A frequency-domain approach for phase noise analysis of integer-N multiplier-type phase-locked loops (PLLs), based on the conversion matrix approach, is introduced that can take all non-linearities ...in the loop into account. It can also characterise all kinds of power spectral densities and correlation between variables and all aspects of phase noise-to-phase noise or amplitude noise-to-phase noise (AN–PN) conversions. The noise transfer between various sidebands is also taken into account. This is especially important for characterising the folding of the voltage-controlled oscillator's phase noise which results in the phase noise augmentation at small frequency offsets. Unlike the linear phase-domain models, the stochastic phase noise local maxima at large offset frequencies are also accurately characterised. Giving the phase/amplitude noise spectra of various PLL blocks, this approach computes the resulting output phase noise spectrum. The validity of the new approach is verified by comparing its results with those of a numerical time-domain stochastic simulation. The proposed method has far much faster runtimes, independent of the time constants in the system, compared to the corresponding time-domain methods that allow a convenient simulation-based design of PLLs especially at radio frequencies.
Equalization enhanced phase noise (EEPN) occurs due to the interplay between laser phase noise and electronic dispersion compensation (EDC) module. It degrades significantly the performance of ...uncompensated long-haul coherent optical fiber communication systems. In this work, a general expression accounting for EEPN is presented based on Gaussian noise model to evaluate the performance of multi-channel optical communication systems using EDC and digital nonlinearity compensation (NLC). The nonlinear interaction between the signal and the EEPN is analyzed. Numerical simulations are carried out in nonlinear Nyquist-spaced wavelength division multiplexing (WDM) coherent transmission systems. Significant performance degradation due to EEPN in the cases of EDC and NLC are observed, with and without the consideration of transceiver (TRx) noise. The validation of the analytical approach has been done via split-step Fourier simulations. The maximum transmission distance and the laser linewidth tolerance are also estimated to provide important insights into the impact of EEPN.
This Letter presents a method of predicting the phase noise limits of static frequency dividers. The proposed phase noise model for free-running and injection-locked modes is based on the circuit ...parameters only. The model provides an intuitive comprehension of the phase noise behaviour of static frequency dividers and is proved to be useful in primary hand calculations. The method was verified against measurement results of a static frequency divider-by-two, operated at 77 GHz and fabricated in a SiGe $0.13 {\rm\mu} {\rm m}$0.13μm process.
Carrier phase recovery (CPR) is a key digital signal processing (DSP) subsystem in optical fiber communications. In this paper, we review recent advances in CPR algorithms and analyze their ...performance under the impact of different system impairments in a long-haul 256 GBaud setting. We study both single- and dual-stage CPR configurations, in the linear and nonlinear regimes, and at different system baud rates. By exploiting CPR algorithms tailored for digital subcarrier multiplexing (DSCM) systems, we are able to reap the benefits of their intrinsic resilience to the two main performance-limiting effects of optical fiber systems: equalization enhanced phase noise (EEPN) and nonlinear interference (NLI). Overall, the paper sheds light on the potential benefits of DSCM and highlights the need for further research into CPR algorithms that specifically target the effect of nonlinear phase noise (NLPN).
High-capacity wireless links at millimeter-Waves are candidate for backhaul infrastructure to small-cell mobile networks. However, the use of high-order modulation schemes sets challenging ...phase-noise specifications for integrated frequency synthesizers. Moreover, the use of adaptive modulation suggests local oscillators exploiting noise scaling, up to several decibel depending on channel conditions. In this paper, multi-core switch-coupled LC voltage-controlled oscillators are proposed to achieve ultra-low phase noise and scalable noise performance according to system requirements in a power-efficient way. A theoretical model investigating the effect of LC core component mismatches shows very good agreement with experiments. Design insights are provided, key in order to take effective advantage from the proposed low-noise technique. A quad-core ~20 GHz oscillator prototype, followed by a frequency quadrupler, has been realized in 55-nm BiCMOS technology. Measured performances are ~70-to-81 GHz frequency range with -106.5-dBc/Hz minimum phase noise at 1-MHz offset from an 80-GHz carrier with 50-mW power consumption and 1.2-V supply. To authors' knowledge, this is the lowest phase noise measured in the E-Band using integrated technologies and CMOS-compatible supplies. When noise requirements are relaxed, auxiliary cores are turned off rising phase noise by 6 dB but with power consumption reduced down to 18 mW only.
An approach to transmitting two independent microwave vector signals on a single optical carrier with one polarization state based on coherent detection and digital phase noise cancellation is ...proposed and experimentally demonstrated. At the transmitter, two independent microwave vector signals are modulated on an optical carrier via a dual-drive Mach-Zehnder modulator (DD-MZM). The modulated optical signals are transmitted over a single-mode fiber (SMF) and sent to a coherent receiver. At the receiver, the optical signals are detected where a local oscillator (LO) optical wave generated by a second free-running laser source is also applied. To recover the two microwave vector signals, a novel digital signal processing (DSP) algorithm is developed and applied to eliminate the joint phase noise terms from the transmitter and the LO laser sources as well as the unstable offset frequency between the two laser sources. An experiment is performed. The transmission of two independent 16 quadrature amplitude modulation (16-QAM) microwave vector signals at 4 GHz with a symbol rate of 1 GSymb/s over a 9-km SMF is demonstrated. The transmission performance in terms of error vector magnitudes (EVMs) and bit error rates (BERs) is also evaluated.
A microwave photonic link (MPL) with quadrupled capacity based on coherent detection and digital phase noise cancellation is proposed and experimentally demonstrated. At the transmitter, a ...continuous-wave (CW) light wave is intensity modulated by four independent microwave vector signals with two having an identical center microwave frequency at a dual-parallel Mach-Zehnder modulator (DPMZM) consisting of two dual-drive MZMs (DEMZMs) with the sub-DEMEMs biased at the quadrature transmission point. Four intensity-modulated optical signals are generated and transmitted over a single-mode fiber (SMF) to a coherent receiver. To perform coherent detection, a second CW laser source as a local oscillator (LO) is also applied to the coherent receiver. To recover the microwave vector signals, a novel digital phase noise cancellation algorithm is developed and applied to eliminate the joint phase noise from the transmitter laser source and the LO laser source as well as the unstable offset frequency between the two laser sources. A theoretical analysis is performed to show the recovery of the microwave vector signals which is verified by an experiment. For four independent 16 quadrature amplitude modulation (16-QAM) microwave vector signals with a symbol rate of 0.5 GSymbol/s, error-free transmission over a 9-km SMF is achieved when the received optical power at the coherent receiver is higher than −18 dBm with forward error correction (FEC).
A method to reduce the spectral linewidth of a laser source by direct phase noise compensation is proposed and demonstrated experimentally. To extract the phase noise information, the laser output is ...phase modulated and the in- and quadrature-phases are detected by homodyne mixing. Phase noise compensation is achieved by simply applying an error signal to an external phase modulator, where the error signal is generated to keep the same power level for the detected in- and quadrature-signals. The spectral linewidth of the laser is reduced significantly from 450 to 60 kHz.
A low-phase noise ring voltage-controlled oscillator (VCO) employing input-coupled dynamic current source is presented. By simply coupling the input signal to the gate node of the current source ...transistor, the proposed inverter has a larger output swing and steeper maximum slope than conventional structures, which directly results in phase noise improvement. Under the same conditions, compared to the conventional structure, the proposed ring VCO achieves 7.5 and 11 dB of phase noise improvement at 100 kHz and 1 MHz offset frequencies, respectively. The proposed ring VCO has a tuning range of 823–1300 MHz and post-layout simulation shows a figure-of-merit of 159–162 dBc/Hz in the entire oscillation frequency range. In the measurement results,the authors recorded a phase noise of −106 dBc/Hz and figure-of-merit reaching 165 dBc/Hz at 1 MHz offset frequency, consuming 1.2 mW from a 1.8 V supply at 1 GHz oscillation frequency. The proposed ring VCO is implemented in 180 nm CMOS process and occupies a size of 0.0024 mm2.
Dispersion uncompensated fiber links are widely used due to their nonlinear benefits. In such links, dispersion requires electronic compensation after down-conversion by the receiver laser. ...Therefore, laser phase noise inevitably affects the received signal. While, in an optimal receiver, the phase noise should be compensated before dispersion, practical phase estimation is only feasible when dispersion is already compensated. Unfortunately, compensating receiver phase noise after dispersion compensation gives rise to equalization-enhanced phase noise (EEPN), which limits the system's performance, especially for high data rates over long system reaches. In this paper, we demonstrate that EEPN can be mitigated through signal processing. We derive the compensation expression and propose two different compensators depending on the availability of the receiver phase noise. Our study demonstrates that by using a simple time-variant finite impulse response filter, one can effectively compensate for EEPN. The simulation study validates these theoretical findings, revealing improved system performance, including enhanced system reach, optimal launch power, and reduced bit error rate compared to existing EEPN-controlled methods. Importantly, we show that the complexity of our compensators is comparable to existing methods, demonstrating its feasibility for practical implementation.
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