A FAST SINGLE-CHIP IMPLEMENTATION OF 8192-COMPLEX POINT FFT

Large-scale single-frequency networks are now being considered in Euro pe as very promising network topologies to achieve drastic savings in spectrum usage for digital terrestrial television transmission. Such n etworks are possible using the COFDM system, with large guard interval s (more than 200 mu s) to absorb long echoes, In order to limit the sp ectral efficiency loss to about 20%, very long size fast Fourier trans forms (up to 8K complex points) have to be performed in real time for the demodulation of every COFDM symbol (every 1 ms), This paper presen ts the first VLSI single chip dedicated to the computation of direct o r inverse fast Fourier transforms of up to 8192 complex points, Due to its pipelined architecture, it can perform an 8K FFT every 400 mu s a nd a 1K FFT every 50 mu s, All the storage is on-chip, so that no exte rnal memories are required, A new internal result scaling technique, c alled convergent block floating point, has been introduced in order to minimize the required storage for a given quantization noise. The chi p, 1 cm(2) large for a 1.5 million transistor, has been designed in 3. 3 V-0.5 mu m triple-level metal and is fully functional. The 8K comple x FFT function could therefore be introduced in the next years in digi tal terrestrial TV receivers at low cost.