Showing papers on "Frequency drift published in 2016"

A 60 GHz Frequency Generator Based on a 20 GHz Oscillator and an Implicit Multiplier

Abstract: This paper proposes a mm-wave frequency generation technique that improves its phase noise (PN) performance and power efficiency. The main idea is that a fundamental 20 GHz signal and its sufficiently strong third harmonic at 60 GHz are generated simultaneously in a single oscillator. The desired 60 GHz local oscillator (LO) signal is delivered to the output, whereas the 20 GHz signal can be fed back for phase detection in a phase-locked loop. Third-harmonic boosting and extraction techniques are proposed and applied to the frequency generator. A prototype of the proposed frequency generator is implemented in digital 40 nm CMOS. It exhibits a PN of $-100\;\text{dBc/Hz}$ at 1 MHz offset from 57.8 GHz and provides 25% frequency tuning range (TR). The achieved figure-of-merit (FoM) is between 179 and 182 dBc/Hz.

A low frequency oscillator using a super-capacitor

Abstract: A low frequency relaxation oscillator is designed using a super-capacitor. An accurate analytical expression for the oscillation frequency is derived based on a fractional-order super-capacitor model composed of a resistance in series with a Constant Phase Element (CPE) whose pseudo-capacitance and dispersion coefficient are determined using impedance spectroscopy measurements. Experimental results confirm our theoretical analysis.

Analytical Concepts for Reactive Power Based Primary Frequency Control in Power Systems

Abstract: This paper introduces a novel idea for adding virtual inertia in power systems by controlling the frequency swing dynamics through voltage channel. The purpose is to develop a frequency-based supplementary VAR modulation to assist governor action during power imbalance events. In this aim, we propose a two-band power system stabilizer, tuned for very low-frequency common swing mode, to adaptively adjust reference voltage of a Synchronous Condenser (SC) and modulate its reactive power on a second-by-second basis. The feasibility of this idea is supported by theoretical and simulation evidences. From theoretical side, we formulate a computational procedure to measure the degree of control impact, accompanied by sensitivity analyses around varying operating points. On the simulation side, we perform extensive studies on four well-known IEEE multi-machine test systems. The results show that VAR modulation by SC has a considerable impact on the minimum post-contingency frequency (frequency nadir), even more than so-called load modulation methods in some cases, which in fact has not been given enough attention in the past. In addition, we show that the proposed method can aid governors to improve primary frequency response particularly in low inertia power systems by reducing post-event frequency settling time and bias.

Impedance-Based Analysis of Active Frequency Drift Islanding Detection for Grid-Tied Inverter System

Abstract: Islanding detection is critical to the safety of grid-tied inverters. This paper presents an impedance-based analysis of the active frequency drift (AFD) islanding detection method. To study this method, the output impedance of a grid-tied inverter is modeled. The $Z_{qq}$ of the inverter impedance features a negative incremental resistor, whose magnitude is equal to the dc impedance magnitude of the local load defined by the test standard. With a large value of feedforward gain $N$ in the AFD method, the phase of $Z_{qq}$ is shown to drop below 180°. Under an islanding condition, due to a lack of phase margin, the inverter system becomes unstable with a frequency drift away from its steady state. The islanding condition is then identified by a frequency detection unit. Experimental results verify the analysis.

Wavelet-Based Characterization of Small-Scale Solar Emission Features at Low Radio Frequencies

Abstract: Low radio frequency solar observations using the Murchison Widefield Array have recently revealed the presence of numerous weak, short-lived and narrow-band emission features, even during moderately quiet solar conditions. These non-thermal features occur at rates of many thousands per hour in the 30.72 MHz observing bandwidth, and hence, necessarily require an automated approach for their detection and characterization. Here, we employ continuous wavelet transform using a mother Ricker wavelet for feature detection from the dynamic spectrum. We establish the efficacy of this approach and present the first statistically robust characterization of the properties of these features. In particular, we examine distributions of their peak flux densities, spectral spans, temporal spans and peak frequencies. We can reliably detect features weaker than 1 SFU, making them, to the best of our knowledge, the weakest bursts reported in literature. The distribution of their peak flux densities follows a power law with an index of -2.23 in the 12-155 SFU range, implying that they can provide an energetically significant contribution to coronal and chromospheric heating. These features typically last for 1-2 seconds and possess bandwidths of about 4-5 MHz. Their occurrence rate remains fairly flat in the 140-210 MHz frequency range. At the time resolution of the data, they appear as stationary bursts, exhibiting no perceptible frequency drift. These features also appear to ride on a broadband background continuum, hinting at the likelihood of them being weak type-I bursts.

A 0.52/1 V Fast Lock-in ADPLL for Supporting Dynamic Voltage and Frequency Scaling

Abstract: In energy-efficient processing platforms, such as wearable sensors and implantable medical devices, dynamic voltage and frequency scaling allows optimizing the energy efficiency under various modes of operation. The clock generator used in these platforms should be capable of achieving a faster settling time and has a wider operating voltage range. In this brief, a fast lock-in all-digital phase-locked loop (ADPLL) with two operation modes (0.52/1 V) is presented. The proposed ADPLL can quickly compute the desired digitally controlled oscillator control code with high accuracy. Therefore, the proposed ADPLL can achieve a fast setting time with frequency errors $\mu \text{W}$ at (0.52 V, 120 MHz).

Rubidium chip-scale atomic clock with improved long-term stability through light intensity optimization and compensation for laser frequency detuning

Abstract: We demonstrate the implementation of a Rb87 chip-scale atomic clock (CSAC) that has improved long-term stability. A simple method of reducing the frequency drift in the CSAC is proposed. As well as the well-known effect of light intensity on the clock frequency, our analysis shows that the frequency drift that is due to laser frequency detuning (LFD) variation originates from asymmetry in the coherent laser fields, and thus, we propose to actively compensate the clock frequency by using variations in the light intensity and LFD. We performed experiments to obtain precise clock frequency sensitivities to the light intensity and LFD, and the frequency drift was reduced from 7.1×10−11/day to 6.9×10−13/day with the frequency compensation method. Additionally, the CSAC with an optimized configuration of light intensity and microwave power showed evident long-term frequency stability improvement, from 8.9×10−11 to 8.7×10−12 at 105 s. Therefore, our method is useful in reducing the frequency drift of CSACs and could be potentially used in applications that require moderate long-term stability of sub-1×10−11.

Comparison of bus frequency estimators for power system transient stability analysis

Abstract: The paper presents a study on the dynamic response of power system frequency control devices considering different approaches to estimate bus frequencies in power system simulators. The frequency signals considered in this paper are obtained based on the center of inertia, a commonly-used washout filter that approximates the derivative of the bus voltage phase angle, and a frequency divider formula developed by the authors. The dynamic behavior of frequency control devices such as thermostatically regulated loads is compared considering the three signals above. Different scenarios are discussed based on the IEEE 14-bus and New England 39-bus, 10-machine test systems.

Gain-Relationship-Based Automatic Resonant Frequency Tracking in Parallel $LLC$ Converter

Abstract: This paper proposes a generic control scheme for automatic resonant frequency tracking (ARFT) in resonant converters. The plant is modeled based on realistic ramp variation of resonant frequency due to slowly varying environmental conditions. The proposed ARFT scheme monitors the gain relationship between an exclusive electrical variable pair to detect frequency drift. An analytical approach is presented to select the most suitable variable pair for gain comparison. The effects of tank parameter variation and circuit nonidealities on the gain relationship of the chosen variable pair have been analyzed. An online correction mechanism is proposed to nullify the influence of load variation on the proposed technique. Second-order generalized integrator-based low-cost analog realization of the proposed strategy is detailed. Analytical predictions are experimentally validated by applying the control scheme to a parallel $LLC$ tank-based resonant dc–dc converter.

Time to digital converter and phase locked loop

Abstract: A phase locked loop is disclosed having a frequency controlled oscillator, a feedback path, a time to digital converter and a memory. The frequency controlled oscillator comprises a first control input for varying the frequency of the output of the frequency controlled oscillator so as to track a reference frequency and a second control input for modulating the frequency of the output signal so as to produce a chirp. The feedback path is configured to provide an input signal to the time to digital converter, and comprises modulation cancelling module operable to remove the frequency modulation resulting from the second control input from the output signal. The memory stores second control input values that each correspond with a desired chirp frequency and which compensate for non-linearity in the response of the frequency controlled oscillator to the second control input. The phase locked loop is operable in a chirp mode, in which the second control input is produced by determining a value for the second control input corresponding with a desired chirp frequency based on the stored second control input values in the memory, and in which the phase locked loop is configured to determine the first control input based on the feedback path from which the modulation cancelling module has removed the frequency modulation resulting from the second control input.

Temperature compensation of a capacitive MEMS accelerometer by using a MEMS oscillator

Abstract: This study reports a temperature compensation method for a capacitive MEMS accelerometer by using a MEMS double-ended-tuning-fork (DETF) resonator integrated with the accelerometer structure on the same die. The proposed method utilizes the frequency information of the clamped-clamped DETF resonator which is oscillating in a closed-loop operation. In order to compensate the temperature dependence of the accelerometer output, frequency drift of the DETF resonator against changing temperature is used, i.e., the resonator frequency is used as the temperature data for compensation purposes. On-chip integration of two sensors allows precise temperature sensing abilities by removing the thermal lag between the DETF resonator and the accelerometer. Tests are held in the −20 °C and 60 °C range by operating both sensors simultaneously in a temperature-controlled oven. The measurement results indicate temperature coefficient of frequency (TCf) of 480 ppm/K for the integrated resonator and temperature dependence of 1,164 µg/K for the accelerometer output, which is decreased to 1.4 µg /K after temperature compensation. Improved noise performances indicate the bias instability of 30 µg and the velocity random walk of 24 µg/sqrt(Hz) with the removal of the temperature ramp (after 30 seconds) in Allan-deviation plot.

Microwave Type III Pair Bursts in Solar Flares

Abstract: A solar microwave type III pair burst is composed of normal and reverse-sloped (RS) burst branches with oppositely fast frequency drifts. It is the most sensitive signature of the primary energy release and electron accelerations in flares. This work reports 11 microwave type III pair events in 9 flares observed by radio spectrometers in China and the Czech Republic at a frequency of 0.80–7.60 GHz during 1994–2014. These type III pairs occurred in flare impulsive and postflare phases with separate frequencies in the range of 1.08–3.42 GHz and a frequency gap of 10–1700 MHz. The frequency drift increases with the separate frequency (fx), the lifetime of each burst is anti-correlated to fx, while the frequency gap is independent of fx. In most events, the normal branches are drifting obviously faster than the RS branches. The type III pairs occurring in flare impulsive phase have lower separate frequencies, longer lifetimes, wider frequency gaps, and slower frequency drifts than that occurring in postflare phase. Also, the latter always has strong circular polarization. Further analysis indicates that near the flare energy release sites the plasma density is about cm−3 and the temperature is higher than 107 K. These results provide new constraints to the acceleration mechanism in solar flares.

A 13.5-MHz relaxation oscillator with ±0.5% temperature stability for RFID application

Abstract: This paper presents a 13.5-MHz low-power, RC on-chip relaxation oscillator with split-capacitor technique for RFID application. This oscillator implements only one comparator and one reference voltage to minimize power consumption and silicon area. A loop delay variation cancellation technique that employs an integrator loop and a split-capacitor architecture helps attained the temperature stability in the proposed oscillator. The proposed design is fabricated in 0.18-μm CMOS process. The relaxation oscillator consumes 48.8 μW at 1.8-V power supply. The measurement results show that the circuit can generate a stable frequency of 13.5 MHz. The output frequency variation is less than ±0.5% of temperature range from −30° C to 120° C, and the supply voltage variation coefficient is 0.5%/V across 1.5 V to 2.1V supply voltage.

Low Phase Noise Free-Running Oscillator Based on High Selectivity Bandpass Filter Using Composite Right/Left-Handed Transmission Line

Abstract: This letter presents a novel low phase noise free-running oscillator based on a high selectivity bandpass filter (BPF) using a composite right/left-handed transmission line (CRLH TL). The oscillator is designed at the spectrum-based quality factor $(Q_{s})$ peak frequency to achieve low phase noise performance. Ata center frequency of 2.05 GHz, the oscillator demonstrates, experimentally, a phase noise of $-$ 150.4 dBc/Hz at 1 MHz frequency, offset with a figure of merit(FOM) of $-$ 207.2 dBc/Hz, less than $-$ 32 dBm spurious harmonics, and total oscillator power consumption of 6.1 mW from a 2 V supply voltage.

Wide-band divide-by-4 injection-locked frequency divider using RLC resonator and capacitive cross-coupled oscillator

Abstract: A wide locking range divide-by-4 injection-locked frequency divider (ILFD) using a standard 0.18 μm CMOS process is presented. The ILFD circuit is realized with a capacitive cross-coupled n-core MOS dual-resonance RLC-tank oscillator to extend the locking range. The core power consumption of the ILFD core is 11.872 mW. The divider's free-running frequency has dual-bands at 2.87 and 2.69 GHz by switching the varactor's control bias, and at the incident power of 0 dBm the locking range is 3.2 GHz (28.82%), from the incident frequency 9.5 to 12.7GHz.

Development of agile frequency synthesizer

Abstract: Frequency synthesizer consists of a voltage controlled oscillator (VCO) and a Phase-locked loop (PLL). Finer frequency synthesis can be achieved by using a direct digital synthesizer (DDS). The PLL accepts an input of 10MHz which is known as the reference frequency and up converts it to an intermediate frequency of 1 GHz, which acts as an input to the direct digital synthesizer (DDS). The DDS can produce an output ranging from 1 Hz to 400 MHz. Here we are generating a frequency of range 360 ± 5 MHz. The final output frequency of the entire system belongs to C Band of Microwaves which is used in Doppler Weather Radar.

Frequency control of a spin-torque oscillator using magnetostrictive anisotropy

Abstract: We report the working principle of a spin-torque oscillator, of which the frequency is efficiently controlled by manipulating the magnetostrictive anisotropy. To justify the scheme, we simulate a conventional magnetic-tunnel junction-based oscillator which is fabricated on a piezoelectric material. By applying mechanical stress to a free layer using a piezoelectric material, the oscillation frequency can be controlled to ensure a broad tuning range without a significant reduction of the dynamic resistance variation. Such controllability, which appears in the absence of an external magnetic field, will not only enable the integration of spin-torque oscillators and conventional complimentary metal-oxide semiconductor technology but will also broaden the applicability of spin-torque oscillators.

Design of a programmable and low-frequency filter for biomedical signal sensing applications

Abstract: A programmable low-frequency filter for biomedical signal sensing application is presented here based on the principle of fifth-order Bessel transconductance capacitor (Gm-C) ladder filter. Current division and current cancellation techniques are used to achieve ultra-low Gm for operation transconductance amplifier (OTA) design. Active inductor is designed through a gyrator structure composed of an OTA and a capacitor. In order to achieve tunable cutoff frequency for the filter, constant Gm and variable capacitor structures are utilized in the design. The cutoff frequency can thus be adjusted as 35Hz, 150Hz and 250Hz through two digital control bits CTRSA and CTRSB. Gm is also adjustable to compensate frequency drift caused by the process and temperature variation. The filter was designed with 0.18µm 1P6M CMOS technology and achieves a THD of 61.2dB and consumes 12.38µW under 1.8V supply voltage.

Improving the Side-mode Suppression Ratio and Reducing the Frequency Drift in an Opto-Electronic Oscillator With a Feedback Control Loop and Additional Phase Modulation

Abstract: We present two stabilization methods for an opto-electronic oscillator. By using a frequency discriminator with a feedback control loop the long-term stabilization was improved, and a frequency drift of 0.05 ppm/K was achieved without any fiber thermal stabilization. In addition, the phase-noise degradation as a result of the discriminator control loop was investigated. To the best of our knowledge, this has not been done before for this type of method. Our study revealed that a properly designed control loop does not increase the phase noise. The second stabilization method was used to increase the side-mode suppression ratio. This was achieved with an additional control loop in the form of an oscillator-loop phase modulation. In this way, a 5-dB increase in the side-mode suppression ratio was recorded. The phase-noise degradation was less than 1 dB in the close-in region. The two methods were designed to operate simultaneously. This design provides both simplicity and cost effectiveness for the stabilized opto-electronic oscillator.

Frequency reference for crystal free radio

Abstract: To reduce the cost of a sensor node, complete system integration implies zero external components. A system solution is therefore presented to calibrate the frequency of an on-chip relaxation oscillator to be used as a frequency reference for low power crystal free wireless communication.

Microwave Type III Pair Bursts in Solar Flares

Abstract: Solar microwave type III pair burst is composed of normal and reverse-sloped (RS) burst branches with oppositely fast frequency drifts. It is the most sensitive signature of the primary energy release and electron accelerations in flares. This work reported 11 microwave type III pair events in 9 flares observed by radio spectrometers in China and the Czech Republic at frequency of 0.80 - 7.60 GHz during 1994 - 2014. These type III pairs occurred in flare impulsive and postflare phases with separate frequency in range of 1.08 - 3.42 GHz and frequency gap 10 - 1700 MHz. The frequency drift increases with the separate frequency (f_{x}), the lifetime of each burst is anti-correlated to f_{x}, while the frequency gap is independent to f_{x}. In most events, the normal branches are drifting obviously faster than the RS branches. The type III pairs occurring in flare impulsive phase have lower separate frequency, longer lifetime, wider frequency gap, and slower frequency drift than that occurring in postflare phase. And the latter always has strong circular polarization. Further analysis indicates that near the flare energy-release sites the plasma density is about 10^{10} - 10^{11},cm^{-3} and temperature higher than 10^{7} K . These results provide new constraints to the acceleration mechanism in solar flares.

Effects of Frequency Drift on the Quantification of Gamma-Aminobutyric Acid Using MEGA-PRESS

Abstract: The MEGA-PRESS method is the most common method used to measure γ-aminobutyric acid (GABA) in the brain at 3T. It has been shown that the underestimation of the GABA signal due to B0 drift up to 1.22 Hz/min can be reduced by post-frequency alignment. In this study, we show that the underestimation of GABA can still occur even with post frequency alignment when the B0 drift is up to 3.93 Hz/min. The underestimation can be reduced by applying a frequency shift threshold. A total of 23 subjects were scanned twice to assess the short-term reproducibility, and 14 of them were scanned again after 2-8 weeks to evaluate the long-term reproducibility. A linear regression analysis of the quantified GABA versus the frequency shift showed a negative correlation (P 0.05). Therefore, a frequency shift threshold at 0.125 ppm (15.5 Hz) can be used to reduce underestimation during GABA quantification. For data with a B0 drift up to 3.93 Hz/min, the coefficients of variance of short-term and long-term reproducibility for the GABA quantification were less than 10% when the frequency threshold was applied.

Oscillation Maps in the Broadband Radio Spectrum of the 1 August 2010 Event

Abstract: We search for indications of waves in the 25-2000 MHz radio spectrum of the 1 August 2010 event (SOL2010-08-01T08:57:00L075C013), where fast propagating waves in the solar corona with the periods of 181, 69, and 40 seconds were detected in UV observations. Using the wavelet technique we construct a new type of map of oscillations for selected periods in the whole domain of the radio spectrum. While the oscillation with the period of 181 seconds was recognized in the whole 25-2000 MHz radio spectrum, oscillations with periods of 69 and 40 seconds were confirmed only in the 250-870 MHz frequency range. In the 800-2000 MHz range we found periods of 50 and 80 seconds. Moreover, in the 250-870 MHz frequency range, the oscillation with the period of about 420 seconds was detected. We also made maps of phases of the 181-second oscillations in order to analyze their frequency drift. At the beginning of the radio event, in the 2000-500 MHz frequency range the phase of the 181-second oscillation drifts towards lower frequencies. On the other hand, at frequencies 25-500 MHz we found that the phase is nearly synchronous. While the phase drift at higher frequencies can be interpreted as being caused by the UV wave, the synchronization of the phase on lower frequencies is explained by the fast-electron beams, whose acceleration is modulated by the UV wave. Owing to this modulation, the electron beams are accelerated with the period of the UV wave (181 seconds). These beams propagate upwards through the solar corona and generate the 25-500 MHz radio emission with the 181-second period. Due to high beam velocity (~c/3, where c is the light speed) the 25-500 MHz radio emission, corresponding to a large interval of heights in the solar corona, is nearly synchronous.

Frequency tuning for dual level radio frequency (RF) pulsing

Abstract: Methods and apparatus for frequency tuning in process chambers using dual level pulsed power are provided herein. In some embodiments, a method for frequency tuning may include providing a first pulsed power at a first frequency while the first frequency is adjusted to a second frequency, wherein the first frequency is a last known tuned frequency at the first pulsed power, storing the second frequency as the last known tuned frequency at the first pulsed power, providing a second pulsed power at a third frequency while the third frequency is adjusted to a fourth frequency, wherein the first pulsed power and the second pulsed power are different and non-zero, and wherein the third frequency is a last known tuned frequency at the second pulsed power, and storing the fourth frequency as the last known tuned frequency at the second pulsed power.

Frequency estimation method and device for all-phase time-shift phase difference

Abstract: The invention belongs to the field of digit signal processing, and provides an improved frequency estimation method and device for all-phase time-shift phase difference, capable of improving precision and robustness and lowering signal-noise ratio threshold. The frequency estimation method includes the steps of inputting M=2N-1+L samples, namely x(-N+1-L) to x(N-1), obtaining a first path phase value phi, conducting all-phase FFT for x(-N+1-L) to x(N-1), directly taking the phase of index value K=K2 at peak spectrum as a second path phase value phi2, multiplying the difference of two paths of phase value (phi-phi2) with 1/delta omega L to obtain the initial frequency bias estimated value epsilon, conducting frequency drift compensation for the initial frequency bias estimated value epsilon to obtain the modified frequency bias estimated value ^ epsilon, and outputting the normalized frequency estimated value as described in the description. The method and apparatus are applicable to digital signal processing.

Far off-resonance laser frequency stabilization using multipass cells in Faraday rotation spectroscopy.

Abstract: We propose a far off-resonance laser frequency stabilization method by using multipass cells in Rb Faraday rotation spectroscopy. Based on the detuning equation, if multipass cells with several meters optical path length are used in the conventional Faraday spectroscopy, the detuning of the lock point can be extended much further from the alkali metal resonance. A plate beam splitter was used to generate two different Faraday signals at the same time. The transmitted optical path length was L=50 mm and the reflected optical path length was 2L=100 mm. When the optical path length doubled, the detuning of the lock points moved further away from the atomic resonance. The temperature dependence of the detuning of the lock point was also analyzed. A temperature-insensitive lock point was found near resonance when the cell temperature was between 110°C and 130°C. We achieved an rms fluctuation of 0.9 MHz/23 h at a detuning of 0.5 GHz. A frequency drift of 16 MHz/h at a detuning of -5.6 GHz and 4 MHz/h at a detuning of -5.2 GHz were also obtained for the transmitted and reflected light Faraday signal.

Broadband microwave sub-second pulsations in an expanding coronal loop of the 2011 August 10 flare

Abstract: Aims. We studied the characteristic physical properties and behavior of broadband microwave sub-second pulsations observed in an expanding coronal loop during the GOES C2.4 solar flare on 2011 August 10. Methods. The complex microwave dynamic spectrum and the expanding loop images were analyzed with the help of SDO/AIA/HMI, RHESSI, and the STEREO/SECCHI-EUVI data processing software, wavelet analysis methods, the GX Simulator tool, and the NAFE method. Results. We found sub-second pulsations and other different burst groups in the complex radio spectrum. The broadband (bandwidth about 1 GHz) sub-second pulsations (temporal period range 0.07−1.49 s, no characteristic dominant period) lasted 70 s in the frequency range 4−7 GHz. These pulsations were not correlated at their individual frequencies, had no measurable frequency drift, and zero polarization. In these pulsations, we found the signatures of fast sausage magnetoacoustic waves with the characteristic periods of 0.7 and 2 s. The other radio bursts showed their characteristic frequency drifts in the range of −262−520 MHz s -1 . They helped us to derive average values of 20−80 G for the coronal magnetic field strength in the place of radio emission. It was revealed that the microwave event belongs to an expanding coronal loop with twisted sub-structures observed in the 131, 94, and 193 A SDO/AIA channels. Their slit-time diagrams were compared with the location of the radio source at 5.7 GHz to realize that the EUV intensity of the expanding loop increased just before the radio source triggering. We reveal two EUV bidirectional flows that are linked with the start time of the loop expansion. Their positions were close to the radio source and propagated with velocities within a range of 30−117 km s -1 . Conclusions. We demonstrate that periodic regime of the electron acceleration in a model of the quasi-periodic magnetic reconnection might be able to explain physical properties and behavior of the sub-second pulsations. The depolarization process of the microwave emission might be caused by a plasma turbulence in the radio source. Finally, the observed EUV flows might be linked with reconnection outflows.

A new algorithm for a high-modulation frequency and high-speed digital lock-in amplifier

Abstract: To increase the maximum modulation frequency of the digital lock-in amplifier in an online system, we propose a new algorithm using a square wave reference whose frequency is an odd sub-multiple of the modulation frequency, which is based on odd harmonic components in the square wave reference. The sampling frequency is four times the modulation frequency to insure the orthogonality of reference sequences. Only additions and subtractions are used to implement phase-sensitive detection, which speeds up the computation in lock-in. Furthermore, the maximum modulation frequency of a lock-in is enhanced considerably. The feasibility of this new algorithm is tested by simulation and experiments.

Space passive hydrogen maser a passive hydrogen maser for space applications

Abstract: For the passive hydrogen maser (PHM) having excellent frequency stability performance and lower frequency drift, it has been chosen as the one of atomic clock in the Beidou navigation satellite system. Beijing Institute of Radio Metrology and Measurement (BIRMM) is responsible for the whole equipment, including Physics Package (PP) and Electronic Package (EP). A Flight Model (FM) has already launched with satellite. This paper gives the results of PHM physics parameters and measurements of PHM. At last, the paper presents the results of PHM phase comparison on board, and gets negligible drift relative to rubidium clock.