一种数字控制的三相移相触发电路

设计了一款用于可控硅控制的三相移相触发电路.针对点电网及现场出现的噪声干扰问题,提出了一种去抖动电路设计方案,阐述了移相电路的基本设计思路.通过仿真和实际测试,该触发器的移相范围达到0°～178°,移相精度为0.35°/mV.     

New preprocessing technique for digital facsimile transmission

A new preprocessing technique which removes unwanted notches and random noise generated by electronic scanners is presented. Using a 3 element by 3 element mask, the central picture element is altered from black to white, or vice versa, if the surrounding elements correspond to a predetermined pattern. A significant improvement in both subjective image quality and coding efficiency is observed.     

Design of digital loaded-line phase-shift networks for microwave thin-film applications

This paper decribes the design approach, fabrication techniques, and electrical performance for two types of microwave hybrid thin-film phase shifters. Emphasis is placed on the practical aspects of the overall design and fabrication. A simplified set of design equations for loaded-line phase-shift networks is presented and divided into three categories based on the type of loading employed. The two circuits presented are a 4-bit 90° network employing single-section multibits to minimize physical size, and a 4-bit 360° network employing the 45° section as a basic building block.     

A digital control technique for a single-phase PWM inverter

This paper describes the closed-loop control of a single-phase pulsewidth modulated (PWM) inverter using the generalized predictive control (GPC) algorithm. This approach determines the desired switching signals by minimizing a cost function that reduces the tracking error and the control signals. Experimental results have demonstrated that the prototype system performs well     

A digital current control technique for voltage-fed induction motor drives

Precise control of stator current is essential to high performance field orientation controlled induction motor drives. Any current error degrades the performance of the drive in the same way as incorrect tuning of field orientation. Previous research has shown that accurate current control can be achieved with intelligent but complex control algorithms. This paper presents a new current control scheme which can achieve high accuracy and fast dynamic response but which is very simple for microprocessor implementation. The scheme was derived using the discrete state space modelling of the induction motor. The control law does not require knowledge of rotor flux and was independent of the field orientation control tuning. Good static and dynamic performances were obtained in both the simulation and experimental verifications. The results also show that the leakage inductance model error might cause a current ripple. However, this parameter can be tuned to its correct value easily by inspecting the current response.     

A new digital speed measurement technique for microprocessor-based control of motors

A new digital speed measurement technique with multiple photoelectric sensors using the vernier principle for frequency multiplication is presented in this paper. The scheme has a low component count and provides directional information along with BCD speed information, suitable for direct interfacing to a microprocessor-based four-quadrant speed control of motors.     

An improved sensorless driving method for SRM using a phase-shift circuit technique

This paper presents an improved sensorless driving method for switched reluctance motor (SRM) using a phase-shift circuit technique. The conventional method consists of impressing short voltage pulses during unenergized phases, measuring the phase current pulses, and finding the correlation between the filtered current signals and rotor position. However, the filtering process causes a signal phase delay which varies with motor speed. This delay must be compensated for in providing the sensorless signal which is proper to the rotor position. A solution for this phase delay compensation, based on a simple analog and digital circuit, is proposed in this paper.     

New digital compensation technique for the design of amicrocomputer compensated crystal oscillator

The study of the stability of frequency sources is a matter of major interest due to the evolution of communication and instrumentation systems resulting in increasing the number of channels in a limited spectrum, and reducing size and power consumption. The paper relates laboratory experiences that explain the behavior versus temperature of thickness-mode quartz crystal resonators (AT- and SC-cut crystals) that are applied to the control of frequency sources, and the performance of digital compensation techniques. Prototypes of microcomputer-compensated crystal oscillators (MCXO's) have been developed to compare the compensation performance using the resonator as the temperature sensor against the use of an external sensor and verify the reduction of compensation errors due to thermal lags and hysteresis. The design of a CMOS integrated circuit for the MCXO is also included. A frequency correction method that does not modify the crystal resonance has been implemented in the circuit. This allows sensing of the temperature by means of the crystal and improving its long-term stability (aging). A new frequency comparator is also introduced. Its aim is to obtain the difference between two very close frequencies at its output, without being affected by the phase variations that the new frequency correction method and the digital circuit introduce. This detector has been implemented to get a high-resolution thermometric frequency and to realize a frequency-locked loop that includes a crystal controlled local oscillator, allowing the use of the MCXO as a good short-term stability source     

A PWM plus phase-shift control bidirectional DC-DC converter

A pulse-width modulation (PWM) plus phase-shift control bidirectional dc-dc converter is proposed. In this converter, PWM control and phase-shift control are combined to reduce current stress and conduction losses, and to expand ZVS range. The operation principle and analysis of the converter are explained, and ZVS condition is derived. A prototype of PWM plus phase-shift bidirectional dc-dc converter is built to verify the analysis.     

An integrated readout circuit for personal dosimetry with phase-shift compensation technique to improve stability

In this paper an integrated CMOS readout circuit for a radiation detector in a personal dosimeter is presented. High counting rate and low power requirements make the stability of the conventional high-pass pulse shaper a big problem. A novel phase-shift compensation method is proposed to improve the phase margin. The principle of the compensation circuit and its influence on noise performance are analyzed theoretically. A readout chip with two channels of conventional structure and one channel of the proposed structure has been implemented in a 0.35 μm CMOS technology. It occupies an area of 2.113×0.81 mm². Measurement results show that the proposed channel can process up to 1 MHz counting rate and provide a conversion gain of about 170 mV/fC at a power dissipation of 330 μW with a 3.3 V power supply. Ac-coupled to a silicon PIN detector, it successfully detects β-rays.     

Dynamic range extension technique for high-order ΣΔADCs by digital level control

A new architecture is presented for a high-order multi-bit ΣΔ ADC which does not require a precision multi-bit DAC in the feedback loop. Local digital level control is employed to extend integrator output dynamic range. A prototype fourth-order modulator is simulated with circuit non-idealities, showing an SNR of ~110 dB     

CCD mosaic technique for large-field digital mammography

The authors present a novel technique for large-field digital mammography. The instrument uses a mosaic of electronic digital imaging [charge coupled device (CCD)] arrays, novel area scanning, and a radiation exposure and scatter reducing mechanism. The imaging arrays are mounted on a carrier platform in a checker-board pattern mosaic. To fill in the gaps between array-active areas the platform Is repositioned three times and four X-ray exposures are made. The multiple image areas are then recombined by a digital computer to produce a composite image of the entire region. To reduce X-ray scatter and exposure, a lead aperture plate is interposed between X-ray source and patient. The aperture plate has a mosaic of square holes in alignment with the imaging array pattern and the plate is repositioned in synchronism with the carrier platform. The authors discuss proof-of-concept testing demonstrating technical feasibility of their approach. The instrument should be suitable for incorporation into standard mammography units. Unique features of the new technique are: large field coverage (18x24 cm); high spatial resolution (14-17 lp/mm); scatter rejection; and excellent contrast characteristics and lesion detectability under clinical conditions.     

Least-squares design technique for digital Hilbert-transform filters

Discrete-time calculation of Hilbert transforms is of increasing importance in digital processing of communication signals. The technique for designing digital Hilbert filters described here makes use of the properties specific to this filter category in arriving at a simple closed-form matrix formulation. The optimality criterion utilised is that of least-squares error (l.s.e.), which results in filter error characteristics that compare reasonably well with minimax designs using the Remez exchange algorithm?achieved with considerably reduced computational burden.     

New zero-voltage-switching phase-shift full-bridge converter with low conduction losses

A new zero-voltage-switching (ZVS) phase-shift full-bridge (PSFB) converter with low conduction losses is proposed. It is based on the PSFB converter with series-connected two transformers, which features wide ZVS ranges. By adding a capacitor, the proposed converter overcomes the disadvantage of the based converter, such as the high circulating energy. Furthermore, the turns ratio of the transformers can be increased as well. Therefore, high efficiency of the proposed converter can be achieved. Operational principles and experimental results for a 100-W (5 V, 20 A) prototype are presented to validate the proposed converter.     

New digital automatic gain control for p.c.m. signals

A new design for digital automatic gain control for p.c.m. telephony is presented. This new design is capable of processing 30 speech channels. It avoids putting highest gain where there is no speech. It has manual and automatic facilities.     

Highly accurate long-span chromatic dispersion measurement system by a new phase-shift technique

A highly accurate long span chromatic dispersion measurement system, which is based on a wavelength-division-multiplexing phase-shift technique and utilizes six laser diodes in1.2 sim 1.6 mum spectral region, has been developed. It is intrinsically free from error due to the fiber length variation caused by temperature changes under the measurement. The measurement accuracies of dispersion and Zero-dispersion wavelength are extremely good and within ±0.02 ps/km . nm and ±0.1 nm in 1250 ∼ 1450 nm spectral region in the case of a 10.5-km single-mode fiber measurement. The dynamic range is over 50 dB excluding system theS/Nmargin of 5 dB. Using this system, chromatic dispersion measurements of a 101.9-km pure-silica-core single-mode fiber and a 100.7 km concatenated dispersion-shifted single-mode fiber have been successfully carried out. The measured result has coincided with the arithmetical mean of those of constituent fibers.     

New codes for digital transmission

Two new pseudoternary codes suitable for digital line transmission are proposed. Each is of 10B7T format. They have digital-sum variation, intersymbol interference, timing content and framing information comparable with 4B3T and MS43, respectively, but offer a higher information capacity for a given symbol rate.