A theoretical analysis of C.C.D. operation with square clock pulses

Currently published analyses of C.C.D. operation have dealt with the case where a fixed voltage is maintained on the gate above the emptying well during the charge transfer process. However, in contrast to this, most C.C.D.'s appear to be operated with square or trapezoidal clock pulses. The consequences of rapidly falling gate voltages are discussed and a simple mathematical model is developed to illustrate the situation. It is shown that if the falling edges of the clock pulses are too steep the operation of the C.C.D. will be degraded in that carriers may be lost by recombination and the overall transfer process will be slowed down due to the smaller electrostatic fields which are developed.     

A technique for double resonant operation of birdcage imaging coils

The type of radio-frequency (RF) coil known as a high-pass birdcage consists of a set of N; wires arranged axially on the surface of a cylinder and connected by capacitors at each end. Such coils are widely used for NMR imaging because of the high degree of field homogeneity they provide. It is shown how to create homogeneous fields at two frequencies, using an unequal distribution of capacitance. A theoretical analysis which uses the discrete Fourier transform of the currents with respect to the angular positions of the N; wires is presented. A perturbation theory analysis indicates a small sacrifice in homogeneity. The root-mean-square deviation of field magnitude around a circle is proposed as a measure of field inhomogeneity. For the case of double resonance at proton and fluorine frequencies, the loss of homogeneity is at worst 1% and is small compared to the natural inhomogeneity for an N=8 wire coil for radii up to one half the coil radius. The presence of a conducting shield degrades the homogeneity. The theoretical ideas were confirmed in a computer simulation of one particular coil design. A working coil was constructed and images obtained of proton and fluorine phantoms.     

Liquid-crystal technique for observing integrated-circuit operation

A nondestructive technique has been developed that enables both the electric fields and temperature distributions at the surface of an operating integrated circuit to be viewed with conventional optical microscopes. Packaged chips or unscribed wafers are coated with a nematic liquid-crystal layer and operated in their normal fashion. Practical preparation and observation procedures have been developed.     

应用电子探针原位微区分析技术测试硅硼钠石矿物

测试样品中的硅硼钠石矿物除了具有规则的晶体形态外,还有一种无定形类别。二者光学特征差异大,定性分析如薄片鉴定、扫描电镜（ SEM）等方法在形貌上的识别难以可靠地确定它们是否同为硅硼钠石矿物。本文应用电子探针原位微区分析（ EPMA）技术,针对微区进行成分分析,精确测试了该矿物。 EPMA具体包括背散射电子图像（ BSEI）分析技术与元素定量分析技术两种主要类型,是定性与定量分析技术的结合。测试硅硼钠石矿物要面对的主要挑战有两点：（1）硼（B）元素处于EPMA检测下限,而且无氧化物标样;（2）钠（Na）元素易迁移。针对这些检测难点,笔者采取了一系列措施,如选用氮化硼（ BN）标样,避开B元素处于低位的分光晶体及加大电子束斑、延长测试时间等等。最终,在薄片分析与能谱定性分析的基础上,通过BSEI分析技术确定矿物显微结构中的均质区域,原位定量分析测试其化学成分,避免了因显微结构与成分不均造成的偏差,有力地提高了测试精度,为正确鉴定该矿物提供了可靠依据。     

M.I.C. TRAPATT oscillator for efficient S band operation

The letter describes the construction and performance of a S band m.i.c. TRAPATT oscillator. The design utilises a system of sliding lumped-element sections to provide optimum performance from unencapsulated silicon p+?n?n+ chips. Efficiencies of greater than 30% at 2.6 GHz and peak output powers up to 40 W are reported. The oscillator is small and self contained and is suitable for ai borne transmitters.     

C.C.D./C.M.O.S. transversal filter using switched-capacitor technique for signal detection

A fully integrated c.c.d. filter has been built with a low power consumption. The c.c.d. filter employs c.m.o.s. support circuits and switched-capacitor techniques for signal detection. The power consumption of the filter is 20 mW.     

Bitline GND sensing technique for low-voltage operation FeRAM

In this sensing technique, pMOS charge transfer maintains the bitline level near the GND when the plate line goes high. It gives 0.5-V higher readout voltages across the cell capacitors and enables a 0.4-V higher differential amplitude in a 512-cell per bitline structure compared with the conventional high-impedance bitline sensing technique. Using the shifted bias plate line layout, only eight cells and eight sense amplifiers per cell mat are activated, and simulations show 8.06 mW at 3 V and 5 MHz, which is about the same power consumption as the conventional device     

Fibre probe far-field technique for mode-field diameter measurementof single-mode fibres

A far-field pattern (FFP) technique using an optical fibre probe to measure the mode-field diameters of single-mode fibres is described. The endface separation between the test fibre and the probe fibre can be reduced to a tenth of the fibre/detector separation in the conventional scanning detector method     

Drift cancellation in a d.c.-coupled computing amplifier

The technique of employing one operational amplifier merely to cancel, or partially cancel, the voltage offsets and drift effects of its twin on the same semiconductor wafer makes possible, at low cost, a d.c. computing amplifier with a drift performance an order of magnitude better than that of a single amplifier used by itself.     

C.W. operation of ion-implanted GaAs read-type IMPATT diodes

Epitaxial and ion-implantation techniques have been combined to form a high/low doping profile for GaAs Schottky-barrier Read-type IMPATT diodes. A c.w. output power of 1.1 W with 25% conversion efficiency was obtained at 11 GHz.     

C.W. anomalous-mode operation in silicon planar IMPATT diodes

Silicon planar IMPATT diodes which operate in the Read mode in the frequency range 4.5?11.5 GHz have been observed to produce c.w. oscillations in the frequency range 0.5?2.0 GHz. These u.h.f. oscillations commence at a current density of 250 A/cm2 and are accompanied by a 15?20% decrease in the diode direct voltage. The d.c./r.f. power-conversion efficiency in the anomalous mode is approximately twice that in the Read mode.     

Fast technique for computing syndromes of B.C.H. and Reed-Solomon codes

A new scheme for reducing the numerical complexity of the standard B.C.H. and Reed?Solomon (R.S.) decoding algorithms is developed. Specifically, the process of calculating syndromes over GF(2m) is shown to require only a small fraction of the number of multiplications and additions that is required by using standard methods. As an example, the calculation of the 32 syndromes of the (255, 223, 33) Reed?Solomon code (NASA standard for concatenation with convolutional codes) is shown to require 90% fewer multiplications and 78% fewer additions than the conventional method of computation. A computer simulation also verifies these results.     

Long-term step response of a chain of a.c.-coupled amplifiers

In the long-distance transmission of television signals, the long-term step response of a chain of a.c.-coupled amplifiers is of interest. A solution is obtained for the asymptotic response, where the transfer functions are first-order, and some speculations are included about generalising the result to higher orders.     

Simple technique for op amp continuous-time 1 V supply operation

A simple scheme for achieving continuous-time low-voltage operation of op amps is discussed. The scheme involves placing a floating battery in series with one of the op amp input terminals. Simulations and experimental results are presented that verify the proposed scheme with the example of a CMOS op amp that operates from a single 1 V supply and with 0.8 V signal swing     

A probe for organ impedance measurement

In this paper, we describe the theory and practical implementation of an electrical impedance probe for making in vivo measurements of the electrical admittance of living tissue. The probe uses concentric annular electrodes and is shown to sample a more localized, yet greater, volume of tissue than the standard four-electrode probe. We have developed a mathematical model for the conduction of current between the probe electrodes assuming that we are investigating a uniform, isotropic, semi-infinite region and taking into account the contact impedance between the electrodes and the organ. The electric fields produced by the probe have been calculated by solving a weakly singular Fredholm integral equation of the second kind. The size and position of the probe electrodes have been optimized to maximize both the accuracy in the admittance measurement and insensitivity to contact impedance. A probe and driving hardware have been constructed and experimental results are provided showing the accuracy of admittance measurements at 50 and 640 KHz.     

A.C. field effect study on PbTe films grown by hot wall epitaxy technique

The field effect mobility on the free surface of PbTe films grown by hot wall epitaxy (HWE) technique ona KCl substrate was studied as a function of frequency in the range 40–200 kHz at different temperatures from 98–156 K. Using Garrett's theory of the frequency dependence of field-effect mobility, the relaxation times of surface states were found to vary from 1.84 to 0.96 μsec in the above temperature range. From Rupprecht's relation on temperature dependence of relaxation times, the energy level of surface states was found to be 0.02 eV below the conduction band with an effective capture cross section of the order 10^?19 cm².     

Reverse photo-lithographic technique for S.A.W. devices

This paper deals with the reverse photolithographic technique for the fabrication of S.A.W. devices such as convolver and correlator etc. In this technique, T-shaped negative relief mask is first applied to the substrate and the film is deposited subsequently. As a result, the film contacts the substrate directly only in the areas left open by the relief mask. The relief mask is finally removed by a solvent which attacks only the mask but not the film material.     

A general technique to correct probe position errors in planarnear-field measurements to arbitrary accuracy

A general theoretical procedure is presented to remove known probe-position errors when planar near-field data are transformed to the far field. The measured data are represented as a Taylor series whose terms contain the error function and the ideal spectrum of the antenna. This representation is then assumed to be an actual near-field existing on an error-free regularly spaced two-dimensional scan plane. By inverting the Taylor series, the ideal spectrum in terms of the measured data and the position errors is obtained. The solution is given by an infinite series of an error operator acting on data containing errors of measurement. This error operator is the Taylor series without the zeroth-order term. The nth order approximation to the ideal near-field of the antenna can be explicitly constructed by inspection of the structure of the error operator. Convergence of the approximation is examined. Computer simulations are used to demonstrate the excellent results obtained with this technique, as well as to demonstrate the convergence of the error-corrected fields to the true solution     

N-folded cascode technique for high frequency operation of lowvoltage op amps

A technique is described which enhances the high frequency operation of a low voltage folded cascode structure by introducing a zero at the nondominant pole position and providing phase compensation. This technique can be used to develop low voltage operational amplifiers with good gain bandwidth properties and no overhead in power consumption