Low-pass Functions Research Articles

Current-Mode Shadow Filter with Single-Input Multiple-Output Using Current-Controlled Current Conveyors with Controlled Current Gain.

In this paper, a novel current-mode shadow filter employing current-controlled current conveyors (CCCIIs) with controlled current gains is presented. The CCCII-based current-mode shadow filters are resistorless and can offer a number of advantages such as circuit simplicity and electronic tuning capability. The proposed shadow filters offer five filtering functions, i.e., low-pass, high-pass, band-pass, band-stop, and all-pass functions, in the same topology. Furthermore, no component matching condition is required to realize all the transfer functions. The natural frequency and quality factor adjustment is possible by using the CCCII current gains without the need to use external amplifiers, all capacitors are grounded, and the filter terminals offer low-input and high-output impedance. To verify the functionality and feasibility of the new topologies, the proposed circuits were simulated using SPICE and the transistor model process parameters NR100N (NPN) and PR100N (PNP) from AT&T's bipolar arrays ALA400-CBIC-R. The simulation results are consistent with the theory. The CCCII experimental setup was designed using commercially available 2N3904 (NPN) and 2N3906 (PNP) transistors with a supply voltage of ±2.5 V. The measurement results confirm the performance of the designed filters.

Design and Verification of a New Universal Active Filter Based on the Current Feedback Operational Amplifier and Commercial AD844 Integrated Circuit.

This paper presents a triple-input and four-output type voltage-mode universal active filter based on three current-feedback operational amplifiers (CFOAs). The filter employs three CFOAs, two grounded capacitors, and six resistors. The filter structure has three high-input and three low-output impedances that simultaneously provide band-reject, high-pass, low-pass, and band-pass filtering functions with single-input and four-output type and also implements an all-pass filtering function by connecting three input signals to one input without the use of voltage inverters or switches. The same circuit configuration enables two unique filtering functions: low-pass notch and high-pass notch. Three CFOAs with three high-input and low-output impedance terminals enable cascading without voltage buffers. The circuit is implemented using three commercial off-the-shelf AD844 integrated circuits, two grounded capacitors, and six resistors and further implemented as a CFOA-based chip using three CFOAs, two grounded capacitors, and six resistors. The CFOA-based chip has lower power consumption and higher integration than the AD844-based filter. The circuit was simulated using OrCAD PSpice to verify the AD844-based filter and Synopsys HSpice for post-layout simulation of the CFOA-based chip. The theoretical analysis is validated and confirmed by measurements on an AD844-based filter and a CFOA-based chip.

Strain gauge measurements of an oscillating heat pipe from startup to stable operation

Oscillating heat pipe (OHP) devices offer high heat flow (Q) and low thermal resistance (Rth) capabilities with convenient form factors for applications in spacecraft and terrestrial thermal management. Though prior measurements have used intrusive strain measurements in a single OHP turn to study the complex thermal-fluid mechanisms of OHP operation, minimally-intrusive external strain measurements on the casing of a multi-turn OHP have not been previously reported. Here, we affix strain gauges to the exterior casing of an ammonia filled flat plate OHP and use strain measurements to quantify the frequency response of ammonia vapor pressure fluctuations over a broad Q range. For all Q, the Fourier transformed strain signals referenced to the Q=0 W background are well-described by a low-pass filter fitting function with a low-frequency amplitude a and characteristic “knee” frequency c. In all cases, a increases with increasing Q due to the enhanced vapor pressure fluctuations at larger thermal loads. In the startup regime of Q<10W, we observe large temporal deviations in the strain response, large Rth>0.1K/W, and c values that increase with increasing Q. In the stable operating regime for Q near 100W, we observe a stable frequency response, a minimum value of Rth=0.02K/W, and Q-independent c values that saturate near 10Hz. Our strain gauge findings are consistent with a mechanism of intermittent boiling near startup followed by stable vapor plug/liquid slug motion at higher Q. Thus, our measurements show that externally placed and minimally invasive strain gauges canprovide diagnostic capabilities and additional insight into operation in both the startup and stable regimes for multi-turn, lightweight OHP devices used in aerospace and terrestrial thermal management applications.

Contrast sensitivity function in deep networks

The contrast sensitivity function (CSF) is a fundamental signature of the visual system that has been measured extensively in several species. It is defined by the visibility threshold for sinusoidal gratings at all spatial frequencies. Here, we investigated the CSF in deep neural networks using the same 2AFC contrast detection paradigm as in human psychophysics. We examined 240 networks pretrained on several tasks. To obtain their corresponding CSFs, we trained a linear classifier on top of the extracted features from frozen pretrained networks. The linear classifier is exclusively trained on a contrast discrimination task with natural images. It has to find which of the two input images has higher contrast. The network’s CSF is measured by detecting which one of two images contains a sinusoidal grating of varying orientation and spatial frequency. Our results demonstrate characteristics of the human CSF are manifested in deep networks both in the luminance channel (a band-limited inverted U-shaped function) and in the chromatic channels (two low-pass functions of similar properties). The exact shape of the networks’ CSF appears to be task-dependent. The human CSF is better captured by networks trained on low-level visual tasks such as image-denoising or autoencoding. However, human-like CSF also emerges in mid- and high-level tasks such as edge detection and object recognition. Our analysis shows that human-like CSF appears in all architectures but at different depths of processing, some at early layers, while others in intermediate and final layers. Overall, these results suggest that (i) deep networks model the human CSF faithfully, making them suitable candidates for applications of image quality and compression, (ii) efficient/purposeful processing of the natural world drives the CSF shape, and (iii) visual representation from all levels of visual hierarchy contribute to the tuning curve of the CSF, in turn implying a function which we intuitively think of as modulated by low-level visual features may arise as a consequence of pooling from a larger set of neurons at all levels of the visual system.

Synthesis of High-Input Impedance Electronically Tunable Voltage-Mode Second-Order Low-Pass, Band-Pass, and High-Pass Filters Based on LT1228 Integrated Circuits

This paper introduces two new high-input impedance electronically tunable voltage-mode (VM) multifunction second-order architectures with band-pass (BP), low-pass (LP), and high-pass (HP) filters. Both proposed architectures have one input and five outputs, implemented employing three commercial LT1228 integrated circuits (ICs), two grounded capacitors, and five resistors. Both proposed architectures also feature one high-impedance input port and three low-impedance output ports for easy connection to other VM configurations without the need for VM buffers. The two proposed VM LT1228-based second-order multifunction filters simultaneously provide BP, LP, and HP filter transfer functions at Vo1, Vo2, and Vo3 output terminals. The pole angular frequencies and the quality factors of the two proposed VM LT1228-based second-order multifunction filters can be electronically and orthogonally adjusted by the bias currents from their corresponding commercial LT1228 ICs, and can be independently adjusted in special cases. In addition, both proposed VM LT1228-based second-order multifunction filters have two independent gain-controlled BP and LP filter transfer functions at Vo4 and Vo5 output terminals, respectively. Based on the three commercial LT1228 ICs and several passive components, simulations and experimental measurements are provided to verify the theoretical predictions and demonstrate the performance of the two proposed high-input impedance electronically tunable VM LT1228-based second-order multifunction filters. The measured input 1-dB power gain compression point (P1dB), third-order IMD (IMD3), third-order intercept (TOI) point, and spurious-free dynamic range (SFDR) of the first proposed filter were -7.1 dBm, -48.84 dBc, 4.133 dBm, and 45.02 dBc, respectively. The measured input P1dB, IMD3, TOI, and SFDR of the second proposed filter were -7 dBm, -49.65 dBc, 4.316 dBm, and 45.88 dBc, respectively. Both proposed filters use a topology synthesis method based on the VM second-order non-inverting/inverting HP filter transfer functions to generate the BP, LP and HP filter transfer functions simultaneously, making them suitable for applications in three-way crossover networks.

0.5 V, nW-Range Universal Filter Based on Multiple-Input Transconductor for Biosignals Processing.

This paper demonstrates the advantages of the multiple-input transconductor (MI-Gm) in filter application, in terms of topology simplification, increasing filter functions, and minimizing the count of needed active blocks and their consumed power. Further, the filter enjoys high input impedance, uses three MI-Gms and two grounded capacitors, and it offers both inverting and non-inverting versions of low-pass (LPF), high-pass (HPF), band-pass (BPF), band-stop (BS) and all-pass (AP) functions. The filter operates under a supply voltage of 0.5 V and consumes 37 nW, hence it is suitable for extremely low-voltage low-power applications like biosignals processing. The circuit was designed in a Cadence environment using 180 nm CMOS technology from Taiwan Semiconductor Manufacturing Company (TSMC). The post-layout simulation results, including Monte Carlo and process, voltage, temperature (PVT) corners for the proposed filter correlate well with the theoretical results that confirm attractive features of the developed filter based on MI-Gm.

Design of Electronically Controllable Multifunction Active Filter with Amplitude Controllability Using Two Commercially Available ICs

In this contribution, the design and analysis of an active multifunction biquad filter that provides five voltage-mode filtering configurations in the same core filtering circuit are presented. The design emphasizes using the commercially available ICs, LT1228, which are easy for off-the-shelf implementation and cheaper compared with the chip implementation. The proposed multifunction filter is realized from two commercial LT1228 ICs as the active function block, combined with five passive elements (three resistors and two capacitors) with three input voltage nodes and a single output voltage node. The following advantages are given for this design: (i) it provides high-pass (HP), low-pass (LP), band-stop (BS), band-pass (BP), and all-pass (AP) filtering functions; (ii) orthogonal and electronic tuning of the natural frequency ω 0 and bandwidth (the quality factor: Q); (iii) output voltage node of the proposed circuit is low impedance; (iv) passband voltage gain is controllable; and (v) matching condition and extra double gain voltage-mode amplifier are not required. The effect of the parasitic element in LT1228 on the filter performance is analyzed and included to strengthen the design idea. The PSpice simulation results using LT1228 with ±5 V and the experimental results tested from the hardware implementation are given to prove the validity of the designed multifunction filter.

Low-Pass NGD Numerical Function and STM32 MCU Emulation Test

This article introduces an original microcontroller unit (MCU) design of numerical low-pass (LP) negative group delay (NGD) function. The innovative theory of the numerical LP-NGD function is developed based on the first-order analog transfer function discretization. The infinite impulse response (IIR) LP-NGD is fundamentally formulated in function of the desired NGD value, cutoff frequency, gain, and the MCU sampling frequency. A STM32 MCU proof-of-concept (POC) is tested to implement the IIR LP-NGD function. Different real-time tests with visualization of input and output analog signals from the MCU LP-NGD POC were performed. As expected, time-advance demonstration tests with milli-second short- and several hour long-duration time-scale with arbitrary waveform signals from temperature and humidity sensors. The signal time-advance is not in contradiction with the causality. The proposed digital MCU function opens a potential future industrial application of LP-NGD function via sensored signal anticipation.

Design of Second-Order Multifunction Filter IC Based on Current Feedback Amplifiers With Independent Voltage Gain Control

This paper presents the integrated circuit (IC) design and implementation of the voltage-mode (VM) second-order gain-controlled multifunction filter (GMF), which consists of three current feedback amplifiers (CFAs), two grounded capacitors and four resistors. The design and implementation of the chip are based on a 0.18 &#x03BC;m process technology, and offers the attractive advantages of high efficiency, high reliability, low voltage, low power consumption, small size and good performance. The VM-GMF chip implements low-pass (LP), inverting band-pass (IBP) and band-stop (BS) filtering functions, and can independently control the gain of LP, IBP and BS filtering functions. The chip operates with a wide input voltage of 1.2 V_pp at &#x00B1;0.9 V supply voltage, and has a figure-of-merit (FOM) of 66.7%. The on-chip measured input power at 1-dB compression point (IP1dB) is about 7.5 dBm with good linearity and the measured power dissipation (PD) is 5.4 mW with low voltage and low power consumption. The measured phase noise (PN) at an offset frequency of 1 kHz is -100.61 dBc/Hz. The measured value of the third-order intermodulation distortion (IMD3) is -57.38 dBc and the third-order intercept point (TOI) is 21.77 dBm. Simulations and on-chip experimental measurements demonstrate the theoretical analysis of the proposed VM-GMF.

Research on application of ground penetrating radar array method based on plane beam signal in different geological models

The traditional common-offset ground penetrating radar method measures point by point along the survey line with a single transmitter and a single receiver. Due to the influence of the antenna radiation power and the low-pass filtering function of the earth medium, an intense amplitude gain cannot be obtained when the signal is intercepted. This article addresses a plane beam signal ground penetrating radar array observation method based on high radiation power gain. The transmitting antenna array simultaneously excites the pulse signal with the same centre frequency. All the transmitted signals interfere with each other at the near surface to form a plane beam signal, and the electromagnetic energy is superimposed mutually to increase the radiation power. We applied the plane beam signal ground penetrating radar array method to different geological models constructed by the finite difference time-domain (FDTD) algorithm for numerical simulation in this research. Since there are various offsets in the array ground penetrating radar observation method, we introduce a composite frequency shift-perfect matching layer (CFS-PML) based on the recursive convolution method as the absorbing boundary condition. It eliminates the problem of secondary reflection caused by the angle variation of the incident wave. The research result shows that the plane beam signal illuminates the target uniformly in space, can eliminate the discontinuity in profile data caused by the directivity of the antenna, improve the stability and quality of the echo signal, and enrich the target response parameters.

Study and experimentation of a 6-dB attenuation low-pass NGD circuit

Because of its counterintuitive nature, the Negative Group Delay (NGD) remains as an uncommon and unfamiliar electronic function. For this reason, the design and analysis of NGD circuits are not well-known for most of electronic designers. This paper initiates a basic and easy to understand theory, in addition to a design methodology for the low-pass NGD function. The circuit theory on the low-pass NGD function is described using an NGD passive topology which is constituted by a RC-parallel network with a resistive load. The NGD analysis and synthesis equations in function of NGD specifications are provided and a proof-of-concept of 6-dB low-pass NGD circuits has been designed, simulated, fabricated and tested. Frequency and time domain analyses have been performed to validate the low-pass NGD function. Theoretical and simulated results are in very good agreement and an NGD has been obtained in measurement for the proposed structure.

Tuning the synaptic behaviors of biocompatible synaptic transistor through ion-doping

Biodegradable and environmentally friendly artificial synapse devices are essential for the future development of neuromorphic computing. The emergence of synaptic transistors based on biocompatible polymer materials provides an ideal approach to achieve green electronics. However, modulating the synaptic properties in a wide range in a fixed biocompatible synaptic transistor is still challengeable, while it is vitally important for improving the adaptability of the synaptic device to achieve neuro-prosthetics in the future. Here, we reported the regulation of the synaptic behavior of biocompatible synaptic transistor through ion-doping, which allows to adjusting the response of the synaptic device according to a specific function. The ions doped into the insulating layer strengthen the formation of electric double layers (EDLs), which enables a remarkable regulation effect on post-synaptic current. Moreover, basic synaptic properties, including excitatory/inhibitory post-synaptic current (EPCS/IPSC), paired-pulse facilitation/depression (PPF/PPD), short-term/long-term memory (STM/LTM) are successfully demonstrated. In addition, high-pass and low-pass filtering functions are also implemented in a single synaptic device, indicating that the synapse attenuation can be effectively transformed according to the needs of the function. More importantly, this is the first work to demonstrate that the accuracy of pattern recognition of synaptic transistors, an important indicator of neuromorphic calculations, can be significantly improved via ion doping (as high as 75.96% relative to undoped devices of 41.68%). Our research provides a feasible strategy for precisely controlling synaptic behaviors, which has a profound impact on improving the adaptability of artificial synaptic devices in the field of neuromorphic computing. • A biocompatible synaptic transistor with tunable synaptic properties base on ion-doped polymer electrolyte material. • Basic synaptic behaviors are demonstrated, such as PPF/D, and STM to LTM. • First work to show the accuracy of pattern recognition of synaptic transistors can be improved via ion-doping.

Reconnection–less reconfigurable low–pass filtering topology suitable for higher–order fractional–order design

The paper discusses a new design of a current–mode reconnection–less reconfigurable fractional–order (FO) low–pass filter of various orders. The filtering structure is based on a 4th–order leap–frog topology using operational transconductance amplifiers as basic building blocks. The resulting order of the filter is given by the setting of current gains (allowing the reconnection–less reconfiguration) alongside with the values of the fractional–order capacitors realized by the RC ladder networks. For this purpose, RC ladder networks of orders 0.3, 0.4, 0.5, 0.6 and 0.7 have been designed. The fractional–order form of the filter contains from one up to four FO capacitors (remaining capacitors (if there are any) are of integer–order) allowing to obtain low–pass functions of order of 3 + α, 2 + α, 1 + α, 2 + α + β, 1 + α + β, α + β, 1 + α + β + γ, α + β + γ and α + β + γ + δ. The proposed filter offers a wide variety of possible order combinations with an increasing degree of freedom as the number of fractional–order capacitors within the structure increases. The proposal is supported by the PSpice simulations of magnitude and phase characteristics, pole frequency adjustment and stability analysis. Moreover, the experimental measurements of the implemented filter were carried out and compared with the simulation results. The possibility of the electronic control of the fractional order is also discussed and presented.

Anticipating Actuator Arbitrary Action With a Low-Pass Negative Group Delay Function

This article investigates the feasibility of anticipating arbitrary signals from mechanical actuators. The anticipator originally operates with a low-pass negative group delay (NGD) function. The properties that enable NGD active topology to realize signal anticipation are analytically described. The NGD design and synthesis method as a function of the operating signal bandwidth is established. A real-time demonstration of the motion anticipation is originally performed with a rotating tunable resistor. Second-order motion angle anticipations are realized by completely considering the arbitrary waveform signals. The relevance of the motion anticipation is confirmed with more than a correlation coefficient between the NGD input and output signals that is more than 90%. Innovative real-time predictions of approximately −0.3 s are demonstrated. The present study indicates potential industrial applications of the NGD function in anomaly detections, future smart engines, and smart factories.

Reconstruction Technique of Distorted Sensor Signals with Low-Pass NGD Function

This paper develops a new reconstruction technique of undesirable signal distortion generated by sensor electronic circuits. The introduced reconstruction technique is originally realized with unfamiliar low-pass negative group delay (NGD) function. The feasibility condition of the proposed reconstruction technique in function of the sensor signal spectrum bandwidth under consideration is elaborated. The reconstruction technique principle is theoretically introduced by means of identification of low-pass NGD function parameters and the appropriated circuit topology. The unfamiliar low-pass NGD function analysis and synthesis equations are established. As an example, for the feasibility study, an RC-network based low-pass active cell is considered to implement the low-pass NGD function. A design method of NGD circuit in function of the sensor distortion transfer function is described in different successive steps. The developed NGD reconstruction technique is validated by different proofs of concept. First, transient simulations are carried out with Gaussian and sinc analytical signals. Then, experimental feasibility study is also performed with arbitrary waveform signal. As expected, the NGD reconstruction technique efficiency is confirmed with improvement of distorted signal integrity parameters and cross correlation better than 97%.

Innovative Theory of Low-Pass NGD via-Hole-Ground Circuit

The via ground (GND) structure constitutes one of the most useful elements for designing high performance printed circuit boards (PCBs). The electrical interconnections with vias become key regular solutions for the implementation of various electronic functions. However, so far, the vias are never being used for designing negative group delay (NGD) circuit. To answer this curious question, an original study on the design feasibility of low-pass NGD function with via ground is introduced in the present paper. After the topological description, the NGD analysis in function of the via parameters is established. The design equations allowing to synthesize the via in function of NGD function specifications are formulated. The developed NGD theory is verified with comparisons between calculations and simulations with a commercial tool. As expected, NGD value in order of hundred-picoseconds over hundred-megahertz cut-off frequencies is obtained with good agreement between the theoretical model and simulation. Furthermore, time domain analyses confirm that the via NGD structure enables to generate output signals in time-advance of arbitrary waveform input signals presenting limited bandwidth.

Electronically tunable current-mode multifunction filter using current-controlled current follower transconductance amplifier

A new electronically tunable current-mode multifunction universal filter with three inputs and one output based on current-controlled current follower transconductance amplifier is presented. The proposed filter can realize low-pass, band-pass, high-pass, band-stop and all-pass filtering functions into single topology. For realize these filtering functions, no passive component-matching conditions, no inverting-type input signal requirements and high-output impedance are possessed. Also the proposed filter offers electronic control of the natural angular frequency, low active and passive sensitivities and use of grounded capacitors which is ideal for integrated circuit implementation. The proposed universal biquadratic filter has been used to realize sixth-order filters. PSPICE simulation results are used to confirm the presented theory.

Realization of Voltage-mode Multifunction Biaquadratic Filter Using Minimum Number of Active Element

The realization of voltage-mode multifunction biquadratic filter has been presented in this research contribution. The proposed circuit contains three input voltage nodes and one output voltage node. The structure of proposed filter is simple consisting of one modified current controlled current conveyor transconductance amplifier (M-CCCCTA) as active building block with one resistor and two capacitors. With electronically controllable property of M-CCCCTA, the parameters, natural frequency (ω0) and quality factor (Q) are electronically controlled by changing the external DC bias currents of the M-CCCCTA. The tuning characteristic of Q is also done without effect the w0. In the same circuit construction, five second order filter responses, all-pass, high-pass (HP), band-reject (BR), low-pass (LP) and band-pass (BP) functions are obtained. The output filter responses are obtained with applying appropriate input voltage to input node without the matching condition of active and passive elements. The performances of the proposed biquadratic filter have been verified through Pspice simulation in TSMC 0.25 μm CMOS technology parameters.

Four-Input One-Output Voltage-Mode Universal Filter Using Simple OTAs

This paper presents a new electronically tunable voltage-mode universal filter with four-input one-output employing six simple operational transconductance amplifiers (OTAs), two grounded capacitors and two MOS resistors. The use of grounded passive components is beneficial for integrated circuit implementation. The proposed filter can realize low-pass, band-pass, high-pass, band-stop and all-pass filtering functions without active and passive component-matching conditions and inverting-type input signals requirements. The natural frequency and quality factor can be tuned independently and electronically by adjusting the bias currents. The voltage-mode filter offers the features of high-input impedance and low active and passive sensitivities. The characteristics of the proposed universal filter are verified using PSPICE simulators through 0.35[Formula: see text][Formula: see text]m CMOS process. Experimental results are used to confirm the workability of proposed circuit through LM13600 commercially available OTAs. Also a digitally programmable filter is shown to confirm the advantage of multiple-input universal filter.

Time-Domain Experimentation of NGD ActiveRC-Network Cell

A theoretical and experimental investigation of low-pass negative group delay (NGD) topology is introduced. The NGD topology is composed of a low noise amplifier (LNA) and RC-parallel series mounted lumped network. The NGD cell theoretical characterization is elaborated. The NGD properties as NGD level, cut-off frequencies and central frequency are established. The synthesis formulas as function of the expected NGD level and gain are established. The NGD proof of concept using monolithic LNA LEE-9+ manufactured by mini-circuits are designed, simulated, fabricated, and measured. The simulated and measured frequency domain results are in good agreement with the circuit theory. As expected, low-pass NGD behavior is observed with −5 ns-NGD level over 32-MHz bandwidth. The low-pass NGD function meaning is illustrated by the advance of the output pulse signal leading and trailing edges compared to the input ones.