A modified N-path filter suited for practical realization

A method is presented which makes it possible to build filters that, in some respect, behave like -path filters but without suffering from the well-known disadvantages associated with the implementation of these latter filters, namely, incomplete cancellation of unwanted sidebands and interference caused by carrier leakage. In conventional -path filters the output signal is formed by summing signals which have been processed by distinct paths, each path containing an intermediate network between input and output modulators. The method to be presented consists in using one single path completely in time division multiplex. This way the generation of interfering sidebands is avoided and carrier leak occurs at frequencies where it causes no trouble. A general output-to-input relationship is derived for the ideal case, and the result is given as a time-varying system function. With the aid of an example the effect of nonideal behavior which is encountered with practical circuits is analyzed. Some practical results are shown.