Digital Demodulation Research Articles

Design of fully interpretable neural networks for digital coherent demodulation.

In this paper, we propose a digital coherent demodulation architecture using fully interpretable deep neural networks (NNs). We show that all the conventional coherent digital signal processing (DSP) is deeply unfolded into a well-structured NN so that the established training algorithms in machine learning can be applied. In contrast to adding or replacing certain algorithms of existing DSP in coherent receivers, we replace all the coherent demodulation algorithms with a fully interpretable NN (FINN), making the whole NN interpretable. The FINN is modular and flexible to add or drop modules, including chromatic dispersion compensation (CDC), the digital back-propagation (DBP) algorithm for fiber nonlinearity compensation, carrier recovery and residual impairments. The resulted FINN can be quickly initialized by straightforwardly referring to the conventional DSP, and can also enjoy further performance enhancement in the nonlinear fiber transmissions by NN. We conduct a 132-Gb/s polarization multiplexed (PM)-16QAM transmission experiment over 600-km standard single mode fiber. The experimental results show that without fiber nonlinearity compensation, FINN-CDC obtains less than 0.06-dB SNR gain than chromatic dispersion compensation (CDC). However, with fiber nonlinearity compensation, 2-steps per span FINN-DBP (FINN-2sps-DBP) and FINN-1sps-DBP bring about 0.59-dB and 0.53-dB SNR improvement compared with the conventional 2sps-DBP and 1sps-DBP, respectively.

Digital demodulation method based on multichannel combined acquisition for near-infrared spectrometer

With the evolution of digital technology, the digital demodulation method has become widely employed in near-infrared (NIR) spectrometers due to its advantages of reducing the volume, enhancing the reliability, and increasing the flexibility of instruments. However, digital demodulation has a lower signal-to-noise ratio (SNR), which can be improved by lowering the measurement precision, speed, and stability. To improve the SNR without sacrificing the measurement speed or stability, an improved digital demodulation method was developed based on multichannel combined acquisition. To validate the proposed method, a multichannel combined acquisition digital lock-in amplifier demodulation system was designed for portable raster scanning NIR spectrometers. In this system, six ADC channels were used in conjunction to acquire the modulated sampling signal. Afterwards, comparative experiments were conducted to compare the conventional and novel methods. The experimental results revealed that the SNR increased from 2499 to 3007 with a measurement time of 16.75 s and 17.08 s, respectively. Furthermore, scanning the reference reflector resulted in a baseline drift of 0.064% and 0.060% with a scanning time of 128.27 s and 128.21 s. Scanning the kaolin sample resulted in a baseline drift of 0.27% and 0.23% with a scanning time of 128.44 s and 128.53 s. In brief, the multichannel combined acquisition method can improve the SNR of spectrometers without compromising their stability or measurement time.

Digitalized phase demodulation scheme of [formula omitted]-OTDR based on cross-coherence between Rayleigh back-scattering beat signals

In this paper, a simple and low-cost phase demodulation scheme for phase sensitive optical time domain reflectometer (φ-OTDR) sensing system is proposed and investigated. By utilizing simulated coherence between different back-scattering beat signals, digital phase demodulation for vibration detection can be achieved without employing hardware phase demodulation components. Experiments were conducted and the results demonstrated that the vibration induced phase change within different lengths of sensing optical fiber can be obtained sensitively by the proposed digital processing demodulation scheme that effectively avoid the noise caused by the hardware and reduce the complexity of the distributed optical fiber sensing system.

Investigation of Algorithms for Identification of Wave Parameters in Solid-State Wave Gyroscopes without Adjusting Calculations to the Frequency of Signals

To improve the efficiency of production operations of diagnostics, adjustment and control in the manufacture of integrating solid-state wave gyroscopes, algorithms for improving the accuracy of identification of wave parameters from measuring signals without their additional adjustment to the frequency of signals are considered. In the first algorithm for processing measurement results, a virtual transition to the moving axes of standing waves was introduced without taking into account the influence of a quadrature standing wave. It is characterized by the lowest potential accuracy, but it is convenient for the formation of initial approximations in the problems of clarifying optimization of identification functions in other algorithms. The second algorithm is based on direct five-parameter numerical minimization of the error feature by the conjugate gradient method. To avoid local extremes, it is recommended to use it as a clarifier. In this case, the initial search points are calculated by other algorithms and therefore selected near extremum. This algorithm allows identification at the shortest time intervals, which may be required when measuring high angular velocities. In the third algorithm, computational conditionality is improved at short identification intervals for increased level of measurement noise. In the fourth algorithm, the measurement results are processed using numerical procedures of digital demodulation under noise conditions. Comparison of the identification algorithms accuracy was carried out by methods of simulation modeling for theoretically set initial signals. This made possible direct comparison of initial and identified characteristics of wave processes: amplitudes of the main and quadrature standing waves, the angle of the main standing wave and its frequency. For the four algorithms considered, the results of simulation in the absence and presence of noise in the measuring signals are given. In the first case, diagrams of identification errors are analyzed depending on the length of the interval with a fixed and variable proportion of digital sampling frequencies and resonator oscillations. In the second case, there are standard identification errors depending on the noise level in the measuring signals (up to 20 percent of the basic amplitude of oscillations). Comparison of the results obtained showed the advantages and disadvantages of the corresponding algorithms, which is important for their practical adjustment when working with real samples of gyroscopes.

A 28 nm Bulk CMOS Fully Digital BPSK Demodulator for US-Powered IMDs Downlink Communications

Low-invasive and battery-less implantable medical devices (IMDs) have been increasingly emerging in recent years. The developed solutions in the literature often concentrate on the Bidirectional Data-Link for long-term monitoring devices. Indeed, their ability to collect data and communicate them to the external world, namely Data Up-Link, has revealed a promising solution for bioelectronic medicine. Furthermore, the capacity to control organs such as the brain, nerves, heart-beat and gastrointestinal activities, made up through the manipulation of electrical transducers, could optimise therapeutic protocols and help patients’ pain relief. These kinds of stimulations come from the modulation of a powering signal generated from an externally placed unit coupled to the implanted receivers for power/data exchanging. The established communication is also defined as a Data Down-Link. In this framework, a new solution of the Binary Phase-Shift Keying (BPSK) demodulator is presented in this paper in order to design a robust, low-area, and low-power Down-Link for ultrasound (US)-powered IMDs. The implemented system is fully digital and PLL-free, thus reducing area occupation and making it fully synthesizable. Post-layout simulation results are reported using a 28 nm Bulk CMOS technology provided by TSMC. Using a 2 MHz carrier input signal and an implant depth of 1 cm, the data rate is up to 1.33 Mbit/s with a 50% duty cycle, while the minimum average power consumption is cut-down to 3.3 μW in the typical corner.

Coherent demodulation of the two-level APSK signals with the symbol amplitude estimation

The study focuses on the algorithms for the coherent demodulation of the two-level amplitude phase-shift keyed signals with an estimate of the received symbol amplitude carried out by its relative comparison with the preceding symbol amplitude. Determining calibrated values of the symbol amplitudes in order to compare them with the preset threshold values is considered unnecessary in this case. Phase demodulation is implemented based on the phase detector of the multi-level phase-shift keyed signals. Symbol amplitudes are determined by the quadrature channels responses. Both analog and digital demodulation algorithms are considered. Simulation of the demodulation algorithm is carried out.

Digital demodulators for analog signals: comparative analysis and simulation

The paper examines digital demodulators for two commonly used techniques of modulating analog signals: amplitude modulation (AM) and frequency modulation (FM). The described demodulators can be used to perform the radio monitoring of narrowband signal ranges including FM broadcasting stations as well as license-free CB, LPD, PMR bands. The demodulators considered in this work are intended for programmable devices with limited memory and computing resources, for example, for STM32F407 microcontrollers and similar ones. The paper presents the analysis and simulation of demodulators for AM signals, FM signals with low modulation indices and for FM signals without restriction on the modulation indices. In addition, the authors demonstrate how to demodulate the phase-modulation signal using a quadrature demodulator. The number of operations that are available for demodulation is limited by IF multiplication and filtering. The simulation of the analyzed demodulation algorithms was carried out in the Scilab environment which is a free analogue of the Matlab environment. To explain the principle of operation of demodulators, block diagrams and graphs of signals in time and frequency domains are shown.

The Design Methodology of Fully Digital Pulse Width Modulation

This paper describes the design methodology and calibration technique for a low-power digital pulse width modulation demodulator to enhance its robustness against the process, voltage, and temperature variations in different process corners, in addition to intra-die variability, which makes it a very good choice for implantable monitoring sensors. Furthermore, the core of the proposed demodulator is fully digital. Thus, along with the proposed design methodology, the proposed demodulator can be simply redesigned in advanced subnanometer CMOS technologies without much difficulty as compared to analog demodulators. The proposed demodulator consists of an envelope detector, a digitizer, a ring oscillator, and a data detector with digital calibration. All the proposed circuits are designed and simulated in the standard 1P9M TSMC’s 40 nm CMOS technology. Simulation results have shown that the circuit is capable of demodulating and recovering data from an input signal with a carrier frequency of 13.56 MHz and a data rate of 143 kB/s with an average power consumption of 5.62 μW.

Full-field laser heterodyne imaging vibrometry using a CMOS-DVR system.

A laser heterodyne imaging vibrometry is proposed for full-field vibration measurement. The vibration responses are imaged and recorded using a CMOS camera and a digital video recorder. A digital demodulation method based on a cumulative distribution function and autocorrelation is designed to demodulate signals affected by speckle noise. The experimental investigations confirm the viability of the proposed method for vibration measurement. Meanwhile, a comparison with laser Doppler vibrometry is performed to further validate the method. The results prove the proposed vibrometry is an effective and precise option for full-field vibration measurement.

An End-to-End Demodulation System Based on Convolutional Neural Networks

The demodulation of digital signal plays a key role in the communication system. The traditional demodulator is usually realized by special hardware platform, which has the disadvantages of high cost and long development cycle. In this paper, we propose an end-to-end digital signal demodulator based on convolutional neural network (CNN). It consists of an encoder and a decoder, in which the encoder encodes the input symbol sequence and maps the signal features to the hidden layer space. Then, the decoder decodes the features of the hidden layer space to obtain the demodulation result of the input sequence. The proposed algorithm can automatically learn how to demodulate the received signal without manually extracting the features. Compared with the traditional demodulator, the proposed CNN demodulator has better bit error rate (BER) performance.

Resolution-Enhancing Structure for the Electric Field Microsensor Chip.

Electrostatic voltage is a vital parameter in industrial production lines, for reducing electrostatic discharge harms and improving yields. Due to such drawbacks as package shielding and low resolution, previously reported electric field microsensors are still not applicable for industrial static monitoring uses. In this paper, we introduce a newly designed microsensor package structure, which enhances the field strength inside the package cavity remarkably. This magnification effect was studied and optimized by both theoretical calculation and ANSYS simulation. By means of the digital synthesizer and digital coherent demodulation method, the compact signal processing circuit for the packaged microsensor was also developed. The meter prototype was calibrated above a charged metal plate, and the electric field resolution was 5 V/m, while the measuring error was less than 3 V, from −1 kV to 1 kV in a 2 cm distance. The meter was also installed into a production line and showed good consistency with, and better resolution than, a traditional vibratory capacitance sensor.

Non-destructive diagnosis of grounding grids based on the electromagnetic induction impedance method

When attempting to detect faults in grounding grids, the electromagnetic induction method is hampered by the failure of fault diagnosis based on magnetic flux density detection. An electromagnetic induction impedance method is proposed to diagnose corrosion faults by detecting the induced impedance. A non-destructive testing prototype was developed. The sensor of the prototype consists of biaxial sensing coils, a frequency selection module, and a dual-channel synchronous demodulator. The biaxial sensing coils are configured as four identical coils forming a cross. This symmetrical structure realizes the detection of unknown topological structures in grounding grids. The frequency selection module improves the signal-to-noise ratio of the system. The digital demodulator synchronously extracts the phase information in two orthogonal directions. The key technical indicators of the prototype, such as the frequency characteristics, the amplitude accuracy, the phase accuracy, the interference resistance, and the amplitude consistency between channels are tested. Experiments were carried out on a real-size physical model, corroded samples, and an actual operating substation. The results confirm the feasibility of the method and the prototype for the detection of topological structures, disconnections, and faults in grounding grids.

High-SFDR 100.8km ROF link with optical homodyne detection and genetic-algorithm-assisted digital demodulation.

Radio-over-fiber (ROF) link based on phase modulation and coherent detection has been widely proposed for linear transmission. Nowadays, there are increasing demands for long-distance analog radio-frequency (RF) signal transmission, as radars and broadcast systems. In this paper, a high spurious-free-dynamic-range (SFDR) analog coherent ROF link based on optical homodyne detection and genetic-algorithm-assisted digital demodulation is proposed and experimentally investigated. The ROF link is designed for transmitting RF signals ranging from 500 kHz to 100 MHz over a long-distance fiber under the environment of wide temperature. We test the link performance by transmitting different groups of two-tone signals (580 kHz and 600 kHz, 9 MHz and 10 MHz, 49 MHz and 50 MHz, 99 MHz and 100 MHz) over a 100.8-km single-mode fiber (SMF) under the temperature varying from -40°C to 70°C, the shot-noise-limited SFDR of the link are measured to be greater than 122 dB·Hz2/3.

Frequency-Division Multiplexing with Graphene Active Electrodes for Neurosensor Applications.

Multielectrode arrays are used broadly for neural recording, both in vivo and for ex vivo cultured neurons. In most cases, recording sites are passive electrodes wired to external read-out circuitry, and the number of wires is at least equal to the number of recording sites. We present an approach to break the conventional N-wire, N-electrode array architecture using graphene active electrodes, which allow signal upconversion at the recording site and sharing of each interface wire among multiple active electrodes using frequency-division multiplexing (FDM). The presented work includes the design and implementation of a frequency modulation and readout architecture using graphene FET electrodes, a custom integrated circuit (IC) analog front-end (AFE), and digital demodulation. The AFE was fabricated in 0.18 μm CMOS; electrical characterization and multi-channel FDM results are provided, including GFET-based signal modulation and IC/DSP demodulation. Long-term, this approach can simultaneously enable high signal count, high spatial resolution, and high temporal precision to infer functional interactions between neurons while markedly decreasing access wires.

Low-Power Wireless Data Transfer System for Stimulation in an Intracortical Visual Prosthesis.

There is a growing interest to improve the quality of life of blind people. An implanted intracortical prosthesis could be the last resort in many cases of visual impairment. Technology at this moment is at a stage that implementation is at sight. Making the data communication to and from the implanted electrodes wireless is beneficial to avoid infection and to ease mobility. Here, we focus on the stimulation side, or downlink, for which we propose a low-power non-coherent digital demodulator on the implanted receiver. The experimentally demonstrated downlink is on a scaled-down version at a 1 MHz carrier frequency showing a data rate of 125 kbps. This provides proof of principle for the system with a 12 MHz carrier frequency and a data rate of 4 Mbps, which consumes under 1 mW at the receiver side in integrated circuit (IC) simulation. Due to its digital architecture, the system is easily adjustable to an ISM frequency band with its power consumption scaling linearly with the carrier frequency. The tested system uses off-the-shelf coils, which gave sufficient bandwidth, while staying within safe SAR limits. The digital receiver achieved a reduction in power consumption by skipping clock cycles of redundant bits. The system shows a promising pathway to a low-power wireless-enabled visual prosthesis.

BPSK Modulation‐Based Local Oscillator‐Free IQ Demodulation for Millimeter Wave Imaging

The precision of local oscillator (LO) signal in in‐phase and quadrature (IQ) demodulation strongly affects the imaging performance of millimeter wave (mmWave) radars. Therefore, to eliminate the requirement for high‐precision LO, a simple yet effective digital IQ demodulation method has been proposed with the aid of a specified sampling scheme in order to eliminate the demand for LO. Based on the bandpass sampling theorem, the characteristic of the intermediate frequency signal of mmWave imaging indicates that the LO is unrequired if the sampling rate is twice of the frequency of the carrier of the intermediate signal. In this way, the in‐phase signal would be directly and accurately obtained by performing the Binary‐Phase‐Shift‐Keying (BPSK) modulation on the samples, based on which the IQ demodulation would be completed by using the Hilbert transform. The proposed method does not employ LO and thus simplifies the demodulation process and is suitable for implementation in a Field‐Programmable Gate Array (FPGA) with fewer hardware resources. To verify the method, a three‐dimensional mmWave radar imaging is carried out at the 30‐34 GHz bandwidth, where the sampling and digital IQ demodulation are realized by an ADC (AD9250) and FPGA (XC7K325T), respectively. The results show a simplified transceiver with lower requirements and the prospect of the proposed method being applied in radar imaging and other related fields.

A Novel Ultrasonic Doppler Fetal Heart Rate Detection System Using Windowed Digital Demodulation

Fetal heart rate (FHR) is an essential indicator of fetal well-being. The ultrasonic Doppler FHR detector is widely used to monitor the fetus’s health due to its advantages of non-invasion, high sensitivity, and good directivity. However, the existing commercial Doppler FHR detector primarily uses an analog multiplier for demodulation, which has limited functions and insufficient sensitivity. The analog demodulation is performed only on a single-sideband signal(in-phase or quadrature) (IQ), which is impossible to derive the fetal heart movement’s vector velocity. Moreover, repetitive recognition of the mitral valve’s positive and negative motion easily causes the measured FHR twice the actual one (FHR doubling). Although the traditional digital demodulation FHR detector can obtain in-phase and quadrature demodulation signals, it needs a high-level field-programmable gate array chip and therefore cannot meet low-power consumption requirements in battery-powered situations. Herein we proposed a novel digital demodulation FHR algorithm using time-domain windowing. Then, we applied the algorithm into a low-power complex programmable logic device to achieve low-cost acquisition of vector velocity and suppress FHR doubling and finally designed a hand-held, noninvasive digital Doppler FHR detection system for continuous perinatal detection. In this work, the comparison curve between the TREND curve generated by the simulator and the measured curve of our FHR detector was obtained. The comparative experiment between the commercial FM-3A FHR detector and our proposed FHR detector was performed, and the relative error and standard error of the obtained FHR data were used to evaluate the two FHR detectors’ detection accuracy. The results showed that our FHR detector showed excellent detection accuracy at an accuracy rate of 98%, which was much higher than the average accuracy of the FM-3A FHR detector and indicated our proposed digital FHR detector showed excellent detection performance. It means that the proposed digital windowed FHR demodulation algorithm is practical, the multi-FHR monitoring system is feasible, and our proposed FHR detector has high detection accuracy, effectively suppresses FHR doubling, and meets the requirements of Chinese national standards. It provides an alternative scheme towards the low-cost hand-held digital demodulation FHR detection application.

Algorithms for Processing Measuring Signals in the Integrating Solid-State Wave Gyroscope

Different variants of algorithms for processing the internal signals of the measuring device of integrating solid-state wave gyroscopes are synthesized. The main attention is paid to the consideration of subtle factors affecting the accuracy of calculation of gyroscope output signals and measurement signals of internal circuits to ensure their effective operation. For this purpose, different models of capacitive sensor signals in the gyroscope measuring device and the measured structure of standing waves in its resonator are preliminarily considered. The traditional aggregation of sensor signals into measuring device signals is described. First, variants of algorithms for capacitive direct-current operating measuring devices are systematized and thoroughly analyzed. They are divided into algorithms with tuning for periodicity of resonant oscillations and without tuning for periodicity. Variants of calculations differing in accuracy are presented for: the angle of the operating standing wave, proportional to the measured rate of the gyroscope base rotation; the amplitude of the operating quadrature standing wave for the internal circuit of its assigned value maintenance; the amplitude of the quadrature standing wave for the internal circuit of its suppression; the frequency of the operating standing wave for tuning of the excitation system of resonator oscillations and for implementation of the digital quadrature coherent demodulator of the measuring device. It is shown that in the majority of practical applications algorithms with tuning to periodicity of resonant oscillations are more preferable from the point of view of the computational complexity. And computationally labor-intensive algorithms without periodicity tuning are intended for measuring increased angular velocities with the reduced time of "freezing" of measured parameters. Further the given algorithms for the direct-current measuring device are generalized on algorithms of processing of measuring signals when operating with the alternating current. The variants of computational algorithms reduction to the algorithms previously synthesized for the direct current are described. They mainly use demodulation of AC voltage signals, including digital processing of modulated signals using a high-speed analog-to-digital converter. In addition, algorithms for information extraction from AC measuring device signals with demodulation at the combined frequency of modulated signals are synthesized. The different variants of single-band demodulation of measurement signals and also algorithm of double-band demodulation of measuring device signals with the extended list of measured quantities are considered. The choice of the necessary algorithm depends on the requirements to the measured angular velocities, on the constructive implementation of the gyroscope measuring device and on the choice of technical characteristics of its components.

Simulation Modeling of the Accuracy of Solid-State Wave Gyroscope Characterization with Tuning of Computational Algorithms to Signal Periodicity

The setting of computational algorithms for four methods of identification of wave characteristics in the free run-out mode of standing waves in the resonator of the integrative solid wave gyroscope on observations of signals of its measuring device at time intervals that are multiples of resonator oscillation is described. In the first roughest method, measurement results are processed without taking into account the influence of the quadrature wave. It is convenient for forming initial approximations in the tasks of clarifying optimization of identification functionality in other methods. In the second method, the refined processing of measurement results is carried out taking into account the phase shift of the signals of the measuring device. In the third method, in order to provide better physical visibility and to process the results of measurements, a virtual transition to mobile axes of standing waves is introduced. In the fourth method, measurement results are processed using numerical digital demodulation procedures. Comparisons have been made for the accuracy of these identification techniques by simulation methods for theoretically set source signals. This made it possible to directly compare the original and identified characteristics of wave processes: the amplitude of the main and square standing waves, the angle of the main standing wave and its frequency. The results are presented in the absence and presence of noise in the measuring signals. The results show the specifics of the practical application of different techniques for real samples of gyroscopes. For short identification intervals, they require a special choice of interval lengths equal to the final number of resonator oscillations. With the lengthening of such intervals, this requirement for the length of the interval is weakened.

Метод демодуляции радиоимпульсов, основанный на применении принципа когерентных выборок

The paper proposes a radio pulse demodulation method which allows to extract the signal envelope by taking coherent samples with a frequency not exceeding the carri-er frequency of the received signal. The paper demonstrates the possibility of creation of inertia-free demodulators based on the proposed method, whose principle of op-eration is reduced to performing basic operations in the time domain and forming samples, whose position corresponds to the expected amplitude values of the carrier oscillation and depends on its frequency. Calculations of the errors in determining the amplitude of demodulated signal, the factors affecting the errors, and ways to reduce them are shown. The specific results of studies of the capabilities of the proposed method obtained on the model of a base-based digital demodulator are presented.