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This work presents a fast-locking and low-jitter fractional- ${N}$ bang-bang phase-locked loop (BBPLL). To break the trade-off between jitter and locking time which is typical of BBPLLs, two novel techniques are introduced. A gear-shift technique, denoted as type-II gear-shift, avoids limit cycles in the phase-locked loop (PLL) frequency transient and optimizes the locking time of the main PLL loop. The adaptive frequency switching (AFS) technique reduces the PLL frequency error upon channel switching exploiting the already existing hardware. The prototype, implemented in a 28-nm CMOS process, has an active area of 0.23 mm2 and achieves a locking time always below 1.56 $\mu \text{s}$ (within 80 ppm accuracy) for frequency jumps up to 1.5 GHz over the 8.5–10 GHz tuning range. The measured rms jitter (integrated from 1 kHz to 100 MHz) is 48.6 fs for integer- $N$ channels and 68.6 fs for near-integer fractional- ${N}$ channels, with a worst case fractional spur of −58.2 dBc. The power consumption is 20 mW, leading to a jitter-power figure of merit of −253.2 and −250.3 dB for integer- $N$ and fractional- $N$ channels, respectively. [ABSTRACT FROM AUTHOR]

The problem of inefficient and unevenly distributed spectrum usage in industrial wireless networks has led to the emergence of the concept of industrial cognitive radio (CR) networks, which have particularly important applications in automotive industry. Industrial CR networks are planned to function in a wide spectrum range; therefore, they have high energy consumption because of frequency switching while other wireless technologies do not have this problem. A distinctive feature of this switching cost is that it depends on the wideness between the two frequency bands. In this article, we formulate the joint frequency assignment and scheduling problem for multihop industrial CR networks with a single transceiver by considering varying amounts of energy consumption that occurs while CR devices switch to different frequency bands. Our optimization problem, which we formulate as an integer linear program, minimizes the energy cost related to frequency switching while making frequency and time slot allocation to the cognitive devices. We prove that even on star graphs, our formulated problem is inapproximable within any polynomial-time computable function $f(n)$ in addition to being $\textsc {NP}\text {-Hard}$ in the strong sense. Therefore, we propose a polynomial-time heuristic algorithm to solve the energy consumption problem due to channel switching. Simulation results demonstrate that the performance of our heuristic algorithm is very close to the results obtained from the integer linear programming implementation by CPLEX optimization software. We also compare our proposed method with the corresponding constant energy consumption for frequency switching case and two state-of-the-art algorithms and demonstrate that taking into account the different energy consumption while switching to different frequency bands is vital for joint frequency assignment and scheduling in multihop industrial CR networks with a single transceiver. [ABSTRACT FROM AUTHOR]

An all-digital reconfigurable multi-output clock generator is presented. A digital phase-locked loop provides a high-frequency clock to multiple independent open loop $\Delta \Sigma $ fractional dividers (FDIVs). A high resolution digital-to-time converter (DTC) whose range is calibrated in background is used to achieve low-jitter performance that is insensitive to process, voltage, and temperature variations. The proposed open loop FDIV operates over a wide frequency range of 20 MHz–1 GHz, and has programmable spread spectrum modulation and instantaneous frequency switching capabilities. Fabricated in a 65-nm process, the prototype FDIV occupies an active area of 0.017 mm2. At 1-GHz output frequency, it consumes 3.2 mW from 0.9-V supply and achieves a worst case integrated jitter of 1.44 psrms. [ABSTRACT FROM AUTHOR]

Fiber-ring-based optical frequency comb generators are analyzed to understand their behavior and limitations. A numerical frequency-domain model is described for studying dispersion and other phase mismatch causing effects in the fiber ring cavity, as well as for predicting the spectral and temporal evolutions of the comb in time. The results from this analysis are verified with experimental measurements. A flat optical comb, with a terahertz span within a 6-dB power envelope and containing 100 comb lines, with a suppressed central comb line, is demonstrated. The comb shows an excellent coherence dependent on the phase noise from the radio frequency synthesizer that drives the comb generator. Improvement in the error correction loop also enables the comb spacing to be set at precise 12.5-MHz intervals without having to adjust the system. Fast frequency switching of the comb line spacing is demonstrated for the first time. The comb line spacing can be switched to any operation frequency with a resolution of 12.5 MHz between 6 and 12.5 GHz, as limited only by the microwave circuit used. The switching time is less than 1 s, and the spectral profile of the comb is maintained. [ABSTRACT FROM PUBLISHER]

The dynamics of a short-cavity, electrooptically tunable microchip laser is studied using the Maxwell-Bloch equations for a unidirectional ring cavity. Within this model, the electrooptic tuning medium is treated rigorously by a wave propagation equation and the electrooptic tuning is equivalent to introducing a time varying perturbation to the boundary condition. With the help of an approximate analytic solution as well as numerical simulations, we find that the laser relaxation does not pose limitations to the intracavity frequency modulation bandwidth. Instead, the bandwidth is a sensitive function of the cavity length and also of the fraction of the cavity length taken up by the electrooptic section. In addition, under large-signal sinusoidal modulation, the numerical solutions reveal complicated dynamical behaviors when the modulation frequencies are near the cavity free spectral range. [ABSTRACT FROM AUTHOR]

The continuous growth of telecommunications traffic has placed huge demands on the traditional networks. Bottlenecks are particularly evident at the routers, where optical to electrical conversion must take place to read the routing information. Using optical-only routing, the traffic flow would be much faster, and more streamlined. A key component in this optical router is the tunable laser. When the laser is switched at high speeds, red-shifted thermal effects, due to the heating effects of the applied currents, cause a drift in the frequency, in the opposite direction to the blue-shifted carrier effects. The thermal effects have been quantified theoretically and experimentally here. The impact of the thermal effects, both on the frequency switching and on the frequency-shift keying (FSK), has been investigated. Methods of compensating for the thermal effects have been developed and verified by simulation and by experiment. [ABSTRACT FROM PUBLISHER]