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In this paper it is proposed and explored the use of the Dickson charge pump (CP) to amplify time-variant signals. The study has been carried out through a theoretical analysis that provides an in-depth comprehension of the behavioral equations and the main design metrics commonly used to evaluate the performance of amplifiers. Starting from the analytical models, we show the conditions upon which the CP can be modeled with an equivalent small signal circuit and can amplify a signal. Then, assuming the CP working in the widest operative conditions, small-signal, large-signal and noise analysis are carried out. The results have been validated by extensive simulations and measurements on a proof of concept using a 130 nm CMOS technology. [ABSTRACT FROM AUTHOR]

This paper presents a new family of conditioning circuits used in electrostatic kinetic energy harvesters (e-KEHs), generalizing a previously reported conditioning circuit known as the Bennet's doubler. The proposed topology implements a conditioning scheme described by a rectangular charge-voltage cycle (QV-cycle) of tunable aspect ratio. These circuits show an exponential increase of the converted energy over operation time if studied in the sole electrical domain. The QV-cycle's aspect ratio can be set to values that were previously inaccessible with other exponential conditioning circuits. After a brief intuitive presentation of the new topology, its operation is rigorously analyzed and its dynamics are quantitatively derived in the electrical domain. In particular, the aspect ratio of the rectangular QV-cycle describing the biasing scheme of the transducer is expressed as a function of the circuit's parameters. Practical considerations about the use of the reported conditioning circuits in actual e-KEHs are also presented. These include a discussion on the applications of the proposed conditioning, a description of the effects of electrical nonidealities, and a proposition of an energy extracting interface. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a fully-integrated reconfigurable charge pump in a 0.18- $\mu \text{m}$ CMOS process; this converter is applicable for self-powered Internet-of-Things applications. The proposed charge pump uses a two-dimensional frequency modulation technique, which combines both the pulse-frequency modulation (PFM) and pulse-skip modulation (PSM) techniques. The PFM technique adjusts the operating frequency of the converter according to the variations in the load current, and the PSM technique regulates the output voltage. The proposed two-dimensional frequency modulation technique can improve the overall power conversion efficiency and the response time of the converter under light load conditions. A photovoltaic cell was chosen as the input source of the proposed converter. To adapt to the variations in the output voltage of a photovoltaic cell under different light illumination intensities, we built a reconfigurable converter core with multiple power conversion ratios of 2, 2.5, and 3 for the regulated output voltage of 1.2 V when the input voltage ranged from 0.53 V to 0.7 V. Our measurement results prove that the proposed capacitive power converter could achieve a peak power conversion efficiency of 80.8%, and the efficiency was more than 70% for the load current that ranged from $10~\mu \text{A}$ to $620~\mu \text{A}$. [ABSTRACT FROM AUTHOR]

This paper employs a time-variant model to determine the exact small-signal loop transmission of second-order charge-pump phased-locked loops. The model predicts that a loop bandwidth of close to half the input frequency can be achieved. The large-signal behavior is also analyzed and two modes of oscillation are identified. The results are confirmed by means of circuit simulations. [ABSTRACT FROM PUBLISHER]

This paper presents an optically-powered wireless tag, integrating a charge pump (CP) and a low-power RF transmitter for batteryless Internet-of-Things (IoT) applications. The proposed charge pump with hysteresis regulation mechanism (HRM) powers the transmitter circuit using indoor light energy. The charge pump enables the transmitter whenever the output capacitor stores sufficient energy and guarantees a short period signal transmission. The proposed low-power transmitter contains the subharmonically injection-locked PLL and the capacitive coupling technique to achieve a large frequency multiplication ratio. The proposed batteryless wireless chip is fabricated in 0.18- $\mu \text{m}$ CMOS process. The measurement results demonstrate that the proposed charge pump provides a 1.1 to 1.3 V hysteresis regulated voltage under indoor light illumination larger than 300 lux. The charge pump achieves 84.1% peak efficiency and the communication distance of 3 meters is demonstrated while only consuming $248~\mu \text{W}$. [ABSTRACT FROM AUTHOR]

An inductive power converter for thermoelectric generator (TEG) is presented in this paper. A novel redundant inverter ring oscillator is proposed to self-oscillate in a very low supply voltage down to 45 mV. An additional self-start assist circuit with a differential clock booster and an exponential charge pump is implemented in the power converter to achieve lower self-start voltage. Boundary continuous-conduction mode, zero current switch (ZCS), and maximum power point tracking (MPPT) features have been incorporated into the power converter. Selective turn-ON dynamical-comparators have been used in ZCS and MPPT circuits to save power and achieve minimum operating supply voltage. Fabricated in 65-nm CMOS process, the chip can self-start at 210 mV. After self-start, only 7-mV input voltage is needed to sustain the power converter operation. With a TEG open circuit voltage of 80 mV and internal resistance of $5~\Omega $ , the chip can provide a maximum output power of 229~\mu \text{W} with end-to-end efficiency of 71.5%. [ABSTRACT FROM PUBLISHER]

This paper proposes charge pumps with improved power efficiency suitable for low-power on-chip applications. Undesired charge transfer, which has a direction opposite to that of the intended current flow, presents a significant source of power loss in charge pumps. The proposed charge pump circuit utilizes charge transfer switches with a complementary branch scheme to significantly reduce undesired charge transfer, thereby improving power efficiency and increasing output voltage effectively. An optimized gate control strategy is applied to further decrease the power loss caused by undesired charge transfer. Simulations of 8-stage charge pumps in a 0.13~\mu \textm standard CMOS technology show that for an input supply voltage of 1.2 V, the proposed charge pump circuit reaches a power efficiency of 58.72% with an output voltage of 7.45 V, when delivering 5-mA load current, and is able to maintain a power efficiency of around 50% and an output voltage of over 5 V as the load current increases to 10 mA. Compared with the other charge pump circuits, the simulation results demonstrate better performance of proposed charge pump circuits in terms of both voltage pumping gain and power efficiency. [ABSTRACT FROM AUTHOR]

Energy harvesting techniques provide solutions for powering battery-free circuits or even for charging storage elements such as batteries or super capacitors. In this paper a self-starting switched-capacitor approach based on three-stage charge pump that is appropriate to thermoelectric and photo-voltaic energy harvesting, is carried out in a 28 nm ultra-thin buried oxide (UTBB) fully-depleted silicon-on-insulator (FD-SOI) CMOS technology. By taking advantage of the FD-SOI substrate characteristics, the forward-body-biasing (FBB) technique is applied in order to improve switch conductances. In addition, a sizing exploration of standard N-type and flipped-well P-type devices operating as switches is advanced, in order to provide optimum balance between their conductances. Extensive simulation results validate the proper operation of the charge pump at a minimum input voltage of 150 mV, and show a maximum efficiency peak of 63.3% at an input voltage of 350 mV and load a current of 500 nA. [ABSTRACT FROM AUTHOR]

In this paper a fairly complete mathematical model of CP-PLL, which reliable enough to serve as a tool for credible analysis of dynamical properties of these circuits, is studied. We refine relevant mathematical definitions of the hold-in and pull-in ranges related to the local and global stability. Stability analysis of the steady state for the charge-pump phase locked loop is non-trivial: straight-forward linearization of available CP-PLL models may lead to incorrect conclusions, because the system is not smooth near the steady state and may experience overload. In this work necessary details for local stability analysis are presented and the hold-in range is computed. An upper estimate of the pull-in range is obtained via the analysis of limit cycles. The study provided an answer to Gardner’s conjecture on the similarity of transient responses of CP-PLL and equivalent classical PLL and to conjectures on the infinite pull-in range of CP-PLL with proportionally-integrating filter. [ABSTRACT FROM AUTHOR]

Flash memory is an important component in many embedded system-on-a-chip applications, which drives the need to generate high write/erase voltages in generic CMOS processes. In this paper, we present a regulated, high-voltage charge pump for erasing Flash memory and floating-gate transistors. This 0.069-mm2 charge pump was fabricated in a 0.35 \mu \text m standard CMOS process. While operating from a 2.5 V supply, the charge pump generates regulated voltages up to 16 V with a PSRR of 52 dB and an output impedance of 6.8 \textk\Omega . To reduce power consumption for use in battery-powered applications, this charge pump uses a variable-frequency regulation technique and a new circuit for minimizing short-circuit current in the clock-generation circuitry; the resulting charge pump is able to erase the charge on floating-gate transistors using only $1.45 \mu J$ . [ABSTRACT FROM AUTHOR]

This paper presents a systematic methodology for the co-design of matching network and rectifier of radio frequency (RF) harvesters that results in maximum power conversion efficiency (PCE) for a given available power. This method is based on our newly developed rectifier model capable of calculating the CMOS Dickson’s rectifier’s input/output voltages at a given input power developed for low/high input power regimes. The proposed model allows for the co-design of the matching network and the rectifier in a fraction of time that takes for the design of the RF energy harvester using previously developed models relying on the knowledge of rectifier’s input voltage levels where a computationally extensive iterative design procedure must be performed because of the interdependence of the rectifier’s input voltage, the input power, and the matching network’s and rectifier’s parameters. The proposed methodology is capable of accurately predicting matching network components’ sizes for both the lossless and lossy matching networks for a maximum power transfer. Utilizing the proposed methodology, the designers can produce efficiency contour plots for a given input power for finding the optimum matching network and rectifier’s parameters for maximum PCE. The model, simulation, and measurement results for different parameters and input power levels in a 130-nm process are in good agreement. [ABSTRACT FROM AUTHOR]

This paper presents a 60 mV input voltage start-up system for thermoelectric energy harvesting. A new process tolerant inverter cell is proposed, which is functional at supply voltages as low as 60 mV. Using the proposed unit cell, a ring oscillator has been implemented. The ring oscillator is followed by 40 charge-pump stages, an ultra-low-power level detector, and a boost converter. The energy harvesting system can generate an output voltage of 1 V and delivers a maximum power of $4.5~\mu \text{W}$ from a 60 mV supply. This system has been implemented in a standard $0.18~\mu \text{m}$ CMOS technology, uses neither zero-threshold voltage (normally-on) negative-channel metal-oxide semiconductor nor microelectromechanical systems switches and occupies 3.3 mm2. [ABSTRACT FROM AUTHOR]

In this paper, a novel thermoelectric energy harvesting system with a reconfigurable array of thermoelectric generators (TEGs), which requires neither an inductor nor a flying capacitor, is proposed. The proposed architecture can accomplish maximum power point tracking (MPPT) and voltage conversion simultaneously via the reconfiguration of the TEG array, and demonstrate significantly improved power conversion efficiency over the conventional switching converter and switched-capacitor architectures. Two systematical scaling approaches—powers-of-two scaling and maximum-factor scaling—are presented and analyzed to serve as the design guideline, catering for reconfigurable TEG arrays of different sizes. In order to optimize the chip area required, a custom-designed, multi-level hierarchy and systematically scalable switch array that requires a reasonable number of switches is also developed to enable the reconfiguration of the TEG array. The 16-node and 12-node versions of the proposed system have been implemented in a standard 0.35- \mu \textm CMOS process. Measurement results verify the analysis, and confirm that the proposed system can maintain a higher than 88.8% efficiency over a wide range of temperature gradients. [ABSTRACT FROM PUBLISHER]

Level crossing sampling (LCS) is a power-efficient analog-to-digital conversion scheme for spikelike signals that arise in many Internet of Things-enabled automotive and environmental monitoring applications. However, LCS scheme requires a dedicated time-to-digital converter with large dynamic range specifications. In this paper, we present a compressed LCS that exploits the signal sparsity in the time domain. At the compressed sampling stage, a continuous-time ternary encoding scheme converts the amplitude variations into a ternary timing signal that is captured in a digital random sampler. At the reconstruction stage, a low-complexity split-projection least squares (SPLSs) signal reconstruction algorithm is presented. The SPLS splits random projections and utilizes a standard least squares approach that exploits the ternary-valued amplitude distribution. The SPLS algorithm is hardware friendly, can be run in parallel, and incorporates a low-cost k-term approximation scheme for matrix inversion. The SPLS hardware is analyzed, designed, and implemented in FPGA, achieving the highest data throughput and the power efficiency compared with the prior arts. Simulations of the proposed sampler in an automotive collision warning system demonstrate that the proposed compressed LCS can be very power efficient and robust to wireless interference, while achieving an approximately eightfold data volume compression when compared with Nyquist sampling approaches. [ABSTRACT FROM PUBLISHER]

This paper presents experimental results from a system that comprises a fully autonomous energy harvester with a solar cell of 1 mm2 as energy transducer and a Power Management Unit (PMU) on the same silicon substrate, and an output voltage regulator. Both chips are implemented in standard $0.18~\mu \text{m}$ CMOS technology with total layout areas of 1.575 mm2 and 0.0126 mm2, respectively. The system also contains an off-the-shelf 3.2 mm $\times2.5$ mm $\times0.9$ mm supercapacitor working as an off-chip battery or energy reservoir between the PMU and the voltage regulator. Experimental results show that the fast energy recovery of the on-chip solar cell and PMU permits the system to replenish the supercapacitor with enough charge as to sustain Bluetooth Low Energy (BLE) communications even with input light powers of 510 nW. The whole system is able to self-start-up without external mechanisms at 340 nW. This work is the first step towards a self-supplied sensor node with processing and communication capabilities. The small form factor and ultra-low power consumption of the system components is in compliance with biomedical applications requirements. [ABSTRACT FROM AUTHOR]

This paper presents an inductor-less switched capacitor based energy harvester, which can simultaneously harvest from 2 energy sources (Solar + Piezo). The proposed harvester employs maximum power point tracking algorithm, by changing the conversion ratios of the charge pumps for piezo and solar sources, and output voltage control by varying the switching frequency. The proposed MPPT algorithm can match the input impedance of two sources simultaneously. Implemented in 65nm CMOS, the proposed harvester can generate a fixed output between 1.8 and 2.5 V output while delivering 35 $\mu \text{W}$ to 70 $\mu \text{W}$ power with a peak power conversion efficiency of 74.6%. [ABSTRACT FROM AUTHOR]

In this paper, a generic, low-noise, negative-voltage generator with wide tuning range and moderate driving capacity is presented. The highly integrated solution, incorporating a fully-integrated charge-pump and a regulator block, requires only one off-chip capacitor that can be shared with the supply decoupling capacitors. The fully integrated charge-pump operation is analyzed quantitatively, and a closed-form expression of its output impedance is derived. Powered from a single 3.3-V dc input, the output has a tuning range from −4.4 to +2.1 V for biasing applications, while the design supports a maximum load current of 250, 550, and $800~\mu \text{A}$ for the regulated output voltage at −3.0, −1.5, and 1.5 V, respectively. The measured steady-state ripple is under 3 mVPP, while the noise voltage at the charge-pump operating frequency harmonics is below 130 $\mu \text {V}_{\mathrm{ rms}}$ and the noise floor is under $5~\mu \text {V}_{\mathrm{ rms}}$. The design is also the application verified with a gallium nitride power amplifier, thus further confirming its low-noise performance. Implemented in CMOS 180-nm process, the prototype chip occupies an area of 0.55 mm2. [ABSTRACT FROM AUTHOR]

The design and analytical modeling of a high efficiency energy harvester comprising a passive voltage-boosting network (VBN) and a switching charge pump rectifier (CPR) is presented in this paper. To improve the power conversion efficiency (PCE), the VBN increases the voltage at the input of the CPR and provides control signals for switching. Unlike traditional Schottky and diode-connected MOS transistor rectifiers, the proposed orthogonally switching CPR (OS-CPR) comprises MOS transistors as voltage-controlled switches. Analytical models for the OS-CPR are developed and presented. Circuit-level optimization techniques are employed to reduce conduction and switching losses. Simulated in a 90 nm standard CMOS technology (IBM 9RF), a 5-stage 915 MHz OS-CPR achieves a dc voltage of 1.35 V and a PCE of 11.9% with a 1 M\Omega load at -18.2 dBm available input power (PS,AV). To show technology scalability of the design, the OS-CPR is also validated using AMS 0.18 \mum high-voltage (HV) CMOS technology. When benchmarked with traditional rectifiers, the OS-CPR (under similar conditions) achieves a higher PCE and a higher output dc voltage. The OS-CPR is easily scalable to operate over multiple sub-GHz ISM frequency bands. [ABSTRACT FROM PUBLISHER]

The charge pump phase locked loop (CP-PLL) is widely used subsystem in modern mixed-signal electronic systems that are utilized in digital and wireless applications such as clock generation, synchronization and frequency synthesis. In the classical mode, the combination of a current switched charge pump and a digital phase and frequency detector (CP-PFD) circuits produces an ideal pulse width modulated constant current during one sampling period, which permits a suitable transient performance. Nevertheless, many commercially used CP-PLL chips (e.g., 4046 family) have a voltage switched charge pump (VSCP) because the design of the constant voltage source is easier than the constant current generator and it is a low cost solution. However, the VSCP delivers a non-constant pump current, which varies during one sampling period related to the electrical load of the loop filter (LF). This effect results in a varying gain of the control system affecting significantly its tracking ability. Furthermore, due to its hybrid structure, the simulation of the CP-PLL at high frequencies is challenging and the analysis of its transient characteristics during its non-linear acquisition procedure is not easy. In this paper, a first ever exact and nonlinear model based on the phase equations of the second order voltage switched charge pump phase locked loop (VSCP-PLL) is established by using an event driven (ED) technique. This exact model is then simplified by using a step-wise quasi-constant current approximation during one sampling period to obtain the analytical phase equations. The derived ED-model is validated at transistor level simulations using 130 nm CMOS process. Furthermore, some typical nonlinear features of the VSCP-PLL are explored and the developed ED-models are compared with the quasi-time-continuous (QTC) theory. [ABSTRACT FROM PUBLISHER]

Capacitive kinetic energy harvesters (KEH) employ conditioning circuits which achieve a dynamic biasing of the transducer's variable capacitor. This paper, composed of two articles Part 1 and Part 2, proposes a unified theory describing electrical and electromechanical properties of an important and wide class of conditioning circuits: those implementing a rectangular charge-voltage cycle. The article Part 1 introduces a basic configuration of conditioning circuit implementing an ideal rectangular QV cycle, and discusses its known practical implementations: the Roundy charge pump with different flyback mechanisms, and configurations based on the Bennet's doubler. In Part 1, the analysis is done in the electrical domain, without accounting for electromechanical coupling, while in Part 2, the full electromechanical system is analyzed. An optimization approach common to all configurations is proposed. A comparison is made between different topologies and operation modes, based on the maximal energy converted in one cycle under similar electrical and mechanical conditions. The last section discusses practical implementation of circuits with smart and adaptive behavior, and presents experimental results obtained with state-of-the art MEMS capacitive KEH devices. [ABSTRACT FROM PUBLISHER]

This paper presents two circuit topologies of battery-less integrated boost oscillators suitable for kick-starting electronic systems in fully discharged states with ultra-low input voltages, in the context of energy harvesting applications based on thermoelectric generators, by coupling a piezoelectric transformer in a feedback loop. With respect to the prior work, the first presented solution is a double polarity circuit designed in a 0.18~\mu \textm CMOS technology able to boost ultra-low positive and negative voltages without using switching matrixes. The circuit exploits a CMOS inverter made up of low threshold transistors, and also includes a hysteretic voltage monitor consuming only ~15 nW to enable an external circuit. The minimum achieved positive and negative oscillation voltages are +15 and −8 mV, which to the best of the authors’ knowledge, are among the lowest start-up voltages achieved in literature up to now without using magnetic components. Moreover, the input impedance in the range of several \textk\Omega makes the presented solution suitable also for high impedances sources, such as rectennas. The second presented circuit, designed in a 0.32~\mu \textm CMOS technology, exploits an input stage based on depletion-mode MOSFETs in a common source stage configuration and achieves a maximum step ratio of ~60. [ABSTRACT FROM AUTHOR]

Previous research results showed that UHF passive CMOS RFID tags had difficulty to achieve sensitivity less than -20~dBm. This paper presents a dual-channel 15-bit UHF passive CMOS RFID tag prototype that can work at sensitivity lower than -20~dBm. The proposed tag chip harvests energy and backscatters uplink data at 866.4-MHz (for ETSI) or 925-MHz (for FCC) channel and receives downlink data at 433-MHz channel. Consequently, the downlink data transmission does not interrupt our tag from harvesting RF energy. To use the harvested energy efficiently, we design a tag chip that includes neither a regulator nor a VCO such that the harvested energy is completely used in receiving, processing, and backscattering data. Without a regulator, our tag uses as few active analog circuits as possible in the receiver front-end. Instead, our tag uses a novel digital circuit to decode the received data. Without a VCO, the design of our tag can extract the required clock signal from the downlink data. Measurement result shows that the sensitivity of the proposed passive tag chip can reach down to -21.2~dBm. Such result corresponds to a 19.6-m reader-to-tag distance under 36-dBm EIRP and 0.4-dBi tag antenna gain. The chip was fabricated in TSMC 0.18-\mum CMOS process. The die area is 0.958 mm \times 0.931mm. [ABSTRACT FROM AUTHOR]

In this paper a low-power switched-capacitor integrator based on a capacitive charge-pump (CP) is presented, and its practical effects are discussed. The CP integrator is employed as the first stage of a \Delta\Sigma ADC. The 0.13 \mum CMOS prototype of the CP based ADC achieves the same performance as a conventional ADC while consuming 66% lower OTA power in the front-end integrator. The CP based modulator realizes 87.8 dB SNDR, 89.2 dB SNR and 90 dB DR over a 10 kHz bandwidth with 148 \muW power consumption. The conventional ADC has similar performance but dissipates 241 \muW. The energy required per conversion-step for the CP based ADC (0.369 pJ/step) is almost 40% lower than that of the conventional ADC (0.607 pJ/step). [ABSTRACT FROM PUBLISHER]

This paper proposes a 2.7 Gb/s referenceless transceiver with weighted PFD for frequency detection of random signals. A single loop referenceless CDR is also proposed to overcome the disadvantages of a dual loop CDR. The ANSI 8b/10b encoder & decoder with the scrambler, the serializer & de-serializer, and the output driver with pre-emphasis are included in the proposed transceiver architecture for DisplayPort v1.1a. The jitter of the generated clock at the Tx PLL is 3.28 psrms at 2.7 Gb/s with 1.2 V supply. The eye opening of the transmitter output with 3 m cable is 0.54 UI. The measured jitter of the recovered clock at the CDR is 1.57 psrms, and BER is less than 10^-12. The receiver consumes 23 mW at 2.7 Gb/s with 1.2 V supply. The CDR core and transceiver occupy 0.07 mm^2 and 0.94 mm^2, respectively, in a 0.13 \mum 1P8M CMOS process. [ABSTRACT FROM AUTHOR]

This paper presents a 5-Gb/s dual-loop clock and data recovery (CDR) circuit with a compact quarter-rate linear phase detector (PD). The proposed PD not only reduces the complexity of the circuit structure but also employs an UP pulse-widening technique to circumvent the problem of existing narrow UP pulses. Meanwhile, it has the least number of output signals among all the other linear PDs with UP pulse-widening technique. It also provides a data recovery circuit to de-multiplex the input data with no systematic phase offset. An unbalanced charge pump (CP) is also proposed to compensate the unbalanced pulse-width of UP and DN pulses as well as the unequal number of signal between UP and DN pulses. A detailed propagation delay analysis and a set of equations to predict the characteristic curve of the proposed PD is given. In addition, a lock detector with hysteresis property is implemented to ensure proper switching of the loops. Fabricated in 0.18- μm CMOS technology, the circuit shows that the peak-to-peak jitter of the recovered clock is 30.4-ps and it consumes 71.9-mW from a 1.8 V supply. [ABSTRACT FROM PUBLISHER]

Supply noise affects the jitter performance of ring oscillator-based phase-locked loops (PLLs) significantly. While the focus of much of the prior art is on supply noise in oscillators, this paper illustrates that supply noise in other building blocks also contribute significantly to PLL output jitter. Analytical expressions for supply-noise sensitivities are derived for each of the circuit blocks used in the PLL and insight into the mechanism through which supply noise appears at the PLL output is provided. Efficient supply-regulation schemes that combine a split-tuned PLL architecture with an optimized low-dropout regulator to achieve better than -22~dB of worst case supply-noise sensitivity for the whole PLL are presented. Fabricated in a 0.18~\mum digital CMOS process, the prototype PLL occupies an area of 0.18~\mum and operates from a 1.8 V supply. At 1.5 GHz, the total power consumption is 3.3 mW, of which 0.54 mW is consumed in the regulators. The measured output peak-to-peak jitter is 33 ps and 41 ps with no supply noise and with a 100-mV amplitude supply noise tone injected at the worst case noise frequency, respectively. [ABSTRACT FROM PUBLISHER]