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|Title:||A Surface Acoustic Wave Wideband FM Discriminator|
|Authors:||Nanayakkara, Somapala T.N.W.M.|
|Keywords:||Electrical and Electronics;Electrical and Electronics|
|Abstract:||<p>The advantages that wideband frequency modulation (FM) offers over amplitude modulation (AM) are minimum transmission power and better output signal-to-noise ratio. The discriminator in the FM receiver is important since its performance dictates the degree of capability of exploiting these advantages. Conventional FM discriminators are faced with limitations such as bandwidth of operation, linearity of conversion characteristics, dynamic range due to FM threshold, frequency of operation, reproducibility, reliability, and economics. These problems are caused by the basic restrictions found in the principle of operation, and the nature of the devices used to realize these discriminators. The subject of this thesis is to explain alternatives to overcome these problems.</p> <p>In the class of narrow band FM discriminators, we have suggested two discriminators whose operation is based on Surface Acoustic Wave (SAW) resonators, and SAW differential delay lines. For wide band FM discriminators we have developed a principle of operation based on a modified M-ary correlation receiver principle. The actual discriminator was realized with a system using a SAW chirped matched filter as the central signal processing element, and a zero-crossing detector technique is employed to minimize the errors in signal detection. The design and fabrication of a SAW chirp filter is discussed. A simple thin film technique to modify the aperture of an interdigital transducer (IDT) in order to obtain the required frequency response is explained and verified experimentally. To prove the principle of operation, a discriminator operating at 70 MHz with a bandwidth of 18 MHz has been produced. The performance evaluation of the device shows the linearity to be better than 1.8% over the bandwidth. The FM threshold occurs at -3 dB of input carrier-to-noise ratio. The parameters and measurement techniques employed to evaluate the noise performance of the chirp filter are explained, and the capability of the principle of operation for further extension of the FM threshold is explained. Finally, as applications we have proposed a multi-frequency position modulation modem. The principle of operation and implementation of this modem is discussed. In addition, applications to dual modulation schemes, such as pulse amplitude modulation - frequency modulation (PAM-FM), and applications to instrumentation systems, are also discussed briefly.</p>|
|Appears in Collections:||Open Access Dissertations and Theses|
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