Waveform Generator Research Articles

Real-time Assistive Reader Pen for Arabic Language

Disability is an impairment affecting an individual's livelihood and independence. Assistive technology enables the disabled cohort of the community to break the barriers to learning, access information, contribute to the community, and live independently. This article proposes an assistive device to enable people with visual disabilities and learning disabilities to access printed Arabic material in real-time, and to help them participate in the education system and the professional workforce. This proposed assistive device employs Optical Character Recognition (OCR) and Text To Speech (TTS) conversion, using concatenation synthesis. OCR is achieved using image processing, character extraction, and classification, while Arabic speech synthesis is achieved through concatenation synthesis, followed by Multi Band Re-synthesis Overlap-Add (MBROLA). Waveform generation in the second phase produces vocal output for the disabled user to hear. OCR character and word accuracy tests were conducted for nine Arabic fonts. The results show that six fonts were recognized with over 60% character accuracy and two fonts were recognized with over 88% accuracy. A Mean Opinion Score (MOS) test for speech quality was conducted. The results showed an overall MOS score of 3.53/5 and indicated that users were able to understand the speech. A real-time usability testing was conducted with 10 subjects. The results showed an overall average of agreements scores of 3.9/5 and indicated that the proposed Arabic reader pen meets the real-time constraints and is pleasant and satisfying to use and can contribute to make printed Arabic material accessible to visually impaired persons and people with learning disabilities.

Self-Switching Kerr Oscillations of Counterpropagating Light in Microresonators.

We report the experimental and numerical observation of oscillatory antiphase switching between counterpropagating light beams in Kerr ring microresonators, where dominance between the intensities of the two beams is periodically or chaotically exchanged. Self-switching occurs in balanced regimes of operation and is well captured by a simple coupled dynamical system featuring only the self- and cross-phase Kerr nonlinearities. Switching phenomena are due to temporal instabilities of symmetry-broken states combined with attractor merging, which restores the broken symmetry on average. Self-switching of counterpropagating light is robust for realizing controllable, all-optical generation of waveforms, signal encoding, and chaotic cryptography.

An improved frequency-quadrupling triangular waveform generation based on external modulation and polarization control

An improved photonic generation of full-duty-cycle triangular waveforms based on external modulation and orthogonal polarization control is proposed. The external modulation configuration consists a dual-parallel Mach–Zehnder modulator (DP-MZM) and a remodulation structure. After external modulation, four main sidebands with uniform frequency interval existed in the optical spectrum. To obtain the target triangular waveform, the modulation indices of modulators need to be carefully adjusted to guarantee the amplitude ration of inner-sideband and outer- sideband is desired 9.5 dB. Subsequently, polarization control is utilized to eliminate the coherent interference of different sidebands. Based on our proposal, triangular waveforms at 10 GHz, 20 GHz, 30 GHz and 40 GHz are achieved. The proposal might be attractive since that the generated signal repetition rate is frequency-tunable and frequency-quadrupled.

Computational evaluation of a new digital tandem quadrupole mass filter.

A tandem mass filter consists of two low-resolution mass filters arranged in series that operate with a small offset between their mass windows. In principle, the overlap of the two individual mass windows defines the tandem window. Tandem operation provides improved resolution and transmission compared to a single mass filter operated with the same mass window. The improvement in transmission is owed to the larger acceptance of the low-resolution quadrupoles. The tandem filter resolution and transmission are adjusted by changing the amount of offset separating the mass windows of the individual filters. Sine wave systems create this offset through voltage changes. Digital tandem mass filters depart from convention because they do not change voltage. The tandem mass window is created when the individual filters are operated with two slightly different duty cycles. Both quadrupoles operate at the same frequency, phase, and voltage. When the frequency, phase, and voltage of each quadrupole are identical, there theoretically are no changes to the Mathieu parameters to cause ion excitation and loss during transition between the quadrupole pair. The work presented here shows that a fixed AC voltage digital tandem mass filter can only operate in higher stability zones. However, unlike sine mass filters, the mass range of a digital system is not limited. This makes the digital tandem mass filter feasible as a commercial product. For the tandem digital mode to be successful, the duty cycles of each quadrupole must be precisely controlled because the duty cycle differences required to shift the mass windows are small. The creation of these mass window offsets requires waveform generation that can obtain high duty cycle resolution. Our method of generating waveforms can meet this demand; however, modifications to our current printed circuit board must be made. These modifications are minor and will be discussed.

Structure of a microtubule-bound axonemal dynein

Axonemal dyneins are tethered to doublet microtubules inside cilia to drive ciliary beating, a process critical for cellular motility and extracellular fluid flow. Axonemal dyneins are evolutionarily and biochemically distinct from cytoplasmic dyneins that transport cargo, and the mechanisms regulating their localization and function are poorly understood. Here, we report a single-particle cryo-EM reconstruction of a three-headed axonemal dynein natively bound to doublet microtubules isolated from cilia. The slanted conformation of the axonemal dynein causes interaction of its motor domains with the neighboring dynein complex. Our structure shows how a heterotrimeric docking complex specifically localizes the linear array of axonemal dyneins to the doublet microtubule by directly interacting with the heavy chains. Our structural analysis establishes the arrangement of conserved heavy, intermediate and light chain subunits, and provides a framework to understand the roles of individual subunits and the interactions between dyneins during ciliary waveform generation.

Design and Experiments of a Waveform Generator Based on DDS Technology

Background: Signal generator plays a crucial role in the field of automatic measurement. However, Domestic signal generator usually uses a number of discrete phases locked loop components, whose circuits are usually complex with low precision and are easily affected by the external environment. Objective: Based on direct digital synthesis (DDS) technology, a small sized high precision economic waveform generator with a simple structure and operational convenience is developed. Methodology: The hardware circuit is designed with an AT89S52 controller, and the corresponding peripheral circuit. A DDS integrated chip AD9834 is employed as a signal source, and the modular programming principle with C and assembly language is used to accomplish the software design, through which the sine wave, square wave, triangular wave signals with adjustable amplitude, frequency, and TTL signal with adjustable duty ratio can be generated. Conclusion: The whole system is advantageous with several aspects such as high frequency precision, wide frequency range, and operational convenience. The experimental results show that the stability and reliability of the waveform generator are good with a simple hardware circuit structure.

Towards the routine use of subdominant harmonics in gravitational-wave inference: Reanalysis of GW190412 with generation X waveform models

We re-analyse the gravitational-wave event GW190412 with state-of-the-art phenomenological waveform models. This event, which has been associated with a black hole merger, is interesting due to the significant contribution from subdominant harmonics. We use both frequency-domain and time-domain waveform models. The PhenomX waveform models constitute the fourth generation of frequency-domain phenomenological waveforms for black hole binary coalescence; they have more recently been complemented by the time-domain PhenomT models, which open up new strategies to model precession and eccentricity, and to perform tests of general relativity with the phenomenological waveforms approach. Both PhenomX and PhenomT have been constructed with similar techniques and accuracy goals, and due to their computational efficiency this "generation X" model family allows the routine use of subdominant spherical harmonics in Bayesian inference. We show the good agreement between these and other state-of-the-art waveform models for GW190412, and discuss the improvements over the previous generation of phenomenological waveform models. We also discuss practical aspects of Bayesian inference such as run convergence, variations of sampling parameters, and computational cost.

Photonic Generation and Transmission of Dual-Band Dual-Chirp Microwave Waveforms at C-Band and X-Band With Elimination of Power Fading

We propose a photonic method to generate and transmit dual-band dual-chirp microwave waveforms based on a dual-polarization dual-parallel Mach-Zehnder modulator (DP-DPMZM). The key novelty of this work is the generation of dual-band dual-chirp waveforms with flexible central frequency relationship to meet the requirement of the dual-band radar system, and transmission of the generated waveforms with elimination of power fading. In the proposed method, dual-band dual-chirp microwave waveforms are generated by applying two different RF signals and a parabolic coding signal to the DP-DPMZM. By properly adjusting the DC biases of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> -DPMZM and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> -DPMZM, dispersion-induced power fading effect in the transmission of the generated waveforms can be compensated. A proof-of-concept experiment is conducted to generate and transmit dual-band dual-chirp microwave signals at C-band and X-band (centered at 7 GHz and 10 GHz) with tunable bandwidth. The proposed system has a simple structure and good reconfigurability, which has great potential in applications such as dual-band radar systems.

Experimental and Numerical Investigations on the Interface Characteristics of Laser Impact-Welded Ti/Brass Joints

The dissimilar welding of metal Ti and alloy brass foils was achieved via laser impact welding. Three laser energies were used, and the interface characteristics of Ti/brass joints were systematically investigated through experiments and smoothed particle hydrodynamics (SPH) simulation. Results indicated that the Ti/brass interfaces under all three laser energies were ring-shaped, and the increase in laser energy resulted in the increase in effective welding area. The phenomena of jet, interface waveform, and cracking were observed at the interface. Jet particles were released from both the Ti flyer and brass target, and interfacial elemental diffusion occurred. SPH simulation results showed that the generation of the interface waveform was related to the collision point position and jet particle ejection direction. The size of the interface waveform increased with the laser energy and increased along the welding direction. This finding was correlated with the horizontal welding velocity, jet velocity, and normal stress. Three different interface failure modes were included in the tensile shear tests, and the maximum tensile force of Ti/brass joints increased with the laser energy.

A High Frequency Self-Reconfigurable Battery for Arbitrary Waveform Generation

This article presents an innovative self-reconfigurable battery (SRB) architecture, which is able to generate directly at its output any waveform signals. Thanks to that specific characteristic of the proposed system, it is even possible to dispense with any AC charger. Although the individual ability of each cell in the battery pack to perform an efficient active cell balancing has been already studied in the literature, the system presented in this article is the first of its kind. This article describes a real prototype of a high frequency SRB of 128 cells and demonstrates that it can be charged without any dedicated charger directly on the electrical grid, by generating a sinusoidal waveform voltage, while perfectly balancing the cells in real time.

Full Custom Design of an Arbitrary Waveform Gate Driver With 10-GHz Waypoint Rates for GaN FETs

Active gate driving of power devices seeks to shape switching trajectories via the gate, for example, to reduce EMI without degrading efficiency. To this end, driver ICs with integrated arbitrary waveform generators have been used to achieve complex gate signals. This article describes, for the first time, the implementation details of a digitally programmable arbitrary waveform gate driver capable of a 10-GHz waypoint rate, including comprehensive design considerations for critical high-speed subsystems that codify the tradeoff in flexibility, speed, and area. The design, which is taped out in a 180-nm high-voltage CMOS process, utilizes buffers that switch up to ten times in a single clock cycle to overcome the limited achievable clock speed of high-voltage silicon integrated circuits and a fully digital architecture to provide robustness under high slew rates of the ground rail. The driver IC has networks of 100-ps delay elements that are configured prior to a switching transient, to selectively control an array of fast, parallel-connected drivers with different output impedances. Key to the high timing resolution are high-speed asynchronous circuits for memory readout, output buffering, and pulse generation. The driver IC is experimentally evaluated to have a 100-ps resolution and to operate reliably in a 400-V gallium nitride (GaN) bridge leg, under ground-rail voltage slew rates peaking at over 100 V/ns. Design rules are provided to obtain an architecture with the least area for a given set of timing and impedance resolution requirements. The reported design methods enable complex driving waveforms to be applied during nanosecond-scale transients of GaN power devices and demonstrate how digitally programmable active gate drivers for GaN power FETs can be designed to meet a given set of application requirements.

Development of neural networks chip generating driving waveform for electrostatic motor

The authors are studying hardware neural networks (HNN) to control the locomotion of the microrobot. The neural networks chip is the integrated circuit chip of the HNN. We proposed the electrostatic motor that is the new actuator of the microrobot in our previous research. The electrostatic motor used the waveform generator to generate the driving waveform. In this paper, the authors will propose the driving circuit using neural networks chip. The cell body model is the basic component of the neural networks chip that outputs 3 MHz frequency of electrical oscillated pulse waveform. Therefore, large capacitors need to connect outside of the neural networks chip to generate the low-frequency driving waveform. The proposal neural networks chip generates a long delay without using large capacitors. In addition, the neural networks chip generated a two-phase anti-phase synchronized waveform by incorporating a mechanism for adjusting synaptic weight. As a result, the proposal neural networks chip can generate the electrostatic motor’s driving waveform with variable frequency. The frequency of the driving waveform could vary from 40 to 126 Hz.

PeriodNet: A Non-Autoregressive Raw Waveform Generative Model With a Structure Separating Periodic and Aperiodic Components

This paper presents PeriodNet, a non-autoregressive (non-AR) waveform generative model with a new model structure for modeling periodic and aperiodic components in speech waveforms. Non-AR raw waveform generative models have enabled the fast generation of high-quality waveforms. However, the variations of waveforms that these models can reconstruct are limited by training data. In addition, typical non-AR models reconstruct a speech waveform from a single Gaussian input despite the mixture of periodic and aperiodic signals in speech. These may significantly affect the waveform generation process in some applications such as singing voice synthesis systems, which require reproducing accurate pitch and natural sounds with less periodicity, including husky and breath sounds. PeriodNet uses a parallel or series model structure to model a speech waveform to tackle these problems. Two sub-generators connected in parallel or in series take an explicit periodic and aperiodic signal (sine wave and Gaussian noise) as an input. Since PeriodNet models periodic and aperiodic components by focusing on whether these input signals are autocorrelated or not, it does not require external periodic/aperiodic decomposition during training. Experimental results show that our proposed structure improves the naturalness of generated waveforms. We also show that speech waveforms with a pitch outside of the training data range can be generated with more naturalness.

Design and Implementation of a Re-Configurable Versatile Direct Digital Synthesis-Based Pulse Generator

Direct digital synthesis (DDS) technology has replaced many traditional analog circuit functions. The frequency, amplitude, and phase of a waveform generated using DDS can be precisely controlled. It is possible to achieve remarkably high-frequency resolution, fast frequency switching, and modulation can be easily introduced in a DDS generator. However, pulse waveform generated using DDS requires re-loading of the pulse waveform in the waveform memory to vary the pulse parameters, which causes phase discontinuity, requires prohibitively large memory to generate pulses with narrow widths and long periods, and suffers from trigger uncertainty of up to 1 clock period when the pulse waveform is triggered by an external event. Moreover, it is not possible to modulate the width and delay of the pulse stored in the waveform memory. This article describes a fully functional, low complexity, low cost, memory less, parallel, and DDS-based pulse waveform generator implemented in a low-cost field programmable gate arrays (FPGA) where pulse parameters such as amplitude, period, width, rise time, fall time, and delay can all be varied without any glitches or phase discontinuity, where the amplitude, frequency and phase, as well as period, width and delay of the pulse can be modulated by an internally generated or external modulating signal and where it is possible to trigger the generation of the pulse or burst of pulses by an external event where the time between the trigger event and the pulse output is fixed.

Design of DDS Multi-waveform Generator Based on CPLD

Traditional Direct Digital Synthesis (DDS) waveform generators were usually completed by DDS chips, which were expensive and poorly customizable. This paper proposed a CPLD-based DDS multi-waveform generator design. DDS was independently developed and programmed by VHDL language. The system could be interfaced with PC. The system was mainly divided into two parts: upper computer and lower computer. The upper computer part mainly included the main interface design of the system, the sending of control commands and the receiving part of data. The sending and receiving of commands and data was realized by serial communication. The upper computer part was programmed by High-level programming language named DELPHI. The lower computer part mainly included DDS design part, the reception of control commands and the transmission of data, etc., the lower computer part mainly adopt VHDL language to be programmed in CPLD. The DDS design part mainly included the design of the phase accumulator, the design of the ROM, the design of the D/A part, and the design of the low-pass filter. The system could adjust the frequency of the output waveform by adjusting the size of the frequency word, and adjust the waveform shape of the system output by adjusting the internal data of the ROM. Simulation and experimental results showed that: the DDS multi-waveform generator designed by CPLD could achieve the expected goal, and the work effect was good.

Triangular-shaped waveform generation with variable symmetry based on dual-polarization modulation

Photonic generation of triangular-shaped waveform with variable symmetry based on dual-polarization modulation is proposed and demonstrated. Based on the external modulation method, a dual-polarization modulator is used to modulate the radio frequency signal to generate the needed optical signal. By setting the modulation index of the modulator and phase shift of phase shifters appropriately, the optical intensity of generated signal can equal approximately the first three terms of the Fourier series expansion of the ideal triangular-shaped waveform, so triangular-shaped waveforms with different symmetry factors can be generated. Most of previous triangular waveform generation schemes generate symmetrical triangular waveform or sawtooth waveform (sawtooth waveform can be regarded as an asymmetrical triangular waveform), and the symmetry factor is not tunable. The tunable range of symmetry factor of triangular-shaped waveform generated by this scheme can reach 0%–100%, which will greatly expand the application range of triangular-shaped waveforms. The root-mean-square error (RMSE) is introduced to measure the similarity between the generated waveform and the theoretical waveform. It can be found that theoretically the triangular-shaped waveform with a symmetry factor in a range from 14% to 86% has a good similarity to the ideal waveform (RMSE &lt; 0.044), and the RMSE of the generated waveform in the simulation is also very close to the theoretical RMSE. Experimentally, the 4GHz triangular-shaped waveforms with different values of symmetry factor (20%–80%) are obtained by using 4GHz radio frequency signal.

Quasi-Periodic WaveNet: An Autoregressive Raw Waveform Generative Model With Pitch-Dependent Dilated Convolution Neural Network

In this paper, a pitch-adaptive waveform generative model named Quasi-Periodic WaveNet (QPNet) is proposed to improve the limited pitch controllability of vanilla WaveNet (WN) using pitch-dependent dilated convolution neural networks (PDCNNs). Specifically, as a probabilistic autoregressive generation model with stacked dilated convolution layers, WN achieves high-fidelity audio waveform generation. However, the pure-data-driven nature and the lack of prior knowledge of audio signals degrade the pitch controllability of WN. For instance, it is difficult for WN to precisely generate the periodic components of audio signals when the given auxiliary fundamental frequency ($F_{0}$) features are outside the $F_{0}$ range observed in the training data. To address this problem, QPNet with two novel designs is proposed. First, the PDCNN component is applied to dynamically change the network architecture of WN according to the given auxiliary $F_{0}$ features. Second, a cascaded network structure is utilized to simultaneously model the long- and short-term dependencies of quasi-periodic signals such as speech. The performances of single-tone sinusoid and speech generations are evaluated. The experimental results show the effectiveness of the PDCNNs for unseen auxiliary $F_{0}$ features and the effectiveness of the cascaded structure for speech generation.

A USRP-Based Testbed for Wideband Ranging and Positioning Signal Acquisition

For validation and demonstration of high accuracy ranging and positioning algorithms and systems, a wideband radio signal generation and acquisition testbed, tightly synchronized in time and frequency, is needed. The development of such a testbed requires solutions to several challenges. Tight time and frequency synchronization, derived from a centrally distributed time-frequency reference signal, needs to be maintained in the hardware of the transmitter and receiver nodes, and wideband signal acquisition requires sustainable data throughput between the receiver and host PC as well as data storage at GB level. This article presents a testbed for wideband radio signal acquisition, for validation and demonstration of high accuracy ranging and positioning. It consists of multiple Ettus X310 universal software radio peripherals (USRPs) and supports high accuracy (<; 100 ps) time-deterministic, sustainable signal transmission and acquisition, with a bandwidth up to 320 MHz (in dual channel mode) and frequencies up to 6 GHz. Generation and processing of wideband arbitrary signal waveforms is done offline. To realize these features, radio frequency on chip (RFNoC) compatible HDL units were developed for integration in the X310 SDR platform. Wideband transmission and signal acquisition at a lower duty cycle is applied to reduce the data offloading throughput to the host's personal computer (PC). Benchmarking of the platform was performed to demonstrate sustainable long duration dual channel acquisition. Indoor range measurements with the synchronous operation of the testbed show a decimeter-level accuracy.

Time-Domain Ultrawideband Chipless RFID Readers

This article evaluates time-domain techniques for the applications of ultrawideband (UWB) chipless radio frequency identification (RFID) readers. In UWB time-domain readers, the chipless RFID tag response to a UWB pulse excitation is simultaneously measured in time domain and then the frequency-domain signature of the tag is calculated by a time-to-frequency conversion method such as fast Fourier transform. A 32-bit UWB chipless RFID tag is designed and three time-domain readers based on impulse radio UWB, chirped-pulse Fourier transform microwave (CP-FTMW), and dual-comb techniques are analyzed and implemented by using microwave equipment including arbitrary waveform generator, network analyzer, and high-speed oscilloscope. It is demonstrated that CP-FTMW reader is a fast, accurate with high signal-to-noise ratio, and high-frequency resolution time-domain technique. Dual-comb reader is slower, however, it offers a viable solution for a low cost and potentially miniaturized and portable chipless RFID readers.

Full-Band LPCNet: A Real-Time Neural Vocoder for 48 kHz Audio With a CPU

This paper investigates a real-time neural speech synthesis system on CPUs that can synthesize high-fidelity 48 kHz speech waveforms to cover the entire frequency range audible by human beings. Although most previous studies on 48 kHz speech synthesis have used traditional source-filter vocoders or a WaveNet vocoder for waveform generation, they have some drawbacks regarding synthesis quality or inference speed. LPCNet was proposed as a real-time neural vocoder with a mobile CPU but its sampling frequency is still only 16 kHz. In this paper, we propose a Full-band LPCNet to synthesize high-fidelity 48 kHz speech waveforms with a CPU by introducing some simple but effective modifications to the conventional LPCNet. We then evaluate the synthesis quality using both normal speech and a singing voice. The results of these experiments demonstrate that the proposed Full-band LPCNet is the only neural vocoder that can synthesize high-quality 48 kHz speech waveforms while maintaining real-time capability with a CPU.