Discrete fourier transform circuit.

摘要

In a transmultiplexer, which is an interface between a number of PCM highways and an FDM group, the conversion between PCM and FDM involves first converting the PCM words into their linear form and filtering them, applying them to a circuit which performs a discrete Fourier transform (DFT) on them followed by a second stage of filtering. An efficient implementation of a DFT is described which reduces the number of multiplications required by making use of certain symmetry properties in a DFT matrix. The whole can be used <<backwards>>, as it were to give an inverse Fourier transform as needed for the FDM-PCM conversion.