Carbon Nanotube Quantum Capacitance for Nonlinear Terahertz Circuits

In this paper, analog circuit applications of a nonlinear carbon nanotube (CNT) quantum capacitance such as frequency doublers and mixers are proposed. We present a balanced circuit implementation and derive the transconductance conversion gain for the nonlinear CNT quantum capacitor circuit. The balanced topology results in robust circuit performance that is insensitive to extrinsic capacitances and parasitic resistances, and is immune to the resistance of metallic nanotubes that may be in the channel. The ballistic quantum capacitance is useful up to several terahertzs (THzs), making it suitable for low-noise THz sources. Additionally, the fundamental bandwidth and performance limitations imposed by the quantum conductance and inductance are discussed.     

A New Quantum Formalism for Damping and Gain in Harmonic Oscillators

Abstract

A new formulation of loss or gain in the quantum theory of harmonic oscillators is put forward using a non-passive reactive circuit which can be readily quantized. The analysis is based on the electrical circuit theory and demonstrates how a circuit, with negative inductance ? L _n and negative capacitance ? C _n, coupled to a conventional harmonic oscillator circuit, of positive inductance L and positive capacitance C, can act as a source or sink of energy and allow for both gain and loss. Classically this series circuit is indistinguishable in its transients from either a + G or ? G conductance shunted across a main LC oscillator circuit. However, unlike the resistive circuit, this coupled circuit can be quantized, maintaining the uncertainty principle. A two-valued solution is found, dependent on whether the circuits are in a state to receive energy or a state to absorb energy. A full correspondence, including second-order frequency shifts, is found between the quantum and the classical solutions with states which are appropriate to thermodynamic equilibrium of a conductance at a temperature T as well as to the classical-like coherent states. While the accessible mode in the + L + C circuit does not exhibit any squeezing directly, the system as a whole is an example of two-mode squeezing discussed by other authors.     

An equivalent circuit model for dielectrics: polymeric materials

Multiple-arc analysis is used in conjunction with a generalized relaxation time distribution (GRTD) to derive an equivalent electric circuit model for dielectric materials that exhibit frequency dispersion. The validity of this new methodology is examined by comparing reported measurements of a.c. conductance and capacitance of a polymeric dielectric with those obtained from the equivalent circuit prediction. The values are shown to agree satisfactorily over the frequency range 100 to 850 kHz.     

Capacitance-type blade-tip clearance measurement system using adual amplifier with ramp/DC inputs and integration

The analysis and prototype results for a dual-amplifier circuit for measuring blade-tip clearance in turbine engines are presented. The capacitance between the blade tip and mounted capacitance electrode within a guard ring of a probe forms one of the feedback elements of an operational amplifier (op amp). The differential equation governing the circuit taking into consideration the nonideal features of the op amp was formulated and solved for two types of inputs (ramp and DC) that are of interest for the application. Under certain time-dependent constraints, it is shown that (1) with a ramp input the circuit has an output voltage proportional to the static tip clearance capacitance, and (2) with a DC input, the output is proportional to the derivative of the clearance capacitance. and subsequent integration recovers the dynamic capacitance. The technique accommodates long cable lengths and environmentally induced changes in cable and probe parameters. System implementation for both static and dynamic measurements having the same high sensitivity is also presented     

The maximal area of superconducting tunneling junction x-ray detectors determined by the required signal-to-noise ratio

The intrinsically high energy resolution of superconducting tunneling junctions (STJ) requires a low noise charge sensitive amplifier circuit. The noise sources of such a junction + amplifier circuit are discussed. The dominant noise sources are the series noise and the flicker noise of the FET input stage, amplified by the large input capacitance of the STJ-detector. Means to reduce this capacitance are discussed. Reducing the preamplifier noise by a factor of two and the height of the potential barrier of the insulating layer by two orders of magnitude, by keeping the large conductance of the junction constant, would allow an increase in junction area by a factor of 15.     

Scanning electrochemical microscopy, 52. Bipolar conductance technique at ultramicroelectrodes for resistance measurements

The bipolar conductance, BICON, technique for the measurement of solution resistance, based on the application of microsecond current pulses, as originally described by Enke and co-workers for measurements with conventional electrodes, was extended for use with ultramicroelectrodes, with a focus on its application in scanning electrochemical microscopy (SECM). When the plateau time used to make the measurement lies within the BICON conditions, the solution conductance can be obtained directly from the output without the need for calibration curves. However, decreasing the size of the ultramicroelectrode decreases the range of values that satisfy these conditions, and one must resort to calibration curves to obtain solution conductance from the measured current, which was nevertheless found to be proportional to electrolyte concentration with electrodes as small as 5 mum in diameter. BICON/SECM approach curves over insulating substrates followed SECM negative feedback theory and approach curves in the presence of low (micromolar) or no added electrolyte are possible once the background conductivity is taken into account. Approach curves to a conducting substrate at open circuit potential are influenced by the solution time constant (solution resistance at the electrode tip x electrode double layer capacitance), which is a function of the tip/substrate distance, as well as the substrate size.     

New Methods of Measuring Capacitance and Resistance of Very High Loss Materials at High Frequencies

Two new circuits for the accurate measurement of specimen capacitance and resistive loss are described. The capacitance measurements are unaffected by the specimen resistance when the parallel resistance is greater than 30 ?. The practicality of the circuit is enhanced by its use of coaxial cable to provide both connection to the sample and the inductance required for circuit operation. An important characteristic of the circuit is its ability to measure capacitance and resistance of very high loss specimens accurately.     

Capacitive Sensor Interface for an Electrostatically Levitated Micromotor

This paper presents the design and performance of a capacitive sensor interface dedicated to a microelectromechanical systems (MEMS) micromotor electrically levitated in five DOFs. The position and orientation of the rotor are detected by measuring differential rotor-electrode capacitances with a set of capacitance-to-voltage converters (CVCs). The sensor contains multiplexed electrodes for both capacitive sensing and force feedback, and a set of common electrodes for carrier exciting with an aim to eliminate ohmic connection with the levitated rotor. The proposed interface circuit is based on a symmetrical structure containing two half ac bridges, more robust against parasitic capacitances, capable of detecting capacitance changes with frequency higher than 10 kHz, and able to decouple multiaxis position signals of a levitated rotor. An electronic equivalent model of the sensing circuit has been developed and used to analyze the sensor performance. The major nonidealities and their effects on the accuracy of the position sensing are discussed. The performance of the sensing circuit was experimentally investigated on a prototype interface circuit. The experimental results confirm the principles of operation and the performance of the interface for the multiaxis levitated devices using capacitive position sensors.     

A Self-Balancing High-Voltage Capacitance Bridge

A self-balancing high-voltage capacitance ratio bridge, especially designed for continuous measurement of corona losses on experimental transmission lines, is described. The instrument is derived by combining a negative-feedback amplifier with a high-voltage capacitance bridge based on the current comparator principle. Manual control is provided for the four most significant decades of the bridge, thus permitting the function of the feedback amplifier to be limited to the balancing of small deviations. In this manner the errors originating in the amplifier and the associated indicating or recording instruments are made insignificant in the overall measurement. The accuracy of the built-in current comparator is 0.001 per cent, of the circuitry associated with the amplifier, 1 per cent. The output of the automatic balancing circuit is instrumented to produce a readout which is proportional to the power loss and reactive volt-amperes. Both components are in the form of small dc voltages and thus are suitable for recording.     

Mobile patient monitoring based on impedance-loaded SAW-sensors

A remotely requestable, passive, short-range sensor network for measuring small voltages is presented. The sensor system is able to simultaneously monitor six small voltages in millivolt-range, and it can be used for Holter-electrocardiogram (ECG) and other biopotential monitoring, or in industrial applications. The sensors are based on a surface acoustic wave (SAW) delay line with voltage-dependent, impedance loading on a reflector interdigital transducer (IDT). The load circuit impedance is varied by the capacitance of the voltage-controlled varactor. High resolution is achieved by developing a MOS-capacitor with a thin oxide, low flat-band voltage, and zero-voltage capacitance in the space-charge region, as well as a high-Q-microcoil by thick metal electroplating. Simultaneous monitoring of multiple potentials is realized by time-division-multiplexing of different sensor signals.     

Capacitance and conductance of single-walled carbon nanotubes in the presence of chemical vapors

Simultaneous conductance and capacitance measurements on a single-walled carbon nanotube (SWNT) network are used to extract an intrinsic property of molecular adsorbates. Adsorbates from dilute chemical vapors produce a rapid response in both the capacitance and the conductance of the SWNT network. These responses are caused by a combination of two distinct physiochemical properties of the adsorbates: charge transfer and polarizability. We find that the ratio of the conductance response to the capacitance response is a concentration-independent intrinsic property of a chemical vapor that can assist in its identification.     

Modeling of the electrical properties of the mixed ionic-electronic conductor BiMg<Subscript>0.25</Subscript>Cu<Subscript>0.75</Subscript>NbO<Subscript>5</Subscript>

A physically justified equivalent circuit of an ionic-electronic conductor has been proposed which accounts for the unusual electrical behavior of BiMg_0.25Cu_0.75NbO₅. The problem of separating the electronic and ionic contributions to its conductance has been resolved by analyzing the frequency dependences of its impedance. A new approach has been proposed for interpreting the temperature dependences of capacitance and conductance for this material.     

Linearized invariant conductance and capacitance meter for liquids

We consider an automatic conductance and capacitance meter for liquids with linear readout. Two variable resistors are used for balancing the circuit. Translated from Izmeritel'naya Tekhnika, No. 9, pp. 44–45, September, 1996.     

A study of a high-resolution linear circuit for capacitive sensors

A circuit for capacitance measurements is described. The circuit permits offset capacitance compensation using a dc voltage. The electronic circuitry with its testing is described. The output voltage is a linear function of the capacitance measured. Experimental data show good agreement with values predicted by the linear formula. Experiments show it is possible to measure capacitance changes with a resolution of a few femtofarads (fF)     

Theory of a reactive method for measuring dielectric losses

Summary Expression (18), in which function A₀ is obtainable in a tabulated form [3], relates the quantities which are to be measured with the parameters of the measuring circuit. Expression (13) can also be used for selecting the grid voltage amplitude for a sufficiently close coupling and the optimum anode supply voltage.Moreover, an analysis of (18) provides a linear scale for the instrument over a sufficiently wide range. This is confirmed experimentally by means of loss angle standards for frequencies of 0.3 and 1.0 Mc developed by the VNIIM (All-Union Scientific Research Institute of Metrology). The residual loss of the instrument determined by means of two loss angle standards of the same capacitance (the error due to the ohmic resistance of the tuned circuit coil is excluded) remains the same over the whole scale.     

A New High-Speed Method of Testing Capacitors

A new high-speed method of determining the capacitance and a quantity which the writers call the pulse series resistance (PSR) of an unknown capacitor is presented. The unknown capacitor is assumed to consist of an ideal capacitor and a series resistor. The test circuit consists of a low-impedance driver, a low-loss coupling capacitor, and a wide-band high-input/low-output impedance video-type amplifier. The unknown capacitor is placed in a negative feedback loop of this amplifier. The input waveform is a trapezoid. The output waveform contains information that is indicative of the capacitance and PSR of the unknown capacitor. The information is obtained by measuring two voltages, one of which is completely independent of the other. Capacitors were measured from approximately 2 pf to 2 ?f with an accuracy of ±5 per cent. The PSR was not available for capacitors less than 100 pF because of test-circuit limitations. The capacitance and PSR of an unknown capacitor could be made available within 500 ?sec with modern voltage-measuring and calculating techniques.     

Analysis of a InGaAs/InP single photon detector at 1550 nm

A new type of single-photon detector is introduced and its related properties characterized. The single-photon detector operating in the Geiger mode uses a new type of cooling system to moderate temperature, which can make the temperature drop to ?65?°C. Besides, the single-photon detector adopts a hold-off time modulation feedback control circuit to decrease the afterpulsing effects and the gate pulse is coupled to the avalanche diode through capacitance. In addition, a suitable delay and comparator with latch function circuit are used to detect avalanche signals. Experimental conditions are that the clock frequency is 10 MHz, refrigeration temperature is ?65?°C, and the width of control pulse is 5 ns. The experimental results indicate that quantum efficiency is about 20.42% and the dark count rate is about 5 × 10^?6 ns^?1 with signal-to-noise ratio 27 dB at the optimum operation point of this detector. The designed single-photon detector achieves a tradeoff between lower dark count rates and high quantum efficiency.     

Capacitive transducer for relative position error galvo mirrors

A transducer was designed to sense small angular displacements of servo-controlled galvo mirrors in rotary optical storage devices. The transducer is differential in nature, and operates on the principle of linear electrical capacitance variation with area overlap of uniquely shaped capacitor plates. These capacitive plates lie in planes normal to the axis of rotation, and consist of many electrically connected wedge-shaped projections aligned radially to the center of rotation. A prototype was fabricated and tested. For optical storage devices, experimentally determined characteristic curves show sufficient linearity and repeatability for relative position error (RPE) feedback applications, at plate spacings of 0.15 mm or less. A design change, for further extending the linear range of the characteristic curve of the transducer beyond RPE feedback requirements, is described. A circuit design to produce voltage variations proportional to differential capacitance changes in the transducer is discussed, and peak-to-peak signal-to-noise ratio is conservatively approximated at 2×10⁴ with 10 kHz bandwidth     

Electrokinetic measurements of membrane capacitance and conductance for pancreatic beta-cells

Membrane capacitance and membrane conductance values are reported for insulin secreting cells (primary -cells and INS-1 insulinoma cells), determined using the methods of dielectrophoresis and electrorotation. The membrane capacitance value of 12.57 (+/-1.46) mFm(-2), obtained for -cells, and the values from 9.96 (+/-1.89) mFm(-2) to 10.65 (+/-2.1) mFm(-2), obtained for INS-1 cells, fall within the range expected for mammalian cells. The electrorotation results for the INS-1 cells lead to a value of 36 (+/-22) Sm(-2) for the membrane conductance associated with ion channels, if values in the range 2-3 nS are assumed for the membrane surface conductance. This membrane conductance value falls within the range reported for INS cells obtained using the whole-cell patch-clamp technique. However, the total 'effective' membrane conductance value of 601 (+/-182) Sm(-2) obtained for the INS-1 cells by dielectrophoresis is significantly larger (by a factor of around three) than the values obtained by electrorotation. This could result from an increased membrane surface conductance, or increased passive conduction of ions through membrane pores, induced by the larger electric field stresses experienced by cells in the dielectrophoresis experiments.     

基于峰值检测的MEMS器件微弱电容检测电路

针对MEMS器件研制中微弱信号的检测问题,提出了一种适用于电容式MEMS器件的微弱电容检测电路.此电路采用峰值检测技术,原理及结构简单;只检测待测电容的变化量,既可用于差分式检测,也可应用于单一待测电容的情况.首先利用正弦载波信号和微分电路对电容量进行载波调制,再通过减法电路得到幅值与电容变化量成比例的正弦信号,最后采用峰值检测方法解调信号,得到直流量输出.利用微小可调电容进行标定,结果表明检测电路的线性度良好,灵敏度约为3.631V/pF,精度达到0.2%.利用该检测电路检测MEMS陀螺上振动频率为2.85kHz的梳齿驱动器的电容量变化,输出信号频率为（2.85±0.02）kHz,误差低于0.7%,说明该电路能够应用于MEMS器件的微弱电容检测.