Nacer Abouchi

Single active element PID controllers

This paper presents a detailed overview of the circuits allowing the realization of PID controllers with single active element. We provide analysis of the circuits using the operational amplifier (OpAmp) and operational transconductance amplifiers (OTA). Based on these analyses, we present an alternative structure using the second generation current conveyer CCII. Compared to the classical solutions, presented controller exhibits improved features such as symmetrical transfers of feedback and reference paths. The paper is completed by the design equations and the example of design.

A 0.01%THD, 70dB PSRR Single Ended Class D using variable hysteresis control for headphone amplifiers

Switching audio amplifiers are widely used in HBridge topology thanks to their high efficiency; however low audio performances in single ended power stage topology is a strong weakness leading to not be used for headset applications. This paper explains the importance of efficient error correction in Single Ended Class-D audio amplifier. A hysteresis control for Class-D amplifier with a variable window is also presented. The analyses are verified by simulations and measurements. The proposed solution was fabricated in 0.13µm CMOS technology with an active area of 0.2mm2. It could be used in single ended output configuration fully compatible with common headset connectors. The proposed Class-D amplifier achieves a harmonic distortion of 0.01% and a power supply rejection of 70dB with a quite low static current consumption.

A phase-shift self-oscillating stereo class-D amplifier for battery-powered applications

This paper presents a highly efficient stereo audio amplifier, based on a self-oscillating modulator. This modulation scheme has been analyzed and shows to have a higher bandwidth and error correction than standard Pulse Width Modulation (PWM). A practical implementation in CMOS 0.25um technology has been done to validate our theoretical and simulation results, based on a modified PWM amplifier. Our amplifier demonstrated a Total Harmonic Distortion plus Noise (THD+N) as low as 0.007%, current consumption is 3.88mA at 3.6V (stereo) and the efficiency reaches 88% into 8Ohms. The integrated circuit measures 1.6×1.6mm and is able to work at supply voltages from 2.3V to 5.5V.

Wireless Sensors for Instrumented Machines: Propagation Study for Stationary Industrial Environments

Wireless sensor networks (WSN) are now being used in a growing number and variety of systems and applications. The present paper addresses the issue of wireless sensors operating in specific, possibly harsh propagation conditions in industrial environments employing instrumented machines. These environments are characterized by almost stationary propagation conditions and no mobility, as well as specific, often conductive, materials used. We use simulations to model a real scenario and separately analyse reflection, diffraction and absorption at different frequency bands. Our simulation results are confirmed by classical propagation theory. The results are then validated by measurements in a machine compartment. We draw a conclusion on potential frequencies to be used for wireless sensors applied to the control of instrumented machines.

A topological comparison of PWM and hysteresis controls in switching audio amplifiers

The switching audio amplifiers are widely used in various portable and consumer electronics because of their high efficiency, but suffer from low audio performances due to inherent nonlinearity. This problem can be limited with efficient feedback from the output power stage. The research community focuses now to the efficient error correction by feedback control systems. This paper proposes a theoretical and practical comparison between the PWM control and our proposed hysteresis solution. These topologies are widely used in a very wide range of applications. This work shows that the hysteresis solution offers both lower power consumption and higher audio performances for embedded audio application.

Zero-derivative method of analog controller design applied to step-down DC-DC converters

In this paper, we present new systematic method for the design of an analog PID controller, applied to the voltage-mode step-down (buck) DC/DC converters. The method relies on the specification of trajectory of the load transient response. Particularly, we are interested to design a controller limiting the voltage under/overshoot to its lowest possible value. It is shown that this lowest possible value is related to the serial resistance of the output LC filter capacitor. We present a mathematical analysis of the method which is based on average model of the converter. Obtained relationships allow simple using of the method with operational amplifier based controllers. The design is validated by measurements on circuits with integrated 0.25 μm CMOS power stage.

An integrated class D audio amplifier based on sliding mode control

Class D amplifiers are becoming the most feasible solution for embedded audio application. However, distortions due to the non-linear nature of switching stage are the main drawback for this amplifier topology. This paper discusses the design and implementation of high fidelity audio class D using sliding mode control scheme. This design method proves to be a cost effective solution for industrial circuit. Experimental IC results, using commercial 0.13 mum CMOS technology, verified the theoretical results: the efficiency is above 90%, THD is lower than 0.01% and PSRR is superior to 70 dB.

A high performance switching audio amplifier using sliding mode control

The switching audio amplifiers are widely used in various portable and consumer electronics due to their high efficiency, but suffers from low audio performances due to inherent nonlinearity. This paper presents an integrated class D audio amplifier with low consumption and high audio performances. It includes a power stage and an efficient control based on sliding mode technique. This monolithic class D amplifier is capable of delivering up to 1 W into 8 Omega load at less 0.01% THD from a 2.3 V power supply voltage in the high fidelity range (20 Hz-20 kHz). The power supply rejection is superior to 70 dB.

An review of fully digital audio class D amplifiers topologies

Class D Amplifiers are widely used in portable systems such as mobile phones to achieve high efficiency. This paper presents topologies of full digital class D amplifiers in order to remove the analog DAC in the amplification path. This approach increases the playback time of embedded system. In first session, open-loop digital class D and digital modulation are discussed. The characterization of an open-loop class D prototype, using a CMOS 130 nm ASIC and a FPGA, confirms the advantage of such systems to reach a long battery life. Then, solutions with closed-loop topologies are proposed to increase linearity and power supply rejection of digital class D. Simulation results of closed-loop topologies, showing an increased in sound quality, are presented as well.

High-performance simulator for digital audio class D amplifiers

A new transient analysis simulator for digital class D amplifiers, which significantly reduces the simulation time (more than ten-fold), and which provides an accurate and robust audio performance analysis, is presented in this study. This simulator, called a hybrid simulator, is of special interest because it provides a better compromise between time and accuracy when compared with previous work. This simulator consists in keeping the most representative states of the transient simulation to process an optimal simulation. The results obtained by this new technique are compared with standard transient simulations (Eldo) and with experimental measurements. The circuit under test has been designed on 0.13 m CMOS technology and, an FPGA is used for digital modulator implementation.