Low-Power Discrete Fourier Transform for OFDM: A Programmable Analog Approach

The modulation and demodulation blocks in an orthogonal frequency-division multiplexing (OFDM) system are typically implemented digitally using a fast Fourier transform circuit. We propose an analog implementation of an OFDM demodulator as a means for reducing power consumption. The proposed receiver implements the discrete Fourier transform (DFT) as a vector–matrix multiplier using floating-gate transistors on a field-programmable analog array (FPAA). The DFT coefficients can be tuned to counteract an inherent device mismatch by adjusting the amount of electrical charge stored in the floating-gate transistors. When compared to a digital field-programmable gate array implementation, the analog FPAA implementation of the DFT reduces power consumption at the cost of a slight performance degradation. Considering the errors in the DFT coefficients as intersymbol interference, the performance degradation can be further mitigated by employing a least mean-square or minimum mean-square-error equalizer.