Virtually scaling-free adaptive CORDIC rotator

Abstract

The authors propose a coordinate rotation digital computer (CORDIC) rotator algorithm that eliminates the problems of scale factor compensation and limited range of convergence associated with the classical CORDIC algorithm. In the proposed scheme, depending on the target angle or the initial coordinate of the vector, a scaling by 1 or 1/√2 is needed that can be realised with minimal hardware. The proposed CORDIC rotator adaptively selects the appropriate iteration steps and converges to the final result by executing on average only 50% of the number of iterations required by the classical CORDIC. Unlike for the classical CORDIC, the value of the scale factor is completely independent of the number of executed iterations. Based on the proposed algorithm, a 16-bit pipelined CORDIC rotator was implemented. The silicon area of the fabricated pipelined CORDIC rotator core is 2.73 mm2. This is equivalent to 38 000 inverter gates in the used 0.25 μm BiCMOS technology. The average dynamic power consumption of the fabricated CORDIC rotator is 17 mW at a 2.5 V supply voltage and a 20 Ms/s throughput. Currently, this CORDIC rotator is used as a part of the baseband processor for a project that aims to design a single-chip wireless modem compliant with the IEEE 802.11a standard.