This paper presents an energy-efficient, single-chip, 1024-point FFT processor. The full-custom, 460,000-transistor design has been fabricated in a standard 0.7 mu m (L-poly = 0.6 mu m) CMOS process and is fully functional on first-pass silicon. At a supply voltage of 1.1V, it calculates a 1024-point complex FFT in 330 mu sec at a clock speed of 16 MHz while consuming 9.5 mW, resulting in an adjusted energy efficiency more than 16 times greater than the previously most-efficient known FFT processor. At 3.3V, it operates at 173 MHz.