Stefano Marsili

Modeling, Control, and Implementation of DC–DC Converters for Variable Frequency Operation

In this paper, novel small-signal averaged models for dc-dc converters operating at variable switching frequency are derived. This is achieved by separately considering the on-time and the off-time of the switching period. The derivation is shown in detail for a synchronous buck converter and the model for a boost converter is also presented. The model for the buck converter is then used for the design of two digital feedback controllers, which exploit the additional insight in the converter dynamics. First, a digital multiloop PID controller is implemented, where the design is based on loop-shaping of the proposed frequency-domain transfer functions. And second, the design and the implementation of a digital LQG state-feedback controller, based on the proposed time-domain state-space model, is presented for the same converter topology. Experimental results are given for the digital multiloop PID controller integrated on an application-specified integrated circuit in a 0.13 μm CMOS technology, as well as for the state-feedback controller implemented on an FPGA. Tight output voltage regulation and an excellent dynamic performance is achieved, as the dynamics of the converter under variable frequency operation are considered during the design of both implementations.

A WiMedia/MBOA-Compliant CMOS RF Transceiver for UWB

A fully integrated WiMedia/MBOA-compliant RF transceiver for UWB data communication in the 3 to 5GHz band is presented. It is designed in a 0.13mum standard CMOS process with 1.5V single supply voltage. The NF is between 3.6 and 4.1dB over all 3 bands. On the TX side, the P1dB is 5dBm supporting an EVM of -28dB and up to -4dBm output power. A single-PLL LO generation is included

UWB Fast-Hopping Frequency Generation Based on Sub-Harmonic Injection Locking

Sub-harmonic injection locking is employed to generate the fast-hopping carriers required in UWB systems for WiMedia . A very small area 90-nm CMOS prototype synthesizes the frequencies of band group #6 with a hop time shorter than 4 ns . It occupies 0.074 mm2 and draws 30 mA from a 1.2 V supply. Phase noise at 8.71 GHz is -112 dBc/Hz at 1 MHz offset. The design is supported by a thorough analysis that emphasizes the tradeoffs in the parameters of the proposed system.

Fixed-frequency Pseudo Sliding Mode control for a Buck-Boost DC-DC converter in mobile applications: A comparison with a linear PID controller

Interest is apparently growing in the four-switch noninverting Buck-Boost converter, which can be effectively used as a power supply for mobile devices. A typical application is a dynamic power supply for third-generation (3G) Wideband Code Division Multiple Access (WCDMA) Power Amplifiers (PA). While several control strategies based on the linear control theory have been proposed recently, there is still room for investigation of nonlinear control techniques. In this paper, a fixed-frequency nonlinear controller based on the sliding mode theory is presented and compared to a classical linear Proportional-Integral-Derivative (PID) implementation. The main differences from the design perspective and in terms of performance are then pointed out and commented. The main advantages of the proposed technique generally include an improvement of the dynamic performance and increased energy efficiency of the conversion. Simulation results are provided in order to evaluate and compare the different control strategies.

5.8 A digitally assisted single-point-calibration CMOS bandgap voltage reference with a 3σ inaccuracy of ±0.08% for fuel-gauge applications

Accurate voltage references are key building blocks for almost all electronic systems. Specifically, fuel gauge applications benefit from very high precision references to allow for extremely precise measurement of battery voltage and current in order to provide an accurate measurement of the state of charge of the battery.

Battery State Estimation Using Mixed Kalman/Hinfinity, Adaptive Luenberger and Sliding Mode Observer

For electric vehicles, the improvement of the range of miles and with it the utilization of the available cell/battery capacity has become an important research focus in the community. For optimization of the same, an accurate knowledge of internal cell parameters like the state-of-charge (SoC) or the impedance is indispensable. Compared to the state-of-the-art, in this paper discrete-time Kalman and H∞ filtering based SoC estimation schemes - up to now applied to linear battery models - are applied to the nonlinear model of a Li-Ion battery. For that, a linearization method is proposed, which utilizes a prior knowledge about the predominant nonlinearities in the model together with a coarse SOC estimate to obtain a linear state estimation problem. Based on that, a mixed Kalman/H∞ filter-, a discrete-time sliding mode observer-, and an adaptive Luenberger based estimation scheme is furthermore investigated for the nonlinear battery model under test. The above-mentioned methods are compared to the state-of-the-art reduced order SoC observer and the Coulomb counting method. In order to compare the performance, an appropriate battery simulation framework is used, which includes measurement and modeling uncertainties. The evaluation is done with respect to the ability to reduce the impact of error sources present in realistic scenarios. For the simulated load current pattern, best results are achieved by the mixed Kalman/H∞ filtering approach, which achieves an average SoC estimation error of less than 1%.

Comparative study and improvement of battery open-circuit voltage estimation methods

Due to the steadily-increasing demands on more powerful electronic devices, an accumulators operating lifetime plays an essential role for the usability of battery-powered devices. To avoid an insufficient utilization of a cells energy and/or lifetime, a reliable and reasonably accurate knowledge of its internal parameters like the state-of-charge (SoC) is indispensable. The determination of the SoC is often directly related to the estimation of a batterys open-circuit voltage (OCV). In this work, various OCV estimation methods are compared with respect to their inherent accuracy. Additionally, the observability-Gramian-based OCV estimation method is extended to deal with expanded kinds of cell currents. Moreover, interpolation-based methodologies are presented which considerably reduce the average OCV estimation error over the entire SoC range, compared to state-of-the-art implementations.

Constant switching frequency techniques for sliding mode control in DC-DC converters

Sliding mode is a very effective control strategy for switch mode DC-DC converters. However, its widespread adoption has been hampered by some of the drawbacks inherent to this control technique. Among these, the most important is apparently the varying operating frequency, which can cause electromagnetic-interference (EMI) problems. This problem is particularly critical in portable devices (e.g. smartphones, e-readers) where it is highly desirable that the DC-DC converters operate at a constant switching frequency to avoid interferences with other parts of the system. Several methods have been proposed in previous literature to stabilize the operating frequency of sliding mode controllers. In this paper, some of the most promising techniques are evaluated and applied to a specific test-case, i.e. a Buck converter for a wireless system. A detailed model of the DC-DC converter has been developed in order to obtain realistic results. The system parameters have been chosen to reflect an actual commercial application.

Comparative study of linear and non-linear integrated control schemes applied to a Buck converter for mobile applications

Energy-efficient conversion of DC voltages is gaining more and more importance in low-power applications, especially in mobile and wireless systems. Several control techniques can be applied to achieve output regulation of a Buck DC-DC converter. In this paper a linear PID (proportional-integral-derivative) control loop, both in analog and digital domain, is derived and its performance is compared to a non-linear regulation loop based on the sliding-mode theory. A goal of this paper is to point out potential advantages and drawbacks of the different solutions. This exploration forms the starting point for the implementation of the most promising concepts in a 65 nm CMOS technology.

SystemC-AMS modeling and simulation of digitally controlled DC-DC converters

In this paper, an innovative method to model and simulate DC-DC converters with a digital or mixed-signal control loop is proposed using the SystemC-AMS hardware-description language. The proposed method was employed to model a specific test case, consisting of a Buck converter with a digital PID regulator. The reliability of the model was checked by comparing the results with MATLAB/Simulink simulations. The SystemC-AMS approach was found to be well suited to model the proposed system and very efficient from a computational point of view, since the simulation time can be strongly reduced with respect to other solutions (e.g. MATLAB/Simulink).