Low Output Impedance Research Articles

Isomorphic Circuits of Independent Amplitude Tunable Voltage-Mode Bandpass Filters and Quadrature Sinusoidal Oscillators

This paper presents isomorphic circuits of voltage-mode (VM) non-inverting bandpass filters (NBPFs) and VM quadrature sinusoidal oscillators (QSOs) with independent amplitude control functionality. The proposed VM NBPFs and VM QSOs exhibit low-output impedance and independent amplitude control, which are important for easily cascading the VM operation and independent control of the amplitude gain. The proposed isomorphic circuits employ three LT1228 commercial integrated circuits (ICs), two grounded capacitors, two grounded resistors and one floating resistor. The use of grounded capacitors is beneficial for the implementation of the IC. Both NBPFs have a high-input impedance and have a wide range of independent amplitude tunable passband gain without affecting the quality factor (Q) and center frequency (fo). The Q and fo parameters of the proposed NBPFs are orthogonal tunability. By feeding back each input signal to the output response of the NBPF, two VM fully uncoupled QSOs are also proposed. The proposed VM fully uncoupled QSOs have two quadrature sinusoidal waveforms with two low-output impedances and one independent amplitude tunable sinusoidal waveform. The frequency of oscillation (FO) and the condition of oscillation (CO) are fully uncoupled and controlled electronically. The performances of the proposed isomorphic circuits have been tested with a ±5 volt power supply and are demonstrated by experimental measurements which confirm the theoretical assumptions.

Wide illumination and communication angle visible light communication system based on low output impedance LED driver amplifier

Wide illumination and communication angle visible light communication system based on low output impedance LED driver amplifier

A New VCII Application: Sinusoidal Oscillators

The aim of this paper is to prove that, through a canonic approach, sinusoidal oscillators based on second-generation voltage conveyor (VCII) can be implemented. The investigation demonstrates the feasibility of the design results in a pair of new canonic oscillators based on negative type VCII (VCII−). Interestingly, the same analysis shows that no canonic oscillator configuration can be achieved using positive type VCII (VCII+), since a single VCII+ does not present the correct port conditions to implement such a device. From this analysis, it comes about that, for 5-node networks, the two presented oscillator configurations are the only possible ones and make use of two resistors, two capacitors and a single VCII−. Notably, the produced sinusoidal output signal is easily available through the low output impedance Z port of VCII, removing the need for additional voltage buffer for practical use, which is one of the main limitations of the current mode (CM) approach. The presented theory is substantiated by both LTSpice simulations and measurement results using the commercially available AD844 from Analog Devices, the latter being in a close agreement with the theory. Moreover, low values of THD are given for a wide frequency range.

A new first-order universal filter consisting of two ICCII + s and a grounded capacitor

In this paper, a new inverting second-generation current conveyor-based first-order current-mode universal filter is proposed. The main features of the proposed filter are described as follows: the use of a grounded capacitor that is attractive for integration, electronically tunable, no passive element matching condition, resistor-less, having the feature of both low input and high output impedances as well as providing all the first-order universal filter responses such as low-pass, high-pass and all-pass ones. As application examples, a sinusoidal oscillator and a four-phase oscillator are given. Many simulations through SPICE program and some experiments are achieved in order to exhibit the performance of the proposed filter.

Tunable Q matching networks for capacitive ultrasound transmitters

Airborne capacitive micromachined ultrasonic transducers (CMUTs) have predominantly large input capacitive reactance with small series radiation resistance. To maximize the acoustic power radiation at resonance we employ low cost LC matching networks between the low output impedance driving source and CMUT transducer. Conventional LC networks, including pi and T-network topologies are employed to provide a high-Q match. An important free parameter that controls the bandwidth of match in pi and T-networks is the center impedance. Since a simple pi-network can be formed from two basic L-sections, the center impedance of two L-sections provides control over the bandwidth of match. Hence these are tunable-Q matching networks. We use the lumped circuit model of CMUT to derive the input impedance of CMUT at resonance. At resonance the lumped equivalent circuit of transducer can be reduced to a series RC circuit consisting of radiation resistance and transducer’s equivalent capacitance only. From the input impedance of CMUT we determine the lumped inductance and capacitances of various LC matching networks. The aim of these matching networks is to cancel the large input capacitive reactance of CMUT cell and to match the cell’s radiation resistance to source resistance at resonance. We report significant improvement in the radiated power when CMUT is driven at resonance using the proposed matching schemes.

A 24–28-GHz Doherty Power Amplifier With 4-W Output Power and 32% PAE at 6-dB OPBO in 150-nm GaN Technology

A 24-28-GHz two-stage GaN Doherty power amplifier (PA) is designed and characterized. At millimeter-wave (mm-wave) frequencies, the low output impedance of the auxiliary transistor loads the Doherty combining network, which lowers the power added efficiency (PAE) in back-off. In this design, a small periphery auxiliary transistor is used to increase the output impedance of the auxiliary transistor. The periphery ratio of the auxiliary and the main transistors is 77%. Even though, compared to symmetric Doherty PAs, the load modulation of the main transistor is reduced, this amplifier still achieves 32% and 23% PAE at 6 and 9-dB output power back-off, respectively. Attributing to the small auxiliary transistor, the amplifier obtains a small signal gain of 19 dB. The maximum output power of the amplifier is 4 W with a peak PAE of 42%.

Universal Filter Based on Compact CMOS Structure of VDDDA.

This paper proposes the simulated and experimental results of a universal filter using the voltage differencing differential difference amplifier (VDDDA). Unlike the previous complementary metal oxide semiconductor (CMOS) structures of VDDDA that is present in the literature, the present one is compact and simple, owing to the employment of the multiple-input metal oxide semiconductor (MOS) transistor technique. The presented filter employs two VDDDAs, one resistor and two grounded capacitors, and it offers low-pass: LP, band-pass: BP, band-reject: BR, high-pass: HP and all-pass: AP responses with a unity passband voltage gain. The proposed universal voltage mode filter has high input impedances and low output impedance. The natural frequency and bandwidth are orthogonally controlled by using separated transconductance without affecting the passband voltage gain. For a BP filter, the root mean square (RMS) of the equivalent output noise is 46 µV, and the third intermodulation distortion (IMD3) is −49.5 dB for an input signal with a peak-to peak of 600 mV, which results in a dynamic range (DR) of 73.2 dB. The filter was designed and simulated in the Cadence environment using a 0.18-µm CMOS process from Taiwan semiconductor manufacturing company (TSMC). In addition, the experimental results were obtained by using the available commercial components LM13700 and AD830. The simulation results are in agreement with the experimental one that confirmed the advantages of the filter.

Electronic-Tuning-Facilitated Input Interface-Supported Load-Insensitive Filter with Extended Frequency Range

A new filter operating in voltage mode and realizing all-pass function is proposed. The circuit requires a single current conveyor with an extra voltage input buffer stage and a floating capacitor, enjoys electronic tuning, needs input interface for easy connection and benefits by low output impedance, hence is load-insensitive and operable at twice the frequency range in comparison to other related circuits. In-depth theoretical and simulation studies are presented in support of the newly designed circuit.

Supplementary DDCC+ based universal filter with grounded passive elements

A new voltage-mode (VM) analog filter is proposed in this paper. The proposed circuit is composed of three plus-type single output DDCCs and only grounded passive elements that are important when the integrated circuit fabrication is involved. It has three high input impedances and one low output impedance. As a result, it has the feature of easy cascadability with other VM structures. Passive element matching constraints and extra additional active devices are not needed for it. Non-ideality analyses such as non-ideal gain and parasitic impedance effects are also given. Many simulations through SPICE program and several experimental studies are included.

Precision rectifier circuit using current-mode approach and grounded resistors

ABSTRACT This article is devoted to a new circuit proposal for precision rectification, which is designed using current feedback operational amplifiers. The new proposed circuit operation is clearly discussed, circuit analysis is performed and the workability is verified through extensive simulations carried out using PSPICE software. The in-built model library of used current feedback operational amplifier (namely, AD844) is used for simulating the proposed circuit. The performance metrics for the proposed circuit, which are verified includes signal precision of 100 mV, signal frequency of 1 MHz and linearity range of ±200 mV and output adjustment through auxiliary scaling block. Other features include low output impedance (100 Ω) for voltage mode cascading, high input impedance for one-half cycle of input, and employment of grounded resistors only. These features are apt for proposed circuit’s actual application perspective for voltage-mode analog design, since cascading requirements are easily fulfilled and use of grounded resistors benefit integration aspects.

CFA BASED UNIVERSAL BIQUAD FILTER

This paper is a review of the organizational structure and challenges that a technological enterprise faces during scaling, from the perspective of the engineering management. After expanding operations internationally, the distributed engineering teams developing hardware and software for internet of things applications, face issues regarding culture, communication, leadership, project planning and management. Relevant literature addressing these issues is presented. We elaborate on already implemented measures for improving the overall efficiency and propose further processes introduced in recent literature that can be beneficial for further optimizing the new product development. Potential knock-on effects by such implementation are also discussed. A universal biquad filter using current feedback amplifiers (CFA) as active devices and a canonical number of capacitors is presented. It realizes the classical feedforward structure through the use of grounded capacitors and MOS transistors, which permit a full integrability. The proposed circuit has attractive characteristics, as the possibility to electronically control the transfer function coefficients and the possibility to be directly inserted within cascaded configurations. The theoretical analysis of the circuit is followed by some PSPICE simulation results in agreement with the theoretical findings. In this paper a universal fully integrable biquad using CFAs as active devices and a canonical number of capacitors is presented. It realizes the classical feedforward structure [3] through the use of grounded capacitors and MOS transistors. The presence of grounded capacitors makes the proposed circuit absorb shunt parasitic capacitances. All the possible kinds of responses can be realized, while in the biquad reported in [2] only the low-pass and band-pass responses can be obtained. The numerator and denominator coefficients of the voltage transfer function of the proposed biquad can be electronically controlled by acting on the gate voltages of the MOS transistors of the circuit. Moreover the presented structure has a low-impedance output and then it can be cascaded without additional buffers.

Electronically Tunable Mixed-Mode Universal Filter Employing a Single Active Block and a Minimum Number of Passive Components

A recently developed active building block, namely Voltage Differencing Extra X Current Conveyor (VD-EXCCII), is employed in the design of multi input single output (MISO), electronically tunable mixed-mode universal filter. The filter provides low pass (LP), high pass (HP), band pass (BP), band reject (BR) and all pass (AP) responses in current-mode (CM), voltage-mode (VM), trans-impedance-mode (TIM) and trans-admittance-mode (TAM). The filter employs a single VD-EXCCII, three resistors and two capacitors. Additionally, a CM single input multi output (SIMO) filter can be derived from the same circuit topology by only adding current output terminals. The attractive features of the filter include: (i) the ability to operate in all four modes, (ii) the tunability of the Q factor independent of pole frequency, (iii) the low output impedance for the VM filter, (iv) the high output impedance current output for CM and TAM filters and (v) no requirement for double/negative input signals (voltage/current) for response realization. The VD-EXCCII and its layout is designed and validated in Cadence Virtuoso using 0.18 µm pdk from Silterra Malaysia with a supply voltage of ±1.25 V. The operation of the filter is examined at the 8.0844 MHz characteristic frequency. A non-ideal parasitic and sensitivity analysis is also carried out to study the effect of process and components spread on the filter performance.

Voltage differencing buffered amplifier based low power, high frequency and universal filters using 32 nm CNTFET technology

This work presents filter applications of carbon nanotube field effect transistors (CNTFET) voltage differencing buffered amplifier (VDBA) based high frequency universal filters using 32 nm CNTFET technology of Stanford University model. CNTFETs are potential candidates to replace conventional silicon-based transistors due to their exceptional material properties. In addition, by changing chirality of carbon nanotube (CNT), the material property can be easily changed from semiconducting material to metallic. The VDBA is an active element of circuit which has high input impedance and low output impedance. These types of blocks provide an advantage for voltage mode circuits allowing cascadability and no critical component matching. The proposed CNTFET VDBA shows much higher frequency response with about 67 GHz at first stage which is well known OTA block and around 30 GHz at second stage, power consumption around 135 times less than 0.35 μm TSMC technology and 2476 times reduction in active area of chip. HSPICE and MATLAB simulation tools are used to perform all simulations.

Novel Electronically Tunable Biquadratic Mixed- Mode Universal Filter Capable of Operating in MISO and SIMO Configurations

In this paper, a novel electronically tunable biquadratic universal mixed-mode filter is presented. The filter is based on extra X current conveyor transconductance amplifier (EXCCTA), recently introduced by authors. The proposed filter employs two EXCCTAs, two capacitors, a switch, and four resistors. The filter can work in both multi-input-single-output (MISO) and single-input-multi-output (SIMO) configurations without change in its structure. The filter provides low-pass (LP), high-pass (HP), band-pass (BP), band-reject (BR) and all-pass (AP) responses in voltage-mode (VM), current-mode (CM), transimpedance-mode (TIM), and transadmittance-mode (TAM). The attractive features of the filter include (i) ability to operate in both MISO and SIMO configurations in all four modes, (ii) no requirement of capacitive matching, (iii) high output impedance in SIMO (CM & TAM) configuration, (iv) tunability of quality factor ( Q ) independent of natural frequency ( ) in MISO & SIMO configurations, (v) use of grounded capacitors in SIMO configuration, (vi) low output impedance for MISO (VM & TIM), (vii) high output impedance explicit current output for MISO (CM & TAM), and (viii) no requirement for double/negative input signals (voltage/current) in MISO configuration. The non-ideal gain and sensitivity analysis is also carried out to study the effects of process variations and passive components spread on filter performance. The filter is designed in Cadence Virtuoso using Silterra Malaysia 0.18µm PDK. The complete layout of the EXCCTA is designed and the parasitic extraction is done. The filter is tested at a supply voltage of ±1.25 V and the obtained results validate the theoretical findings.

Neural network-based integral sliding mode backstepping control for virtual synchronous generators

As an important component of microgrid system, the grid-connected inverter is composed of power electronic devices, which makes the system lack physical inertia and exhibit low output impedance. Especially in the transition process of grid connection, a large current impact will be generated, which may make the system unstable. Therefore, in response to these problems, a nonlinear control method is proposed that enables the grid-connected inverter to switch freely between grid-connected mode and island mode. The linear control part introduces the mechanical equations of the rotor of the synchronous motor, which has virtual inertia and damping, and at the same time derives the corresponding mathematical model. As regards the nonlinear control part, the nonlinear controller is designed by integrating the integral sliding mode control method and backstepping control method. Meanwhile, considering the uncertainties including external disturbances, measurement errors and modelling errors, an observer based on the radial basis function neural network (RBFNN) is proposed to estimate the uncertainties to offset their influence. Then, the stability of the control system is proved by Lyapunov stability criterion. Finally, the simulation results prove that the proposed control scheme can realize the stability of the microgrid system in several operation modes and ensure the sound dynamic performance with quick response comparing with other nonlinear control methods.

Low Impedance-Guaranteed Gain-Scheduled GESO for Torque-Controlled VSA With Application of Exoskeleton-Assisted Sit-to-Stand

This article investigates a closed-loop torque-controlled variable stiffness actuator (VSA) combined with a disturbance observer for enhancing low output impedance. We implement the generalized extended state observer (GESO) for conveniently testing the stability of the time-varying VSA system. In our application, the GESO is also required to serve the operation of the low- and high-impedance task. Here, the most important aspect is to consider the influence of the physical stiffness on the output impedance, because the VSA has been regulated with the closed-loop torque control. Through the interaction-torque experiments, we verify that using the fast dynamics GESO with the low-stiffness actuator can achieve low output impedance and stable interaction under the reachable frequency of a human. These properties contribute to perform the low-impedance task. When performing the high-impedance task, where a large torque command is needed, the high-stiffness actuator and the slow dynamics GESO are implemented to achieve high bandwidth and proper tracking performance. The continuously variable observer responses in accordance with the stiffness values are achieved via the gain-scheduling control. Moreover, the present closed-loop linear parameter varying system can be verified to be quadratically stable. The VSA system is then implemented on a knee exoskeleton for a sit-to-stand application. The reference command of the exoskeleton is a joint torque, calculated from the inverse dynamics. This torque signal is also used as the reference command of the stiffness motor of the VSA. The effectiveness of the exoskeleton system is experimentally verified with one healthy volunteer. Subsequently, another two healthy volunteers also successfully experienced the system.

A New PID Controller Circuit Design Using CFOAs

In this study, a new CFOA-based PID controller circuit is designed and implemented by a systematic approach employing signal-flow graph theory which is a powerful tool for active circuit design. The proposed circuit has independently adjustable PID parameters ( $$K_\mathrm{P}$$ , $$K_\mathrm{I}$$ , $$K_\mathrm{D}$$ ) which are independently controlled by only one passive element. Having high input and low output impedances, it has the ability to cascade with other circuits. The proposed PID circuit is examined in a closed-loop control system with an example plant circuit. Mathematical analyses are performed and discussed. The PID controller is realized by using commercially available integrated circuit elements, and results are given to demonstrate the performance of the proposed PID controller.

New mixed‐mode second‐generation voltage conveyor based first‐order all‐pass filter

A new plus-type second-generation voltage conveyor (VCII+) based first-order mixed-mode (MM) all-pass (AP) filter is proposed in this study. The proposed MM AP filter employs two VCII+s, three resistors and one grounded capacitor. It has low input and high output impedances for the current-mode selection while it has low input and low output impedances for the transimpedance-mode selection. The AP filter gain is unity for the current output while it is adjustable for the voltage output via a grounded resistor. However, a single passive component matching condition is needed for the proposed MM AP filter. Complete non-ideal analysis by taking into account all the parasitic resistors and non-ideal gains of the VCII+ is performed. The presented theory is verified through SPICE simulations by using supply voltage of ± 0.9 V and 0.18 μm Taiwan Semiconductor Manufacturing Company complementary metal oxide semiconductor technology parameters.

The CMOS Highly Linear Current Amplifier with Current Controlled Gain for Sensor Measurement Applications.

This paper introduces a new current-controlled current-amplifier suitable for precise measurement applications. This amplifier was developed with strong emphasis on linearity leading to low total harmonic distortion (THD) of the output signal, and on linearity of the gain control. The presented circuit is characterized by low input and high output impedances. Current consumption is significantly smaller than with conventional quadratic current multipliers and is comparable in order to the maximum processed input current, which is ±200 µA. This circuit is supposed to be used in many sensor applications, as well as a precise current multiplier for general analog current signal processing. The presented amplifier (current multiplier) was designed by an uncommon topology based on linear sub-blocks using MOS transistors working in their linear region. The described circuit was designed and fabricated in a C035 I3T25 0.35-µm ON Semiconductor process because of the demand of the intended application for higher supply voltage. Nevertheless, the topology is suitable also for modern smaller CMOS technologies and lower supply voltages. The performance of the circuit was verified by laboratory measurement with parameters comparable to the Cadence simulation results and presented here.

Resistorless current mode precision rectifier using EXCCII

In this paper, a new current mode precision rectifier circuit is proposed using a single EXCCII and two nMOS transistors. The novelty of the circuit is that it can provide all the possible rectified outputs, namely ± full wave as well as ± half wave simultaneously without any alteration of topology. Moreover, it has low input impedance and high output impedance, which is suitable for fully cascadable operation. It is suitable for a very high frequency of operation. The operating frequency is found to be 125 MHz and above. The temperature, average DC voltage output, noise, power consumption, input dynamic range (± 500 µA), Monte-Carlo and total harmonic distortion analysis are carried out to check the performance quality. The conversion of sinusoidal signal to root-mean-square circuit is also included here as an application of the proposed rectifier The proposed circuit is simulated using Cadence ORCAD PSpice simulator with 0.18 µm CMOS technology parameters. Simulation results agree well with the theoretical analysis.