pF Capacitance Research Articles

New proposed method for traceability dissemination of capacitance measurements

Capacitance measurements at the National Institute of Standards (NIS), Egypt, are traceable to the Bureau International des Poids et Mesures (BIPM). It calibrates the main NIS standard capacitors, AH11A. In this paper, traceability of the BIPM capacitance measurements could be used to evaluate a new accurate measurement method through an Ultra-Precision Capacitance Bridge. The new method is carefully described by introducing some necessary equations and a demonstrating chart. Verification of this new method has been realized by comparing its results for the 10 pF and 100 pF capacitance standards with the results obtained by the conventional substitution method at 1 kHz and 1.592 kHz. The relative differences between the two methods are about 0.3 µF/F, which reflect the accuracy of the new measurement method. For higher capacitance ranges, the new measurement method has been applied for the capacitance measurements up to 1 μF at 1 kHz. The relative differences between the two methods are in the range of 5.5 µF/F on the average which proves the acceptable accuracy and the reliability of the new method to be used.

Ns-pulsewidth pulsed power supply by regulating electrical parameters for AFM nano EDM of nm-removal-resolution

Nano electro discharge machining (nano EDM), as a frontier processing method in the research stage of exploration, has an important application prospect in the machining of metal and alloy materials for achieving nanoscale removal resolution. A pulsed power supply used in nano EDM is expected to limit a single pulse energy to nJ order of magnitude for improving the removal resolution of single pulsed discharge even to nanoscale. One developing direction is to decrease pulsewidth of the pulsed power supply. Conventional pulsed power supplies hardly output a single pulse and continuous pulses with nanosecond (ns) pulsewidth, resulting in too large single pulsed energy of μJ order of magnitude usually. In this research, a novel pulsed power supply is designed for realizing the ns-pulsewidth with controllable pulsewidth and peak voltage. The key novelty lies in a cascaded circuit with two triodes working in the state of ultra-fast avalanche conduction, where pF capacitors are applied to adjust the pulsewidth and pulsed energy precisely. Performance tests verified that a single pulse of 5 ns pulsewidth or continuous pulses up to 9 MHz can be outputted. Furthermore, nano EDM experiments of single pulsed discharge are carried out under the conditions of nanometer (nm) discharge gap and nm-tip tool electrode based on an atomic force microscope (AFM) system. The special results are achieved: a single pulsed energy can reach down to 1.75 nJ by outputting a pulsewidth of 10 ns, and a nano-EDM crater is only about 182 nm in diameter with regular shape and little recasting. Those results verify the possibility of AFM-tip-based nano EDM for machining nanostructures.

Efficiency Improvement of Dual-Band Wireless Power Transfer (DB-WPT) System with U-shape Resonator and Capacitively Loaded E-shape Defected Ground Structure (DGS)

This paper suggests a design for dual-band wireless power transfer systems that use E-shape defected ground structure resonator loaded with a 1.5 pF capacitor and U-shape resonator at the top layer. When the two resonators of the proposed design are coupled back-to-back, it transfers to a dual band-pass filter leading to an efficient WPT system working at 0.9 GHz and 1.4 GHz. A compact size of 20 mm × 20 mm is fabricated achieving a WPT efficiency of more than 97% at a distance of 16 mm for both bands. Good concurrences among the equivalent circuit model (ECM), the theoretical studies, and the measurements have been attained.

Magnetic Sensor Based on Giant Magneto-Impedance in Commercial Inductors

Magnetic sensors have various applications in navigation, power distribution, robotics, factory automation, and medical diagnosis. The development of highly sensitive magnetic sensors usually requires complicated and costly fabrication process. Herein, we report giant magneto-impedance of 41036% in the commercially available ferrite core inductors. A magnetic field detection limit of 10 nT at 1 Hz has been obtained by directly measuring the impedance of the as-obtained inductor without any optimization. With a 100 pF capacitor in series connection with the inductor where lower impedance facilitates the measurement process, a limit of detection of 625 pT at 1 Hz has been obtained in the series <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RLC</i> resonator. These results can be understood in terms of the magnetic field-dependent self-resonance in the inductors which act as lumped <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RLC</i> resonators. Compared with the traditional electromagnetic induction sensing mode, the magneto-impedance sensing mode shows 5000 folds improvement in the magnetic field detection capability.

A cross-coupled symmetric floating impedance scaler with enhanced bandwidth and accuracy

Capacitors realized using symmetric floating impedance scaling (SFIS) are area efficient. They are preferred for the implementation of fully differential filters for biomedical applications. The SFIS reported in the literature has poor accuracy and lower effective bandwidth. In this paper, a cross coupled symmetric floating impedance scaling (CC-SFIS) with enhanced bandwidth and accuracy is proposed. To evaluate its performance, a 500 pF capacitor is implemented in UMC 180 nm CMOS technology with a base capacitor (Cb) of 10 pF using both CC-SFIS and source follower based SFIS (SF-SFIS). The magnitude and phase of the impedance of the capacitor realized using CC-SFIS and SF-SFIS are obtained through post-layout simulations. CC-SFIS requires 53.68% lower area, 62.39% lower power consumption, and 88% higher accuracy than SF-SFIS. Fully differential 2nd order Butterworth low pass filters with cutoff frequency of 100Hz are implemented in UMC 180 nm technology using both CC-SFIS and SF-SFIS capacitors. Their performances are evaluated through simulation. From this, it is found that the deviation in the cut off frequency of the filter using CC-SFIS is smaller (2%) compared to that using SF-SFIS (40%) circuit.

Noise-Resistant CECG Using Novel Capacitive Electrodes.

For years, capacitive electrocardiogram (CECG) has been known to be susceptible to ambient interference. In light of this, a novel capacitive electrode was developed as an effective way to reduce the interference effect. This was done by simply introducing the capacitive elector in series with a 1 pF capacitor, and the 60 Hz common mode noise induced by AC power lines was cancelled using a capacitive right leg (CRL) circuit. The proposed electrode did as expected outperform two counterparts in terms of SNR, and particularly gave an up to 99.8% correlation between RRIs extracted from an ECG and a CECG signal, a figure far beyond 52% and 63% using the two counterparts. This capacitive electrode was originally designed for long-term noncontact monitoring of heart rate, and hopefully can be integrated to portable devices for other medical care services in the near future.

High current operational amplifier with current limiting protection circuit

In this work, a class-AB operational amplifier is to be presented, which is developed in a 0.5 μm CDMOS technology. The proposed amplifier is composed of a folded cascade input stage and a class-AB output stage. Owing to the special design of the operational amplifier, the robustness of the whole circuit has been enhanced. The proposed system can drive a wide resistance load range from 10 Ω to 100 kΩ with a 10 pF capacitance load without distortion and stability problems. In addition, a current-limit technique that stems from the design of a low dropout linear regulator is adopted to protect the output stage of the operational amplifier from being damaged by a huge transient current under unexpected conditions (when the output terminal is shorted to ground or V DD). Measurement results show that the maximum output current is nearly 390 mA with an 800 mA DC current limiting protection circuit on the single 5 V power supply at room temperature. This design can stably work at the industrial temperature range from −40 to 125°C. What is more, the total static current consumption of the whole circuit is 624 μA and the chip area is 0.419 mm2.

Capacitively-Loaded Feed Line to Improve mm-Wave and Sub-6 GHz Antenna Co-Existence

The co-existence of millimeter-wave (mm-wave) and sub-6GHz antennas in a smartphone presents many performance-limiting aspects. When both antennas are attached to the metal frame, the feed lines of the mm-wave antennas might short-circuit the sub-6GHz antennas, and thus, may significantly affect their performance. This paper presents a method to design feed lines that function as transmission lines at mm-wave frequencies but correspond to open circuits at sub-6GHz. This study determines, in theory, the smallest achievable capacitive loading with different line types and experimentally validates the approach. The capacitive loading due to the feed line is small enough to maintain the sub-6GHz performance. At the mm-wave band, the insertion loss of the line is 1dB with a measured reflection coefficient below −10dB. The introduced common-mode capacitive load of the feed line on the sub-6GHz antennas corresponds to 0.19pF capacitance.

A Generic Test Board for the Electrical Characterization of ULP and ULV Fully-Differential Integrated Analog Circuits

The characterization of ultra-low power (ULP) fully-differential/balanced amplifiers and active filters is challenging due to the incompatibility with the classical single-ended (SE) and 50 Ω impedance equipment. Interface circuits between the device under test (DUT) and the equipment are needed to perform the signal conversion and to work as voltage buffers. In this work, we propose a generic test circuits to be used in the characterization of ULP and ultra-low voltage (ULV) analog circuits. The test board includes balun transformers to the signal conversion, a high input impedance and low capacitance output driver and voltage regulators to provide the target DUT supply voltage. The characterization of the proposed PCB demonstrates a bandwidth of 30 MHz, output driver input impedance of 5 MΩ with 2.5 pF capacitance and low input-referred noise. The proposed circuit was applied to the electrical characterization of two fully-differential ULV and ULP analog integrated circuits.

Design of Demodulation Circuit And Arduino Uno Microcontroller Syncronization For Capacitance Sensor

An AC signal is produced by oscillator or a similar circuit that includes demodulation. In addition to thedemodulation circuit, there is also need interface circuit which include signal conditioning, signal processing anddata acquisition. So that, the frequency can be read digitally. The purpose of this research was to createdemodulation circuit in form of colpitts-crystal oscillator and microcontroller. This research carried out severalstage. There are making colpitts-crystal oscillator, microcontroller synchronization, data retrieval and processingoutput. The DC voltage variations are 3.2 V, 9 V and 15.9 V and capacitor variations are 470 pF, 4.7 nF and 33nF. Output data in form of frequencies measured by using oscilloscope. Futhermore, the data is tested for accuracyand precision. From the test result using 470 pF, 4.7 nF and 33 nF capacitors when given 3.2 V input voltage, theprecision values were 91.35%, 93.06% and 96.17% and the accuracy value were 97.72%, 97.96%, and 98.17%.For 9 V input voltage, the precision values were 99.82%, 97.67% and 97.52% and the accuracy value were 99%,98.90%, and 98.92%. Whereas 15.9 V input voltage, the precision values were 93.43%, 96.92% and 93.66% andthe accuracy value were 98.08%, 98.75%, and 97.60%. From these data, it can be concluded that a good voltagevalue used in this ciecuit is 9 V with 470 pF capacitor where the precision value was 99.82% and the accuracyvalue was 99%.

A High Gain, 808MHz GBW Four-Stage OTA in 65nm CMOS

A four-stage operational transconductance amplifier (OTA) with a novel compensation structure combining multipath [Formula: see text]-[Formula: see text] compensation and no capacitor feed-forward compensation is proposed in this paper. Based on the small-signal model, stability analysis and design consideration are carried out to demonstrate the stability of the compensation technique. To verify the effectiveness of the compensation scheme, the proposed OTA which drives a 2 pF capacitance, is simulated in TSMC 65[Formula: see text]nm 1.2[Formula: see text]V CMOS process, achieving 808[Formula: see text]MHz gain-bandwidth, 119[Formula: see text]dB DC gain, 585[Formula: see text]V/[Formula: see text]s slew rate (SR) and 6 ns 1% settling time. The circuit is operated at the single supply voltage of 1.2[Formula: see text]V with power consumption of 2.17[Formula: see text]mW and the layout area is 0.011[Formula: see text]mm2.

Supply-Inverted Bipolar Pulser and Tx/Rx Switch for CMUTs Above the Process Limit for High Pressure Pulse Generation.

A combined supply-inverted bipolar pulser and a Tx/Rx switch is proposed to drive capacitive micromachined ultrasonic transducers (CMUTs). The supply-inverted bipolar pulser adopts a bootstrap circuit combined with stacked transistors, which guarantees high voltage (HV) operation above the process limit without lowering device reliability. This circuit generates an output signal with a peak-to-peak voltage that is almost twice the supply level. It generates a bipolar pulse with only positive supply voltages. The Tx/Rx switch adopts a diode-bridge structure with the protection scheme dedicated to this proposed pulser. A proof- of-concept ASIC prototype has been implemented in 0.18-μm HV CMOS/DMOS technology with 60 V devices. Measurement results show that the proposed pulser can safely generate a bipolar pulse of -34.6 to 45 V, from a single 45 V supply voltage. The Tx/Rx switch blocks the HV bipolar pulse, resulting in less than 1.6 V at the input of the receiver. Acoustic measurements are performed connecting the pulser to CMUTs with 2 pF capacitance and 8 MHz center frequency. The variation of acoustic output pressures for different pulse shapes were simulated with the large signal CMUT model and compared with the experimental results for transmit pressure optimization. A potential implementation of the methods using MEMS fabrication methods is also described.

Parameterized Nanosecond Pulse Realization Through Parametrical Modulation of Timing Sequence of Switches in Marx Circuit

The characteristics of gas discharge are closely related to the features of high-voltage pulses, especially to the rising and falling time of pulse. A parameterized pulse control method based on improved Marx generator is proposed to obtain parameterized nanosecond high-voltage pulses to match different discharge circumstances. Different parameters of nanosecond pulses are realized in real time by parametrical modulating timing sequences of switches in an improved Marx generator. Experimental results indicate that the ability of generating pulses is with 0–20 kV amplitude, 0–1 ms width (flat top), 50–500 ns or faster rising/falling time, below 5% overshoot, and a maximum 5 kHz repetitive frequency at 20 kV on a matched 0–100 pF capacitance load. The shape of pulse waveform including triangular, rectangular, or the combination of the two kinds of pulse waveform can be achieved. The discharge characteristics in the dielectric barrier discharge device driven by the parameterized pulse, especially changing the rising time of pulse, are investigated. The uniform discharge is observed, and the discharge intensity is doubled while reducing the rising time of pulse from 500 to 50 ns, and the intensity of the N2 spectrum increased to 2.5 times.

Monolithic radio frequency SiNx self-rolled-up nanomembrane interdigital capacitor modeling and fabrication

Monolithic capacitors operating at radio frequencies (RF) serve as critical components in integrated circuits for wireless communication. Design and fabrication innovations for high capacitance density RF capacitors are highly desired for the miniaturization of RFIC chips. However, practical and simple solutions are limited by existing capabilities in three-dimensional (3D) structure construction and the effective configuration of electrodes. We report a unique route to achieve unprecedentedly high capacitance density at a high operating frequency through a capacitor configuration of 3D coil interdigital electrodes using planar semiconductor processing compatible materials and fabrication methods. A systematic mechanical-electrical design principle is demonstrated, and fabricated devices show a maximum 21.5 pF capacitance, which is 17.2× larger after rolling up. The corresponding capacitance density is as large as 371 pF mm−2, with resonant frequency of 1.5 GHz. The performance could be improved significantly by simply rolling up more turns with minimal change to the area footprint.

A HEMT-based cryogenic charge amplifier with sub-100 eVee ionization resolution for massive semiconductor dark matter detectors

We present the measured baseline ionization resolution of a HEMT-based cryogenic charge amplifier coupled to a CDMS-II detector. The amplifier has been developed to allow massive semiconductor dark matter detectors to retain background discrimination at the low recoil energies produced by low-mass WIMPs. We find a calibrated baseline ionization resolution of $\sigma_E = 91\,\text{eV}_{ee}$. To our knowledge, this is the best direct ionization resolution achieved with such massive ($\approx$150 pF capacitance) radiation detectors.

Traceability Chain at KRISS from DC Quantum Hall Resistance to Farad Using Coaxial Bridges

A national traceability chain from dc quantum Hall resistance (QHR) to capacitance has been established at Korea Research Institute of Standards and Science using various impedance standards and coaxial bridges. An ac–dc calculable resistance standard of nominal value of 12.9 $\text{k}\Omega $ was used as a transfer standard from dc to ac at the frequency of 1.541 kHz. Two ac coaxial bridges, developed by INRiM, were employed: a ratio bridge, linking the 103- $\text{k}\Omega $ ac resistor to the 12.9- $\text{k}\Omega $ ac–dc calculable resistor calibrated in terms of the dc QHR and a quadrature bridge, calibrating the 1000 pF capacitors versus the 103- $\text{k}\Omega $ ac resistors. The ratio bridge defines the 103- $\text{k}\Omega $ resistor as a two-terminal-pair (2TP) standard and the 12.9- $\text{k}\Omega $ resistor as a four-terminal-pair standard; a cable correction was applied to the 2TP defined standard. The stability of all standards has been monitored for more than 3 years to be within a few parts in 106. The capacitance value, obtained with the new traceability chain, shows an agreement (a few parts in 107) in a comparison with the reference values, traced from the National Institute for Standards and Technology (USA).

Practical Application of Latest Optimal Hollow Active Auxiliary Electrode in Vertical Calculable Cross-Capacitor at NIM

After continuous investigation on the electrical compensation method for the end effect error in the new vertical calculable cross-capacitor (VCCC), the latest optimal hollow active auxiliary electrode (OHAAE) has been developed and successfully substituted for the current geometrical nosepiece at one end of the movable guard electrode at the National Institute of Metrology, China (NIM). The critical electrical characteristics of the latest OHAAE are investigated by the model tests and eventually implemented with the least mechanical modifications to the new VCCC at NIM. The standard uncertainty of the reproduction of 1 pF capacitance unit from the new VCCC by adopting the latest OHAAE is decreased to $10.5 \times 10^{-9}$ in comparison with that of $20.0 \times 10^{-9}$ by the geometrical nosepiece.

Area and power efficient flipped voltage follower based symmetrical floating impedance scaler with improved accuracy for fully differential filters

A Source Follower based Symmetrical Floating Impedance Scaler (SF-SFIS) circuits are reported in the prior works, which realize large capacitors with the low area for a fully differential filter. In this paper, a novel Flipped Voltage Follower based Symmetrical Floating Impedance Scaler (FVF-SFIS) with high accuracy is presented. The proposed circuit based on flipped voltage follower with cascaded current mirrors can detect low base capacitors which have lower area and power than the prior SF-SFIS circuits. In order to evaluate its performance and comparison, a 500 pF capacitor is realized by multiplying the base capacitor of 10 pF using both FVF-SFIS and SF-SFIS methods. The magnitude and phase of these impedance scalers are obtained through post-layout simulation. It is found that the proposed impedance scaler requires 51.58% lower area, 69.23% lower power dissipation, and 91.33% higher accuracy than the SF-SFIS. The accuracy of the proposed FVF-SFIS is compared with SF-SFIS circuit by designing a 3rd order Chebyshev low pass filter (LPF) using FVF-SFIS and SF-SFIS with cut-off frequency 100 Hz. The circuit has been designed and simulated in UMC 180 nm technology.

Triode Electron Gun of the LUE-200 Linear Accelerator, IREN Facility of the Laboratory of Neutron Physics, Joint Institute for Nuclear Research

The electron injector (electron gun (EG)) is a triode system (cathode–control grid–anode with a second grid “wall”) with a grounded anode and an isolated filament shielded cathode supplied with a high-voltage (up to –240 kV) pulse from the thyratron modulator through a pulse transformer. The composition of the main systems is as follows: (1) triode gun, (2) pulse modulator of the gun, (3) pulse transformer, and (4) the equipment of the stand (high-voltage pulsed charging modulator, synchronizer with startup system, DC sources, vacuum equipment, power systems of control and monitoring, and focusing system). The triode gun is an electron injector with a heated oxide-barium cathode and a controlled startup on the grid of the cathode–grid node from the GS-34 microwave tube. The modulator consists of PFN of 380 pF capacitors with a total capacity of 12 nF with inductors of 0.66 µH composing a double forming line. The PFN charging is supplied from the high voltage source of TDK Lambda. Starting the grid with an adjustable delay to adjust the pulse duration from 40 to 400 ns of the beam injected from the cathode is done from the starting pulse of the cathode node from the first channel of the synchronizer. The thyratron modulator is launched from the second channel. As a result of adjustment, a beam with a current pulse of 5 A at focusing current 3.1 A of ML1 focusing solenoid at voltage 200–220 kV with a beam with a diameter of 5 mm at a frequency of 25 Hz is obtained. To switch to a frequency of 50 Hz, the current of the focusing solenoid is reduced to 1.5 A. In this case, the beam diameter increases to 1 cm. A stable mode of operation of the electron source is recorded for several tens of shifts.

Improved reversed nested miller frequency compensation technique based on current comparator for three-stage amplifiers

This paper attempts to propose a newly modified method to improve the frequency compensation of three-stage operational trans-conductance amplifiers. In the topology of the new frequency compensation, a current comparator is placed on the feedback path, while the common node of Miller compensation capacitors, the feedforward path, is removed by eliminating the right-half plane zero. This tremendously improves the phase margin, stability, and gain band width product. Compared with other available frequency compensation methods, the newly proposed method manages to improve the figure of merits and lower power consumption while significantly decreasing the dimensions of capacitors in the compensation network. The superiority of the new method over other conventional methods for reversed nested Miller compensation has been examined by a three stage amplifier that has been designed and simulated through a 180 nm standard library CMOS. The results indicate that the new amplifier has achieved a power consumption of 285 µW, gain band width product of 14 MHz, and phase margin of 86° with 100 pF capacitance load at the supply voltage of 1.8 V.