We present an active full-wave rectifier with offset-controlled high speed comparators in standard CMOS that provides high power conversion efficiency (PCE) in high frequency (HF) range for inductively powered devices. This rectifier provides much lower dropout voltage and far better PCE compared to the passive on-chip or off-chip rectifiers. The built-in offset-control functions in the comparators compensate for both turn-on and turn-off delays in the main rectifying switches, thus maximizing the forward current delivered to the load and minimizing the back current to improve the PCE. We have fabricated this active rectifier in a 0.5-μm 3M2P standard CMOS process, occupying 0.18 mm2 of chip area. With 3.8 V peak ac input at 13.56 MHz, the rectifier provides 3.12 V dc output to a 500 Ω load, resulting in the PCE of 80.2%, which is the highest measured at this frequency. In addition, overvoltage protection (OVP) as safety measure and built-in back telemetry capabilities have been incorporated in our design using detuning and load shift keying (LSK) techniques, respectively, and tested.

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An Integrated Power-Efficient Active Rectifier With Offset-Controlled High Speed Comparators for Inductively Powered Applications

A piezoelectric (PE) energy harvesting system with one-cycle maximum power point (MPP) sensing is presented. The one-cycle MPP sensing method uses a very small size sensing capacitor and it can make the transducer output voltage reach the open circuit voltage within one cycle. The proposed MPP sensing block can sense the open circuit voltage with a proposed peak detector and stores the MPP voltage using charge sharing blocks. The one-cycle MPP sensing approach simplifies the design of an MPP tracking algorithm and greatly reduces the tracking time. All control blocks are self-biased and choose the higher voltage between the input or output voltages of the switching converter as a supply voltage (V $_{DD}$ ). Therefore, a voltage multiplexer and a low-power ramp generator with V $_{DD}$ independence are also proposed to control the system without additional DC to DC converter. The entire system has been implemented in a 0.35 µm BCDMOS process. It operates at 90 kHz with a 10-mH inductor. The total power dissipation of the controller is 10 µW at a V $_{DD}$ of 2.7 V. The MPP tracking time is only 9.09 ms/V when the input voltage of the switching converter is changed from 3.4 V to 1.2 V.

23.7 Self-powered 30μW-to-10mW Piezoelectric energy-harvesting system with 9.09ms/V maximum power point tracking time

This paper presents a multi-MHz buck regulator for portable applications using an auto-selectable peak- and valley-current control (ASPVCC) scheme. The proposed ASPVCC scheme can enable the current-mode buck regulator to reduce the settling-time requirement of the current sensing by two times. In addition, the dynamically biased shunt feedback technique is employed to improve the sensing speed and the sensing accuracy of both the peak and valley current sensors. With both ASPVCC scheme and advanced current sensors, the buck regulator can thus operate at high switching frequencies with a wide range of duty ratios for reducing the required off-chip inductance. The proposed current-mode buck regulator was fabricated in a standard 0.35-μm CMOS process and occupies a small chip area of 0.54 mm2. Measurement results show that the buck regulator can deliver a maximum output current of 500 mA, operate at 5 MHz with a wide duty-ratio range of about 0.6, use a small-value off-chip inductor of 1 μH, and achieve the peak power efficiency of 91%.

A 5-MHz 91% Peak-Power-Efficiency Buck Regulator With Auto-Selectable Peak- and Valley-Current Control

A 100-MHz PWM fully integrated buck converter utilizing standard package bondwire as power inductor with enhanced light-load efficiency which occupies 2.25 mm2 in 0.13-μm CMOS is presented. Standard package bondwire instead of on-chip spiral metal or special spiral bondwire is implemented as power inductor to minimize the cost and the conduction loss of an integrated inductor. The accuracy requirement of bondwire inductance is relaxed by an extra discontinuous-conduction-mode (DCM) calibration loop, which solves the precise DCM operation issue of fully integrated converters and eliminates the reverse current-related loss, thus enabling the use of standard package bondwire inductor with various packaging techniques. Optimizations of the power transistors, the input decoupling capacitor (CI), and the controller are also presented to achieve an efficient and robust high-frequency design. With all three major power losses, conduction loss, switching loss, and reverse current related loss, optimized or eliminated, the efficiency is significantly improved. An efficiency of 74.8% is maintained at 10 mA, and a peak efficiency of 84.7% is measured at nominal operating conditions with a voltage conversion of 1.2 to 0.9 V. Converters with various bondwire inductances from 3 to 8.5 nH are measured to verify the reliability and compatibility of different packaging techniques.

An 84.7% Efficiency 100-MHz Package Bondwire-Based Fully Integrated Buck Converter With Precise DCM Operation and Enhanced Light-Load Efficiency

A novel single-inductor-dual-output (SIDO) boost regulator with sequential-control is presented. This control can handle large loads or unbalanced loads with minimized cross interference between channels. A constant-charge-auto-hopping (CCAH) control is also presented to further extend the power handling capacity of the regulator with a predictable system switching noise spectrum. The switching frequency of the converter can be automatically hopped between 1 MHz and 1 MHz/N where N = 2 to 7 according to the total loads and during load transient. To minimize cross-regulation during frequency hopping, the inductor peak current is set to a predefined value according to the switching frequency information from the frequency detection unit to deliver a constant charge per switching period to the unchanged outputs. The response of the transient output is also enhanced with this inductor peak current prediction method. A prototype has been fabricated with a 0.35 μm CMOS process to verify the effectiveness of the CCAH control. With 1.8 V-2.4 V input voltage, two regulated output voltages between 3.0 V and 3.6 V, with maximum 400 mA to 600 mA driving capability and maximum power efficiency of 91.6% is achieved at total output power of 1.15 W. Load transient measurements show that the worst-case cross-regulation is 0.033 mV/mA with a 300 mA load current change at output A and 0.0714 mV/mA with a 280 mA load current change at output B. No noticeable cross-regulation can be observed with a less than 200 mA load current change.

A Wide-Load-Range Constant-Charge-Auto-Hopping Control Single-Inductor-Dual-Output Boost Regulator With Minimized Cross-Regulation

A 0.9-V input discontinuous-conduction-mode (DCM) boost converter delivering 2.5-V and 100-mA output is presented. A novel low-voltage pulse-width modulator is proposed. The modulator can be directly powered from the 0.9-V input instead of using the 2.5-V output as in general modulator designs. Sophisticated low-voltage analog blocks, which normally consume a large amount of power and chip area, are not required in the modulator. The impact of output-voltage ripple and transient-induced output-voltage perturbation on the operation of analog blocks inside the modulator is eliminated. Boost converter start-up sequence is also greatly simplified. A CMOS-control rectifier (CCR) is also proposed to improve converter power efficiency. The CCR is used to replace the conventional rectifying switch to provide adaptive dead-time, which helps to minimize charge-sharing loss and body-diode conduction loss. Corresponding thermal stress on the rectifying switch is hence minimized. The CCR also enables the use of small off-chip inductor and capacitor at sub-MHz switching frequency to improve light-load efficiency. This converter has been implemented in a 0.35- mum CMOS process. It is designed to operate at ~ 667 kHz with a 1 mu H inductor and 4.7 mu F output capacitor to reduce both switching loss and form factor. Experimental results prove that the converter can be directly powered from 0.9-V input with ~ 85% efficiency at 100-mA output.

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T.Y. Man

Papers

A 0.9-V Input Discontinuous-Conduction-Mode Boost Converter With CMOS-Control Rectifier