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Frequency combs are powerful tools for many applications and high performances are achieved by stabilizing these lasers. For operation in the mid‐infrared, quantum cascade lasers (QCL) are ideal candidates as they present numerous advantages. However, stabilized QCL‐combs lack a detailed characterization of their noise properties due to the sensitivity limits of current analyzing techniques. To overcome these challenges, what is believed to be the first tightly locked dual QCL‐comb system is developed. Its use is twofold. First, phase noise analysis of the dual‐comb signal shows residual phase noise below 600 mrad for all comb lines, and the comb coherence as well as the performances of the repetition frequency locking mechanism is characterized. Second, coherent averaging with a 7 × 105 Hz1/2 figure‐of‐merit system is demonstrated, which is compatible with high‐precision spectroscopy. [ABSTRACT FROM AUTHOR]

This paper concerns the behavior of time-periodic solutions to 1D dissipative autonomous semilinear hyperbolic PDEs under the influence of small time-periodic forcing. We show that the phenomenon of forced frequency locking happens similarly to the analogous phenomena known for ODEs or parabolic PDEs. However, the proofs are essentially more difficult than for ODEs or parabolic PDEs. In particular, non-resonance conditions are needed, which do not have counterparts in the cases of ODEs or parabolic PDEs. We derive a scalar equation which answers the main question of forced frequency locking: Which time shifts u (t + φ) of the solution u(t) to the unforced equation do survive under which forcing? [ABSTRACT FROM AUTHOR]

Frequency combs are powerful tools for many applications and high performances are achieved by stabilizing these lasers. For operation in the mid‐infrared, quantum cascade lasers (QCL) are ideal candidates as they present numerous advantages. However, stabilized QCL‐combs lack a detailed characterization of their noise properties due to the sensitivity limits of current analyzing techniques. To overcome these challenges, what is believed to be the first tightly locked dual QCL‐comb system is developed. Its use is twofold. First, phase noise analysis of the dual‐comb signal shows residual phase noise below 600 mrad for all comb lines, and the comb coherence as well as the performances of the repetition frequency locking mechanism is characterized. Second, coherent averaging with a 7 × 105 Hz1/2 figure‐of‐merit system is demonstrated, which is compatible with high‐precision spectroscopy.

Radiofrequency (RF) injection locking and spectral broadening of a terahertz (THz) quantum-cascade vertical-external-cavity surface-emitting laser (QC-VECSEL) is demonstrated. An intracryostat VECSEL focusing cavity design is used to enable continuous-wave lasing with a cavity length over 30 mm, which corresponds to a round-trip frequency near 5 GHz. Strong RF current modulation is injected to the QC-metasurface electrical bias to pull and lock the round-trip frequency. The injection locking range at various RF injection powers is recorded and compared with the injection locking theory. Moreover, the lasing spectrum broadens from 14 GHz in free-running mode to a maximum spectral width around 110 GHz with 20 dBm of injected RF power. This experimental setup is suitable for further exploration of active mode-locking and picosecond pulse generation in THz QC-VECSELs.

This paper presents a novel jitter reduction technique for a voltage-controlled ring oscillator (VCRO). This technique is helpful in employing VCRO-based circuits like Analog to Digital Converter (ADC), Phase Locked Loop (PLL) and time-based circuits whose performance is severely degraded by high jitter. In the proposed technique, the jitter is extracted using Excess Phase Discrimination (EPD) block and is transformed into Pulse Width Modulated (PWM) signal, which is then fed into the Phase Compensator (PC) block. This block reduces the jitter by about half its value after enabling the Single Ended Injection Locking (SEIL). The proposed work is designed in SCL 180 nm CMOS technology at 1.8 V supply. On enabling the proposed circuit, the Root Mean Square (RMS) jitter reduces from 5.94 to 2.58 ps (about 56%) for VCRO running at 58 MHz and consumes a total power of 375.84 μ W. The overall performance of the proposed circuit does not vary much in the post-layout simulations, hence demonstrating the effectiveness of the proposed technique. [ABSTRACT FROM AUTHOR]

The paper investigates the terahertz performance of a mutually injection-locked multi-element high electron mobility avalanche transit time (HEM-ATT) source based on AlGaN/GaN two-dimensional electron gas (2-DEG). Utilizing a nanostrip patch type planar coupling circuit, mutual injection locking between adjacent elements is achieved. The paper provides a comprehensive analysis of the integrated power combining technique in the mutually injection-locked multi-element HEM-ATT oscillator. A ten-element mutually injection-locked integrated power combined source is designed for operation at 1.0 THz, and simulation studies are conducted to examine its DC, large-signal, and avalanche noise characteristics. The capability of generating a narrow-band terahertz wave is verified by introducing various levels of structural mismatches between the elements. Results indicate that the ten-element HEM-ATT oscillator can deliver 2.27 W peak power with a 17% DC to THz conversion efficiency at 1.0 THz. The average noise measure of the oscillator is found to be 12.54 dB. Additionally, the terahertz performance of the mutually injection-locked ten-element HEM-ATT oscillator is compared with other state-of-the-art THz sources to evaluate its potentiality as an excellent integrated THz radiator.

A compact high-power four-port circulator aiming to simplify the conventional, complex, and bulky injection-locking magnetron system is proposed. To reduce the performance deterioration and the risk of ferrite rupture under long-term high-microwave-power condition, the method of breaking a monolithic ferrite into three discrete ferrites in a conventional three-port circulator is proposed. To miniaturize the size and cost of the four-port circulator, a butterfly-shaped waveguide structure is proposed, with a stub inserted into the cavity at the central point and with no connecting waveguide. Multiphysics simulation results show that the temperature coefficient of variation (COV) at the surface of the discrete ferrites is 12.4% lower than that of a monolithic ferrite circulator, with input microwave power of 10 kW. The size of the proposed four-port waveguide circulator is 27% less than the assembly of two three-port circulators, and way smaller than a conventional differential phase shift circulator (DPSC). The simulated and measured S-parameters match well, and the measured power capacity of the fabricated circulator is higher than 3 kW (limited by the experimental condition). A magnetron is successfully locked using only one designed compact circulator. The research in this paper promotes the development of injection-locking magnetron and provides a design example for the compact, high-power circulator. [ABSTRACT FROM AUTHOR]

This paper presents an injection locked digitally controlled ring oscillator (IL-DCRO). To reduce jitter variations, minimize oscillator spurious signals, and eliminate periodical phase error, a double edge-injection (window injection) scheme with synchronized edge directions is proposed. A combinational edge generator is utilized to substitute the sequential edge generators for injection timing requirements relaxation. By biasing devices in deep triode, digitally controlled delay cells currents are adopted for frequency tuning. This helps reducing the devices flicker (1/f) noise and minimize the DCRO overall phase noise. At 1 MHz offset of frequency, the proposed oscillator has a measured phase noise of −125.95 dBc/Hz and −115.6 dBc/Hz at oscillation frequencies of 913.4 MHz and 432.6 MHz, respectively. Fabricated in 350 nm CMOS process, with a maximum power consumption of 3.3 mW, and oscillating at 913.4 MHz, this DCRO achieves a tuned oscillator figure of merit (FoM) of −197.35 dBc/Hz. The core area of this edge-injection-based DRCO is only 0.08 mm2. [ABSTRACT FROM AUTHOR]

We designed a single‐frequency green laser system that can deliver a 60‐mW frequency‐tunable single‐longitudinal‐mode laser beam, having a 6.5 MHz linewidth at around 519 nm. An external cavity diode laser can provide a wavelength‐tunable single frequency laser beam, but its output power is limited. Therefore, an injection‐locked laser was designed with a Fabry–Perot type green InGaN laser diode in an external Littrow‐type cavity as the master laser and another laser diode of the same model as the slave laser. Injection locking can effectively enhance the output power and narrow the linewidth of the master laser. We found that the injection locking occurred at longitudinal mode matching between the master laser and slave laser diodes, which is located at a specific frequency for a periodical applied current. The side peaks of the injection locking due to the transverse mode mismatching were recorded and analyzed. [ABSTRACT FROM AUTHOR]

A highly-stable and effective Er-doped random fiber laser (RFL) is proposed and experimentally demonstrated based on external optical injection locking technology. By adjusting the optical injected wavelength, the lasing wavelength can be selected precisely and emitted separately within the spectral bandwidth of 1555.5 nm to 1563.5 nm. The wavelength and output power fluctuation are less than 0.004% and 2.9%, respectively, indicating that optical injection locking of the RFL is quite stable over a long time. The optical injection locking technology is used in the half-open cavity incoherent RFL systems based on the random distributed Rayleigh scattering scheme, which provides an effective method to control or select the wavelength emission with high stability in a RFL. [ABSTRACT FROM AUTHOR]

The 1 / f additive phase noise of one-port injection-locked oscillators is experimentally characterized and analyzed using a simple analytic model based on the generalized 1 / f Kurokawa theory. To experimentally verify the prediction of the simple analytic model proposed, two negative-conductance transmission line pHEMT oscillators operating at 2.4828 GHz and 2.485 GHz were designed and fabricated. A new configuration for integrating an additive phase noise measurement system with a large signal network analyzer (LSNA) is introduced to jointly acquire both the noise and RF waveforms of the one-port injection-locked oscillator. The Kurokawa derivatives needed for the analytic expression were experimentally obtained using the LSNA measurements and optimized to accurately model the corner frequency. A good agreement between the predicted and experimental results was obtained for both the injection-locked and free-running oscillators. In contrast to phase noise measurements of the free-running oscillator, which can only characterize the oscillator-upconverted 1 / f 3 noise, the additive phase noise characterization of the injection-locked oscillator is shown to provide the means to directly observe and characterize the input-referred intrinsic 1 / f noise source of the oscillator negative resistance. [ABSTRACT FROM AUTHOR]

A noise circulating voltage‐controlled oscillator (VCO) with an intrinsic injection locking tripler is introduced. Based on the conventional frequency tripling scheme, by integrating the injection transistor pair into the fundamental VCO core, the current of the fundamental VCO core is reused by the injection transistor pair, and the phase noise is reduced due to the noise circulating behavior. The proposed VCO may achieve the fundamental and 3rd harmonic outputs, simultaneously. A protype design is implemented in a standard 65 nm CMOS process, with a tuning range of 33.68–40.11 GHz (17.4%). The phase noise at 1‐MHz offset varies between −101.2 and −97.9 dBc/Hz among the tuning range. The FoMT is in the range of 190.4 and 187.9 dBc/Hz, at 1‐MHz offset. [ABSTRACT FROM AUTHOR]

This paper presents an LO phase shifter with frequency tripling for 28-GHz 5G transceivers. The phase shifting and frequency tripling are achieved using an injection-locked oscillator and injection-locked frequency tripler, respectively. A phase detector based on third harmonic mixing is also implemented and is used to detect the applied phase shift, supporting automatic calibration of the phase shifter. Additionally, an algorithm to automatically tune the oscillators to their respective locking frequency is presented. To test the phase shifter, a 24–30-GHz sliding-IF receiver is implemented. Simulations show that a > 360 ∘ tuning range over the full 24–30 GHz span is achieved, with a gain variation of 0.11 dB or less, and that the phase detector has an rms phase error of < 2.5 ∘ . The circuit is implemented in a 28nm FD-SOI CMOS process and the entire chip measures 1080 μ m × 1080 μ m , including pads, and consumes 27–29 mW from a 1 V supply. [ABSTRACT FROM AUTHOR]

With a 65-nm CMOS process, a V-band wideband injection locking (IL) frequency tripler is proposed by cascading a multiplier and a driver amplifier stage. Concerning high output power and efficiency performance over a wideband locking range (LR), two transformer-based IL topologies are analyzed in the multiplier and driver stages, in which the cross-coupled pair is connected at the input and output ports of the transformer, respectively. Moreover, the active device is carefully designed in terms of the operating point of the harmonic generator and device sizing in the driver amplifier stage. With measurements, the proposed tripler achieves a maximum measured output power of 7.3 dBm with 22.4% output-to-DC power efficiency and 26.8% LR from 50.4 to 66 GHz. Including the output driver amplifier, the IL tripler consumes 24 mW DC power. The measured fundamental and 2nd-harmonic rejection ratios (HRR) are both better than 30 dBc, while the measured phase noise (PN) degradation is in close agreement with the theoretical value. • The wideband injection locking technique is utilized with two transformer-based IL topologies to improve the third-harmonic output power over a broadband locking range. • The design guidelines for injection locking tripler are presented including the passive networks and the active devices. • Thanks to the simultaneous consideration of both wide locking range and high output power, this tripler achieves the best figure-of-merit (FoM) and output power, advancing the state of the art. [ABSTRACT FROM AUTHOR]

Phase noisehas become the single most critical factor to be addressed in the design of modern communication systems. Facing the challenging requirements of 5G cellular communication, our paper describes a new theoretical framework to calculate the phase noise of LC oscillators, relying on easy to implement closed form solutions for phase noise calculations. Using closed form phase noise solutions enables oscillator designers to easily implement multiple phase noise calculation options for a number of oscillator circuits, which would be very difficult to implement with the existing mathematically complex phase noise theories. The analytic methods of our theory rely on modeling all real oscillators as having non-ideal or latent behaviors in addition to their primary nature for generating a carrier wave operating at a single frequency with a single amplitude. It is a cascade of these non-ideal transformation processes that produce non-ideal oscillator outputs containing the phase noise sidebands. Enhanced qualitative and quantitative insights into oscillator phase noise performances are achieved by using this approach. We validate our methods by comparing their results with phase noise simulations carried out for a sample CMOS LC voltage-controlled oscillator in 90 nm RFCMOS process using SpectreRF simulator. The results for the oscillator's output 1/f2 thermal phase noise, 1/f noise upconversion into 1/f3 phase noise and the 1/f3 corner frequency of phase noise spectrum using our theory yields −136 dBc/Hz at 10 MHz offset, −21.3 dBc/Hz at 1 kHz offset and 2.6 MHz respectively. The corresponding values obtained with SpectreRF simulation are −135.9 dBc/Hz, −23.4 dBc/Hz and 2.1 MHz. The carrier frequency is 5.4 GHz with output power of 9.78 dBm.

Detecting extremely small forces helps exploring new physics quantitatively. Here we demonstrate that the phonon laser made of a single trapped 40Ca+ ion behaves as an exquisite sensor for small force measurement. We report our successful detection of small electric forces regarding the DC trapping potential with sensitivity of (2.41 ±0.49) zN / Hz , with the ion only under Doppler cooling, based on the injection-locking of the oscillation phase of the phonon laser in addition to the classical squeezing applied to suppress the measurement uncertainty. We anticipate that such a single-ion sensor would reach a much better force detection sensitivity in the future once the trapping system is further improved and the fluorescence collection efficiency is further enhanced. [ABSTRACT FROM AUTHOR]

An injection-locked ring oscillator-based phase-locked-loop targeting clock recovery for space application at 3.2 GHz is presented here. Most clock recovery circuits need a very low phase noise and jitter performance and are thus based on LC-type oscillators. These excellent performances come at the expense of a very poor integration density. To alleviate this issue, this work introduces an injection-locked ring oscillator-based PLL circuit. The combination of the injection-locking process with the use of ring oscillators allows for the benefit of excellent jitter performance while presenting an extremely low surface area due to an architecture without any inductor. The injection locking principle is addressed, and evidence of its phase noise and jitter improvements are confirmed through measurement results. Indeed, phase noise and jitter enhancements up to 43 dB and 23.3 mUI, respectively, were measured. As intended, this work shows the best integration density compared to recent similar state-of-the-art studies. The whole architecture measures 0.1 mm2 while consuming 34.6 mW in a low-cost 180 nm CMOS technology. [ABSTRACT FROM AUTHOR]

Terahertz (THz) beamforming arrays are critical to address emerging applications in wireless communication, sensing, and imaging. Enabling such architectures, particularly with respect to synchronization of distributed radiating THz sources, is very challenging due to the sensitivity of such synchronizations to variations of process, voltage, temperature (PVT), and device mismatches. In this article, we propose and demonstrate a multi-layer THz array architecture to address robust frequency synthesis, optimal harmonic THz power generation, and scalable phase generation for THz beamforming. The bottom-most layer of this multi-layer network consists of a scalable 2-D negative transconductance (−Gm) cells that collectively oscillates at the center frequency of 69.3 GHz, thereby establishing a robust frequency and phase distribution across the entire chip. By eliminating independent oscillation capability of each node and merging resonator and coupling structures into one single network, the 2-D mesh removes the possibility of moving out of synchronization due to PVT variations or device mismatches and forms the underlying frequency synthesis layer. Local frequency multiplication and radiating elements are placed across the 2-D THz array, and beamforming is enabled through varactor control in the $-G_{m}$ cells. We demonstrate the proposed architecture in a $4\,\times \,4$ array with effective isotropic radiation power (EIRP) of +14 dBm at 0.416 THz in a lensless setup using a 65-nm CMOS process with the beamforming capability of ±30° in both ${E}$ - and ${H}$ -planes. [ABSTRACT FROM AUTHOR]

A standard-cell-based fractional-N synthesizable phase-locked loop (PLL) [or multiplying-delay-locked loop (MDLL)] is proposed, where the multiple phases of the three-stage ring digitally controlled oscillator (DCO) are utilized for injection. The required digital-to-time converter (DTC) range is reduced to one third of the DCO’s period, resulting in higher linearity, less jitter, lower power consumption, and smaller area. The issue of the mismatches among DCO’s stages is solved by the proposed dithering-assisted local skew calibration, which removes the skews in the injection path and smears out the periodic pattern at the PLL side to reduce spurs. Most of the dithering noise is suppressed by the injection locking and the phase tracking loop. Measured at 1.0095-GHz output frequency with 24-MHz reference frequency, with the proposed solution, the integrated root-mean-square (rms) jitter can be reduced from 6.40 to 2.55 ps, and the power consumption is 3.36 mW. This translates to −226.6-dB figure of merit (FoM) and −232.8-dB FoMref. The measured fundamental fractional spurs range from −56 to −45 dBc. [ABSTRACT FROM AUTHOR]

The influence of anode voltage ripple on injection locking of a magnetron with frequency pushing effect has been studied systematically. Theoretical analysis shows that, when power supply ripple and injection ratio are constant, frequency pushing effect will increase the magnetron's locking bandwidth. Meanwhile, the locking bandwidth decreases with the increase of power supply ripple. Thus, to achieve injection locking, both power supply ripple and frequency pushing effect must be considered. The experiment results show that at injection ratio μ of 0.003, frequency pushing effect at 0.5, and power supply ripple increases from 0% to 1% and 2.5%, the locking bandwidth of magnetron decreases by 0.32 MHz, 2.12 MHz. With the amplitude of ripple increasing, the spectrum after injection locking deteriorates, and output amplitude reduces, which verifies the theoretical analysis. Considering anode voltage ripple and frequency pushing effect, the research results contribute to the realization of high-quality output of injection locked magnetrons. [ABSTRACT FROM AUTHOR]

We demonstrate the generation, of a mmWave signal via the injection of an optical frequency comb (OFC) into an integrated tunable dual distributed Bragg reflector (DBR) laser as well as the fiber transmission and the processing of this signal by an optical beamforming network (OBFN). The dual DBR laser is based on a hybrid indium phosphide (InP) – polymer photonic integrated circuit (PIC). Two different cases have been examined in which the microwave signal is centered around 39 GHz and 60 GHz respectively, carrying quadrature amplitude modulation (QAM) formats at 0.5 Gbaud. In this proof-of-concept scenario, the OBFN consists of two optical paths, where the relative true time delay is induced by an optical delay line (ODL). Extensive comparison between the back-to-back (B2B) case and scenarios with transmission over 25 km of standard single-mode fiber (SSMF) has been made using the error-vector magnitude (EVM) and the bit-error ratio (BER) as evaluation criteria. In all cases, error-free transmission was suggested for all QPSK signals, whereas a worst-case EVM of 11.8% was observed for 16-QAM transmission, successfully showcasing the concept’s potential. The generated microwave signal’s frequency can be set arbitrarily high, provided that high-speed photodetection equipment is available for the detection and down-conversion of the signal. Extension to higher antenna elements (AEs) numbers is straight-forward, relying only on the number of available photodetectors. [ABSTRACT FROM AUTHOR]

In this paper, injection‐locked coupled ring oscillators (ROs) are studied regarding their capabilities for process, voltage, and temperature (PVT) compensated reference clock generation. A PVT resilient RO is implemented by means of injection‐locked coupled ROs where the injection locking mechanism is realized by employing adjustable coupling factors. It is shown that the oscillation frequency can be highly compensated for temperature‐related variations through the coupling factors. In addition, it is possible to compensate the center oscillation frequency for process‐induced variations and supply voltage fluctuations. The proposed technique is fully open loop without any frequency tracking loop and can be easily adopted by other architectures of oscillators such as RC and LC counterparts. A 2.4 GHz reference clock generator is implemented in a 0.18 μm standard CMOS process. While the temperature coefficient (TC) of the free‐running ROs is about 640 ppm/°C, the coupled structure offers a TC of 80 ppm/°C. Furthermore, the phase‐noise of the coupled structure is about 4 dB lower compared with the free‐running ROs. The proposed RO consumes about 2.8 mW and occupies a silicon area of 0.09 mm2. [ABSTRACT FROM AUTHOR]

In this paper, we introduce a unified nonlinear injection locking model of a large class of 1:2 frequency dividers. The model is valid for two-stage dividers, injected with two-phase or single-phase current or voltage sources. We show that this class of dividers can be rigorously analyzed using the theory of planar nonlinear dynamical systems. We provide accurate compact expressions for the locking range, amplitude, frequency and phase noise. The formulas are validated for two types of frequency dividers using simulations. [ABSTRACT FROM AUTHOR]

Various coherent power combining schemes have been developed with high power magnetrons to meet the increasing industrial demands of HPM and Wireless Power Transfer applications.In this paper, we propose a power combining scheme for two 1.25 kW magnetrons, based on phase‐shifter less philosophy. The proposed scheme utilizes a single signal generator synthesizing the injection signal for both magnetrons. A single RF Power Amplifier (PA) amplifies the injection signal for both magnetrons to the power level required by Adler's criteria. The amplified signal is then divided by 2:1 RF power divider. The divided signals are subsequently used for injection locking of both magnetrons through same length coaxial cables. The output power of the two magnetrons is combined in a symmetric H‐plane T‐combiner. Since both magnetrons follow the phase of a common injection source the instantaneous phase deviation in their injection‐locked responses is minimal, leading to a combining efficiency of 95%. [ABSTRACT FROM AUTHOR]

This article proposes a dual injection locking technique to significantly enhance the locking range (LR) of the injection-locked frequency tripler (ILFT). Compared with the conventional circuit topology that typically suffers from limited LR due to $G_{m}$ degeneration, the proposed technique employs drain injection and source injection together to increase the LR, with power consumption increased only a little. Fabricated in standard CMOS 65-nm technology, the ILFT prototype measures a 39.4% LR at 0-dBm input power while consuming 8.16 mW from a 1-V supply. The chip area is 0.32 mm2 including the pads. The proposed ILFT is applicable for local oscillation generation in the 5G transceiver. [ABSTRACT FROM AUTHOR]

This brief presents a comprehensive tutorial on the recent advances of injection-locking techniques used for millimeter-wave (mm-Wave) and terahertz (THz) signal generation systems. Injection locking has the potential to significantly improve the system performance in terms of low phase noise and low power consumption. The focus will be on the state-of-the-art injection-locking techniques to effectively widen the locking range and reduce the phase noise, including injection-locked frequency dividers (ILFDs), injection-locked frequency multipliers (ILFMs), and sub-harmonic injection-locked phase-locked loops (IL-PLLs). [ABSTRACT FROM AUTHOR]

• A novel scheme is proposed to generate microwave local oscillator (LO) signals with low near-carrier phase noise based on cascaded optoelectronic oscillators (OEOs), including an active mode-locking OEO (AML-OEO) and an injection-locked OEO (IL-OEO). • AML-OEO is used to generate a coherent microwave comb with low near-carrier phase noise. • IL-OEO is used to extract a single comb tooth from the microwave comb via injection locking effect. • The low near-carrier phase noise of the AML-OEO can be transferred to the regenerated microwave LO signal from the IL-OEO cavity. • The characteristics of the phase noise, the spurious suppression ratio, and the stability of the regenerated microwave LO signal are discussed. A new scheme to generate microwave local oscillator (LO) signals with low near-carrier phase noise is proposed based on cascaded optoelectronic oscillators (OEOs). In the proposed scheme, an active mode-locking OEO is utilized to generate a microwave comb with low near-carrier phase noise. Through injecting the generated microwave comb into another OEO with a well-designed loop delay, microwave LO signals with low near-carrier phase noise can be generated. The feasibility of the scheme is numerically and experimentally demonstrated. In the experiment, a microwave LO signal at 10.0005 GHz is generated with a spurious suppression ratio of 25 dB and a near-carrier phase noise of −91 dBc/Hz@100 Hz. Compared with the microwave LO signal directly generated by using the OEO without injection, the near-carrier phase noise is reduced by 23 dB. The proposed scheme can thus be used to enhance the sensitivity of the pulse Doppler radar system for detecting small targets with low altitude and slow speed. [ABSTRACT FROM AUTHOR]

• It is theoretically proved that the −1st comb tooth power is related with the modulation depth and the frequency difference between f m (the modulation frequency) and f rep (the free-running repetition rate). • An optical closed-loop injection locking technology is realized using the −1st comb tooth as error signal for the soliton microcomb repetition rate (f rep) long-term stabilization. • The SSB phase noise of the closed-loop locked f rep have no obvious change in long-term, which is about 20 dB lower compared with the open-loop locking case. And the Allan deviation of the closed-loop locked f rep maintains at 1.8 × 10-13@0.1 s for a long time, which improves by three orders of magnitude compared with the open-loop locking case. We demonstrate an optical closed-loop injection locking technology for the soliton microcomb repetition rate (f rep) stabilization. Using the power of the −1st comb line (−1st represents the first comb tooth on the left side of the pump laser) as an error signal, the pump laser frequency is auto-tuned to ensure f rep locked at an optimal level. After injection locking for 2 h, the single-sideband (SSB) phase noise of the closed-loop locked f rep decreases by 20 dB compared with the open-loop locked f rep within the offset frequency range of 20 Hz to 30 kHz. After locking one and a half hours, the Allan deviation of the closed-loop locked f rep reaches 1.8 × 10−13@0.1 s, which improves by three orders of magnitude. The experimental results prove the feasibility of the optical closed-loop injection technology for long-term f rep stabilization. The proposed scheme has excellent locking performance, simple structure and low cost, which has the potential application for stable microwave generation, precision ranging, etc. [ABSTRACT FROM AUTHOR]

This article presents an injection-locked (IL) ring-oscillator-based fractional- ${N}$ digital phase locked loop (DPLL) supporting Bluetooth low energy (BLE) frequency modulation with an frequency-shift keying (FSK) error between 2.4% and 3.3%. As the fractional spur cannot be suppressed by IL-DPLL, this work proposes a random edge injection (REI) to reduce the spur. This technique also speeds up the convergence time of gain calibration of the digital-to-time converter (DTC). Furthermore, the proposed background calibration schemes allow the DPLL to achieve stable performance across all BLE channels, including both integer- ${N}$ and fractional- ${N}$ channels. This work was fabricated in the 40-nm CMOS technology occupying a 0.09-mm2 area. A fractional spur of −44 dBc and a reference spur of are achieved while consuming 2.76 mW when REI is activated. The background calibrations also ensure stable performance across BLE channels. [ABSTRACT FROM AUTHOR]

We present a high-accuracy, low-jitter, multi-phase clock generator (MPCG) based on a multi-phase, injection-locked ring oscillator (MPIL-ROSC) with a quadrature delay-locked loop (QDLL). The QDLL tunes the ring oscillator (ROSC) self-oscillation frequency (${f}_{{0}}$) and provides it with multi-phase injection signals. The proposed architecture breaks the intrinsic tradeoff between jitter and phase accuracy in two-phase injection-locked ROSCs. The MPCG’s eight-phase output clock drives a 7-bit phase interpolator (PI) for phase and frequency deskew. A 1.2-V 65-nm CMOS MPCG prototype chip has a better-than-1° eight-phase accuracy and $58.8~\mathrm {fs}_{\mathrm {rms}}$ jitter (integrated from 100 kHz to 1 GHz), while consuming 15.6 mW at 7 GHz, yielding a −252.7-dB figure of merit ($\mathrm {FOM}_{\mathrm {jitter}}$). The peak-to-peak integral nonlinearity (INL) and the peak-to-peak differential nonlinearity (DNL) of the PI are less than 1.9 and 1.2 LSB, respectively, across a frequency range from 5 to 8 GHz. [ABSTRACT FROM AUTHOR]

This work investigates an injection-locked power oscillator inductively coupled to an external resonator for wireless power transfer. The system allows a high transfer efficiency, while ensuring a constant oscillation frequency versus the coupling factor, unlike free-running implementations. An analytical formulation provides insight into the impact of the coupling factor on the locked-operation ranges. Two types of qualitative behavior, delimited by a codimension-two bifurcation, are distinguished. The investigation is extended to a Class-E oscillator at 13.56 MHz, analyzed with a new harmonic balance (HB) method that provides the family of locked-solution curves in a single simulation. Very good agreement is obtained with the measurement results. [ABSTRACT FROM AUTHOR]

Internet-of-Things (IoT) devices are compact and low power. A voltage-controlled oscillator (VCO)-based analog-to-digital converter (ADC) benefits from scaled CMOS transistors in representing analog signals in the time domain and therefore meets those demands. However, we find the potential drawback of VCO-based ADCs for the electromagnetic susceptibility (EMS) to RF disturbances that are essentially present in an IoT environment. It is exhibited that the single and even differential designs of VCO-based ADC suffer from the EMS by RF disturbance, which behaves differently from the known common-mode noise rejection. A 28 nm CMOS 11-bit VCO-ADC prototype exhibits sensitivity against RF signals in the widely used 2.4 GHz frequency band. [ABSTRACT FROM AUTHOR]

The optoelectronic oscillator is a delay line oscillator that leverages optical fibre technology to realize the large delay required for low phase noise systems. Spurious sidemodes are an artefact of the delay line oscillator, yet treatments of injection locking of optoelectronic oscillators have relied on the application of classical injection locking theory valid only for single mode oscillators. The large delay contributed by the optical fibre delay line is accounted for by the classical theory only in part through the quality factor Q that captures the round-trip group delay in a neighborhood of the oscillation frequency. This paper presents a new formulation of time delay oscillators subject to injection that describes all the essential features of their dynamics and phase noise. The common assumptions of a single mode oscillator and weak injection are removed. This is important to correctly predict the lock-in range, the suppression of sidemodes and the phase noise spectrum. The findings of the analysis are validated by experimental measurements provided by an optoelectronic oscillator under injection by an external source. [ABSTRACT FROM AUTHOR]

This letter presents an injection locking doubler chain centered at 208 GHz in 65-nm CMOS technology. The doubler chain consists of a doubler and two injection locking oscillators (ILOs). The doubler uses push–push topology to generate wideband second-harmonic output. Both ILOs are based on T-embedding network oscillator for high gain and high efficiency. The measured injection locking range is 188.4–225.6 GHz with the input injection power less than 0 dBm. The peak output power with the minimum injection input is 4.6 dBm (2.9 mW), and the 3-dB bandwidth is 200–220 GHz (9.5%). The power consumption is 83 mW under 1.2-V supply, and the peak power-added efficiency (PAE) reaches 3.2% at 211 GHz. Moreover, the total size of the chip excluding pads is 530 $\mu \text{m}\,\,\times200\,\,\mu \text{m}$. To the best of the author’s knowledge, this work demonstrates the highest PAE among CMOS doubler chains in similar frequency ranges reported by far. [ABSTRACT FROM AUTHOR]

We report on the generation and transmission of 30 GHz millimeter-wave (MMW) beat-tone signals employing external- (EIL) and self-injection-locked (SIL) InAs/InP quantum-dash based dual-wavelength laser (QD-DWL) sources emitting in mid L-band. Later, successful transmission of 2 Gbps quadrature phase-shift-keying (QPSK) signal over clear weather conditions on 2 m wireless (WL), and hybrid channels consisting of 20 km single-mode fiber (SMF) and 2 m WL, and 20 km single-mode fiber (SMF), 5 m free-space-optics (FSO) and 2 m WL, are demonstrated employing both MMW sources, with a slight ∼1.4 dBm extra received optical power requirement from SIL QD-DWL. Lastly, examining the effect of dusty weather conditions on the MMW transmission over 20 km SMF, 0.9 m FSO and 1 m WL hybrid channel, considering both EIL and SIL sources, showed maximum visibility range (V) of 12 ± 2 m and 16 ± 2 m for successful transmission, respectively. These investigations reinforce the simple, cost-effective, and energy-efficient SIL QD-DWL as a candidate L-band millimeter-wave (MMW) source compared to the EIL counterpart in 5G and next-generation radio-over-fiber wavelength-division multiplexing networks.

Spontaneous locking of the phase of a coherent phonon source to an external reference is demonstrated in a deeply sideband-unresolved optomechanical system. The high-amplitude mechanical oscillations are driven by the anharmonic modulation of the radiation pressure force that result from an absorption-mediated free-carrier/temperature limit cycle, i.e., self-pulsing. Synchronization is observed when the pump laser driving the mechanical oscillator to a self-sustained state is modulated by a radiofrequency tone. We employ a pump-probe phonon detection scheme based on an independent optical cavity to observe only the mechanical oscillator dynamics. The lock range of the oscillation frequency, i.e., the Arnold tongue, is experimentally determined over a range of external reference strengths, evidencing the possibility to tune the oscillator frequency for a range up to 350 kHz. The stability of the coherent phonon source is evaluated via its phase noise, with a maximum achieved suppression of 44 dBc/Hz at 1 kHz offset for a 100 MHz mechanical resonator. Introducing a weak modulation in the excitation laser reveals as a further knob to trigger, control and stabilize the dynamical solutions of self-pulsing based optomechanical oscillators, thus enhancing their potential as acoustic wave sources in a single-layer silicon platform.

Harmonic balance provides steady-state solutions only and has significant shortcomings when addressing oscillatory regimes. As a result, complementary methodologies are required both to ensure the stability of the solution obtained and to design/simulate oscillator circuits. The complexity of the stability analysis increases with the number of active elements and the intricacy of the topology, so there can be uncertainties in the case of complex structures. On the other hand, as recently demonstrated oscillators enable a compact and low-cost implementation of RFID readers and radar systems, which comes at the expense of a more complex performance, very difficult/impossible to simulate with commercial HB. This work presents a review of recent advances on stability and oscillation analysis at circuit level and through semi-analytical formulations. At circuit level, a method for the stability analysis of complex microwave systems is presented, based on the calculation of the characteristic determinant, extracted from the commercial simulator through a judicious partition of the system into simpler blocks. This determinant will be used for the first time to obtain the stability boundaries through a contour-intersection method, able to provide multivalued and disconnected curves. At a semi-analytical level, a realistic numerical model of the standalone oscillator, extracted from HB simulations, is introduced in an analytical formulation that describes the oscillator interaction with other elements. Here it will be applied to a self-injection locked radar, in which the oscillator is injected by its own signal after this signal undergoes propagation and reflection effects. A procedure to determine the stability properties considering the time delay of the signal envelope is presented for the first time. Using the same self-injection concept, a new stabilization method to reduce the phase-noise of an existing oscillator with minimum impact on its original frequency is described.

FitzHugh-Nagumo, FHN, is a most critically significant Neural Cell method which is effectively capable of modeling the synaptic behavior by leveraging van-der-pol oscillators. The FitzHugh-Nagumo model makes use of common circuitry of FHNs, remarkably similar to the very conventional LC oscillators. Conventional LC oscillators, needless to say, have been largely deployed and comprehensively studied for quite some time. Notwithstanding its similarity to other LC oscillators, FitzHugh-Nagumo contains a resistor in series with the circuit that makes it inconsistent with other LC oscillator models. In this paper, a productive circuit technique is used to make FitzHugh-Nagumo circuit analogous to a LC conventional oscillator, which consequently provides the capability of using analytical approaches on these systems. This gives the designer of neural cells the opportunity of taking advantage of the vast knowledge about oscillatory systems. The proposed circuit model has been verified in terms of accuracy and compatibility for free-running, locked, and unlocked states. In addition, a theoretical analysis, aiming to clarify the background principle of the FitzHugh-Nagumo design process, is also provided. The simulation results which are performed using TSMC 180 nm CMOS technology represent a good agreement between theory and simulation. [ABSTRACT FROM AUTHOR]

A low power consumption Amplitude Shift Keying (ASK) modulator employing current reuse cross‐coupled (CRC) LC‐VCO topology and direct injection locking (IL) technique at 10.5‐GHz frequency is presented in this paper. The modulator consumes 864 μW with a DC supply of 1.2 V drawing an average current of 720 μA. The differential VCO is composed of a PMOS‐NMOS pair in stacked series cross‐coupled connection enabling current reuse which results in reduction of the average current drawn from the power source. For comparison, the ASK modulator is also realized with conventional cross‐coupled (CC) topology using NMOS pair. Both circuit approaches are carried out in GF 130‐nm CMOS technology and the post‐layout simulation results of 0.5 × 0.5 mm2 integrated circuits (ICs) show that the CRC topology consumes less power and half of the average current compared to CC topology. Owing to low power requirements, the CRC ASK modulator can be used in self‐powered active Radio Frequency Identification (RFID) tag transmitters for higher data rates. [ABSTRACT FROM AUTHOR]

The recently introduced Zero-IF self-oscillating mixers (SOMs) enable a direct frequency conversion, of interest for the implementation of compact and low consumption radio frequency identification (RFID) tags, among other applications. In previous works, the Zero-IF SOM is placed in only one of the terminals of the wireless link, the other one being based on a conventional scheme. In this article, a system made up of two wirelessly locked Zero-IF SOMs, operating as a frequency upconverter and downconverter, will be analyzed to evaluate its potential for low-cost short-range communications. A complete formulation describing the system under antenna and propagation effects will be presented, which, as a particular case, is able to predict the behavior of the previously proposed Zero-IF SOM, locked by an independent signal. The formulation based on oscillator models extracted from harmonic balance allows deriving design criteria for an optimum and robust performance and can predict the maximum communication range, as well as the stability properties and phase-noise behavior. The operation under modulated conditions is analyzed with a novel envelope-transient formulation, accounting for the time differentiation caused by the propagation effects. The methods have been applied to a system of two Zero-IF SOMs operating at 900 MHz. [ABSTRACT FROM AUTHOR]

Frequency multipliers are key components for high-quality millimeter-wave signal generations. However, the harmonic spurs generated by the frequency multipliers significantly affect the system performance. As a result, a high harmonic rejection is required in the frequency multiplier design. In this article, we present a multi-ratio (MR) frequency multiplier that exhibits $\times 5$ and $\times 7$ switchable multiplication ratios. Three processes of frequency multiplication, harmonic generation, harmonic amplification, and harmonic selection, are analyzed, and the corresponding techniques for harmonic suppression are introduced. The harmonic spurs can be suppressed by these three techniques: high-efficiency harmonic generation, injection locking, and tunable fourth-order resonator. First, the high-efficiency harmonic generation is realized by chopping the drain current, which enables a harmonic-rich spectrum to be generated, and the shape of the spectrum can be controlled by the biasing voltage. The second technique, injection locking, can suppress the harmonic spurs by its frequency-modulation (FM) and amplitude-modulation (AM) nature. The third technique, the tunable fourth-order resonator, can select the desired harmonic and suppress others. An MR injection-locked frequency multiplier was implemented in a 65-nm CMOS process as the proof-of-concept design. The multiplier operates from 22.4 to 40.6 GHz, and the measured harmonic rejection ratio is 57.7 dBc at 28 GHz and 51.7 dBc at 39 GHz with 10.0-mW power consumption. [ABSTRACT FROM AUTHOR]

We report a homogeneous quantum cascade laser (QCL) emitting at terahertz (THz) frequencies, with a total spectral emission of about 0.6 THz, centered around 3.3 THz, a current density dynamic range Jdr = 1.53, and a continuous wave output power of 7 mW. The analysis of the intermode beatnote unveils that the devised laser operates as an optical frequency comb (FC) synthesizer over the whole laser operational regime, with up to 36 optically active laser modes delivering ∼200 µW of optical power per optical mode, a power level unreached so far in any THz QCL FC. A stable and narrow single beatnote, reaching a minimum linewidth of about 500 Hz, is observed over a current density range of 240 A/cm2 and even across the negative differential resistance region. We further prove that the QCL FC can be injection locked with moderate radio frequency power at the intermode beatnote frequency, covering a locking range of 1.2 MHz. The demonstration of stable FC operation, in a QCL, over the full current density dynamic range, and without any external dispersion compensation mechanism, makes our proposed homogenous THz QCL an ideal tool for metrological applications requiring mode-hop electrical tunability and a tight control of the frequency and phase jitter.

In this work, injection locking in switching power amplifiers (PAs) is studied. Traditionally, injection-locked PAs (ILPAs) have supported phase modulation, with injection locking used primarily to improve the power-added efficiency by reducing the power required to drive the ILPA. Since the output power in conventional ILPA architectures is mainly contributed by the locked oscillator in an ILPA, the amplitude modulation is difficult to achieve unless supply modulation is employed. In the ILPA presented in this work, it is shown that by injection locking a switching PA and a power oscillator, improvement in both power-added efficiency and drain efficiency can be achieved as compared to just a switching PA. Moreover, amplitude modulation at a fixed supply voltage is achieved using an RF-DAC approach to scale both the switching PA and the locked oscillator. This approach employs variable injection-strengths varying from ≤1 (weak injection locking) to >1 (strong injection locking) to achieve the required power back-off. Accordingly, new formulations are introduced to extend the existing injection locking theory for injection strengths >1 case in ILPAs. Benefits of a larger injection strength on lock-range, maximum allowable symbol rate, AM-PM distortion and phase noise performance for an ILPA is provided. An ILPA is designed to support 64-QAM and implemented in a standard 65-nm bulk CMOS process. A peak drain efficiency of 42.7% and power-added efficiency of 40% is measured at the highest output power of 23 dBm, operating from a 1.45 V PA power supply at 2.5 GHz. Modulation tests with 5/50 MSym/s 64-QAM signals achieve the measured RMS EVM of 1.9%/3.1% with the average output power, drain efficiency and power-added efficiency of 18.1 dBm, 27.9% and 25.8% at 2.5 GHz, respectively.