Evaluation of the design requirements for the electrical part oftransmission-type optical smoke detector to improve its thresholdstability to slowly varying influences

The output signal sensitivity to optical component contamination and other slowly varying parasitic influences in the transmission-type smoke detector is analyzed. The analysis carried out the new topology characterized by the selective feedback loop incorporating the optical part of the detector. Depending on the loop gain frequency shaping in the electrical part of the loop, dual-stability enhancement of the input threshold level can be achieved. The stable dc output signal can be preserved by the high dc loop gain value, as an option to the standard serial filter dc rejection. The detector passband gain stability is achieved by the high loop gain selectivity, eliminating feedback at very low or passband frequencies. The proposed topology can be easily adopted to both digital and low-cost analog detector designs. The special case of the threshold sensitivity neutralization through the cancellation of the output dc signal sensitivity and passband gain sensitivity is considered, too, as an option suitable for low-cost detectors. In addition to the described linear settlement, two nonlinear solutions are presented, the first of them based on the foregoing linear circuit analysis. Despite its nonlinear nature, this alternative solution is not troublesome for analog implementation, since the nonlinear function required is realized by the standard variable gain amplifier. Another nonlinear method requires logarithmic function implementation, so that its suitability depends on the particular design requirements     

Compact light-emitting-diode sun photometer for atmospheric optical depth measurements

A new compact light-emitting diode (LED) sun photometer, in which a LED is used as a spectrally selective photodetector as well as a nonlinear feedback element in the operational amplifier, has been developed. The output voltage that is proportional to the logarithm of the incident solar intensity permits the direct measurement of atmospheric optical depths in selected spectral bands. Measurements made over Ahmedabad, India, show good agreement, within a few percent, of optical depths derived with a LED as a photodetector in a linear mode and with a LED as both a photodetector and a feedback element in an operational amplifier in log mode. The optical depths are also found to compare well with those obtained simultaneously with a conventional filter photometer.     

New interferometric fiber-optic gyroscope with amplified optical feedback

A novel interferometric fiber-optic gyroscope with amplified optical feedback by an Er-doped fiber amplifier (EDFA) is proposed and theoretically investigated (the proposed gyroscope is named the feedback EDFA-FOG, FE-FOG in what follows). The FE-FOG functions like a resonant fiber-optic gyro (R-FOG) because of its multiple utilization of the Sagnac loop; however, it is completely different because a low-coherence light source is used. In addition, the gyro output signal is pulsed because the modulation frequency of the phase modulator placed in the Sagnac loop is selected to match the total round-trip time delay of the light, which includes the Sagnac-loop delay plus that of the feedback loop of the fiber amplifier. The sharpness of the output pulse can be adjusted by both the gain of an EDFA and the modulation depth of the phase modulator. When rotation occurs the peak position of the output pulse is shifted as a result of the Sagnac effect. The resolution of the rotation measurement depends on the sharpness of the output pulse. The techniques of both the open-loop and closed-loop methods are described in detail, which shows the great advantage of the proposed gyroscope over the to the conventional interferometric fiber-optical gyroscope (I-FOG).     

多指灵巧手双闭环模糊控制

设计一种双位置闭环模糊控制器,用于多指灵巧手的位置控制。利用电机码盘反馈构成内位置环控制,采用一般的PID控制律;通过关节位置反馈形成外位置环控制,采用模糊控制算法。这种两层位置反馈控制可弥补只有码盘反馈的半闭环控制结构的不足,使具有强非线性的钢缆传动系统包含在闭环内,从而提高系统的稳定性和鲁棒性。实验证明跟踪精度明显提高。     

A Fast-Acting Feedback Loop for Pulse Amplitude Ratio Measurement

Design and operating details of a voltage ratio measuring circuit are presented. The circuit employs a wide bandwidth function multiplier as a variable gain amplifier. The denominator voltage activates a feedback loop causing multiplier gain adjustment. Adjustment proceeds until the multiplier output is equal to a Zener reference voltage. The multiplier gain is then equal to the ratio of Zener reference voltage to denominator voltage. Multiplier gain is stored by an integrator serving as a memory. The numerator voltage does not activate the feedback loop, but is simply amplified by the multiplier. The resulting output voltage is the ratio of the input voltages referred to a Zener reference. Null-balance time of 5 ?S allows ratio measurement of 16-kc pulse pairs.     

A magnetic feedback modulator for improved FM carrier recording

Magnetic multivibrators are often used as voltage-controlled oscillators in FM carrier recording systems. These oscillators generally consist of two switching transistors connected to a center tapped coil on a square loop magnetic core. The transistors operate alternately in saturation, driving the core between its positive and negative saturation limits. Frequency then depends upon saturation flux and applied voltage. In the Magnetic Feedback Modulator, stability and linearity improvement of an order of magnitude is possible with a new method of applying negative feedback to a square-loop core magnetic multivibrator. In addition, circuit complexity is reduced considerably over previous methods using conventional frequency detectors to derive feedback voltage. Based on Faraday's Law, a voltage which is a function of frequency and flux change is derived from the magnetic circuit. This voltage is then used as negative feedback to the dc differential amplifier to drive the magnetic multivibrator. Since the magnetic circuit is included in the negative feedback loop, frequency errors occurring in the modulator cause corresponding changes in the magnetic feedback voltage. The errors are then reduced in magnitude by the negative feedback.     

A Technique for Measuring the Equivalent RMS Input Noise of A/D Converters

A simple accurate technique is described for measuring the equivalent rms input noise of A/D converters. Noise can typically be measured with 10-percent accuracy in 1 s, and the method has successfully been applied to converters with up to 16 bits of resolution. The measurements are made at input voltages corresponding to the test converter's decision levels, where the effects of noise are most pronounced. A feedback loop incorporating the unit under test locates and locks onto these levels. The method utilizes a theoretical relationship between the input noise and an expected number of counts derived digitally from the feedback loop response. A low-noise wide-band operational amplifier is the only critical component required.     

Parameter estimation in strongly nonlinear circuits

The combination of the generalized Volterra approach to compute the steady-state output of strongly nonlinear systems with the maximum likelihood estimator (MLE) developed by J. Schoukens et al. (see ibid., vol.IM-37, p.10-17, 1988) yields a powerful tool to estimate the parameters in strongly nonlinear circuits. As a result, it is possible to determine system characteristics that cannot be measured directly or are difficult to obtain. The latter is illustrated by means of an inverting amplifier built around an operational amplifier causing slew-induced distortion. Two different models are used to represent the operational amplifier. The first considers only one nonlinearity, namely a saturating current source characterized by two parameters, but can only describe symmetric slew-induced distortion. The other model uses two diodes and results in a six-parameter model capable of addressing the asymmetric case. By comparing the results obtained for these approaches with measurements on the actual circuit, the capability of the identification technique for strongly nonlinear systems is demonstrated     

Measurement of gain tilt and its contribution to composite second-order distortion in the analog-digital transmission systems with Er/Yb fiber amplifiers

Fiber-optic-based analog or digital community antenna television systems experience composite second-order (CSO) distortion caused by the interaction between the gain tilt of the doped fiber amplifier and the laser chirp due to modulation. The gain tilt for an analog-digital transmission system with a high-power erbium/ytterbium-codoped fiber amplifier has been experimentally measured and its contribution to the CSO distortion of the system is evaluated. The results are in good agreement when compared with the direct measurement of the CSO distortion of the transmission system with and without the amplifier. The dependence of the gain tilt on the modulation frequency and wavelength of the input light is also investigated.     

Recent Advances in High-Frequency Performance of Feedback Amplifier-Transformer Combinations

The high-frequency limitations inherent in systems dependent upon performance of amplifier-transformer combinations have often restricted ac calibration in the high audio range. Three recent advances in design of feedback amplifiers incorporating transformers make possible significant improvements in bandwidth, linearity, and computing accuracy in this range. The first method compensates for the leakage reactance-output capacitance resonance that frequently constitutes the basic bandwidth limitation in feedback amplifier systems which incorporate output transformers. The second approach introduces resonant stabilization, allowing more loop gain for distortion reduction at specific harmonics. The third technique employs two or more computing amplifier-ratio transformer combinations effectively in parallel. This configuration can yield worst-case computing errors inversely proportional roughly to loop gain raised to a power equal to the number of parallel combinations. Applications of the three techniques in a practical, all-solid-state 20 kHz ac calibration source are described. The output amplifier-transformer combination supplies an external load with 20 VA to 20 kHz and 1 kV, with distortion of 0.03 to 0.05 percent at the high-frequency end. At the same time, parallel sets of computing amplifier-ratio transformer combinations within the source furnish ratio transformer scaling accuracy in division. This, in turn, permits overall linearity which is typically ±0.01 percent to 5 kHz, ±0.02 percent to 20 kHz, over a ten-to-one output amplitude range, expressed in percent of local (rather than full-scale) output voltage.     

A novel nonlinear distortion characterisation standard for RF andmicrowave communication systems

Theoretical results obtained with a simplified third order memoryless nonlinear system have shown that multitone test characteristics can be directly related to the more usual two-tone test figures. These theoretical developments have also proved that the noise power ratio (NPR) gives an optimistic measure of co-channel distortion. A corrected co-channel power ratio (CCPR) characterisation standard and its associated laboratory measurement set-up have therefore been proposed to circumvent the failings of the NPR. The usefulness of this approach is illustrated by some measurements of a practical C-band amplifier circuit     

Photon-echo amplification by an external-cavity amplifier

We demonstrate as much as 2.5 × 10(5) amplification of a photon-echo signal using a simple external-cavity amplifier. The method may be useful in regeneration of photon echo and memory refresh in a dynamic photon-echo optical memory system. We propose an image storage system that is capable of regeneration and amplification of phase-conjugate images in a feedback loop.     

Estimation of co-channel nonlinear distortion and SNDR in wireless systems

The effective signal-to-noise and distortion ratio (SNDR) at the output of a nonlinear amplifier is defined through the decomposition of the nonlinear output into correlated output and uncorrelated distortion. The analysis is based on the orthogonalisation of the nonlinear behavioual model that allows the accurate estimation of the effective in-band (or co-channel) distortion and hence determination of SNDR. Fundamental issues regarding the evaluation of the effective in-band distortion and its effect on digitally modulated signals are discussed. Simulations of in-band distortion and SNDR of WCDMA signals are verified experimentally using feed-forward cancelation.     

Picosecond soliton transmission by use of concatenated gain-distributed nonlinear amplifying fiber loop mirrors

Stable picosecond soliton transmission is demonstrated numerically by use of concatenated gain-distributed nonlinear amplifying fiber loop mirrors (NALMs). We show that, as compared with previous soliton transmission schemes that use conventional NALMs or nonlinear optical loop mirror and amplifier combinations, the present scheme permits a significant increase of loop-mirror (amplifier) spacing. The broad switching window of the present device and the high-quality pulses switched from it provide a reasonable stability range for soliton transmission. We also show that a soliton self-frequency shift can be suppressed by the gain-dispersion effect in the amplifying fiber loop and that soliton-soliton interactions can be partially reduced by using lowly dispersive transmission fibers.     

A look-up-table digital predistortion technique for high-voltage power amplifiers in ultrasonic applications

In this paper, we present a digital predistortion technique to improve the linearity and power efficiency of a high-voltage class-AB power amplifier (PA) for ultrasound transmitters. The system is composed of a digital-to-analog converter (DAC), an analog-to-digital converter (ADC), and a field-programmable gate array (FPGA) in which the digital predistortion (DPD) algorithm is implemented. The DPD algorithm updates the error, which is the difference between the ideal signal and the attenuated distorted output signal, in the look-up table (LUT) memory during each cycle of a sinusoidal signal using the least-mean-square (LMS) algorithm. On the next signal cycle, the error data are used to equalize the signal with negative harmonic components to cancel the amplifier's nonlinear response. The algorithm also includes a linear interpolation method applied to the windowed sinusoidal signals for the B-mode and Doppler modes. The measurement test bench uses an arbitrary function generator as the DAC to generate the input signal, an oscilloscope as the ADC to capture the output waveform, and software to implement the DPD algorithm. The measurement results show that the proposed system is able to reduce the second-order harmonic distortion (HD2) by 20 dB and the third-order harmonic distortion (HD3) by 14.5 dB, while at the same time improving the power efficiency by 18%.     

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.     

Phase series echography with prior waveform distortion for evaluating posterior waveform distortion

We describe a pulse-echo ultrasound method for measuring nonlinear waveform distortion. First, two artificially distorted ultrasound pulses, one of which is transformed into the other by using a linear transform, are prepared prior to the measurement. The linear relationship does not hold for nonlinear propagation. Second, different initial-phase versions of the two pulses are separately transmitted to a specimen one after another, then the echoes with the same turnaround time are placed in order of the initial phase. The placed echoes, called a phase series, have complete information on the posterior waveform distortion. We formulate a waveform distortion index by using these two techniques. The waveform distortion index has a monotonic increasing relationship with the nonlinear parameter B/A. As an example application, we performed tissue characterization of boiled eggs. As a result, egg whites and yolks were clearly distinguished. This method should be useful for biological tissue characterization.     

Extending the continuous tuning range of an external-cavity diode laser

The continuous tuning range of an external-cavity diode laser can be extended by making small corrections to the external-cavity length through an electronic feedback loop so that the cavity resonance condition is maintained as the laser wavelength is tuned. By maintaining the cavity resonance condition as the laser is tuned, the mode hops that typically limit the continuous tuning range of the external-cavity diode laser are eliminated. We present the design of a simple external-cavity diode laser based on the Littman-Metcalf external-cavity configuration that has a measured continuous tuning range of 1 GHz without an electronic feedback loop. To include the electronic feedback loop, a small sinusoidal signal is added to the drive current of the laser diode creating a small oscillation of the laser power. By comparing the phase of the modulated optical power with the phase of the sinusoidal drive signal using a lock-in amplifier, an error signal is created and used in an electronic feedback loop to control the external-cavity length. With electronic feedback, we find that the continuous tuning range can be extended to over 65 GHz. This occurs because the electronic feedback maintains the cavity resonance condition as the laser is tuned. An experimental demonstration of this extended tuning range is presented in which the external-cavity diode laser is tuned through an absorption feature of diatomic oxygen near 760 nm.     

A Delay Generation Technique for Narrow Time Interval Measurement

A new architecture for the on-chip measurement of short-time intervals is proposed in this paper. The measurement method is similar to a typical low-voltage measurement setup where the input signals are first amplified and then measured to relax the dynamic range of the succeeding analog-to-digital converter. In the proposed method, narrow time intervals are first amplified by a time amplifier (TAMP) and then measured by a time-to-digital converter. A delay-locked-loop (DLL) circuit is utilized to design a feedback time amplifier in which the gain is readily programmed by input data to any integer value within a range specified by the number of delay cells in the DLL. The TAMP's gain remains rather unchanged under process and temperature variations due to the inherent negative feedback of the DLL system. The circuit is implemented using complementary metal--oxide semiconductor (CMOS) 0.18- $muhbox{m}$ technology occupying less than 0.63 $hbox{mm}^{2}$ of the silicon area. The simulation results show that the proposed scheme can successfully be employed to measure time intervals in the range of a few tens of picoseconds with acceptable accuracy.      

Modeling of quartz crystal oscillators by using nonlinear dipolar method

A quartz crystal oscillator can be thought of as a resonator connected across an amplifier considered as a nonlinear dipole the impedance of which depends on the amplitude of the current that flows through it. The nonlinear amplifier resistance and reactance are obtained by using a time domain electrical simulator like SPICE (Simulation Program with Integrated Circuit Emphasis): the resonator is replaced with a sinusoidal current source of the same frequency and a set of transient analyses is performed by giving the current source a larger amplitude. A Fourier analysis of the steady-state voltage across the dipolar amplifier is performed to calculate both real and imaginary parts of the dipolar impedance as a function of the current amplitude. From these curves, it is then possible to accurately calculate the oscillation amplitude and frequency without having to perform unacceptably long transient analyses needed by a direct oscillator closed loop simulation. This method implemented in the Analyse Dipolaire des Oscillateurs a Quartz or Quartz Crystal Oscillators Dipolar Analysis (ADOQ) program calculates the oscillation start-up condition, the oscillation steady-state features (oscillation amplitude and frequency), and the oscillator sensitivity to various parameters. The oscillation nonlinear differential equation is solved by using the slowly varying function method so that the program quickly and accurately calculates the current amplitude and frequency transients. Measurements performed on an actual amplifier show a very good agreement with the results obtained by the simulation program.