RLC Filter Research Articles

HISTORY AND PROGRESS OF THE KERWIN–HUELSMAN–NEWCOMB FILTER GENERATION AND OP AMP REALIZATIONS

The history of Kerwin–Huelsman–Newcomb (KHN) second-order filter is reviewed. A generation method of the KHN filter from passive RLC filter is presented. Two alternative forms of the KHN circuit using operational amplifier are reviewed. The effect of finite gain-bandwidth of the op amps is considered and expressions of the actual ω0and Q are given. Two KHN circuits with inherently stable Q factor are also included. Two new partially compensated inverted KHN circuits are introduced. Active compensation methods to improve the KHN and the inverted KHN circuit performance for high Q designs are summarized. Spice simulation results are given. The progress of the KHN realizations using the current conveyor is also summarized briefly.

HISTORY AND PROGRESS OF THE TOW–THOMAS BI-QUADRATIC FILTER PART I: GENERATION AND OP AMP REALIZATIONS

The history of Tow–Thomas second-order filter is reviewed. Two alternative generation methods of the Tow–Thomas filter are discussed. The first is a generation method from the second-order passive RLC filter and the second is from the multiple feedbacks inverting low-pass filter using a single op amp. Several forms of the circuit are briefly reviewed. Passive and active compensation methods to improve the circuit performance for high-Q designs are summarized. Spice simulation results are included.

A Note on the Multiplicity of Poles in the Vector Fitting Macromodeling Method

Vector fitting is a robust macromodeling tool for rational approximation of spectral data obtained by full-wave electromagnetic simulators or high-frequency measurements. The technique iteratively calculates a suitable set of poles, and solves the residues of the transfer function in a two-step procedure. If poles with a higher order multiplicity occur during the pole-identification step, numerical problems and inaccuracies can result, especially if the normal equations are solved. This problem is illustrated on an RLC filter, and a generalization of the basis functions is proposed to resolve the issue

A Novel Inverter-Output Passive Filter for Reducing Both Differential- and Common-Mode $dv/dt$ at the Motor Terminals in PWM Drive Systems

A novel inverter-output filter, which cannot only filter the differential-mode voltage dv/dt but also suppress the common-mode voltage dv/dt and their rms values, is proposed in this paper. The filter is in combination with a conventional RLC filter and a common-mode transformer. The main advantage is that the functions of filtering a differential-mode voltage and suppressing a common-mode voltage can be integrated into a single system. Furthermore, the structure and design of the proposed filter are rather simple because only passive components are used. Simulations and experiments are conducted to validate the performance of the proposed filter. Both of their results indicate that about 80% of the rms value of the common-mode voltage are suppressed, while the demand of differential-mode voltage filtering is still met

Pulse generation scheme for low-power low-complexity impulse ultra-wideband

A pulse generation scheme for low-power, low-complexity impulse ultra-wideband is presented. By employing the finite impulse response function inherent in digital circuitry to shape the spectrum, the analogue pulse shaping filter could be reduced to a low-Q RLC filter, and the designed composite pulses could be generated and efficiently amplified in the digital domain. This scheme is demonstrated with generation of two composite pulses for the two potential IEEE 802.15.4a bands.

A compensator for attenuation of wave reflections in long cable actuator–plant interconnections with guaranteed stability

The wave reflection phenomenon that appears when actuator and plant are connected through long cables is studied in this paper. In several applications, the perturbation induced by the presence of these reflected waves is non-negligible and seriously degrades the performance of the control and the operation of the system. Standard compensation schemes are based on matching impedances at specific frequencies (possibly infinity) and are realized with the addition of linear RLC filters. Impedance matching is ineffective if there is no single dominant frequency in the system and/or the plant is highly uncertain. In a recent paper the authors proposed a novel compensator design framework, based on the scattering representation of the transmission line, which is applicable for the latter scenario. In contrast with standard schemes the compensators are active and require for their implementation regulated sources placed either on actuator or on plant side. The use of active compensators raises the issues of well-posedness and stability of the design. The former was addressed in our previous work making a critical discretization assumption that generated an approximated finite-dimensional model; on the other hand, the stability question was left open. Both issues are fully solved in the present note for the complete infinite-dimensional system. We propose a family of adaptive compensators that requires only knowledge of the line propagation delay and guarantees stable asymptotic regulation for all (unknown) linear plants and actuators with passive impedances. Furthermore, under some additional reasonable assumptions, transient performance improvement is ensured. Some simulation results on a benchmark example of voltage overshoot suppression in AC drives are shown.

Improving the performance of hysteresis direct torque control of IPMSM using active filter topology

This paper describes an active filter topology to improve the performance of hysteresis direct torque control (HDTC) of interior permanent magnet synchronous motor (IPMSM). The filter topology consists of an active filter and two RLC filters, and is connected to the main power circuit through a 1:1 transformer. The active filter is characterized by detecting the harmonics in the motor phase voltages and injecting equivalent harmonic voltages to produce almost sinusoidal voltage waveform to the motor terminals. The active filter uses hysteresis voltage controller while the motor main circuit uses hysteresis direct torque control. The simulation results of this combined control structure show considerable torque ripple reduction in the steady state range and adequate dynamic torque performance as well as considerable harmonic voltage and EMI noise reduction.

Measurements of a Persistent-Current Qubit Driven by an On-Chip Radiation Source

Monolithic integration of control electronics with superconducting qubits will facilitate scalability of a superconducting quantum computer by reducing the room temperature electronics necessary for performing quantum state manipulation. We report the experimental results of the monolithic integration of an on-chip radiation source with a persistent-current (PC) qubit and dc SQUID measurement device. The devices were fabricated at MIT Lincoln Laboratory in a Nb/Al/AlOx/Nb trilayer process. The two PC qubit states were detected by measuring the switching current of an underdamped dc SQUID magnetometer inductively coupled to the qubit. The radiation source comprised an overdamped dc SQUID operating in the voltage state and inductively coupled to the qubit and measurement SQUID through a low-Q RLC filter. The oscillator was designed to have tunable amplitude and frequency to satisfy the requirements for coherent quantum manipulation of a superconducting PC qubit. We will discuss the measurements in the millikelvin regime and the effects of the oscillator noise on the state of the qubit.

Filter Networks for Long Cable Drives and Their Influence on Motor Voltage Distribution and Common-Mode Currents

Filter networks for long cable drives have been studied in the last decade to solve the overvoltage problem at the motor terminals. However, little research has been dedicated to analyze their influence on the voltage distribution in the motor stator winding and on the circulation of the common-mode currents. In this paper, the project of dv/dt filters through simulation and analysis from previous work is extended, including the motor voltage distribution and common-mode current analysis. Simulation and experimental results are presented, demonstrating the usefulness of the filter networks on the motor overvoltage mitigation. Three filter topologies will be discussed and compared here: RLC filter at the motor terminals, RLC filter at the inverter output and reactor filter, which is extensively used in the industry. Simulation and experimental results demonstrate that the RLC filter at the inverter output is the most interesting solution among the main types of passive filter networks.

Low-reflection bandpass filters with a flat group delay

Recently, low-reflection low-pass RLC filters with a linear phase characteristic have been reported. This paper is an extension of this study on bandpass filters, including their realizations with lumped-element and distributed-parameter networks. A topology particularly suitable for microstrip techniques is proposed. It yields a compact design that enables miniaturization and is easy for manufacturing and tuning.

A COMPENSATOR FOR ATTENUATION OF WAVE REFLECTIONS IN LONG CABLE ACTUATOR-PLANT INTERCONNECTIONS WITH GUARANTEED TRANSIENT PERFORMANCE IMPROVEMENT

The wave reflection phenomenon that appears when actuator and plant are connected through long cables is studied in this paper. In several applications, the perturbation induced by the presence of these reflected waves is non–negligible and seriously degrades the performance of the control and the operativity of the system. Standard compensation schemes are based on matching impedances at specific frequencies (possibly infinity) and are realized with the addition of linear RLC filters. Impedance matching is clearly ineffective if there is no single dominant frequency in the system and–or the plant is highly uncertain. In a recent paper the authors proposed a novel compensator design framework, based on the scattering representation of the transmission line, that is applicable for the latter scenario. In contrast with the standard schemes the compensators are active and require for their implementation regulated sources placed either on actuator or plant side. The use of active compensators raises the issue of ensuring stability of the design, a point left open in our previous work, that is fully solved in the present note. We propose a family of compensators that requires only knowledge of cable characteristics and—under some practically reasonable assumptions—guarantees transient performance improvement and asymptotic tracking for all (unknown) plants with passive impedance.

Overvoltage Suppression Filter Design Methods Based on Voltage Reflection Theory

To reduce voltage overshoot at the motor terminal, RLC filters are used at the inverter side with an objective of increasing the rise time, while RC filters are used at the motor side as a means of reducing the load impedance at high frequency. However, no clear optimal method for determining the filter parameters has appeared. In this work, we propose filter design methods that fully utilize given conditions such as cable length, cable inductance, cable capacitance, and the reflection coefficient at the inverter side. For determining the parameters of the RLC filter, the filter transfer function is utilized to make the rise time long enough to achieve desirable overshoot level at motor terminals. In choosing the parameters of the RC filter, the reflection coefficient is regarded as a transfer function between the incident and reflected voltages, and the capacitance is chosen so that cancellation occurs between the reflected voltage and its resulting incident voltage. The validity of the proposed design method is supported by simulation results, which are also compared with the experimental results.

Damping of capacitive voltage substations ferroresonance using a suitable RLC filter

The underlying theory and model of capacitive voltage substations and its associated problems are described. This system is intended to supply electricity to rural communities directly from high-voltage transmission lines. This technique leads to important cost reductions when compared with conventional alternatives. However, in several transient cases, some problems such as ferroresonance and overvoltages could occur in these substations. Using a developed capacitive substation model these transient cases are simulated. A suitable filter is designed to damp overvoltages due to ferroresonance. Analytical aspects of filter design are presented and some computer simulation tests are provided to highlight the usefulness of the proposed filter.

On a class of low-reflection transmission-line quasi-gaussian low-pass filters and their lumped-element approximations

Gaussian-like filters are frequently used in digital signal transmission. Usually, these filters are made of lumped inductors and capacitors. In the stopband, these filters exhibit a high reflection, which can create unwanted signal interference. To prevent that, a new low-reflection ladder network is introduced that consist of resistors, inductors, and capacitors. The network models fictitious transmission lines with Gaussian-like amplitude characteristics. Starting from the analysis of this network, a procedure is developed for synthesis of a new class of lumped-element RLC filters. These filters have transmission coefficients similar to the classical Bessel filters. In contrast to the Bessel filters, the new filters exhibit a low reflection both in the stopband and passband, they have a small span of element parameters, and they are easy for manufacturing and tuning.

Next generation integral passives: materials, processes, and integration of resistors and capacitors on PWB substrates

Integral passives are becoming increasingly important in realizing next generation electronics industry needs through gradual replacement of discretes. The need for integral passives emerges from the increasing consumer demand for product miniaturization thus requiring components to be smaller and packaging to be space efficient. In this paper, the feasibility of integration of polymer/ceramic thin film (∼5 μm thick) capacitors (C) with other passive components such as resistors (R) and inductors (L) has been discussed. An integrated RC network requiring relatively large capacitance and resistance is selected as a model for co-integration of R and C components using low temperature PWB compatible fabrication processes. This test vehicle is a subset of a large electrical circuit of a functional medical device. In order to produce higher capacitance density and reduce in-plane device area, multi-layer (currently two-layer) capacitors are stacked in the thickness direction. A commercially available Ohmega-Ply resistor/conductor material is selected for integral resistors. Resistors were fabricated using a multi-step lithography process with the utilization of two separate masks. Bottom copper electrodes for capacitors were also defined during the resistor fabrication process. Photodefinable epoxies filled with a high permittivity ceramic powder were used for fabrication of thin film capacitors. Epoxy and ceramic powders were mixed in the required proportion and blended using a high shear apparatus. The coating solution was homogenized in a roll miller for 3 to 5 days prior to casting in order to prevent settling of the higher density ceramic particles. Capacitors were fabricated by spin-coating on the sub-etched copper electrodes. The deposited dielectric layers were dried, exposed with UV radiation, patterned, and thermally cured. Top capacitor electrodes (copper) were deposited using a metal or an e-beam evaporator. The electrodes were patterned using the standard photolithography processes. Selected good samples were used for depositing the second capacitor layer. The RC network is extended to incorporate electroplated polymer/ferrite core micro-inductors through the fabrication of an industry prototype low pass RLC filter. Meniscus coating was evaluated for large area manufacturing with high process yield. A capacitance density of ∼3 nF cm−2 was obtained on a single layer capacitor with ∼6 μm thick films. The capacitance density was increased to ∼6 nF cm−2 with the two-layer deposition process. The capacitors were relatively stable up to a frequency range of 120 Hz to 100 KHz. Meniscus coating was qualified to be a viable manufacturable method for depositing polymer/ceramic capacitors on large area (300mm x 300mm) PWB substrates. Dielectric constant values in the range of 3.5 to 35 with increase in filler loading up to 45 vol% were achieved in the epoxy nanocomposite system where the dielectric constant of the host polymer was limited to ∼3.5. Higher dielectric constant polymers are required to meet the increasingly higher capacitance needs for the next generation electronics packaging. Possible avenues for achieving higher capacitance density in polymer/ceramic nanocomposite system have been discussed.

Generation of current conveyor based lowpass filters from a passive RLC filter

It is shown that three recently reported current conveyor based lowpass filters are originated from a passive RLC filter. Two new grounded-capacitor current mode lowpass filters are also introduced. Frequency limitation equations based on the non-ideal current conveyors are given. PSpice simulation results are included.

Generation of CCII and CFOA filters from passive RLC filters

It is shown that low-sensitivity active filters employing the current conveyor (CCII) or the current feedback operational amplifier (CFOA) as the active element can be generated directly from passive RLC filters. New current-mode filters using CCII and voltage mode filters using the CFOA are generated from three alternative passive RLC filters. The proposed circuits have the advantage that compensation of the dominant parasitic elements of the CCII or the CFOA can be easily achieved. PSpice simulation results are included.

A CMOS programmable balanced output transconductor for analogue signal processing

A new CMOS programmable balanced output transconductor (BOTA) is introduced. The BOTA is a useful block for continuous-time analogue signal processing. A new CMOS realization of the BOTA is given. The proposed realization is based on the cascaded connection of a new voltage controlled differential transconductor, a voltage controlled MOS grounded resistor and a balanced output transconductor stage. Applications of the BOTA in realizing a floating resistor, a balanced output differential integrator, a continuous-time balanced output bandpass–lowpass filter, a floating inductor and the active realization of the RLC filters using a minimum number of the BOTA are given. PSpice simulation results for the BOTA circuit and for its applications are also given.

A Si 1.8 GHz RLC filter with tunable center frequency and quality factor

A second-order active bandpass filter using integrated inductors was implemented in Si bipolar technology. The filter uses special techniques to make the quality factor and the center frequency tunable. For a nominal center frequency of 1.8 GHz and a quality factor of 35, the filter has 1 dB compression dynamic range of 40 dB, and draws 8.7 mA from a 2.8 V supply.

RLC active filters with electronically tunable centre frequency and quality factor

The Letter discusses techniques for the electronic tuning of inductors and capacitors, and for the active compensation of their losses and thus the enhancement of their quality factors. Applications to integrated RLC filters using on-chip inductors are considered.