Conversion nonlinearity errors of bolometer and diode mixers of superheterodyne attenuation meters

Translated from Izmeritel'naya Tekhnika, No. 5, pp. 41–43, May, 1989.     

Extending the bandwidth of magnetic tunnel junction sensors by abuffer amplifier

A simple buffer amplifier, consisting of a transistor in an emitter-follower configuration, is proposed to extend the bandwidth of magnetic tunnel junction read sensors. To maximize the bandwidth improvement, the buffer should be used on the slider or on the suspension as near to the slider as possible. The channel front-end (sensor, buffer, interconnect, and preamp) bandwidth is still somewhat limited by the RC product of the sensor resistance and shunt capacitance. However, the buffer can reduce the shunt capacitance to subpicofarad levels, allowing for bandwidths near 1 GHz. Merging the buffer with an interconnect and preamp gives a low-frequency signal-to-noise ratio (SNR) reduction at the preamp input of 0.1 dB and an SNR improvement of 5 to 10 dB over a no-buffer configuration for frequencies between 100 MHz and 1 GHz     

How to enlarge the bandwidth without increasing the noise in OP-AMP-based transimpedance amplifier

Increasing the bandwidth without degrading the noise performance represents the main challenge in the design of transimpedance amplifiers. This paper presents a novel circuit topology for a transimpedance amplifier that allows obtaining an improved tradeoff between equivalent input noise and bandwidth with respect to the conventional approach. The effectiveness of the new topology has been demonstrated by designing and testing a prototype of a transimpedance amplifier based on the proposed topology.     

On the theory of a plasma-beam superheterodyne free-electron laser with H-ubitron pumping

The scheme of a plasma-beam superheterodyne free-electron laser (PBSFEL) with H-ubitron pumping is analyzed and several possible variants of its practical implementation are considered. Some variants represent sources of highly monochromatic signals, while the other generate signals with a rather broad spectrum. The increment of wave growth in PBSFELs is estimated and it is established that, under otherwise equal conditions, these FELs are characterized by much greater gain increments than the equivalent two-stream devices. The proposed PBSFELs have good prospects as sources of high-power electromagnetic radiation in the millimeter wavelength range.     

基于解析法的旁支管共振消声带宽计算

旁支管是应用广泛的共振消声结构。应用解析方法推导旁支管共振结构的传递损失和共振频率计算公式,考虑三维修正,给出旁支管共振消声带宽与各种参数的定量关系,定义消声带宽与共振频率的比值为带宽参数,研究带宽参数与传递损失以及旁支管其他参数的变化关系,最终给出旁支管共振消声带宽计算公式。最后,通过三维有限元方法(Finite Element Method,FEM)计算旁支管的消声带宽并与文中公式结果进行比较,结果显示,两种结果吻合良好,验证了计算公式的可靠性和准确性。     

Improvement of speckle statistics in double-wavelength superheterodyne interferometry

In this paper we analyze the probability density function of the superheterodyne signal obtained in a two-wavelength interferometer from the beat of a local oscillator laser beam with a speckled return beam from a rough target. Theoretical investigation shows that, by using an increased number of spatially separated detectors, one can improve noticeably the detection probability of the superheterodyne signal. Experimental results obtained with a four-quadrant detector are in good agreement with theory.     

Accuracy of a Bellows vacuum meter with an LC-generator

Errors of pressure measurement are considered. The error as a function of the pressure for a vacuum gauge rated at up to 1000 Pa is calculated as an example. It is 0.15 ≤ δp/p ≤ 0.2% over a pressure range of 14 ≤ p ≤ 1000 Pa and it increases hyperbolically up to 100% with p = 0.01 Pa. The parametric reliability of the instrument and its immunity to an accidental increase in pressure the atmospheric level is substantiated. __________ Translated from Izmeritel’naya Tekhnika, No. 9, pp. 37–41, September, 2006.     

Information-handling characteristics of an amplifier

Conclusions Our investigation of the carrying capacity of an amplifier showed that this parameter is characterized by the informational determinant of the active component. The maximum carrying capacity is attained when the stage gain is 2.72 and proportional to the number of stages.Translated from Izmeritel'naya Tekhnika, No. 8, pp. 65–67, August, 1971.     

Propositions to widen the frequency bandwidth of an integrator

The transfer function, T, of an ideal integrator is 1/taus. Its phase, equal to -pi/2, is independent of the frequency value, whereas the gain decreases in a proportional way with this value of omega. However, on the one hand, it is usually necessary to limit the DC gain so that the transfer function takes the shape T = k/(1 + ktaus). On the other hand, the active components such as operational amplifiers (op. amps.) or current feedback operational amplifiers are not perfect and they bring a supplementary pole at a high frequency. Therefore the bandwidth where the integrator phase is equal to -pi/2 is included between omega_MIN and omega_MAX. For a couple DC gain and an op. amp. given, increasing the ratio omega_MAX/omega_MIN to a maximum is proposed.     

The design of a hand-held K-factor meter using an air-core currenttransformer

This paper describes in detail the design of a portable microcontroller-based K-factor meter, or transformer harmonic derating factor meter. This innovative instrument is based on the recently developed time domain method for K-factor determination. K-factor is measured from the ratio of the rms value of the time derivative of a current to the rms value of this same current. The meter employs the properties of an air-core current transformer, or Rogowski coil, to acquire the time derivative of a current and then numerical integration, of this digitized signal, to obtain the current waveform itself. This method avoids the noise of the numeric differentiation, characteristic of the time domain approach to K-factor measurement, as well as the computational effort of the fast Fourier transform in the frequency domain approach. In addition, the instrument incorporates thermal demand models for both K-factor and rms current to assess transformer harmonic heating over a user selected time interval. A prototype meter, using a MC68HC16 microcontroller, was built and tested with a variety of actual and synthesized power system waveforms     

Design of an integrating cavity absorption meter

The design of integrating cavity absorption meters of general geometry is analyzed for cases in which the incident illumination of the cavity is spatially uniform and isotropic, such as the meter of Fry et al. [Appl. Opt. 31, 2055 (1992)]. The analysis by Kirk [Appl. Opt. 34, 4397 (1995)] for the probability of photon survival in a spherical meter is extended to general geometries. An estimate of the effect of the shape of the cavity on the estimated absorption coefficient is given.