An Analog Mixed Signal Fourier Transform Pre-Processor for OFDM Receivers

An FFT pre-processing architecture that reduces the constraints on the analog-to-digital converter in broadband orthogonal-frequency-division-multiplexing receivers is presented. System simulations demonstrate that the proposed approach has an improved dynamic range over the conventional approach. The proposed pre-processor replaces the typically 6-bit ADC and digital FFT processor in the broadband OFDM receiver with a more power efficient, wider dynamic range architecture. The new architecture is based on sequential sampling of the OFDM symbol and an analog-mixed-signal FFT preprocessor that transforms the OFDM symbols prior to digitization. This reduces the information conversion burden on the ADC, allowing the requisite six bits of ADC resolution to be reduced to two, thereby significantly lowering system power consumption. The increased dynamic range allows sensitivity to be improved as weak sub-channels are amplified before quantization and not subjected to the limitations of the conventional 6-bit ADC. A proof-of-concept 1-GigaSample per second IC in currently being fabricated in 130nm CMOS.