Low-pass Response Research Articles

Reconfigurable microwave photonic filter based on polarization modulation and an optical filter

We present a reconfigurable microwave photonic filter (MPF) based on polarization modulation and a tunable optical bandpass filter (TOBPF). The MPF is possible to switch between a low-pass and bandpass responses by simply setting a polarizer. Furthermore, the cutoff frequency of the low-pass MPF, the central frequency, and the bandwidth of the bandpass MPF are widely tunable by adjusting the TOBPF. The proposed MPF is theoretically analyzed and experimentally verified.

A Power-Efficient Reconfigurable OTA-C Filter for Low-Frequency Biomedical Applications

A power-efficient operational-transconductance-amplifier-capacitor (OTA-C) filter for biomedical applications is presented with detailed noise analysis. This filter consists of a cascade of biquadratic sections, each of which is configured via a serial-peripheral-interface circuit embedded with non-volatile memories to provide low pass or bandpass response. All filter parameters, including the gains, natural frequency, and quality factor, are orthogonally adjustable by programming charges on floating-gate bias transistors. The reconfigurable biquadratic section is composed of four power-efficient linearized OTAs. Each OTA consists of complementary hextuple-diffusor-quadruple-differential-pairs (HDQDPs) and a floating-gate common-mode feedback scheme. A developed computer algorithm for transistor dimension optimization is adopted to extend the input linear range of the HDQDP based on nonlinearity cancellation. A prototype chip is designed and fabricated in a $0.35~ \mu {\mathrm{ m}}$ CMOS process to demonstrate reconfigurability and performance of the proposed filter. Each biquadratic section occupies $0.12{\mathrm{ mm}}^{2}$ with a frequency tuning range more than five decades. Measured spurious-free dynamic ranges (SFDR) at the low pass and bandpass outputs from one of the biquadratic sections are 52.6 and 54.55 dB, respectively, when the natural frequency is programmed at 2 kHz with power consumption of 107.2 nW. A fourth-order Chebyshev low pass and an eighth-order Butterworth bandpass responses are implemented with characterized SFDRs of 50.43 and 48.3 dB, respectively.

New Configuration for OFCC-Based CM SIMO Filter and its Application as Shadow Filter

This paper puts forward a new operational floating current conveyor (OFCC)-based current mode (CM) single input multiple output (SIMO) filter configuration which uses two grounded capacitors, three grounded resistors and three OFCCs. The attractive features of the proposed filter are—use of grounded passive elements; availability of low pass, band pass, high pass and notch filter responses simultaneously at high output impedance; and independent adjustment of filter parameters. These features make the proposed filter suitable from fabrication viewpoint and allow easy cascading. Effect of nonidealities on proposed filter response is also examined. A CM shadow filter is also built by introducing an OFCC-based amplifier and connecting it in a feedback loop of the proposed SIMO filter. This configuration allows adjustment of filter parameters through gain of amplifier. MOS-based implementation of grounded resistors is incorporated to facilitate electronic tuning of filter parameters. The operation of the proposed filters is verified through SPICE simulations using $$0.5\,\upmu \hbox {m}$$ technology model parameters from MOSIS (AGILENT). Proposed CM SIMO filter is prototyped using commercially available IC AD844, and experimental response is found to be in close agreement with theoretical ones.

A Compact Microstrip T-Type Switch for Narrowband Applications

This paper presents a compact T-type switch that involves three different operational states providing high flexibility in signal routing. Two of the states are between adjacent ports, while the other is a crossover state. T-type switches are mainly used as building blocks of redundancy matrices for satellite communications systems, although mobile applications also take advantage of switching devices. The proposed structure uses p-i-n diodes located in specific points to control each state with a specific bias dc voltage, creating open and short circuits. The symmetry of the structure allows even–odd mode analysis in order to obtain the design equations. To validate the concept, a compact microstrip T-type switch is fabricated and measured. The resulting device shows a good performance in terms of transmission and isolation for each state, in agreement with the simulations. The switch exhibits a band-pass response for the crossover state, while low-pass and high-pass responses result for the other two states.

Impact of light-adaptive mechanisms on mammalian retinal visual encoding at high light levels.

A persistent change in illumination causes light-adaptive changes in retinal neurons. Light adaptation improves visual encoding by preventing saturation and by adjusting spatiotemporal integration to increase the signal-to-noise ratio (SNR) and utilize signaling bandwidth efficiently. In dim light, the visual input contains a greater relative amount of quantal noise, and vertebrate receptive fields are extended in space and time to increase SNR. Whereas in bright light, SNR of the visual input is high, the rate of synaptic vesicle release from the photoreceptors is low so that quantal noise in synaptic output may limit SNR postsynaptically. Whether and how reduced synaptic SNR impacts spatiotemporal integration in postsynaptic neurons remains unclear. To address this, we measured spatiotemporal integration in retinal horizontal cells and ganglion cells in the guinea pig retina across a broad illumination range, from low to high photopic levels. In both cell types, the extent of spatial and temporal integration changed according to an inverted U-shaped function consistent with adaptation to low SNR at both low and high light levels. We show how a simple mechanistic model with interacting, opponent filters can generate the observed changes in ganglion cell spatiotemporal receptive fields across light-adaptive states and postulate that retinal neurons postsynaptic to the cones in bright light adopt low-pass spatiotemporal response characteristics to improve visual encoding under conditions of low synaptic SNR.

A Digital Frequency Adaptive Synchronization Unit for On- and Off-Grid Systems

This paper presents the analysis and implementation details of a frequency adaptive synchronization unit (FASU) capable of extracting the positive, negative, and zero sequence components of a three-phase signal as well as real-time tracking of the amplitude, phase, and frequency of the positive sequence component. The FASU consists of three subsystems: First, a sequence component extractor block based on a fast retrieval technique, second, a zero-crossing peak detection system with dynamic dc compensation and, third, a frequency adaptive multi-input multioutput low-pass finite-impulse response filter. The frequency adaptive filter is able to provide filtering of the positive sequence component over a wide frequency range (40–2000 Hz), in the presence of significant input signal distortion (total harmonic distortion as high as 100%). The system achieves a worst case transient response time of one and a half-cycle of the input period, in the event of input transients such as balanced/unbalanced amplitude sags and swells, balanced/unbalanced phase steps, and positive/negative frequency ramps (up to 700 Hz/s). The proposed system is suitable for use in islanded microgrids, in the aerospace industry, and as a phasor measurement unit. The system is implemented as a proof of concept on a field programmable gate array hardware platform.

Grounded capacitor based fully cascadable electronically tunable current-mode universal filter

A novel current-mode (CM) universal filter configuration composed of five plus-type second-generation current conveyors (CCII+s) as active components besides three resistors and three grounded capacitors as passive elements is proposed in this paper. The proposed filter can simultaneously provide high-pass, band-pass and low-pass responses. Also, it can realize all-pass and notch responses with interconnection of convenient output currents. It can be cascaded with other CM ones easily because it has low input and high output impedances. It offers orthogonal control of angular resonance frequency and quality factor. An electronically tunable universal filter can be easily obtained if plus-type current controlled current conveyors are replaced instead of each of the five CCII+s and all the three resistors are removed. Nevertheless, it needs a single passive element matching constraint for notch and all-pass filter responses. Some simulation and experimental test results are included to confirm the theory.

(1+α) Fractional-order transfer functions to approximate low-pass magnitude responses with arbitrary quality factor

The coefficients of three fractional-order low-pass transfer functions are presented to aid in the design of these filters based on their arbitrary quality factors. These coefficients are found by minimizing the error between these fractional-order transfer functions and the second-order transfer function using numerical least squares optimization. Coefficients and design equations are presented for fractional-orders between one and two. Stability of the transfer functions with the presented coefficients is examined and possibilities of characteristic frequency shifting are shown. The results are verified by PSpice simulation of a conveyor-based low-pass filter with fractional order of 1.5 and quality factor Q=5.

Electronically Tunable Current Controlled Current Conveyor Transconductance Amplifier-Based Mixed-Mode Biquadratic Filter with Resistorless and Grounded Capacitors

A new electronically tunable mixed-mode biquadratic filter with three current controlled current conveyor transconductance amplifiers (CCCCTAs) and two grounded capacitors is proposed. With current input, the filter can realise lowpass (LP), bandpass (BP), highpass (HP), bandstop (BS) and allpass (AP) responses in current mode and LP, BP and HP responses in transimpedance mode. With voltage input, the filter can realise LP, BP, HP, BS and AP responses in voltage and transadmittance modes. Other attractive features of the mixed-mode biquadratic filter are (1) the use of two grounded capacitors, which is ideal for integrated circuit implementation; (2) orthogonal control of the quality factor (Q) and resonance angular frequency (ωo) for easy electronic tenability; (3) low input impedance and high output impedance for current signals; (4) high input impedance for voltage signal; (5) avoidance of need for component-matching conditions; (6) resistorless and electronically tunable structure; (7) low active and passive sensitivities; and (8) independent control of the voltage transfer gains without affecting the parameters ωo and Q.

Experimental Evaluation of Low-Pass Shock Isolation Performance of Elastomers Using Frequency-Based Kolsky Bar Analyses

Elastomeric materials are used as shock isolation materials in a variety of environments to dampen vibrations and/or absorb energy from external impact for minimizing energy transfer between two objects or bodies. Some applications require the shock isolation materials to behave as a low-pass mechanical filter to mitigate the shock/impact at high frequencies but transmit the energy at low frequencies with minimal attenuation. In order to fulfill this requirement, a shock isolation material needs to be carefully evaluated and selected with proper experimental design, procedures, and analyses. In this study, a Kolsky bar was modified with pre-compression (up to 15.5 kN) and confinement capabilities to evaluate low-pass shock isolation performance in terms of acceleration attenuation through a variety of elastomers. The effects of preload and specimen geometry on the low-pass shock isolation response were also investigated.

A Comparative Analysis of CMUT Receiving Architectures for the Design Optimization of Integrated Transceiver Front Ends.

A formal comparison between fundamental RX amplifier configurations for capacitive micromachined ultrasonic transducers (CMUTs) is proposed in this paper. The impact on both RX and the pulse-echo frequency response and on the output SNR is thoroughly analyzed and discussed. It is shown that the resistive-feedback amplifier yields a bandpass RX frequency response, while both open-loop voltage and capacitive-feedback amplifiers exhibit a low-pass frequency response. For a given power dissipation, it is formally proved that a capacitive-feedback amplifier provides a remarkable SNR improvement against the commonly adopted resistive feedback stage, achieved at the expense of a reduced pulse-echo center frequency, making its use convenient in low-frequency and midfrequency ultrasound imaging applications. The advantage mostly comes from a much lower noise contributed by the active devices, especially with low- Q , broadband transducers. The results of the analysis are applied to the design of a CMUT front end in BIPOLAR-CMOS-DMOS Silicon-on-Insulator technology operating at 10-MHz center frequency. It comprises a low-power RX amplifier, a high-voltage Transmission/Reception switch, and a 100-V TX driver. Extensive electrical characterization, pulse-echo measurements, and imaging results are shown. Compared with previously reported CMUT front ends, this transceiver demonstrates the highest dynamic range and state-of-the-art noise performance with an RX amplifier power dissipation of 1 mW.

In-Motion Initial Alignment for Odometer-Aided Strapdown Inertial Navigation System Based on Attitude Estimation

This paper investigates the in-motion initial alignment for odometer-aided strapdown inertial navigation system with main focus on handling the severe disturbance inherent in the odometer. An attitude estimation-based alignment method is proposed through ingeniously attitude matrix decomposition and velocity rate equation reconstruction. The attitude estimation-based method can attenuate the disturbance in the odometer to a certain extent and can avoid some additional approximations. However, the severe disturbance in the odometer cannot be handled adequately by the attitude estimation structure. In this respect, a low-pass finite impulse response digital filter is used to attenuate the disturbance in the odometer preliminarily. Experimental results are reported to validate the effectiveness of the proposed alignment methods and the superiority of attitude estimation-based method over attitude determination-based method.

Compact semi‐lumped dual‐ and tri‐wideband bandpass filters

This study presents a novel design approach of semi-lumped dual-wideband bandpass filters (DWB-BPF) and tri-wideband-BPF (TWB-BPF). One or two pairs of λ/4 uniform-impedance open stubs first generate the desired transmission zeros (TZs) to divide the lowpass frequency response based on radial stub loaded high-impedance microstrip line (RSHIML) into a dual- or tri-band lowpass-bandpass frequency response. Then, a pair of lumped-element capacitors are series to the input and output ports to suppress the direct current signal, so as to transform the lowpass passband to the bandpass passband. Moreover, the other RSHIML is also introduced not only to produce a TZ located at the lower transition band of the first passband to improve its passband selectivity, but also to enhance the passband flatness. As examples, a semi-lumped DWB-BPF and a semi-lumped TWB-BPF are designed and fabricated, which exhibit the merits of wide passbands, low insertion loss and compact size.

Reconnection-less Electronically Reconfigurable Filter with Adjustable Gain Using Voltage Differencing Current Conveyor

This paper presents a novel reconnection-less and electronically reconfigurable analogue filter. It employs two active elements, Voltage-Differencing Current Conveyor (VDCC) and Dual-Output Current Amplifier (DO-CA) with two independently tunable gains. Filter has the single input and single output topology (SISO). The current-mode transfer function of the filter can be tuned electronically from the low-pass (LP) response to the high-pass (HP) response, via the band-stop (BS) response, without reconnection of the input or output terminal. It is designed in order to provide tuning of both the stop-band gain and also pass-band gain of all the transfer functions, because also transfer functions with additional and intended zero in transfer function are available. The theoretical presumptions are confirmed by both simulations and lab measurements with available devices. DOI: http://dx.doi.org/10.5755/j01.eie.22.6.17221

Intracerebral evidence of rhythm transform in the human auditory cortex.

Musical entrainment is shared by all human cultures and the perception of a periodic beat is a cornerstone of this entrainment behavior. Here, we investigated whether beat perception might have its roots in the earliest stages of auditory cortical processing. Local field potentials were recorded from 8 patients implanted with depth-electrodes in Heschl's gyrus and the planum temporale (55 recording sites in total), usually considered as human primary and secondary auditory cortices. Using a frequency-tagging approach, we show that both low-frequency (<30Hz) and high-frequency (>30Hz) neural activities in these structures faithfully track auditory rhythms through frequency-locking to the rhythm envelope. A selective gain in amplitude of the response frequency-locked to the beat frequency was observed for the low-frequency activities but not for the high-frequency activities, and was sharper in the planum temporale, especially for the more challenging syncopated rhythm. Hence, this gain process is not systematic in all activities produced in these areas and depends on the complexity of the rhythmic input. Moreover, this gain was disrupted when the rhythm was presented at fast speed, revealing low-pass response properties which could account for the propensity to perceive a beat only within the musical tempo range. Together, these observations show that, even though part of these neural transforms of rhythms could already take place in subcortical auditory processes, the earliest auditory cortical processes shape the neural representation of rhythmic inputs in favor of the emergence of a periodic beat.

Two lossy integrator loop based current-mode electronically tunable universal filter employing only grounded capacitors

In this paper, a novel single-input and multiple-output second-order current-mode universal filter is proposed where lossy integrator blocks, scaling blocks and summing blocks are employed. The proposed filter can simultaneously generate all the five universal filter responses namely; low-pass, high-pass, band-pass, notch and all-pass responses without requiring any critical passive component matching conditions. It uses only two grounded capacitors as passive components and BJTs as active elements; thus, it can be classified as an active-C filter. Both resonance frequency and quality factor of the proposed filter can be tuned electronically. Approximately 1.5 decades adjustable input frequency range for all the universal filter responses and high quality factor for band-pass response are obtained. Obtained PSpice simulation results confirm the theoretical design. Non-ideality and Monte Carlo analyses are also given. A practical realization of the single lossy integrator is accomplished. All the presented results are discussed.

Five-inputs single-output voltage mode universal filter with high input and low output impedance using VDDDAs

The design of analog filter using active building block has been gained significant attention and has become an interesting research topic. A five-inputs single −output voltage-mode universal biquadratic filter using active building block, namely voltage differencing differential difference amplifier (VDDDA) is presented in this paper. The proposed filter consists of two VDDDAs and two grounded capacitors. The presented circuit has high impedance for all input voltage nodes and low impedance for output voltage node which is ideal for cascade in voltage-mode circuit without the use of buffer circuits. It can provide five output voltage functions which are band-pass (BP), low-pass (LP), band-reject (BR), high-pass (HP) and all-pass (AP) responses. For high-pass and band-pass functions, the inverting and non-inverting response can be achieved. The matching condition, the inverting and double gain amplifier are not required which is easy to select the output response by digital method. The natural frequency and quality factor can be electronically tuned that is attractive for microcomputer or microcontroller controllability. To verify the validity of proposed filter, the PSPICE simulation and experimental results using VDDDA constructed from commercially available IC are included. The measured results agree well with theoretical expect.

Switchable Microwave Photonic Filter Between Low-Pass and High-Pass Responses

A novel and simple microwave photonic filter (MPF) is proposed and experimentally demonstrated. The MPF can be switched between low-pass and high-pass frequency responses. The MPF is realized by using an electro-optic phase modulator (EOPM) and two cascaded tunable optical bandpass filters (TOBFs). One TOBF (TOBF1) is used to change the modulation format of the phase modulated signal and, consequently, switch the MPF between low-pass and high-pass frequency responses. The other TOBF (TOBF2) is used to adjust the cutoff frequencies of the low-pass and the high-pass frequency responses. In the experiment, a switchable MPF from 0 to 40 GHz is demonstrated. By changing the center wavelength of TOBF2, the cutoff frequencies of the low-pass and the high-pass frequencies are continuously changed from 2.9 to 20.1 GHz and from 15.4 to 31.2 GHz, respectively.

Second-Order Voltage-Mode Universal Filters Using Two DVCCs, Two Grounded Capacitors and Four Resistors

In this paper, two new second-order voltage-mode universal filters are proposed. Both of the proposed filters use only two differential voltage current conveyors (DVCCs), four resistors and two grounded capacitors which are advantageous from integrated circuit technology point of view. They can simultaneously provide second-order low-pass, high-pass, band-pass, notch and all-pass responses. They offer orthogonal control of angular resonance frequency and quality factor. However, they have a single matching condition for only all-pass responses. A number of simulations based on SPICE program are accomplished in order to demonstrate the performance of both filters.

Rod Electroretinograms Elicited by Silent Substitution Stimuli from the Light-Adapted Human Eye.

PurposeTo demonstrate that silent substitution stimuli can be used to generate electroretinograms (ERGs) that effectively isolate rod photoreceptor function in humans without the need for dark adaptation, and that this approach constitutes a viable alternative to current clinical standard testing protocols.MethodsRod-isolating and non-isolating sinusoidal flicker stimuli were generated on a 4 primary light-emitting diode (LED) Ganzfeld stimulator to elicit ERGs from participants with normal and compromised rod function who had not undergone dark-adaptation. Responses were subjected to Fourier analysis, and the amplitude and phase of the fundamental were used to examine temporal frequency and retinal illuminance response characteristics.ResultsElectroretinograms elicited by rod-isolating silent substitution stimuli exhibit low-pass temporal frequency response characteristics with an upper response limit of 30 Hz. Responses are optimal between 5 and 8 Hz and between 10 and 100 photopic trolands (Td). There is a significant correlation between the response amplitudes obtained with the silent substitution method and current standard clinical protocols. Analysis of signal-to-noise ratios reveals significant differences between subjects with normal and compromised rod function.ConclusionsSilent substitution provides an effective method for the isolation of human rod photoreceptor function in subjects with normal as well as compromised rod function when stimuli are used within appropriate parameter ranges.Translational RelevanceThis method of generating rod-mediated ERGs can be achieved without time-consuming periods of dark adaptation, provides improved isolation of rod- from cone-based activity, and will lead to the development of faster clinical electrophysiologic testing protocols with improved selectivity.