Amplitude Control Loop Research Articles

Amplitude Control Loop to Compensate for I/Q Mismatch in an Accurate Quadrature LC Oscillator

In this paper, a novel parallel-coupled quadrature LC oscillator (PC-QO) is presented that can automatically eliminate imbalances of output phase and amplitude resulting from mismatches in the LC tanks. The method of using unequal coupling factors in a parallel-coupled quadrature oscillator is the base of this design; canceling the phase and amplitude errors takes place by tuning the imbalanced coupling factor using tuneable tail currents. First, the proposed circuit senses the amplitude error and then adjusts the coupling factors according to the situation. We show that using the inversely proportional coupling factors can eliminate the phase and amplitude error simultaneously. In other words, this design uses the amplitude control loop to cancel the phase and amplitude error. The circuit has been simulated using TSMC 0.18 CMOS practical model to confirm the high accuracy of the analysis and capability of the canceling [Formula: see text]/[Formula: see text] mismatch technique. The simulation results show that the phase noise of the proposed quadrature voltage controlled oscillator (QVCO) is −123.9 dBc/Hz at 1[Formula: see text]MHz offset from 4.4[Formula: see text]GHz operation frequency. The total power consumption of the QVCO is 3.4[Formula: see text]mW.

Identification and suppression of driving force misalignment angle for a MEMS gyroscope using parametric excitation

We report for the first time an implementable method to identify and suppress the driving force misalignment angle for a MEMS gyroscope working either in amplitude modulated (AM) or Lissajous frequency modulated (LFM) mode using parametric excitation. By introducing driving force misalignment angle into gyroscope dynamic equations, we illustrate that gyroscope angular rate output is affected by driving force misalignment angle and cross-axis damping jointly. We propose parametric excitation as a way to both identify and calculate the driving force misalignment angle. The identification results for a gyroscope working in both AM and LFM mode are similar, which indicates the effectiveness of the proposed identification method. Instead of using traditional amplitude control loop by adjusting the driving force, we do the automatic gain control by adjusting the parametric pump voltage so that a fixed drive voltage can be used, which also indicates fixed force coupling. Experimental results show that after suppression, the bias instability (BI) of AM mode is improved from 4.7° h−1 to 2.3° h−1 and the BI of LFM mode is improved from 1.4° h−1 to 0.9° h−1 which is the lowest result reported for LFM gyroscope.

Coupled Double Closed-Loop Control for an MEMS Resonant Accelerometer.

There is mutual coupling between amplitude control and frequency tracking control in the closed-loop control of micromechanical resonant sensors, which restricts sensor performance. This paper introduces the principle of an in-plane vibration micromechanical resonant accelerometer with electrostatic stiffness. The characteristic parameters of the microaccelerometer were obtained through computer-aided dimension measurement and an open-loop frequency sweep test of the fabricated microstructure. An accurate numerical model was established based on the accelerometer’s dynamic principle and characteristic parameters. We established the double closed-loop driving analysis model of amplitude automatic gain control and resonant frequency phase-locked tracking. We used the averaging method to analyze the steady-state equilibrium point and the stable condition. We concluded that the integral coefficient can improve the startup overshoot when the amplitude automatic gain control loop satisfies the stability condition. Under the constraint of frequency tracking, the sizeable coefficient of the integrator can improve the system instability of the amplitude control loop. The theoretical analysis and simulation were helpful in the design and debugging of the system circuit.

A Temperature-Compensated Crystal Oscillator With Piecewise Polynomial Varactor Compensation Achieving ±3.75-ppm Inaccuracy From −30°C to 90°C

This brief presents a low-complexity temperature-compensated crystal oscillator (TCXO). The frequency error compensation over temperature is realized by employing the proposed piecewise polynomial varactor (PPV). The PPV operation is determined by a temperature-dependent voltage generator. The temperature compensation is achieved without using an accurate mapping table and high-resolution data converters. In addition, an amplitude-control loop (ACL) is incorporated to maintain a stable XO operation under process, temperature, and supply voltage variations. This brief is fabricated in a 180-nm CMOS process. The frequency inaccuracy of the proposed 40-MHz TCXO is ±3.75 ppm from −30°C to 90 °C. Operating from a 1.8-V supply, the overall current consumption, including the proposed compensation and ACL, is 0.3 mA.

A novel amplitude and frequency demodulation algorithm for frequency-modulation atomic force microscope

Frequency-modulation atomic force microscope (FM-AFM) has been a widely-used instrument to achieve atomic or subatomic resolution imaging. However, the low bandwidth of automatic gain control circuit for amplitude control loop and the low setting rate of frequency demodulation loop have been a big stumbling block for FM-AFM to realize fast measurement. In this article, a novel demodulation algorithm for FM-AFM is proposed. The Kalman filter approach is proposed to realize amplitude demodulation, and the FM signal is processed as a phase modulation signal (indirect FM signal). The performance of the algorithm is verified through experiment on field-programmable gate array, and compared with existing methods. Through the proposed method, the tracking performance of FM-AFM can be improved and the response rate can be increased without loss of precision.

A 92 fs<sub>rms</sub> jitter frequency synthesizer based on a multicore class-C voltage-controlled oscillator with digital automatic amplitude control

This letter presents a frequency synthesizer based on a multicore Class-C voltage-controlled oscillator (VCO) with a digital automatic amplitude control (AAC) loop. A novel digital tail current estimation is adopted to mitigate the risks of unexpected VCO oscillation failure, due to current shortage during frequency calibration. Meanwhile, a digital amplitude recalibration is proposed to provide continuous amplitude control, avoiding noise distortion resulted from amplitude drift after a conventional disposable amplitude calibration. The digital AAC loop achieves a specific VCO amplitude with good stability and introduces no extra noise. Fabricated in a 28 nm CMOS process, the presented frequency synthesizer occupies an active area of 1.43 mm2. By measuring a 3 GHz carrier, the open loop VCO phase noise is -132 dBc/Hz at 1 MHz offset and the close loop root mean square jitter is 81 fs.

Design of a digital control system of gyroscope

This paper introduces a digital control system of gyroscope. The control circuit includes amplitude control loop, phase control loop and detection circuit. The amplitude control loop realizes the stability of driving mode vibration signal amplitude. The phase control loop consists of coarse phase locking loop and precise phase locking loop. At the initial stage, coarse phase locking is used to realize the rapid start-up of the gyroscope. Then after resonance frequency settles into the lock-in range of PLL, precise phase locking is used to realize the precise phase locking. The detection circuit realizes the output of gyro angular velocity signal. The design is implemented on PCB. The test results show that the scheme can realize the stable operation of gyroscope.

A method to improve tracking ability of drive control of MEMS gyroscopes

PurposeA high-precision gyroscope is an important tool for accurate positioning, and the amplitude stability and frequency tracking ability of the drive control system are important and necessary conditions to ensure the precision of micro-electro-mechanical systems (MEMS) gyroscopes. To improve the precision of MEMS gyroscopes, this paper proposes a method to improve the amplitude stability and frequency tracking ability of a drive control system.Design/methodology/approachA frequency tracking loop and an amplitude control loop are proposed to improve the frequency tracking ability and amplitude stability of the drive control system for a MEMS gyroscopes. The frequency tracking loop mainly includes a phase detector, a frequency detector and a loop filter. And, the amplitude control loop mainly includes an amplitude detector, a low-pass filter and an amplitude control module. The simulation studies on the frequency tracking loop, amplitude control loop and drive control system composed of these two loops are implemented. The corresponding digital drive control algorithm is realized by the Verilog hardware description language, which is downloaded to the application-specific integrated circuits (ASIC) platform to verify the performances of the proposed method.FindingsThe simulation experiments in Matlab/Simulink and tests on the ASIC platform verify that the designed drive control system can keep the amplitude stable and track the driving frequency in real time with high precision.Originality/valueThis study shows a way to design and realize a drive control system for MEMS gyroscopes to improve their tracking ability. It is helpful for improving the precision of MEMS gyroscopes.

A Low-Voltage Robust Class-C VCO With Dual Digital Feedback Loops

This brief presents a low-supply-voltage robust class-C voltage-controlled oscillator (VCO) with the dual digital feedback loops. One is the digital adaptive bias loop (DABL) which is proposed to ensure startup robustness and improve the phase noise performance of the VCO. And the other is the digital amplitude control loop (DACL), which is adopted to stabilize the oscillation amplitude over process, voltage and temperature (PVT) variations. Moreover, a cooperative algorithm is also proposed in order to make the dual digital loops work properly. Besides, the offset canceling comparators are adopted to guarantee the stability of the digital loops. The proposed VCO is implemented in SMIC 0.18 $\mu \text{m}$ CMOS process, achieving a phase noise of −123.3 dBc/Hz at 1 MHz offset from a 2.55 GHz carrier and a 2.2-2.7 GHz frequency tuning range. The figure-of-merit (FoM) is −190.4 dBc/Hz with the total power consumption less than 1.28 mW at the 0.8 V supply voltage.

Design and Verification of a Digital Controller for a 2-Piece Hemispherical Resonator Gyroscope.

A Hemispherical Resonator Gyro (HRG) is the Coriolis Vibratory Gyro (CVG) that measures rotation angle or angular velocity using Coriolis force acting the vibrating mass. A HRG can be used as a rate gyro or integrating gyro without structural modification by simply changing the control scheme. In this paper, differential control algorithms are designed for a 2-piece HRG. To design a precision controller, the electromechanical modelling and signal processing must be pre-performed accurately. Therefore, the equations of motion for the HRG resonator with switched harmonic excitations are derived with the Duhamel Integral method. Electromechanical modeling of the resonator, electric module and charge amplifier is performed by considering the mode shape of a thin hemispherical shell. Further, signal processing and control algorithms are designed. The multi-flexing scheme of sensing, driving cycles and x, y-axis switching cycles is appropriate for high precision and low maneuverability systems. The differential control scheme is easily capable of rejecting the common mode errors of x, y-axis signals and changing the rate integrating mode on basis of these studies. In the rate gyro mode the controller is composed of Phase-Locked Loop (PLL), amplitude, quadrature and rate control loop. All controllers are designed on basis of a digital PI controller. The signal processing and control algorithms are verified through Matlab/Simulink simulations. Finally, a FPGA and DSP board with these algorithms is verified through experiments.

DESIGN AND ANALYSIS OF A 2.4 GHz HYBRID TYPE AUTOMATIC AMPLITUDE CONTROL VCO WITH FORWARD NOISE REDUCTION

This paper presents a voltage-controlled oscillator (VCO) with automatic amplitude control (AAC) loop. The proposed AAC VCO employs a hybrid type AAC loop and targets the Industrial, Scientific and Medical (ISM) band applications. The proposed AAC loop can also prevent the AAC from generating extra noise to the VCO and avoid stability problem which is common for conventional AAC loop. Detail transient analysis of this AAC VCO is derived. Based on this analysis, design steps applicable for such type of AAC loop is obtained. Measurement result shows the peak amplitude variation over the operation range of 2.25–2.54 GHz is less than 9 mV (without the AAC loop, amplitude variation can be as large as 40 mV, or 22.2% for 180 mV amplitude). Power consumption of the proposed AAC VCO is 4.5 mW while the power consumed by the loop is 0.8 mW and phase noise is -105 dBc/Hz at 100 kHz offset frequency. Worst case settling time is less than 10.5 μs.

A Drive Control Scheme Based on Phase-control for Silicon Micromechanical Gyroscopes

A drive control scheme based on phase-control for silicon micromechanical gyroscopes (SMG) is studied and implemented. By analyzing the dynamical characteristics of the drive mode, the elementary principle of phase control scheme upon which the control loop is built is described and the stability of the loop is presented using the theory of self-sustained oscillation. The phase model of the loop is modeled where a special factor is introduced to realize the conversion from phase-error to frequency-error which is the difference between current working frequency and the resonance-frequency of the drive mode. By building the frequency closed-loop corresponding to the phase-control loop, we find that the order of the loop-filter is just one when considering loop-filter as a first-order-model, which is different from the general phase locked loop (PLL) that is second-order. Elaborate design of the digital phase-control circuit is carried out based on the FPGA platform where a linear phase-detector is applied. Aided by an amplitude control loop, a double-closed-loop drive control circuit is realized. Results show that the drive control loops work precisely.

Special type of three-phase oscillator using current gain control for amplitude stabilization

The main aim of this work is to demonstrate the use of electronically controlled second-generation current conveyor in providing electronic control to the condition of oscillation (CO) of a new active RC sinusoidal oscillator. Electronic control of the CO, which is independently set and does not affect the oscillation frequency, is enabled by the use of an auxiliary amplitude control loop to regulate the amplitude and provide very good total harmonic distortion performance. The proposed oscillator employs only one standard second-generation current conveyor, one electronically controlled second-generation current conveyor, five passive elements and is capable of providing three voltage outputs having phase shifts 45 and 90°, if specific design requirements are fulfilled. Similar simple types of oscillators do not provide such features. Non-ideal analysis of the circuit has also been carried out and the proposed oscillator has been verified by both PSpice simulations and experimental measurements using commercially available integrated circuits. Key words: Three-phase oscillator, special features, electronic control, electronically controllable current conveyor (ECCII), second generation current conveyor (CCII).

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 Low Power, Startup Ensured and Constant Amplitude Class-C VCO in 0.18 $\mu {\rm m}$ CMOS

A low power and robust class-C voltage-controlled oscillator (VCO) is presented in this letter. It features 1) an automatic startup loop to achieve the optimal point and address the inherent risk of startup failure and 2) a digital amplitude control loop to stabilize amplitude and enhance the PVT (process, voltage and temperature) tolerance. The design is implemented in a 0.18 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu {\rm m}$</tex></formula> CMOS process. Measurement demonstrates the VCO has a 20% tuning range and phase noise of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$-123.0~{\rm dBc}/{\rm Hz}$</tex></formula> at 1 MHz offset from a 3.1 GHz carrier while consuming 1.57-mW power from a 1 V supply, yielding a Figure-of-Merit (FoM) of 191.1. While operating under the minimum power of 560 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$\mu {\rm W}$</tex></formula> , it produces <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$-111.3~{\rm dBc}/{\rm Hz}$</tex></formula> phase noise at 1 MHz offset from a 3.1 GHz carrier showing a 183.8 FoM.

Simple quadrature oscillator for BIST

A simple quadrature oscillator for the built-in self-test (BIST) of integrated analogue filters is proposed. A new hardware-efficient approach for amplitude control is described, the main assets being: (i) the technique requires little hardware, which makes it very useful for BIST; (ii) the oscillation amplitude is well defined, and (iii) the distortion-level introduced by the amplitude control loop is under the control of the designer.

DFIG-Based Power Generation System With UPS Function for Variable-Speed Applications

The power generation system with a doubly fed induction generator (DFIG), which can be used as an autonomous power system after the loss of mains in a distributed generation network, is described. After the mains outage, a fixed frequency and an amplitude of the output voltage are obtained, despite the variable rotor speed. For this reason, it can be successfully applied in the variable-speed wind turbines, adjustable speed water plants, or diesel engines. Moreover, the stand-alone operation of DFIG is useful in a flywheel-based high-energy rotary uninterruptible power supply system. An output voltage is controlled directly by the synchronization of an actual voltage vector with the reference vector represented in a synchronously rotating polar frame. The rotor current angular speed is obtained as a result of vectorial phase-locked loop operation. Any sensors or estimators of the rotor speed or position are unnecessary. Both amplitude and angle control loops are linear. The use of stand-alone operation in grid-connected systems requires mains outage detection. Also, the grid voltage recovery requires a method of synchronization and soft connection of a generator to the grid. The proposed methods of output voltage control, synchronization, and detection of mains loss were tested in a laboratory system.

A CMOS Readout Circuit for SOI Resonant Accelerometer With 4-$\mu \rm g$ Bias Stability and 20-$ \mu\rm g/\sqrt{{\hbox{Hz}}}$ Resolution

A fully differential CMOS readout circuit for SOI resonant accelerometer is reported. The readout circuit is essentially an oscillator, consisting of an oscillator and a low noise automatic amplitude control (AAC) loop. A differential sense resonator is proposed to facilitate fully differential circuit topology and improves the SNR under a 3.3-V supply. A second-order AAC loop filter and a novel chopper stabilized rectifier are employed in the AAC loop to remove the noises, in particular, the 1/f noise, and to minimize the phase noise caused by the amplitude stiffening effect. The strong driving feedthrough is avoided by separating the drive and sense operation in the time domain, while using the same electrodes. The complete resonant accelerometer operates under a 3.3-V supply and achieves 140-Hz/g scaling factor, 20 mug/radicHz resolution and 4 mug bias stability. The readout circuit draws 7 mA under 3.3-V supply.

A 5 GHz, 192.6 dBc/Hz/mW FOM, LC–VCO System With Amplitude Control Loop and LDO Voltage Regulator in 0.18 &lt;formula formulatype="inline"&gt; &lt;tex&gt;$\mu$&lt;/tex&gt; &lt;/formula&gt;m CMOS

To reduce phase noise degradation from oscillator tail current sources, this letter presents an inductor-capacitor voltage-controlled oscillator (LC-VCO) biased by triode metal-oxide-semiconductor transistors. The VCO system also includes an amplitude control loop and a voltage regulator to endure process, voltage, and temperature variations and to enhance power supply rejection ratio. Fabricated in a 0.18 mum CMOS process, the measured results show the adopted topology achieves a better phase noise than the conventional saturation current source. At 5.181 GHz, the VCO system demonstrates a phase noise of -104.8 dBc/Hz at 100-kHz offset, and -127.1 dBc/Hz at 1 MHz offset, while dissipating 4.2 mA from a 1.8 V supply voltage. The corresponding figures of merit at 100 kHz and 1 MHz offset are 190.3 and 192.6 dBc/Hz/mW, respectively.

A Stable Loss Control Feedback Loop for VCO Amplitude Tuning

In practical implementations of LC oscillators in which the quality factor of the tank is dominated by the quality factor of the inductor, due to dependence of the oscillation amplitude on the square of the oscillation frequency and the bias current of the LC tank, a stable amplitude control loop is essential to maintain a constant oscillation amplitude over the tuning range of the voltage-controlled oscillator (VCO) and to optimally bias the VCO over different conditions. In this paper, an enhanced loss control scheme incorporating an integral feedback to automatically tune the oscillation amplitude of LC oscillators is proposed. The proposed loss control feedback (LCF) loop is conditionally stable with an easy stability requirement to meet and its stability is examined: 1) by linearizing the system around the stable point using a perturbation method; and 2) by numerically solving the nonlinear differential equation of the LCF loop describing the transient behavior of the step response of the loop. A prototype including the LC VCO and the proposed LCF loop has been implemented in TSMC 0.35-mum CMOS process and occupies an area of 0.057 mm2 and consumes 8.1 mA from a 2.8-V power supply. The LCF loop, with respect to the VCO, has an overhead of 25% on the area and consumes only 1.3% of the total power. Measurement results of the proposed LCF loop show an 11 dBm amplitude tuning range from -16 dBm to -5 dBm at any frequency over the 2-2.5-GHz tuning range of the VCO. The step response of the loop has a settling time less than 0.5 ns