TV Ghost Cancellation System Using Switched Capacitor Circuits
Mahmoud, Seedahmed Sharif (1998) TV Ghost Cancellation System Using Switched Capacitor Circuits. Masters thesis, Universiti Putra Malaysia.
In the TV reception, picture quality has been one of the primary criterion in its design. The presence of ghost signals, which are due to reflections of TV signal from high rise building, towers, mountains, etc., is one of the major causes of distortion and is Iiot avoided at the receiver end. The ghost signals are in fact time delayed versions of tht:: actual transmitted signals at the receiver and have many adverse effects on picture quality due to partial cancellation of main signal. The perceptibility of the ghost signal is strongly subj ective and is a function of picture content and quality. Thus it is essential to filter the ghost signals for better reception. In this thesis we present the design of a television ghost cancellation system using switched capacitor circuits. Ghost cancellation is a nullifying operation and allows one to reduce its effect on the picture quality as much as possible. In this thesis two-stage switched capacitor (SC) transversal filter has been used for reduction of distortion. The system has been able to suppress ghosts with delays ranging from 0.1 µs to 20 µs with ghost suppression threshold at 1 % amplitude. The algorithm uses a special training signal to determine the ghost's characteristics. For a single ghost once the ghost's parameters have been determined, the transversal filter delays the incoming signal by td (the time delay of ghost) and multiplies it by a factor - G (G being the gain of ghost). The result signal is added to original signal. We obtain an output which gives no output due to original ghost but adds up another ghost. The process is repeated until the ghost's amplitude is within acceptable limits. In this thesis we have simulated the system at the block diagram level using MATLAB and at component level using PSpice. The results of the simulation are in close conformity with the theoretical value. This suggested circuit can be fabricated using the MOS technology allowing the manufacturer to provide a better quality in TV reception.
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