Frequency Synthesizer Research Articles

Анализ и разработка высокоточного генератора частоты w-диапазона с низким уровнем паразитных гармоник

For millimeter waves applications in the W-band 93.5-95.5 GHz, improved frequency synthesizers are highly demanded. Improved frequency synthesizer should be tunable synthesizer with high step resolution and possess high phase noise performance, low spurious harmonic levels and short locking time. These parameters are conflicting parameters in developing a high precision frequency oscillator with a pure spectrum. Therefore, it's necessary to make a compromisation between them. In this paper we present a frequency synthesizer based on a Gunn diode, two stable finely tuned frequency sources, a phase locked loop, and a 10th order subharmonic mixer in the feedback loop is built. The phase noise, spurious levels, and tuning step size of the phase locked loop generator are then analyzed, and the effect of each parameter on the others is introduced. To test the performance of the proposed frequency synthesizer using a spectrum analyzer, the output spectrum of the intermediate frequency was measured on a subharmonic mixer, which corresponds to the spectrum of a phase-locked loop generator. The results show that the proposed phase-locked loop generator can be tuned in steps of less than 1 Hz, and the first two spurious harmonics are far from the fundamental harmonic. These results can be used for designing an enhanced high precision frequency synthesizer with a low level of spurious harmonics and high phase noise performance in millimeter waves applications such as CW RADAR.

Dynamical low-noise microwave source for cold-atom experiments.

The generation and manipulation of ultracold atomic ensembles in the quantum regime require the application of dynamically controllable microwave fields with ultra-low noise performance. Here, we present a low-phase-noise microwave source with two independently controllable output paths. Both paths generate frequencies in the range of 6.835 GHz ± 25 MHz for hyperfine transitions in 87Rb. The presented microwave source combines two commercially available frequency synthesizers: an ultra-low-noise oscillator at 7GHz and a direct digital synthesizer for radio frequencies. We demonstrate a low integrated phase noise of 480µrad in the range of 10 Hz to 100 kHz and fast updates of frequency, amplitude, and phase in sub-µs time scales. The highly dynamic control enables the generation of shaped pulse forms and the deployment of composite pulses to suppress the influence of various noise sources.

Microwave Frequency Synthesizers: A Tutorial

Microwave Frequency Synthesizers: A Tutorial

A Low-Power 130-GHz Tuned Frequency Divider in 90-nm SiGe BiCMOS

This letter presents a tuned frequency divider in a 90-nm SiGe BiCMOS process. The operating bandwidth is 120–140 GHz with a self-oscillation frequency of 130 GHz. The input sensitivity at 130 GHz is -25 dBm and remains less than -4 dBm at 120–134 GHz. The chip consumes 45.1 mW from a 2-V supply, with a core power consumption of 36 mW. Potential applications include frequency synthesis in the 120–140-GHz band.

0.18-μm CMOS process 40 MHz–4.41 GHz frequency synthesizer with high linearity low phase noise varactor-reconstruction LC-VCO

A 40 MHz–4.41 GHz fractional-N frequency synthesizer (FS) with varactor-reconstruction VCO (VRVCO) fabricated in the standard 0.18-μm CMOS process is demonstrated. In the conventional VCO, owing to non-linearity of varactor and parasitic effects of switched-MOSFET, the top and bottom of the tuning curves show nonlinearity. The novel design of VRVCO for tuning sensitivity base on series-shunt hybrid capacitor-varactor part and optimized switched-capacitor bank is incorporated into the 4.41 GHz FS design to reduce the variation of the VCO gain, realize high linearity tuning curves and improve phase noise performance. Furthermore, a noise reduction topology is adopted to decrease phase noise of VRVCO. Simulated results show the proposed VRVCO can improve linearity of tuning frequency over the entire tuning range. The measured results show the overall tuning range exceeds 115% from 1.92 to 4.41 GHz including three VRVCOs with high linearity (fine-tuning sensitivity: 131%, coarse-tuning sensitivity: 106%) and the phase noise is −120dBc/Hz at 1 MHz offset from the carrier frequency of 4.41 GHz.

Vernier microcombs for high-frequency carrier envelope offset and repetition rate detection

Recent developments in Kerr microcombs may pave the way to a future with fully stabilized ultralow size, weight, and power consumption (SWaP) frequency combs. Nevertheless, Kerr microcombs are still hindered by a bandwidth/repetition rate trade-off. That is, the octave bandwidth needed for self-referencing is typically realized only with ∼THz repetition rates beyond the range of standard commercial photodetectors. The carrier envelope offset frequency is often likewise too high for detection. Dual-comb techniques for the measurement of THz repetition rates have made exciting progress, but the fCEO detection problem remains largely unaddressed. In this work, utilizing a Vernier dual-comb configuration, we demonstrate simultaneous detection of the electronically divided repetition rate and fCEO carrier envelope offset frequency of an octave-spanning microcomb. This, in turn, could help usher optical atomic clocks, low-noise microwave generators, and optical frequency synthesizers into various real-world applications.

R&D of an Innovative OFDM Communication Payload for Small-Size AUV

With its superiorities of low cost, high flexibility and deployment convenience, small-size autonomous underwater vehicles (AUVs) have been extensively applied to perform a variety of undersea missions. While underwater acoustic (UWA) communication provides a practical way to establish a wireless link, it still poses a significant challenge due to the strict limitations of a small-size AUV platform in terms of load capacity, energy supply and cost. Orthogonal frequency division multiplexing (OFDM) has drawn extensive attention due to its high data rate capability and relative robustness to multipath, the performance of which is unfortunately sensitive to the widespread Doppler effect. While efficient Doppler compensation is significantly crucial for UWA OFDM mobile communication, most of the conventional approaches are conducted using software resampling, thus rendering a huge burden on memory and calculation capability as well as a considerable processing delay. In this paper, from the perspective of hardware completion an UWA OFDM communication payload based on STM32F407 processor is designed and implemented to facilitate agile Doppler compensation with low computational overhead. In particular, after estimating Doppler by calculating the time compression or extension of the preamble signal, Doppler compensation is performed by directly adjusting the direct digital frequency synthesizer (DDS)-driven sampling rate of the analog-to-digital converter (ADC). As the Doppler is compensated parallel to the ADC acquisition, processing delay and memory requirement can be avoided. Finally, hardware-in-loop (HIP) simulation is performed to demonstrate the effectiveness and superiority of the proposed system. The results show that the designed system has the potential to achieve an effective communication rate of 3.19 kbps with the admissible implementation overhead. Future work will entail the integration and performance evaluation of the proposed UWA OFDM communication payload on a practical small-size AUV platform.

The assessment and management of deep neck space infections in adults: A systematic review and qualitative evidence synthesis.

To summarise current practices in the diagnosis and management of deep neck space infections (DNSIs). To inform future studies in developing a framework in the management of DNSIs. This review was registered on PROSPERO (CRD42021226449) and reported in line with PRISMA guidelines. All studies from 2000 that reported the investigation or management of DNSI were included. The search was limited to English language only. Databases searched included AMED, Embase, Medline and HMIC. Quantitative analysis was undertaken with descriptive statistics and frequency synthesis with two independent reviewers. A qualitative narrative synthesis was conducted using a thematic analysis approach. Secondary or tertiary care centres that undertook management of DNSIs. All adult patients with a DNSI. The role of imaging, radiologically guided aspiration and surgical drainage in DNSIs. Sixty studies were reviewed. Thirty-one studies reported on imaging modality, 51 studies reported treatment modality. Aside from a single randomised controlled trial, all other studies were observational (n = 25) or case series (n = 36). Computer tomography (CT) was used to diagnose DNSI in 78% of patients. The mean percentage of management with open surgical drainage was 81% and 29.4% for radiologically guided aspiration, respectively. Qualitative analysis identified seven major themes on DNSI. There are limited methodologically rigorous studies investigating DNSIs. CT imaging was the most used imaging modality. Surgical drainage was commonest treatment choice. Areas of further research on epidemiology, reporting guidelines and management are required.

Digital twin-based thermal analysis of a frequency synthesizer

A frequency synthesizer is a key component of radars and plays an important role in radar radio frequency transceiver systems. In this study, a digital twin (DT) model of the virtual entity of a frequency synthesizer is proposed to perform thermal analysis. First, the virtual entity of the DT model is established according to the physical entity of the frequency synthesizer. Then, based on the designed DT model of the virtual entity of the frequency synthesizer, the temperature distribution of the model and cooling channel is analyzed, and the temperature distribution of the key components is obtained. Finally, using the results from the DT virtual entity model, a frequency synthesizer temperature prediction method based on a stochastic configuration network (SCN) algorithm is proposed. In the test phase, the characteristic and virtual temperature vectors are used as the input and output of the SCN training set, respectively. Then, 10 different sets of inputs are selected to obtain 10 sets of simulated temperatures and SCN predicted temperatures. The results indicate that the SCN algorithm based on the DT frequency synthesizer can accurately predict the temperature of the physical frequency synthesizer. The thermal analysis of the frequency synthesizer based on the DT provides accurate solutions and reduces the time required by physical components to adjust to high temperatures.

Free‐Electron‐Driven Frequency Comb

AbstractFree‐electron radiations prompt numerous advanced applications such as particle detectors, biological imaging, and light sources from microwave to X‐ray. While their polarization, directionality, and phase could be shaped with prosperous metamaterials, their natural broad spectra have not been tailored to yield frequency combs, which are state‐of‐the‐art technology in metrology, spectroscopy, and precision frequency synthesis. Here, the frequency comb directly emitted from the free‐electron radiation is demonstrated by simultaneously exciting a series of modes with equidistant spectral lines. Both the offset and repetition frequencies are readily adapted by structural parameters, and relative spectrum intensities between the comb teeth are customizable based on selective coupling, thus permitting flexible tunability over broadband. Moreover, the repetition rate is experimentally verified at the microwave regime. The proposed methodology implies that swift electrons present a natural and versatile platform for generating frequency combs, facilitating the development of metrology and spectroscopy in the terahertz band.

New Associate Editor

It is with great pleasure that I welcome Bodhisatwa (Bodhi) Sadhu to the editorial board of the IEEE Journal of Solid-State Circuits as a new Associate Editor. Dr. Sadhu is an expert in RF and mm-wave circuits and systems, including phased arrays and frequency synthesizers.

28-nm CMOS 공정을 이용한 고속 첩 신호 합성기 설계

This study proposes a frequency synthesizer with fast frequency modulation using a 28-nm CMOS process. The synthesizer used a two-point modulation technique that divides the frequency range into high- and low-pass regions to lock the frequency. In the high-pass region, continuous frequency modulation was achieved using a charge-digital-to-analog converter, while in the low-pass region, the synthesizer was set to the desired frequency using a divider and a delta-sigma modulator. The manufactured signal generator is capable of oscillating at frequencies between 14.1 GHz and 16.2 GHz, with a phase noise of −100.14 dBc/Hz at 1 MHz offset frequency. For chip signal generation, the generator had a chip time of 42.8 s and a bandwidth of 860 MHz. The chip area was 1,070×700 μm2.

Photonic Generation of Background-Free Phase-Coded Pulses With Low Power Fluctuation Over the Multi-Octave Frequency Range

In this article, a photonic microwave signals generation scheme for background-free phase-coded (PC) radar pulse with multioctave tuning is experimentally demonstrated. Firstly, an optical frequency comb (OFC) demultiplexing technology based on optical injection locking (OIL) provides a power-equalized coherent optical local oscillator (LO) with ultra-broadband tuning capability. Then, a phase-modulated optical signal is produced based on the conversion intensity modulation to phase modulation. Finally, a background-free phase-coded signal can be obtained by beating the optical signal with LO at a balanced photodetector (BPD). The proposed scheme features a flat frequency response over an ultra-wideband frequency range without needing a broadband modulator and radio frequency (RF) synthesizer. A proof-of-concept experiment demonstrates that the power fluctuation of 0.5 Gbps background-free PC pulses is lower than 3.12 dB within 3∼24 GHz carrier frequency. Furthermore, the pulse compression performance and system stability are investigated, respectively.

Full C-band wavelength-tunable, 250 MHz repetition rate mode-locked polarization-maintaining fiber laser

We demonstrate a full C-band wavelength-tunable mode-locked fiber laser with a repetition rate of 250 MHz, representing the highest repetition rate for C-band tunable mode-locked lasers thus far to the best of our knowledge. The polarization-maintaining fiber-based Fabry–Perot cavity enables a fundamental repetition rate of 250 MHz with a semiconductor saturable absorber mirror as a mode-locker. We observed a stable and single soliton mode-locking state with wide tunability of the center wavelength from 1505 to 1561 nm by adjusting the incident angle of a bandpass filter inside the cavity. The wavelength-tunable high-repetition-rate mode-locked laser covering the full C-band is expected to be a compelling source for many frequency-comb-based applications, including high-precision optical metrology, broadband absorption spectroscopy, and broadband optical frequency synthesizers.

A Low Spur 5.9-GHz CMOS Frequency Synthesizer with Loop Sampling Filter for C-V2X Applications

In this paper, a very low spur 5.9-GHz integer-N frequency synthesizer designed for a Cellular Vehicle-to-Everything (C-V2X) receiver is presented. The PLL is referenced to a 10-MHz crystal oscillator and the design is implemented in a 65-nm CMOS process. The output of the synthesizer has differential quadrature topology and provides the local oscillator signal to a downconverter mixer of C-V2X receiver. Post-layout simulations show that the reference spurs are better than −88[Formula: see text]dBc through loop sampling technique which was implemented in a 11.8-GHz VCO design for the first time to the best of our knowledge. The best spur level without the loop sampling technique applied is limited to −55[Formula: see text]dBc. Using the loop sampling technique provides a spur reduction of 33[Formula: see text]dB which is a significant improvement at this frequency. Based on post-layout simulations, the design has a phase noise of −97/−99/−114[Formula: see text]dBc for 10[Formula: see text]kHz/100[Formula: see text]kHz/1[Formula: see text]MHz frequency offsets, respectively, which presents competitive numbers with the designs in the literature. The design has 1.2-V nominal supply voltage for the analog and digital blocks. The total power dissipation of the synthesizer core is 6[Formula: see text]mW from a 1.2-V supply while the output buffers driving a 100-fF load consumes 18[Formula: see text]mW.

Optimized MASH-SR Divider Controller for Fractional-N Frequency Synthesizers

The divider controller in a conventional phase-locked loop fractional- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> frequency synthesizer modulates the instantaneous division ratio of the feedback divider. The divider controller is typically a digital circuit that performs quantization of its input signal. Multi-stage noise shaping digital delta-sigma modulators (MASH DDSMs) and successive requantizer (SRs) are two representative divider controller architectures offering lower complexity and better spur performance, respectively. The MASH-SR, as a hybrid of these two classes of divider controllers, can achieve both lower hardware cost than the SR and better performance against spurs than a MASH DDSM. In this work, we present an optimized MASH-SR hybrid and compare the design with its conventional MASH DDSM and SR counterparts.

Research and Implementation of a Numerical Control Oscillator with Improved Pipelined CORDIC Algorithm

As the recognized core of electronic systems, frequency synthesizers have been applied in many communication fields. NC oscillator (NCO) is the main component of the frequency synthesizer. It helps to generate high-precision and high-frequency signals, so it has been widely used. NCO implementation methods include table lookup method, polynomial expansion method, coordinate rotation digital computer (CORDIC) algorithm, etc. CORDIC algorithm is one of many commonly used methods in trigonometric function calculation and digital signal processing, and is often used as the core of DDS (direct digital synthesis) to generate signals. Compared with table lookup and polynomial expansion, CORDIC algorithm has higher efficiency in signal generation and hardware utilization. In view of the disadvantages of traditional CORDIC algorithm, which takes up large resources and has relatively slow calculation speed, in order to improve the output efficiency, this paper uses an efficient 12-stage pipelined CORDIC architecture and a very small lookup table (LUT) to implement a sine wave generator. The system is coded and simulated in Quartus and ModelSim. The results show that the proposed structure can increase the operating speed of the system from 217.77 MHz to 291.04 MHz, and improve the output efficiency of the system.

Photonic comb-rooted synthesis of ultra-stable terahertz frequencies

Stable terahertz sources are required to advance high-precision terahertz applications such as molecular spectroscopy, terahertz radars, and wireless communications. Here, we demonstrate a photonic scheme of terahertz synthesis devised to bring the well-established feat of optical frequency comb stabilization down to the terahertz region. The source comb is stabilized to an ultra-low expansion optical cavity offering a frequency instability of 10−15 at 1-s integration. By photomixing a pair of comb lines extracted coherently from the source comb, terahertz frequencies of 0.10–1.10 THz are generated with an extremely low level of phase noise of –70 dBc/Hz at 1-Hz offset. The frequency instability measured for 0.66 THz is 4.4 × 10−15 at 1-s integration, which reduces to 5.1×10−17 at 65-s integration. Such unprecedented performance is expected to drastically improve the signal-to-noise ratio of terahertz radars, the resolving power of terahertz molecular spectroscopy, and the transmission capacity of wireless communications.

Proposal for a hybrid clock system consisting of passive and active optical clocks and a fully stabilized microcomb.

Optical atomic clocks produce highly stable frequency standards and frequency combs bridge clock frequencies with hundreds of terahertz difference. In this paper, we propose a hybrid clock scheme, where a light source pumps an active optical clock through a microresonator-based nonlinear third harmonic process, serves as a passive optical clock via indirectly locking its frequency to an atomic transition, and drives a chip-scale microcomb whose mode spacing is stabilized using the active optical clock. The operation of the whole hybrid system is investigated through simulation analysis. The numerical results show: (i) The short-term frequency stability of the passive optical clock follows an Allan deviation of σy(τ) = 9.3 × 10-14τ-1/2 with the averaging time τ, limited by the population fluctuations of interrogated atoms. (ii) The frequency stability of the active optical clock reaches σy(τ) = 6.2 × 10-15τ-1/2, which is close to the quantum noise limit. (iii) The mode spacing of the stabilized microcomb has a shot-noise-limited Allan deviation of σy(τ) = 1.9 × 10-11τ-1/2. Our hybrid scheme may be realized using recently developed technologies in (micro)photonics and atomic physics, paving the way towards on-chip optical frequency comparison, synthesis, and synchronization.

Optical and Microwave Metrology at the 10−18 Level with an Er/Yb:glass Frequency Comb

AbstractOptical frequency combs are essential tools for precision metrology experiments ranging in application from remote spectroscopic sensing of trace gases to the characterization and comparison of optical atomic clocks for precision time‐keeping and searches for physics beyond the standard model. Presented here is a description of the architecture and a full characterization of a telecom‐band, self‐modelocking frequency comb based on a free‐space laser with an Er/Yb co‐doped glass gain medium. The laser provides a robust and cost‐effective alternative to Er:fibre laser based frequency combs, while offering stability and noise performance similar to Ti:sapphire laser systems. Finally, the utility of the Er/Yb:glass frequency comb is demonstrated in high‐stability frequency synthesis using two ultra‐stable optical references at 1157 nm and 1070 nm and in low‐noise photonic microwave generation by dividing these references to the microwave domain.