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A DC-DC converter, which tracks minimum power loss under various conditions, is presented in this paper. With this DC-DC converter, a new approach for optimum efficiency, which implements theoretical equations intactly at the circuit level, was adopted. This approach has high reliability against process variation. The concept of lossless soft-switching was also adopted in discontinuous-conduction-mode (DCM) operation. The proposed DC-DC converter has a maximum power efficiency of 91% at the switching frequency of 1 MHz. The proposed converter is able to maintain a maximum power efficiency of around 90% over the whole range of input voltage from 2.9 to 4.5 V and output voltage from $-$ 3.8 to $-$ 5.9 V. This chip is implemented in a 0.35 $\mu$ m BCD process and occupies an area of 2.1 $\times $ 1.4 mm $ ^{2}$ .

This paper presents a novel on-chip compensation scheme, the Time-Mode Miller Compensation (TMMC), for DC-DC converter in which the compensation components are integrated on-chip. Using this proposed scheme, the DC-DC converter is stably compensated and insensitive to process variations, with significantly small compensation components ( 1 pF and 80 kΩ in this work) consuming very small silicon area owing to the characteristic of the TMMC. The small compensation components make the chip size small, with 0.12 mm2 of core area (w/o power transistors) using 0.18 μm I/O process. This core size is as small as that of the digital DC-DC converters implemented with less than sub-50 nm process. The measurement result shows that the maximum power efficiency of 90.6% is obtained at the load current of 220 mA with the switching frequency of 1.15 MHz when the input and the output voltages are 3.3 V and 2 V, respectively.

This paper proposes a new control scheme of zeroth-order control (ZOC) for PWM DC-DC converters in which the pole frequencies of the control loop are no longer dependent on the values of the inductor, output capacitor, or the output load current. In the proposed scheme, the output voltage of the converter is regulated by a comparator. The main control loop of the converter regulates the inductor energy which is built up to an optimum value to be delivered to the output by means of the time interval between the rising edge of the main switch driving pulse and the comparator output pulse. A boost DC-DC converter with the proposed ZOC has been implemented and fabricated in a commercial 0.35 μm BCDMOS process. A maximum efficiency of 88% is achieved at a total output power of 480 mW with the switching frequency of 833 kHz when the input voltage and the output voltage are 3.7 V and 8 V, respectively. Over 85% efficiency is maintained for a wide range of the output load current from 40 mA to 300 mA.

While the demand for micro-energy harvesters (μEHs) is increasing (for seamless energy source in applications such as wireless sensor node), two major problems still obstruct versatile use of them. The first problem is the self-startup capability. Because many wireless sensor nodes are likely to be located where human-maintenance is difficult, starting them up manually can be as difficult as replacing the battery. Its realization has been difficult because μEHs must be able to turn itself on without any stored energy. Some previous works have reported such a function: some needed high voltage [1] or vibration [2] and one used a transformer as a starter [3]. The other problem is the maximum power point tracking (MPPT) capability. Because it is known that MPPT algorithms usually require considerable power consumption [4], using them in μEHs is impractical. This paper suggests a new boost converter architecture and MPPT control method which can bring μEH into practical use.