Lower Corner Frequency Research Articles

A High Gain and Low Flicker Noise CMOS Mixer with Low Flicker Noise Corner Frequency Using Tunable Differential Active Inductor

This paper presents the design of a high conversion gain and low flicker noise down conversion CMOS double balanced Gilbert cell mixer using $$0.18\,\upmu \hbox {m}$$ 0.18 μ m CMOS technology. The high conversion gain and low flicker noise mixer is implemented by using a differential active inductor (DAI) circuit and cross-coupled current injection technique within the conventional double-balanced Gilbert cell mixer. A cross-coupled current bleeding circuit is used to inject the current to the switching stage to decrease the flicker noise. Instead of spiral inductor, a DAI with high tunability of the inductor and quality factor is used to tune out the parasitic capacitance effect and decrease the leakage current that has a harmonic component and produce the flicker noise. By tuning the DAI, the flicker noise corner frequency is reduced to 150 Hz. The proposed circuit is simulated with Cadence Spectra and the simulation results shows the NF of 11.2 dB, conversion gain of 23.7 dB and IIP3 of $$-6$$ - 6 dB for an RF frequency of 2.4 GHz. The excellent LO-RF, LO-IF, RF-LO and RF-IF isolations of $$-60, -110, -52$$ - 60 , - 110 , - 52 and $$-64$$ - 64 dB are achieved respectively. The total power consumption is 10.5 mW from a 1.8 V DC power supply.

Passive mixer with OPA filter for DVB-H front-end in 65 nm digital CMOS technology

This paper presents a passive mixer combined with a 1st-order active low-pass filter implemented in a purely digital low-power 65nm CMOS technology. The filter consists of a four-stage operational amplifier with two feed-forward paths for a 3dB corner frequency of 4MHz. The mixer offers a very low flicker noise corner frequency of 80Hz for DVB-H application. A fabricated test chip with integrated clock regeneration circuit offers even for a very small clock input signal amplitude a maximum gain of 26dB. The combination offers an IIP3 of −5dBm while the mixer consumes 12.27mA and the filter 4.42mA from a 1.25V supply.

Effects of temporal fine structure stimulation on Mandarin speech recognition in cochlear implant users

Conclusion: The investigated experimental coding strategies significantly improved tone identification as compared with the participants’ everyday audio processor settings. However, this benefit could not be attributed entirely to temporal fine structure stimulation but seems to be caused by decreasing the lower corner frequency of the filter bank. The 6 week habituation period used in this study might have been too short to allow the listeners to derive additional lexical information from the unfamiliar stimulation patterns. Objectives: To evaluate a cochlear implant coding strategy that explicitly conveys temporal fine structure information in the context of the tonal language Mandarin. Methods: The study was designed as a longitudinal, monocentric, prospective, controlled, and randomized cross-over study and included 12 postlingually deafened adults, who were experienced cochlear implant users. Two experimental coding strategies, one of which explicitly presents temporal fine structure information, were compared to the participants’ personal TEMPO+ speech processors, which do not convey fine structure information. Results: Both experimental coding strategies improved tone identification by approximately 11 percentage points. This improvement was significant in the female speaker test. Sentence perception, as assessed with the M-HINT test, and quality of life scores were identical with all three coding strategies.

Low Group Delay 3.1–10.6 GHz CMOS Power Amplifier for UWB Applications

This letter proposes the design of a low group delay ultra-wideband (UWB) power amplifier (PA) in CMOS technology. The PA design employs a three-stage cascade common source topology that has a different design concept from other multi-stage topology to provide a broad bandwidth characteristic, gain flatness of , and low group delay variation of . A resistive shunt feedback technique is adopted at the first stage of the amplifier to achieve good input matching, which controls the upper frequency of the UWB system. The third stage realizes the gain at the lower corner frequency and the second stage is used to smooth the flatness of the gain curve. By using this method, the proposed design has the lowest group delay variation among the recently reported CMOS PAs for 3.1 to 10.6 GHz applications.

Cascadia tremor spectra: Low corner frequencies and earthquake-like high-frequency falloff

The discovery of non-volcanic tremor (NVT) has opened a new window to observe major Earth plate boundaries. However, the spectral characteristics of NVT have not been well studied due to poor signal-to-noise ratio (SNR) on individual seismograms. We estimate the spectral content of Cascadia tremor between 2.5 and 20 Hz by suppressing noise using array analysis, and compute empirical path corrections using nearby small earthquakes. We demonstrate that the displacement spectra of the Cascadia tremor have corner frequencies around 3–8 Hz and fall off at f−2 to f−3 at higher frequencies. Our results have the following implications. (1) The high-frequency falloff of tremor agrees with the observations of regular earthquakes, suggesting that tremor can be analyzed using standard spectral models. Prior analyses that have shown a tremor spectral falloff proportional to f−1 may reflect only the spectral behavior over a limited frequency band. (2) Tremor may be no different from a swarm of microearthquakes with abnormally small stress drops on the order of kPa, likely due to the presence of fluids. Alternatively the low corner frequencies of tremor may reflect abnormally slow ruptures. (3) Fitting a standard Brune (1970) spectral model implies a moment release rate of Cascadia tremor of 3.8 × 1010 N·m/s assuming the tremor signals are P waves (or 1.4 × 1010 N·m/s assuming S-waves). This implies that a typical 20-day long tremor episode releases moment equivalent to Mw 5.1 (P-wave) or Mw 4.9 (S-wave), although these may be underestimates if the spectra deviate substantially from the Brune model at very low frequencies.

Large impacts detected by the Apollo seismometers: Impactor mass and source cutoff frequency estimations

Meteoroid impacts are important seismic sources on the Moon. As they continuously impact the Moon, they are a significant contribution to the lunar micro-seismic background noise. They also were associated with the most powerful seismic sources recorded by the Apollo seismic network. We study in this paper the largest impacts. We show that their masses can be estimated with a rather simple modeling technique and that high frequency seismic signals have reduced amplitudes due to a relatively low (about 1 s) corner frequency resulting from the duration of the impact process and the crater formation. If synthetic seismograms computed for a spherical model of the Moon are unable to match the waveforms of the observations, they nevertheless provide an approximate measure of the energy of seismic waves in the coda. The latter can then be used for an estimation of the mass of the impactors, when the velocity of the impactor is known. This method, for the artificial impacts of the LM and SIVB Apollo upper stages, allows us to retrieve the mass within 20% of relative error. The estimated mass of the largest impacts observed during the 7 years of activity of the Apollo seismic network provides an explanation for the non-detection of surface waves on the seismograms. The specifications of future Moon seismometers, in order to provide the detection of surface waves, are given in conclusion.

Dynamic corner frequency in source spectral model for stochastic synthesis of ground motion

The static corner frequency and dynamic corner frequency in stochastic synthesis of ground motion from finite-fault modeling are introduced, and conceptual disadvantages of the two are discussed in this paper. Furthermore, the non-uniform radiation of seismic wave on the fault plane, as well as the trend of the larger rupture area, the lower corner frequency, can be described by the source spectral model developed by the authors. A new dynamic corner frequency can be developed directly from the model. The dependence of ground motion on the size of subfault can be eliminated if this source spectral model is adopted in the synthesis. Finally, the approach presented is validated from the comparison between the synthesized and observed ground motions at six rock stations during the Northridge earthquake in 1994.

Low-noise differential transimpedance amplifier structure based on capacitor cross-coupled gm-boosting scheme

This paper presents a capacitor cross-coupled gm-boosting scheme for differential implementation of common-gate transimpedance amplifier (CG-TIA). A differential transimpedance amplifiers (DTIA) is designed by this scheme using two modified floating-biased CG stage with improved low corner frequency. Despite conventional methods for single-ended to differential conversion that increase the power and the noise for the same gain, the new DTIA gives a higher gain and hence reduces the input-referred noise power. Design of the DTIA circuit using 0.13μm CMOS technology illustrates near 1.7dB improvement in the circuit sensitivity and 5.2dB enhancement in transimpedance gain compared to its single-ended counterpart. Operation at very low frequencies and stable dc coupling to photodiode are other features of the proposed DTIA.

Impact of carbon concentration on 1∕f noise and random telegraph signal noise in SiGe:C heterojunction bipolar transistors

The influence of carbon concentration on the low-frequency noise (LF noise) of Si∕SiGe:C∕Si heterojunction bipolar transistors (HBTs) is investigated. When carbon is incorporated into these HBTs, representative noise spectra of the input current spectral density SIB show significant generation-recombination (GR) components. On the other hand, for transistors without carbon incorporation, no GR components were observed. When only 1∕f noise component is observed, the 1∕f noise level is found to be independent of the carbon concentration and the associated figure of merit of the normalized noise magnitude KB has a very good value of ∼4×10−10μm2. In order to relate the 1∕f noise and the high-frequency performance of the transistor, we studied and modeled the figure of merit defined as the ratio fc∕fT (fc is the low-frequency corner frequency and fT the unity current-gain frequency). Then we performed a detailed analysis of the GR components associated with the presence of the carbon. We found that the observed Lorentzian spectra are associated with random telegraph signal (RTS) noise. However, no RTS noise was measured in carbon-free devices. It is believed that the RTS noise is due to electrically active defects formed by the addition of carbon, typically observed for concentrations above the bulk solid solubility limit in silicon. The RTS amplitude (ΔIB) is found to scale with the base current, to decrease exponentially with temperature, and to be independent of the carbon concentration. The mean pulse widths (tH,tL) of the RTS are found to decrease rapidly with bias voltage, as 1∕exp(qVBE∕kT) or stronger. Our results confirm that electrically active C-related defects are located in the base-emitter junction, and the RTS amplitude is explained by a model based on voltage barrier height fluctuations across the base-emitter junction induced by trapped carriers in the space charge region. The observed bias dependence of mean pulse widths seems to indicate that two capture processes are involved, electron and hole capture. These C-related defects behave like recombination centers with deep energy levels rather than electron or hole traps involving trapping-detrapping processes.

Low 1∕f noise, full bridge, microcantilever with longitudinal and transverse piezoresistors

This paper reports on low 1∕f noise, low corner-frequency, piezoresistive microcantilevers suitable for static and slowly time varying, force and displacement sensing applications such as chemical and biosensing. We demonstrate a full bridge, piezoresistive cantilever with greater than 140dB dynamic range, a noise amplitude spectral density floor of 3.7nV∕V√Hz at 0.1Hz. At 1.0Hz, the noise spectral density is 1.2nV∕V√Hz equivalent to 10pN∕√Hz or 5pm∕√Hz. The force resolution over the frequency band of 0.1–100Hz is 100pN.

Gm-boosted differential transimpedance amplifier architecture

A modified floating biased common-gate transimpedance amplifier with improved low corner frequency is introduced. It is also shown that gm-boosting technique can be utilized for differential implementation of this transimpedance amplifier, without degrading the circuit sensitivity or using any off-chip components. HSPICE simulations for differential implementation illustrate more than two orders of magnitudes improvement of low corner frequency, about 80% increase in gain, and 20% reduction in input referred noise, compared to those of conventional single-ended floating biased common gate transimpedance amplifier.

Determinants of Spatial and Temporal Coding by Semicircular Canal Afferents

The vestibular semicircular canals are internal sensors that signal the magnitude, direction, and temporal properties of angular head motion. Fluid mechanics within the 3-canal labyrinth code the direction of movement and integrate angular acceleration stimuli over time. Directional coding is accomplished by decomposition of complex angular accelerations into 3 biomechanical components-one component exciting each of the 3 ampullary organs and associated afferent nerve bundles separately. For low-frequency angular motion stimuli, fluid displacement within each canal is proportional to angular acceleration. At higher frequencies, above the lower corner frequency, real-time integration is accomplished by viscous forces arising from the movement of fluid within the slender lumen of each canal. This results in angular velocity sensitive fluid displacements. Reflecting this, a subset of afferent fibers indeed report angular acceleration to the brain for low frequencies of head movement and report angular velocity for higher frequencies. However, a substantial number of afferent fibers also report angular acceleration, or a signal between acceleration and velocity, even at frequencies where the endolymph displacement is known to follow angular head velocity. These non-velocity-sensitive afferent signals cannot be attributed to canal biomechanics alone. The responses of non-velocity-sensitive cells include a mathematical differentiation (first-order or fractional) imparted by hair-cell and/or afferent complexes. This mathematical differentiation from velocity to acceleration cannot be attributed to hair cell ionic currents, but occurs as a result of the dynamics of synaptic transmission between hair cells and their primary afferent fibers. The evidence for this conclusion is reviewed below.

Cut-off frequency variation in optical waveguides due to photon tunnelling

We show that the cut-off frequency (low corner frequency) for an undersized waveguide can change due to the photon tunnelling phenomenon. The Helmholtz wave equation will be used to calculate the tunnelling time of a photon through a refraction index barrier. We report an analytical expression for the transit time of the photon in a refraction index barrier as well as the transmission coefficient. It is predicted that the tunnelling time depends on the refraction index, the thickness of the barrier and also on the incident wave frequency. We will exploit this idea to obtain light coupling to a classically forbidden region, hence describing the cut-off frequency variation. A comparison with the experimental data is also reported.

Seismic attenuation of the inner core: Viscoelastic or stratigraphic?

Broadband velocity waveforms of PKIKP in the distance range 150° to 180° are inverted for inner core attenuation. A mean Qα of 244 is determined at 1 Hz from 8 polar and 9 equatorial paths. The scatter in measured Q−1 exceeds individual error estimates, suggesting significant variation in attenuation with path. These results are interpreted by (1) viscoelasticity, in which the relaxation spectrum has a low‐frequency corner near or slightly above the frequency band of short‐period body waves, and by (2) stratigraphic (scattering) attenuation, in which attenuation and pulse broadening are caused by the interference of scattered multiples in a velocity structure having rapid fluctuations along a PKIKP path. In the scattering interpretation, PKIKP attenuation is only weakly affected by the intrinsic shear attenuation measured in the free‐oscillation band. Instead, its frequency dependence, path variations, and fluctuations are all explained by scattering attenuation in a heterogeneous fabric resulting from solidification texturing of intrinsically anisotropic iron. The requisite fabric may consist of either single or ordered groups of crystals with P velocity differences of at least 5% and as much as 12% between two crystallographic axes at scale lengths of 0.5 to 2 km in the direction parallel to the axis of rotation and longer in the cylindrically radial direction, perpendicular to the axis of rotation.

Description and demonstration of a CMOS amplifier-based-system with measurement and stimulation capability for bioelectrical signal transduction

An extracellular recording system incorporating an electrode array and an amplifier/stimulator CMOS chip is described and characterized. Important features of this custom VLSI chip include 16 instrumentation amplifiers with a gain of 50 and the incorporation of a cross-point array allowing designation of an extracellular microelectrode as either a stimulator or sensor. The planar array consisted of 32 microelectrodes, 14 μm in diameter, and four larger reference electrodes. Microelectrodes, interconnecting traces, and bond pads were patterned with a 500-nm layer of gold. The interconnecting traces were passivated with a 1-μm thick layer of silicon nitride to provide chemical and electrical insulation and microelectrode impedance was lowered utilizing electrode position of platinum black. The amplifier exhibited a nearly flat frequency response with high pass and low pass corner frequencies of 0.7 Hz and 50 kHz, respectively. The input referred noise over the 50 kHz bandwidth was 12–16 μV RMS, well below the magnitude of previously reported extracellular potentials. Crosstalk between neighboring channels resulted in an output signal below the amplifier noise level, even for relatively large extracellular potentials. Using this system, extracellular recordings were demonstrated yielding typical peak-to-peak biopotentials of magnitude 0.9–2.1 mV and 100–400 μV for chick cardiac myocytes and rat spinal cord neurons, respectively. The key components of this extracellular recording system can be manufactured using industry standard thin film photolithographic techniques.

Using a Large-Aperture Scintillometer to Measure Absorption and Refractive Index Fluctuations

The contributions of refraction and absorption fluctuations to the measured scintillations are observed for a near-infrared absorption region using a NOAA designed large-aperture scintillometer. The logarithmic amplitude spectra are shown to decay with frequency as f-8/3 for both the absorption and scattering mechanisms. For the absorption mechanism this is in line with similar observations made at microwave and infrared frequencies. However, for finite transmitting and receiving apertures, theory predicts a stronger decay of the scattering mechanism due to aperture averaging. The spectral shape is characterised by a region of low frequency absorption, higher frequency refraction and separated by a flattish transition zone. The upper observed corner frequency (fC2) compares well with values calculated using the measured transverse windspeed (v) for a known aperture radius. The lower corner frequency (fC1) position is shown to be sensitive to the ratio of the real and imaginary part of the refractive index structure parameter, (C nR 2 /C nI 2 )3/8, and v. The part of the spectrum associated with the absorption scintillations is observed to be much less than that due to refraction through the day until evening, when decreasing C nR 2 causes C nR 2 /C nI 2 to decrease and absorption to become significant. If absorption is ignored, this may have consequences for calculating nocturnal surface fluxes. During unstable, daytime conditions the large aperture scintillometer is most sensitive to refractive scintillations despite having an infrared source transmitting in a lossy atmosphere. But also under these conditions, the low frequency absorption part of the spectrum is observable.

Source scaling of microearthquakes at Mt. Etna Volcano and in the Calabrian Arc (southern Italy)

Microearthquake data recorded at Mt. Etna volcano and in the Calabrian Arc (Southern Italy) have been used to study the scaling of the main source parameters. After correction of the P‐wave displacement spectra for both path attenuation and the site amplification effects, an inverse method has been applied to compute spectral parameters (low frequency spectral level, corner frequency and high frequency roll‐off). Results show that seismic moments (M0) range from ca. 1016 to 1021 dyne‐cm at Mt. Etna and from ca 1017 to 1020 dyne‐cm in southern Calabria. Corner frequencies range from ca. 3 to 15 Hz. In both areas we found that the stress drop decreases (from ca. 100 to few bars) with decreasing seismic moment. A simple Brune source model is not able to explain the source scaling, because the typical fall‐off observed at higher frequencies (ω−3 as an average) is larger than that of Brune's theory. Furthermore, the relation between the seismic moment and the corner frequency points to a scaling law behaving as M0∝ωc−4.5 and M0∝ωc−3.6 on average, at Mt. Etna and in southern Calabria respectively, and higher for smaller events in both areas. Therefore, the cube law (M0 ∝ ω−3) generally accepted for large earthquakes does not hold true for the analysed microearthquakes, neither for those which occur along the tectonic structures of southern Calabria, or along those hosting the roots of the feeding system of the largest European volcano.

An integrable single-pole lowpass filter for low-frequency operation

A continuous-time lowpass filter circuit capable of achieving very low corner frequencies using integrated circuit components is reported. Corner frequencies as low as a few hertz can be economically achieved on an integrated circuit chip without using external components.

Calculation of PSDF of scintillation for 7 μm band TDL beam around water vapour line

We derive the temporal PSDFs theoretically by combining Filho's temporal PSDF and parameters of the absorption line stated in the optical line parameter compilation, and explain some interesting phenomena of the experimental temporal PSDFs by using the derived theoretical temporal PSDF, especially enhancement in the lower frequency region. The theoretical PSDFs tell us that the increasing of the absorption causes the lower corner frequency to shift to the higher frequency. Besides, the magnitude shifting of the lower corner frequency depends on the value of the absorption coefficient as well as the concentration of the absorbing medium. On the other hand, under the same atmospheric conditions, the profiles of the theoretical PSDFs for different wavelengths overlap each other in the higher frequency region, and the higher corner frequency has no relationship to the absorption. We show that the absorption affects the lower frequency region of the PSDFs of the infrared light, while the higher frequency regions of the PSDFs are affected by the refraction of the light like visible light waves.

Calibration of the STS-1 seismometer; preliminary results

Abstract The cross-spectrum method has been applied to the random binary calibration of the STS-1 seismometers (VBB option) installed at the Incorporated Research Institutions for Seismology/Internal Deployment of Accelerometers (IRIS/IDA) stations. It proves to be highly efficient at reducing the effect upon the derived response of the ground noise present in the output signal. The residual noise is smaller than 0.5% in amplitude and 0.5° in phase, for frequencies ranging from 0.5 to 100 mHz, provided that data series as long as 12 h are available. Except for a few cases, we observe that the actual transfer function remains within 2% in amplitude and 1.2° in phase relative to the generally accepted model, also referred to as the ‘nominal’ transfer function. The deviations are attributed essentially to inaccurate values of the low-frequency corner of the response. We also have evidence of other small deviations owing to the setting of the mechanical free period of the seismometer upon installation in the field, and to the approximations introduced in the nominal model. We propose a corrected model which better describes the behavior of the instrument in the low-frequency range. The results presented here involve a relative calibration of the sensors; the determination of the absolute value of the sensitivity factor must be obtained from a different procedure.