Programmable Impedance Research Articles

Analog Memristor-Based Dynamic Programmable Analog Filter

The memristor study now generally exhibit threshold voltage characteristics. The memristance changes when the voltage across the memristor is greater than the threshold voltage. Otherwise, the memristance is almost constant. Based on this feature, we design a general-purpose memristor programmable circuit that is simple to operate. In the field of communication and signal processing, programmable analog filters are required, and memristors with multi-valued characteristic are suitable as programmable impedance elements for such circuits. Through simulation and physics experiments, we demonstrate a memristor-based programmable low-pass filter using the designed programmable circuit to realize the dynamic adjustment of circuit parameters.

CBRAM technology: transition from a memory cell to a programmable and non-volatile impedance for new radiofrequency applications

Electrical resistance control programming of conductive bridging random access memory (CBRAM) radio frequency (RF) switches could benefit the development of electronically controlled non-volatile RF attenuators and other reconfigurable devices. The object of this study is to adapt a conventional CBRAM based memory cell to be used as an RF switch, and to demonstrate the feasibility of programming non-volatile RF CBRAM switches to achieve specific target resistances within a range of continuous values. The memory-RF technologic transition implies a drastic increase of the geometry in order to handle a much higher power, a decrease of the transition capacitance in order to operate at much higher frequencies, and a decrease of the LRS to a few ohms, which is critical for RF applications. These studies are initially performed on an in-house made RF CBRAM cell array at DC frequency, and then extended successfully to a co-planar waveguide (CPW) based shunt mode RF switch with an integrated CBRAM cell. Reliability of the proposed technique is validated through detailed analysis of factors like repeatability of the process, time stability of programmed states, and statistics of time taken to converge to a desired resistance value for an arbitrary RF CBRAM switch.

Digital Impedance Emulator for Battery Measurement System Calibration.

Meaningful information on the internal state of a battery can be derived by measuring its impedance. Accordingly, battery management systems based on electrochemical impedance spectroscopy are now recognized as a feasible solutions for online battery control and diagnostic. Since the impedance of a battery is always changing along with its state of charge and aging effects, it is important to have a stable impedance reference in order to calibrate and test a battery management system. In this work we propose a programmable impedance emulator that in principle could be used for the calibration of any battery management system based on electrochemical impedance spectroscopy. A digital finite-impulse-response filter is implemented, whose frequency response is programmed so as to reproduce exactly the impedance of a real battery in the frequency domain. The whole design process of the filter is presented in detail. An analytical expression for the impedance of real battery in the frequency domain is derived from an equivalent circuit model. The model is validated both through numerical simulations and experimental tests. In particular, the filter is implemented on a low-cost microcontroller unit, and the emulated impedance is measured by means of a custom-made electrochemical impedance spectroscopy measuring system, and verified by using standard commercial bench instruments. Results on this prototype show the feasibility of using the proposed emulator as a fully controllable and low-cost reference for calibrating battery impedance measurement systems.

A Three‐stage programmable impedance scaling circuit

AbstractLarge capacitances are needed for low‐frequency active filters to process biomedical signals. The large capacitance can be implemented on a chip by an impedance scaling circuit. However, the characteristics of the circuit are affected by process variations. Then, we have proposed a digitally programmable impedance scaling circuit using electrical switches to compensate for the process variations. This paper describes a technique to reduce power consumption as compared with the conventional circuit. The proposed circuit is composed of a three‐stage current mirror circuit and electrical switches. To reduce the power consumption, the only signal current is amplified by current mirror circuits and bias current sources. The tuning range of the scaling factor of capacitance is from −35% to +28%, and the tuning accuracy is 1% using six switches. The validity of the proposed method is confirmed by simulations using HSPICE. The power consumption of the proposed circuit is reduced by 51% as compared with the conventional circuit. The proposed circuit is applied to a filter whose cutoff frequency is 100 Hz. From the tuning result, the tuning error is less than 1% for ±30% of ±3σ global variation and ± 3% of ±3σ local variation. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

A Programmable Impedance Tuner with a High Resolution Using a 0.18-um CMOS SOI Process for Improved Linearity

In this paper, a novel coupler/reflection-type programmable electronic impedance tuner combined with switches that were fabricated by a 0.18-um complementary metal–oxide–semiconductor (CMOS) silicon-on-insulator (SOI) process is proposed for replacement of the conventional mechanical tuner in power amplifier (PA) load-pull test. By employing the multi-stacked field-effect transistors (FETs) as a single-branch switch, the proposed tuner has the advantage of precise impedance variation with systematic and magnitude and phase adjustment. Additionally, it led to high standing wave ratio (SWR) coverage and a good impedance resolution with a high power handling capability. Furthermore, the double-branch based on multi-stacked FET was applied to switches for additional enhancement of the intermodulation distortion (IMD) performance through the mitigated drain-source voltage of the single-FET. Drawing upon the measurement results, we demonstrated that SWR changed from 2 to 6 sequentially with a 12–15° phase angle step over a mid/high-band range of a 1.5–2.1 GHz band for 3G/4G handset application. In addition, the PA load-pull measurement results obtained using the proposed tuners verified their practicality and competitive performance with mechanical tuners. Finally, the measured linearity using the double-branch switch demonstrated the good IMD3 performance of −78 dBc, and this result is noteworthy when compared with conventional electronic impedance tuners.

Impedance-Controlled Variable Stiffness Actuator for Lower Limb Robot Applications

We present a novel application of the variable stiffness actuator (VSA)-based assistance/rehabilitation robot-featured impedance control using a cascaded position torque control loop. The robot follows the adaptive impedance control paradigm, thereby achieving an adaptive assistance level according to human joint torque. The feedforward human joint torque command is used to cooperatively adjust the impedance controller and the stiffness trajectory of the VSA (this functional architecture is referred to as the cooperative control framework). In this way, the task performance during movement training can be improved regarding: 1) safety —for example, when the subject intends to contribute considerable effort, low-gain impedance control is activated with a low stiffness actuator to further decrease output impedance and 2) tracking performance —for example, for the subject with less effort, high-gain impedance control is used while pursuing high stiffness to enhance the torque bandwidth. Regarding the safety aspect, we demonstrate that the torque controller designed at low stiffness can be sensitive to the disturbance for low output impedance while maintaining tracking performance. A precondition for this is to treat the input disturbance separately. This is guaranteed by our previously proposed torque control of the VSA using the linear quadratic Gaussian technique. This approach is also employed here, but with additional discussion on the observer design to serve the proposed cooperative control approach. Here, the effectiveness of the proposed control system is experimentally verified using a VSA prototype and a one-degree-of-freedom lower limb exoskeleton worn by a human test person. Note to Practitioners —Control of “physical human–robot interaction” can be achieved by the mechanical parts of the variable stiffness actuator (VSA). However, the mechanical construction for stiffness variation may limit the capacity to achieve low output stiffness and fast stiffness variation in speed. These limitations may become more evident in the assistance/rehabilitation robot applications. To overcome these limitations, the impedance control scheme can be employed to achieve a programmable impedance range and impedance variation speed. This control scheme has been widely applied on the fixed-compliance joint but lacks a way to be implemented on the VSA joint because of its existing capacity to control the impedance with the mechanical construction. This article presents a novel application of the impedance-controlled VSA used on a lower limb robot. We describe how to adjust the actuator stiffness to cooperatively work with the adaptive impedance control scheme. Based on our approach, the robot with the impedance-controlled VSA joint can extend the capacity of bandwidth and low output impedance. This is an improvement on the impedance-controlled fixed-compliance joint. The cooperative control framework presented here was tested on an exoskeleton system with two healthy test persons and is also applicable to other actuator prototypes. Future research aims to employ this system for actual patient training.

A +25-dBm IIP3 1.7–2.1-GHz FDD Receiver Front End With Integrated Hybrid Transformer in 28-nm CMOS

A highly linear receiver (RX) front end with integrated hybrid transformer (HT) for frequency-division duplexing mobile communications is reported. The HT, implemented with a three-winding coplanar transformer, is used to interface the RX front end with the antenna and the power amplifier. The primary is driven at its center tap with the transmitted signal and at one input with the antenna signal, while the other input is connected to an on-chip programmable balancing impedance. The two secondary drives a differential push–pull common-gate low-noise amplifier (LNA). Assuming a perfectly linear hybrid only 45 dB of transmitter (TX)–RX isolation and 35 dB of common-mode rejection are required to meet the intermodulation specs thanks to the +25-dBm receiver IIP3. This would drastically simplify hybrid balancing and adaptation loop. Cascaded noise figure of duplexer, LNA, and baseband is below 6.7 dB and TX insertion loss below 4.3 dB from 1.7 to 2.1 GHz. The implemented prototype in 28-nm CMOS has an active area of 0.7 mm2 and requires only 26 mW.

On the development of a novel high VSWR programmable impedance tuner

Impedance tuners are key instruments used for load- and source–pull measurements. They are crucial for any active microwave components, circuits, and systems characterization and optimization. This paper reports theoretical, simulated, and experimental results related to the development of a novel programmable impedance tuner offering high-voltage standing wave ratio (VSWR). After presenting the proposed tuner principle, a fabricated prototype operating at microwave frequencies and based on a 3.5 mm coaxial line is introduced with experimental results. Depending on the targeted frequency band, different pairs of slugs, with optimized length and characteristic impedance, can be used to obtain an optimal VSWR. This first prototype allowed us to demonstrate the interest of the proposed impedance synthesis principle and to identify ways forward to further improve its performances and push forward this promising technology.

Inter-catheter impedance variation during internal atrial defibrillation

Introduction: According to the European Society of Cardiology, atrial fibrillation (AF) has a prevalence of 1–2% in the general population, rising to over 5.5% in individuals over 55 years of age and accounts for in excess of 30% of all arrhythmia related hospital admissions. For chronic AF sufferers (where all other therapies have proved ineffective), restoration of sinus rhythm through electrical shock remains the treatment of choice. Internal atrial defibrillation thresholds as low as 1.27 joules have been reported. However, at low energies, complex electro-mechanical interac- tions at the catheter-tissue interface have long been suspected as a major source of variation in the amount of electrical energy required to terminate this arrhythmia. The objective of this work was to characterise the variation of inter-catheter impedance during internal atrial defibrillation.Methods: For this study, a custom low-power programmable impedance spectrometer was built to deliver a sinusoidal current of ± 200 μA in magnitude from 1–100 kHz in frequency. Using this system, the complex impedance between a pair of defibrillation electrode poles (placed in the distal coronary sinus and wall of the right atrium) was recorded between successive atrial defibrillation attempts.Results: A total of ten porcine models were investigated. Measurements detected inter-catheter impedance variations ranging from 15.5% to 28.9%. Subsequent data analysis revealed a mean inter-catheter impedance of 43.9 Ω with a variance of approximately 20.1% recorded.Conclusions: Complex electro-mechanical interactions at the catheter-tissue interface have been identified as a cause of significant variation in inter-catheter impedance; which alters the associated cardioversion threshold during internal atrial defibrillation. Further research will be required to fully understand and mitigate adverse effects of the physical mechanisms involved.

Evidence for the Flexible Sensorimotor Strategies Predicted by Optimal Feedback Control

Everyday movements pursue diverse and often conflicting mixtures of task goals, requiring sensorimotor strategies customized for the task at hand. Such customization is mostly ignored by traditional theories emphasizing movement geometry and servo control. In contrast, the relationship between the task and the strategy most suitable for accomplishing it lies at the core of our optimal feedback control theory of coordination. Here, we show that the predicted sensitivity to task goals affords natural explanations to a number of novel psychophysical findings. Our point of departure is the little-known fact that corrections for target perturbations introduced late in a reaching movement are incomplete. We show that this is not simply attributable to lack of time, in contradiction with alternative models and, somewhat paradoxically, in agreement with our model. Analysis of optimal feedback gains reveals that the effect is partly attributable to a previously unknown trade-off between stability and accuracy. This yields a testable prediction: if stability requirements are decreased, then accuracy should increase. We confirm the prediction experimentally in three-dimensional obstacle avoidance and interception tasks in which subjects hit a robotic target with programmable impedance. In additional agreement with the theory, we find that subjects do not rely on rigid control strategies but instead exploit every opportunity for increased performance. The modeling methodology needed to capture this extra flexibility is more general than the linear-quadratic methods we used previously. The results suggest that the remarkable flexibility of motor behavior arises from sensorimotor control laws optimized for composite cost functions.

Clinical potential and design of programmable mechanical impedances for orthotic applications

A person with a moderate or severe motor disability will often use specialised or adapted tools to assist their interaction with a general environment. Such tools can assist with the movement of a person's arms so as to facilitate manipulation, can provide postural supports, or interface to computers, wheelchairs or similar assistive technologies. Designing such devices with programmable stiffness and damping may offer a better means for the person to have effective control of their surroundings.This paper addresses the possibility of designing some assistive technologies using impedance elements that can adapt to the user and the circumstances. Two impedance elements are proposed. The first, based on magnetic particle brakes, allows control of the damping coefficient in a passive element. The second, based on detuning the P-D controller in a servo-motor mechanism, allows control of both stiffness and damping. Such a mechanical impedance can be modulated to the conditions imposed by the task in hand. The limits of linear theory are explored and possible uses of programmable impedance elements are proposed.

Computer Models for Complex Plant & System Based on Terminal Measurements

A method for obtaining models of complex plant and systems for use in transient voltage studies is described. The method is based upon determining the terminal impedance/ frequency characteristics of the plant or system under study over a wide frequency range. These characteristics are obtained from measurements performed at sampled frequencies with a programmable impedance meter and microcomputer. A method for correcting results for measuring lead length errors is also described. The method is shown to be applied to obtain models of single and three-phase transformers. These are validated comparing measured and calculated input impedances. The impedance/frequency characteristics are used to calculate the transfer functions across any two terminals of the system. The response to any excitation is calculated first in the frequency domain as the product of the frequency spectra and the transfer functions, and second in the time domain by the inverse Fourier transformation. This method is applied to calculate the second-pole-to-close switching transient generated in a breaker/cable/motor system. Again, measured and calculated results show excellent agreement. Although some limitations of this method appear at frequencies of up to 10 KHz, it is generally applicable to all items of system plant and to systems.

Digitally programmable ratio transformer bridge

We describe a digitally programmable impedance bridge, used here for low-temperature resistance thermometry, and a compatible digital programming and data logging interface. The bridge employs a commercial programmable ratio transformer to achieve high resolution with minimum circuit complexity. We measure the ratio of the resistances of a carbon thermometer and a fixed reference resistor, both near 2 K, with a resolution limited by Johnson noise in the resistors. The bridge circuit described here is suitable for a variety of programmable or self-balancing impedance measurements.