Minimum Phase Margin Research Articles

A low‐power low‐dropout regulator with improved transient response and power supply rejection

SummaryA high‐precision fast‐settling low‐dropout (LDO) regulator has been presented in this paper. A novel frequency compensation scheme has been proposed to acquire wider bandwidth while sufficient stability is guaranteed for all loading conditions without using external compensation capacitors. Moreover, novel auxiliary circuits have been proposed to improve the slew rate and minimize the settling time. The new LDO has been designed in a standard 0.18‐μm CMOS process. Postlayout simulation results show that the LDO achieves 2.7‐ and 2.48‐MHz unity‐gain frequency for 100 and 0 mA of load current, respectively, while the minimum phase margin is 64°. The results also demonstrate that the worst‐case settling time is almost equal to 1.95 μs. It is shown that by using the new slew rate enhancement technique, the settling time has been reduced from 18 to 1.9 μs. The LDO consumes a quiescent current of 21.5 μA, and the power supply rejection is −46 dB at 10‐kHz offset, which makes the LDO capable of adequately suppressing input supply ripples. The large loop gain of the proposed circuit improves the accuracy of the LDO, and the load and line regulations are 0.1 mV/mA and 0.1 mV/V, respectively.

Adaptive fuzzy-based stability control and series impedance correction for the grid-tied inverter

The regenerative braking in the tram allows the energy to be returned to the power grid through a power inverter. Since the inverter location between the tram and the power grid is not fixed, resulting in a wide variety of impedance networks at grid coupling points, posing a severe threat to the stable operation of the grid-tied inverter (GTI). By independently changing the loop characteristics of the GTI, the adaptive fuzzy PI controller (AFPIC) can adjust according to different impedance network parameters. It is challenging to fulfill the stability margin requirements of GTI under high network impedance since the PI controller has phase lag characteristics. A correction method of series virtual impedance is proposed, which connects the inductive link in a series configuration with the inverter output impedance, correcting the inverter equivalent output impedance from resistance-capacitance to resistance-inductance and improving the system stability margin. Feedforward control is adopted to improve the system's gain in the low-frequency band. Finally, the specific series impedance parameters are obtained by determining the maximum network impedance and setting the minimum phase margin of 45°. The realization of virtual impedance is simulated by conversion to an equivalent control block diagram, and the effectiveness and feasibility of the proposed method are verified by simulation and a 1 kW experimental prototype.

Improved reversed nested miller frequency compensation techniques using flipped and folded flipped voltage follower with resistor for three stage amplifier

This paper presents three circuits to improve frequency compensation in three stage amplifier for large capacitive load of 100 pF. The first proposed circuit introduces Flipped Voltage Follower (FVF) in inner loop of Reversed Nested Miller Compensation (RNMC) to combat RHP zero whereas both second and third proposed circuits employ A Folded Flipped Voltage Follower (FFVF). The third proposed circuit uses an additional resistor in the outer compensation loop for double pole-zero cancellation. Further feed forward path has been used in all proposed circuits to improve the large signal response. The functionality is verified using TSMC 0.18 µm CMOS technology parameters in Tanner tool. The simulation results show maximum gain-bandwidth product (GBW) of 30 MHz, minimum phase margin (PM) of 60° and slew rate (SR) of 10 V/µS, and minimum common mode rejection ratio (CMRR) of 37.2 dB at unity gain frequency. The input-referred noise of the proposed circuits varies from 16.6 nV/Hz to 18.2 nV/Hzat unity gain frequency. Corner analysis is also included to show the robustness of the circuits.

Increasing the damping of oscillatory systems with an arbitrary number of time varying frequencies using fractional-order collocated feedback

This paper studies the active damping of the oscillations of lightly damped linear systems whose parameters are indeterminate or may change through time. Systems with an arbitrary number of vibration modes are considered. Systems described by partial differential equations, that yield an infinite number of vibration modes, can also be included. In the case of collocated feedback, i.e. the sensor is placed at the same location of the actuator, a simple fractional order differentiation or integration of the measured signal is proposed that provides an effective control: (1) it guarantees a minimum phase margin or damping of the closed-loop system at all vibration modes, (2) this feature is robustly achieved, i.e., it is attained for very large variations or uncertainties of the oscillation frequencies of the system and (3) it is robust to spillover effects, i.e., to the unstabilizing effects of the vibration modes neglected in the controller design (especially important in infinite dimensional systems). Moreover, the sensitivity of the gain crossover frequency to such variations is assessed. Finally, these results are applied to the position control of a single link flexible robot. Simulated results are provided.

Interaction Assessment and Stability Analysis of the MMC-Based VSC-HVDC Link

This paper investigates the dynamic behavior of a modular multi-level converter (MMC)-based HVDC link. An overall state-space model is developed to identify the system critical modes, considering the dynamics of the master MMC and slave MMC, their control systems, and the HVDC cable. Complementary to the state-space model, an impedance-based model is also derived to obtain the minimum phase margin (PM) of the system. In addition, a relative gain array (RGA) analysis is conducted to quantify the level of interactions among the control systems of master and slave MMCs and their impacts on stability. Finally, with the help of the results obtained from the system analysis (eigenvalue, phase margin, sensitivity, and RGA), the system dynamic performance is improved.

Overvoltage Protection Circuits for Ultrasonically Powered Implantable Microsystems.

This paper presents a novel overvoltage protection technique for ultrasonically powered microsystems. The proposed idea benefits from voltage-current characteristics of the piezoelectric harvesters, and limits the amplitude of the harvested signal by regulating the current consumption of the system. For this purpose, a low-area low-power overvoltage regulator is proposed, analyzed and simulated in transistor level in standard TSMC 0.18μm CMOS technology occupying a silicon area of 285μm2. Furthermore, to avoid unnecessary power consumption of the overvoltage regulator, it is proposed to take advantage of an ultrasonic burst detection block to deactivate the regulator in the absence of ultrasonic waves. According to our simulation results, the quiescent power consumption of the proposed circuit in the presence and absence of ultrasonic waves are 37 and 3μW respectively, and the minimum phase margin of the negative feedback loop is 68 degree.

Power flow management of triple active bridge for fuel cell applications

<p>The power conditioning circuits which are used in fuel cell systems should carefully be designed to prolong the life span of the system, for the reason of the dynamic nature, such that the unexpected and extreme changes in load decreases the life of the fuel cells. This paper presents the triple active bridge (TAB) and it’s average small signal modelling, which is used for design of the system controllers for stable operation. The extended symmetrical optimum method is used for realized the proportional integral (PI) controller, to control the output/Load voltage and power flow in the fuel cell/Source with a guaranteed minimum phase margin for the system with a variable process gain in addition to other accepted desired performances. This method ensures the maximum phase margin at a minimum required value at the desired gain crossover frequency with a compromise between system’s peak overshoot, rise time and settling time. This model and this approach helps in designing TAB suitable for healthy and uninterrupted fuel cell power generation systems as a part of a renewable /clean energy system. MATLAB/Simulink is used to simulate the proposed controllers with TAB.</p>

Fractional order PD controller design for non-monotonic phase systems

This paper presents a novel technique for the analytical design of the fractional order controller for non-monotonic phase systems. The PD controller is designed for non-monotonic system based on gain crossover frequency and phase margin specifications. The method provides a minimum phase margin in the desired bandwidth. The proposed method redefines the concept of phase margin for non-monotonic system with decreasing phase. Introduction of the fractional power parameters offers some advantage in terms of robust performance. For comparison, the proposed non-monotonic method and the conventional method are chosen for the same set of tuning constraints.

An Improved Analytical PID Controller Design for Non-Monotonic Phase LTI Systems

An improved technique of analytical design of proportional-integral-derivative (PID) controllers in frequency-domain for non-monotonically decreasing phase systems by means of gain crossover frequency and phase margin specifications is presented in this brief. The proposed method guarantees a minimum phase margin inside the desired bandwidth, assuring better performance to step response for the closed-loop system. In order to achieve this feature, it is necessary to redefine the concept of phase margin when the uncontrolled process presents a non-monotonically decreasing phase inside the bandwidth. Hence, the phase margin can still be used as a good robustness indicator and allows the Bode stability criterion to be used for monotonic minimum-phase or non-monotonic minimum-phase systems.

Converting a Three-Stage Pseudoclass-AB Amplifier to a True-Class-AB Amplifier

We convert a low-voltage low-transistor-count wide-swing multistage pseudoclass-AB amplifier proposed by Mita et al. to a true-class-AB amplifier. The conversion is made possible using gate-drain feedback to combine two inverting common- source amplifiers to form a single noninverting stage. Both the pseudoclassand true-class-AB amplifiers were fabricated in a 0.5-μm CMOS 2P3M process. They are designed to operate from ±1.25-V supplies at a nominal quiescent current of 175 μA and a minimum phase margin of 45° when driving capacitive loads from 1 to 200 pF and resistive loads from 500 Ω to 1 MΩ. The total com- pensation capacitance of the proposed class-AB amplifier is 12 pF, which is 50% less than the pseudoclass-AB amplifier. The simu- lated unity-gain frequency of the class-AB amplifier is 4.9 MHz at a load of 25 pF||1kΩ, which is 88% higher than that of the pseudoclass-AB amplifier. Experimental measurements show that the proposed amplifier has a maximum total bias current of 175 μA, as compared with 1.05 mA for the pseudoclass-AB am- plifier. Measured slew rates of the proposed amplifier are 2.7 and 3.3 V/μs, twice as much as those of its pseudoclass-AB counterpart.

Analysis of FLC with changing fuzzy variables in frequency domain

This paper discusses a simple method for analyzing FLC in frequency domain based on describing function. Since nonlinear characteristics of FLC make it difficult FLC analysis, it usually requires a big deal of trial-and-error procedures based on computer simulation. The proposed method is simple and easy to understand, because it is based on the Nyquist stability criterion used to analyze absolute and relative stability, phase and gain margin of a linear system. To linearize in frequency domain, a describing function for FLC is derived by using a piecewise linearization of the FLC response plot. This describing function is represented as a function of magnitude of input sinusoid and nonlinear parameters x1 and x2 which change consequence fuzzy variables and nonlinearity of FLC. The describing function is redefined without the magnitude of sinusoid input because maximum values of the describing function can explain the stability of the system. This redefined describing function is used to get minimum stability characteristic, an absolute stability, phase margin and gain margin, of FLC. Using this function, we can explicitly figure out various characteristic of FLC according to x1 and x2 in frequency domain. In this work, we suggest a minimum phase margin (MPM) and a minimum gain margin (MGM) for FLC which can be used to determine whether the system is stable or not and how stable it is. For simplicity, we use one-input FLC with three rules. For various nonlinear response of FLC, changing fuzzy variables of a consequence membership function is used. Simulation results show that these parameters are effective in analyzing FLC.

PID autotuning algorithm based on relay feedback

A PID autotuning algorithm based on relay feedback has the capability of exploring different points of the process frequency response before performing the actual tuning procedure. In addition, the algorithm minimises the amount of a prioriinformation required on the process; in fact, the user is only asked to specify the minimum phase margin required for the closed-loop system. Some experimental results, obtained by laboratory simulation, are also presented.

Operation of 3µm bubble serial loop devices designed on single level masking

An all-permalloy single mask level design for a serial loop circuit has been developed and successfully operated using 3 μm bubbles. The design of individual elements for a single level circuit such as generator, replicator and annihilator which were compatible with half-disk propagation patterns was successfully investigated and optimization of permalloy and SiO 2 spacer film thickness was achieved. The small capacity test chips fabricated provided 13-16 Oe window margins with circular drive field ranges of 40 to 50 Oe at 100 kHz. The critical stretching pulse phase margin for replication, which was the minimum phase margin for all functions was found to be 10 degrees. Details of design and characteristics are also discussed including operating margin dependence on frequency and temperature.