FM Modulation Research Articles

A Volterra Series Nonlinear Model of the Sampling Distortion in Flash ADCs Due to Substrate Noise Coupling

This brief presents a Volterra series model to evaluate the impact of substrate noise on Flash analog-to-digital converters. The proposed approach first relates substrate noise to the induced timing uncertainty of the comparator by means of an analytical linear model. The analysis then expresses the resulting sampling distortion power by also considering the comparator's nonlinearities and thus models the signal-to-noise-and-distortion ratio (SNDR) of the converter. In particular, it is shown that substrate noise causes an FM modulation of the clock, and the resulting timing error is a joint effect of AM-FM modulation of the input signal and the coupled noise. The derivation of the analytical expression is also valid for any multitone ground perturbation and is validated on a high-resolution Flash converter. The developed nonlinear model for the SNDR is found to almost double the noise amplitude range compared with the linear model, thus predicting the impact of realistically large noise signals.

Short‐comings in direct translations of names for hearing sensations: A case study regarding the roughness sensation.

Many psychoacoustic models, now widely used, were first developed in Germany, especially at Zwickers laboratory, and originally named with German terms that correspond to hearing sensations as named by German subjects. Often the terms were readily translated into other languages, especially English and French for publication and nowadays these translations are widely used and accepted. This also applies to the concept of psychoacoustic roughness, named “Rau(h)igkeit” in German. The Munich school developed the first models to describe the sensation of Rau(h)igkeit, found to be caused by fast AM or FM modulation, also present in the spoken German “R” which initiates the term Rau(h)igkeit. Even when the direct translation of the term Rau(h)igkeit and roughness to other languages seems to be quite adequate particularly for Brazilian Portuguese it has been found, by means of subjective evaluation of different signals and signal analysis that this translation is problematic as the corresponding term in Portuguese (“aspero”) is used by naive and non‐naive Brazilian subjects to name the auditory sensation due to stochastic signals, especially white noise which is unmodulated. So far the hearing sensation described as aspero does not correspond to the sensation of originally described as Rau(h)igkeit and roughness models will fail.

A New High-Performance Digital FM Modulator and Demodulator for Software-Defined Radio and Its FPGA Implementation

This paper deals with an FPGA implementation of a high performance FM modulator and demodulator for software defined radio (SDR) system. The individual component of proposed FM modulator and demodulator has been optimized in such a way that the overall design consists of a high-speed, area optimized and low-power features. The modulator and demodulator contain an optimized direct digital frequency synthesizer (DDFS) based on quarter-wave symmetry technique for generating the carrier frequency with spurious free dynamic range (SFDR) of more than 64 dB. The FM modulator uses pipelined version of the DDFS to support the up conversion in the digital domain. The proposed FM modulator and demodulator has been implemented and tested using XC2VP30-7ff896 FPGA as a target device and can operate at a maximum frequency of 334.5 MHz and 131 MHz involving around 1.93 K and 6.4 K equivalent gates for FM modulator and FM demodulator respectively. After applying a 10 KHz triangular wave input and by setting the system clock frequency to 100 MHz using Xpower the power has been calculated. The FM modulator consumes 107.67 mW power while FM demodulator consumes 108.67 mW power for the same input running at same data rate.

Performance Evaluation of FM-COOK Chaotic Communication System

In this paper, the performance evaluation of Frequency Modulated Chaotic On-Off Keying (FM-COOK) in AWGN, Rayleigh and Rician fading channels is given. The simulation results show that an improvement in BER can be gained by incorporating the FM modulation with COOK for SNR values less than 10dB in AWGN case and less than 6dB for Rayleigh and Rician fading channels.

Estimation of Respiratory Rate From ECG, Photoplethysmogram, and Piezoelectric Pulse Transducer Signals: A Comparative Study of Time–Frequency Methods

We compare the performance of two different time-frequency-based breathing rate (BR) detection algorithms when used on three different physiological signals: the ECG, the photoplethysmogram (PPG), and the piezoelectric pulse transducer (PZO) signal. Studies carried out over the past have shown the existence of amplitude and/or FMs due to respiration in physiological signals, such as those mentioned. In a recent study, we analyzed the PPG signal and detected the FM and amplitude modulation effect that controlled breathing had on it, and inferred the rate of respiration using the time-frequency spectrum (TFS) (via a wavelet (WT) or complex demodulation (CDM) approach). We showed that such TFS BR detection methods were very accurate and consistently outperformed the exclusively time-domain autoregressive modeling (AR) method, especially in the real-time (data length of 1 min) case. We now explore the possibility of using these methods on the ECG and the finger PZO signal, of which only the former has been previously used with some success to derive BR. Testing performed on 15 healthy human subjects for a range of BR and two body positions showed that though the PPG signal gave the most consistently high performance, the ECG and PZO also proved to be reasonably accurate over longer time segments. Furthermore, the CDM approach was on average either better than or comparable to the WT method in terms of both accuracy and repeatability of the detection.

A new method for blood velocity measurements using ultrasound FMCW signals

The low peak power of frequency-modulated continuous wave (FMCW) radar makes it attractive for various applications, including vehicle collision warning systems and airborne radio altimeters. This paper describes a new ultrasound Doppler measurement system that measures blood flow velocity based on principles similar to those of FMCW radar. We propose a sinusoidal wave for FM modulation and introduce a new demodulation technique for obtaining Doppler information with high SNR and range resolution. Doppler signals are demodulated with a reference FMCW signal to adjust delay times so that they are equal to propagation times between the transmitter and the receiver. Analytical results suggest that Doppler signals can be obtained from a selected position, as with a sample volume in pulse wave Doppler systems, and that the resulting SNR is nearly identical to that obtained with continuous wave (CW) Doppler systems. Additionally, clutter power is less than that of CW Doppler systems. The analytical results were verified by experiments involving electronic circuits and Doppler ultrasound phantoms.

Focus on test and measurement

Focus on test and measurement

A linear, low‐power, wideband CMOS VCO for FM‐UWB applications

AbstractA linear, low‐power, wideband 0.18‐μm CMOS VCO for UWB applications is presented, as part of a PLL‐based direct FM modulator for the 3.1–5‐GHz UWB band. It consists of a frequency control circuit and a differential ring core, coupled to the antenna output and the PLL prescaler by two single‐ended inverter buffers. The measured VCO exhibits a linear tuning range of 0.5–5.0 GHz, low power consumption of 2.5–10.5 mW, and an output power of −10 ± 1 dBm. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1955–1958, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23547

Reliability Analysis of the Circuit and FM Modulation Parameters for the First Harmonic Level Reduction of the Forward Switching Power Supplies

In this paper, the sensitivity of flrst harmonic of switching power supplies with the FM modulation of switching signal is investigated. Inspections are done with respect to the circuit and FM modulation parameters. In this regard, sets of orthogonal experiments are designed based on the Latin Cubes concept. Then the results of the experiments (i.e., the level of the 1st harmonic) are interpolated on a response surface. The response surface shows the self and the mutual efiects of the factors on the level of the 1st harmonic. It is seen that the minor changes of the circuit and modulation parameters has a major efiect in the level of the 1st harmonic. Consequently, after circuit design process, sensitivity analysis must be done with respect to the circuit parameters and the level of 1st harmonic can be reduced by small changes in the circuit parameters. It is seen that the response surface can be readily used for analysis of the efiects of parameters and with the small amounts of experiments, suitable results are achievable on the level of the 1st harmonic. The harmonic level is more sensitive to the reactive elements and the load than the parameters of modulation. Therefore in the design for low EMI, reactive elements must be selected with care. Dominant interference depends on the load. The efiect of load has positive sign in response surface. Therefore increasing the load intensifles the harmonic level.

Transcutaneous microvalve activation system using a coreless transformer

Conventional spinal implants show an invariable behavior that is not adapted to patients post-surgery evolution (e.g. scoliosis in children). They work as static and rigid structures that underpin the skeleton. A new visco-elastic spine implant is non-invasively controlled by means of a transcutaneous transformer, for progressive correction of spinal deformities. The bending moment and the torque applied to the spine with this new implant will be externally controlled by activating three intracorporeal microvalves. The power and control signal to activate the appropriated microvalve will be obtained by means of a parallel resonant converter (PRC) with a transcutaneous transformer. Adding a slight oscillation in the frequency control circuit of the power topology, a FM modulation is converted into an AM + FM output modulation on the transcutaneous dc–dc converter. A microcontroller analyses the output voltage envelope of a PRC and activates the corresponding intracorporeal microvalve in a non-intrusive way. Three valves are individually selectable to modify the prosthesis structure although the number of valves can be extended.

Range measurement in ultrasound FMCW system

AbstractThe low peak power of FMCW radar is attractive for application to various fields, such as vehicle collision warning systems and airborne radio altimeters. This paper describes a sonar system to provide ultrasound cross‐sectional images for diagnosis based on the same principle as the FMCW radar. Adoption of the sawtooth waveform is proposed for FM modulation to attain sufficient range resolution. The baseband received signal is analytically estimated to calculate the spectrum and range resolution. The calculation results suggest that the sonar system has similar range resolution to conventional pulse sonars, whose instantaneous power has a very high peak.The theoretically estimated spectrum also suggests that the FMCW sonar system operates well in the case of simultaneous acceptance of reflected signals from multiple points because its excellent range resolution enables distinguishing the contributions from different reflection points.The calculation results are verified by an experiment in which an electric delay line is used instead of human tissue to avoid ambiguity caused by unexpected reflection points in the measuring setup. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 90(1): 9–19, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.20244

A new paradigm for plasma transport and zonal flows

Most tokamak experimental results indicate dependence of the ion thermal conductivity on the isotopic mass close to χ⊥∼mi−0.5, i.e., inverse gyro-Bohm. This is in stark contradiction to most present theoretical models predicting Bohm (mi0) or gyro-Bohm (mi0.5) scaling. A basic physics isotopic scaling experiment [V. Sokolov and A. K. Sen, Phys. Rev. Lett. 89, 095001 (2002)] on the anomalous ion thermal conduction due to ion temperature gradient (ITG) instabilities in two different gases (hydrogen and deuterium) closely confirms the tokamak results. Another series of experiments designed to explore the physics basis of this scaling appears to lead to a new model for this scaling based on 3-wave coupling of two ITG radial harmonics and an IA wave. The resulting isotopic scaling of transport is ∼mi−0.5 dictated primarily by the IA damping. This basic physics may be extrapolated to tokamaks resolving the paradox [V. Sokolov and A. K. Sen, Phys. Rev. Lett. 92, 165002 (2004)]. Last, the much discussed theoretical role of zonal flows in transport regulation is critically examined by another set of experiments. A novel diagnostic has been developed on the basis of the observation that the effect of zonal flow can be seen in the FM modulation (at zonal flow frequency) of the carrier frequency of the large equilibrium Doppler shift frequency of ITG modes both in tokamaks and in the Columbia Linear Machine [V. Sokolov, X. Wei, and A. K.Sen, APS DPP meeting, Savannah (2004)]. The present results indicate zonal flow levels close to the theoretical prediction, but its shear is much lower than that predicted by theory for transport regulation.

Naturally sampled triangle carrier PWM bandwidth limit and output spectrum

This paper first presents a general theory predicting harmonic components in naturally sampled pulse-width modulation (PWM) output signals, so that any input signal with a Fourier series representation may be handled. This theory provides a basis for the mathematical analysis of PWM systems, such as converters transmitting a main signal and a broadband of feedback or feedforward signals, or Class D amplifiers. Ultimately, the results of this theory are applied to two concrete problems, and conditions similar to the Nyquist theorem or Carson's rule for FM modulation are derived for the cases of recovery of an input signal consisting of a main signal and a bandwidth of small feedback or feedforward signals and a bandlimited signal consisting of several harmonics of comparable magnitude. A rule of thumb, and conservative estimate of the bandwidth in both cases is one third of the carrier frequency (/spl omega//sub upper/<(1/3)/spl omega//sub c/). This research has been based on the premise that the results obtained will provide valuable insight into the general behavior of PWM systems, and provide a supporting theory for concrete systems utilizing signals of this kind, such as PWM converters whose purpose is to ensure a dominant sinusoidal waveform along with a broadband frequency channel for small feedback signals.

Perfect Recovery and Sensitivity Analysis of Time Encoded Bandlimited Signals

A time encoding machine is a real-time asynchronous mechanism for encoding amplitude information into a time sequence. We investigate the operating characteristics of a machine consisting of a feedback loop containing an adder, a linear filter, and a noninverting Schmitt trigger. We show that the amplitude information of a bandlimited signal can be perfectly recovered if the difference between any two consecutive values of the time sequence is bounded by the inverse of the Nyquist rate. We also show how to build a nonlinear inverse time decoding machine (TDM) that perfectly recovers the amplitude information from the time sequence. We demonstrate the close relationship between the recovery algorithms for time encoding and irregular sampling. We also show the close relationship between time encoding and a number of nonlinear modulation schemes including FM and asynchronous sigma-delta modulation. We analyze the sensitivity of the time encoding recovery algorithm and demonstrate how to construct a TDM that perfectly recovers the amplitude information from the time sequence and is trigger parameter insensitive. We derive bounds on the error in signal recovery introduced by the quantization of the time sequence. We compare these with the recovery error introduced by the quantization of the amplitude of the bandlimited signal when irregular sampling is employed. Under Nyquist-type rate conditions, quantization of a bandlimited signal in the time and amplitude domains are shown to be largely equivalent methods of information representation.

Chaos-based FM signals: application and implementation issues

Constant-envelope wideband signals are useful excitations in many engineering tasks. Here, we consider their hardware-based generation, reviewing recent results and adding new ones. We focus on a synthesis technique based on FM modulators and discrete-time chaotic sources. The degrees of freedom offered by this approach are discussed and managed to satisfy common requirements. We show that good rate-of-mixing chaotic sources are highly desirable; then, given that most current-generation chaotic sources do not provide adequate values, we illustrate how their designs can be improved. We conclude by suggesting possible developments regarding weakly mixing chaotic sources.

Spatial averaging of time-frequency distributions for signal recovery in uniform linear arrays

This paper presents a new approach based on spatial time-frequency averaging for separating signals received by a uniform linear antenna array. In this approach, spatial averaging of the time-frequency distributions (TFDs) of the sensor data is performed at multiple time-frequency points. This averaging restores the diagonal structure of the source TFD matrix necessary for source separation. With spatial averaging, cross-terms move from their off-diagonal positions in the source TFD matrix to become part of the matrix diagonal entries. It is shown that the proposed approach yields improved performance over the case when no spatial averaging is performed. Further, we demonstrate that in the context of source separation, the spatially averaged Wigner-Ville distribution outperforms the combined spatial-time-frequency averaged distributions, such as the one obtained by using the Choi-Williams (1989) distribution. Simulation examples involving the separation of two sources with close AM and FM modulations are presented.

Designs for an asymmetric gradient set and a compact superconducting magnet for neural magnetic resonance imaging

Imaging of the head and neck is the most commonly performed clinical magnetic resonance imaging (MRI) examination [R. G. Evans and J. R. G. Evans, AJR 157, 603 (1991)]. This is usually undertaken in a generalist MRI instrument containing superconducting magnet system capable of imaging all organs. These generalist instruments are large, typically having a bore of 0.9–1.0 m and a length of 1.7–2.5 m and therefore are expensive to site, somewhat claustrophobic to the patient, and offer little access by attending physicians. In this article, we present the design of a compact, superconducting MRI magnet for head and neck imaging that is less than 0.8 m in length and discuss in detail the design of an asymmetric gradient coil set, tailored to the magnet profile. In particular, the introduction of a radio-frequency FM modulation scheme in concert with a gradient sequence allows the epoch of the linear region of the gradient set to be much closer to the end of the gradient structure than was previously possible. Images from a prototype gradient set demonstrate the effectiveness of the designs.

Speech analysis and synthesis using an AM–FM modulation model

In this paper, the AM–FM modulation model is applied to speech analysis, synthesis and coding. The AM–FM model represents the speech signal as the sum of formant resonance signals each of which contains amplitude and frequency modulation. Multiband filtering and demodulation using the energy separation algorithm are the basic tools used for speech analysis. First, multiband demodulation analysis (MDA) is applied to the problem of fundamental frequency estimation using the average instantaneous frequency as estimates of pitch harmonics. The MDA pitch tracking algorithm is shown to produce smooth and accurate fundamental frequency contours. Next, the AM–FM modulation vocoder is introduced, which represents speech as the sum of resonance signals. A time-varying filterbank is used to extract the formant bands and then the energy separation algorithm is used to demodulate the resonance signals into the amplitude envelope and instantaneous frequency signals. Efficient modeling and coding (at 4.8–9.6 kbits/sec) algorithms are proposed for the amplitude envelope and instantaneous frequency of speech resonances. Finally, the perceptual importance of modulations in speech resonances is investigated and it is shown that amplitude modulation patterns are both speaker and phone dependent.

Theory of combined AM and high-harmonic FM mode locked laser

Closed form solutions for a simultaneously AM and high-harmonic FM mode locked laser system is presented. Analytical expressions for the pulsewidth and pulsewidth-bandwidth products are derived in terms of the system parameters. The analysis predicts production of 17 ps duration pulses in a Nd:YAG laser mode locked with AM and FM modulators driven at 80 MHz and 1.76 GHz for 1 W modulator input power. The predicted values of the pulsewidth-bandwidth product lie between the values corresponding to the pure AM and FM mode locking values.

SBS Suppression Using a Multichannel Tunable Laser with Data-Encoding Capability

We demonstrate stimulated Brillouin scattering (SBS) using a new laser transmitter. The device uses an integrated FM modulator for both SBS suppression and channel tuning, and an integrated AM modulator for data encoding. We measure thresholds of 25 dBm on four separate wavelength division multiplexing channels. The required modulation signal is very small, 95 mVpp, and the residual AM is only 1 %.