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This article presents a power-efficient low-jitter fractional-N digital phase-locked loop (DPLL) that resolves phase error (PE) in the fully differential voltage (FDV) domain. Compared with adopting a traditional time-to-digital converter (TDC), which relies on gate delay in the time domain, power-efficient quantization of PE by the proposed conversion scheme in the FDV domain can be accomplished with a higher power-supply/common-mode rejection ratio (PSRR/CMRR), lower process, voltage, and temperature (PVT) sensitivity, finer resolution, and better linearity. The implemented DPLL covers the fractional-N operation by a 10-bit differential current digital-to-analog converter (DAC) with a resistive load to represent the fractional phase/time. A differential dv/dt ramp is employed to linearly transfer the preset initial voltage into a small phase/voltage error, which is digitized by a narrow-range fine-resolution 7-bit self-timed successive-approximation-register analog-to-digital converter (SAR-ADC). The prototype DPLL, implemented in 130-nm CMOS, achieves 101-fs rms jitter, integrated from 10 kHz to 40 MHz, in the fractional-N mode with sub-12-bit fractional-frequency-control words, using an 80-MHz reference clock (REF), consuming 9.2 mW. This corresponds to a figure of merit (FoM) of −250.3 dB. The measured worst case fractional spur level is −56 dBc. [ABSTRACT FROM AUTHOR]

In this article, an efficient technique is introduced to extract the quantization noise of a multi-phase voltage-controlled oscillator (VCO)-based quantizer (VCOQ) in the time domain as a pulsewidth modulated (PWM) signal. Using this technique, a new highly linear VCO-based 1-1 multi-stage noise shaping (MASH) delta–sigma analog-to-digital converter (ADC) structure is presented. This architecture does not require any operational transconductance amplifier (OTA)-based analog integrators or power-hungry linearization methods. The first stage is a closed-loop multi-phase VCO-based voltage-to-phase (V-to-P) converter, and the second stage is an open-loop multi-phase VCO-based voltage-to-frequency (V-to-F) converter. Using the proposed technique, the phase quantization error of the first stage is extracted as a pulse signal and then fed to the second stage. The input of the first VCO is a very small amplitude signal, and the input of the second VCO is a two-level PWM signal. Therefore, the VCO non-linearity does not limit the overall ADC performance, mitigating the need for power-hungry linearization methods. The prototype achieves second-order noise shaping with a DR/SFDR/SNR/SNDR of 82.7/88.7/80.3/79.7 dB for an input signal BW of 2 MHz. The fabricated design consumes 1.248 mW from a 0.9-V supply. [ABSTRACT FROM AUTHOR]

This paper investigates the output feedback $ {\mathcal {H}_{\infty }}$ control problem for a class of continuous-time nonlinear systems with both output and input quantization. The nonlinear plant is represented by a Takagi–Sugeno fuzzy model. The measurement output and the control input signals will be quantized by dynamic quantizers. The attention of this paper is focused on the design of the output feedback controller and quantizers such that the fuzzy closed-loop system is asymptotically stable and also achieves a prescribed $ {\mathcal {H}_{\infty }}$ noise attenuation level with respect to the effect of quantization. In the presence of quantization, two novel $ {\mathcal {H}_{\infty }}$ performance analysis criteria are presented for the considered fuzzy systems based on the descriptor representation approach. Then, sufficient conditions for the existence of the feedback $ {\mathcal {H}_{\infty }}$ controller gain and the quantizers’ dynamic parameters are expressed in terms of linear matrix inequalities. An adjusting scheme on quantizers’ parameters is proposed for the fuzzy system. Simulation examples are provided to show the effectiveness of the proposed design method. [ABSTRACT FROM AUTHOR]

In this paper, we describe ac and dc quantum Hall effect measurements at temperatures above 1.5 K, which is beyond the commonly used value for high precision measurements of the quantum Hall resistance (QHR). It is shown that GaAs devices with high electron density of about $5\times 10^{11}$ cm2 can be used as reliable dc resistance quantum standards with quantization of $R_{\mathrm {H}}$ (2) value with accuracy within a few parts in 109 even at temperatures up to 4.2 K. The devices have exhibited well-developed quantum Hall plateaus in the ac regime too, again at temperatures up to 4.2 K. The measurement system consists of a self-made cryogenic probe with TO-8 type socket together with coaxial wiring and a digitally assisted bridge suitable for ac quantum Hall effect measurements. The experiments were performed with devices placed in new double-shielded TO-8 holders. Our investigations and the evaluation of the measurement system are dedicated for the future realization of the quantum impedance standard based on ac QHR. [ABSTRACT FROM AUTHOR]

In this paper, we propose two non-uniform quantization (NUQ) codebook-based hybrid precoding schemes for two main hybrid precoding implementations, i.e., the full-connected structure and the sub-connected structure, to reduce the feedback overhead in millimeter wave single user multiple-input multiple-output systems. Specifically, we firstly group the angles of the arrive/departures (AOAs/AODs) of the scattering paths into several spatial lobes by exploiting the sparseness property of the millimeter wave in the angular domain, which divides the total angular domain into effective spatial lobes’ coverage angles and ineffective coverage angles. Then, we map the quantization bits non-uniformly to different coverage angles and construct NUQ codebooks, where high numbers of quantization bits are employed for the effective coverage angles to quantize AoAs/AoDs and zero quantization bit is employed for ineffective coverage angles. Finally, two low-complexity hybrid analog/digital precoding schemes are proposed, which utilize the NUQ codebooks. Simulation results demonstrate that the proposed two NUQ codebook-based hybrid precoding schemes achieve near-optimal spectral efficiencies and show the superiority in reducing the feedback overhead compared with the uniform quantization codebook-based works. [ABSTRACT FROM AUTHOR]

The High Efficiency Video Coding (HEVC/H.265) standard achieves great improvement in compression efficiency over the widely used H.264/AVC standard at a cost of much higher complexity. When encoding videos using HEVC, the selection of the quantization parameter (QP) can significantly affect the coding efficiency. Typical algorithms for adaptive quantization employ fixed bitrate budgeting or fixed QP offsets for different frames and different blocks, without considering detailed input video characteristics, some of which might be captured using computer vision methods. The problem of determining adaptive settings of HEVC coding parameters has not been satisfactorily solved. In this paper, we proposed a Hadamard (“HAD”) energy-based optimized HEVC video encoder, in which HAD energy is used to measure the amount of residual information to be encoded in a block so as to determine the QP value for each block for a better coding efficiency. HAD energy is also used to expedite the time-consuming mode decision process and for a precise scene change detection to avoid flicker artifacts. Experiment using the widely used open source HEVC encoder $\times$ 265-v1.8 showed that the proposed algorithm was able to achieve an average of 14% saving in Bjøntegaard-delta-rate and an average of 20% saving in encoding time as compared the “medium” preset of $\times$ 265, while the proposed algorithm also produced an improvement of 3.3% in coding efficiency for the HEVC reference software HM-16.6. [ABSTRACT FROM AUTHOR]

Interference alignment (IA) is a promising technique to effectively manage the interference. The realization of IA requires a proliferation of feedback bits. In a general centralized feedback model, the feedback rate of the precoder and the decoder affects the performance of the IA directly. In this paper, to improve the feedback efficiency of the precoder and the decoder, a strategy that can adaptively allocate the feedback bits of the precoder and the decoder is proposed. We consider the effect of link loss on the throughput loss caused by the quantization error of the precoder and decoder. An upper bound of leaked interference as a function of the link loss and the feedback bits of the precoders and the decoders is derived. The feasibility conditions for dynamically allocating the feedback bits of the precoder and the decoder are analyzed. It is proven that the properties of general asymmetric interference network can satisfy the feasibility conditions for dynamic feedback scheme. According to the simulation results, our proposed scheme achieves higher throughput compared with the conventional schemes in the asymmetric interference network. [ABSTRACT FROM AUTHOR]

Receiver diversity combining methods play a key role in combating the detrimental effects of fading in wireless communication and other applications. A novel diversity combining method is proposed, where a universal, i.e., channel independent, orthogonal dimension-reducing space-time transformation is applied prior to quantization of the signals. The scheme may be considered as the counterpart of Alamouti modulation, and more generally of orthogonal space–time block codes. [ABSTRACT FROM AUTHOR]

Low-resolution digital-to-analog converter (DAC) has shown great potential in facilitating cost- and power-efficient implementation of massive multiple-input multiple-output (MIMO) systems. We investigate the performance of a massive MIMO downlink network with low-resolution DACs using regularized zero-forcing (RZF) precoding. It serves multiple receivers equipped with finite-resolution analog-to-digital converters (ADCs). By taking the quantization errors at both the transmitter and receivers into account under spatially correlated channels, the regularization parameter for RZF is optimized with a closed-form solution by applying the asymptotic random matrix theory. The optimal regularization parameter increases linearly with respect to the user loading ratio while independent of the ADC quantization resolution and the channel correlation. Furthermore, asymptotic sum rate performance is characterized and a closed-form expression for the optimal user loading ratio is obtained at a low signal-to-noise ratio. The optimal ratio increases with the DAC resolution while it decreases with the ADC resolution. Numerical simulations verify our observations. [ABSTRACT FROM AUTHOR]

This paper analyzes how the distortion created by hardware impairments in a multiple-antenna base station affects the uplink spectral efficiency (SE), with a focus on massive multiple input multiple output (MIMO). This distortion is correlated across the antennas but has been often approximated as uncorrelated to facilitate (tractable) SE analysis. To determine when this approximation is accurate, basic properties of distortion correlation are first uncovered. Then, we separately analyze the distortion correlation caused by third-order non-linearities and by quantization. Finally, we study the SE numerically and show that the distortion correlation can be safely neglected in massive MIMO when there are sufficiently many users. Under independent identically distributed Rayleigh fading and equal signal-to-noise ratios (SNRs), this occurs for more than five transmitting users. Other channel models and SNR variations have only minor impact on the accuracy. We also demonstrate the importance of taking the distortion characteristics into account in the receive combining. [ABSTRACT FROM AUTHOR]

This paper addresses the optimal design of a two-stage Wyner-Ziv scalar quantizer with forwardly or reversely degraded side information (SI) for finite-alphabet sources and SI. We assume that the binning is performed optimally and address the design of the quantizer partitions. The optimization problem is formulated as the minimization of a weighted sum of distortions and rates. The proposed solution is globally optimal when the cells in each partition are contiguous. The solution algorithm is based on solving the single-source or the all-pairs minimum-weight path (MWP) problem in certain weighted directed acyclic graphs. When the conventional dynamic programming technique is used to solve the underlying MWP problems, the time complexity achieved is $O(N^{3})$ , where $N$ is the size of the source alphabet. A so-called partial Monge property is additionally introduced, and a faster solution algorithm exploiting this property is proposed. Experimental results assess the practical performance of the proposed scheme. [ABSTRACT FROM AUTHOR]

We investigate the upper and lower bounds on the quantization distortions for independent and identically distributed continuous sources in the finite block-length regime. We derive a lower bound on the quantization distortion, as well as an upper bound on the quantization distortion based on random quantization codebooks. Moreover, we apply the obtained bounds to the continuous Gaussian source. For the Gaussian source, we propose a computationally tractable method to numerically compute the upper and lower bounds, for both bounded and unbounded quantization codebooks. Numerical results show that the gap between the upper and lower bounds is small for the block length of several hundreds, and the upper and lower bounds are tighter than those proposed in the existing works. [ABSTRACT FROM AUTHOR]

Sampling above the Nyquist rate is at the heart of sigma–delta modulation, where the increase in sampling rate is translated to a reduction in the overall (mean-squared-error) reconstruction distortion. This is attained by using a feedback filter at the encoder, in conjunction with a low-pass filter at the decoder. The goal of this paper is to characterize the optimal trade-off between the per-sample quantization rate and the resulting mean-squared-error distortion under various restrictions on the feedback filter. To this end, we establish a duality relation between the performance of sigma–delta modulation and the performance of differential pulse-code modulation when applied to (discrete-time) band-limited inputs. As the optimal trade-off for the latter scheme is fully understood, the full characterization for sigma–delta modulation, as well as the optimal feedback filters, immediately follows. [ABSTRACT FROM AUTHOR]

In this paper, the target tracking problem is investigated for a class of wireless localization systems with degraded measurements and quantization effects. The measurement degradations induced by unreliable channels are characterized by a random parameter matrix, and the quantization effects are modeled by sector-bounded uncertainties. A recursive filtering algorithm is proposed in order to track the plant states as accurately as possible. An upper bound on the filtering error covariance is first derived and such an upper bound is then minimized by properly designing the filter gain at each sampling instant. The desired filter parameters are obtained by solving two sets of Riccati-like difference equations that are in a recursive form suitable for online application. Finally, a simulation experiment is carried out for the scenario of personnel localization/tracking problems in a mine industrial site and the effectiveness of the proposed filter method is demonstrated. [ABSTRACT FROM AUTHOR]

This paper presents a highly configurable non-linear compression scheme and its implementation as a configurable, compressive successive approximation register analog-to-digital converter (ADC). The non-linear ADC takes advantage of the input signal amplitude statistics and application sensitivity to maximize the information content of the digitized signal. This allows for potential power savings in the ADC conversion and the digital post-processing that follows it. This paper is the first mixed-signal interface that is fully configurable in terms of its non-linear quantization approach, supporting a wide variety of quantization functions. A 90-nm CMOS proof-of-concept chip operating at 33 kS/s is presented. The versatility and broad applicability of this proposal are further demonstrated with various case studies. [ABSTRACT FROM AUTHOR]

We study a two-user multiple-input single-output Gaussian interference channel with limited rate feedback and transmitter cooperation. Each receiver quantizes the channel state information of the direct and cross channels, and sends the codebook indices back to the transmitters through two sum-rate-limited feedback channels. The quantization errors reduce the beamforming gain from the direct transmitter, and cause interference leakage from the cross transmitter. Under an assumption of high signal-to-noise ratio, we first approximate the average transmission rate of each link, and use the sum rate to find the optimal transmit power and corresponding feedback bit allocation. We show that the maximum sum throughput is achieved using full transmit power, and the achievable sum rate under limited feedback is bounded above by a constant. We then extend the results to the case where secrecy is desired. In contrast to the first problem, increasing the transmit power beyond a certain point decreases the secrecy performance. Additionally, we analyze the asymptotic behavior of the solutions when the total feedback bandwidth and the number of transmit antennas grow large. We derive all results in closed form. Simulations validate the theoretical analysis and demonstrate the significant performance gains that result from the use of optimal transmit power control and intelligent feedback bit allocation. [ABSTRACT FROM AUTHOR]

It is revealed that there is a link between the quantization approach employed and the dimension of the vector parameter which can be accurately estimated by a quantized estimation system. A critical quantity called inestimable dimension for quantized data (IDQD) is introduced, which does not depend on the quantization regions and the statistical models of the observations but instead depends only on the number of sensors and on the precision of the vector quantizers employed by the system. It is shown that the IDQD describes a quantization-induced fundamental limitation on the estimation capabilities of the system. To be specific, if the dimension of the desired vector parameter is larger than the IDQD of the quantized estimation system, then the Fisher information matrix for estimating the desired vector parameter is singular, and, moreover, there exist infinitely many nonidentifiable vector parameter points in the vector parameter space. Furthermore, it is shown that under some common assumptions on the statistical models of the observations and the quantization system, a smaller IDQD can be obtained, which can specify an even more limiting quantization induced fundamental limitation on the estimation capabilities of the system. [ABSTRACT FROM AUTHOR]

In this paper, we consider the problem of sensor fusion over networks with asymmetric links, where the common goal is linear parameter estimation. For the scenario of bandwidth-constrained networks, existing literature shows that nonvanishing errors always occur, which depend on the quantization scheme. To tackle this challenging issue, we introduce the notion of virtual measurements and propose a distributed solution LS-DSFS, which is a combination of a quantized consensus algorithm and the least squares approach. We provide detailed analysis of the LS-DSFS on its performance in terms of unbiasedness and mean square property. Analytical results show that the LS-DSFS is effective in smearing out the quantization errors, and achieving the minimum mean square error (MSE) among the existing centralized and distributed algorithms. Moreover, we characterize its rate of convergence in the mean square sense and that of the mean sequence. More importantly, we find that the LS-DSFS outperforms the centralized approaches within a moderate number of iterations in terms of MSE, and will always consume less energy and achieve more balanced energy expenditure as the number of nodes in the network grows. Simulation results are presented to validate theoretical findings and highlight the improvements over existing algorithms. [ABSTRACT FROM AUTHOR]

This paper analyzes the limitations of a reduced-order model for modular multilevel converters (MMCs) by elucidating the relation between its accuracy, operating frequency, and converter parameters. A reduced-order simplifies the analysis of the MMC and thereby may provide additional information about the converter behavior. However, the accuracy of such model depends on several factors. In this paper, the effect of approximating the converter as a continuous system by neglecting quantization issues associated with having a finite number of modules is studied in detail. The analysis is done based on Fourier-series approximations with which it is possible to elucidate the relationship between the resonant frequencies of the MMC and the error of the reduced-order model. With the Fourier approximation, it is also possible to characterize resonant frequencies of the converter, both numerically and analytically, in terms of the converter parameters. The results can serve as a tool to identify situations when the reduced-order model produces good and also less accurate approximations especially when a low number of modules is available. [ABSTRACT FROM PUBLISHER]

A fundamental problem of Einsteins theory of classical general relativity is the existence of singularities such as the big bang. All known laws of physics end at these boundaries of classical space-time. Thanks to recent developments in quantum gravity, supercomputers are now playing an important role in understanding the resolution of big bang and black hole singularities. Using supercomputers, explorations of the very genesis of space and time from quantum geometry are revealing a novel picture of what lies beyond classical singularities and the new physics of the birth of our universe. [ABSTRACT FROM AUTHOR]

We consider the problem of recovering a high-dimensional structured signal from independent Gaussian linear measurements each of which is quantized to $b$ bits. The focus is on a specific method of signal recovery that extends a procedure originally proposed by Plan and Vershynin for one-bit quantization to a multi-bit setting. At the heart of this paper is a characterization of the optimal trade-off between the number of measurements m$ and the bit depth per measurement b$ given a total budget of B = m \cdot b -error in estimating the signal. It turns out that the choice b = 1$ is optimal for estimating the unit vector (direction) corresponding to the signal for any level of additive Gaussian noise before quantization as well as for a specific model of adversarial noise, whereas in a noiseless setting the choice b = 2$ is optimal for estimating the direction and the norm (scale) of the signal. Moreover, Lloyd–Max quantization is shown to be an optimal quantization scheme with respect to -estimation error. Our analysis is corroborated by the numerical experiments showing nearly perfect agreement with our theoretical predictions. This paper is complemented by an empirical comparison to alternative methods of signal recovery. The results of that comparison point to a regime change depending on the noise level: in a low-noise setting, the approach under study falls short of more sophisticated competitors while being competitive in moderate- and high-noise settings. [ABSTRACT FROM PUBLISHER]

This letter presents an algorithm for the design of fixed-rate unrestricted polar quantizer (FUPQ) for bivariate circularly symmetric sources. The proposed algorithm is globally optimal for the class of FUPQs with the magnitude quantizer thresholds restricted to some predefined finite set. The solution algorithm is based on dynamic programming, which is further accelerated by exploiting the monotonicity property of the cost function. The time complexity of the accelerated algorithm is $O(KN^2)$ , where $N$ is the number of target qunatizer levels and $K$ is the size of the predefined set of possible thresholds. The experimental results show that our approach outperforms the previous tractable designs when the total number of quantizer levels ranges between 25 and 256. [ABSTRACT FROM AUTHOR]

This letter proposes a novel ternary-event-based particle filtering ( $\text{TEB-PF}$ ) framework by introducing the ternary-event-triggering mechanism coupled with a non-Gaussian fusion strategy that jointly incorporates point-valued, quantized, and set-valued measurements. In contrast to the existing binary-event-triggering solutions, the $\text{TEB-PF}$ is a distributed state estimation architecture where the remote sensor communicates its measurements to the estimator, residing at the fusion centre, in a ternary-event-based fashion, i.e., holds on to its observation during idle epochs, transfers quantized ones during the transitional epochs, and only communicates raw observations during event epochs. Due to joint utilization of quantized and set-valued measurements in addition to the point-valued ones, the proposed $\text{TEB-PF}$ simultaneously reduces the communication overhead, in comparison to its binary triggering counterparts, while also improving the estimation accuracy specially in low communication rates. [ABSTRACT FROM AUTHOR]

This paper presents a dual quantization lateral-axis capacitive electromechanical sigma–delta modulator (EM- \Sigma \Delta \mathrm M ) vibratory wheel gyroscope under mode-matched condition. A symmetric wheel gyroscope structure was designed, fabricated, and wafer-level packaged under vacuum. The EM- \Sigma \Delta \mathrm M interface loop adopts a fourth-order multifeedback and local resonator \Sigma \Delta \mathrm M noise shaping structure, taking advantage of single-bit and multibit quantization in a single-loop modulator. To evaluate the influence of quantization noise, various numbers of bits of the multibit quantizator were compared and the optimal number of bits was calculated. The interface circuit system was implemented in hardware based on a low-noise front-end application-specified integrated circuit and a back-end discrete-time EM- \Sigma \Delta \mathrm M realized in a field-programmable gate array chip. The system clock was generated using a self-clocking scheme, which allows interfacing to gyroscope with a wide range of drive frequencies. Experimental evaluation indicated that the digital gyroscope system achieved a scale factor of 2073LSB(4.1 mV)/deg/s, with a nonlinearity of 0.046%, a noise floor of 3.1 m°/s/ $\surd $ Hz within a bandwidth of 100 Hz, and a bias instability of 1.3 deg/hr. [2017-0081] [ABSTRACT FROM PUBLISHER]

Nearest neighbor search is a problem of finding the data points from the database such that the distances from them to the query point are the smallest. Learning to hash is one of the major solutions to this problem and has been widely studied recently. In this paper, we present a comprehensive survey of the learning to hash algorithms, categorize them according to the manners of preserving the similarities into: pairwise similarity preserving, multiwise similarity preserving, implicit similarity preserving, as well as quantization, and discuss their relations. We separate quantization from pairwise similarity preserving as the objective function is very different though quantization, as we show, can be derived from preserving the pairwise similarities. In addition, we present the evaluation protocols, and the general performance analysis, and point out that the quantization algorithms perform superiorly in terms of search accuracy, search time cost, and space cost. Finally, we introduce a few emerging topics. [ABSTRACT FROM PUBLISHER]

The first folding-flash time-to-digital converter (TDC) based on the remainder number system (RNS) is reported. In this paper, fine quantization of an input time interval is performed directly with dual free-running ring oscillators without additional circuitry to record the coarse bits. The RNS architecture reduces hardware complexity significantly without speed impairment relative to the full flash counterpart employing delay chains. As a proof-of-concept design, 490 quantization levels using only 84 delay stages achieve a sample rate of 215 MS/s and an LSB size of 9.4 ps. Without trimming or calibration, the measured differential nonlinearity and integral nonlinearity of the RNS TDC prototype are +0.53/−0.57 and +1.1/−1.1 LSBs, respectively. [ABSTRACT FROM AUTHOR]

A two-stage continuous-time $\Delta \Sigma $ modulator with voltage-controlled oscillator based quantizer (VCOQ) is presented. The presented modulator suppresses the VCOQ voltage-to-frequency nonlinearity through dual path cancellation to achieve high linearity. As an added advantage, this architecture exhibits strong immunity to the first stage quantization error leakage to the output due to gain mismatches between the two stages. Fabricated in a 65 nm CMOS technology, the prototype modulator operates at 1.5 GS/s and achieves 76.1 dB SNR, 73.5 dB SNDR, 88 dB SFDR, and 76.1 dB dynamic range (DR) in 50 MHz bandwidth. This prototype demonstrates robust performance with less than 1.5 dB variation in SNDR for ±10% gain mismatch between the two stages. Also, the SNDR variation remains within 1 dB for a temperature variation of 0°C–80°C. The modulator consumes 51.8 mW of power leading to a Walden FoM of 134 fJ/conv-step. [ABSTRACT FROM AUTHOR]

We address the problem of sparse signal recovery in compressed sensing when a fraction of acquired measurements is invalid or damaged. This may occur due to some system malfunction or unreliable transmission medium. The current solution requires increasing the number of measurements to achieve accurate signal recovery, otherwise recovery performance is jeopardized. We study the performance impact of prefiltering the acquired measurements by detecting and omitting potentially invalid measurements prior to signal recovery. We demonstrate analytically and numerically that this approach significantly reduces the number of measurements required for accurate recovery, which leads to overall improvement of recovery performance, especially when a large fraction of measurements is invalid. Therefore, this approach enhances the ability of compressed sensing to tolerate realistic implementation challenges. [ABSTRACT FROM AUTHOR]

This paper shows the generation of a local oscillator (LO) signal for cellular transceivers by means of a phase-locked loop and a phase interpolator (PI) digital-to-time converter (DTC). The PI-DTC allows arbitrary frequency shifts over a wide range. We derive a closed-form description of the spurs in the spectrum of the LO signal caused by quantization and nonlinear effects for the PI-DTC. Furthermore, we show the existence of a new class of spurs generated due to noise processes in the PI. Measurement and simulation results are in good agreement with our closed-form solution. [ABSTRACT FROM AUTHOR]

Hybrid analog-digital beamforming is a well-known cost-efficient signal processing method for massive MIMO systems. In this paper, we propose a hybrid beamforming massive MIMO system based on Rotman lens analog beamforming with beam selection and digital beamforming. Rotman lens is a low-cost true-time-delay analog beamforming network supporting wide bandwidth signals, which is thus more attractive than the analog beamforming networks based on conventional high-cost phase shifters. To study our system based on Rotman lens, we first examine two potential array architectures, i.e., full-array and subarray architectures, concerning the RF design feasibility, insertion loss, and system scalability. Since the beam selection is required in our system, we propose two beam selection algorithms, i.e., greedy search-based method and branch- and bound-based method, aiming to optimize the hybrid beamforming system in terms of error-rate performance for both the full-array and subarray architectures. To validate our system in practice, the proposed system is also investigated and verified experimentally. In particular, we design and fabricate a sample of Rotman lens operating in the 5-GHz band, whose measured results agrees well with the computer simulation results. The measurement results are incorporated into the Monte-Carlo simulation with the proposed beam selection algorithms to study the error-rate performance. Our simulation results show that the hybrid beamforming system using the low-cost Rotman lens has performance comparable to that of the system using the high-cost phase shifters, and exhibits wideband capability and superior performance over the small-scale MIMO system under the same number of RF transceivers. [ABSTRACT FROM PUBLISHER]

A nonlinearity calibration technique is proposed for an open-loop phase modulator (PM), for wideband phase modulation, and for multiple-output, low-jitter clock generation. The design considerations and key performance aspects of the calibration technique are discussed. The PM integrates a digital phase-locked loop, local oscillator distribution network, and digital calibration. A prototype was implemented in 0.13- \mu \textm CMOS 1.8-GHz Gaussian frequency shift keying (GFSK) transmitter integrated circuit. Measurements on the prototype show that out-of-band quantization noise is 56 dB lower than that of the signal when transmitting 20-Mb/s GFSK signal and the rms error is only 3.2%. The power consumption of the PM is 18 mW. The measured spurious tones of the clock generation unit are below −46 dBc. [ABSTRACT FROM PUBLISHER]

This paper proposes the use of the coplanar waveguide (CPW) odd mode, also known as the parasitic slotline mode, as a design parameter. It presents a novel equivalent circuit model for the CPW cross-junction, where each CPW has two modes: the even mode, which is the conventional CPW mode also known as the coplanar mode, and the odd mode. The model is simple, intuitive, and physical-based. It can be used in different combinations including the case of slotline cross-junction. The model paves the way to design novel air-bridge free CPW applications. Among them, two are presented in this paper: CPW-to-slotline transition (balun) and Wilkinson power divider. For both applications, closed form expressions for the operating point are derived. Results are verified by EM simulations. An air-bridge free CPW power divider that combines both applications is fabricated and characterized. Simulations and measurements are in a very good agreement. [ABSTRACT FROM PUBLISHER]

In this paper, we investigate the problem of impulsive noise cancellation in systems that use jointly overcomplete expansion representations, namely the cyclic geometrically uniform (CGU) frame and sigma-delta (SD) quantization. We first describe the existing analogy between the CGU frames and Reed–Solomn (RS) codes and how it can be exploited in order to reformulate the impulsive noise cancellation problem. As the impulsive noise does by nature represent a sparse signal, it fits the compressed sensing (CS) framework. This is why we investigate how to remodel our impulsive noise cancellation in a CGU-/SD-based system as a CS problem. Then, we study the use and limitations of some existing CS recovery techniques, namely Smoothed L0 (SL0), orthogonal matching pursuit (OMP), compressive sampling matching pursuit (CoSaMP), and Bayes-based approach (BBA). In order to overcome such limitations, we propose how to improve such techniques, and we show that their related improved versions, namely Improved SL0 (I-SL0), I-OMP and I-CoSaMP, and I-BBA efficiently, cancel the impulsive noise of CGU/SD systems and do lead to a quasi-optimal performance. Simulation results are given to support our claims. [ABSTRACT FROM PUBLISHER]

This paper describes an evaluation of the Keysight 3458A digital multimeter (DMM) noise performance. A DMM noise model is given in closed form for all ranges and integrating analog-to-digital converter (IADC) aperture times. When the DMM is used for sampling, different sources of noise contribute to the total noise of the sampled signal. Their combined effect was measured using both short-circuited input terminals and spectrally pure Josephson arbitrary waveform synthesizer. Both white noise and 1/ f noise were evaluated. The results confirmed that the internal IADC can be used to measure DMM input referred noise when the IADC quantization noise is smaller than the instrument front-end analog circuitry-related noise. Further, it is shown that the DMM noise can be effectively measured with short-circuited input terminals when using double integer output format, but not always when using single integer output format. The manufacturer specifications were confirmed on all but the 100-V range. [ABSTRACT FROM AUTHOR]

Fin-type field-effect transistors (FinFETs) are promising substitutes for bulk CMOS for nanoscale technologies. In this paper, the viability of a mixed-signal design for FinFET-based technologies using a nanoscale current-starved voltage controlled oscillator (VCO) is investigated. Design issues are analyzed and a comparison between a CMOS VCO and a FinFET-based VCO is presented. The figures-of-merit used for comparison are center frequency and frequency–voltage ( f – V ) characteristics under process variation. Models are developed for the f – V characteristics of both the CMOS and FinFET VCOs. In addition, width quantization-aware modeling has been performed for the FinFET-based VCO using a polynomial metamodel, which can be used for further optimization. The quantization aware modeling is highly accurate as evident from a correlation coefficient R^2 of 0.999 and root mean square error of 6.2 MHz. The FinFET VCO has 5.5 \times faster oscillation frequency with 2.6% variability as opposed to 19.7% for the CMOS VCO. To the best of the authors’ knowledge, this is the first paper that examines FinFET technology with respect to process variation in mixed signal designs at the circuit level, and presents a quantitative as well as qualitative comparison between CMOS and FinFET technologies. [ABSTRACT FROM PUBLISHER]

We describe the implementation of new commercial pulse-bias electronics that have enabled an improvement in the generation of quantum-accurate waveforms both with and without low-frequency compensation biases. We have used these electronics to apply a multilevel pulse bias to the Josephson arbitrary waveform synthesizer and have generated, for the first time, a quantum-accurate bipolar sinusoidal waveform without the use of a low-frequency compensation bias current. This uncompensated 1 kHz waveform was synthesized with an rms amplitude of 325 mV and maintained its quantum accuracy over a 1.5 mA operating current range. The same technique and equipment was also used to synthesize a quantum-accurate 1 MHz sinusoid with a 1.2 mA operating margin. In addition, we have synthesized a compensated 1 kHz sinusoid with an rms amplitude of 1 V and a 2.7 mA operating margin. [ABSTRACT FROM PUBLISHER]

Bitstream transmitters based on bandpass or envelope delta–sigma modulation promise high power efficiency for broadband communications with nonconstant-envelope modulations, but at the price of elevated quantization noise. An active noise filtering technique is proposed in this paper to address the quantization noise issue of such transmitters. The essential concept of active noise cancellation is to utilize multiple power amplifiers (PAs) with identical or similar transfer characteristics fed with the same input, but with different time delays. The difference in time delay determines whether the outputs of the PAs are combined in phase or out of phase at a certain frequency, which forms the passband or the stopband of the active filter. The active noise filtering technique can potentially replace the external high-Q passive bandpass filter typically needed for such transmitters. A two-channel bitstream transmitter with active noise cancellation operating at the $X$ -band is fabricated with 0.25- \mu \text{m} discrete GaN HEMT devices. It has been demonstrated experimentally that the proposed active noise filtering architecture effectively suppresses quantization noise as expected and delivers a 34.5-dBm output power with 37.6% drain efficiency and 30% power added efficiency for a single-channel WCDMA signal with 100-MHz bandwidth and 5.3-dB peak-to-average ratio. Adjacent channel leakage power ratio (ACLR) at 100-MHz offsets is measured to be 36.6/35.4 dBc without using digital predistortion. [ABSTRACT FROM AUTHOR]

Sampling of physical fields with mobile sensor is an emerging area. In this context, this work introduces and addresses some aspects of a fundamental question: can a spatial field be estimated from samples taken at unknown sampling locations? In a field (signal) sampling setup, unknown sampling locations, sample quantization, unknown bandwidth of the field, and presence of measurement-noise present difficulties in the process of field estimation. In this work, except for quantization, the other three issues will be tackled together in a mobile-sampling framework. Spatially bandlimited fields are considered. It is assumed that measurement-noise affected field samples are collected on spatial locations obtained from an unknown renewal process. That is, the samples are obtained on locations obtained from a renewal process, but the sampling locations and the renewal process distribution are unknown. In this challenging unknown sampling location setup, it is shown that the mean-squared error in field estimation decreases as $O(1/n)$ where $n$ is the average number of samples collected by the mobile sensor. The average number of samples collected is determined by the inter-sample spacing distribution in the renewal process. An algorithm to ascertain spatial field’s bandwidth is detailed, which works with high probability as the average number of samples $n$ increases. This algorithm works in the same setup, i.e., in the presence of measurement-noise and unknown sampling locations. [ABSTRACT FROM PUBLISHER]

This letter presents a perceptually weighted analysis-by-synthesis vector quantization (VQ) algorithm for low bit rate MFCC codec. Different from conventional VQ of mel-frequency cepstral coefficients (MFCCs) vector, this algorithm uses an analysis-by-synthesis technique and aims to minimize the perceptually weighted spectral reconstruction distortion rather than the distortion of MFCCs vector itself. Also, to reduce the computational complexity, we propose a practical suboptimal codebook searching technique and embed it into the split and multistage VQ framework. Objective and subjective experimental results on Mandarin speech show that the proposed algorithm yields intelligible and natural sounding speech for speech coding at 600–2400 bit/s. Compared to current VQ in MFCC codec, the output speech quality is substantially improved in terms of frequency-weighted segmental SNR, short-time objective intelligibility score, perceptual evaluation of speech quality score, and mean opinion score. [ABSTRACT FROM PUBLISHER]