An investigation of square law devices

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Copyright: Longfoot, John Elms
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Abstract
A Square Law Device may be considered as being any circuit or arrangement of components, capable of producing an output proportional to the mathematical square of the input. These devices may be electrical, mechanical, hydraulic or any combination of these. The thesis is confined to electrical square law devices, which are by far the most numerous. The input and output quantities are usually represented as voltages or currents. A literature survey was conducted and a large number of different types of square law devices were revealed. These have been classified into sections, depending on the mode of squaring, and each has been examined for various properties. Some devices have been examined theoretically, and others by actually developing and constructing a circuit and taking a series of measurements, in each case a conclusion is drawn concerning the accuracy, frequency response and dynamic range. This classification and examination of square law devices showed that, although there were many devices excelling in one property, there were very few having excellent all round performance. Either a method for improving the performance of existing devices or a completely new device with excellent all round properties would be needed to improve the position, it was decided to attempt to develop a method to improve the properties of existing devices, and the last and major section of the thesis is devoted to the treatment of a method for reducing distortion due to odd powers in the nominal square law transfer function. A large fundamental co-efficient is one of the most common forms of distortion in these devices. The thoughts leading to the method of improvement are given, with an analysis proving the mathematical possibility. A square law device was constructed using the method and rigorous tests carried out to compare the performance of the device on its own, with that when it is incorporated in the circuit for improving the distortion. The thesis shows that a large improvement in both the accuracy and dynamic range is possible.
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Author(s)
Longfoot, John Elms
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Publication Year
1961
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Thesis
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Masters Thesis
UNSW Faculty
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