Nanofiber frequency doublers

Nanoscaled, needle-shaped frequency doublers have been generated via self-assembled surface growth from functionalized quaterphenylene molecules with a designed large hyperpolarizability. The nanofiber frequency doublers exhibit very weak fluorescence centered around 430 nm but emit a strong, resonance-enhanced second-harmonic signal when excited with infrared 80 fs laser pulses. The frequency doublers are employed to correlate second-harmonic response and morphology via two-dimensional true second-harmonic images of individual nanoaggregates obtained with the help of a femtosecond laser scanning microscope.     

Square-rooting and absolute function circuits using operational amplifiers

A method for implementing square-rooting and absolute function circuits using operational amplifiers (opamps) as only active elements is introduced. The realisation technique is provided through the use of the opamp supply-current sensing, which utilises an inherently quadratic characteristic of the opamp class-AB output stage. The proposed circuits are attractive in terms of simple configuration and low cost. The performances of the circuits are discussed in detail. Experimental results demonstrating the characteristics of the circuits using commercially available opamps are also included.     

Extending the frequency range of a Wien-bridge oscillator usingcomposite operational amplifiers

The author describes the use of composite operational amplifiers to extend the useful operating frequency range of an operational amplifier-based Wien-bridge oscillator. The effect of the finite gain-bandwidth product (GB) of the operational amplifier (OA) is analyzed. This analysis shows that for a certain GB the frequency of oscillation is less than the theoretical value and that the error increases with frequency. A composite OA is then used to decrease the errors due to GB. This is verified theoretically and experimentally. Although the composite OA improves the frequency performance of the oscillator, the amplitude of the output decreases with frequency. An automatic-gain control circuit is incorporated to keep an output amplitude constant over the useful frequency range. Distortion measurements are presented     

Chopper-stabilized operational transconductance amplifiers

A technique for chopper-stabilizing commercial linearized operational transconductance amplifiers (OTAs) to remove output offset current errors is described. Design equations which illustrate performance tradeoffs as a function of component values are given. The results are verified experimentally using a common bipolar OTA     

Long-term behavior of operational amplifiers

The voltage and current offsets of two typical precision operational amplifiers (OPAs) with BJT and FET input, respectively, were continuously measured for two years. The paper presents the experiment, explains the method of data analysis, and discusses the results. The long-term stability turns out to be limited mainly by random walk processes     

Two-color interferometer for surface characterization using two frequency doublers and a four-phase-step method

A high-accuracy, two-color interferometer for characterizing a processed surface is described. It is composed of two frequency doublers. It is not affected by air turbulence and mechanical vibration because it is a complete common-path interferometer, and the effects from different reflectivities of various materials are canceled by a four-phase-step technique that shifts the phase of the interference fringe in steps of π/2. The processed surface is measured with subnanometer resolution.     

Dual-mode design of fully differential circuits using fully balanced operational amplifiers

Fully differential (F-D) analogue circuits are usually designed focusing only on their differential-mode (DM) behaviour, without considering common-mode (CM) responses. A technique is presented for the design of both DM and CM circuit responses, using fully balanced operational amplifiers (FBOAs) as analogue building blocks. FBOAs work with CM and DM voltages as a whole, having an ideally infinite gain for both modes. This allows independent design of CM and DM dynamics. Inverting and non-inverting F-D topologies can be implemented in a simple way, similar to the implementation of their single-ended counterparts. Some typical application circuits are analysed and discussed and, as a design example, a 'double-mode oscillator' (a circuit that has independent CM and DM oscillations) was built and experimentally evaluated.     

Experimental investigation of saturation effects in ferrite frequency doublers

Saturation of ferrite frequency doublers due to the reaction of the generated second-harmonic field back on the sample, the excitation of unstable spin waves by transverse pumping, and the excitation of unstable spin waves by longitudinal pumping is investigated experimentally. An expression for the second-harmonic power as a function of the power absorbed by the ferrite, which holds for any degree of processional motion ellipticity of the magnetization, is derived including the effect of the reaction field. An experimental method of observing the three saturation effects through the introduction of an externally impressed second-harmonic field is described. Experimental observations of all three saturation mechanisms are reported, and the results are compared with theory. The upper bound on conversion efficiency of a ferrite doubler, assuming adequate output coupling circuits can be devised, is set by longitudinally-pumped spin waves. This upper bound on efficiency is measured experimentally for a typical doubler.     

Applications of operational amplifiers in strain gauge circuits

Operational amplifiers, originally developed for analogue computation, are now widely used in analogue instrumentation, signal conditioning, servo controls, voltage and current regulators and an extensive range of other functions. In experimental mechanics, operational amplifiers are ideally suited to applications involving strain gauges. Both Wheatstone bridge and ballast (potentiometer) circuits are examined together with the limitations and constraints imposed by amplifier and external circuit considerations. These limitations are important, whether relatively simple operational amplifiers or the more complex instrumentation amplifiers are used. Many manufacturers provide a wide range of 'off-the-shelf' integrated circuit and discrete amplifiers, together with comprehensive specifications, permitting selection of a suitable device. Before discussing strain gauge applications, the properties of operational amplifiers will be reviewed briefly.     

Cryogenic ultra-low power dissipation operational amplifiers with GaAs JFETs

To realize a multipixel camera for astronomical observation, we developed cryogenic multi-channel readout systems using gallium arsenide junction field-effect transistor (GaAs JFET) integrated circuits (ICs). Based on our experience with these cryogenic ICs, we designed, manufactured, and demonstrated operational amplifiers requiring four power supplies and two voltage sources. The amplifiers operate at 4.2 K with an open-loop gain of 2000. The gain–bandwidth product can expect 400 kHz at a power dissipation of 6 μW. In performance evaluations, the input-referred voltage noise was 4 μV_rms/Hz^0.5 at 1 Hz and 30 nV_rms/Hz^0.5 at 10 kHz, respectively. The noise power spectrum density was of type 1/f and extended to 10 kHz.     

Systematic design of programmable operational amplifiers with noise-power trade-off

A methodology for the systematic design of a programmable operational amplifier (opamp) is described. With this methodology, the opamp is programmable concerning noise and power consumption while keeping the stability for the whole operation range with a constant phase margin of phi_res=70deg. The theoretical model is developed with the help of the transfer characteristics of the opamp determining the degrees of freedom. Experimental results for a 0.35-mum CMOS opamp show either ultra low-noise of 2 nV/radicHz or low-power consumption of 140 muW while keeping the opamp stable over the whole range of programmability     

基于运放测试大输入范围ADC电路的设计

为测试大输入范围的ADC电路,综合考虑测试机的输出信号能力以及ADC输入范围要求,设计出合适的放大电路来扩展ATE输出信号范围,并根据噪声分析理论以及ADC电路参数测试对运放性能的要求选择前端驱动放大器。通过测试ADI公司AD7894的实例对比使用两种不同运放电路的实际测试效果表明计算公式有效可行,放大器的分析选择科学合理,为基于运放扩展ATE输出信号范围测试大输入范围ADC电路的设计提供可靠依据。     

High-speed voltage buffers for the experimental characterization ofCMOS transconductance operational amplifiers

Two voltage buffers realized with discrete components are presented which provide very low input capacitance and input bias current, high-frequency capability and low-output resistance. This performance means they are well suited for employment in the characterization of operational amplifiers and specifically CMOS transconductance operational amplifiers     

Utilization of operational amplifiers for raising the input impedance of measuring circuits

Summary The analysis and testing of a matching circuit consisting of two operational dc amplifiers have shown that it is possible by means of this circuit to match dc voltage circuits with a large internal resistance (up to 10 meg) to circuits with a small internal resistance (up to 10 kohm).     

A simple method to estimate gain-bandwidth product and the secondpole of the operational amplifiers

A method for realizing a sine-wave voltage-controlled oscillator (VCO) with a linear frequency to control voltage characteristics over three decades of frequencies, or more, in one sweep is discussed. The method employed is the conversion of a simple integrated square-wave VCO into a sine-wave VCO by separating the first-harmonic component and providing frequency shifting to achieve the desired output range. The sources of distortion of the output waveform are shown to be higher-order components of the square-wave used and higher-order components produced in the mixer. Possible improvements of the circuit are suggested, including the use of higher-order filters to reduce distortion and the use of a square-wave VCO operating at higher frequencies to provide operation at higher frequencies or over wider sweep ranges     

Calculation of the frequency characteristics of DC amplifiers with modulation-demodulation

The frequency characteristics of dc amplifiers with modulation-demodulation are calculated with allowance for the limitation on the frequency characteristic of the carrier amplifier in the low-frequency region. Examples are used to show that the carrier frequency in these amplifiers can exceed the maximum frequency in the spectrum of the amplified signal only by a factor of 1.1–1.2. Translated from Izmeritel’naya Tekhnika, No. 8, pp. 51–53, August, 1996.