Frequency Control Circuit Research Articles

A low-noise X-band microwave source with digital automatic frequency control for electron paramagnetic resonance spectroscopy

We report a new design of microwave source for X-band electron paramagnetic resonance spectrometer. The microwave source is equipped with a digital automatic frequency control circuit. The parameters of the digital automatic frequency control circuit can be flexibly configured for different experimental conditions, such as the input powers or the quality factors of the resonator. The configurability makes the microwave source universally compatible and greatly extends its application. To demonstrate the ability of adapting to various experimental conditions, the microwave source is tested by varying the input powers and the quality factors of the resonator. A satisfactory phase noise as low as −135 dBc/Hz at 100-kHz offset from the center frequency is achieved, due to the use of a phase-locked dielectric resonator oscillator and a direct digital synthesizer. Continuous-wave electron paramagnetic resonance experiments are conducted to examine the performance of the microwave source. The outstanding performance shows a prospect of wide applications of the microwave source in numerous fields of science.

Operation of synthetic inertia units in electric power systems of various densities

This study is aimed at improving the efficiency of photovoltaic plants operated in the electric networks of various densities by adjusting the synthetic inertia algorithm and automatic frequency control circuits. To this end, the automatic control system of a photovoltaic plant was investigated using hybrid modelling methods in an all-mode online simulation complex of electric power systems. It was shown that the stability of photovoltaic power plants could be improved through the use of synthetic inertia. According to the conducted research, effective operation of this algorithm can be ensured by a correct determination of the bandwidth of automatic frequency control. Operation of this automatic frequency control circuit can lead to the oscillations of various frequencies during the installation of photovoltaic power plants in low-current electrical networks (electrical networks with the short circuit coefficient of less than 10 a.u.) and, subsequently, negatively affect the operability of the synthetic inertia algorithm. In addition, in high-current networks with an increased bandwidth of the automatic frequency control unit, the value of the network frequency reduction decreases (optimal bandwidth of 50 Hz). Conversely, in low-current networks, the automatic frequency control unit, under an increase in the bandwidth, decreases the response rate of the synthetic inertia algorithm, which leads to an increase in the frequency reduction value (optimal bandwidth of 0.3 Hz). Thus, the conducted investigations showed that the automatic frequency control circuit in the control system of a photovoltaic power plant can be used to alter the operation of the synthetic inertia algorithm. However, the nature of this effect depends on the electrical network density and can be both positive and negative. The effect observed in the tested power system was confirmed for a real-dimension power system.

Influence of time constants of frequency regulators on the amplitude of power exchange fluctuations in autonomous diesel power plants

The application of autonomous electrical complexes with parallel diesel generator sets based on synchronous generators is considered. The problem of the existence of exchange power fluctuations in such technical systems is described. A mathematical model has been developed that allows conducting research of an autonomous electrical complex. It is proposed to implement graphical visualization of the dependence of the amplitude of power exchange fluctuations on time constants in the speed control circuits of diesel generators in the form of configuration maps. An example of using the proposed method for a specific electrical complex is given. The possibility of reducing the amplitude of exchange power fluctuations by reducing the values of time constants of frequency control circuits is justified, which is the basis of a new method for eliminating exchange power fluctuations and makes it possible to improve the method, which is based on changing the transmission coefficients of frequency regulators.

Highly Sensitive Signal Processing Devices for Capacitive Transducers of Micromechanical Accelerometers

In this paper, the principles of the open-loop frequency-based signal processing devices for capacitive MEMS accelerometers are used to develop three CMOS IP-core (Intellectual Property core) projects of highly sensitive signal processing devices with frequency output. Signal processing devices designed in accordance with the considered method form an output of rectangular pulses whose frequencies equal a difference of signal frequencies from two identical generators with micromechanical accelerometer capacitive transducers in their frequency control circuits. First, the analog project scheme uses two harmonic LC oscillators and an analog mixer to form an output rectangular-shape differential-frequency signal, the frequency of which is dependent on the measured acceleration. Second, the digital project is fully scalable for various CMOS-technologies due to oscillators of rectangular pulses and a digital mixer. Third, the mixed-signal project combines the advantages of the analog and digital projects. The signal processing device projects were developed, modeled and compared to comprehensively solve the problems of increasing sensitivity, dynamic range, noise immunity and resistance to destabilizing factors (e.g., to temperature changes).

A constant loop bandwidth in delta sigma fractional-N PLL frequency synthesizer with phase noise cancellation

This work presents the design of a new and unique design technique of constant loop bandwidth and phase-noise cancellation in a wideband ΔΣ fractional-N PLL frequency synthesizer. Phase noise performance of the proposed ΔΣ fractional-N PLL frequency synthesizer has been verified using CppSim simulator with the help of transistor level simulation results in Cadence SpecctreRF. Transient response of the proposed ΔΣ fractional-N PLL has been verified in transistor level simulation using Cadence SpectreRF in 0.13 μm standard CMOS process. The proposed phase-noise cancellation and constant loop bandwidth in wideband ΔΣ fractional-N PLL reduces the out of band phase noise by 18 dBc/Hz at 2 MHz offset frequency for a closed loop bandwidth of 1 MHz, when ICP,max is equal to 2.6 mA. PLL locking time has been reduced with phase-noise cancellation and a constant loop bandwidth calibration circuits using the proposed CP unit current cell for the mismatch compensated PFD/DAC in wideband ΔΣ fractional-N PLL frequency synthesizer. Optimum phase noise performance can be achieved with the help of proposed design technique. Proposed ΔΣ fractional-N PLL frequency synthesizer is locked within 14.0 μs with an automatic frequency control circuit of the LC VCO and a constant loop bandwidth calibration circuit through the use of proposed CP unit current cell for the mismatch compensated PFD/DAC for the phase-noise cancellation in worst case condition of KVFC = 10 and KLBC = 150. Our new design technique can be extensively integrated for wideband fractional-N PLL for new type of wireless communication paradigm using the thinnest channel subharmonic transistor and low power devices, and it has the potential to open a new era of fractional-N PLLs for wideband application.

Analytical Approach in the Development of RF MEMS Switches

Currently, the technology of microelectromechanical systems is widely used in the development of high-frequency and ultrahigh-frequency devices. The most important requirements for modern and advanced devices of the ultra-high-frequency range are the reduction of weight and size characteristics, power consumption with an increase in their functionality, operating frequency and level of integration. Radio frequency microelectromechanical switches are developed using the technology of the manufacture of CMOS-integrated circuits. Integrated radio frequency control circuits require low control voltages, the high ratio of losses to the isolation in the open and closed condition, high performance and reliability. This review is devoted to the analytical approach based on the knowledge of materials, basic performance indices and mechanisms of failure, which can be used in the development of radio-frequency microelectromechanical switches.

A fast and efficient constant loop bandwidth with proposed PFD and pulse swallow divider circuit in [formula omitted] fractional-N PLL frequency synthesizer

This work presents the design of a ΔΣ fractional-N PLL frequency synthesizer with a new loop bandwidth calibration and automatic frequency control (AFC) circuit, applicable for wide band RF communication system. This new and unique loop bandwidth calibration circuit has been implemented using logarithmic and anti-logarithmic (Base2) architecture. This architecture is an efficient design technique as well as faster operation in CMOS domain. The operating frequency range of the ΔΣ fractional-N PLL frequency synthesizer is from 2.158 to 5.133GHz. The variation of LC VCO gain (KVCO) is obvious due to wide band application and it varies from 30.65MHz/Volt to 368MHz/Volt for the frequency range of 2.158–5.133GHz. Constant loop bandwidth is maintained by controlling the charge pump current. Power consumption of the ΔΣ fractional-N PLL frequency synthesizer is 34mW from a 1.2Volt power supply and the work has been carried out in 0.13μm standard CMOS process. Also, this design includes an automatic frequency control unit for the LC VCO circuit which is coarsely tuned within 1.825μs for KVFC=10 for worst case condition and it completes the loop bandwidth (LBW) calibration within 7.84μs for KLBC=150 for worst case condition. The maximum locking time of the ΔΣ fractional-N PLL frequency synthesizer with loop bandwidth calibration and automatic frequency control circuit is 12.7μs for KVFC=10 and KLBC=150 for worst case condition. The ΔΣ fractional-N PLL is locked much faster than any work reported earlier using the proposed PFD, CP, proposed pulse swallow divider, efficient AFC circuit for LC VCO and a new loop BW calibration technique in transistor level simulation using Cadence SpectreRF. The main advantage of this loop bandwidth calibration technique is that the calibration time can be adjusted according to the PLL output frequency, loop bandwidth calibration accuracy and tuning frequency range of the LC VCO.

A low phase noise and low spur PLL with auto frequency control circuit for L1-band GPS receiver

A low phase noise and low spur phase-locked loop (PLL) for L1-band global positioning system receiver is proposed in this paper. For obtaining low phase noise for PLL, All-PMOS LC-VCO with varactor-smoothing technique and noise-filtering technique is adopted. To reduce the reference spur, a low current-mismatch charge pump is carefully designed. A quasi-closed-loop auto frequency control circuit is used to accelerate the lock process of PLL. The PLL is fabricated in 180nm CMOS Mixed-Signal process while it operates under 1.8V supply voltage. The measured output frequency of PLL is 1.571GHz and output power is −1.418dBm. The in-band phase noise is −98.1 dBc/Hz @ 100kHz, while the out-band phase noise is −130.3dBc/Hz @ 1MHz. The reference spur is −75.8dBc at 16.368MHz offset. When quasi closed-loop AFC is working, the measured lock time is about 10.2μs.

System Level Design of Timing and Frequency Control Circuit

System Level Design of Timing and Frequency Control Circuit

Hardware Technology Research on Ultra-High Pressure Water Jet Ship Rust Control System Based on PLC

Ultra-high pressure water jet ship rust is one development direction of ship rust removal technique. In order to ensure the normal working of the system, how to control each equipment is the key-part of the design. This study presents the analytical research on hardware technology of the control system of ultra-high pressure water jet ship rust system, the analysis of the principle of frequency control system and circuit design and control circuit of PLC, by analysis the structure and principles of ultra-high pressure water jet rust, and then demonstrates through experimental test that the hardware electronic circuit works properly.

근거리에서 효율 향상을 위해 적응 주파수 제어 회로를 갖는 HF-대역 무선 전력 전송 시스템

본 논문에서는 근거리에서 효율 향상을 위해 적응 주파수 제어 회로를 갖는 HF-대역 무선 전력 전송 시스템을 제안하였다. 일반적으로 무선 전력 전송 시스템은 공진기 간의 이격 거리가 가까워짐에 따라 결합 계수가 변하게 되며, 이는 반사 임피던스에 의한 임피던스 부정합을 발생시킨다. 본 연구에서 제안한 방식은 전압제어 발진기의 공진 주파수를 이격 거리에 따라 자동으로 가변함으로써 공진기 간의 거리가 가까워 임피던스 부정합이 큰 경우에도 전송 효율의 저하를 막을 수 있다. 적응 주파수 제어 회로는 방향성 결합기, 검파기 및 루프 필터로 구성된다. 본 논문에서 제안한 방법의 유용성을 입증하기 위하여 HF-대역에서 동작하는 30<TEX>${\times}$</TEX>30 <TEX>$cm^2$</TEX> 크기의 루프 안테나를 갖는 무선 전력 전송 시스템을 설계하여 측정한 결과 근거리에서 효율이 개선됨을 확인하였다. In this paper, we proposed an HF-band wireless power transfer system with adaptive frequency control circuit for efficiency enhancement in a short range. In general, a wireless power transfer system shows an impedance mismatching due to a reflected impedance, because a coupling coefficient is varied with respect to separation distance between two resonating loop antennas. The proposed method can compensate this impedance mismatching by varying input frequency of a voltage-controlled oscillator adaptively with respect to separation distance. Therefore, transmission efficiency is enhanced in a short distance, where large impedance mismatch occurs. The adaptive frequency circuit consists of a directional coupler, a detector, and a loop filter. In order to demonstrate the performance of the proposed system, a wireless power transfer system with adaptive frequency control circuits is designed and implemented, which has a pair of loop antennas with a dimension of 30<TEX>${\times}$</TEX>30 <TEX>$cm^2$</TEX>. From measured results, the proposed system shows enhanced efficiency performance than the case without adaptive frequency control.

Frequency and Phase Estimation for Coherent QPSK Transmission With Unlocked DFB Lasers

This letter presents a hardware-efficient frequency estimator and an advanced phase estimation algorithm capable of tracking the phase noise of a 10-GBaud optical quadrature phase-shift-keying transmission system with standard distributed-feedback lasers in the presence of a frequency mismatch up to 1.2 GHz. This algorithm allows us to implement a digital coherent receiver without an analog frequency control circuit.

Children’s anti-scoliotic fixators with transcutaneous electronic activation

Conventional spinal implants are static and rigid structures which underpin the skeleton, not adapted to patient’s post-surgery evolution (e.g. growth in scoliotic children). A new active spinal implant uses mechanical energy from the patient’s body to perform an active, progressive dynamic correction. It is growth-compatible and can be extracted after completion of skeletal amendment. It is non-invasively controlled by means of a transcutaneous transformer. The core of the prosthesis is an internal hydraulic mechanism, which allows the appropriate corrective forces, bending moments and torques to be applied on the spine. The actions of the prosthesis on the skeleton can be periodically modified, under medical supervision, by activating several built-in, remote controlled micro-valves. The power and control signal to transiently activate the intracorporeal microvalves will be obtained by means of a PRC (parallel resonant converter) with a transcutaneous transformer. Telemetry is obtained by adding a slight oscillation in the frequency control circuit, resulting in an AM + FM modulated output signal. This signal is analyzed by a microcontroller in order to activate the selected intracorporeal microvalve. The new implant allows a progressive correction thanks to the non-invasive control of its modifiable geometry and its visco-elastic behaviour.

A linear, low‐power, wideband CMOS VCO for FM‐UWB applications

AbstractA linear, low‐power, wideband 0.18‐μm CMOS VCO for UWB applications is presented, as part of a PLL‐based direct FM modulator for the 3.1–5‐GHz UWB band. It consists of a frequency control circuit and a differential ring core, coupled to the antenna output and the PLL prescaler by two single‐ended inverter buffers. The measured VCO exhibits a linear tuning range of 0.5–5.0 GHz, low power consumption of 2.5–10.5 mW, and an output power of −10 ± 1 dBm. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1955–1958, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23547

High-Precision AFC Circuit Applied to 64QAM Point-to-Multipoint Burst Communications

In this paper, we propose a novel open-loop Automatic Frequency Control (AFC) circuit suitable for 64QAM point-to-multipoint (P-MP) burst communications. The proposed AFC contains two frequency offset detectors. One estimates the phase rotation over long intervals to obtain accurate estimates at the cost of phase ambiguity. The other estimates the phase rotation over short intervals and its output is used to resolve the ambiguity in the following phase ambiguity'compensator. Thus, the proposed AFC circuit calculates the phase rotation over sufficiently long periods to yield accurately estimate the carrier frequency offset while suppressing the phase-unwrapping problem. The proposed AFC approaches the Cramer-Rao bound (CRB) and so achieves very small residual frequency offset. The proposed AFC circuit can be implemented with much smaller circuit scale than the conventional devices. Computer simulations and experiments confirm that its residual frequency error is less than of 10 -5 for the frame format considered; this performance is sufficient for the 64QAM - 40 Mbaud system targeted.

Transcutaneous microvalve activation system using a coreless transformer

Conventional spinal implants show an invariable behavior that is not adapted to patients post-surgery evolution (e.g. scoliosis in children). They work as static and rigid structures that underpin the skeleton. A new visco-elastic spine implant is non-invasively controlled by means of a transcutaneous transformer, for progressive correction of spinal deformities. The bending moment and the torque applied to the spine with this new implant will be externally controlled by activating three intracorporeal microvalves. The power and control signal to activate the appropriated microvalve will be obtained by means of a parallel resonant converter (PRC) with a transcutaneous transformer. Adding a slight oscillation in the frequency control circuit of the power topology, a FM modulation is converted into an AM + FM output modulation on the transcutaneous dc–dc converter. A microcontroller analyses the output voltage envelope of a PRC and activates the corresponding intracorporeal microvalve in a non-intrusive way. Three valves are individually selectable to modify the prosthesis structure although the number of valves can be extended.

RF MEMS and their applications in NASA's space communication systems

Radio frequency (RF) and microwave communication systems rely on frequency, amplitude, and phase control circuits to efficiently use the available spectrum. Phase control circuits are required for electronically scanning phase array antennas that enable radiation pattern shaping, scanning, and hopping. Two types of phase shifters, which are the phase control circuits, are most often used. The first is comprised of two circuits with different phase characteristics such as two transmission lines of different lengths or a high pass and low pass filter and a switch that directs the RF power through one of the two circuits. Alternatively, a variable capacitor, or varactor, is used to change the effective electrical path length of a transmission line, which changes the phase characteristics. Filter banks are required for the diplexer at the front end of wide band communication satellites. These filters greatly increase the size and mass of the RF/microwave systems, but smaller diplexers may be made with a low loss varactor or a group of capacitors, a switch and an inductor.

Variable directional coupler with LC resonator

A new directional coupler with a frequency control circuit and parallel LC resonator is presented. An exact analysis for a variable directional coupler is derived. Changing the resonance frequency of the parallel resonator for the proposed directional coupler can provide tunable frequency characteristics and a wide operating frequency range.

Electronically Tunable Surface-Coil-Type Resonator for L-Band EPR Spectroscopy

The automatic frequency control (AFC) circuit in conventional electron paramagnetic resonance (EPR) spectrometers automatically tunes the microwave source to the resonance frequency of the resonator. The circuit works satisfactorily for samples stable enough that the geometric relations in the resonance structure do not change in a significant way. When EPR signals are measured during in vivo experiments with small rodents, however, the distance between the signal source and the surface-coil detector can change rapidly. When a conventional AFC circuit keeps the oscillator tuned to the resonator under those conditions, the resultant frequency change may exceed ±5 MHz and markedly shift the position of the EPR signal. Such a shift results in unacceptable effects on the spectra, especially when the experimenter is dealing with narrow EPR lines. The animal movement also causes a mismatching of the resonator and the 50-ohm transmission line. Direct results of this mismatching are increased noise; shifts in the position of the baseline; and a high probability of overdriving the signal preamplifier with consequent loss of the EPR signal. We therefore designed, built, and tested a new surface-coil resonator using varactor diodes for tuning the resonance frequency to the fixed frequency oscillator and for capacitive matching of the resonator to the 50-ohm transmission line. The performance of the automatic matching system was tested in vivo by measuring EPR spectra of lithium phthalocyanine implanted in rats. Stability and sensitivity of the spectrometer were evaluated by measuring EPR spectra with and without the use of the automatic matching system. The overall experimental performance of the spectrometer was found to significantly improve during in vivo experiments using the automatic matching system. Excellent matching between the 50-ohm transmission line and the resonator was maintained under all experimental circumstances that were tested. This should allow us now to carry out experiments that previously were not possible.

A 1–2 GHz pulsed and continuous wave electron paramagnetic resonance spectrometer

A microwave bridge has been constructed that performs three types of electron paramagnetic resonance experiments: continuous wave, pulsed saturation recovery, and pulsed electron spin echo. Switching between experiment types can be accomplished via front-panel switches without moving the sample. Design features and performance of the bridge and of a resonator used in testing the bridge are described. The bridge is constructed of coaxial components connected with semirigid cable. Particular attention has been paid to low-noise design of the preamplifier and stability of automatic frequency control circuits. The bridge incorporates a Smith chart display and phase adjustment meter for ease of tuning.