Multi-beam 4 GHz Microwave Apertures Using Current-Mode DFT Approximation on 65 nm CMOS

Abstract: A current-mode CMOS design is proposed for realizing receive mode multi-beams in the analog domain using a novel DFT approximation. High-bandwidth CMOS RF transistors are employed in low-voltage current mirrors to achieve bandwidths exceeding 4 GHz with good beam fidelity. Current mirrors realize the coefficients of the considered DFT approximation, which take simple values in ${0, \pm1, \pm2}$ only. This allows high bandwidths realizations using simple circuitry without needing phase-shifters or delays. The proposed design is used as a method to efficiently achieve spatial discrete Fourier transform operation across a ULA to obtain multiple simultaneous RF beams. An example using 1.2 V current-mode approximate DFT on 65 nm CMOS, with BSIM4 models from the RF kit, show potential operation up to 4 GHz with eight independent aperture beams.