Stephan J. G. Gift

The application of all-pass filters in the design of multiphase sinusoidal systems

Abstract The design of even and odd phase sinusoidal systems using all-pass networks is presented. The all-pass network has the unique characteristic of unity gain at all frequencies and a frequency-dependent phase relationship between output and input. It produces up to 180° phase shift which allows the easy implementation of multiphase systems. The network is implemented using the widely available operational amplifier which results in low harmonic distortion, low frequency error, large output voltage swing and low output impedance from a simple structure. The operating frequency is limited only by the gain–bandwidth product of the op-amp.

A high-performance full-wave rectifier circuit

A new circuit that enables basic operational amplifiers (op amps) such as the LM741 to produce precise full-wave rectification for frequencies up to and exceeding 100 kHz without waveform distortion is presented. The circuit is based on a standard op amp precise rectifier that is modified by the inclusion of a current conveyor to improve the rectifying process.

An enhanced current-mode instrumentation amplifier

An enhanced current-mode instrumentation amplifier is presented. The circuit is based on a current conveyor-operational amplifier combined configuration that offers significant improvement in accuracy as compared with the basic current-mode instrumentation amplifier based on current conveyors only.

A new design topology for low-voltage CMOS current feedback amplifiers

A new topology for designing low-voltage current feedback amplifiers (CFAs) is presented. By employing a second-generation positive current conveyor followed by an operational amplifier in an unconventional manner, the design circumvents the problem of trying to achieve large transimpedance in a low-voltage environment. It is shown that this CFA configuration also results in near gain independent closed-loop bandwidth defined by a single feedback resistor. The proposed amplifier was verified experimentally by a chip designed using Taiwan Semiconductor Manufacturing Companys 0.18-mum digital CMOS process of a single-ended power supply of 1.8 V

Multiphase sinusoidal oscillator using inverting-mode operational amplifiers

This paper describes a simple multiphase sinusoidal oscillator based on inverting operational amplifiers (OPAs). The system comprises n cascaded inverting first-order low-pass stages and produces n odd-phase equal amplitude signals that are equally spaced in phase, from low-impedance sources. The basic scheme utilizes self-oscillation and can produce 2n even-phase signals by the inclusion of n unity gain inverters. A modified system employing signal injection through the associated phase-shifting network is also discussed. The negative feedback around the OPAs results in extremely good frequency and distortion performances that are unmatched by other multiphase system implementations. Moreover, the system has a large output voltage swing, high current drive capacity, and utilizes readily available components.

Versatile Precision Full-Wave Rectifiers for Instrumentation and Measurements

This paper analyzes the performance of a family of high-quality precision full-wave rectifiers that utilize operational conveyors. The circuits have high precision, wide bandwidth, and high accuracy and are superior to the corresponding operational-amplifier (op amp)-based circuits. Using the LF351 op amp, they are able to rectify signals up to 100 kHz and beyond with little or no distortion. PSPICE results for the circuits are presented.

Improving the bandwidth gain-independence and accuracy of the current feedback amplifier

A high-performance current feedback amplifier circuit referred to as an operational current feedback amplifier is described in this paper. The technique employed involves the incorporation of the input circuit of the current feedback amplifier in the feedback loop of an operational amplifier to reduce the input impedance at the inverting terminal of the current feedback amplifier. The new circuit possesses the gain accuracy and bandwidth of the current feedback amplifier but realizes significant improvement in bandwidth accuracy and bandwidth gain-independence. Experimentally, using AD844s, an order of magnitude reduction in bandwidth variation with changing gain was achieved in the noninverting configuration and almost complete bandwidth invariance was realized in the inverting configuration.

Multiphase sinusoidal oscillator system using operational amplifiers

A simple multiphase sinusoidal oscillator using operational amplifiers is described. The system is made up of n cascaded first-order low-pass stages along with n unity gain inverters (n > 3). It produces 2n even phase signals that are equally spaced in phase and of equal amplitude, from low impedance sources. Two schemes are presented; one utilizing self-oscillation under the Barkhausen criterion and the other employing external signal injection through the phase-shifting network of the first. The negative feedback utilized in the operational amplifiers results in frequency and distortion performances that are superior to similar systems based on current conveyors.

On the Realization of Multiphase Oscillators Using Fractional-Order Allpass Filters

In this paper multiphase oscillators built using fractional-order allpass filters are presented. We examine the theory behind their operation and demonstrate their usefulness in the design of both multiphase and quadrature oscillators. Case design examples are given for various scenarios, while PSPICE and experimental results verify their operation

Light speed invariance is a remarkable illusion

Though many experiments appear to have confirmed the light speed invariance postulate of special relativity theory, this postulate is actually unverified. This paper resolves this issue by first showing the manner in which an illusion of light speed invariance occurs in two-way light speed measurement in the framework of a semi-classical absolute space theory. It then demonstrates a measurable variation of the one-way speed of light, which directly invalidates the invariance postulate and confirms the existence of the preferred reference frame of the absolute space theory.