Minimum Modulation Depth Research Articles

An ASK Data Demodulator Circuit for Implantable Medical Devices Supporting a Minimum Modulation Depth of 0.034.

Amplitude shift keying (ASK) data demodulation method has been widely used for simultaneous wireless data and power transfer in implantable medical devices (IMDs). Small amplitude modulation depth (MD) is usually preferred as it helps promote energy harvesting efficiency. This paper presents an ASK data demodulator that has good immunity to disturbances and can demodulate ultra-low MD ASK signal. A three-stage amplifying structure (3SAS) is proposed, in which the common-mode level of each amplifier is set between the high and low levels of its input signal envelope to prevent amplifier gain saturation and maximize the amplification of the envelope difference. Two envelope detectors (EDs) are used before and after the 3SAS respectively. The first one is to obtain a coarse envelope for 3SAS input and the second one is to further suppress the residual carrier interference and get a fine envelope. The proposed demodulator is implemented in 0.18-μm high-voltage Bipolar-CMOS-DMOS (BCD) technology. The detectable MD is measured as low as 0.034%, showing that the proposed demodulator can work smoothly and robustly in some extreme cases of simultaneous data and power transferring.Clinical Relevance- The ASK data demodulator proposed in this paper supports ultra-low modulation depth. This reduces the bit error rate of the data link and keeps a highly power conversion efficiency for wireless power and data transfer in implantable medical devices.

Forward masking of amplitude modulation detection includes a large perceptual effect

Forward masking of amplitude modulation (AM) detection is tuned: target sinusoidal AM (SAM) is masked more easily by masker SAM with a similar, rather than dissimilar, rate. This finding has been interpreted either as a sensory effect related to adapting neural units tuned to the target’s AM rate, or as a perceptual effect related to the perceived similarity of the acoustically similar AM. This study investigated these two alternative possibilities. The minimum modulation depth required to detect 96-Hz target SAM was measured following exposure to suprathreshold masker AM applied to the same broadband-noise carrier. Three forward masker modulators were tested: (1) 32-Hz SAM; (2) a 32-Hz square wave; (3) and 96-Hz SAM with a modulation index equivalent to that of the third harmonic of the square wave. The 96-Hz masker SAM produced substantial amounts of forward masking; the 32-Hz sine- and square-waves, however, did not. These findings were inconsistent with the hypothesis that detection of the target SAM was mediated by adapting neural units tuned to the target’s AM rate, suggesting, instead, that forward masking of AM detection includes a large perceptual effect.

A Novel Envelope Detector Based on Unipolar Metal-Oxide TFTs

The lack of an envelope detector (ED) hinders the realization of bidirectional communication between radio frequency identification (RFID)/near field communication (NFC) tags and readers in metal-oxide thin film transistor (TFT) technology. To solve this, we present a novel ED implementation based on unipolar metal-oxide TFTs. The ED is fully integrated by n-type TFTs and has a novel topology. It can detect an amplitude shift keying (ASK) signal with a minimum modulation depth of 15% and a maximum envelope rate of 8kbit/s, and its minimum supply voltage reaches 2.5 V. These characteristics are greatly improved compared with those of previous works based on complementary organic or hybrid organic/metal-oxide TFTs.

High Resolution Microwave B-Field Imaging Using a Micrometer-Sized Diamond Sensor**Support by the Jiangsu Distinguished Professor Program under Grant No RK002STP15001, and the NJUPT Principal Distinguished Professor Program under Grant No NY214136.

We propose a diamond-based micron-scale sensor and perform high-resolution B-field imaging of the near-field distribution of coplanar waveguides. The sensor consists of diamond crystals attached to the tip of a tapered fiber with a physical size on the order of submicron. The amplitude of the B-field component B is obtained by measuring the Rabi oscillation frequency. The result of Rabi sequence is fitted with a decayed sinusoidal. We apply the modulation-locking technique that demonstrates the vector-resolved field mapping of the micromachine coplanar waveguide structure (CPW). B-field line scan was performed on the CPW with a scan step size of 1.25 μm. To demonstrate vector resolved rf field sensing, a full field line scan acts (was performed) along four NV axes at a height of 50 μm above the device surface. The simulations are compared with the experimental results by vector-resolved measurement. This technique allows the measurement of weak microwave signals with a minimum resolvable modulation depth of 20 ppm. The sensor will have great interest in micron-scale resolved microwave B-field measurements, such as electromagnetic compatibility testing of microwave integrated circuits and characterization of integrated microwave components.

Dynamically tunable broadband terahertz modulation based on monolayer graphene metamaterials

Dynamically tunable cut wire and split ring resonators (SRRs) based on monolayer graphene metamaterials are presented in terahertz regime. As the Fermi level of the graphene pattern increasing, the resonance frequency presents blue shift and higher intensity. Two resonant peaks that can be modulated dynamically in the range of 2.4-3.4THz and 4.1-5.8THz appear. The monolayer graphene metamaterials realize dynamically broadband terahertz modulation with a minimum modulation depth 63.9% at 2.74THz, and the highest modulation depth 93.3% at 3.4THz.

Broadband efficient modulation of light transmission with high contrast using reconfigurable VO2 diffraction grating.

Ultra-compact dynamically reconfigurable modulation of optical transmission has been widely studied by using subwavelength-spaced resonant metasurface structures containing reconfigurable optical materials. However, it has been difficult to achieve high transmissivity, large modulation depth, and broad bandwidth simultaneously with the conventional resonance-based metasurface schemes. Here, we propose a reconfigurable phase-transition diffractive grating, made of thick VO2 ridge waveguides, for achieving the above-mentioned three goals simultaneously in the near-infrared range. Based on the large dielectric-to-plasmonic transition characteristic of VO2 in the near-infrared range, diffraction directivity of dual-VO2 ridge waveguide is designed to be tuned by thermally driven phase transition of VO2 for transverse electrically polarized illumination. Then, the diffractive VO2 ridge waveguide grating composed of the periodically arranged dual VO2 ridge waveguides is designed with on-state efficiency around 0.3 and minimum modulation depth about 0.35 over a broad bandwidth of 550 nm (1100-1650 nm). The working principle and excellent modulation performance are thoroughly verified through numerical and experimental studies.

Ultra-compact electro-optical graphene-based plasmonic multi-logic gate with high extinction ratio

In this paper, we present a graphene-based plasmonic electro-optical multi-logic gate (MLG) operating at THz frequency. The designed MLG supports AND, XNOR, and NOR logic gates in a graphene-dielectric-metal structure, simultaneously. The propagation length of the surface plasmons (SPs), stimulated by a 27.35 THz incident TM wave, is about 62 times larger in ON state compared to OFF state. Simulation results by the finite difference time domain (FDTD) method show the minimum extinction ratio (ER) of 29.41, 97.38, and 29.40 dB for AND, XNOR, and NOR logic gates, respectively. Also, the minimum modulation depth (MD) is obtained 99.99% for XNOR and 99.88% for AND and NOR logic gates. The proposed MLG provides a high extinction ratio and ultra-compact logical block for using in digital processing circuits and THz applications.

Numerical study on the minimum modulation depth of a saturable absorber for stable fiber laser mode locking

We conducted a numerical study to investigate the minimum modulation depth of a saturable absorber that is essentially required for stable optical pulses to be generated from a passively mode-locked fiber laser cavity. More specifically, an extended nonlinear Schrodinger equation was numerically solved in order to analyze the impact of the cavity group velocity dispersion (GVD), cavity χ(3) nonlinearity, and saturation gain of an active fiber on the minimum modulation depth that is required. The net cavity GVD is shown to significantly influence the required minimum modulation depth level of a saturable absorber. A cavity with little net anomalous dispersion was found to be readily mode locked through the use of a saturable absorber with a very small amount of modulation depth. Furthermore, the reason that a fiber laser cavity with a zero cavity GVD becomes unstable and needs a much higher modulation depth was investigated, and such a condition was found to be associated with the fiber χ(3) nonlinearity. The minimum modulation depth was also shown to vary according to the saturation gain level of an active fiber.

Association of Auditory Steady State Responses with Perception of Temporal Modulations and Speech in Noise

Amplitude modulations in the speech convey important acoustic information for speech perception. Auditory steady state response (ASSR) is thought to be physiological correlate of amplitude modulation perception. Limited research is available exploring association between ASSR and modulation detection ability as well as speech perception. Correlation of modulation detection thresholds (MDT) and speech perception in noise with ASSR was investigated in twofold experiments. 30 normal hearing individuals and 11 normal hearing individuals within age range of 18–24 years participated in experiments 1 and 2, respectively. MDTs were measured using ASSR and behavioral method at 60 Hz, 80 Hz, and 120 Hz modulation frequencies in the first experiment. ASSR threshold was obtained by estimating the minimum modulation depth required to elicit ASSR (ASSR-MDT). There was a positive correlation between behavioral MDT and ASSR-MDT at all modulation frequencies. In the second experiment, ASSR for amplitude modulation (AM) sweeps at four different frequency ranges (30–40 Hz, 40–50 Hz, 50–60 Hz, and 60–70 Hz) was recorded. Speech recognition threshold in noise (SRTn) was estimated using staircase procedure. There was a positive correlation between amplitude of ASSR for AM sweep with frequency range of 30–40 Hz and SRTn. Results of the current study suggest that ASSR provides substantial information about temporal modulation and speech perception.

Spectrotemporal Modulation Sensitivity as a Predictor of Speech Intelligibility for Hearing-Impaired Listeners

A model that can accurately predict speech intelligibility for a given hearing-impaired (HI) listener would be an important tool for hearing-aid fitting or hearing-aid algorithm development. Existing speech-intelligibility models do not incorporate variability in suprathreshold deficits that are not well predicted by classical audiometric measures. One possible approach to the incorporation of such deficits is to base intelligibility predictions on sensitivity to simultaneously spectrally and temporally modulated signals. The likelihood of success of this approach was evaluated by comparing estimates of spectrotemporal modulation (STM) sensitivity to speech intelligibility and to psychoacoustic estimates of frequency selectivity and temporal fine-structure (TFS) sensitivity across a group of HI listeners. The minimum modulation depth required to detect STM applied to an 86 dB SPL four-octave noise carrier was measured for combinations of temporal modulation rate (4, 12, or 32 Hz) and spectral modulation density (0.5, 1, 2, or 4 cycles/octave). STM sensitivity estimates for individual HI listeners were compared to estimates of frequency selectivity (measured using the notched-noise method at 500, 1000, 2000, and 4000 Hz), TFS processing ability (2 Hz frequency-modulation detection thresholds for 500, 1000, 2000, and 4000 Hz carriers) and sentence intelligibility in noise (at a 0 dB signal-to-noise ratio) that were measured for the same listeners in a separate study. Eight normal-hearing (NH) listeners and 12 listeners with a diagnosis of bilateral sensorineural hearing loss participated. STM sensitivity was compared between NH and HI listener groups using a repeated-measures analysis of variance. A stepwise regression analysis compared STM sensitivity for individual HI listeners to audiometric thresholds, age, and measures of frequency selectivity and TFS processing ability. A second stepwise regression analysis compared speech intelligibility to STM sensitivity and the audiogram-based Speech Intelligibility Index. STM detection thresholds were elevated for the HI listeners, but only for low rates and high densities. STM sensitivity for individual HI listeners was well predicted by a combination of estimates of frequency selectivity at 4000 Hz and TFS sensitivity at 500 Hz but was unrelated to audiometric thresholds. STM sensitivity accounted for an additional 40% of the variance in speech intelligibility beyond the 40% accounted for by the audibility-based Speech Intelligibility Index. Impaired STM sensitivity likely results from a combination of a reduced ability to resolve spectral peaks and a reduced ability to use TFS information to follow spectral-peak movements. Combining STM sensitivity estimates with audiometric threshold measures for individual HI listeners provided a more accurate prediction of speech intelligibility than audiometric measures alone. These results suggest a significant likelihood of success for an STM-based model of speech intelligibility for HI listeners.

Temporal codes for amplitude contrast in auditory cortex.

The encoding of sound level is fundamental to auditory signal processing, and the temporal information present in amplitude modulation is crucial to the complex signals used for communication sounds, including human speech. The modulation transfer function, which measures the minimum detectable modulation depth across modulation frequency, has been shown to predict speech intelligibility performance in a range of adverse listening conditions and hearing impairments, and even for users of cochlear implants. We presented sinusoidal amplitude modulation (SAM) tones of varying modulation depths to awake macaque monkeys while measuring the responses of neurons in the auditory core. Using spike train classification methods, we found that thresholds for modulation depth detection and discrimination in the most sensitive units are comparable to psychophysical thresholds when precise temporal discharge patterns rather than average firing rates are considered. Moreover, spike timing information was also superior to average rate information when discriminating static pure tones varying in level but with similar envelopes. The limited utility of average firing rate information in many units also limited the utility of standard measures of sound level tuning, such as the rate level function (RLF), in predicting cortical responses to dynamic signals like SAM. Response modulation typically exceeded that predicted by the slope of the RLF by large factors. The decoupling of the cortical encoding of SAM and static tones indicates that enhancing the representation of acoustic contrast is a cardinal feature of the ascending auditory pathway.

Discrimination of auditory gratings in birds

Auditory gratings (also called auditory ripples) are a family of complex, broadband sounds with sinusoidally modulated logarithmic amplitudes and a drifting spectral envelope. These stimuli have been studied both physiologically in mammals and psychophysically in humans. Auditory gratings share spectro-temporal properties with many natural sounds, including species-specific vocalizations and the formant transitions of human speech. We successfully trained zebra finches and budgerigars, using operant conditioning methods, to discriminate between flat-spectrum broadband noise and noises with ripple spectra of different densities that moved up or down in frequency at various rates. Results show that discrimination thresholds (minimum modulation depth) increased as a function of increasing grating periodicity and density across all species. Results also show that discrimination in the two species of birds was better at those grating periodicities and densities that are prominent in their species-specific vocalizations. Budgerigars were generally more sensitive than both zebra finches and humans. Both bird species showed greater sensitivity to descending auditory gratings, which mirrors the main direction in their vocalizations. Humans, on the other hand, showed no directional preference even though speech is somewhat downward directional. Overall, our results are suggestive of both common strategies in the processing of complex sounds between birds and mammals and specialized, species-specific variations on that processing in birds.

Controlled destruction of chaos in the multistable regime

Autonomous nonlinear systems commonly exhibit simultaneous coexistence, in the phase space, of chaos and stable steady states, created by subcritical Hopf bifurcation. We show that such chaotic instability can be destroyed by small-amplitude modulation of any system parameters. The chaotic attractor undergoes boundary crisis due to a modulation-induced collision with an unstable periodic orbit (UPO). Such a boundary crisis exhibits a new resonance that we refer to as "crisis resonance" in the control parameter space. Crisis resonance implies that crisis occurs at minimum modulation depth due to resonant evolutions of the UPOs and the chaotic attractor. Crisis resonance occurs close to some critical frequency (we refer to it as "crisis resonance frequency") or its multiples. The UPO frequency is a good estimate of the crisis resonance frequency. The small-amplitude parameter modulation destroys chaos in the presence of noise as well. These features are observed theoretically with the paradigm of autonomous systems, namely, Lorenz equations of thermal hydraulics and are in excellent agreement with the experimental results, obtained with an analog circuit of Lorenz equations.

Temporal characteristics of extraction of size information in speech sounds

We can identify vowels pronounced by speakers with any size vocal tract. Together, we can discriminate the different sizes of vocal tracts. To simulate these abilities, a computational model has been proposed in which size information is extracted and separated from the shape information. It is important to investigate temporal characteristics of the size extraction process. Experiments were performed for listeners to detect the size modulation in vowel sequences. All the sequences had six segments. Each segment contained one of three Japanese vowels: ‘‘a,’’ ‘‘i,’’ and ‘‘u.’’ Size modulation was applied by dilating or compressing the frequency axis of continuous, STRAIGHT spectra. Modulation was achieved by changing the dilation/compression factor in sinusoidal functions. The original F0 pattern of the base sequence, except for warping of the time axis, was used for all stimuli. The minimum modulation depth at which listeners were able to detect the existence of modulation was measured as a function of th...

Sensitivity to spatial and temporal modulations of first-order and second-order motion

This study characterises the spatiotemporal “window of visibility” for first-order motion (luminance-modulated noise) and three varieties of second-order motion (contrast-modulated, polarity-modulated and spatial length-modulated noise). Direction-identification thresholds (minimum modulation depth producing 79.4% correct) were measured for each motion pattern (acuity permitting) over a five octave range of spatial and temporal frequencies (0.5–16 c/deg and 0.5–16 Hz respectively). Thresholds were converted into modulation sensitivity (1/threshold). For first-order motion patterns, sensitivity functions were generally bandpass. However, for second-order motion patterns, functions were predominantly lowpass in nature. In particular, the functions corresponding to contrast-modulated and polarity-modulated noise were virtually identical in terms of shape and sensitivity. However, sensitivity to modulations of spatial length was extremely poor and more lowpass, suggesting that additional strategies, perhaps a feature-based system, may be required for encoding motion of images of this type.

Analysis of the modulation depth affected by the polarization orientation in polarization interference imaging spectrometers

The influence of the orientations of both polarizer and analyzer on modulation depth of spatially distributed interferograms for static polarization interference imaging spectrometer (SPIIS) is analyzed. A generally, theoretical relationship to determine the modulation depth of a SPIIS is derived. The special cases of maximum modulation depth ( V=1) and the minimum modulation depth ( V=0) are examined. Our results will provide a theoretical and practical guide for studying, developing and engineering polarization interference imaging spectrometers.

Scattering due to randomly distributed charge particles in photorefractive crystals

Scattering due to noisy gratings produced by randomly distributed charge particles in photorefractive crystals is considered. The scattering cross section is analyzed in terms of the fluctuation of the refractive index introduced by the random space-charge field through the Pockels effect. We also consider the noise in photorefractive gratings due to such scattering. A signal-to-noise ratio of 1 leads to a minimum modulation depth for an index grating.

Single unit responses in cochlear nucleus of horseshoe bats to sinusoidal frequency and amplitude modulated signals

1. In the cochlear nucleus (CN) of Horseshoe bats, recordings were made from 148 single neurons to constant frequency (CF) signals and to sinusoidally frequency modulated (SFM) and sinusoidally amplitude modulated (SAM) signals, which in a first approximation simulate the periodic modulations of echoes returning from wing beating insects. 2. The probability of obtaining synchronized discharge activity to modulations was independent of the neurons' best frequencies (BFs). Neurons belonging to separate response pattern categories to CF-signals differed in the synchronization pattern to periodic modulations. While the response patterns of tonic neurons were characterized by an image-like reproduction of the time course of frequency or amplitude changes, phasic neurons respond with an activity peak to distinct portions of the modulation cycles. Neurons with build up patterns to CF-signals (n= 8) and three phasic neurons did not lock their discharges to SFM- or SAM-signals. Response patterns were essentially similar for SFM- and SAM-signals and systematically depended on modulation magnitude, carrier frequency and intensity parameters of the signals. 3. The effects of decreasing modulation magnitude were tested for 45 neurons with SFM- and for 46 neurons with SAM-signals. Asymmetries in the response patterns present at high modulation magnitudes disappeared with smaller modulation magnitudes and histogram envelopes approach sinusoidal form. Synchronized responses to SFM-signals were present down to modulation heights of ±20 Hz and to SAM-signals of 6%. Sensitivity for small modulation heights of the SFM-signal was highest in sharply tuned neurons in the frequency range of 81–88 kHz (‘filter neurons’). No correlations between minimum modulation depth of the SAM-signal and the neurons' BFs were found. 4. The carrier frequency of the SFM-signal was systematically varied in 19 neurons. Sensitivity for small modulation heights could be improved by positioning the carrier frequency near the flanks of the excitatory response area. The response to SAM-signals was less influenced by the carrier frequency. 5. The intensity parameter was studied in 18 neurons with SFM- and 25 neurons with SAM-signals. While synchronization was clearly present in the range of 10 to 30 dB SPL above minimum threshold, the response peaks to individual modulation cycles of tonic neurons tended to fuse at higher intensities. In sharply tuned neurons, individual response peaks to SFM-signals could be distinguished over wider intensity ranges than with SAM-signals. 6. Periodically amplitude modulated SFM-signals with different phase relations between amplitude maximum and particular frequency components were used for stimulation of 22 neurons. Due to their sharp tuning properties, the response pattern of filter neurons systematically changed depending on the phase relations of AM and FM, whereas the response pattern of neurons in other frequency ranges resembled the pattern to SAM-stimuli. 7. In order to determine the limiting rate of frequency and amplitude change for synchronization of response activity, the modulation frequency was varied between 50 Hz and 2,000 Hz in 59 neurons with SFM- and 46 neurons with SAM-stimuli. The range of modulation frequencies covered by synchronized activity was broad, with most neurons (n=41 SFM,n=28 SAM) reaching upper rates between 400 and 800 Hz, or even higher (n=6 SFM,n=14 SAM). Neurons with limiting rates below 400 Hz were rare (n=12 SFM,n=4 SAM). Low, medium and high limiting rates were found in tonic as well as phasic neurons. Some phasic neurons (n=3), required minimum modulation frequencies of 200 Hz to start synchronization. Synchronization behavior depended on intensity, center frequency, modulation magnitude and could be different for SFM- and SAM-signals in the same unit. 8. Data are discussed in relation to single unit recordings to periodically modulated signals in CN of other mammals and to results obtained from higher order auditory nuclei of Horseshoe bats.