.56 MHz with a small ${\text{R}}_{X}$ coil (7 mm $\times $ 7 mm), while achieving a maximum receiver power efficiency of 67.8% for battery charging.

A power-and hardware-efficient radiation detection system is presented for mobile dosimeter. Thanks to the duty quantizer embedded in boost converter for driving radiation detector, the radiation signal can be converted to digital value without implementing seabsparate sensor interface circuits. The prototype IC is implemented using 0.18-µm BCD process, and achieves 0.217µA rms of integrated input referred noise enough low to measure radiation signal without using complex readout IC.

Although the capacity of a battery with a small form factor is extremely low, demand for long usage time of Internet of Things (IoT) products is increasing. Owing to this limitation of the battery, power management integrated circuits (PMICs) are used for extending the battery usage time with high efficiency. In particular, since IoT devices are mostly in the sleep mode in the idle state, PMICs should achieve high efficiency for ultralight loads in the sleep mode as well as for heavy loads in the active mode. In this paper, an accurate bang-bang zero-current detector (to prevent a reverse inductor current) and a triple-mode switched inductor-capacitor dc-dc buck converter with a reusable flying capacitor are presented, these techniques can maintain high efficiency over a wide load current range. The proposed buck converter was fabricated in a 0.18-&mu, m 1P4M CMOS process. A power conversion efficiency exceeding 85% was achieved in the load range of 100 &micro, A to 300 mA.

This paper presents a $1.7 \times 4.1 \times 2$ mm3 pH sensor that is a fully integrated, stand-alone and implantable system. Instead of a bulky cm size Ag/AgCl electrode, we use a mm-size integrated platinum electrode, and differential sensing using ISFET and REFET pair to compensate for unstable fluid potential. We also propose a drift compensation technique in which the leakage from the source and drain through the gate oxide is canceled, reducing drift $> 100 \times $.

A dual-path step-down converter (DPNC) is presented for achieving high power efficiency in mobile PMICs. The proposed DPNC supplies a load current $(I_{LOAD})$ via two parallel paths using a hybrid structure with one inductor and one flying capacitor, solving an intrinsic problem of conventional buck converter topology (CBT) which is a significant power loss from a large DCR of inductor $(R_{DCR})$. Therefore, DPNC not only achieves a high efficiency, but also reduces a heating problem. Additionally, DPNC can shrink a volume of PMIC set with a low manufacturing cost, by alleviating a $R_{DCR}$ specification of inductor. Although a $250\text{m}\Omega$ of large-Dcr inductor was used, this paper achieved a 96.2% of peak-efficiency, and the total loss from parasitic resistance of external components was reduced to up to 30% compared to CBT. Furthermore, DPNC achieved much higher efficiency not only in a wide $I_{LOAD}$ range, but also in a wide $V_{OUT}/V_{IN}$ range.

This paper presents a comparator-based Quasi-Digital LDO (QDLDO) for the negative supply which has an ultra-fast transient response for the PCRAM systems. Even under the sharp spike of a load current having a peak value of 80 mA with a short rising time of 2.5 ns, the QDLDO effectively minimized a voltage spike on the output voltage, reducing it to 150 mV within only 40 ns. With I/O transistors to withstand I/O voltage stress, this LDO achieved the bestFOM of 0.042 V/um2, among the other state-of-the-art LDOs fabricated in more advanced technologies.

Lithium-ion batteries are generally used in mobile devices, but the voltage range of the battery varies from 2.7 to 4.2V. To provide a mid-3V-range output from the battery, a converter capable of step-up/down-conversion is necessary. For this purpose, non-inverting buck-boost topologies with multimode control [1-3] have been widely used. However, they have limited efficiency slightly higher than 90%, which comes from the fact that a main current path always encompasses two switches. To increase the efficiency in the buck mode where the converter operates for most of the usage time, a flying capacitor buck-boost (FCBB) was proposed in [4]. Despite its high power efficiency, it requires large-size LDMOS to endure a large voltage range up to 8V at switching node, resulting in cost inefficiency. Since all these topologies have a common controller that covers both buck and boost modes of operation, compensator design is challenging. Moreover, a non-minimum-phase system of boost operation makes it hard to achieve a fast loop response. In this paper, we propose a step-up/down DC-DC converter based on buck operation only over the whole input voltage range, which greatly simplifies the controller design and consequently gives fast response. Furthermore, it achieves high efficiency because of the reduced effective resistance on the main current path.

DC-DC boost converters are widely used to increase the supply voltage in various applications, including LED drivers, energy harvesting, etc. [1-5]. The conventional boost converter (CBC) is shown in Fig. 27.5.1, where the switches S 1 and S 2 are turned on and off alternately at φ 1 and φ 2 , respectively, and the inductor current (I L ) is built up and delivered to the output. There are some critical issues in CBC because the output delivery current (I S ) is not continuous. As a result, the I L can be much larger than the load current (I LOAD ) as φ 1 becomes longer. Since a bulky-size inductor having a low parasitic DC resistance (R dcr ) is not usable for mobile applications with a strictly limited space, this large I L results in significant conduction loss in the large R DCR of a small-size inductor. Another issue is that the discontinuous I S in φ 2 causes large voltage ripple (AV OUT ) at the output. Moreover, switching spike voltages can cause over-voltage stress on the loading block due to large di/dt of I S combined with parasitic inductances of the GND path.

Wireless power transfer (WPT) has been widely adopted in various applications, such as biomedical implants and wireless sensors. A conventional voltage-mode receiver (VM-RX) uses a rectifier or a doubler for AC-DC conversion [1,2]. This requires a sufficiently large input power (P, N ) inducing a large voltage (V AC ) in the LC tank of the receiver (RX) due to the limited voltage conversion efficiency. A subordinate DC-DC converter is also required for voltage regulation or battery charging, which reduces the overall power-conversion efficiency (PCE) due to the 2-stage structure. To overcome these limitations, the resonant current-mode receiver (RCM-RX) has been proposed for direct battery charging [3] and voltage regulation [4,5]. The RCM-RX has two operation phases: a resonance phase (PH re ) that accumulates energy in the LC tank during optimal resonant cycles (N OPT ) to track the maximum efficiency [3], and a charging phase (PH ch ) that delivers the energy of the LC tank to the output, when the resonant current (I AC ) is at its peak. However, the RCM-RX typically operates at low resonant frequency f RESO (50kHz to 1MHz) because it is challenging to accurately detect the peak timing of I AC due to the intrinsic delay and offset of the comparator used in the peak timing detector. Operating at low f RESO causes the coil size to increase, making a burden on a size-constrained implant. In addition, the RCM-RX has a LC-tank resonance-loss interval PH ch , which hinders optimal power transfer from the transmitter (TX) to the RX because the reactive impedance is not cancelled out but appears on the TX side. Because the LC tank and the output are not isolated during PH ch , the power-transfer efficiency (PTE) can also be affected by load variation, such as the battery-voltage (V BAT ) variation. These problems become worse as N OPT is reduced to lower number.

This paper presents a high SNR self-capacitance sensing 3D hover sensor that does not use panel offset cancelation blocks. Not only reducing noise components, but increasing the signal components together, this paper achieved a high SNR performance while consuming very low power and die-area. Thanks to the proposed separated structure between driving and sensing circuits of the self-capacitance sensing scheme (SCSS), the signal components are increased without using high-voltage MOS sensing amplifiers which consume big die-area and power and badly degrade SNR. In addition, since a huge panel offset problem in SCSS is solved exploiting the panel's natural characteristics, other costly resources are not required. Furthermore, display noise and parasitic capacitance mismatch errors are compressed. We demonstrate a 39dB SNR at a 1cm hover point under 240Hz scan rate condition with noise experiments, while consuming 183uW/electrode and 0.73mm2/sensor, which are the power per electrode and the die-area per sensor, respectively.

The number of mobile device users increases every year. Each mobile device is usually equipped with a Li-ion battery having voltage that varies from a minimum of 2.7V to a maximum of 4.2V. Therefore, as the battery voltage decreases with time, a DC-DC converter is required for a regulated supply lower or higher than the battery voltage. A simple buck converter is not suited for this case, since step-up conversion is not available [1]. Instead, a non-inverting buck-boost converter can be a solution over the entire range of the battery voltage [1–4]. Many research studies related to buck-boost converters operated on Li-ion batteries set the target output voltage at around 3.4V [3,4]. Since Li-ion batteries have a wide plateau from 3.6V to 3.8V and a small energy storage below the plateau, DC-DC converters are generally operated on step-down mode at most of the battery voltage range, as shown in Fig. 10.4.1 top. Notwithstanding, step-up conversion is also required for extracting the energy below the plateau even if it is a small amount in the battery. Therefore, in DC-DC converters, it is critical to maintain high efficiency over the whole range of the battery voltage when it operates on both step-down and step-up modes to prolong the battery usage effectively. However, if the conventional buck-boost topology of Fig. 10.4.1 bottom-left is used for step-up and step-down purposes, there are always two switches (S 1 and S 3 ) conducting in the main current path through the inductor. Thus, the switches become large in size to minimize the conduction loss. As the switching loss also increases when the switch size is larger, the efficiency of this structure is usually lower than that of the simple buck (or boost) converter [1]. In this respect, this paper proposes a topology named a flying-capacitor buck-boost (FCBB) converter suitable for such an application by obtaining both step-up and step-down operations with high efficiency throughout the whole range of the battery voltage.

This paper presents a reconfigurable SIMO system with 10-output dual-bus DC-DC converter having two buses for heavy and light load outputs, respectively. The converter controls the load condition for each bus to be well balanced. Under diversified load condition, a group allocator assigns each output to the corresponding bus properly depending on its load current. Due to such load balancing function, severe regulation issues which could occur under diversified load condition are resolved with output voltage ripples below 25mV, and over 81% efficiency is achieved under wide range of load (0–300mA).

The issues of a single-inductor multiple-output DC-DC converter were studied. Poor cross regulation, low efficiency, low current capability, and large ripple are the major disadvantages of the single-inductor multiple-output converter compared with a conventional DC-DC converter. Several studies to overcome these problems are introduced in this paper.

Reducing the number of large external components, especially inductors, is a very important issue for Power-Management ICs (PMICs). Single-Inductor Multiple-Output (SIMO) converters are excellent candidates to meet this requirement [1-3]. However, there are several issues with SIMO converters, such as cross regulation, instability and inefficiency at light load. Under normal load conditions, comparator-based controlled SIMO converters [1,2] show good cross regulation performance due to the fast response of the comparator. However, the switching loss remains constant and degrades light load efficiency due to the fixed switching frequency of output switches. The low-efficiency characteristic when any output is under light load condition is a critical issue that must be solved because a SIMO converter is very suitable for light load applications. In addition, the cross regulation issue appears again when any output is under no load because the output receives energy from the inductor every cycle despite the load condition. To solve these issues, a SIMO converter was previously reported to support Pulse Frequency Modulation (PFM) mode [3]. However, the mode change control method increases the complexity of the control loop, which makes it unsuitable for a multi-output SIMO converter. In this paper, an Error Based Controlled (EBC) SIMO converter is presented to resolve the problems raised above using load-dependent Adaptive Pulse Modulation (APM). A hybrid topology composed of a switching converter and a linear regulator is also presented to minimize the cross regulation issue. To highlight the advantages, a 10-output SIMO converter is designed.