An automatic filter using switched capacitors—performance as an automatic equalizer at low s/n

An automatic filter with an analog transfer characteristic is desirable as a receiver filter for data transmission over a channel in which both the channel distortion and the additive noise are generated and these interferences fluctuate. In this study an automatic filter that is easily integrated and readily controlled digitally is realized with SCF and its capability is demonstrated. As the fundamental configuration, the Laguerre function system is employed and the gradient method by zero crossing spacing is used as the automatic adjustment algorithm. The analog pre-filter, indispensable in a sampled-value system, is practically eliminated since the only resistor in the automatic filter is used for this function as well. This is made possible by choosing the switching frequency of SCF sufficiently higher than the baseband. The experiments have been performed for the preset type and for the adaptive type and the symbol error rate has been obtained. It is found that the present type exhibits a performance close to the theoretical value of the optimum filter, and the adaptive type also demonstrates a sufficiently acceptable performance.