Gain Control Loop Research Articles

Force to Rebalance Control of HRG and Suppression of Its Errors on the Basis of FPGA

A novel design of force to rebalance control for a hemispherical resonator gyro (HRG) based on FPGA is demonstrated in this paper. The proposed design takes advantage of the automatic gain control loop and phase lock loop configuration in the drive mode while making full use of the quadrature control loop and rebalance control loop in controlling the oscillating dynamics in the sense mode. First, the math model of HRG with inhomogeneous damping and frequency split is theoretically analyzed. In addition, the major drift mechanisms in the HRG are described and the methods that can suppress the gyro drift are mentioned. Based on the math model and drift mechanisms suppression method, four control loops are employed to realize the manipulation of the HRG by using a FPGA circuit. The reference-phase loop and amplitude control loop are used to maintain the vibration of primary mode at its natural frequency with constant amplitude. The frequency split is readily eliminated by the quadrature loop with a DC voltage feedback from the quadrature component of the node. The secondary mode response to the angle rate input is nullified by the rebalance control loop. In order to validate the effect of the digital control of HRG, experiments are carried out with a turntable. The experimental results show that the design is suitable for the control of HRG which has good linearity scale factor and bias stability.

A tri-mode Compass/GPS/Galileo RF receiver with all-digital automatic gain control loop

A tri-mode RF receiver with all digital automatic gain control (AGC) loop and non-uniform 2-bit analog-to-digital converter (ADC) is designed for the bands of GPS-L1, Galileo-E1 and Compass B1 in 0...

Evaluation of temperature degradation in hydraulic flow networks

The degradation of the temperature difference between supply and return flow reduces the efficiency of chilled water systems as well as central heating systems. In both applications, the problem is caused by excessive water flow rates under part load conditions and equipment oversizing. Remedies to address this ΔT degradation by reducing bypass flow have been recommended and documented over the last 25 years, especially in the field of chilled water systems. This paper addresses ΔT degradation caused by a set of common faults: hydraulic network imbalance, control valve oversizing, incorrect inherent valve characteristic, and inadequate control loop gain parameters. To allow for the quantitative evaluation of the numerous possible causes that contribute to ΔT degradation, a dynamic simulation environment was developed and employed in the presented analysis that couples pressure–flow relationships in the hydraulic network with the dynamic thermal loads of the building under investigation. Relative to the reference case of a properly designed and tuned hydraulic subsystem, a ΔT degradation of over 6K in a sample central heating system is predicted, well aligned with commissioning reports of large chilled water and district heating plants. In district heating systems, this significant ΔT degradation of 6K would lead to an increase of the primary energy consumption between 4 and 12%.

Analysis and Design of Drive Closed-Loop for MEMS Vibratory Gyroscope

The principle of drive closed-loop for tuning fork comb MEMS vibratory gyroscope is analyzed. The core of the closed-loop is to keep the vibration speed stable by adding driving force offset the damping force. The closed-loop with a single Automatic Gain Control (AGC) loop is chosen to maintain the vibration speed stable, and then the closed-loop with AGC is analyzed to obtain its transfer function. The transfer function simplifies the nonlinear AGC system to a linear system which is easy analyzed its parameters impacting the system. The values of two important parameters of AGC were chosen via simulation. The whole closed-loop system was simulated in SIMULINK. The circuit is built and tested in accordance with the theory of analysis and simulation. Experimental results demonstrate that the stability of the amplitude of vibration speed is 90ppm; and that of the frequency of vibration speed is 114ppm.

A 0.3–1.4 GHz All-Digital Fractional-N PLL With Adaptive Loop Gain Controller

A 0.3–1.4 GHz all-digital phase locked loop (ADPLL) with an adaptive loop gain controller (ALGC), a 1/8-resolution fractional divider and a frequency search block is presented. The ALGC reduces the nonlinearity of the bang-bang phase-frequency detector (BBPFD), reducing output jitter. The fractional divider partially compensates for the large input phase error caused by fractional-N frequency synthesis. A fast frequency search unit using the false position method achieves frequency lock in 6 iterations that correspond to 192 reference clock cycles. A prototype ADPLL using a BBPFD with a dead-zone-free retimer, an ALGC, a fractional divider, and a digital logic implementation of a frequency search algorithm was fabricated in a 0.13- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu{\hbox {m}}$</tex></formula> CMOS logic process. The core occupies 0.2 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\hbox {mm}}^{2}$</tex> </formula> and consumes 16.5 mW with a 1.2-V supply at 1.35-GHz. Measured RMS and peak-to-peak jitter with activating the ALGC are 3.7 ps and 32 ps respectively.

A low power automatic gain control loop for a receiver

This paper proposes a new structure to lower the power consumption of a variable gain amplifier (VGA) and keep the linearity of the VGA unchanged. The structure is used in a high rate amplitude-shift keying (ASK) based IF-stage. It includes an automatic gain control (AGC) loop and ASK demodulator. The AGC mainly consists of six-stage VGAs. The IF-stage is realized in 0.18 μm CMOS technology. The measurement results show that the power consumption of the whole system is very low. The system consumes 730 μA while operating at 1.8 V. The minimum ASK signal the system could detect is 0.7 mV (peak to peak amplitude).

A High-Speed Current-Mode Data Driver With Push-Pull Transient Current Feedforward for Full-HD AMOLED Displays

A push-pull transient current feedforward driver is designed to have a complete push-pull function and loop gain control that enhances the data current drivability. The sink and source current capability of the proposed driver makes it insensitive to the initial voltage levels on the data lines and provides a reduced settling time. The gain control in the positive feedback loop offers a fast settling time without ringing over the complete range of pixel drive currents. The data driver exhibits a settling time of better than 6 μs for drive currents from 20 nA to 5 μA into an equivalent full-HD AMOLED display panel parasitic load of 4 kΩ series resistance and 90 pF shunt capacitance. The driver consumes a static current of 4.5 μA/channel.

A New Feedback Method for PR Current Control of LCL-Filter-Based Grid-Connected Inverter

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> For a grid-connected converter with an LCL filter, the harmonic compensators of a proportional–resonant (PR) controller are usually limited to several low-order current harmonics due to system instability when the compensated frequency is out of the bandwidth of the system control loop. In this paper, a new current feedback method for PR current control is proposed. The weighted average value of the currents flowing through the two inductors of the LCL filter is used as the feedback to the current PR regulator. Consequently, the control system with the LCL filter is degraded from a third-order function to a first-order one. A large proportional control-loop gain can be chosen to obtain a wide control-loop bandwidth, and the system can be optimized easily for minimum current harmonic distortions, as well as system stability. The inverter system with the proposed controller is investigated and compared with those using traditional control methods. Experimental results on a 5-kW fuel-cell inverter are provided, and the new current control strategy has been verified. </para>

Analysis of Parallel Operation of Uninterruptible Power Supplies Loaded Through Long Wiring Cables

This paper discusses and analyses the parallel operation of uninterruptible power supplies (UPS) when loaded through long wiring cables having non-negligible inductance and resistance. This scenario is often encountered in practice, as the UPS power supplies are often located far from each other and from the load they are actually powering. The analysis demonstrates how long cable connections between the power supply system and the load deeply modify the behavior of the single UPS unit. It is shown how the cable inductance interacts with the UPS closed-loop output impedance modifying the control loop gain, ultimately generating resonance phenomena, which deteriorate or even compromise system stability and performances, if suitable provisions are not taken at the design stage. Experimental results carried out on two paralleled three phase, 40 kVA UPS units based on voltage-source inverters topologies confirm the validity of the theoretical discussion and the practical relevance of the phenomenon.

An Ultra-Low-Power Pulse Oximeter Implemented With an Energy-Efficient Transimpedance Amplifier

Pulse oximeters are ubiquitous in modern medicine to noninvasively measure the percentage of oxygenated hemoglobin in a patient's blood by comparing the transmission characteristics of red and infrared light-emitting diode light through the patient's finger with a photoreceptor. We present an analog single-chip pulse oximeter with 4.8-mW total power dissipation, which is an order of magnitude below our measurements on commercial implementations. The majority of this power reduction is due to the use of a novel logarithmic transimpedance amplifier with inherent contrast sensitivity, distributed amplification, unilateralization, and automatic loop gain control. The transimpedance amplifier, together with a photodiode current source, form a high-performance photoreceptor with characteristics similar to those found in nature, which allows LED power to be reduced. Therefore, our oximeter is well suited for portable medical applications, such as continuous home-care monitoring for elderly or chronic patients, emergency patient transport, remote soldier monitoring, and wireless medical sensing. Furthermore, our design obviates the need for an A-to-D and digital signal processor and leads to a small single-chip solution. We outline how extensions of our work could lead to submilliwatt oximeters.

Experimental analysis and characterization of electrostatic-drive tri-axis micro-gyroscope

A planar micro-machined tri-axis gyroscope in decoupled-mode mechanical structure is presented, verified for superior detection capability and analyzed by experiments in this paper. Initially, the natural frequencies of sense modes are successfully tuned to match the natural frequency of drive mode by polarization voltages onto the associated sensing electrodes so that the inherent bias frequency at each sense mode can be removed. Secondly, the undesired cross-axis coupling effects between drive mode and sense modes are substantially suppressed by the cooperation of mechanical design and an integrated Automatic Gain Control (AGC) loop for drive mode. For highly reliable tuning to ensure resonance, the AGC and PLL (Phase Lock Loop) are integrated with a PID (Proportional, Integral and Differential) feedback controller to eliminate steady-state errors and overshoots. The performance of the micro-gyroscope is analyzed and evaluated by experiments. The achieved scale factors (the reflected voltage to the detected angular rate) of the proposed tri-axis micro-gyroscope are 50.4 μV/°/ s, 60.3 μV/°/ s, and 71.2 μV/°/ s for X-, Y- and Z-axes (principal axis: Z-axis) respectively. The resulted resolutions are about 0.72 ° / s / Hz , 143 ° / s / Hz and 0.42 ° / s / Hz for X-, Y- and Z-axes respectively. The Cross-axis sensitivities are reduced down to 22%, 9% and 1.84% for X-, Y- and Z-axes respectively. S/N ratios reach 59.3, 13.8, and 140.1 for X-, Y- and Z-axes respectively. The experimental results illustrate that the gyroscope exhibits superior to detect exerted angular rate, in addition to successful suppression upon the cross-axis perturbation between drive mode and sense mode. Principle-axis sensitivity, resolution and floor noise are all numerically evaluated. Further more, cross-axis sensitivity, Signal-to-Noise Ratio (SNR) and measurement error are investigated. Finally, a few comparisons with the other typical types of gyroscopes are reported.

Improved Online Identification of a DC–DC Converter and Its Control Loop Gain Using Cross-Correlation Methods

Recent progress in the identification of switching power converters using an all-digital controller has granted network analyzer functionality to the control platform. In particular, the cross-correlation technique provides a nonparametric identification of a converter's small-signal control-to-output frequency response. The literature shows the viability of this technique as well as a few improvements to the basic technique. This online network analyzer functionality allows new flexibility in the areas of online monitoring and adaptive control. In this paper, several improvements to the cross-correlation method of system identification are proposed that aim to further improve the accuracy of the frequency response identification, particularly at high frequencies near the desired closed-loop bandwidth frequency. Additionally, an extension to the cross-correlation method is proposed that allows measurement of the control loop gain without ever opening the feedback loop. Thus, performance and stability margins may be evaluated while maintaining tight regulation of the output. Simulation and experimental results are shown to verify the proposed improvements and extension.

Airtime Fair Distributed Cross-Layer Congestion Control for Real-Time Video Over WLAN

We propose a distributed cross-layer congestion control algorithm that provides enhanced quality of service QoS and reliable operation for real-time uplink video over WiFi applications. Such applications are characterized by many wireless devices transmitting video at various PHY rates over a relatively congested channel. Unfortunately, today's off-the-shelf 802.11 equipment can be easily demonstrated to suffer catastrophic failure when subject to these conditions-let alone provide acceptable perceptual quality to the user. We show that in order to remedy these issues, it is preferable to apply airtime fairness with a cross-layer approach. The idea is to use a fast frame-by-frame control loop in the carrier sense multiple access/collision avoidance (CSMA/CA)-based medium access control (MAC) layer while simultaneously exploiting the powerful control loop gain attainable by performing source-rate adaptation in the application layer. We support the proposed algorithm through both simulation and experimentation with various channel and PHY rate scenarios.

Development of a Prototype Miniature Silicon Microgyroscope

A miniature vacuum-packaged silicon microgyroscope (SMG) with symmetrical and decoupled structure was designed to prevent unintended coupling between drive and sense modes. To ensure high resonant stability and strong disturbance resisting capacity, a self-oscillating closed-loop circuit including an automatic gain control (AGC) loop based on electrostatic force feedback is adopted in drive mode, while, dual-channel decomposition and reconstruction closed loops are applied in sense mode. Moreover, the temperature effect on its zero bias was characterized experimentally and a practical compensation method is given. The testing results demonstrate that the useful signal and quadrature signal will not interact with each other because their phases are decoupled. Under a scale factor condition of 9.6 mV/°/s, in full measurement range of ± 300 deg/s, the zero bias stability reaches 15°/h with worse-case nonlinearity of 400 ppm, and the temperature variation trend of the SMG bias is thus largely eliminated, so that the maximum bias value is reduced to one tenth of the original after compensation from -40 °C to 80 °C.

AUTOMATIC GAIN CONTROL FOR UNITY FEEDBACK CONTROL SYSTEMS

In this paper, an automatic gain control scheme is proposed for analyses and designs of unity feedback control systems. It is consisted of a fast command tracking loop and a slow gain adaptive loop. The overall system is equivalent to a conventional automatic gain control loop with command tracking error input. It gives good command tracking behaviour while keeping robust characteristic of the original automatic gain control loop. It gives good robustness for coping with fast large parameter and load disturbance variations also. The stability of the controlled systems and effective of the proposed method are verified by root-loci, time responses, frequency responses, large parameter variations and fast large load disturbances testing with two numerical examples.

Interference Cancellation in Broadband Wireless Systems Utilizing Phase-Aligned Injection-Locked Oscillators

We demonstrate an interferer suppression method based on feed-forward cancellation that uses an injection-locked oscillator (ILO) to extract interferers from the incident spectrum in an auxiliary receiver. The technique is expected to be useful in environments where a strong narrowband interferer appears along with a wideband desired signal, such as ultra-wideband (UWB) and emerging cognitive-radio applications. The ILO is further embedded within a phase-locked loop which allows self-tuning of the ILO center frequency and automatic phase alignment between the main signal path and auxiliary path. An IC that uses this approach is implemented in a 0.18 mum CMOS process. In measurement, the chip demonstrates 20 dB suppression for phase- and frequency-modulated interferers while maintaining around 18 dB power gain and a noise figure below 5 dB, including an off-chip balun for the desired signal. Techniques for canceling amplitude modulated interferers, though not included in the fabricated chip, can also be implemented by adding an amplitude tracking gain-control loop.

자동이득 제어루프를 이용한 진폭제어방식의 공진형 가속도계 설계

본 논문에서는 안정된 진동을 얻기 위한 자동 이득 제어(AGC) 루프를 이용하여 자가 유지 특성을 갖는 공진형 가속도계를 설계하였다. 제안된 가속도계의 기본 원리는 가속도 입력시, 가변 진동의 진폭을 일정하게 유지시키는 방법을 이용한다. 시스템 모델링과 진동의 포락선을 고려한 루프 설계 및 변환를 통하여 다양한 가속도 입력 하에서 진동 신호의 진폭을 일정하게 유지하도록 제어기를 설계하였고, 시뮬레이션 결과를 통해 실현가능성을 확인하였다. 따라서 고안된 공진 가속도계는 산업과 민간 응용 분야에 있어서 제어용 등급의 관성 측정 시스템에 적용될 수 있을 것으로 기대한다. In this paper, we introduce a new design approach for self-sustained resonant accelerometer, that takes advantage of the automatic gain control (AGC) loop to achieve a stabilized oscillation dynamics. Fundamental idea of this accelerometer is to maintain uniform amplitude of oscillation under input accelerations. Through system modeling and loop transformation considering the envelope of oscillation, the controller is designed to maintain uniform amplitude in oscillation under dynamic input acceleration. The simulation results demonstrate the feasibility of the proposed accelerometer design, which is applicable to control grade inertial measurement system in industrial and civil application fields.

70 dB Dynamic Range CMOS Wideband Digital Variable Gain Amplifier for AGC in DVB-T/H Receivers

This paper presents a novel variable gain amplifier (VGA) design which is applied in the automatic gain control loop of digital video broadcasting (DVB) receivers designed for standards DVB-T/H. The VGA is composed of three cascaded tunable gain stages to provide a 70 dB dynamic range with 2 dB gain steps. Each gain stage is based on a digital variable gain amplifier (DVGA) which is composed of a plurality of gain blocks (GBs) and a fully differential degeneration amplifier (FDDA). The GBs of the DVGA are digitally controlled current mirrors. A common-mode feedback circuitry is used to stabilize the FDDA by providing a stable common-mode voltage. Physical measurements on silicon show that the gain error is merely 0.55 dB given a 70 dB tuning range.

Development of a lateral velocity-controlled MEMS vibratory gyroscope and its performance test

The objective of this paper is to present a velocity-controlled vibratory MEMS gyroscope that achieves consistent output characteristics in the lateral driving dynamics of the system. Through a systematic automatic gain control loop design process, the driving mode dynamics of the gyroscope is first transformed to take account of the velocity envelope; a reference tracking integral control is then employed. For stabilized loop construction, a mathematical development and stability analysis of the feedback loop is presented, which is followed by numerical simulation using practical sensor parameters. The mechanical structure was fabricated using the conventional deep reactive ion etching process and the anodic wafer bonding method. Vacuum-packaged devices were used for the resonant gyroscope operation. An essential fabrication process for realizing the electrical connection through a thick glass substrate was possible by applying a sandblasting process and spin coating process of conductive epoxy. Finally, loop simulation and experimental results verified that the amplitude-controlled property in the driving loop is preserved under the system parameter variation which resulted in enhanced gyroscope output performance in comparison with other driving schemes.

Implementation-Friendly Constraint for Adaptive Finite Impulse Response Filters for Equalization

In read channels in magnetic recording systems, a finite impulse response (FIR) filter is often used as an equalizer, and the filter coefficients are adapted via a least mean squares (LMS) algorithm. This equalizer adaptation loop can interfere with the timing recovery (TR) loop and the automatic gain control (AGC) loop that are also present in such channels. In a previous paper by L. Du et al., a linear constraint is proposed for the LMS loop so that it is decoupled from the TR and the AGC loops. In this paper, we generalize that constraint, and propose a new constraint that offers the advantage of easier implementation.